Yesterday I tried soldering them for the first time.The first chip was a complete disaster. I used way too much solder lead. I tried removing it with some solder wick but that was no success.
After watching a video on drag soldering, things started to go a bit better, and on the third chip, a 100 leg QFP, it got very good (except for a bent first leg).
My method ended up being this:
- Apply a tiny amount of solder on the lower left leg (on the PCB of course).
- Position the chip using SMD pliers. Once the chip is in the right spot, tack down the lower left leg with the soldering iron (in my left hand, even though I am right handed) while still holding the chip with my right hand.
- Adjust the chip if necessary (NB: Only do adjustments while the solder is still liquid, reheat if necessary.
- When all legs are in the right position, solder the upper right leg. The chip will now stay in place.
- Now apply a generous amount of liquid flux to all legs. This is very important for a good result.
- On each side, melt a tiny amout of solder onto the two first legs, in effect creating a solder bridge. Then drag the soldering iron across the legs several times. The solder will spread nicely. I use a huge chisel shaped tip, using the corner of it works very well. If you get a solder bridge, move the iron from the legs and outwards and it will disappear (if you haven't used too much solder).
I had to wear a pair of magnifying glasses to be able to do this properly. It is actually really hard to see if you get any solder between the legs and the PCB at all. To be sure, I had my wife bring them to her lab (she's a PhD student working on hormones and using fish cells for her work, so she has some really powerful microscopes in her lab) and take some close up photos of the result
Here are the photos. In my experience, 10 x magnification would be great for soldering while 20 x is perfect for studying the result in detail.
|My second and third attempts.|
|I managed to bend the first leg while tacking down the chip, so this will never work. The rest look good though|
|The mishap at maximum magnification|
|I am rather pleased with the result, especially since this is the first time I've tried to do it.|
|My wife's kick-ass stereo microscope. I want one but they sell for $4000+ used... There are cheaper models out there though.|