All;

Fr4 type laminate material is, by nature, hydroscopic, it absorbs moisture.
Boards with soldermask on them, go through a baking cycle, to cure the mask.
This also takes out any absorbed moisture. If the board hang around the shop
for any length of time, they begin to absorb moisture. If they hang around
the assembly shop, they continue to absorb moisture. The IPC recommends a
bake cycle prior to any assembly operation, for these very reasons.


At 01:55 PM 6/24/96 -0500, ROGER HELD wrote:
>     
>     To everyone,
>     
>     We have, in the past, had problems with bare board warp and 
>     delamination in our assembly process (reflow).  We have solved this 
>     problem by instituting a baking process at our vendor or in house 
>     prior to assembly.  My questions are as follows:
>     
>     1. Is baking a standard PCB fab process (before shipping)?
>     
>     2. If so, what is the standard profile?
>     
>     3. If not, why do some vendors' boards need to be baked to prevent     
>        warp and delamination while others don't?
>     
>     4. Does baking cure both delamination and warp or does it just cure    
>        warp?
>     
>     5. My understanding is that moisture is getting trapped in the board   
>        during laminate press (or contamination of some sort) which is      
>        leading to the problem during assembly.  Can the moisture           
>        entrapment be avoided?  Should we claim to our vendor that he       
>        better control contamination in the process?
>     
>     5. It seems to me that if boards need to be baked before delivering to 
>        a customer that there is some poor process control going on.
>     
>     Someone, please educate me.  Maybe, my perspective is in error.
>     
>     Thanks,
>     
>     Roger Held
>     Hitachi Computer Products (America), Inc.
>     [log in to unmask]
>
>
Regards,

Gary Ferrari
Tech Circuits
(203)269-3311
[log in to unmask]