Hi all,
Hit a bit of a snag at work. I've been consulting with our factory in China but just looking for some more ideas. I'm working on an AC/DC power adapter design. Cost is a priority. Just about everything we make is 100% wave-soldered, as we have a high mix of SMT and THT parts, and the SMT parts are always SOIC, SOT-23, 0603-1206 sized. But, for this design we have no choice but to incorporate a QFN package IC.
So far the options are:
1. Two pass process: First, reflow QFN and surrounding parts. Then, pass through wave. This requires a special wave solder mask/pallet to block the QFN circuit from the wave. This may wind up being a fairly economical approach.
2. Daughter board with pin headers: Transplant the QFN circuit to a small daughter board, and wave solder the board to the main board. Unfortunately, due to tricky space constraints, it doesn’t look like this will work.
And finally...
3. Daughter board with castellated/half holes: This is something I’ve been thinking about but am not sure the practicality.
- Reflow solder QFN circuit to daughter board with half-holes, like those commonly seen on RF modules
- Red glue the daughter board to the solder side of the PCB.
- Pass through wave-solder to connect half-holes to main PCB. No mask/pallet used. Is wave soldering a compatible process for half-hole PCBs?
The idea is to save on tooling since we’re not sure about production volumes yet. If we go this route, I think the daughter board’s components will need to be red-glued down, to prevent them from falling off in the wave. Can red glue go through more than one process, i.e. reflow then wave, reliably? Anyone ever tried to glue down a QFN…4 dots, 1 in each corner maybe?
Does it sound ridiculous? Just tool up for the proper masking pallet?
Thanks!