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BGA soldering

pranav

#26169

BGA soldering | 24 October, 2003

I am re-designing a MLB Printed Circuit Board which has thro' hole chips and a BGA. I am planning to go for reflow soldering for the BGA on one side and wave soldering for the thro' hole parts on the opposite side. Is there any concern or any sequence to be followed? Wave followed by reflow or reflow followed by wave? will the wave soldering affect the reliability of the BGA already soldered ?

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Stephen

#26186

BGA soldering | 27 October, 2003

The most common way is to screen print paste for the SMT placement, then then SMT placement then reflow then TH placement followed by wave solder. You won't be able to screen print for the BGA after reflow unless you use a mini stencil. Or you could use a paste dispencer. Or you could use tacky flux for the BGA.

One concern for doing it the normal way I've heard is Via's under the BGA allowing too much heat through. But no matter how you do it, run profiles with strategic placement of thermocouples.

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#26190

BGA soldering | 28 October, 2003

Running a soldered BGA through a wave solder pot is very risky: * 230-240*C temperature of the pot could damage the device. * Solder in the pot will certainly cause bridging between BGA solder balls. * Solder in the pot could melt BGA solder balls.

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#26191

BGA soldering | 28 October, 2003

It is possible to use a selective wave soldering fixture to "mask" the BGA devices from the wave. Unless you have a very thick board or one that is tough to heat, you should have no problem with BGA.

Of course you should run some process experiments with your board to determine the what kind of temps your BGA site sees at the wave.

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Gabriele

#26192

BGA soldering | 28 October, 2003

After following the suggestions above, and where it would not be possible to mask BGA by soldering fixture, a Kapton tape (pre-punched) can be placed under BGA ( wave solder source side ) it can help to keep temperature low enough avoiding "secondary" reflow of ball solder joint.

Gabe

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Stephen

#26194

BGA soldering | 28 October, 2003

I just reread your message. The wave soldering is on the other side? I.E. The Through hole parts are on the same side as the BGA. This would be the only way to do it. But reading the message again it could be interepted as the through hole parts are on the opposite side. This you would not want to do.

Another possibility might be paste in hole and reflow everything but this is not always practicle.

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#26197

BGA soldering | 28 October, 2003

We theorize a secondary [bottom] side BGA can be wave soldered with planning. Issues are: * Keepout between the BGA and one side of the board that is clear of PTH parts requiring wave soldering, so to support the fixture. * Keepout around the BGA. * Ability to pump solder to the board surface, given the high component height if the BGA and the thickness of the fixture.

If you were very clever, [and you are stuck with a dopey design that's going run through labor like beer at a chunder party]: * Design holes in the board near each corner of the BGA that would accept push-through clips on the corners of a piece of Durostone or other wave fixture material. * Use hi-temp rubber shunts

We've seen BGA reach 160+*C on the primary [top] side during wave soldering.

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Gabriele

#26202

BGA soldering | 29 October, 2003

I am sorry, my understanding ( English is not my language)was to have BGA on SMT side, I mean destination solder of wave. But after your clarifiation, now I am in front to a DFX more that a Design for Manufacturing. In this case every think can be done, it is only matter of cost. Thank you gabe

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