I have not got a copy of the fishbone diagram yet but I have some thoughts
on what fabrication related defects squeak through the various quality
systems and gets to the OEM or end used.
Some of the most common PCB defects (associated with the PCB fabricator)
that escape to the end users are “latent” defects that are not routinely
found by mechanical and visual inspection, microscopic evaluations or
electrical testing (continuity or impedance). These are the defects that
demonstrate themselves as intermittent opens and increased resistances only
after the stresses associated with the thermal excursions inherent in
standard (or lead free) assembly and rework cycles. This type of defect can
get through the fabricator’s and assembler’s quality system and to the end
user.
Demonstrated as field failures, these defects include accumulating
degradations over time associated with interconnection separation, barrel
fatigue/cracks and microvia (MV) failures. One of the most insidious MV
failures is one where the microvias come off the capture pad during a
heating or cooling cycle but repair themselves at ambient and/or elevated
temperatures.
Expect shorting and cross talk in association with conductive anodic
filament (CAF) formation in response to inner layer and behind the hole wall
ionic contaminates and dielectric delamination. Again, this is often a
latent defect that demonstrates itself over time with thermal cycling in
humid environments.
These are defects that can have roots in the fabricators process or
practices but not be found until product is in the end use environment.
These types of defects can also be caused by various assembly and rework
processes and practices where the robustness of the PCB is compromised by
high time at temperature excursions, repeated thermal cycles and poor
cleaning techniques. These defects are particularly hard to assess, and
there is so much opportunity for the proverbial “finger pointing”, that the
root cause is often not established.
Paul Reid
PWB Interconnection Solutions Inc.
-----Original Message-----
From: Kristopher J. Keating [mailto:[log in to unmask]]
Sent: Tuesday, August 17, 2004 2:17 PM
To: [log in to unmask]
Subject: [TN] Most common PCB failure modes
Hello,
Could some of you share what are the most common PCB defects that escape to
your customers?
Thanks
Kristopher J. Keating
Circuit-Wise, Inc.
400 Sackett Point Rd.
North Haven, CT 06473
tel. (203) 281-6511 x 410
fax (203) 287-8409
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ingemar Hernefjord
(KC/EMW)
Sent: Tuesday, August 17, 2004 3:16 AM
To: [log in to unmask]
Subject: Re: [TN] thin film
Seal Science say they have it all:
http://www.sealscience.com/html/products/VacuumCupsPdfs/15about.pdf
ultrahighvacuum guys use pure gold gaskets:
http://www.sisweb.com/catalog/F39.pdf
ourselves, we use as simple as butyl rubber:
http://www.allstategasket.com/materials.asp (not Ultravacuum, of course)
Butyl rubber group includes ordinary rubber used in your mountainbike tire,
can keep vacuum or pressure for very long time.
/Ingemar
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Crepeau, Phil
Sent: den 17 augusti 2004 02:25
To: [log in to unmask]
Subject: Re: [TN] thin film
hi,
i believe you should be able to use a gasket material such as viton.
phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Douglas O. Pauls
Sent: Monday, August 16, 2004 2:02 PM
To: [log in to unmask]
Subject: [TN] thin film
Good day all,
I am in need of a recommendation for a thin film sealant material. I need
it to be 15-20 mils thick, cuttable, and preferrably non silicone. We have
considered the Sil-Pad technology, but as this will be used in a vacuum seal
operation, I am concerned about silicone outgassing or cross contamination.
Are there any thin gasket materials from the engineered rubbers that anyone
would recommend?
Doug Pauls
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