The definition of crazing in The Printed Circuit Handbook 6th edition, ed.
Coombs, Crazing is "a base material condition in which connected white
spots or crosses appear on or below the surface of the base material". It is
due to the separation of fibers in the glass cloth and connecting weave
intersections. See slides 14 and 15 of this EPTAC presentation
http://www.eptaccanada.ca/wp-content/uploads/2011/12/webinar_eptac_09_16_09.
pdf
The pictures shown in the e-mail below are due to poor drilling, but I don't
think they fall into the definition of crazing.
When the glass fibers/resin interface at the hole is disturbed by drilling,
the subsequent plating process can create a shorter distance between the
anode and cathode and therefore increase the risk of CAF because the rate of
formation increases as the separation distance decreases. If the drilling
causes a crack from one side to the other, either plating salts, or actual
plated copper will fill the crack and one should see a short when the system
is exposed to bias and humidity. This is not CAF.
Laura
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: December-17-13 9:32 AM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
Hi Victor,
Pattern plating does have a profound affect on crazing. Crazing is formed
first by pIf the droor drilling. The pattern plating does permeate down the
crazing producing a condition called wicking at the defect sight next to the
drilled hole. The plating solution continues deep in the crazed glass
bundles. Wicking is generally considered to end where the copper plating
ends but if you read the definition of wicking it is the moisture
penetration down the glass fibers and is not limited to where the copper
plating has occurred. The capillary action formed by the crazing is enough
to have the plating bath wick into the spaces between the epoxy and the
glass fiber. The copper plating seals the end of the wicking trapping
plating solution in the space formed by the separation between the epoxy and
the glass fibers.
The contaminant is trapped in the space between the glass fibers and the
epoxy waiting to grow into 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]
________________________________
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: December 16, 2013 8:06 AM
To: Paul Reid
Cc: [log in to unmask]
Subject: RE: [TN] Crazing - the pictures
How does pattern plating effect crazing? Many oversea shops pattern
plate.
Victor,
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Friday, December 13, 2013 3:09 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
Hi Wayne,
There are a number of things that bring these boards into question. What I
am concerned with is the crazing.
I think that the fabricator has an automated plating line that requires two
passes to get the copper thickness.
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 Wayne Thayer
Sent: December 13, 2013 1:13 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
Hi Paul-
Nice sections.
Aren't they supposed to have the drill actually spin when they push it
through the board?
What's going on with the two layers of plating? That first layer is more
than electroless would normally put down. I guess maybe they checked hole
size reduction to see how much plating they put down, realized they'd missed
a minimum on the hole wall, and put it back into the bath.
I tend to think of the defect you have been talking about as "heavily
damaged fibers", and think of crazing as voids/cracks within the prepreg. I
agree that I would be very concerned about the long term reliability of
these boards and would like to know how much fallout the fabricator had due
to plating shorts along these damaged fibers.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paul Reid
Sent: Friday, December 13, 2013 12:49 PM
To: [log in to unmask]
Subject: [TN] Crazing - the pictures
Hi Everyone,
I finally found Steve Gregory's email address. He has kindly posted some the
pictures of the crazing that I found.
http://stevezeva.homestead.com/6494_2_1_mod.jpg
http://stevezeva.homestead.com/6494_M_001.jpg
http://stevezeva.homestead.com/6496_2_10.jpg
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]
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