Simply, there will be little solder left as it all runs out the hole. With
some of the first BGA's I worked with, about 6 years ago, I designed boards
especially to determine solder drain off. I wanted a better "self aligning"
feature as no equipment was avaialable then ot place these devices. Ten mil
through holes, and blind vias, were as small as we could go. The applied
solder paste went first, then most of the eutectic balls. The high temp
balls stayed, of course, but had no solder joints formed.

Some in the microwave business claim to require holes in pads. Some
assemblying them, run the boards through two soldering passes attempting to
"plug" the holes. Sometimes, this works to a small degree. Mostly, the
solder joints don't form.

Earl Moon

----- Original Message -----
From: Rick Thompson <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 21, 1999 2:50 PM
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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