Hi TechNetters,

I have a question for board gurus, as I'm almost lost.

Here is a story. A panel of four simple 4 layers FR4 twists after
going through the first side re-flow and flatten out after the second
side is re-flowed.   It does the same thing with and without the
components placed.

The panels are from  new vendor and the old ones had never exhibited
the problem. What confused me is that both boards (from both of the
vendors) were built identically: dielectric layers and  Cu
layers are look identical thickness- wise.

There are no signs of resin recession or delamination in
cross-sections which could have pointed out at incomplete curing.

Glass bundles look also identical.

What else it could be?

Any suggestions are deeply appreciated.
-- 
Best regards,

Vladimir Igoshev. PhD                          mailto:[log in to unmask]

SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca


______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 16.0
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------