Pete,
Don't forget the old classic causes for shorts: FOD and incomplete etch.
We still see both of these cases from time-to-time.
Mike
Michael W. Paddack
Engineering Specialist
Materials, Processes, and Physics
C3 Networks
The Boeing Company
5301 Bolsa Ave. MC H013-C335
Huntington Beach, CA 92647-2099
714-896-2981 (Office) 714-896-2797 (Fax)
714-762-3301 (Lab) 714-349-6762 (Cell)
-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, July 29, 2009 10:54 AM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Latent short question
Werner - answers embedded
1. The finished hole size is .035.
A: Drill size .042"
2. All temp cycling is done in dry nitrogen atmosphere so we don't
introduce moisture.
A: did you moisture bake prior to cycling?
Assemblies are baked at 61C for 8 hours prior to conformal coat.
3. The rigid material is Polyimide/ the Flex is AP9XXX
A: Hygroscopic
4. We have all of our boards evaluated by an independent test service
before we accept them. I looked at the report for this lot of boards and
the drilling looked good and all boards in this lot were accepted. I
would paste a photo of a section but the report is locked and I can't
copy out of it. So if my issue is poor drilling it would have to be
specific to the holes in the board.
A: Drills wear-so it depends whether a drill is new or near the end of
its life.
Wear or a broken drill bit.
5. This is a unit level thermal cycle and it is powered up.
A: Do not know what that means.
This is a complete unit as opposed to temp cycling an individual board.
The point I'm trying to make is that power is applied during the temp
cycle.
6. The bare board saw 100 cycles (no power) before this unit level test
- no issues noted.
A: CAF takes some time and the application of a voltage.
Werner
Future webinars:
September 15, "Fundamentals in Solder Joint Reliability"
September 16, "Root Cause Analysis of Solder Joint Failures"
September 17, "Solder Joint Reliability for Pb-Free Solders"
Future workshops:
September 24, IPC Midwest, Schaumburg, IL "Fundamentals in Solder Joint
Reliability"
-----Original
Message-----
From: [log in to unmask]
To: [log in to unmask]
Sent: Wed, Jul 29, 2009 12:57 pm
Subject: Re: [IPC-600-6012] Latent short question
There were a number of questions this group has asked about this
failure. I think I have them answered here...
1. The finished hole size is .035.
2. All temp cycling is done in dry nitrogen atmosphere so we don't
introduce moisture.
3. The rigid material is Polyimide/ the Flex is AP9XXX
4. We have all of our boards evaluated by an independent test service
before we accept them. I looked at the report for this lot of boards and
the drilling looked good and all boards in this lot were accepted. I
would paste a photo of a section but the report is locked and I can't
copy out of it. So if my issue is poor drilling it would have to be
specific to the holes in the board.
5. This is a unit level thermal cycle and it is powered up.
6. The bare board saw 100 cycles (no power) before this unit level test
- no issues noted.
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Francis
Byle
Sent: Wednesday, July 29, 2009 12:14 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Latent short question
Without seeing the physical layout, it's hard to say what may or may not
be a root cause. If the board has seen high humidity at the
high-temperature end, it raises the possibility of CAF, or of dendritic
growth across the PWB surface. 0.050" hole pitch is pretty tight, but
what is the d
rilled diameter? That makes a lot of difference.
Here's some non-destructive approaches you might take in analyzing it:
1.) Locally heat the PWB in area(s) where the short location is
suspected. Monitor resistance while heating. If short location can be
localized, proceed to do detailed visual and x-ray examination of that
area.
2.) Remove components that are across the circuit one at a time.
Carefully inspect prior to removal, and take care not to over-stress the
components during removal. After each removal, assess whether the short
can still be replicated. If not, proceed with failure analysis on the
last component removed. If all components are removed and short
persists, the PWB must be the source.
If localization and root cause identification has failed at this point,
destructive analysis may be required. One or more traces can be cut in
order to localize the defect. Once localized, detailed failure analysis
in the area of the defect should yield the root cause.
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Wednesday, July 29, 2009 10:09
To: [log in to unmask]
Subject: [IPC-600-6012] Latent short question
I have an 8 layer assembled rigid flex board that developed a 800 ohm
'short' between two traces after 18 thermal cycles (-55 to + 65C)_. The
short developed on the hot cycle (+65C) and we can occasionally get the
short back by moving it from room temp to +65.
The short is between two .010" traces / .015" spacing, the holes for
these traces are .050" centers all 1 ounce copper.
We haven't ruled anything out, it could be component related or FOD but
what has stuck with my customer is a corrective action this board shop
gave them about 6 years ago - at that time the board shop identified the
cause of latent shorts to be from poor drilling - I'm having a hard
time wrapping my arms around poor drilling causing latent shorts - any
thoughts or comments on how this problem could be bare board related?
Thanks,
Pete
Pete Menuez
Supplier Quality Engineering Manager
L-3 Communications Cincinnati Electronics
7500 Innovation Way
Mason, Ohio 45040
[log in to unmask]
513-573-6401 Voice
513-573-6767 Fax
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