Prototype SMD assembly

SMD assembly is not as hard as it looks, and you can get pretty good results with hobbyist grade equipment in your home workshop. A microscope is nice to have, but not a necessity.


I got some of my boards made over at OSH park. They are very nice quality, and pretty affordable. The only downside to the OSH park PCBs is the left over tab on the edge. Can’t complain though as it is a prototype PCB and if I was going to do a batch of more boards you can get the boards routed out properly, with their medium run service.


Nothing a quick file can’t fix.


A quick wipe with IPA and the board is ready for applying solder paste. I really like the ENIG finish too.


I applied the solder paste by hand with a syringe. It doesn’t have to be perfect.


I highly recommend using a nice pair of SMD tweezers, as they will make your life so much easier. They are also non-magnetic so the components don’t get stuck to the tweezers.

All the components are placed. Again this doesn’t have to be perfect, as when the solder re-flows, the surface tension will pull the components into place, most of the time. The board is ready to go in the re-flow oven.


I place the board on some scrap boards to keep it off the grills, which can act as a heat sink and components directly above the metal grill might not get hot enough. I also tape the thermocouple with some Kapton tape to the scrap board, to avoid disturbing the components on the board you just placed components on.


The re-flowed board. A few things still need to be fixed up though, because I applied the solder paste by hand, some pads had too much paste, others not enough.


The re-flow is complete, and everything looks pretty good. Could have used a tiny bit less solder paste on R12, R13, R9. It’s pretty easy to wick a bit up though.


There are also a couple of bridges on the QFP100.


Flux is your friend.


A quick touch with the iron, and you can drag them to one edge where it is easier to wick away the excess.


I like to use a curved tip.


All bridges are removed.


Also there might be a few solder balls hanging around.


Which are easily removed with a nice pair of tweezers.


The reworked board, with all excess solder removed. It’s covered in flux. Time for a clean.


I placed the board in an ultrasonic cleaner, with Electrolube Safewash Super SWAS I can’t recommend this stuff enough, it works great, and after 15-20 minutes in the ultrasonic cleaner.

I rinsed the board off with filtered water (to reduce water spots if you have hard water) and placed the board into the re-flow oven again. This time with a temperature of 80-90 degrees C for about 10 minutes, which is enough to evapourate the water, but not enough to melt the plastic connectors. You have to be careful though, not all plastic connectors are created equal.

Take the assembled PCB out of the oven and let it cool. The board is now immaculately clean.

Prototype SMD assembly

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