Making Printed Circuit Boards (PCBs)
Making PCB’s (Printed Circuit Boards) isn’t overly difficult for the hobbyist if you’ve got the right equipment and skills, but there are some pitfalls for the uninitiated and in this article I'm going to try and explain some of them.
I'll explore a traditional technique for producing good quality single-sided PCBs and also look at alternatives for some of the more expensive items of equipment that are required. It should be stressed that there are several methods that can be used for making PCB’s, but this article will only focus on one of them specifically; making single-sided boards using UV light exposure.
Following a series of steps, we want to get from a plain piece of copper clad board to a completed and ready to be soldered PCB.
I'll explore a traditional technique for producing good quality single-sided PCBs and also look at alternatives for some of the more expensive items of equipment that are required. It should be stressed that there are several methods that can be used for making PCB’s, but this article will only focus on one of them specifically; making single-sided boards using UV light exposure.
Following a series of steps, we want to get from a plain piece of copper clad board to a completed and ready to be soldered PCB.
 Plain copper clad board |
 Completed PCB ready for assembly |
The materials and processes used
Before we start with too much detail, it will be helpful if we go over the basic materials, process and the equipment involved.
Copper board or laminate, comes in different size flat sheets that are either single or double sided and are supplied either plain or with the addition of a UV sensitive emulsion coating; boards with this emulsion coating are often called pre-sensitised board.
Copper board or laminate, comes in different size flat sheets that are either single or double sided and are supplied either plain or with the addition of a UV sensitive emulsion coating; boards with this emulsion coating are often called pre-sensitised board.
Figure 1 - The different layers that make up copper laminate board
The bottom layer of the board is the layer that forms the bulk of the board and gives it its rigidity. Its usually made from Fibreglass or SRBP (synthetic resin bonded paper ) and you may also hear it called by other names including: FR2 / FR4 (Flame Retardant 2/4), Fotoboard or CEM/1.
Fotoboard 2 is very common and popular with hobbyists as it’s fairly cheap and easy to cut and drill. It can be rather flexible though and has a habbit of curling or bowing in the middle if left to it's own devices. The fiberglass board is a higher quality and much stronger; it's also more expensive.
The next layer up is the actual copper. This layer is very thin and measured either by thickness or weight. Laminate with a copper thickness of 35 microns or a weight of 1oz is probably the most common for hobby use.
For pre-sensitised laminate there are two additional layers. The next layer up is the UV sensitive emulsion and on top of this, a low-tac peel-able plastic layer is added to protect the UV sensitive layer from damage and the affects of light.
In use, the black plastic layer is peeled away, and Ultra Violet (UV - 340nm to 420nm wavelength) light is passed though a transparent sheet that contains the image to be transferred to the board; in this case the transparent sheet containing the artwork is a positive and not a negative as used in traditional photography. The UV light passing through the artwork causes a shadow to be cast on the emulsion layer of the laminate.
Rays of UV light that are not blocked by dark areas by the image on the transparent sheet hit the corresponding areas on the emulsion layer and destabilise it.
If you hold your hand under a desk lamp, the closer your hand is to the desk surface, the darker and sharper the shadow image will be, and the same is true when we expose the board to UV light that passes through the artwork; The closer the artwork is to the face of the board, the sharper the image will be.
After sufficient exposure to UV light, the board is placed into a developer solution and this reacts with the areas of the board that were exposed to UV light, and these exposed areas are then dissolved away.
The laminate is now inserted into an acid solution that attacks and eats away or “etches” any area of copper that is not still protected by the emulsion layer. When the waste copper has been etched away, the board is washed, dried and then component mounting holes are drilled.
In overview that’s what needs to be done... now for the detail.
Fotoboard 2 is very common and popular with hobbyists as it’s fairly cheap and easy to cut and drill. It can be rather flexible though and has a habbit of curling or bowing in the middle if left to it's own devices. The fiberglass board is a higher quality and much stronger; it's also more expensive.
The next layer up is the actual copper. This layer is very thin and measured either by thickness or weight. Laminate with a copper thickness of 35 microns or a weight of 1oz is probably the most common for hobby use.
For pre-sensitised laminate there are two additional layers. The next layer up is the UV sensitive emulsion and on top of this, a low-tac peel-able plastic layer is added to protect the UV sensitive layer from damage and the affects of light.
In use, the black plastic layer is peeled away, and Ultra Violet (UV - 340nm to 420nm wavelength) light is passed though a transparent sheet that contains the image to be transferred to the board; in this case the transparent sheet containing the artwork is a positive and not a negative as used in traditional photography. The UV light passing through the artwork causes a shadow to be cast on the emulsion layer of the laminate.
Rays of UV light that are not blocked by dark areas by the image on the transparent sheet hit the corresponding areas on the emulsion layer and destabilise it.
If you hold your hand under a desk lamp, the closer your hand is to the desk surface, the darker and sharper the shadow image will be, and the same is true when we expose the board to UV light that passes through the artwork; The closer the artwork is to the face of the board, the sharper the image will be.
After sufficient exposure to UV light, the board is placed into a developer solution and this reacts with the areas of the board that were exposed to UV light, and these exposed areas are then dissolved away.
The laminate is now inserted into an acid solution that attacks and eats away or “etches” any area of copper that is not still protected by the emulsion layer. When the waste copper has been etched away, the board is washed, dried and then component mounting holes are drilled.
In overview that’s what needs to be done... now for the detail.
Step 1. Design the PCB Artwork.
There are several methods and tools available for this stage and it would be impossible to list all of them. If you can, you want a purpose built PCB design software package; though some people prefer standard graphics packages, and there are probably hundreds of PCB design packages available but the full versions can be quite expensive to purchase. However, for hobbyists use there are often “lite” versions of these products available, the only restriction usually being on the maximum size of the laminate sheet you can work with, or limits placed on the number of pads you can have.
Here are a couple of places where you can download free “lite” versions of software. Do make sure that whichever free version you choose, allows you to save and print your artwork and check the licence conditions before use:
www.cadsoft.de (Limit on the board size)
www.diptrace.com (Limit on the number of holes allowed)
www.freepcb.com
We’re not going to discuss actual layout and design techniques for PCBs as that’s an entire subject in itself, but there are a couple of things you should watch out for.
Firstly experiment with different layouts designs. Move components around and see how easy it is to connect everything together. Over time you will get quite proficient at knowing what’s going to work, and what’s going to require jumper wires all over the place. Don’t worry too much about saving board space at this stage of the process. Just get your circuit layout on the board, and then you can start to move things around and tighten it up.
Here are a couple of places where you can download free “lite” versions of software. Do make sure that whichever free version you choose, allows you to save and print your artwork and check the licence conditions before use:
www.cadsoft.de (Limit on the board size)
www.diptrace.com (Limit on the number of holes allowed)
www.freepcb.com
We’re not going to discuss actual layout and design techniques for PCBs as that’s an entire subject in itself, but there are a couple of things you should watch out for.
