Stephen R. Gregory wrote:

> I still would like to know why I should need to bake them, because I recieved
> a few responses at the time I first had the problem that it was probably a
> problem with the lamination process (resin starvation or something) that I
> was getting the blisters...but for some reason, it seems that baking them
> does prevent the blisters.
>

Steve,

I agree with what you say.  Why do I need a non-value added operation, like pwb baking,
added to my processes?  One more que, one more handling and one more opportunity for
something to screw up.  When is the baking process initiated? 3 months? 6 months? a
year?

I have been told by board manufacturers that delams can be caused by resin starvation;
not enough time, temperature and/or pressure during pressing, problems with the oxide
(it can apparently loose it's tooth if not processed properly), and moisture
absorption.  I have had some manufacturers tell to bake after six months in-house and
others tell baking would not be necessary.

All of our pwbs are stored in air conditioned areas, where humidity levels reach 50% RH
in the worst part of summer and it is always much lower once the heat kicks on.  And
yet,  I can have three assemblies out of one hundred delam, when all were stored in the
same place for six months or more. Hmmm.  I have had pwbs stored for over a year in
these conditions and have never had delams on them during processing.  I have also had
delams show up at wave soldering when the units looked just fine after reflow and
adhesive cure passes.  It seams like the opportunity to entrap moisture in inner layers
is greater during the pwb's manufacture than sitting in my stockroom.

 Don't get me wrong, its not that delams have been a big problem for us.  Over the
years they have always been rather scattered occurrences. But some have been costly for
us and our suppliers, and, of course, you always have the unhappy customer that is
waiting for us to ship product (what a food chain).

 I guess I would like to know what the best practice regarding baking.  From replies I
have read on Technet, SOP (black boot army - standard operating procedure) is that
there is no SOP.  Have any studies been done to quantify the level of humidity and time
necessary for delams to be created in FR4 pwbs?

Just my experiences,

Gary Camac

##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe:   SUBSCRIBE TECHNET <your full name>
To unsubscribe:   SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################