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May 2001

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Subject:
From:
"Busko, Wolfgang" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 30 May 2001 09:58:44 +0200
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Hi Phil,
my first thought reading your discription was also " hey, there´s different
thermal mass with these microvias, so it needs a different profile ". It´s
the most obvious difference and I would look at that first.

Wolfgang

-----Ursprüngliche Nachricht-----
Von: Werner Engelmaier [mailto:[log in to unmask]]
Gesendet am: Mittwoch, 30. Mai 2001 01:48
An: [log in to unmask]
Betreff: Re: [TN] Pad in Via for BGA's - Part II

Hi Phil,
I think your pads/solder balls with vias run somewhat cooler than those w/o
vias for the same machine reflow profile, i. e., the actual reflow profile
for these pads/solder balls with vias is lower. this is because the via
copper structure and connected copper traces act like a heat sink. Normally
the PCB runs hotter the the components, however, because the BGAs shield the
PCB from both convection and radiation, the PCB portion underneath BGAs is
cooler. I would recommend running actual profiles at these locations if you
need convincing.
It is likely that your profile does not have much excess peak temperature,
thus the affected solder balls are not liquid long enough at a high enough
temperature for low viscosity to let the bubbles move fully up. Remember,
solder does get pasty at its Liquidus not Solidus temperature.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com

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