Chris,
Thank you very much for your input. The rephrasing will make things
clearer.
In this case, we need to take care also of the first note:

Note 1 to table 3-3 : "Does not apply to microvias. Blind vias have
greater than 1:1 aspect ratio ."

For example, an outer 0.25 mm core with a 0.30 mm diameter hole , has an
AR less than 1:1. It should be included in the same category.
Regards,
Roberto

Roberto Tulman, CTO
Eltek  

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Chris
Mahanna
Sent: Thursday, February 25, 2010 5:16 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] copper thickness for blind vias

Roberto,
Coincidental that you ask this question today.  On Monday, my only
comment to the ballot version of 6012C was to reword:

"Through Holes, Blind and Buried Vias > 2 layers" to
"Buried Vias > 2 layers, Through Holes, and Blinds"

The qualifier ">2" applies to buried only.

The definition of microvia is more contentious than you might think.
While mechanical tapered drills are common for blinds these days, they
have to less than 0.15mm [6 mils] diameter on the entry side to be
classified as micro.  Same applies to those lased holes that are
notorious for having a 7 mil diameter at the target.

Chris


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


-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Roberto
Tulman
Sent: Thursday, February 25, 2010 9:56 AM
To: [log in to unmask]
Subject: [IPC-600-6012] copper thickness for blind vias

Dear all

 

I'd like to have your opinion about the interpretation of the IPC-6012.

A multilayer is sequentially built and has a (pre-drilled and plated)
core for layers 1 and 2. 

This core is not laser drillable and can be only mechanically drilled.

 

Table 3-3 applies to Through Holes, Blind and Buried Vias > 2 layers.

What about blind vias equal to 2 layers? (Such as layer 1-2 made of a
drilled and plated core). Table 3-5 applies to a 2 layers core, but is
defined as a buried core only.

 

Note 1 to table 3-3 : "Does not apply to microvias. Blind vias have
greater than 1:1 aspect ratio ."

Note 1 to table 3-4 :" Microvias are defined as less or equal to 1:1
aspect ratio ( excludes mechanical drill),  or mechanically drilled <_
0.15 mm."

 

Which standard shall apply to blind vias that have an aspect ratio less
or equal to 1:1 -  for example layer 1-2 made of  a drilled and plated
core : 

Case A : 0.25 mm thick core with 0.25 mm mechanically drilled holes .

Case B : 0.25 mm thick core with 0.20 mm mechanically drilled holes.

 

Just to compare: what is your opinion  for the copper needed for a
double sided PCB with filled vias

 

Regards,

Roberto Tulman, CTO

Eltek


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