Hi Phil,

What I stated before stands. 

Wicking, if it does not produce an outright short, gives CAF a head
start. The CAF may develop over time if the PWB is exposed to any
humidity and temperature cycling.

Usually there is crazing (a loss of adhesion between glass fiber and
epoxy) associated with wicking. The copper penetrates the crack as far
as it can but there is usually a silver colored area where the copper
cannot penetrate. It is this crazing that may propagate over time and is
one of the concerns with CAF.

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] 

 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: November 5, 2013 7:03 PM
To: [log in to unmask]
Subject: [TN] IPC-6012 Copper Wicking Defect in PTH

I know what the spec limits are for wicking and I have a coupon that
just barely violates the maximum requirement for class 3A.

I was asked what kind of failure this would lead to if it were used and
I could not answer the question.

I researched the Technet archives and found an email from Paul Reid
where he stated:

"The worst-case condition is a short between holes drilled on a tight
grid.  The most insidious condition that wicking is a site for CAF
(conductive anodic filament) growth."

There is no tight grid on this board so the short between holes is not
going to happen.  CAF is always a concern but I would have thought that
a failure would be related to some kind of stress point mechanism of
failure based on how rough the hole looks.  I know a picture would make
this a lot easier but I am not at liberty to release it.  The copper in
the hole is very thick but the entire hole looks like it had a bad drill
and overly agressive desmear operation.  There is wicking all up and
down the wall of the hole but only excessive in length in one spot.

So the question is:  How does excessive wicking cause a failure?  This
was the kind of question that I used to send to Werner to get further
education on.

Any and all comments are appreciated.

Phil

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