Soldering SMD (Surface Mount Device) components.
Soldering SMD (Surface Mount Device) components is a great way to induce a mild panic attack in people that have never tried this before. With mental images of components too small to see or handle, the engineer can be filled with apprehension at just the thought of it and so never reaps the benefits that SMD has to offer.
However, with more and more components only available in SMD format, sooner or later you’re going to have to bite the bullet.
I started using SMD components around 3 years ago and after a couple of mistakes, some obvious, some stupid, I’ve really taken to them and I’d like to share with you some ideas and thoughts to get you started.
Whilst not strictly related to soldering SMD components, always remember when designing your PCB which side the component will be mounted on, and consequently, when dealing with IC’s, which end is pin 1. I told you some of my initial mistakes were stupid.
So, let’s look at what were going to have to deal with.
SMT components are usually small and sometimes not much bigger than a grain of sand. I've personally managed to almost totally avoid these molecule sized components as they are really only suited for computer controlled machine placement, or the very occasional hand soldering.
The humble SMT resistor is available in several sizes or styles, including the following:
Style Size
0402 1.00 x 0.50 x 0.35 mm These are like grains of sand and very difficult to use
0603 1.60 x 0.85 x 0.30 mm
0805 2.05 x 1.25 x 0.50 mm Small but manageable.
1206 3.10 x 1.60 x 0.50 mm Quite large but useful if you need to route a track or two under the device or need the additional power handling capabilities.
However, with more and more components only available in SMD format, sooner or later you’re going to have to bite the bullet.
I started using SMD components around 3 years ago and after a couple of mistakes, some obvious, some stupid, I’ve really taken to them and I’d like to share with you some ideas and thoughts to get you started.
Whilst not strictly related to soldering SMD components, always remember when designing your PCB which side the component will be mounted on, and consequently, when dealing with IC’s, which end is pin 1. I told you some of my initial mistakes were stupid.
So, let’s look at what were going to have to deal with.
SMT components are usually small and sometimes not much bigger than a grain of sand. I've personally managed to almost totally avoid these molecule sized components as they are really only suited for computer controlled machine placement, or the very occasional hand soldering.
The humble SMT resistor is available in several sizes or styles, including the following:
Style Size
0402 1.00 x 0.50 x 0.35 mm These are like grains of sand and very difficult to use
0603 1.60 x 0.85 x 0.30 mm
0805 2.05 x 1.25 x 0.50 mm Small but manageable.
1206 3.10 x 1.60 x 0.50 mm Quite large but useful if you need to route a track or two under the device or need the additional power handling capabilities.
They're small... very small...
Figure 1 – Somebody’s very handsome thumb modelling 0603, 0805 & 1206 style SMD resistors
My preferred style is the 0805. For one thing you can see them, and if your carful you won’t lose too many of them. I had to use some 0603’s for a special project and whilst I eventually did manage to solder them, I promised myself never again.
As you can see from figure 1, the two larger styles at least have markings; these are all 2.2K 5% resistors. On ceramic SMD capacitors don’t expect any markings at all, and if you mix different values up you’re in real trouble; like wise for transistors and most other parts. If you’re lucky you do get some obscure markings; long gone are the manufacturers mark, part number and possible date code. IC’s do tend to still have readable markings on.
Now to handle these tiny blighters you’re going to need some fine tools and plenty of good quality light as you don’t want shadows being cast over your work area as you position your tools or hands, and this may mean you actually need multiple light sources.
A good quality soldering iron is of course essential even for general assembly work, however probably more important for SMT soldering is the soldering irons bit size. Size does matter, and in this one case, it really can’t be too small. I found that the Antex 1mm bit is too big for most SMT work and you may do better with their 0.5mm bits.
As you can see from figure 1, the two larger styles at least have markings; these are all 2.2K 5% resistors. On ceramic SMD capacitors don’t expect any markings at all, and if you mix different values up you’re in real trouble; like wise for transistors and most other parts. If you’re lucky you do get some obscure markings; long gone are the manufacturers mark, part number and possible date code. IC’s do tend to still have readable markings on.
Now to handle these tiny blighters you’re going to need some fine tools and plenty of good quality light as you don’t want shadows being cast over your work area as you position your tools or hands, and this may mean you actually need multiple light sources.
A good quality soldering iron is of course essential even for general assembly work, however probably more important for SMT soldering is the soldering irons bit size. Size does matter, and in this one case, it really can’t be too small. I found that the Antex 1mm bit is too big for most SMT work and you may do better with their 0.5mm bits.
 Figure 2 - My tweezers, 1mm Antex iron bit and a 0.8mm bit from my Xytronic iron |
 Figure 3 – Scalpel with a number 11 blade, tweezers, Antex 1mm bit (lower),
Xytronic 0.8mm bit (upper) and a set of picks |
I switched from my trusty Antex several years ago as I wanted a temperature controlled iron and my preferred distributer had a special offer on Xytronic so I gave it a go and never looked back.
