Solder Wave

Some causes of lack of top side fillets (hole fill) are:

1. Not enough pre-heat (a top side preheat will help, if no-clean flux, be sure to follow flux mfrs specification for top side board temp just before hitting wave) 2. Not enough flux 3. Flux is too weak- re-oxidation can occur (OA flux works best) 4. Wave band width to short (need at least 2 second contact time)

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In addition to Pete's fine tips, here's one we have successfully used in similar situations as long as you're using OA flux. Get some kind of pump action spray bottle (like hair spray comes in) and fill is with some of your wave flux. Use the bottle to manually spray the top side of board, and process it as usual. This would obviously not work well with no-clean flux.

90 degrees for top side preheat sounds a little low to me, I would try pushing this board to the upper end of your flux manufacturer's preheat specs for improved top side fill.

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You are not correct in assuming bot side temp as related to top side. This is entirely dependant upont the board. e.g. a PCB that is .4mm thick will almost be exactly the same temp top and bottom whereas this 2.4mm will be significantly less at the top compared to the bottom. You need to reach a topside of at least 120C for a PCB of this nature.

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Those temp stickers are useless unless you can stick them into the copper barrel. They can only determine "skin" temperature which has nothing to do with what is happening in the barrels.

Your solder is filling the barrel then going cold. I'll guarantee the solder stops at a (inner) copper layer. I have done hundreds of cross-sections and the most common root cause when the problem is repeatable:

1. Insufficient preheat 2. Poor setup on ultrasonic spray fluxers or excess air knife pressure on foam fluxers 3. Poor (read "NONE" thermal relief)

The thing you have to remember about wave soldering is this: It's what works that counts. He said 130C topside, she said 120C topside...blah, blah, blah. If your assembly needs 150C to achieve acceptable soldering results then that is what counts.

I was asked to consult on a power distribution backplane that was having wave solder issues. The holes were capped because the preheat was way low. This board was 0.110 thick with 3oz copper planes. When I finished we had zero defect, 100% fill in all holes and a "radical" profile that was a signifficant departure from the "norm". Big boards need big heat. Period.

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