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October 2009

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Subject:
From:
Ian Hanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ian Hanna <[log in to unmask]>
Date:
Wed, 21 Oct 2009 11:44:04 -0400
Content-Type:
text/plain
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text/plain (142 lines)
Hi Paul -- there could be adhesive failure, or delamination, in c-stage
no? Ian

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Wednesday, October 21, 2009 9:53 AM
To: [log in to unmask]
Subject: Re: [TN] delamination signatures

Hi Chris,

I think that the signatures of material damage should be taken as an
indicator not an absolute for determining root cause. 

I cannot bring myself to call cracks in areas that were never laminated,
adhesive delamination. I can thank my colleague Jason Furlong who, years
ago, said to me "If that area was never laminated how can you call the
crack delamination?" As it stands now I can't call cracks in the middle
of the B or C stage adhesive delamination. For me if the crack does not
follow an internal interface it is "cohesive failure" not adhesive
delamination.

If we can agree that adhesive failures tend to be a breakdown of an
internal interface, cohesive failure a breakdown of the epoxy system and
crazing a separation between the individual glass fibers and the epoxy
system then these symptoms may give indication of where to look for root
cause. At least this interpretation of failure signature could direct
you to look into areas that would contribute to those types of failures.

Consider the alternative. If each delamination signature does not narrow
the area of investigation for root cause then one could naively start
with material shelf life and storage, move to lamination (cycle, times,
pressures, platen planarity, heat distribution, etc), go on to drilling
(feeds, speeds, and hit count etc) and proceed through the other 97
steps of PCB fabrication, (not forgetting oxide coating, cleaning,
rinsing etc.). If that investigation is not fruitful then move on to
design and methods engineering variables like grid size, % resin etc.
You might find out in the end you were using a DICY cured laminate in a
lead/free HDI application and the material damage was cohesive failure.

There may be hundreds of root causes of material degradation I can think
of at least a hundred. I say - Let the cross section talk to you and
narrow your investigation based on observation and experience.

Don't forget... when in doubt bake! It doesn't much help but it does
give one reason to hope.

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 Chris Mahanna
Sent: October 19, 2009 9:24 PM
To: [log in to unmask]
Subject: [TN] delamination signatures

Hello TN,

I'm wondering how certain one can be about the root cause of delam.
simply by reading its signature.  Our experience is similar to Paul
Reid's (post attached below).  One obvious question: what about when it
is both co and adhesive failure?
Are there other features to the signature that are important in
determining primary root cause?

Chris

------------------------------------------------------------------------
------------------

My sense is that moisture induced delamination presents as adhesive
delamination that is horizontal cracks that resemble blisters and are
located at a laminated interface (b-stage to c-stage or copper, or along
bundles of glass). It may be that the vapor pressure exerted by trapped
moisture induces a mechanical failure at laminated interfaces.

Material degradation induced delamination more often presents as
cohesive failure that may exhibit cracks with vertical sections, often
bifurcating and spanning across b-stage and c-stage material, even
through glass bundles, and tend to propagate with sharper angles. This
failure mode appears to be more a chemical degradation of the epoxy
system.

Sincerely,

Paul Reid


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