Teri:

I would suggest electroless gold flash for the BGA's (min.5 millionths AU
over 100 millionths Ni) followed by selective bondable gold for the wire
bond lands. Be sure to couple this with LPI mask of course. When it comes to
BGA's co-planarity followed by surface cleanliness is of prime importance.
Secondly, it is critical that the pad geometry is matched to the lead size
to ensure a quality soldering result. Too large a pad in relation to the
lead will negatively affect solder wicking.
I would caution your design team on placing a QFP in the shadow of a BGA. I
have found problems in reflow due to heat draw of some BGA parts and in how
the IO are connected to power and ground.

Currently, as a board fabricator and assembler, our biggest issues revolve
around BGA placement and design so it would be beneficial if you included
your fabricator AND assembly people in the design/lay-out discussion. It
will save you alot of pain later.

Best Regards,
Charlie McMahon
McMahon Sales Company

prevent
----- Original Message -----
From: Houston, Terri <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, October 26, 1999 7:19 AM
Subject: [TN] Board finish for BGAs and wirebonds


> Hi,
>   We're designing boards that will use both solderable (BGA and QFP)
> components and wirebonded die (that need gold bond pads). It also looks
like
> the QFPs will be on the backside of the board in the "shadow" of the BGA
> topside component.
>
>    I would appreciate any advice on:
>          (1) recommended surface finish on the board
>          (2) component placement guidelines
>
> Thanks,
> Terri
>
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