Firstly experiment with different layouts designs. Move components around and see how easy it is to connect everything together. Over time you will get quite proficient at knowing what’s going to work, and what’s going to require jumper wires all over the place. Don’t worry too much about saving board space at this stage of the process. Just get your circuit layout on the board, and then you can start to move things around and tighten it up.
Measure everything twice
Figure 2 - Measuring a connector with a caliper
Measure the size of components to make sure they will actually fit. The number of times people have gone through the entire PCB manufacture process only to find that a capacitor or connector is actually bigger than they thought and is mounted too close to another component and things don't quite fit correctly.
A cheap calliper or micrometer can be found on EBay and is ideal for this purpose. You don’t need micro-millimetre accuracy, just an assurance that you’ve left enough room to actually get your parts mounted on the board.
A cheap calliper or micrometer can be found on EBay and is ideal for this purpose. You don’t need micro-millimetre accuracy, just an assurance that you’ve left enough room to actually get your parts mounted on the board.
Figure 3 - Completed artwork
Make sure when designing your artwork that the track widths and component hole sizes are adequate for your needs. Most PCB software packages assume that you are going to have your board professionally manufactured, and some of the default hole sizes and track widths are often a little too small really.
Component pad holes for transistors, IC’s and resistors etc should be around 0.8mm. Power diodes, bridge rectifiers, TO220 transistors and voltage regulators, Molex connectors and Vero pins (terminal pins) should have the pad hole size set to around 1mm.
Also remember which side of the board you’re designing for. In figure 3 above, pin 1 of IC1 is the bottom left pin because it’s a standard through-hole component. If you were using an SMD version of this part, which would be mounted on the underside, pin 1 would be in the bottom right corner.
At this stage it may be an idea to print your artwork out on plain paper to check it. You can place components on the paper by pushing the leads through the paper to make sure that everything will fit. Also, if you have had to design any non standard component patterns for use in your layout, this is a good opportunity to make sure they are also correct.
As a final tip, the more copper area that you leave on your design, the faster the board will etch and the longer the etch solution will last.
Component pad holes for transistors, IC’s and resistors etc should be around 0.8mm. Power diodes, bridge rectifiers, TO220 transistors and voltage regulators, Molex connectors and Vero pins (terminal pins) should have the pad hole size set to around 1mm.
Also remember which side of the board you’re designing for. In figure 3 above, pin 1 of IC1 is the bottom left pin because it’s a standard through-hole component. If you were using an SMD version of this part, which would be mounted on the underside, pin 1 would be in the bottom right corner.
At this stage it may be an idea to print your artwork out on plain paper to check it. You can place components on the paper by pushing the leads through the paper to make sure that everything will fit. Also, if you have had to design any non standard component patterns for use in your layout, this is a good opportunity to make sure they are also correct.
As a final tip, the more copper area that you leave on your design, the faster the board will etch and the longer the etch solution will last.
Step 2. Print the artwork
Once you’ve drawn and checked your artwork you need to print it out, and this is the part of the process that really dictates the quality of the completed board. Poor final results are often down to poor artwork print quality.
Remember what we are trying to accomplish; we want UV light to hit areas of the board where we eventually want the copper to be removed from. In all other areas we want the copper to remain and so limit as much as possible these areas to UV light.
Figure 3 shows the artwork as it’s displayed in the editor or PCB design window of a PCB graphics application. As it looks on the screen this isn’t suitable for use as it contains a lot of graphic content that we don’t actually want.
Remember, whatever is on the final artwork, will be transferred to the board!!
I’ve fallen foul of this on several occasions, especially if I’m rushing or tired.
Remember what we are trying to accomplish; we want UV light to hit areas of the board where we eventually want the copper to be removed from. In all other areas we want the copper to remain and so limit as much as possible these areas to UV light.
Figure 3 shows the artwork as it’s displayed in the editor or PCB design window of a PCB graphics application. As it looks on the screen this isn’t suitable for use as it contains a lot of graphic content that we don’t actually want.
Remember, whatever is on the final artwork, will be transferred to the board!!
I’ve fallen foul of this on several occasions, especially if I’m rushing or tired.
Figure 4 - Artwork with, and without the silk screen layer printed; printed side face up
By default my PCB package wants to produce the image with the silk screen layer visible (top half of figure 4). The red is actually the silk screen layer and it’s rarely needed, and when we come to make the actual PCB it should never be included on the copper mask layer, shown in black.
When printing, make sure that your print scale is set to 100% as we need the artwork to be full size. Also print your artwork in black, never colour.
Notice how the text in the bottom left hand corner is back to front. When the image is transferred to the board it will come out the correct way around.
The reason the artwork is printed mirrored (back to front) is so that the ink side on the artwork can be placed as close to the copper layer as possible and the closer the artwork is to the board, the darker and sharper the image will be.
If with the printed ink side facing you, the text or images appear the correct way around on your artwork then it's wrong. Look for a "mirror" option or setting in your PCB software !
To print out your computer generated artwork you’re going to need a printer, and it’s fair to say that some printers are better than others. Just about any inkjet printer will suffice and they are affordable and fast, but the ink cartridges are expensive and they tend to dry out if you leave them unused for too long. If you have a choice, you should make sure that you choose an inkjet printer that can at least take a separate black ink cartridge as you will use a lot of black ink. Make sure that any economy ink or toner settings for your printer are switched off. The aim is to make sure that dark areas on the artwork are as black as possible. Also set your printer to the highest dpi / resolution it will support.
You need to be careful using cheap ink jet cartridges or refill kits as often the ink is a bit thin and may not cover as well as original manufacturer cartridges. Many people have found that whilst these cheap replacement cartridges are fine for standard printing on paper, they are not satisfactory for PCB artwork production.
A alternate solution if you can is to use a laser printer, but it must have a resolution of at least 1200 dpi; 2400 dpi is better.
Laser printers work by printing a series of dots on the paper and because they are so close together it appears to be a solid area, but a microscope shows the true picture.
When printing, make sure that your print scale is set to 100% as we need the artwork to be full size. Also print your artwork in black, never colour.
Notice how the text in the bottom left hand corner is back to front. When the image is transferred to the board it will come out the correct way around.
The reason the artwork is printed mirrored (back to front) is so that the ink side on the artwork can be placed as close to the copper layer as possible and the closer the artwork is to the board, the darker and sharper the image will be.
If with the printed ink side facing you, the text or images appear the correct way around on your artwork then it's wrong. Look for a "mirror" option or setting in your PCB software !
To print out your computer generated artwork you’re going to need a printer, and it’s fair to say that some printers are better than others. Just about any inkjet printer will suffice and they are affordable and fast, but the ink cartridges are expensive and they tend to dry out if you leave them unused for too long. If you have a choice, you should make sure that you choose an inkjet printer that can at least take a separate black ink cartridge as you will use a lot of black ink. Make sure that any economy ink or toner settings for your printer are switched off. The aim is to make sure that dark areas on the artwork are as black as possible. Also set your printer to the highest dpi / resolution it will support.
