John;

Solder resist is supposed to removed, or not applied, to the card guide
areas of a circuit board (see IPC-D-275). Therefore the thickness is
measured, st that point, from laminate to laminate. Other circumstances
require knowing the overall thickness, over all the respective coatings.

At 01:42 PM 6/4/96 CST, [log in to unmask] wrote:
>     
>     Why would "thickness" (as specified by the customer) be measured 
>     before solder resist application?  The customer is designing around 
>     and will receive a finished product (which includes solder resist) to 
>     be installed in a higher-level assembly.
>     
>     What am I missing here?
>     
>     John R. Kretsch, P.E.
>     Engineer, Design Assurance
>     [log in to unmask]
>
>
>______________________________ Reply Separator
_________________________________
>Subject: FAB:  PCB thickness
>Author:  [log in to unmask] at internet-mail
>Date:    06/04/96 12:30
>
>
>Let me contribute my observations on thickness.
>     
>The quality manual here says (written by me) that boards will be built to 
>class A tolerances in the latest revision of IPC-D-300, unless otherwise 
>specified by the customer.
>     
>That said, I have questioned IPC about the meaning of "thickness".  David 
>Bergman and Lisa Williams did some investigating and thinking and advised 
>me that thickness was to be measured over plated copper, but before solder 
>resist application.  They also told me that the committee responsible for 
>D-300 planned on expanding upon the present statement on baords thickness 
>in the standard, to direct the user to specify board thickness in any 
>areas of importance.
>     
>Lou Hart
>     
>     
>.
>     
>
>
Regards,

Gary Ferrari
Tech Circuits
(203)269-3311
[log in to unmask]