Jack,

 

It is drilled to 8 mil and finished at 6.

 

Thanks,

 

Larry

 

From: Jack Olson <[log in to unmask]> 
Sent: Thursday 28 May 2020 17:53
To: Larry Brophy <[log in to unmask]>; TechNet <[log in to unmask]>
Subject: Re: [TN] IPC Class 2 v 3

 

don't forget, there is a difference between the drill size and the finished plated hole diameter.

(just trying to help)

 

On Tue, May 26, 2020 at 12:34 PM <[log in to unmask] <mailto:[log in to unmask]> > wrote:

Jack,

My PCB supplier can drill to 6 mil with a tolerance of +/-2mil.  That allows me to have a pad of 14mil and meet the minimum of 2mil outer annular ring for IPC-6012 Class 3.

I could use laser microvias and buried vias but there is a significant cost going that way.

My preference is to use a 6mil drilled via but I'm not sure that will qualify for Class 3.

Anyone know if there are exemptions that allow a 6mil via for Class 3.

Thanks all,

Larry

-----Original Message-----
From: TechNet <[log in to unmask] <mailto:[log in to unmask]> > On Behalf Of Jack Olson
Sent: Tuesday 26 May 2020 18:24
To: [log in to unmask] <mailto:[log in to unmask]> 
Subject: Re: [TN] IPC Class 2 v 3

On Fri, 22 May 2020 16:54:20 +0100, Larry Brophy <[log in to unmask] <mailto:[log in to unmask]> > wrote:
>
>Sorry I have another question and it is again to do with what you have 
>said , it is a conflict between the two specifications.
>We need to use a micro BGA.  Based on our PCB manufactures capabilities 
>in the BGA area we need to use a blind via drilled at 6mil with a 14mil 
>pad to guarantee a 2mil annular ring.
>But IPC-2221 states that the smallest blind via is 8 mil.  Table 9-4.  
>This is just another design guide v IPC-6012 issue?

I thought Table 9-4 referred to the minimum mechanically DRILLED hole size, (laser can be smaller diameter?) but after reviewing the document, it does not seem clear to me.
(good question, but I only have the 2221C Working Draft OCT2013 to look at right now)