It doesn't make much sense at least to me, as the boards go back to normal after second re-flow. Once cured, epoxy can not go back!!!!
Vladimir
SENTEC Testing Laboratory Inc.
11 Canadian Road, Unit 7.
Scarborough, ON M1R 5G1
Tel: (416) 899-1882
Fax: (905) 882-8812
www.sentec.ca
-----Original Message-----
From: Joyce Koo <[log in to unmask]>
Sender: TechNet <[log in to unmask]>
Date: Thu, 29 Sep 2011 13:47:19
To: <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Joyce Koo <[log in to unmask]>
Subject: Re: [TN] Board question
Did you check the degree of cure of the pcb? (or delta Tg of incoming pcb, (1st scan - 2nd scan) using either TMA or DSC? If less than 5C, the stuff is properly cured.. Otherwise, it is not). My 2 cents.
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Vladimir Igoshev. PhD
Sent: Thursday, September 29, 2011 12:50 PM
To: [log in to unmask]
Subject: [TN] Board question
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
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