The diffusion speed of water molecules varies a lot in different stuff, even metal alloys let some water pass! Says expertise. I have been a little involved and it seems to be at least some truth in the said. Built-in microscopic humidity is then hard to avoid and hard to get rid of. My addition to this is not sensentional in any means, just agree with some mailers: we don't make special bakeout any more, controlling the environment seems better.
Ingemar
-----Original Message-----
From: d. terstegge [mailto:[log in to unmask]]
Sent: den 5 juni 2000 09:09
To: [log in to unmask]
Subject: Re: [TN] Baking of boards
It's been seven years ago that I was involved in a study about baking of bare boards at an AT&T (now Lucent) factory. Based on the results, and on advise of several bare board vendors, we completely stopped the baking operations. Less work and better for solderability, we thought.
This worked fine during the whole summer. But in the autumn the relative humidity raised to about 80 or 90% for several weeks. I've never seen so many delaminations in such a short time, both from the reflow and from the wave, with several partnumbers from all our board vendors.
Blowholes was not the problem.
Kind regards
Daan Terstegge
Unclassified mail
Personal website: http://surf.to/smtinfo
>>> Lee Whiteman <[log in to unmask]> 06/01 2:59 pm >>>
Martin
I agree with Brian Ellis and Jarmo Kiiski.
Adding my thoughts, baking boards will also depend on the board material
used. For example, polyimide boards absorb moisture very well. I've seen
circumstances where polyimide boards were baked at 80C to 125C from 4 to 24
hours. Temperature and time was dependent upon the complexity of the boards
(SMT vs. PTH), board thickness, and component density.
In a prior life, I ran a study where on FR4 boards, I had the moisture
content measured. After the measurements, I ran the material through an
aqueous cleaner and measured the moisture content (Somebody was afraid that
the boards would have to be for 24 hours baked after aqueous cleaning). Then
I baked the boards at 100C for up to 4 hours. After the first hour, minimum
moisture was found.
Hope this answers your question. Good Luck.
Lee Whiteman
Senior Manufacturing Engineer
ACI / EMPF
Telephone: (610) 362-1200; Ext. 208
FAX: (610) 362-1290
E-Mail: [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Martin Christie
Sent: Thursday, June 01, 2000 4:48 AM
To: [log in to unmask]
Subject: [TN] Baking of boards
Hi Technetters,
What is (or where can I find) the recommended bake parameters for baking
boards before reflow?
Martin Christie
ACW Technology Ltd.,
Hylton Road,
Petersfield,
Hants.
GU32 3XX
Tel: 01730 300000 ext 146
Fax: 01730 266045
e-mail: [log in to unmask]
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