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November 2000

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Subject:
Re: Warp/Bow after reflow
From:
Earl Moon <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 13 Nov 2000 10:23:15 -0600
Content-Type:
text/plain
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text/plain (49 lines) 
Wes,

I just finished a consulting assignment in Connecticut concerning the very
same thing. I have done many of these contracts recently as everyone seems
to be having the same problems.

As I told Tom Gervascio (another Siemens person), first read my article on
the SMTnet (their newsletter) in the September 1999 edition. It speaks
clearly, though technically, to this and other issues concerning MLB
technology. I am assuming boards, on the panel, are this type even though
double sided types also may perform this way.

1) The MLB construction, beyond balanced copper planes, as material
selections. Also, material availability becoming more of a problem due to
glass fiber shortages (much being diverted to fiber optics industry - what a
surprise!)

2) The lamination process not effectively managed as press cycle from ramp
through pressure, time, and temperatures used.

3) Lamination press issues as non parallel press plattens, thermal problems
as uniform heat transfer or heater elements not working, etc.

4) Number of books in each press opening along with thermal lag material,
etc.

5) Total cure not effected during lamination

6) Variations in your assembly process as reflow profiles, including cool
down.

7) The type scoring used and how well the process managed

8) A thin panel that is too large (how large are the panels?) especially
when not effectively supported during reflow.

9) Other variables not so common

Earl Moon, Proof Of Design

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