We did similar tests, but on 120/240 V panels. Silicone coatings 
     performed the best, although no part was over 500C. Arcing was induced 
     by saltwater dropped directly over the 120/240V input lines.
     
     Silicone can burn, but is inherently flame resistant. 
     
     Organics can be formulated for similar effects, but only silicones can 
     withstand 500C for over a brief exposure without damage.
     
     Suppliers evaluated:
        Dow Corning
        W. R. Grace, also known as "Emmerson & Cumming" or "Grace Specialty 
        Polymers"
     
     Good luck.


______________________________ Reply Separator _________________________________
Subject: ASSY: Conformal Coating Flammability Problems
Author:  [log in to unmask] at internet
Date:    11/26/96 6:45 PM


During field trials of our existing coating (High Solids Xersin) on high 
powered PCA applications, we found that due to a component failure, that the 
PCA suffered badly from fire damage (an area about 75mm sq was severely burnt - 
even the copper tracks were melted).
     
Upon testing (using a coated resistor - to specified thickness & making it 
fail) we found that generally the solvent based coatings showed a noticeable 
increase in the flame produce, when subject to high temperatures (eg components 
failure - over 500oC).  Additionally, the organic based coatings also produced 
an unacceptable amount of carbon and it was these two factors which we believe 
damaged our PCA (the carbon increased the area shorting from being localised).
     
Could anyone suggest a Conformal Coating that may be acceptable to high powered 
PCA applications, suitable for application by a select coat system?  We believe 
that Silicon based coatings may be the best choice, but samples are slow in 
coming to Australia for trial and all the coating spec's mention that they pass 
flammability tests.
     
Thanks,
Paul Moro
Manufacturing Engineer
COM10 (Austrialia)
Tel 61-2-9722 3310
[log in to unmask]
     
     
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