Ken,

Depending on the application, plugging only one side of a via may work
well. Often with BGA and similar design the preferred method is to plug
top and bottom.

It's really not difficult to do. A method we prefer is to plug one side
and ensure (bake or added cure) no moisture (either water or chemical)
is entrapped in the opposite exposed via. The repeat the process with
the opposite side of the board. We use an automatic screen coater on the
majority of work we perform, for this type coating we do it the old
fashion way...by hand. Screening by hand, especially the second coat
allows us to the mask in a way as to ensure complete filling of the via.
If you don't completely fill the via there is a good chance the gas
trapped in the void will expand viol;ently in subsequent thermal
processes.

Hope this helps.

Franklin

Ken Patel wrote:
>
> Fab experts,
> After getting few responses on my previous email on via plugging, I was
> surprise to find one response saying that plugging of the via is not going
> to fill the via complete but it will rather be towards the side it applied.
>
> So, the question is that then there is a possibility of chemical entrapment
> from the other side so do I have to tell the fab house to plug it from both
> sides?
>
> re,
> ken patel
>
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