The buried cap thickness is not that significant if there is no microvia
attached to the cap. Well actually it is significant if the cap, wrap
and foil are so thick that the dielectric above the cap is greatly
reduced. Then we could get, to quote Randy Reed, "glass lock" or "glass
crush" between the cap and the adjacent copper layer. Imagine the buried
via foil, wrap and cap as a post sticking up into the b-stage material.

When there is a microvia attached to the cap, cap thickness counts.

For a reliable circuit we need to balance the thickness of the cap, wrap
and b-stage dielectric. All three contribute to three or four failure
modes. We could get cracks in the cap at the knee of the buried, cracks
around the base of the microvia, laser ablation through the cap, glass
lock or glass crush (which provides a path for conductive filament
growth). 

Do you think we should define some parameters?

Sincerely, 
Paul Reid 

Program Coordinator 
PWB Interconnect Solutions Inc. 
235 Stafford Rd., West, Unit 103 
Nepean, Ontario 
Canada, K2H 9C1 
613 596 4244 ext. 229 
Skype paul_reid_pwb 
[log in to unmask] <mailto:[log in to unmask]> 


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Chris
Mahanna
Sent: February 9, 2011 4:38 PM
To: [log in to unmask]
Subject: [IPC-600-6012] buried cap thickness

I assume that we purposely did not include a caveat for buried cap
thickness in 6012C?

My particular interest is the case where the design predates 6012C and
gives no more specifics than: "fill, planarize and cap"

Thanks
Chris

Chris Mahanna
President, Technical Manager
Robisan Laboratory Inc.
6502 E. 21st Street
Indianapolis, Indiana 46219
317-353-6249


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