Phil-

We're quite interested in 2-sided reflow process tuning.

Could you clarify what is meant, below, by "...pad mating to lead wetting
area..."? And how does the described multiplication by the number of leads
introduce the "grams" units?

I'm sure a picture would help a lot with this, but could you try to describe
these 2 calculated areas a bit more?

Thanks

Michael Alderete
Aerojet



Phil Zarrow wrote...
------------------------------

Date:    Thu, 4 Mar 1999 10:20:41 EST
From:    [log in to unmask]
Subject: Re: double-sided reflow

It actually is the pad mating to lead wetting area that you use.  This is
multiplied by the the number of leads and if the ratio is less than 30
grams/sq. in.   - it won't fall off.+
I've used this formula for years and Bob Willis and I have postulated that
it
is far too conservative.  Bob has generated some newer calculations that I
have sworn to review (see Bob, I haven't forgotten).  Some have found the
ratio to be as much as 44 grams/sq in but in this forum, I'd rather be
conservative.
In any event, this includes most components - most QFPs, SOP, TSOPS, even
PBGA
(lots of surface mating area).  PLCCs, too, but I've had mixed luck with
84's
(though 68's are no problema).  As Steve pointed out, you must have a smooth
running conveyor on your reflow system - which you want anyway.
Hey, if you can remove the gluing process, you should.  Try this one at
home,
kids!
Phil Zarrow
SMT Process Consultant
ITM, Inc.
Durham, NH  USA
www.ITM-SMT.com

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