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May 2005

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Subject:
From:
Karl Sauter <[log in to unmask]>
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Date:
Wed, 18 May 2005 09:38:33 -0700
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Besides the increased PCB Fab manufacturing cost, even when only filling
vias that have a size and aspect ratio allowing filling in a single
pass, it can still be difficult to completely eliminate voids in the via
fill material.  Any voids in the fill material that are adjacent to
surface mount pads can out-gas during board assembly causing large voids
in those solder joints.

Karl Sauter
Sun Microsystems


Dave Seymour wrote:
> Here is a fabrication note I worked up with the fab shop.
>
> "All vias drilled equal to or less than .0xx shall be plated, then
> filled with non conductive material, such as Peter's paste # SD-2361,
> or equivalent. Surface to be planar prior to final plating and
> metalization.
> Boards must be suitable for via in pad technology."
>
> http://www.peters.de/
>
> I would recommend working with your fabricators to find the best solution
> to your requirement. Without mentioning names, Most large fab houses can
> handle
> this either internally or through subcontractors.
>
>
> .028 is pretty big these days to fill. (?)
>
> Most prefer to flood the entire board, rather than be selective.
>
>
> Hope this helps,
>
> Dave
>
>
> Allen T. Maddox wrote:
>
>> We have a couple engineers who are insisting on using Via in (SMT)
>> pad. I'm not talking about micro via in a BGA pad. I'm talking about
>> vias with a 10 to 28 mil hole in a 0805, PLCC, QFP, and other SMT pad.
>> In order for this to work in manufacturing they must be filled,
>> without voids, and capped flush on the solder surface.
>> Does anyone know of a board house that does this process?
>>
>> Would you have an idea what the general cost effect to a board for
>> this process and does it make a difference if it's one via or 500
>> vias? Cost difference between electrically conductive and thermally
>> conductive fill?
>>
>> Any information would be helpful,
>>
>>
>> Allen Maddox C.I.D.
>> Sr. PC Board Designer
>> GAI-Tronics, Corp
>> 610-796-5854
>> PO Box 1060
>> Reading, PA 19607-1060
>>
>> [log in to unmask]
>> www.gai-tronics.com
>>
>>
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>
> --
> Dave Seymour, CID+
> Catapult Communications Inc.
> 800 Perimeter Park Dr, Suite A
> Morrisville, NC 27560
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