The tables you are referring to are from the unreleased 6012 Rev C that is
out for ballot.  If you use rev B and your hole does not meet the micro-via
criteria, you would have to treat it as a blind via and inspect to the 25
um average if using class 3.


Table 3-3 says (Embedded image moved to file: pic31499.gif)

The grater than 2 layers applies to the buried vias only.  A blind via that
does not meet the micro-via requirements is covered by table 3-3.

Unfortunately, you point out that the document has a gap that was created
by the footnote stating that blind vias have an aspect ration of > 1:.  We
have a telecon tomorrow to discuss negative votes on the document.  I will
bring this up and my recommendation would be to delete that portion of the
footnote.  As the spec did in rev B, I would use table 3-3 for all blind
vias that do not meet the microvia criteria.


Joe Schmidt
Raytheon Product Development Engineering
P. O. Box 11337 Bldg. 807 MS J6
Tucson, Arizona 85734
Tel (520) 794-4229
Pgr (520) 489-9286
Email [log in to unmask]


                                                                                                                                 
  From:       Roberto Tulman <[log in to unmask]>                                                                                
                                                                                                                                 
  To:         [log in to unmask]                                                                                               
                                                                                                                                 
  Date:       02/25/2010 08:12 AM                                                                                                
                                                                                                                                 
  Subject:    [IPC-600-6012] copper thickness for blind vias                                                                     
                                                                                                                                 
  Sent by:    IPC-600-6012 <[log in to unmask]>                                                                                
                                                                                                                                 





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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