I have a batch of beta PCBs which we have to assemble in our lab. We have an APS manual pick-and-place machine and a tabletop reflow oven so I thought assembly tomorrow would be easy and straight forward until our technician bought up a point.
The PCB to be assembled has a mix of both through-hole and SMT parts. We'd planned to place and bake all of the SMT components first, and then hand assemble the through-hole parts. But out tech is concerned that in reflowing the SMT parts some or all of the through-hole footprints might close up. This is our first attempt of an in-house build so we are looking for how others may have approached a mixed build.
If the through-hole parts can all tolerate the reflow heat curve we can add them to the PCB and reflow all of the parts at once. The through-hole parts would essentially keep the holes from filling, but if they did no harm would be done. Of course, the through-hole parts would still be hand soldered after reflow. Is this a reasonably good approach?
Best Answer
Both approaches are valid.
Hand assembly would require that the paste mask for the SMT devices prevents putting any paste on the thru-hole pads at all. Then you use wire solder as usual during the hand assembly phase.
Thru-hole devices can be soldered in the reflow oven; this requires a technique called "paste-in-hole" — but it doesn't work with all components, and the PCB has to be designed for this from the start.