You need to be careful using cheap ink jet cartridges or refill kits as often the ink is a bit thin and may not cover as well as original manufacturer cartridges. Many people have found that whilst these cheap replacement cartridges are fine for standard printing on paper, they are not satisfactory for PCB artwork production.
A alternate solution if you can is to use a laser printer, but it must have a resolution of at least 1200 dpi; 2400 dpi is better.
Laser printers work by printing a series of dots on the paper and because they are so close together it appears to be a solid area, but a microscope shows the true picture.
Figure 5 - Back-lit artwork printed on a plastic transparency sheet with a 1200 dpi laser printer
Everything looks fine with this artwork until you back-light it (as will happen when UV is shone through, then you can then clearly see the tiny pin pricks or mesh affect and this artwork will produce a bad board if the UV exposure is too high. Meshing seems to be a bigger problem with larger areas of black but it can also affect smaller areas including fine tracks. As can be seen, the three round pads in figure 6 are almost perfect, but the rectangular pad on the far right is suffering from a little meshing, and the larger area at the bottom of the image is terrible.
Affects of meshing on the finished board
Figure 6 - Meshing on copper board after etching
Inkjet printers tend to suffer a lot less from meshing than laser printers, because the ink is fired at the paper and you get a tiny splash affect; the ink hits the paper and then spreads out a little bit causing the dots to blur into the surrounding dots and giving a good uniform coverage. They do however sometimes cause stripes or bands to appear on the artwork.
To counteract meshing, people have all sorts of tricks up their sleeve like printing out multiple copies of the artwork and sandwiching them together to make the dark areas darker still, or they re-run the artwork back through the printer and overprint it multiple times, but there are many problems with these approaches. Trying to align multiple layers of artwork can be incredibly difficult and quite often when the artwork is aligned on one axis, it will then be out on the other. Re-feeding plastic transparencies or any media back through a laser printer should be avoided as the plastic sheet becomes less flexible after the first pass and can damage the drum, and if it gets stuck half way through the printer, it can make a terrible, expensive mess. Re-feeding other media can contaminate the laser drum with gritty toner particles lifted of the paper.
A sometimes better alternative to plastic transparency sheets is tracing paper. The sheets need to be of a fairly heavy weight if they are to be acceptable and not jam, around 90 to 150 g/m2 is ideal.
To counteract meshing, people have all sorts of tricks up their sleeve like printing out multiple copies of the artwork and sandwiching them together to make the dark areas darker still, or they re-run the artwork back through the printer and overprint it multiple times, but there are many problems with these approaches. Trying to align multiple layers of artwork can be incredibly difficult and quite often when the artwork is aligned on one axis, it will then be out on the other. Re-feeding plastic transparencies or any media back through a laser printer should be avoided as the plastic sheet becomes less flexible after the first pass and can damage the drum, and if it gets stuck half way through the printer, it can make a terrible, expensive mess. Re-feeding other media can contaminate the laser drum with gritty toner particles lifted of the paper.
A sometimes better alternative to plastic transparency sheets is tracing paper. The sheets need to be of a fairly heavy weight if they are to be acceptable and not jam, around 90 to 150 g/m2 is ideal.
Figure 7 - Artwork printed on tracing paper with a 1200 dpi laser printer
Notice how there is virtually no meshing visible in the image in figure 7.
So, what to use; tracing paper, plastic transparency or specialist papers? You will have to experiment for yourself and see which works best for you with your printer, but I’d start with whichever is the cheapest and simplest for you to obtain.
So, what to use; tracing paper, plastic transparency or specialist papers? You will have to experiment for yourself and see which works best for you with your printer, but I’d start with whichever is the cheapest and simplest for you to obtain.
Step 3. Prepare the copper board
Once you’ve printed out your artwork the next job is to prepare the copper board for use.
As we’ve already discussed, there are many different types of copper clad board around, but the type we are interested in is pre-sensitised, single sided.
The board is supplied in sheets from the supplier and chances are you will have to cut it down to size and there are various methods for doing this. A hacksaw is as good a way as any but for a faster and cleaner cut you can use proper PCB shears, but they are quite expensive.
As we’ve already discussed, there are many different types of copper clad board around, but the type we are interested in is pre-sensitised, single sided.
The board is supplied in sheets from the supplier and chances are you will have to cut it down to size and there are various methods for doing this. A hacksaw is as good a way as any but for a faster and cleaner cut you can use proper PCB shears, but they are quite expensive.
Cutting the board
Figure 8 - PCB shears
Many people also use mini circular saws, modified electric tile cutters, band-saws, and electric jigsaws. Whatever you use you should be careful. The base material on some board is made from fibreglass and the dust from this can cause health problems if you inhale too much of it. Economy board is made from a paper composite and is much safer to use but you should still try and avoid breathing in the dust.
One problem is that depending on how you cut the board, you may end up with some very rough edges.
One problem is that depending on how you cut the board, you may end up with some very rough edges.
Figure 9 - Rough edges after the board has been cut with a saw
These rough edges shown in figure 9 need to be filed off before you proceed as they can cause problems during the UV exposure stage and it’s imperative that nothing comes between the artwork sheet and the board surface.
So, now you should have a piece of board that’s still got it black plastic protective sheeting on, and has nice smooth edges.
So, now you should have a piece of board that’s still got it black plastic protective sheeting on, and has nice smooth edges.
Step 4. Transfer the artwork to the board
Figure 10 - Using UV light to expose a copper board
UV Light is shone through the artwork. Where the artwork is dark; there is ink; the UV light is stopped (hopefully) from reaching the UV sensitive layer on the copper board. Where the artwork is transparent the UV light reaches the sensitive layer and a chemical reaction occurs that changes the stability of the emulsion layer in that spot.
If you hold your hand under a table lamp you will see a shadow on the table surface. The closer your hand is to the table, the smaller and sharper the outline of your hand will be, and this process is exactly the same for UV exposure.
Since the artwork was printed to the correct scale, the slightest gap between the artwork and the surface of the board will cause the shadow cast on the board’s surface to be slightly larger than it should be. The reason we print the artwork mirrored, is that we place it ink side down on the board. This means there is virtually no gap between the ink on the artwork, and the surface of the board so the darkest and sharpest shadow possible is cast.
If it’s cold and your UV exposure box has florescent type tubes in it, the tubes should be pre-warmed. When florescent tubes are cold they flicker and give off an uneven or reduced light output, and that could cause an uneven exposure. Close the lid on the unit and just run it with the tubes on for five minutes or so; that will warm them up nicely.
This following video shows how a set of cold UV florescent tubes act when they are first turned on and one tube is clearly having problems starting and then they can be seen with excessive flicker until they have warmed up.
