Fair enough , didn't know SBGA's go so fast through IR,
but take it from you Phil .
Sounds like my memories of "wave" soldering over a fry pan.
Just kept the flow on safe side .

Joy, no effect on reliability as far as my validations went,
Earl or Werner (remember the "column flex" constructions stories)
would know more .
The support on vibration is more than sufficient,
and the taller they stand the more reliable they are.

paul

-----Original Message-----
From: Phil Zarrow [mailto:[log in to unmask]]
Sent: Monday, 1 May 2000 21:36
To: [log in to unmask]
Subject: Re: [TN] I can't X-ray through this BGA!!!


Regarding reflow of these "slabs" -
Don't worry too much about a "shadow" effect.  In my experience (including
going back to Convection/IR reflow of early BGAs, it is a myth that most of
the reflow is air flowing under the component.  If it were, Convection/IR
would never have worked (and it did/does - just ask Compaq) and you;d have
to
forget about flip-chips (what with 0.006" height).
Almost all of the heat reflowing a BGA (or similar area array) is conducted
to the site through the circuit board as well as through the component
itself.  So the real concern here is the mass of the component and the
amount
of energy it will take to effect reflow.  Of course the composition of the
PCB substrate will either facilitate or hinder things as well.
Regards and Happy Heating to all,
Phil Zarrow
ITM Consulting
Durham, NH  USA
www.ITM-SMT.com

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