Separation of fibers would be a different failure mode than hollow fibers though in some cases they may have the same electrical effect/signature. Her is a chance to separate different observations/symptoms/causes and may be give them different names to distinguish them from one another.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Laura J Turbini
Sent: Tuesday, December 17, 2013 1:43 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing - the pictures
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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