If you hold your hand under a table lamp you will see a shadow on the table surface. The closer your hand is to the table, the smaller and sharper the outline of your hand will be, and this process is exactly the same for UV exposure.
Since the artwork was printed to the correct scale, the slightest gap between the artwork and the surface of the board will cause the shadow cast on the board’s surface to be slightly larger than it should be. The reason we print the artwork mirrored, is that we place it ink side down on the board. This means there is virtually no gap between the ink on the artwork, and the surface of the board so the darkest and sharpest shadow possible is cast.
If it’s cold and your UV exposure box has florescent type tubes in it, the tubes should be pre-warmed. When florescent tubes are cold they flicker and give off an uneven or reduced light output, and that could cause an uneven exposure. Close the lid on the unit and just run it with the tubes on for five minutes or so; that will warm them up nicely.
This following video shows how a set of cold UV florescent tubes act when they are first turned on and one tube is clearly having problems starting and then they can be seen with excessive flicker until they have warmed up.
Figure 11 - Artwork in place, inkside up. Notice how the text is backwards (in the red outlined panel)!
UV exposure boxes have their light source either below, or above the artwork. Whichever type you have, you have to place the artwork so that the ink side is closest to the face of the board.
Don’t worry too much if your artwork won’t lay flat. It will once the board is positioned on it and the lid closed.
Next, peel off the black plastic protective film from the board and place it so that the copper side (and this has usually a yellow tint to it which is the photo resist layer) is next to the ink side of the artwork.
Don’t worry too much if your artwork won’t lay flat. It will once the board is positioned on it and the lid closed.
Next, peel off the black plastic protective film from the board and place it so that the copper side (and this has usually a yellow tint to it which is the photo resist layer) is next to the ink side of the artwork.
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Figure 12 - Board placed face down over the artwork and then with the UV light switched on - you should of course have the lid closed!
Now, carefully close the lid so you don’t disturb anything, and switch on the exposure unit. Depending on your artwork quality, what it’s printed on, and the intensity of your UV light source the exposure times will vary. However, start out with around three minutes.
Step 5. Develop the board
Once the board and artwork have been exposed to UV for the desired time, the board can be developed and this is accomplished by inserting the board into developer solution.
There are propriety developer solutions available but you can manage perfectly well with caustic soda (sodium hydroxide) and it should be as pure as possible. You don’t want it to have lemon fresh scent added or anything like that.
Mix a fresh batch of developer solution before you need it. You can develop several boards with a single batch but once the solution starts to go very dark or cold, you need to change it.
*** Safety Warning ***
Caustic soda / sodium hydroxide is nasty stuff. It’s poisonous, will burn the skin and your clothes. Treat with caution and keep out of the way of children and animals. NEVER add water to caustic soda as it could easily spit up in your face or explode.
Always add caustic soda to water... slowly !!
There are propriety developer solutions available but you can manage perfectly well with caustic soda (sodium hydroxide) and it should be as pure as possible. You don’t want it to have lemon fresh scent added or anything like that.
Mix a fresh batch of developer solution before you need it. You can develop several boards with a single batch but once the solution starts to go very dark or cold, you need to change it.
*** Safety Warning ***
Caustic soda / sodium hydroxide is nasty stuff. It’s poisonous, will burn the skin and your clothes. Treat with caution and keep out of the way of children and animals. NEVER add water to caustic soda as it could easily spit up in your face or explode.
Always add caustic soda to water... slowly !!
Developer solution
Figure 13 - Bottle of caustic soda, measuring cap and a tupper-ware container with 2 litres of warm water
Getting the mix right is a bit of a black art and once you find the right quantities you should stick to them. I use a small cap from a WD40 spray can and fill it with caustic soda; that’s around 15g of caustic soda.
Slowly poor that into 2 litres of WARM (not hot or boiling) water. Use a plastic or wooden dowel to slowly stir the solution around.
The developer solution should be warm. If it's too cold it can take a long time to develop the board, if it's too warm it will strip off all the emulsion and ruin the board. You should happily be able to stick your hand in the warm water and it feel comfortable.
Slowly poor that into 2 litres of WARM (not hot or boiling) water. Use a plastic or wooden dowel to slowly stir the solution around.
The developer solution should be warm. If it's too cold it can take a long time to develop the board, if it's too warm it will strip off all the emulsion and ruin the board. You should happily be able to stick your hand in the warm water and it feel comfortable.
Next you need to immerse the board into the solution. You MUST wear rubber gloves for this and you can usually find cheap boxes of latex gloves on EBay that are perfect for PCB making.
Hold the board in the solution so it’s fully immersed and slowly move it around. Quite quickly you should start to see some coloured dye, usually purple, coming off the board and you will see the artwork image start to appear at the same time.
Every few seconds take the board out and watch the colour of the drips of liquid coming off the bottom edge of the board. When the drips are starting to run clear you’ve just about done. One final soak for a few seconds for luck and then rise with fresh cold water.
Don't be tempted to leave the board in the developer too long. The caustic soda will first eat away the bits of the emulsion resist we no longer need, but then it will turn its attention to the rest of the resist layer. It will strip a board clean or seriously reduce the finished quality if you leave it too long.
It shouldn’t really take more than about two minutes to develop the board !!
You should now see a copy of the artwork on the copper surface and this time, all the text and images should be the correct way around.
Here’s a video that I made of a board being developed.
Hold the board in the solution so it’s fully immersed and slowly move it around. Quite quickly you should start to see some coloured dye, usually purple, coming off the board and you will see the artwork image start to appear at the same time.
Every few seconds take the board out and watch the colour of the drips of liquid coming off the bottom edge of the board. When the drips are starting to run clear you’ve just about done. One final soak for a few seconds for luck and then rise with fresh cold water.
Don't be tempted to leave the board in the developer too long. The caustic soda will first eat away the bits of the emulsion resist we no longer need, but then it will turn its attention to the rest of the resist layer. It will strip a board clean or seriously reduce the finished quality if you leave it too long.
It shouldn’t really take more than about two minutes to develop the board !!
You should now see a copy of the artwork on the copper surface and this time, all the text and images should be the correct way around.
Here’s a video that I made of a board being developed.
Meshing
Figure 14 - Artwork has been transfered but there is a little meshing
The image should also have nice sharp edges. Any blurring of the image is often cause by the artwork not being pressed up against the board during UV exposure and a prime candidate for this is rough edges where the board was cut.
Figure 14 shows that the artwork has been transferred, but the board was either overexposed to UV light for too long, or the artwork used was of too low a quality. See area in red square for meshing.
This problem is usually only really apparent in large filled areas and so whilst the finished article may not look overly pretty, it may still be perfectly usable.
The dark areas are where we want the copper to be left alone. The coppery coloured areas will be removed during etching.
Sometimes you get stubborn areas of resist that won’t come away from the board and you can spot these areas simply enough with a quick visual inspection of the developed board; all thr artwork should now be clearly visible.
