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Wave Soldering Thick PCBs - Foam vs Spray Fluxing

HOSS

#31844

Wave Soldering Thick PCBs - Foam vs Spray Fluxing | 27 December, 2004

Need some feedback here. We're running a foam fluxer using WS chemistry (AIM 715M). We have been running almost exclusively .062 and a few .093" PCBs but we've recently started running some boards that are .100 and .125 thickness and are having trouble getting proper fluxing to the topside of the PCB.

We've played some with our airknive and flux density and have a few other things to look at but I wanted to throw a general question out there: Would a spray fluxer work any better in this situation or should we expect a foam fluxer to work with the right parameters?

Thanks in advance.

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jdengler

#31845

Wave Soldering Thick PCBs - Foam vs Spray Fluxing | 27 December, 2004

HOSS, Most spray fluxers won't help. If you get a spray fluxer that uses a high velocity spray gun, it might. That being said I had less problems with top side wetting from a foam fluxer myself. Make sure the foam height is good. Also had some problems from very small lead to hole deltas. Are you sure flux is not getting to the top or is the top cold?

Good luck Jerry

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#31849

Wave Soldering Thick PCBs - Foam vs Spray Fluxing | 28 December, 2004

In almost every application an ultrasonic spray fluxer will out perform foam fluxing. Better soldering results are what most expereince after making the change to U/S spray. There are good ultrasonic units from USI and Sono-Tek.

www.ultraspray.com www.sono-tek.com

A top side preheater may help more than a spray fluxer. Also, try slowing down the conveyor speed a bit.

Try turning the air-knife to a greater angle to force more flux up the holes.

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#31851

Wave Soldering Thick PCBs - Foam vs Spray Fluxing | 28 December, 2004

Assuming the poor hole fill is not localized, try: * Inadequate preheat * Flux specific gravity is low * Low solder temperature * Conveyor is running too fast * Solder pot is contaminated

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KEN

#31853

Wave Soldering Thick PCBs - Foam vs Spray Fluxing | 28 December, 2004

When using a foam fluxer:

1. Bubble size is important. What stones are you using? Ever clean them? Too large a bubble will NOT help your situation. (I forget bubble size range....check with your fluxer mfgr.) 2. Thinner will help in capilary mobility. Follow flux mfgr's recommendations. 3. When using an air knife more is NOT better. If your pressure is too high you will squeegee off and blow out the flux from the TH's. Also, the slight air knife pressure AIDS in hole fill (for the flux)

I foam flux 2 oz. copper multi-layer back planes 0.250 inch thick. These are back planes used for cellular amplifiers...and yes, there is topside wetting and 100% barrel fill. It can be done.

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