Per the limited information I have I would say that I would like to see higher thermal decomp numbers and the T288 numbers near 15 minutes. The killer in my comfort zone is Tg of 175ºC. I am concerned any time that a material is exposed to a temperature exceeding its Tg for a prolonged period of time. Are they attempting a secondary cure or do they really believe that temperature is required for baking. I do not believe that and therefore would not accept the PBs.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rob Strecker
Sent: Monday, May 11, 2009 9:40 AM
To: [log in to unmask]
Subject: Re: [TN] PCB baking
Dewey,
The laminate material is Shengyi S1170.
Rob Strecker
Senior Process Control Specialist
Interalia
(403) 288-2706 ext.312
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey (EHCOE)
Sent: Monday, May 11, 2009 10:32 AM
To: [log in to unmask]
Subject: Re: [TN] PCB baking
You didn't say what the laminate material was, but even at that I would not accept PBs that were baked at 180ºC for two hours.
Dewey
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rob Strecker
Sent: Monday, May 11, 2009 8:51 AM
To: [log in to unmask]
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 bake out 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
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www.digico.cc <http://www.digico.cc/>
P N'imprimer que si nécessaire - Print only if you must
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