Hi Rob,
Some how my response from a couple of hours ago did not make it to Technet—here it is again.
Hi Rob,
Shengyi S1170 or any other PCB resin—bake at any temperature is no
substitute for a bad lamination process—your boards are scrap if the
problem is bad lamination.
You need to understand what happens during the lamination process.
1) the purpose of the lamination process is to a) join the laminate
layers by using the prepreg layers, and b) to fill the spaces where Cu
was etched away with resin;
2) the prepreg layers consist of sheets of woven glass impregnated with partially cured resin;
3) during lamination, the pressure first facilitates good heat transfer
from the press platens, the resin partially liquefies, excess resin is
squeezed out [the amount depends on whether you use regular, low-flow,
or no-flow prepregs] forming beats around the panel circumference;
4) adequate heating in the lamination press results in the curing of
the prepreg resin [however, the cure is never totally complete—it takes
too long—that is why the resin content in prepreg layers is higher than
in laminate layers and the layers have different properties];
5) delaminations can occur for two reasons: a) not enough curing time
in the lamination press, b) too much pressure in the lamination press
resulting in resin-starved prepreg layer.
You need to determine which of these two root causes you have—but in
neither case will baking at any temperature improve=2
0what you have—SCRAP.
Werner
-----Original Message-----
From: Rob Strecker <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, 11 May 2009 11:50 am
Subject: Re: [TN] PCB baking
Sorry for not letting this thread die but... we are still battling with our PCB
supplier with regards to baking PCBs at 180C for 2 hours.
We started to see delimitation again and the root cause was an insufficient
pressing time. The center boards in the stack when pressing did not reach the
required temperature. The corrective action is to bake all PBCs at 180C for 2
hours. We do not agree with this corrective action. I would like to know why
180C??
My assumption here is we are not dealing with PCB moisture absorption (water),
we are dealing with uncured prepreg. I assume that requires a higher
temperature to complete the curing process?
Would anyone out there accept reworked boards that were baked at 180C for 2
hours due to the above root cause? BTY, boards are ENIG.
Rob Strecker
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Monday, May 04, 2009 1:00 PM
To: [log in to unmask]
Subject: Re: [TN] PCB baking
Hi Ioan,
I agree with Werner.
As you know we have performed reliability testing on almost every material
available for PWB fabrication in almost every PWB configuration. We test both
the copper and material reliability.
A moderate bake at 105°C is adequate for all
but exotic materials (which may
have volatiles other then water). What is often overlooked is many low Tg
materials, particularly if the PWB has sequential lamination processing, are
greatly degraded by baking near 125°C. I mean by degradation, the inherent
strength of the dielectric is degraded, chemically changed. Concurrently, along
with the degradation, the increased force attributed to the difference in vapor
pressure of water at 105°C compared to 125°C conspire to damage the PWB. It is
better to remove the water slowly at a lower temperature, that is less degrading
to the dielectric, and produces less force from increased vapor pressure.
You have to consider the fabrication process, material robustness, product build
and surface finish degradation in selecting the bake temperature. Generally a
lower temperature is better for overall PWB reliability.
Stay away from temperatures near Tg as measured by TMA.
Sincerely,
Paul Reid
Program Coordinator
PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1
613 596 4244 ext. 229
Skype paul_reid_pwb
[log in to unmask] <mailto:[log in to unmask]>
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Monday, May 04, 2009 9:25 AM
To: [log in to unmask]
Subject: [TN] PCB baking
Dear Technos,
I know this has been oftenly discussed here, but I would like to lively up the
traffic a little bit...
Is there any IPC standard reglementing the bake20out time for PCBs, in terms of
temperature/dwell time?
Thanks,
Ioan Tempea, ing.
Ingénieur Principal Fabrication / Sr. Manufacturing Engineer
30 ans déjà! - Already 30 years!
950 rue Bergar, Laval, Québec, H7L 5A1
t : 450-967-7100 ext : 244
Mtl : 514-990-5762
f : 450-967-7444
[log in to unmask] <mailto:[log in to unmask]>
www.digico.cc <http://www.digico.cc/>
P N'imprimer que si nécessaire - Print only if you must
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