Pete,
For orientation purposes, let's say this microsection is the X axis.
Microsection the copper coated fiber in the Y axis and look for copper
on the surface of the glass and/or between the glass strands.
A disturbed glass filament or bundle near a PTH will transmit a copper
hue along the fiber. The Y axis microsection confirms the presents of
copper.
Randy
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
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Sent: Tuesday, December 01, 2009 4:39 AM
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Subject: Re: [IPC-600-6012] High Resistance Shorts - revisited
Randy,
Thanks for the comments.
Here is a vertical section - not a very good picture but the best I have
right now. This picture shows copper growth along the fiberglass and I
don't see any delamination. I also have a picture where there is a
huge crack in the laminate (that picture doesn't show copper but there
is electrical conduction).
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Reed,
Randy
Sent: Monday, November 30, 2009 9:00 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] High Resistance Shorts - revisited
Pete,
If this anomaly formed in 40 hours after assembly with only a few cycles
of temperature cycling, I doubt seriously the failure is CAF. The
timeframe is much too short for the spacing and voltage you are
reporting.
The SEMs and photographs do not convince me you have CAF. I see some
disturbed glass filaments. Do a vertical microsection and cut the fibers
in question. If there CAF forming along the glass filaments, the copper
will be evident.
I also recommend a vertical microsection to make sure this failure is
from hole to hole. The failure could be from plane to hole. I am
referring to the plane below the failure location. Knowing the path of
the failure is helpful in determining the cause.
Typically an anomaly that forms this quick is a pre-existing latency
that was a near failure.
Another test that would be helpful is doing the dielectric withstanding
test on 1-2 of the remaining boards with the worst resistance reading.
If the failure is a pre-existing near failure, this test will typically
detect the latency.
A large field of view of the laminate would be nice. This would help to
determine the glass wetting quality.
Randy
Randy Reed, CQE
Merix Corporation
Global Reliability Group, North America
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503.992.4421-direct l 503.545.0150-cell
-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of
[log in to unmask]
Sent: Monday, November 30, 2009 3:01 PM
To: [log in to unmask]
Subject: [IPC-600-6012] High Resistance Shorts - revisited
All:
A few weeks ago I sent out a question to the community - Why do I have
low resistance isolation between isolated circuits. The general answer
that came back was - I have CAF. Fast forward a couple weeks and I
have more information - I don't think I have a CAF issue - I may have
invented something new.
Quick description: 14 layer, polyimide material. Single lamination
cycle (no blind/buried vias), .093" thick. We have identified the
shorts to be created between layers 7/8. I have gone as far as milling
down through layers 1 - 7 and evaluated the entire board. There are no
anomalies until we get to the dielectric layer between 7/8. There are
cracks/delaminations between holes in the BGA socket area but nowhere
else on the board.
Pictures of what we are seeing are below.
The first horizontal section shows cracks/delamination - the resistance
measured 150 ohms (or so), That coupon was sent out for analysis. We
received back some SEM photos with an explanation that the copper plated
from one hole to the other. One hole acted as a cathode, the other an
anode and the moisture in the board was the carrier. We in essence
created a mini plating cell. In these pictures you'll see copper
plating actually plating around the fiberglass bundles. The voltage on
this device is 3.3 volts. The shorts showed up in hours of operation
(maybe up to 20- 40 hours). The boards were not baked prior to
assembly. The boards do get temperature cycled (-53 - +54 C) but this
short will appear with just 0 or 1 cycle. (I have 4 boards with no
thermal cycles other than assembly).
Any suggestions on what I actually have?
Thanks,
Pete
Horizontal Cross section
<<Picture (Device Independent Bitmap)>>
You can see three areas with delamination - all three areas have reduced
resistance.
We had this section evaluated with SEM/EDS which revealed:
<<Picture (Device Independent Bitmap)>>
Higher magnification of the same location:
<<Picture (Device Independent Bitmap)>>
The light areas are identified as copper.
<<Picture (Device Independent Bitmap)>>
New sample - horzonatal view of copper connecting holes.
Pete Menuez
Supplier Quality Engineering Manager
L-3 Communications Cincinnati Electronics
7500 Innovation Way
Mason, Ohio 45040
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513-573-6401 Voice
513-573-6767 Fax
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