A good quality metal pair of tweezers is also essential. They should be none magnetic as most SMD components seem to be ferrous and “jump” up onto the tweezers when you move in for the grab, making it very difficult to pick the components up properly. I invested in a fairly expensive pair of Bernstein tweezers as they had excellent reviews and the points are razor sharp; I’ve stabbed myself a couple of times with them so I keep them in their protective case until needed and only ever use them for SMD work. I’ve got other cheaper pairs for more general work.
Don’t use plastic as they will melt, and the metal ones also act as a heat sink which is useful.
A scalpel with a number 11 sharp blade is great for all sorts of general jobs like cutting PCB tracks that are wrong or are not etched properly. It’s also useful for holding a component in place on the board until the first pin is soldered.
I found a set of picks on EBay that were designed for model builders and these are also ideal for holding small parts in place whilst you solder that first tricky pin. There also great for slipping under the body of a component that you need to remove before you start de-soldering the pins.
A good quality metal pair of tweezers is also essential. They should be none magnetic as most SMD components seem to be ferrous and “jump” up onto the tweezers when you move in for the grab, making it very difficult to pick the components up properly. I invested in a fairly expensive pair of Bernstein tweezers as they had excellent reviews and the points are razor sharp; I’ve stabbed myself a couple of times with them so I keep them in their protective case until needed and only ever use them for SMD work. I’ve got other cheaper pairs for more general work.
Don’t use plastic as they will melt, and the metal ones also act as a heat sink which is useful.
A scalpel with a number 11 sharp blade is great for all sorts of general jobs like cutting PCB tracks that are wrong or are not etched properly. It’s also useful for holding a component in place on the board until the first pin is soldered.
I found a set of picks on EBay that were designed for model builders and these are also ideal for holding small parts in place whilst you solder that first tricky pin. There also great for slipping under the body of a component that you need to remove before you start de-soldering the pins.
Plastic Petri dishes are very useful
Figure 4 - Plastic Petri dishes
SMD components are small fiddly blighters and if you’re not very careful you will lose them, and because their markings are either tiny or none existent, mixing different parts together should be avoided at all costs.
For this reason I tend to solder all parts of the same type and value at the same time.
I keep my SMD parts either in storage trays, compartmentalised storage boxes or the bags they were supplied in (my main supplier uses zip-lock bags which are ideal for storage) and only remove them when I’m ready. Most SMD parts are supplied on paper or plastic tape strips and I would suggest that you keep them like that till you need them.
For this reason I tend to solder all parts of the same type and value at the same time.
I keep my SMD parts either in storage trays, compartmentalised storage boxes or the bags they were supplied in (my main supplier uses zip-lock bags which are ideal for storage) and only remove them when I’m ready. Most SMD parts are supplied on paper or plastic tape strips and I would suggest that you keep them like that till you need them.
Many SMD components are supplied in strips
Figure 5 - SMD Resistors
What I tend to do is cut a strip with the required number of parts, then using a scalpel, gently peel off the front transparent plastic strip and let the components fall into the Petri dish. A gentle tap with the handle of the tweezers on the bottom of the dish will cause the components to jump slightly and often flip over; this is a great way to persuade the components to land with their markings face up, if they have any.
Petri dishes are available in plastic or glass.
Don’t use the glass ones even if you have them to hand!!
That was stupid mistake two.
Petri dishes are available in plastic or glass.
Don’t use the glass ones even if you have them to hand!!
That was stupid mistake two.
Different solder wire sizes
Figure 6 – Different solder gauges. From top to bottom, 32, 22 and 18 swg
Figure 6 shows 3 different gauges of solder. Trying to use standard hobbist 22 swg for high density SMD ICs like the one in the picture is extremely tricky; it’s hard enough using 32 swg.
Fortunately, solder is available right down to 32 swg and this is another case where smaller is better.
You will also find complete SMD re-work solders and kits available but I've never really bothered with them or found the need... yet.
Fortunately, solder is available right down to 32 swg and this is another case where smaller is better.
You will also find complete SMD re-work solders and kits available but I've never really bothered with them or found the need... yet.
Soldering SMD simple components
I’ve experimented with a couple of different techniques but the best I’ve found so far, is to tin just one of the PCB pads with solder first.
Figure 7 - Sequence of events for soldering an SMD device
Video showing how to solder an 0805 resistor.
Soldering SMD ICs and components with more than two or three pins
Figure 8 - Component held in place by first pin soldered... but out of alignment
Now, check very carefully to make sure that the component is in the correct position and orientation and none of the pins are straddling multiple pads.
A magnifying glass is an ideal aid here and I use a small hand held gem stone x10 magnifier.
As can be seen in figure 8, the SMD part has moved and should be repositioned before continuing.
Once you’re happy that the component is positioned correctly, proceed to solder the remaining pins making sure that the component doesn’t over heat whilst you’re doing this. Remember they are designed for this and I’ve never damaged a part during soldering… yet… just be carful.
