Hi,

We have had similar problems years ago. I am not sure what you refer to when
you say preheat - does this mean preheating in the wave process?
If stored for too long the FR4 boards tend to absorb moisture. Our solution
was to slow bake for 24 hours hence no temperature shock which even preheat
could cause.  Since then we receive our boards vacuum sealed. All unsealed
boards undergo 24 hour baking at 60 deg.C prior to use.

Hope this helps.


> -----Original Message-----
> From: Tempea, Ioan [SMTP:[log in to unmask]]
> Sent: 09 July 1999 17:18
> To:   [log in to unmask]
> Subject:      [TN] PCB blistering during wave
>
> Fellow technetters,
>
> we are presently fighting with some ultra low-end TH only PCBs. During
> waving they blister a lot. We tried many things like hotter-colder
> preheating, hotter-colder solder temp, faster-slower speed. No result.
>
> Are there any other tricks to try, or we send them back to the fab?
>
> Thanks, Ioan