Jay:
As I understand it, you are putting passive components onto the
substrate of the BGA and then soldering the BGA to the PCB. My first
instinct is to ask why? If you have a cap or resistor that needs to be
that close to the component, you're probably better off putting the
passive into the silicon.

Anyway, the typical substrate used in BGA's these days is BT. BT has a
X/Y CTE of 14-17ppm/C; however, it has a z axis CTE of 48-64ppm/C. It is
likely that you may be fighting the moving BT during reflow.

As for other substrates, the only other materials I'm aware of are
hi-temp materials using BN or BNC. These are costly by comparison and
may not be appropriate.

Hope this helps...

> Bill Davis, Ph.D.
> Diamond Multimedia Systems
> Senior Scientist
> Tel. 408.325.7868
> Cell. 408.888.5650
> e-mail: [log in to unmask]
>
>


-----Original Message-----
From: Jay Bitanga [mailto:[log in to unmask]]
Sent: Thursday, January 14, 1999 1:10 AM
To: [log in to unmask]
Subject: [TN] BGA Substrate


Hi Everyone,

I would like to ask your opinions regarding our problem with our BGA
board.  You see, a problem occured during our placement of
components, specifically 0402 comps,  on the substrate. Because of
the density of the circuit, a test point is mistakenly registered as
a fiducial mark since it is vey close to the latter.  The fiducial is
square  solid shaped (15 mils).  We considered that the shape of
the fiducial is the factor involved in the registration error so what
we did was change the shape of the fiducial but adapted the same
measurement of it (cross-hair).  Is this possible ???  Are there also
problems that we do not see ???  Are there standards available  for
substrates for BGA and other types of new technologies ???

Thank you very much for taking time in answering these questions.
Any information is much appreciated.



Regards,

Jay Bitanga
Electronic Assemblies Inc.
[log in to unmask]

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