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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Glass Wicking

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Glass Wicking | 4 November, 2006

Can someone educate me what is 1)glass wicking failure on PCB 2)Crack of TH Barrel How it happens and how this can be rosolved?

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Glass Wicking | 4 November, 2006

Well, I can't tell you what the "glass wicking failure on PCB" are but for a standard FR4-pcb the Tg temp. or the so called glass temp. is 176 celcius degr. This means that the pcb is in between a firm and a buoyant condition. This is really a bit of fun, since the FR4-pcb:s should not be able to stand the reflow process. It is even more interesting when it comes to FR4-RoHS pcb:s which have to withstand a higher reflow temp. Anybody who has some experience with micro-vias should know that this isn't so fun to deal with and most of the time when the pcba fails, it is due to the fact that it couldn't stand the reflow process.. /

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Glass Wicking | 7 November, 2006

We/ve never heard of "glass wicking failure" in regards to board fab. Boat fab, yes. Look here:

Barrel cracking appears after 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, so look to resin selection * Plating thickness SB GT 0.0001" * Thick (0.093" or GT) boards made of low Tg material * Circumferental void: Caused by drilling debris partially plated-over * Circumference void: Caused by hole processing (ie, desmear, metalization) * Electrolytic plating has "hour-glass" shaped plating thickness - thin near center of the hole

Careful review of your sections should point you towards the cause of this problem.

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Glass Wicking | 11 November, 2006

Hi, "glass wicking failure" we don't know what this is, but we suspect that the reflow process could very well be the root cause for some of our pcba with micro vias failure. Micro vias pcb we know to well (we don't like them at all). There are No pcb manufactories out there that can say for sure, that a 14-layer pcb 200 x 250 mm with micro vias is easy to fabricate, If they say so, then they never got a customer reply on pcb-failures! Not to mention to assembly, especially in RoHS conditions! On top of that, the press-in connectors at the rear end will affect the micro-via pcba, if there are even the slightest board warpage. This is what we are facing today and any suggestions of how to improve the process will be greatly appreciated. /Thanks

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Glass Wicking | 11 November, 2006

Maybe you should start a new thread on this one... Yet interesting subject.

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