We have been vacuum baking PWB's for about 15 or more years. There has never
been a documented failure or problem with baking on our products many of
which go into outer space. We normally bake before assembly, conformal
coating and staking. When not in process the boards are stored in a dry
nitrogen atmosphere. Baking has improved the quality of our vapor phase
reflow operation and has reduced soldering and board defects. I suppose that
if you "toast" the boards you could suffer some problems, but for us it has
been nothing but improvements. Some of our customers have specified that the
boards be pre-baked and the manufacturers of our conformal coatings have
highly recommended it to prevent moisture entrapment. Until we encounter a
problem or failure we will continue to bake as we have done in the past.
Ron Dieselberg
-----Original Message-----
From: Alain Savard [mailto:[log in to unmask]]
Sent: Tuesday, October 26, 1999 12:29
To: [log in to unmask]
Subject: Re: [TN] HELP!!! - flow solder problems RT
Most polymer do continue to cross-link after the usually claimed
full cure time (polymer chemistry class in university). I got the
information originally from a DMG training session with David
Gendrau from Scottsdale Arizona.
This was a few years ago and I can't get the references off hand. But
we now avoid baking boards unless we feel it's absolutely required.
It also reduces processing time and the company I work for likes that.
Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]
-----Original Message-----
From: Howieson, Rick [mailto:[log in to unmask]]
Alain,
I have been in board fab AND assembly for quite some time and have never
heard baking reduces the life and reliability. What data do you have to
substantiate this claim?
Rick Howieson
>-----Original Message-----
>From: Alain Savard [SMTP:[log in to unmask]]
>Sent: Tuesday, October 26, 1999 8:51 AM
>To: [log in to unmask]
>Subject: Re: [TN] HELP!!! - flow solder problems RT
>
>Hi Richard,
>
>Now you know why some assemblers request test coupons.
>For the age of the boards, you might have a DATE CODE on
>the board. It's usually 4 digits, 2 of them are the week number
>and the other 2 are the fabrication year. (example: 99-12 or
>12-99 represent the 12th week of 1999).
>
>Boards older then 6 months may start to have a substantial
>amount of water absorbed into the laminate. They may also
>have a fair amount of oxidised tin forming on the surface of
>traces and inside the PTH.
>
>Do NOT bake the boards unless necessary, it slightly reduces
>the reliability and life expectancy of the board.
>
>You might have to sacrifice a board to microsection it and see
>any problems with the internal structure (mostly the plating).
>
>If you are scrapping any boards, use the area affected.
>
>If the failures are always at the same component, the batch of
>components may need to be looked at for solderability.
>
>Finally check the wave and preheat temperature. (You could do
>this first actually).
>
>Good luck,
>
>Alain Savard, B.Sc.
>Chemical Process Analyst
>CAE Electronics Ltd.
>e-mail: [log in to unmask]
>
>-----Original Message-----
>
>Hello Richard,
>
>HELLO ALAIN
>
>A few things to look at:
>- Did you perform a solderability test on the test coupons?
>NO COUPONS WERE SUPPLIED.
>
>- How old are these boards?
>NOT ENTIRELY SURE - WE GET THEM FROM AN EXTERNAL SUPPLIER.
>
>- Did you verify plating thickness and voiding in the test coupons?
>NO COUPONS SUPPLIED.
>
>- are your components pre-tinned?
>NOT BY US. FITTED AS SUPPLIED.
>
>RICHARD TILBROOK
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