I agree that the soldermask should be equal to or lower then the pad 
     for the best assembly with the lowest defect level.  


______________________________ Reply Separator _________________________________
Subject: PTF - screened EMI shielding
Author:  [log in to unmask] at corp
Date:    12/8/95 12:44 PM


     
    \0
   TO:         I1263600 IBMMAIL   ipc internet technical query
     
   FROM:       DSTEWART EX2       D.Stewart        - Product Development
Manager.
     
   DATE:       8 December 1995
   SUBJECT:    PTF - screened EMI shielding 
   REFERENCE:  assembly
     
    I have just read an article from Circuitree on the use of screen 
    printed polymer thick film for EMI shielding. This technology has 
    been known by us for some time, but up to now it has not been asked 
    for. Before I start a project to characterise the process, I would 
    like to know if people are using this process for their EMI 
    shielding on SMD boards.
           As all the SM gurus and solder paste experts keep telling
    you assembly people that, ideally soldermask must be below the 
    level of the pad, how do you cope with effectively 3 layers of 
    soldermask and one layer of copper paste, over the top of your 
    tracks (which always seem to end in a pad !!)?
     
           Circuit Wise, Photocircuits and AMP+Akzo are all mentioned
    in this article as using this technology, so let's hear from you, 
    if not your customers, on what effect this has.
     
    Dougal Stewart
    Exacta Circuits
    Scotland