If you’re soldering a compnent with a lot of pins, give it time to cool down after you’ve completed a few pins if needed. Don’t try and force cool the part as the thermal shock could destroy it.
A magnifying glass is an ideal aid here and I use a small hand held gem stone x10 magnifier.
As can be seen in figure 8, the SMD part has moved and should be repositioned before continuing.
Once you’re happy that the component is positioned correctly, proceed to solder the remaining pins making sure that the component doesn’t over heat whilst you’re doing this. Remember they are designed for this and I’ve never damaged a part during soldering… yet… just be carful.
If you’re soldering a compnent with a lot of pins, give it time to cool down after you’ve completed a few pins if needed. Don’t try and force cool the part as the thermal shock could destroy it.
Building bridges isn't always a good thing
Figure 9 - Bridged pins
If you should happen to bridge a couple of the pins on a component, don’t panic as there are a couple of things you can do. Firstly, allow the joint to completly cool down; move on to other pins and re-visit this at the end.
Often, heating the joint and swiping the soldering iron bit away from the component can persuade the excess solder to travel down the copper track and thus, break the bridge,
Also, a standard de-soldering tool will remove the offending bridge. Just heat up the bridged pins and suck up the excess solder from the bridge. Give the component time to cool if needed and then carefully re-solder the pins. Leaving a little time between each adjacent pin to allow the joint to cool fully reduces the possibility of the pins bridging again.
Once all the pins are soldered, check back and redo the first pin that was used to "tack" the component in place if needed.
Often, heating the joint and swiping the soldering iron bit away from the component can persuade the excess solder to travel down the copper track and thus, break the bridge,
Also, a standard de-soldering tool will remove the offending bridge. Just heat up the bridged pins and suck up the excess solder from the bridge. Give the component time to cool if needed and then carefully re-solder the pins. Leaving a little time between each adjacent pin to allow the joint to cool fully reduces the possibility of the pins bridging again.
Once all the pins are soldered, check back and redo the first pin that was used to "tack" the component in place if needed.
There's small... and there's small...
Figure 10 - A 4066 CMOS 14 pin SOIC next to a PIC 18F6722 FQFP-64/10 x 10
If SMD work is something you are going to be doing a lot of, you may want to invest in some additional tools.
Simple components like resistors, capacitors and most of the discrete semiconductors can be soldered by eye and then just checked with a x10 magnifier to just check that everything looks ok. But with some of the higher density parts, I prefer something with a little more “grunt”.
Simple components like resistors, capacitors and most of the discrete semiconductors can be soldered by eye and then just checked with a x10 magnifier to just check that everything looks ok. But with some of the higher density parts, I prefer something with a little more “grunt”.
A close work inspection microscope
Figure 11 - A GX-Microscope Long reach microscope with articulated arm
This bad boy is perfect for SMD soldering and a host of other inspection tasks as well. Most microscopes are designed to look at backlit objects; cells, bugs and other creepy crawlies. This microscope illuminates the work from above; you can see the white ring at the bottom of the microscope head. This contains 30 white LED’s and a dimmer circuit.
There are many styles available from different companies but I quickly got rid of my monocular version and replaced it with this binocular one as I found looking through just one eye piece was straining my eye and I was walking around with a strange squint on my face.
It’s also fully articulated and simply swings out of the way when not needed.
Actually, this scope has a trinocular head fitted; you can see the 5 mega-pixel USB camera on the black tube coming from the top of the head assembly and we use the camera for quality control and diagnostic inspection documentation. It also took the images for figures 6, 8, 9 and 10.
The other item that you can’t see is an auxiliary objective 0.5x magnification lens. The normal object working distance of this head is around 60mm; not enough room to get a soldering iron underneath the scope to the board. With the auxiliary objective fitted, the focal distance increases to around 140mm which is ideal. It’s important that you check the focal distance before you buy.
For reference, this is a GXMXTL3TV7 from GX-Microscopes (http://www.gxmicroscopes.com/)
Happy SMD soldering.
There are many styles available from different companies but I quickly got rid of my monocular version and replaced it with this binocular one as I found looking through just one eye piece was straining my eye and I was walking around with a strange squint on my face.
It’s also fully articulated and simply swings out of the way when not needed.
Actually, this scope has a trinocular head fitted; you can see the 5 mega-pixel USB camera on the black tube coming from the top of the head assembly and we use the camera for quality control and diagnostic inspection documentation. It also took the images for figures 6, 8, 9 and 10.
The other item that you can’t see is an auxiliary objective 0.5x magnification lens. The normal object working distance of this head is around 60mm; not enough room to get a soldering iron underneath the scope to the board. With the auxiliary objective fitted, the focal distance increases to around 140mm which is ideal. It’s important that you check the focal distance before you buy.
For reference, this is a GXMXTL3TV7 from GX-Microscopes (http://www.gxmicroscopes.com/)
Happy SMD soldering.
