The purpose of baking is to remove moisture. I don't think you need to
bake at the glass transition of the laminate. I have mentioned common
sense in the TrainerNET forum and it certainly can be applied in this
forum.
Bueno, Bye
Rick Howieson

>-----Original Message-----
>From:  Alain Savard [SMTP:[log in to unmask]]
>Sent:  Tuesday, October 26, 1999 9:37 AM
>To:    [log in to unmask]
>Subject:       Re: [TN] HELP!!! - flow solder problems RT
>
>It increases cross linking inside the epoxy of the laminate,
>making is slightly more brittle and harder every time you
>bake it. It alsoi ncreases the speed of tin oxide formation,
>in effect it ages the board.
>
>It has also been suggested that a high temperature bake
>(> Tg) may cause warpage in a pressed board.
>
>Alain Savard, B.Sc.
>Chemical Process Analyst
>CAE Electronics Ltd.
>e-mail: [log in to unmask]
>
>-----Original Message-----
>
>Why does baking the board  reduce
>the reliability and life expectancy of the board?
>
>> -----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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