I managed to hand-solder one of my transceiver boards — the one that includes many 0402 components and one CSP (chip-scale package). Here’s my handiwork:
I used some ancient 0.030″ rosin-core solder and equally-ancient Xytronic Auto-Temp soldering iron. Both were purchased about 20years ago. The tip on the iron is much larger than the components I’m soldering, and the rosin-core solder is probably killing me a little bit with every breath I take. Maybe I should consider upgrading my equipment. A little defluxer wouldn’t hurt either.
First, I tackled the CC2500 chip. I figured if I couldn’t get that to stick correctly, I shouldn’t waste my time soldering the other parts on the board. I did the customary thing of putting a slight blob of solder on one pad and then reheating that blob as I rested the part on the blob, in the correct location. I had to adjust the position a little bit by reheating that pin and nudging the part until the pins were aligned with the pads along all four sides. Once the part was in place, I’d clean the tip of the iron and put a fresh bit of solder on the end. Then I’d touch that bit to one or more unsoldered pins (”one or more” because my soldering iron tip is way larger than a single pin on this IC). I’d give the solder a couple of seconds to flow, and then pull the tip directly away from the part. Moving the iron directly away from the part lowers the chance of creating a solder bridge between parts, as the solder surface tension will be mostly between the pin(s) and the iron tip. What’s nice about the CC2500 chip-scale package is that the pins are difficult to damage, unlike a PQFP package with spindly leads several millimeters long. I did not put any solder on the center pad under the chip. I’m hoping I can get away with this, as I’m not sure how I’ll flow solder in from the other side — the via holes through the board are likely too narrow.
Next, the 0402 components. Again, I used the common practice of blobbing one of the pads a bit. Then I’d place the part on top of the blob and melt the blob. Sometimes the part would still be a bit crooked, or maybe it wasn’t sitting flat on the board. So I’d use the tweezers or my fingernail to push the part into place while I reheated the pad. Then I’d put a big blob down on the opposite pin — sometimes that’s what it took to get good flow with the very small exposed portion of the pad. If the resulting blob was disgustingly big, I’d shrink it a bit with solder wick.
The only other tricky part was flat-pack microcontroller. This was perhaps the trickiest part. I pinned down two pins on opposite sides of the package. Then I soldered each pin, but went too heavy on the solder. In cleaning it up with solder wick, I pushed some solder blobs behind the pins. My only option was to re-wet the area with solder and clean it up with solder wick. (Surface tension is so handy sometimes!) I tried again, using a technique more like the one I used with the CC2500 (described earlier).
I checked for conduction between pins on all the packages using my multimeter. It has very fine probes, and with patience and a steady hand, you can tell if you’re going to let the smoke out when you hook up your project. Of course, you should also check for continuity and resistance between power and ground.
My shopping list: First, I should get smaller-diameter solder — perhaps 0.020 or finer. A finer soldering iron tip would be nice (maybe I can grind down the one I have). I should also get some solder flux I can apply before or after. I need a means to clean up the flux — sensitive and high-frequency projects can misbehave and suffer from the contamination. I’ve heard that rubbing alcohol can deflux, so I’m going to give that a try before I buy something special. I should also improvise some means of venting all the fumes.
