Rick,
        Look for a few major problems. The first is the wicking away of a
large volume of solder through the via, with potential opens or minimal
contact as a result. The second is a virtual guarantee of extremely large
voids in any joint that contains a via in the pad, with the possibility of
short/long term reliability issues. Finally, unless you temporarily mask off
the vias on the bottom side before wave, any via-in-pad joints will see a
secondary reflow cycle during wave solder. This will duplicate/increase the
first two problems of wicking and voids, and may entrap wave solder flux
within the voids. I have had to process such assemblies before, and it is no
picnic. Impress upon your customer the need for redesign to improve quality
and reliability.

Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX  77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]

> -----Original Message-----
> From: Rick Thompson [SMTP:[log in to unmask]]
> Sent: Tuesday, September 21, 1999 4:50 PM
> To:   [log in to unmask]
> Subject:      [TN] Via in BGA Pad?
>
> We have a customer who wants us to run a board that uses a 256 pin BGA.
> The
> problem is, he has placed vias for signal routing in the center of the BGA
> pads.  The vias are plated with a 10mil finished size.  There is no solder
> mask tenting these vias on the bottom of the PCB.  I realize this isn't
> normally recommended, but as they already have the boards, re-layout isn't
> an option.  My question is basically, what types of problems will I have?
> I
> know I may get wicking of solder through the PTH, but given the hole size,
> how bad is it likely to be?  Anyone have any experience attaching BGAs to
> this type of pad configuration?
>
> Thanks in advance.
>
>
> Rick Thompson
> Ventura Electronics Assembly
> 2665A Park Center Dr.
> Simi Valley, CA 93065
>
> +1 (805) 584-9858 voice
> +1 (805) 584-1529 fax
> [log in to unmask]
>
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