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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Conductive filled Vias on BGA

Paddy

#30898

Conductive filled Vias on BGA | 8 October, 2004

Hello,

I am wondering if anybody has process experiance of designs which use the above. I understand that the filled via is an excellent thermal cnductor, which is great from a design point of view, but how do these solder through the reflow ovens. ?? Any help appreciated.

Paddy

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#30901

Conductive filled Vias on BGA | 8 October, 2004

First, don't get too excited about the thermal capabilities of conductive epoxy. An epoxy like DuPont CB-100 increases the amount of heat conducted through the barrel, but many over estimate what it can do.

Calculations show for a 0.020" drilled hole with 0.001" copper barrel thickness, adding CB-100 increases the amount of heat by less than 5%. The reason is the CB-100 has a thermal conductivity of 5.23 W/mK versus 395 W/mK for copper. Even though CB-100 makes up the majority of the cross sectional area, it only adds a little to the "thermal" cross section.

Second, in response to one part of your question, we manufacturing types want you to keep via plugs at or just barely below the surface of the solder mask. If you allow epoxy above that level, it will affect the amount of solder on SMT components.

Finally, in response to the other part of your question, epoxy has poor adhesion to tin and its alloys.

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#38152

Conductive filled Vias on BGA | 30 November, 2005

Dave,

Do you know if such thermal transfer study with CB-100 (or equivalent) is available for review? My customer is pursuing this option and I am curious on how much improvement I would see by specifying a conductive via fill on the board.

Rgds, Peter

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#38155

Conductive filled Vias on BGA | 30 November, 2005

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