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______________________________ Reply Separator _________________________________
Subject: (Fwd) Re: Military Polyimide Board Failures
Author:  [log in to unmask] at _internet
Date:    3/29/96 7:31 PM


Address,
     
Does anyone happen to have a 1800 EDN # on hand, so that I can 
call and get said article from '79/'80.  Thank you in advance.
     
John Gulley 
email: [log in to unmask]
     
------- Forwarded Message Follows ------- 
Date:          Fri, 29 Mar 1996 11:54:22 -0500
To:            TED JONES <[log in to unmask]>
From:          [log in to unmask] (George Franck  X2648  N408) 
Subject:       Re: Military Polyimide Board Failures
Cc:            [log in to unmask]
     
Tom,
In the 1979-1980 time frame, studies were done showing migration along 
glass filaments (EDN Sept 5, '79 and Apr 20, '80).  Drilling problems 
creating high heat are credited with creating seperations which wick 
materials into them.  This was all pertaining to FR-4 (GFN).  The report 
predicted failures at[ 65 deg C/ 80% RH / 10 mil space / 20 volts ] after 
100 days.
     
If it applies to Poly-amide, then a failure could have been caused a poor 
drilling process weakening the materials resistance to moisture and 
impurity penetration along the glass fibers, which over time caused the 
pink ring and created the short.  Read the Sept 5 EDN article.  The numbers 
you quote are close to the predictions.  The study was given at a IEEE 
symposium, and conducted by Bell Labs, Whippany NJ (I wonder what name is 
on that building now) by JN Lathi and DJ Lando.
     
Please get back to me with what you find out.  I have the same 
applications, except for the high voltages, as you do.  But no failure of 
this type, er...none  yet!?
     
     
>The Navy has recently experienced field failures (shorts) on three 
>7-layer polyimide PWBs.  The boards had operated for 300 hours in a 
>sealed chamber.  The chamber is maintained at 50C, with constant 
>humidity.
>
>The shorts (about 8 ohms of resistance) developed between a PTH and 
>ground plane on layer 5.  There is a voltage potential of 30 volts 
>(+15/-15) between the PTH and plane.  The clearance between the PTH's 
>pad and the plane is 10 mils.
>
>Horizontal microsections of the failed areas do not show any obvious 
>migration path.  The only anomaly noted on the failed pad is that it 
>demonstrates much more pink ring than pads on adjacent PTHs.
>
>We're looking for ideas on the most likely cause of the shorts. 
>
>Have there been any studies done that indicate pink ring will or will 
>not contribute to this type of failure?
>
>Has anyone seen similar failures?
>
>




     
     
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