Phil,

In the old days excessive oxide treatment usually lead to delamination
because you would get two layers of copperoxide dendrites on top of each
other and after lamination they would separate, one sticking to the trace
the other sticking to the dielectric.  I believe that the current oxide
chemistries are self limiting and do not have that problem.  I have not
heard of oxide treatments reducing the thickness of the trace width to a
degree that the resistance is increased.

Do you see evidence of delamination?

The most likely cause of increased resistance is small etch outs on the
trace width called "mouse bites" or "dish downs" cause by the etching
process undercutting the resist in a "print and etch" application.  These
localized etch-outs on the side of the trace (mouse bite) or across the
trace (dish down) are visible a under scope before lamination. Automated
optical inspection (AOI) of the inner layer before lamination usually would
finds these conditions.

Does your fabricator use AOI?

The next most likely cause of high resistance in a trace is interconnect
breakdown (post separation) or barrel cracks due to z axis expansion of the
dielectric.  If the resistance changes with a moderate application of heat
to the suspect area I would lean toward interconnect breakdown or barrel
cracks.  If the trace is not heat sensitive I would consider the defect
likely to be a reduction in the cross sectional area of the trace due to
mouse bites or dish downs.

Is your trace heat sensitive?

Paul Reid
PWB Interconnect Solutions

-----Original Message-----
From: R Sedlak [mailto:[log in to unmask]]
Sent: Sunday, December 12, 2004 8:54 PM
To: [log in to unmask]
Subject: Re: [TN] Resistive internal layers


Phil:  You are probably on the right track looking at the oxide.

Since the assembly people are so fixed on the appearance of the
oxide...(sigh), the fabricators may re-run panels down the oxide line if
they come out initially looking "weird"...
Each time they are run down the modern "alternate" oxide line, they lose
about 2 microns (80 microinches) of Copper.  Would this cause the problem
you are seeing?

Rudy Sedlak
RD Chemical Company

DUTTON Phil <[log in to unmask]> wrote:
Hello Technetters,

We have a multilayer board that is exhibiting higher than expected
resistance on an internal layer track.
The track is 0.006" and about 1.5 inches long, yet has a resistance of
approximately 1 ohm. From what we can tell, the track has not been over
etched.
I'm wondering if anyone can shed some light on what could be the cause
of this.
I'm thinking that the layer may have had an excessive 'black oxide'
treatment to promote adhesion. Is this possible?

thanks,

Phil Dutton C.I.D.

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