Hi Gerry,
Based on the responses from "everyone" I am sure that crazing is a
defect that is a concern. It is just that one company is playing
"specmanship" with IPC's rules and I don't like it.
The rules state that a microsection is not needed to inspect for
crazing. Therefore, according to the fabricator, one cannot inspect for
crazing using a microsection. The specification does not state that a
microsection is prohibited in the inspection for crazing however. IPC A
600 states that crazing ".. does not require a microsection evaluation".
Regardless of how I found the defect it is the intent of IPC to reject
this condition if it violates 50% spacing rules.
I found this condition "along the way" and I raised the flag. That is
all I can do.
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 Gerry Gagnon
Sent: December 13, 2013 8:49 PM
To: [log in to unmask]
Subject: Re: [TN] Crazing
Hi Richard,
Have enjoyed your posts over the years and agree with you frequently.
The answer is that it "depends".
Yes, the magnifications and switching rules are the "front matter" that
a lot of folks gloss over from time to time.
I am sure that if you were looking to verify a certan non-conformance
and found something along the way that was lethal for your product or
application, you would have no problem raising that flag.
By the way "along the way" is just a figure of speach I was using.
Definitely not proper specification language.
Gerry
> Date: Mon, 9 Dec 2013 12:52:28 +0000
> From: [log in to unmask]
> Subject: Re: [TN] Crazing
> To: [log in to unmask]
>
> I am not sure I accept that "along the way" theory completely.
> Prevalent in all of the IPC standards, all defect categories are
provided a magnification level for inspection. For example, if a
non-metallic particle is seen on the PWB while inspecting solder joints
at 20X magnification on a conformal coated CCA, the inspector is
supposed to switch to the required magnification for the particulate
matter (4X-7X). If the particulate matter cannot be seen at that range,
it is not considered to be a defect.
> If you want to entertain your "along the way" theory, then have fun
counting up the rework hours to strip away the coating, remove the
particles, clean, dry, and re-coat. No matter what you do short of
building all product in a Class 10 clean room, this unnecessary rework
will never end.
>
> Of course, one must understand that there are certain exceptions to
this; I am just saying that you cannot allow an "along the way"
philosophy in the factory. It will put you out of business.
> In regards to your example, two questions come to mind:
>
> 1. What is the magnification required when inspecting for particulate
matter between conductors at the PWB level, and what is the minimum
electrical clearance between the two traces you describe? If the
material was visible at the required magnification, it was an escape,
and should have been caught at the higher magnification you describe
anyway, and is a real defect.
> 2. Did you measure the resistance again after the tiny piece of
material was removed, and did it make any difference?
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gerry Gagnon
> Sent: Friday, December 06, 2013 7:21 AM
> To: [log in to unmask]
> Subject: Re: [TN] Crazing
>
> Hi Paul,
>
> Hope you and Bill B. are doing fine.
>
> I am assuming that you you were looking for something else and
detected a "non-conforming" level of crazing.
>
> In my mind, this is an easy one because you found the non-conformance
"along the way" while examining your microsection.
>
> Let me give you an easier analogy.
>
> While examining a region of an IST test coupon in transverse mount, I
find a tiny piece of material bridging two conductors at high mag.
> Clearing away the conductor surfaces enough to measure if there is a
resistance, I get a value in the MegOhm range.
>
> Is it a short?
>
> Unless things gave changed, Bare board continuity thresholds will not
detect this phenomenon.
> Let's also say that innerlayer AOI (if performed) has a very high
escape rate for this type of phenomenon or may not even detect it at
all.
>
> Is the phenomonon a short per IPC A-610?
> My answer is yes, it is an unwanted connection, albeit a high
resistance connection, and is difficult to detect.
>
> Does the fact that I found this short in a cross section under high
magnification, while I was looking for something else, change anything?
>
> I don't think so, and I do not think IPC A-610 allows non-conformances
that are found "along the way".
>
> Have a good one.
> Gerry
>
>
>
>
> > Date: Thu, 5 Dec 2013 16:05:41 -0500
> > From: [log in to unmask]
> > Subject: [TN] Crazing
> > To: [log in to unmask]
> >
> > I was just on a conference call where we found crazing (a separation
> > between glass fibers and the epoxy system), in a microsection. The
> > fabricator stated that this had to be evaluated looking at a board
> > macroscopically and could not be evaluated microscopically.
> >
> >
> >
> > Crazing is called out in IPC-A- 600 in section 2, paragraph 2.3.2
page
> > 18, which is "Externally Observable Characteristics". In A-600 there
> > is picture of a microsection showing the defect but it states that a
> > microsection is not required.
> >
> >
> >
> > In IPC 6012-2010 crazing is call out in 3.3.2.2, page 12, which
states
> > (I am paraphrasing), "Crazing shall not violate greater than 50% of
> > the distance between adjacent conductors..." The document then
refers
> > to IPC A 600.
> >
> >
> >
> > What is your take on their argument that crazing should not be
> > evaluated microscopically as per IPC?
> >
> >
> >
> > 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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