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October 1999

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Subject:
From:
Bill Davis <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 26 Oct 1999 09:05:08 -0700
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Terri:
I agree with the majority that gold flash seems to be the right pad finish;
you should check with the designers however to ensure that you haven't
overcome the Tg of the FR4 (assuming this is FR4). Most BGA's lose 80% of
their heat out the backside if the center balls of the BGA are attached to
the device substrate (very effective way of removing heat by the way). This
coupled with a high power consumption part in on the back side may give rise
to board movement which exceeds the shear strength of the BGA ball array
(very dependent on BGA package size/ball count/underfill).

Not only does the thermal need to be look at, but also the EMI emissions.
Again, back to the designers- are they absolutely sure these parts will not
generate crosstalk?

Hope this helps...
>
> Bill Davis, Ph.D.
>408-325-7868/408-273-2921
 [log in to unmask]



-----Original Message-----
From: Houston, Terri [mailto:[log in to unmask]]
Sent: Tuesday, October 26, 1999 4:19 AM
To: [log in to unmask]
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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