We have an application on a 2 layer board with through hole
     technology which requires an insulating material
     laminated/applied to one surface/side. Initially we thought
     of having a prepreg material laminated to one surface but are
     unsure if this is the most cost effective method. Anyone out
     there who knows of a method or material which would support
     this requirement please respond.
     Some of our requirements are;


>>>>>>Have you considered solder mask!!!!

     1. Must be a UL recognized material

>>>>>>>>yes

     2. Must provide at least 500V of dielectric insulation

>>>>>>>>>solder mask is typically 40V per micron, so to
provide 500V requires a minimum of 12.5um of resist, easily
achievable by double coating wet on dry.

     3. Would preferably be thin, .001-.003 thick.

>>>>>>>>>see above

     Some questions we have are;

     1. What type of relief would be needed around PTH?
 >>>>>>>>photoimageable = print tolerance     2. How thick would the material need to be?
 >>>>>>>>see above     3. Who is doing this type of fabrication today?
 >>>>>>>>everyone     4. Can it be applied selectively?
 >>>>>>>>photoimage     5. What is the typical cost impact to a double sided board?
 >>>>>>>>do you want % or in cents - or do you already have the
the answer and its on your board already?

Dougal Stewart
Exacta Circuits
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