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

Printed Circuit Board Assembly & PCB Design Forum

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Cracked vias

#22717

Cracked vias | 15 December, 2002

Has anyone heard of vias cracking (barrel from pad) when being wave soldered. Was told this was a big problem by contract pcb designer, he always tent vias because of this. The reason was that the solder filling the vias caused stressing and then seperation of barrel from pad.

Have not encountered this personally, is it really a problem out there or have these people just had bad experiences with poor bare pcb manufacturers or poorly setup solder waves.

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RDR

#22721

Cracked vias | 16 December, 2002

I have never had this problem. It sounds like you are right in imagining that there must have been a bad supplier of PCBS or an inadequate design rule being followed, or a very bad wave process to have this cracking over wave solder. Some books require that all vias must be filled with solder if processed over a wave. It is my understanding that this requirements assures greater strength in the via/trace interconnect. (I could be wrong)

My thoughts

Russ

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#22726

Cracked vias | 16 December, 2002

Knee of barrel and pad crack: Caused by thermal stress during soldering, because epoxy expands in the "z" 3X more than "x" or "y" which are restricted by the fiber. Related to: * Design of pads too large relative to hole diameter * Temperature at or near holes is as hot as any place on the board * Plating thickness SB GT 0.001" * Manual soldering too hot, too long * Thick (0.093" or GT) boards made of low Tg material

Search the fine SMTnet Archives on barrel cracking. I think these's more there.

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