I recommend that you read : "Compatibility of Epoxy-based PCBs to
Lead-Free Assembly" by Sylvia Ehrler; in the June issue of CircuiTree (you
can read it on-line from their web site http://www.circuitree.com/). It discusses the effects of design on reflow - and specifically large
ground areas are prone to delamination at those temperatures; it discusses
the effect of the choice of laminate, between dicy-cured and
phenolic-cured (aka: "Lead Free capable"); and it also discusses the
effect of the fabrication process on the final reflow compatibility of the
material. You need both capable material AND it needs to be processed in a
specific way; some lamination cycles enhance the LF capability, while
others are either neutral or detract from that inherent capability.
I think I have done a fairly good job at giving an overview of the
article. It is well done, long, and full of information.
my answers to your questions would be:
No;
Either not a capable laminate, or a capable laminate but not ideally
processed;
Go back to the supplier and get them involved.
Regards,
Valerie
"Wenger, George M." <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
08/25/2005 10:35 AM
Please respond to TechNet E-Mail Forum; Please respond to "Wenger, George
M."
To: [log in to unmask]
cc:
Subject: Re: [TN] Blistering of PCB at lead-free temperatures
Ioan,
Is your reflow profile a "Ramp to Spike" or a "Ramp to Soak to Spike"?
Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Tempea, Ioan
Sent: Thursday, August 25, 2005 10:19 AM
To: [log in to unmask]
Subject: [TN] Blistering of PCB at lead-free temperatures
Hi Technos,
wanted to start a pilot run, but the first PCB that we soldered ended up
full of blisters when it came out of the oven. It is a 6 layers, full
ground and power planes, about 6"x7", not a high density one, pretty light
stuff on it, the toughest part is a transformer which needs a little more
heating. The profile peaks at 250C on the PCB itself and the PCB is made
out of FR4, Tg 170.
I said to myself that it must be humidity, so I baked 1 board, 8H @ 125C,
and passed it through the reflow again. Same blistering, almost to the
same extent. Then I took a totally different PCB that was hanging around
on my desk for about 3 months, reflowed it at 250C and got just a tiny
blister, probably due to humidity this time.
The questions I have are:
is 250C too much for a properly manufactured PCB?
If it's not the humidity what else could it be?
Any other test that I could do to get a better idea of the root cause?
Thanks,
Ioan
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