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Solder Wave

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Solder Wave | 11 August, 2005


I have a 2.4mm pcb 8layer with a lot of copper on board.

I am having some problems with solder not travelling up through the holes.

Looking from the bottom of the board it looks fine .


To measure temp. of board through preheat zones (two bottom no top convection) I use temp. stickers .

Am I right in saying if the top reaches say 90degrees that the bottom should be +10-15 degrees higher?

any help appreciated.


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Solder Wave | 11 August, 2005

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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Solder Wave | 11 August, 2005

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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Solder Wave | 11 August, 2005

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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Sue PH


Solder Wave | 11 August, 2005

The soldering handbook that I use gives a 'rule of thumb' for best preheat temps for wave soldering. For multilayer brds that are metal core it suggests 110 to 130 degrees C topside temp to get the best solder fillet. We do a lot of multilayer metal core brds here, and my experience has shown that the closer I get my topside temp to 130 C, the better results I have. I use 186 rosin flux, which can stand up to the heat.

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Solder Wave | 11 August, 2005

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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Solder Wave | 12 August, 2005

Guys ,

Thanks for all your inputs on this one.

I have had to increase preheats dramatically aswell as increasing conatct time over lambda wave.

Joints are perfect.


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