Holding the board over your developer solution tank, dip a gloved finger into the developer solution and then very gently run the wet finger over the stubborn areas of the board, and then immerse the entire board back in developer for a few seconds. Don't press too hard with your finger as your not trying to scrub the board clean; you just want to work the solution into the etch resist and "persuade" it to losen up a little.
Figure 14 shows that the artwork has been transferred, but the board was either overexposed to UV light for too long, or the artwork used was of too low a quality. See area in red square for meshing.
This problem is usually only really apparent in large filled areas and so whilst the finished article may not look overly pretty, it may still be perfectly usable.
The dark areas are where we want the copper to be left alone. The coppery coloured areas will be removed during etching.
Sometimes you get stubborn areas of resist that won’t come away from the board and you can spot these areas simply enough with a quick visual inspection of the developed board; all thr artwork should now be clearly visible.
Holding the board over your developer solution tank, dip a gloved finger into the developer solution and then very gently run the wet finger over the stubborn areas of the board, and then immerse the entire board back in developer for a few seconds. Don't press too hard with your finger as your not trying to scrub the board clean; you just want to work the solution into the etch resist and "persuade" it to losen up a little.
Step 6. Remove the unwanted copper or "etch" the board
Were now going to immerse the board in a Ferric Chloride acid solution which will eat away all the unwanted copper.
*** Safety Warning ***
Ferric Chloride is poisonous and corrosive so keep well clear of children and animals,
Don't use it near anything that you don't want stained and that includes kitchen worktops and sinks, and don't even think about pooring it down a stainless steel sink. It will eat it sooner than you can scream mummy!
NEVER add water to Ferric Chloride as it could easily spit up in your face, or explode.
Always add Ferric Chloride to water... slowly !!
*** Safety Warning ***
Ferric Chloride is poisonous and corrosive so keep well clear of children and animals,
Don't use it near anything that you don't want stained and that includes kitchen worktops and sinks, and don't even think about pooring it down a stainless steel sink. It will eat it sooner than you can scream mummy!
NEVER add water to Ferric Chloride as it could easily spit up in your face, or explode.
Always add Ferric Chloride to water... slowly !!
Ferric Chloride
Figure 15 - Packet of Ferric Chloride crystals
Ferric Chloride is available as either crystals or premixed liquid. Whichever you obtain follow the manufacturer’s instructions carefully about use, storage and disposal.
In an ideal world you would have a professional bubble etch tank for the etching part. These tanks have a heater that can warm the solution up to the correct operating temperature and a small air pump to blow bubbles through the solution, and over the surface of the board. The bubbles force the mixture to keep circulating and mixing and coupled with the solution being at the correct temperature, even large boards can be etched in only a few minutes. The problem is, they are rather expensive and not many hobbiests have them.
Figure 16 - Mega bubble etch tank
You can of course make your own etch tank from a simple plastic container just like the one shown in figure 13, that can hold around 2.5 – 3 litres of liquid. As it stands, this is fine for hobby purposes but addition of a bubbler will save you standing over the board watching it. If your container also has a tight fitting lid, it’s ideal for storage of the solution when not in use. Don’t forget to clearly label the container with its contents.
You can, if you prefer, use a plastic tray to etch your boards in. The problem with this is that if you place the board copper side up, a layer of debris builds up on the board that can hinder the etching process. If you place the board copper side down, you can’t see how the board is doing. You also have to keep transferring the Ferric Chloride too and from the tray for use and storage and it can all get a little messy.
You will need some way of suspending the board in the solution and for retrieving it when it’s done. I’ve used an all plastic clothes peg in the past, but whatever you use, make sure that it has no exposed metal as it will corrode in the blink of an eye. You can of course just dive in there with a pair of rubber gloves on, or drill a small hole and tie a piece of nylon fishing line to the board before you immerse it.
When ready, insert the board into the solution for 30 seconds and then lift it out. All the copper areas that are going to be etched away should now be a pinky colour. If there are any areas that you were expecting to be etched but have not turned pink, wash the board in cold water, and then back into the developer for a little while longer. Again, you can rub your finger over the offending area and loosen the resist. Once your done, wash the board and then back into the etch tank.
Now you have to wait. The speed of the etch process depends on the temperature and strength of the Ferric Chloride, the thickness of the copper and the amount of copper area to be removed; the warmer the Ferric Chloride, the faster the etching process with be. Check back every five minutes or so to make sure you don’t over etch.
As waste copper is removed from the board, the Ferric Chloride starts to undercut the resist layer and eat at the copper you do want to keep. Leave the board for too long in the solution, and it will eat all the copper off the board!
You can, if you prefer, use a plastic tray to etch your boards in. The problem with this is that if you place the board copper side up, a layer of debris builds up on the board that can hinder the etching process. If you place the board copper side down, you can’t see how the board is doing. You also have to keep transferring the Ferric Chloride too and from the tray for use and storage and it can all get a little messy.
You will need some way of suspending the board in the solution and for retrieving it when it’s done. I’ve used an all plastic clothes peg in the past, but whatever you use, make sure that it has no exposed metal as it will corrode in the blink of an eye. You can of course just dive in there with a pair of rubber gloves on, or drill a small hole and tie a piece of nylon fishing line to the board before you immerse it.
When ready, insert the board into the solution for 30 seconds and then lift it out. All the copper areas that are going to be etched away should now be a pinky colour. If there are any areas that you were expecting to be etched but have not turned pink, wash the board in cold water, and then back into the developer for a little while longer. Again, you can rub your finger over the offending area and loosen the resist. Once your done, wash the board and then back into the etch tank.
Now you have to wait. The speed of the etch process depends on the temperature and strength of the Ferric Chloride, the thickness of the copper and the amount of copper area to be removed; the warmer the Ferric Chloride, the faster the etching process with be. Check back every five minutes or so to make sure you don’t over etch.
As waste copper is removed from the board, the Ferric Chloride starts to undercut the resist layer and eat at the copper you do want to keep. Leave the board for too long in the solution, and it will eat all the copper off the board!
Stubborn areas that refuse to etch
Figure 17 - An area of the board that refuses to etch properly
You may find that after a while some areas are being etched faster than others and that’s fine. Just keep checking back every so often but sometimes there’s a stubborn area that seems to refuse to etch.
As previously stated, areas of the board refusing to etch are caused by the resist emulsion protecting the underlying copper that were trying to remove. All you can do is wash the board in cold water, place it back into the developer and rub your finger over the problem areas, working in the developer solution to soften the resist. Wash the board in fresh water and then place it back into the etch tank.
When all the waste copper is removed, wash the board in water and then inspect it closely. If there are any small short circuits between tracks, and it does happen sometimes, they can be fixed later with a sharp craft knife or you can again try and remove the resist from the offending areas and place back in the etch solution for a little while.
As previously stated, areas of the board refusing to etch are caused by the resist emulsion protecting the underlying copper that were trying to remove. All you can do is wash the board in cold water, place it back into the developer and rub your finger over the problem areas, working in the developer solution to soften the resist. Wash the board in fresh water and then place it back into the etch tank.
