There is no actual requirement, it is more of a factual moisture absorption
effect. Polyimide absorbs water a lot faster then FR4. I don't know of much
of a problem with using FR4 up to 6 months old. After that we may recommend
prebake. This is an in-house specification, I don't know of any IPC
specification for it.



Alain Savard, B.Sc.
Chemical Process Analyst
CAE Electronics Ltd.
e-mail: [log in to unmask]

-----Original Message-----
From: Dewey Whittaker
Subject: Re: [TN] Baking FR4 boards


"Howieson, Rick" wrote:
Out of curiosity, where are these requirements stated?
Rick
>-----Original Message-----
>From:  Dewey Whittaker
>Subject:       Re: [TN] Baking FR4 boards
>
>Alain Savard wrote:
>
>> Isn't the 72 hours before bake a requirement for polyimide instead of
FR4?
>>
>> Alain Savard, B.Sc.
>> Chemical Process Analyst
>> CAE Electronics Ltd.
>> e-mail: [log in to unmask]
>>
>> -----Original Message-----
>> From: Dewey Whittaker
>> 1. Typically, for multi-layer (6-8 layers), FR4, SMT boards stored in an
>>air
>>
>> conditioned environment at about 50+/- 10% RH, how many months would you
>> allow
>> to pass before you would recommend baking them prior to reflow?
>> 2. What would be your bake cycle?
>> Thanks,
>> Charlie B.

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