Wendi,

Agreed.  We run across this often when larger HWP requirements are on the drawing.
IMO this was addressed when we moved from explicitly stating 1/2 could be removed to a hard minimum dimension for class 2 and 3.
Then class 3/A is strictly intended as a list of supplants to class 3.  If it isn't listed, class 3 applies.

This is certainly a weakness in the 3/A implementation.  However, TAEC sure isn't going to let us have an "official" fourth class.
The silver lining is that 3/A doesn't have to address new issues at the same cadence as 6012 proper, assuming we are happy with the class 3 requirements.

All of that said, it is a little counterintuitive, as HWP has decades of history of applying to surface and hole.

One interesting legality of the rev C 3/A is that more 3/A product is moving to HDI, Flex/Rigid and "Microwave".  In which case, there is a tendency to leave the old screwy contracts in place, as 6013,16,18 don't have 3/A. 

Chris



-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Gary Ferrari
Sent: Tuesday, August 17, 2010 6:23 PM
To: [log in to unmask]
Subject: Re: [IPC-600-6012] Class 3/A requirements

  Wendy,

I'm in agreement with all. The wording, as such, implies the PTH wall. 
This is the way I've interpreted it for 3/A programs.

Regards,

Gary


On 8/17/2010 5:07 PM, Wendi Boger wrote:
> I need some clarification on the requirement for Plating/Coating
> Thickness.  The 3/A page requires additional copper thickness above
> class 3 to be added to tables 3-3, 3-4 and 3-5.  Does this also apply to
> the minimum wrap thickness?  (Example) Is it required for a
> non-conductive filled through via to have .944 mils of wrap (table 3-3)?
> It's a bit confusing as it says to apply to minimum copper average and
> minimum thin areas.
>
>
>
> Wendi
>
>
>
>
>
>
>
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