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  • About

     

     

     

    This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Australia (CC BY-NC-SA 3.0)

    Surface Mount is Easy

     

    Using SMD or surface mount components is often regarded as difficult and to be avoided at all costs - but that is a great waste.

    Not only are surface mount devices relative easy to solder they also open up a world of sophisticated devices for you to use - from accelerometers to high performance microcontrollers.

    Prototyping and soldering these devices might use a different technique from the normal soldering style - but it is not difficult.  All you need is a good soldering iron and a steady hand.

    This page summarises my views and techniques on using these components.  It is aimed at the hobbyist who might want to assemble a few projects using some surface mount devices and does not want to turn it into a major production.



    Just Solder It

    I suppose that the central message is that you should just solder the components to the board by hand using a soldering iron.  This may sound like heresy but it is the simplest and easiest approach.  

    If you are like me and have searched the Internet on this subject you will have come across many web sites promoting soldering techniques using almost every heat source imaginable including SMD ovens, toaster ovens, infra red lamps and more.  When I started on this path I seriously considered buying an SMD oven (cost >$1000) but fortunately I decided to experiment first.

    I tried a hot air gun, an electric frypan and a toaster oven and found that the main problem is not the source of heat but applying the solder paste.  When you apply the solder paste by hand it is almost impossible to get a consistent layer on the right spots on the PC board - too little and the component will not solder correctly and too much will create a blob causing shorts.  The solder paste also tends to smear when applied by hand and that will make a mess or cause shorts between closely spaced pads.  Big manufacturers will use a stencil to get the right coverage but getting a stencil made up for each design is expensive and complicated when you just want to assemble one or two boards.  Buying solder paste is also a major hassle, it is expensive, has a limited life and must be kept in a refrigerator.

    In the end I reverted to simply hand soldering the devices and that turned out to be the easiest and most straight forward method.  I could explain the technique but the Curious Inventor have an excellent video (Surface Mount Soldering 101) that shows you everything that you need to know.  As you can see from the video, you do not need much equipment but you do need a steady hand.

    The photo on the right shows a recent project where all the components (including the big IC) were hand soldered and the result is excellent. The photo at the top of this page shows the microcontroller chip from a different angle - the pins on the chip are separated by just 0.2mm but the result is just as good as an expensive SMD oven.

    The Tools

    The video shows you most of the tools that are necessary but I cannot resist adding a few observations of my own.

    First a temperature controlled soldering iron is important. It does not have to be fancy (mine is a cheap model) but it must be temperature controlled.  I have found that a 1.6mm chisel tip suits me but probably a 0.8mm would be better.  You need a reasonably large sized chisel tip as you often need to carry solder on the iron's tip to the joint and a fine pointed tip will not hold enough solder.

    You also need a good liquid flux (I use Electrolube SMF12P).  This is because with SMD soldering you often carry the solder to the joint and the flux in the solder core will have boiled off.  The remedy is to use a good flux on the joint before you apply the iron and the result is like magic, the solder will flow freely and quickly resulting in a great joint with the minimum of heat.

    A pair of fine tipped tweezers are also invaluable as you need to pickup and manipulate components that are only a millimetre or two in size.

    For me the most important tool is a good magnifier (my eyes are not that great).   A magnifying loup with a power of x10 is a good start but I found that the one that I bought only focused at a distance of 20 to 30mm and that was dangerously close to my face while I was waving the soldering iron about.  I ended up buying a cheap Binocular Dissecting Microscope (from Amscope) and that is perfect.  You do not need a high magnification, selectable x10 for soldering and x20 or x30 for close inspection of the joint works for me.

    Prototyping

    One argument against using surface mount components is the difficulty of prototyping with them.  I have found that this is not a problem as there are many adapter boards (or breakout boards) that you can buy to suit most SMD packages.  All you need to do is solder the chip to the board and then you have access to the pins on a 0.1 inch pitch.

    A good source is Futurlec, but SparkFun have quite a few and if you search eBay you will find many more.

    Design Techniques

    When you decide to use surface mount devices you do not have to make everything surface mount unless you want to make your gadget as small as possible.  A good example is the Maximite (described elsewhere on this site) which uses just one surface mount chip - the rest of the components are easy to solder standard sized devices.

    Another technique is to purchase surface mount components that are already soldered to a breakout board.  This means that you can treat the board/chip combination as a large IC and plug it into your project as it is.  The photo on the right shows a pre assembled Bluetooth module that I designed into a project as a plug in module. 

    The photo below shows the full board with the Bluetooth module and an accelerometer mounted on a header board. The accelerometer is an example of where you must use a pre assembled header board as the chip is a QFN package which has the solder tabs on the underside of the chip and is therefore impossible to hand solder.

    The best supplier for pre assembled header boards is SparkFun who have a huge range covering USB interface chips, Ethernet chips, special SMD connectors and more.  Also, more and more vendors on eBay are following suit so there is a wide range of sophisticated components that are available and ready to plug into your circuit.