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May 2009

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Subject:
From:
Rob Strecker <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rob Strecker <[log in to unmask]>
Date:
Mon, 11 May 2009 11:18:34 -0600
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text/plain (286 lines)
Here is what our supplier said about the baking profile:

"The re-worked baking time for 2 hr (boards' temp. ramp-up time included ) but actually the boards were baked under 170-180C just for around half hour, the room temperature boards ( 5 boards /stack ) had to take at least
80-90 min. to reach 170C under 180C environment.

From technical point of view , the baking process before shipping ( in Tg temperature ) could reduce  the internal stress of laminate , it can improve the board dimensional stability , some company also consider to apply it 
in production."

It might be time to change suppliers.

Rob Strecker 


-----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

 

[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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