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January 2006

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From:
"Kane, Joseph E (US SSA)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kane, Joseph E (US SSA)
Date:
Fri, 6 Jan 2006 15:34:22 -0500
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Conformal coat, no matter what kind, doesn't adhere very well to sharp
points.  Surface tension effects pull the coating away from the point,
and even if some thin layer can be convinced to stay, it flakes or
rubs off pretty easily after cure.

If you have a need to cover the lead tip, like to prevent corona
discharge
or shorting due to condensed moisture, you might need to encapsulate
the leads.  We've used fumed silica (i.e. Cab-O-Sil) to thicken some 
coatings.  Of course, you then have to glob it on to individual leads
with a 
dispenser, because it's too thick to spray.

Joe Kane
BAE Systems
Johnson City, NY


-----Original Message-----
From: Brad Saunders [mailto:[log in to unmask]] 
Sent: Friday, January 06, 2006 1:56 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coatings


John,

We don't have a problem coating connector pins although some are tougher
than others.  A nice rounded pin soldered and protruding from the solder
side of board by .010-.030 coats wonderfully.  The same pin that has
been cut in order to maintain ceiling height can be a challenge in
adhesion.  A compliant pin coating is particularly interesting in that
if it is coated then the conformal coat material can and will creep up
and into the connector pins and body wreaking havoc.  For this reason
some folks have their bare boards conformal coated prior to insertion of
compliant pin components.  Taping or masking is very important for cc of
connecters including the interface area on the PWB, secondly the
dimensions need to be realistic and lastly don't cc keying. 

Brad
  ----- Original Message ----- 
  From: Babcock John<mailto:[log in to unmask]> 
  To: [log in to unmask]<mailto:[log in to unmask]> 
  Sent: Friday, January 06, 2006 12:58 PM
  Subject: [TN] Conformal Coatings


  Does anyone have any experience with placing a coating on protruding
  connector pins.  What kinds of conformal coatings does one use as a
  material callout?
   
  John Babcock
  PCB Designer III
  Isothermal Systems Research (ISR)
  2218 N. Molter Rd
  Liberty Lake, WA 99019
  [log in to unmask]<mailto:[log in to unmask]>
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