IPC-2221 is a design guide, and Table 9-1 is one of the factors used in the
minimum pad size calculation in section 9.1.1.  This would be used if you
were working on a new design and trying to decide what size pads to use.  My
reference to Class 2 vs Class 3 annular ring is based on IPC-6012, which is
the industry standard performance/acceptance spec.  So you'd use IPC-2221 to
design your boards so that they can ultimately meet IPC-6012.  There are
plenty of conflicts that can be found, but I don't see a conflict in Table
9-1.  But I might be misunderstanding your question.

Morgan Viggers
Field Applications Engineer
ISU Petasys
503.675.3877

-----Original Message-----
From: [log in to unmask] [mailto:[log in to unmask]] 
Sent: Friday, May 22, 2020 6:54 AM
To: 'Morgan Viggers' <[log in to unmask]>; 'TechNet E-Mail Forum'
<[log in to unmask]>
Subject: RE: [TN] IPC Class 2 v 3

Morgan,

Thank you so much for answering.  I agree with you.

However this seems to contradict  IPC-2221 Section 9.1.1 Looking at Table
9-1 it is stating a minimum of 0.2mm or 7.874 mil

Am I missing something here?

Thanks,

Larry

-----Original Message-----
From: Morgan Viggers <[log in to unmask]>
Sent: Friday 15 May 2020 20:08
To: 'TechNet E-Mail Forum' <[log in to unmask]>; [log in to unmask]
Subject: RE: [TN] IPC Class 2 v 3

Larry - there are a few major differences, but the one that most commonly
requires design changes is the via/PTH pad size.  Class 2 allows 90 degree
drill to pad breakout, but Class 3 requires 1 mil annular ring remaining, so
Class 3 designs will typically need larger pads.  Many other Class 3 items
(like plating thickness) often do not require any layout changes.  A lot of
the other Class 2 vs Class 3 differences are in the sample and inspection
plans.  If the design is already done, I suggest to just sent it to your
fabricator and ask them to review.  They will be sure to point out any
design issues that currently prevent it from being fabricated to Class 3 -
and they make even be able to make any needed design changes themselves.

Morgan Viggers
Field Applications Engineer
ISU Petasys
503.675.3877

-----Original Message-----
From: Larry Brophy [mailto:[log in to unmask]]
Sent: Friday, May 15, 2020 3:24 AM
To: [log in to unmask]
Subject: [TN] IPC Class 2 v 3

Quick question,

 

If a PCB is designed to IPC Class 2, can I get the PCB manufacture to make
it Class 3?

 

If not, what areas do I need to ask the PCB designer to look at to make it
possible to manufacture as Class 3?

 

Thanks,

 

Larry