Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Wave Solder

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Wave Solder | 1 March, 2007

How many times can you safely run a board across the wave solder? We have an unwritten rule here saying that twice is all that we can do. But it has been an unwritten rule for so long that no one knows where it orginated. Thanks for your imput.

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Wave Solder | 1 March, 2007

My own personal "unwritten rule" has always been - no more that 3 times. Anymore than once, I'm not sure what the implications are. If you think about the mechanics of wave solder. It's around 200 Deg. F of preheat, and then immersed in 480 to 500 deg. F of molten solder for about 3-5 seconds (depending on your configuration and profile).

Components and Boards undergoing this more than twice doesn't sound appealing. I doubt any studies have been done on this, and I'm sure there's a board out there somewhere, perhaps even a board that's in some type of "life-sustaining" capacity, that's been through more than 3 Wave Solder heat cycles, and I betcha it's been doing just FINE!

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Wave Solder | 1 March, 2007

Samir, thanks for the reply. We are wondering if this idea came dowm from a customer a long time back, or maybe from Mil Std 2000. I've never worked with Mil Std 2000, so I don't know about that. We can not find anything in Jstd or 610 about it. Jstd only says that the period of exposure to the solder bath should not degrade the board or parts, but doesn't say how many chances you got to get it right.

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Wave Solder | 1 March, 2007

From our notes ...

An intense evaluation was completed in 1992 that involved testing of three board types [6 layer FR4, 6 layer ceramic copper thick film, and a 4 layer copper-invar-copper board] by the Navy Surface Warfare Center, Crane, IN. [Obviously, the study is dated now, because of changes in flux and solder formulations, new heating control and application methodology, and different kinds of pad/lead finishes now available, but there is some core info that could very well be beneficial to process development.]

The study found that with controlled heat cycles at minimal temperatures, intermetallic growth was minimal, and there was no reason to suspect or predict solder joint fractures with as many as 8 assembly heat cycles. Additionally, the pad thickness didn't seem to decrease at the rate predicted in an earlier study. Perhaps the intermetallic actually acted as a barrier to further dissolution.

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Wave Solder | 2 March, 2007

Dave, our facility does only military and aeorspace contracts, we still use only tin/lead solder and 186 Rosin Flux, so this info is just what I need. Thanks for your imput.

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