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August 2002

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Subject:
From:
Dougal Stewart <[log in to unmask]>
Reply To:
Dougal Stewart <[log in to unmask]>
Date:
Fri, 9 Aug 2002 17:04:11 +0100
Content-Type:
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have a look at article written by Bob Neves in April 2002 PCFab available
on-line

Dougal Stewart

email:  [log in to unmask]
phone: +44 1896 822204
mob:    +44 7984 629667
----- Original Message -----
From: "Earl Moon" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, August 09, 2002 5:29 AM
Subject: [TN] CAF


> 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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