IPC-6012 APPENDIX A says:
Dielectric Thickness 90 um (0.0035 in.) min. if not specified, but may
be specified thinner.  
This applies to all Classes and refers to paragraph 

3.6.2.14        DIELECTRIC THICKNESS:
The minimum dielectric spacing shall be specified on the procurement
documentation.

NOTE: Minimum dielectric spacing may be specified t be 30um (0.001 in.);
however, low profile copper foils should be used and the voltages
employed should be taken into consideration so as not to cause breakdown
between layers. If the minimum dielectric spacing and the number of
reinforcing layers are not specified, the minimum dielectric spacing is
90 um (0.0035 in.) and the number of reinforcing layers may be selected
by the supplier.

Barbara J. Burcham, C.I.D.
Fairfield Industries, Inc
281-275-7687
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Franklin D Asbell
Sent: Thursday, March 04, 2004 4:12 PM
To: [log in to unmask]
Subject: [TN] Dielectric thickness of Class 3 boards

Can anyone quote me the requirement for dielectric thickness for Class 3
boards, as stated in IPC 6012A.

I've loaned my copy to a company down the street...thanks for a swift
response...anyone...please...

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