When all the waste copper is removed, wash the board in water and then inspect it closely. If there are any small short circuits between tracks, and it does happen sometimes, they can be fixed later with a sharp craft knife or you can again try and remove the resist from the offending areas and place back in the etch solution for a little while.
Step 7. Drill the PCB holes
Most PCB’s have holes drilled though, unless your board is totally used for surface mount components, and these need to be drilled by hand and is probably the most labour intensive and time consuming part of the PCB manufacture process.
Any of the many 12v hobby drills that are available is ideal for drilling PCB holes. For small boards or infrequent use, you can hold and drill by hand. For more than the odd occasional boards, you will want some sort of drill press holder for your drill; it makes the entire process much simpler, accurate and faster.
Any of the many 12v hobby drills that are available is ideal for drilling PCB holes. For small boards or infrequent use, you can hold and drill by hand. For more than the odd occasional boards, you will want some sort of drill press holder for your drill; it makes the entire process much simpler, accurate and faster.
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Figure 18 - A small hobby drill on the left, and a larger bench drill on the right.
My personal preference is a full size bench press drill. Their advantage is that they tend to be a lot cheaper than a small hobby drill (even though they are several times the size), are very sturdy and can be used for all sorts of other workshop drilling tasks as they tend to have full size chucks fitted. On mine I did fit a small electric fan to the underside of the motor to force cool it as after 10 minutes of drilling it starts getting rather warm.
You are going to be drilling holes with a very small diameter, and for that you will need drill bits which are easy to lose, and even easier to break.
If you’re drilling by hand, you have little choice but to use HSS (High Speed Steel) drill bits. Because they are steel they are slightly flexible and won’t snap if there is a little bit of movement in your hand when drilling. If you’re drilling using a drill press, you can use Tungsten Carbide bits if you can find them. They tend to be more expensive than HSS bits, but they are available in very small sizes and will last many times longer than HSS bits.
The PCB industry uses Tungsten Carbide bits by the bucket load, and luckily for us, they are quite expensive so they return the blunt used bits to the manufacturer. These bits are then reground and sold to hobbyists; industry can’t re-use these bits as they are now slightly shorter due to the regrinding process. This means that hobbyists can usually obtain these bits at a significant cost saving. Rapid Electronics in the UK sell a box of 10 x 0.8mm Tungsten Carbide bits in a storage case for around £12.
You are going to be drilling holes with a very small diameter, and for that you will need drill bits which are easy to lose, and even easier to break.
If you’re drilling by hand, you have little choice but to use HSS (High Speed Steel) drill bits. Because they are steel they are slightly flexible and won’t snap if there is a little bit of movement in your hand when drilling. If you’re drilling using a drill press, you can use Tungsten Carbide bits if you can find them. They tend to be more expensive than HSS bits, but they are available in very small sizes and will last many times longer than HSS bits.
The PCB industry uses Tungsten Carbide bits by the bucket load, and luckily for us, they are quite expensive so they return the blunt used bits to the manufacturer. These bits are then reground and sold to hobbyists; industry can’t re-use these bits as they are now slightly shorter due to the regrinding process. This means that hobbyists can usually obtain these bits at a significant cost saving. Rapid Electronics in the UK sell a box of 10 x 0.8mm Tungsten Carbide bits in a storage case for around £12.
 Standard HSS drill bit |
 Box of Tungsten Carbide bits |
Figure 19 - HSS and Tungsten Carbide drill bits
Make sure you have plenty of light so you can see exactly what you’re doing. I’ve seen some arrangements where a light is placed under the board and then helps illuminate the areas to be drilled. I've not personaly liked this arrangement but it suits some people.
When drilling, start with the largest holes to warm up your hand eye coordination; these are the PCB mounting holes (usually 3mm to 4mm diameter) and are drilled with standard HSS bits.
Next move onto the larger component holes; power diodes, rectifiers, TO22 voltage regulators, Molex connector pins etc. These can be drilled with 1mm Tungsten Carbide bits.
Finally, drill the remainder of the through mounted component holes. These are usually drilled with a 0.8mm Tungsten Carbide bit.
When drilling, a fair amount of debris will collect on the board. You may find it simpler to just drill the holes that you can clearly see, blow the debris away and then start drilling again, rather than blowing the debris away after each hole.
Update: I've just invested in a second-hand air compressor from EBay used for artists air brushes. I've mounted the hose to it dangles close to the tip of the drill bit and does an excellent job of blowing away the debris.
Apply pressure slowly and evenly, and especially when using tungsten carbide bits, never attempt to re-drill the same hole; any slight sideways movement of the bit or the board will cause the bit to snap. Just drill all the way to the other side and then back out.
Step 8. Finishing off
Figure 20 - Polifix block
You now have an etched and drilled board, but were not quite finished as the remaining emulsion needs to be removed and the board needs to be protected from corrosion.
Removing the rest of the emulsion layer can simply be done by soaking a piece of paper towel with surgical spirit and rubbing the board. Almost instantly, the paper towel will start to turn green as the emulsion is removed. Now, surgical spirit contains a very small amount of caster oil and this makes it ideal as when the spirit evaporates, it leaves the tiny amount of oil on the board to help protect the copper.
If you leave a piece of shiny copper in the open air it will start to tarnish and corrode immediately, and the same is true for copper on PCB’s. Many hobby PCB’s fail when in service because the thin tracks on the board corrode and eventually break. To prevent this, we can spray on a special flux that keeps the air away from the copper, and also has the added benefit of helping the soldering process, but first the board must be cleaned.
The Polifix polishing block in the image above is a soft material mixed with a fine grit. Rubbing it gently over the copper on the board will bring the copper up to a nice shine. As soon as you’ve completed this, spray the board with PCB flux to stop any further corrosion.
Removing the rest of the emulsion layer can simply be done by soaking a piece of paper towel with surgical spirit and rubbing the board. Almost instantly, the paper towel will start to turn green as the emulsion is removed. Now, surgical spirit contains a very small amount of caster oil and this makes it ideal as when the spirit evaporates, it leaves the tiny amount of oil on the board to help protect the copper.
If you leave a piece of shiny copper in the open air it will start to tarnish and corrode immediately, and the same is true for copper on PCB’s. Many hobby PCB’s fail when in service because the thin tracks on the board corrode and eventually break. To prevent this, we can spray on a special flux that keeps the air away from the copper, and also has the added benefit of helping the soldering process, but first the board must be cleaned.
The Polifix polishing block in the image above is a soft material mixed with a fine grit. Rubbing it gently over the copper on the board will bring the copper up to a nice shine. As soon as you’ve completed this, spray the board with PCB flux to stop any further corrosion.
Flux Spray
Figure 21 - PCB Flux spray
A single coat of PCB flux spray will seal the board and also help with soldering.
