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Voids in every Lead-free BGA solder Joint

Ben

#22468

Voids in every Lead-free BGA solder Joint | 21 November, 2002

I'm doing SMT of lead-free solder BGA on FR4 Ni-Au PCB. The solder paste I'm using is Sn/Ag/Cu and reflow with peak temp at 240C. I found there are voids(1-2) in almost every solder joint(500 micron in dia) under xray. And the void size is violate the IPC-7095 standard. I tried to find out which parameter in my process cause the void. I tried different solder paste(different brand, composition, even Pb/Sn), differnt reflow peak temp(220 to 260), different heating rate, duration above melting point, multiple reflow.....There are still voids in my every solder joint. And finally I even have voids in my lead-tin solder joint. This is really a big headache to me. Could anyone please help. I've almost tried everything I can. Thanks and every input are welcomed.

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Kris

#22489

Voids in every Lead-free BGA solder Joint | 22 November, 2002

What type of reflow profile are you using ? There is a void reduction profile recommeded by some paste manufacturers, Try that it might help. Did you check the components or the board and see if they have absorbed mositure ? try baking the boards and components for about 8 hours in a regulated oven at 110 c.

Just another thing we might overlook is if your flux has seperated from the paste when you assembled.

Are the boards clean ? contaimination on the board finish can be checked

thanks

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#22490

Voids in every Lead-free BGA solder Joint | 22 November, 2002

Search the fine SMTnet Archives for background discussion on BGA voids.

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Ben

#22522

Voids in every Lead-free BGA solder Joint | 25 November, 2002

Thanks for the advise. I got the advise from my solder paste vendor to increase the time above melting point for flux outglassing to escape. I tried but no big help. For the moisture issue, actually I've try to bake both the PCB and components at 125C for 24 hours. Voids are still there. Anyway, I'm keep trying to change each parameter of my reflow profile as it is the major reason of causing voids from most literature. But there is constraint of changing duration of each zone as the oven I'm using is a small (4-5 feets length) with 4 zones reflow oven. THanks for the inputs.

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