Why wouldn't it just be considered a process indicator?
After all, a process indicator is not a defect and it indicates a non-desired output that would warrant further investigation or counter measures to correct? The material is still deemed acceptable just not ideal.
I do believe it is not a defect and agree if we were to identify every concern found under magnification above the specified/agreed upon requirement, there would be a long list of issues to address and costs would skyrocket. Isn't that why we have standards for this sort of thing?
Ted T
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, December 09, 2013 6:52 AM
To: [log in to unmask]
Subject: Re: [TN] Crazing
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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