Re: gEDA-user: via in pad

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

I have used via in pads on a board for a 896 pin device. It worked very
very well and we had wonderfull yields.

The way to beat the solder wicking is that the vias are esentially
filled with solder durring the pressing of the pcb layers and then the
bottom surface is coated with an epoxy like substance (this is from
memory) as I recall.

Steve Meier



On Wed, 2006-07-12 at 15:09 -0700, ldoolitt@xxxxxxxxxxxxxxx wrote:
> Friends -
> 
> In PCB, I put down an exposed-paddle part (like the CY7C68013A-56LFXC),
> and then put vias in the central region as recommended for both thermal
> transfer and electrical connection.  Just like the rest of the pad,
> those vias are clear of solder mask.
> 
> According to the manufacturer's sheet, however, those vias should get
> covered by mask, to keep solder from wicking down the via during reflow.
> There is a nice picture of that near the end of the Cypress data sheet
> for the CY7C68013A.
> 
> Has anyone found (or put in) a method to accomplish this in PCB?  The
> Gerber file for the mask layer (negative) would need a paint/scratch
> sequence to get the pad exposed, and then the via covered.
> 
>    - Larry
> 
> 
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