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November 2005

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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Wed, 23 Nov 2005 08:44:32 -0600
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I think my confusion is because Bogert is speaking of a two-termination
tantalum chip capacitor, and are you referring to a multi-termination
leadless castellated chip carrier package? I do not understand how Pb90
solder spheres can be attached to each end of a chip capacitor.  Or
perhaps I just need more coffee.....

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Wednesday, November 23, 2005 8:08 AM
To: [log in to unmask]
Subject: Re: [TN] Making existing PWB land areas larger

Hi richard,
No, this is not an 'Unicum' process, but it is how BGAs were developed.
When larger LLCCCs [for those of you too young--leadless ceramic chip
carriers] could not be used because of premature SJ failures, we removed
the sidewall metallisations at the castellations [thus eliminating the
solder fillets] which allowed the LLCCCs to swim up. When this proved to
be insufficient for SJ reliability, we used solder balls and cast tin
columns [the first BGAs and components with solder (tin) columns--Bell
Labs has a couple of patents on this].
You put the solder balls onto the component by a reflow process [same as
a BGA--it is the high-temperature hand soldering that is the problem
with these components] and you unsolder the components by touching the
PCB pad and the high-melt solder ball, not the component.



Werner

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