Folks,

I really am a rookie. I can't get over how much I don't know but want to
know. I need one more lifetime to get even a little more knowledgeable. Our
good friend David Douthit provided some very important input as the
following sample as it pertains to cleanliness etc:

Test Method 2.6.25
Title: Conductive Anodic Filament (CAF) Resistance Test
Stage: Working Draft
Date: May 2002
Originating Task Group: Electrochemical Migration Task Group (5-32e)

1.0 Scope  This test method provides a means to assess the propensity for
conductive anodic filament (CAF) growth, a form of electrochemical migration
within a printed wiring board (PWB). Conductive anodic filaments may be
primarily composed of conductive salts rather than cationic metal ions. This
test method can be used to assess PWB laminate materials, PWB design and
application parameters, PWB manufacturing process changes and press-fit
connector applications.

2.0 Applicable Documents

2.1 IPC
XXX-YYYY-04 CAF Test Board
IPC-6012 Qualification and Performance Specification for Rigid Printed Boards
IPC-9201 Surface Insulation Resistance Handbook
ICP-TM-650, Section 2.6.14.1 Electrochemical Migration Resistance Test
(note: covers only surface electrochemical migration)
TR-476A - Electrochemical Migration: Electrically Induced Failures in
Printed Wiring Assemblies

2.2 American Society for Testing and Materials (ASTM)
ASTM D-257-93 Standard Test Methods for DC Resistance or Conductance of
Insulating Materials


3 Test Specimens

3.1 IPC XXX-YYYY-04
The IPC XXX-YYYY-04 has 10 layers and dimensions are about 5 x 7 inches.
Test board designs for evaluating CAF resistance shall have varying drilled
hole wall to drilled hole wall distances for plated holes. These distances
can range from as low as 0.006 inches separation for alternate laminate
materials expected to have very high CAF resistance and minimal copper
wicking out from the plated-through hole (PTH), to as high as 0.035 inches
separation for evaluating press-fit connector applications. The drilled hole
size, rather than the finished hole size, is specified in the chart on the
bare board fabrication drawing to ensure consistent spacing. Internal layer
thieving may be added to plane layers around the perimeter. Test boards
should be manufactured so that the machine direction of the woven fiber
reinforcement is perpendicular to the rows of same-net daisy chain vias for
A1-A4 (machine direction tends to fail first). Test board designs shall have
sufficient minimum spacings on outer layers to ensure that surface
insulation resistance failures do not occur. Layout of the IPC XXX-YYYY-04
test board structure (CAF Test Board) is shown below (Figure 1).

I know David knows about this. Is anyone else on this forum aware or
involved. Jeez, I got lost on the QFP coplanarity issue thinking that was
way past history and learned a whole bunch.

MoonMan

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