Our company has been designing .0135" diameter via's for 18 years. We 
     use .025" pad for internals and .030" pads for the external. Our 
     product ranges form .062" to .030" thk. Many of our designs typically 
     have 2,500 to 3,000 via's. All military and commercial flight 
     hardware. We usually spec the hole at .014"/.016" drilled diameter 
     before plating. By the way we have the Flight Management Computer 
     product on every model 737-300 and up.


______________________________ Reply Separator _________________________________
Subject: Des: Via Hole and Pad size.
Author:  [log in to unmask] at SMTPpost1
Date:    2/5/97 1:22 PM


Good Morning:
     
I would like to take a quick survey of designers/fab shops about thru 
hole vias for comparison with our internal practices.
     
1) For a via DRILLED with a .0135" drill in a .062 MLB:
   A) How is the hole defined?
   B) What Pad sizes would you typically use/expect for Inners and 
Outers?
     
2) What size via holes do you typically use/expect for .062 MLB?
     
Any comments like: I would be OK for my Gateway 2000, but not in the 
Boeing 737 I fly on?
     
Based on my understand, I would answer the survey as follows:
     
1A) Define hole as .012 - .007. (if you care about a minimum size) 
1B) From IPC-D-275 Class 3 Level B,  (Para 5.3.2.1)
    30 inner and 32 outer. ( a+2b+c = 12+2*1+16 = 30.. )
     
I think designs typically use smaller pads, hence the survey.
     
Thanks for your input!
     
-- 
     
George Franck Jr
Raytheon E-Systems
Falls Church Va.
     
"The opinions expressed are those of the author, and are not necessarily those 
of the Raytheon Corporation."
     
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