It takes a little while to dry and goes soft when it gets warm and you can easily leave your thumb print in it.
That’s it, the board is complete.
It takes a little while to dry and goes soft when it gets warm and you can easily leave your thumb print in it.
That’s it, the board is complete.
When it all goes wrong
It will go wrong from time to time, and this section aims to give you some pointers to fixing the problems.
Now it’s unlikely that you will have a bad batch of laminate. I’ve only ever heard of one case and its suspect if that really was the cause, that said, there are a couple of sensible precautions you should observe. Don’t buy too much laminate at a time, especially if you’re not intending to use it for a long time. Keep it in a cool dry place out of any direct light, and store it flat to help stop it from bowing. I tend to keep a reasonable stock handy, and whenever I order board, I write the date on it in pencil so I always use the oldest first. If it's not from my regular supplier I always write on where I purchased it from as well; just in case there are problems with it.
I’ve certainly seen some pre-sensitised laminate that doesn’t have the emulsion layer running all the way to the edges which is very annoying. There isn’t really anything you can do about this as there’s a good chance that the first time you see the problem is after you’ve cut the board to size and just peeled off the black plastic layer.
Mix a fresh batch of developer solution for each PCB making session. Don’t be tempted to use a batch that was made yesterday as it will now be cold; caustic Soda is so cheap that it’s not worth risking a piece of laminate on.
Most problems with PCB production are related to the art work, and the problems are quite simple; either too much UV light gets to the wrong places, or not enough gets to the right places, so we want artwork that has transparent areas as transparent as possible, and dark areas as dark as possible.
Now it’s unlikely that you will have a bad batch of laminate. I’ve only ever heard of one case and its suspect if that really was the cause, that said, there are a couple of sensible precautions you should observe. Don’t buy too much laminate at a time, especially if you’re not intending to use it for a long time. Keep it in a cool dry place out of any direct light, and store it flat to help stop it from bowing. I tend to keep a reasonable stock handy, and whenever I order board, I write the date on it in pencil so I always use the oldest first. If it's not from my regular supplier I always write on where I purchased it from as well; just in case there are problems with it.
I’ve certainly seen some pre-sensitised laminate that doesn’t have the emulsion layer running all the way to the edges which is very annoying. There isn’t really anything you can do about this as there’s a good chance that the first time you see the problem is after you’ve cut the board to size and just peeled off the black plastic layer.
Mix a fresh batch of developer solution for each PCB making session. Don’t be tempted to use a batch that was made yesterday as it will now be cold; caustic Soda is so cheap that it’s not worth risking a piece of laminate on.
Most problems with PCB production are related to the art work, and the problems are quite simple; either too much UV light gets to the wrong places, or not enough gets to the right places, so we want artwork that has transparent areas as transparent as possible, and dark areas as dark as possible.
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Figure 22 - Affects of dirty toner transfer drums on the laser printer
Figures 22 show what happens if there’s dirt or debris on the toner transfer drum. There are many causes for this, one is re-feeding sheets back into the laser printer; toner peels off the sheet and sticks to the drum.
Over exposure of the board to UV light is also a common problem. The amount of time to expose the board to UV depends on the wattage and age of your UV tubes, how close the tubes are to the artwork and board, the type of media your artwork is printed on, the density of the dark print areas, the ambiant temperature and the type and age of the laminate.
In the beginning it can be very difficult to calculate the amount of time required for exposure so it's worth trying a simple experiment before you start attempting to produce large, expensive boards.
Over exposure of the board to UV light is also a common problem. The amount of time to expose the board to UV depends on the wattage and age of your UV tubes, how close the tubes are to the artwork and board, the type of media your artwork is printed on, the density of the dark print areas, the ambiant temperature and the type and age of the laminate.
In the beginning it can be very difficult to calculate the amount of time required for exposure so it's worth trying a simple experiment before you start attempting to produce large, expensive boards.
Figure 23 - Exposure test strip
The exposure test strip is a great way of figuring out exactly how much UV exposure is required for your setup and materials you use.
Create a PCB artwork image that is a solid rectangle and then print it on your artwork media paper.
Place the artwork between the UV light source and a scrap of PCB laminate and expose the entire board for 1 minute. Because the ink on the media "should" shield the laminate from UV, in theory none of the board should be exposed to UV light.
After 1 minute, stop the exposure and slip a piece of thin cardboard between the artwork and the laminate to shield 1/5th of the board. Expose again for 1 minute and then move the cardboard to sheid 2/5ths of the board, and continue until you have completed a total of 5 exposures.
At the end of this process, 1/5 of the board has have 1 minute of exposure time, and the last 1/5 of the board has has a full 5 minutes of exposure time.
Now develop and etch the board in the method described above.
Figure 23 shows what happed when I created my test strip and shows between 1 and 6 minutes of UV exposure though my dark artwork. Even after only 2 minutes enough UV light has managed to get through the dark area and attach the coating on the board. After 6 minutes the section has been almost totally etched. This test strip told me that exposure times of around 1.5 minutes were an idea starting point.
Next I did a trial exposure using a proper piece of artwork on a scrap of board.
Create a PCB artwork image that is a solid rectangle and then print it on your artwork media paper.
Place the artwork between the UV light source and a scrap of PCB laminate and expose the entire board for 1 minute. Because the ink on the media "should" shield the laminate from UV, in theory none of the board should be exposed to UV light.
After 1 minute, stop the exposure and slip a piece of thin cardboard between the artwork and the laminate to shield 1/5th of the board. Expose again for 1 minute and then move the cardboard to sheid 2/5ths of the board, and continue until you have completed a total of 5 exposures.
At the end of this process, 1/5 of the board has have 1 minute of exposure time, and the last 1/5 of the board has has a full 5 minutes of exposure time.
Now develop and etch the board in the method described above.
Figure 23 shows what happed when I created my test strip and shows between 1 and 6 minutes of UV exposure though my dark artwork. Even after only 2 minutes enough UV light has managed to get through the dark area and attach the coating on the board. After 6 minutes the section has been almost totally etched. This test strip told me that exposure times of around 1.5 minutes were an idea starting point.
Next I did a trial exposure using a proper piece of artwork on a scrap of board.
Figure 24 - Speck of dust on the original artwork
Notice the speck of copper in the red circle. When I was making this board I noticed a grain of dirt on the artwork; static electricity attracts everything you don’t want, and I decided to leave it there to show what happens.
 Figure 25 - Artwork used for PCB in figure 24 |
Notice how the artwork is suffering from very bad meshing, but because I limited the UV exposure to the minimum, it didn’t come out on the board when etched.
If you change your exposure unit (or the tubes), decide to use different paper or even a different developer, you should redo this test and adjust the UV exposure times accordingly. |
 Figure 26 - Transparency sheet printed with printer paper set to 'transparency' |
 Figure 27 - Transparency sheet printed with printer paper set to 'paper' |
Look at the pictures in figures 26 & 27 of two pieces of artwork take under a microscope. They show what the affect the “paper type” options have when printing your artwork out. Both were printed on the same HP Laser Printer on the same meda; only the paper type settings were changed.
