SMT Soldering Tutorial
What you need
First of all you need an soldering iron. It does not have to be fancy or expensive or professional or anything like that. Your soldering iron should just fulfill some requirements:
- It must be regulated. If not it will overheat or have some random temperature – but not the one you need. It does not need to have a adjustable temperature (though it helps).
- It should have a suitable tip. For SMT you do not need a very fine tip (they do not heat very well), but it should not be too wide. For SMT I like them pencil shaped, a flat one, shaped like a screw driver is fine too. As you can see by comparing this to an AA battery – it is not very thin. If it is similar to the size of the 0805 pads it is fine. For smaller chip packages I really like to use bigger screw driver type tips – they make it easy to apply solder to several pins.
- It should have some power. 15-20 Watt is fine. If yours has some higher rating it is better (but it must be temperature regulated – else it will get too hot). The power does not matter to heat up smaller pads. It is just useful to heat up pads, which are connected to a ground plane or something similar.
Of course you need solder. It does not matter if it is lead free or leaded. Lead free is better for the environment, for me leaded is easier to solder. It is easier to solder if it is thin. You can much better control how much solder you put on a pad. Mine is 0,5mm which is comparable to 24AWG.
You need a good pair of tweezers. Mine is an special SMT one, with bended tips. I like it a lot. Do not go cheap – you should never go cheap on tools (as my grand pa put it: “If you buy cheap you buy twice”). A good pair of tweezers can last for many years.
Get some flux. Flux is your friend. You probably have to reheat one or another pad (especially if you solder the fine pitched controller). So have some flux handy and use it liberal on the board if you reheat a connection. It will do wonders. It should match the flux in your solder. There are two general kinds of flux: No clean and the other one (I do not remember its name). It should be the same kind. Mine is not – it does not do any damage and works great.
Get some solder wick. It is necessary to remove excessive solder or remove some solder bridges. Get a good one (mine is from the German equivalent of Radio Shack and not very good. Not recommended, but works). If you use it always clip a clean end and use the end. It helps to put a bit solder on the tip when using it (it sounds contra intuitive – but if there is some solder between the tip of the soldering iron and the wick it heats much easier).
How to actually solder SMT components
Curious Inventor got a very nice overview about the whole process, just check the video:
I do not use that many flux as they do. But flux never hurts.
Here is a nice example how to solder all those nifty 0805 (the same applies to 0603 and 0402 components – on a smaller scale):
Unfortunately without comments, but I think the way to do it is clear: Apply some solder to on pad – if one pad is connected to a (ground or VCC) plane it is easier to not start at this pad. I think the tip used in the video is far to thin. You will get better results with bigger tips, really.
Be sure to check out the SMT tutorial over at Tangentsoft. It is very comprehensible. And he mentions the magic trick where to begin soldering: In the middle. At least it is the way I do it. If you work from the middle of the board to the outside allready soldered component do not come into your way, blocking access to solder pads – often.
Keep in mind: For all parts with more than two pins first align, solder one pin, realign (do not realign a chip more than 5° without reheating the joint. You will probably bend the pin too much or even break it!), then solder another (opposite pin). After that solder the rest of the pins. The whole process is explained in this video quite well:
If you have some bridges in your parts there are some techniques to remove them. The easiest is to wick it away. Add more solder (yes, it is easier to remove a bigger blob of solder), cover the spot with the end of the wick. It is easier, since one end will heat up easier than some part in the middle. Less heat is dissipated by the wick. And again. Do use flux. Smaller bridges can be removed with a clean tip, like shown here:
But be careful not to damage the silk screen. I damaged several boards by no being careful enough.
And yes, it takes some time, practice and the right tip to solder like this: