Higher Tg materials that we have tested perform worse as the temps above
240C, as the Td is lower than standard FR4 and the degradation to the Td
is more acute than standard system. This is also influenced by the
package design and construction of the board - utility planes,
glass/resin ratio, dielectric thickness, etc. High Tg materials are
good performers at operating temp but not as the Td is approached.
Jeffrey Bush
Director, Quality Assurance and Technical Support
VERMONT CIRCUITS INCORPORATED
76 Technology Drive - POB 1890
Brattleboro, Vermont 05302
Voice: 802.257.4571.21 Fax: 802.257.0011
http://www.vtcircuits.com
-----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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