I'd go with you Francis ; rather than the steam ;
badly (surface only) cured liquid photo on the low end is common indeed .
Explanation was not enough time under UV lamps (or the cpacity of lamps)

Ioan , if the mask blisters on copper ' apart from remasking (messy) ; you
can do little .
Only if the ground/shield (copper) areas are too large > netting those will
prevent the blistering .

paul

-----Original Message-----
From: Francis Lai [mailto:[log in to unmask]]
Sent: Saturday, July 10, 1999 11:55 AM
To: [log in to unmask]
Subject: Re: [TN] PCB blistering during wave


"Tempea, Ioan" wrote:

> 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

Probably there was some problem at the chemical wet PTH process when
processing the PCB such as not long enough in the Metex cleaner which
causes separation under thermal stress. I don't think there is anything
you can do. Correct me if I am wrong!!!!

Francis