Figure 28 - Transparency printed on a HP DeskJet inkjet printer
Figure 28 is a close up image of a Staedtler-Lumocolor transparency sheet that was printed on an InkJet printer. These sheets have an almost sticky feel to one side and are designed to help the ink adhere better. Unfortunatly under the microscope you can see that actually the black areas are fragmented and not at all solid. In this case you would need to reduce the UV exposure time down to a minimum.
You will need to experiment with your printer settings and print media to find which gives the best quality print.
One thing I've noticed is that sometimes it's easy to ever expose the board to UV and this can cause meshing. What I've done is place a piece of tracing paper over the glass, then the art work and then the board. The tracing paper seems to help defuse and slightly reduce the UV slightly, and I've noticed better results for doing this. ALWAYS make sure the glass in the UV unit is spotless.
You will need to experiment with your printer settings and print media to find which gives the best quality print.
One thing I've noticed is that sometimes it's easy to ever expose the board to UV and this can cause meshing. What I've done is place a piece of tracing paper over the glass, then the art work and then the board. The tracing paper seems to help defuse and slightly reduce the UV slightly, and I've noticed better results for doing this. ALWAYS make sure the glass in the UV unit is spotless.
Storage and disposal of chemicals
Storage of Ferric Chloride
When not in use, you can store ferric chloride in a glass or air-tight plastic container; make sure that it has no metal caps or seals. I would also stand the container in a tray, just in case, and keep it well out of the way of children and animals.
When in use the water in the solution evaporates and the level can be topped off with fresh water. You will also find that over time, your boards start to take longer to etch. You can return the solution back to near its full strength by adding some more ferric chloride, but at some point you will have to discard the solution and replace it with fresh.
The point at which to do this is difficult to know as it depends on how much copper has been absorbed into the solution. You will see as you use the solution a sludge start to form at the bottom of the tank. This is left over waste from the etching process and is normal but you don’t want to let too much of it build up, as it can block the air holes if you are using a bubbler, and it also affectively reduces the depth of the solution making it difficult to etch larger boards.
Even if you only use the solution periodically, as a minimum, I would suggest that you replace the solution every two years.
Heres a great article here that discusses the chemistry of the ferric chloride and copper reaction and provides some usefull hits and tips on it's use and how to tell it's condition. http://www.artmondo.net/printworks/articles/ferric.htm
Disposal of Ferric Chloride
This will depend on local laws. DO NOT poor it down the drain. Speak to your local waste recycling centre and ask them, remembering to tell them that you are disposing on a couple of litres a year, and not a million. I personally mix my waste solution with an equal volume of caustic soda solution, then poor the mix into a bucket full of plaster. When it goes hard, I take it to the tip and drop it in the hardcore waste skip.
Disposal of caustic soda solution.
This is easy, straight down the outside drain. After all, caustic soda is drain cleaner.
Making your own equipment.
There are three items of equipment that you have to have to make PCB’s.
• A developer tank
• An etch tank
• A UV exposure unit.
Many people opt for simple plastic Tupperware type containers for the developer and etch tanks.
Since you should mix a batch of developer for each session, there is little requirement for any external heating. A simple container will do.
The UV exposure unit is by far the most expensive item of equipment needed. Fortunately there are some alternatives available now.
Read here for how to make a simple UV exposure unit for around £15.
The etch tank can be customised for faster etching by the addition of a bubbler and a heater.
A bubbler can be made from a simple plastic Biro pen that’s had its insides removed. Drill some 2mm holes along its length, seal off one end with some hot-melt glue, and then force a piece of plastic piping into the other end; seal with hot-melt.
The assembly can now be fixed to the base of the container with holt-melt.
The tube is then connected to an aquarium air pump, but you MUST install a one way valve in case the solution tries to siphon back up the tube when the pump is switched off.
To heat the Ferric Chloride an aquarium heater can be installed, making sure that ONLY the glass part is submerged in the liquid. You should also make sure that you have a tight fitting lid for this container; this will keep splashes that are caused by the bubbles from jumping all over the place.
When not in use, you can store ferric chloride in a glass or air-tight plastic container; make sure that it has no metal caps or seals. I would also stand the container in a tray, just in case, and keep it well out of the way of children and animals.
When in use the water in the solution evaporates and the level can be topped off with fresh water. You will also find that over time, your boards start to take longer to etch. You can return the solution back to near its full strength by adding some more ferric chloride, but at some point you will have to discard the solution and replace it with fresh.
The point at which to do this is difficult to know as it depends on how much copper has been absorbed into the solution. You will see as you use the solution a sludge start to form at the bottom of the tank. This is left over waste from the etching process and is normal but you don’t want to let too much of it build up, as it can block the air holes if you are using a bubbler, and it also affectively reduces the depth of the solution making it difficult to etch larger boards.
Even if you only use the solution periodically, as a minimum, I would suggest that you replace the solution every two years.
Heres a great article here that discusses the chemistry of the ferric chloride and copper reaction and provides some usefull hits and tips on it's use and how to tell it's condition. http://www.artmondo.net/printworks/articles/ferric.htm
Disposal of Ferric Chloride
This will depend on local laws. DO NOT poor it down the drain. Speak to your local waste recycling centre and ask them, remembering to tell them that you are disposing on a couple of litres a year, and not a million. I personally mix my waste solution with an equal volume of caustic soda solution, then poor the mix into a bucket full of plaster. When it goes hard, I take it to the tip and drop it in the hardcore waste skip.
Disposal of caustic soda solution.
This is easy, straight down the outside drain. After all, caustic soda is drain cleaner.
Making your own equipment.
There are three items of equipment that you have to have to make PCB’s.
• A developer tank
• An etch tank
• A UV exposure unit.
Many people opt for simple plastic Tupperware type containers for the developer and etch tanks.
Since you should mix a batch of developer for each session, there is little requirement for any external heating. A simple container will do.
The UV exposure unit is by far the most expensive item of equipment needed. Fortunately there are some alternatives available now.
Read here for how to make a simple UV exposure unit for around £15.
The etch tank can be customised for faster etching by the addition of a bubbler and a heater.
A bubbler can be made from a simple plastic Biro pen that’s had its insides removed. Drill some 2mm holes along its length, seal off one end with some hot-melt glue, and then force a piece of plastic piping into the other end; seal with hot-melt.
The assembly can now be fixed to the base of the container with holt-melt.
The tube is then connected to an aquarium air pump, but you MUST install a one way valve in case the solution tries to siphon back up the tube when the pump is switched off.
To heat the Ferric Chloride an aquarium heater can be installed, making sure that ONLY the glass part is submerged in the liquid. You should also make sure that you have a tight fitting lid for this container; this will keep splashes that are caused by the bubbles from jumping all over the place.