Please... just be aware that the designing to the "minimum" is not
always the best 'recommended' practice... :) Some people make the
mistake of using the minimum numbers to design to and their
companies/employers/customers end up paying for it in the long run.
And while I agree with using the IPC specs to set a standard for your
board design, I do not always agree with the IPC specs about some of the
choices that they made... for instance... in IPC-2222 9.2.1.2 they want
drill sizes expressed in a min/max definition, and not a +/- tolerance
expression... however, the nominal diameter information is lost in that
scenario... and I usually have a target hole size that is nominal, or
'perfect' if you will, for the application that I need. To express it in
say '.188 to .210' for example... may not communicate or imply to the
board shop that I really want a .200 hole and I want the vendor who is
making the board to try to hit that target size.
Main thing is to do the math, and express things in a way to get the
point across to the board vendor so that you get consistent results that
work.
The IPC standards are not rules... they are a standard way of doing
things that gets generally successful results... but they in no way
should limit the designer's options in doing things... the designer
needs to know how the board will be used, what it's service life will
be, how it will be mistreated and what expectations need to be met for
survivability, and what the cost targets and volume of production is
expected...
Ah... I guess I'm on the soap box... I must be feeling better this week.
Take care...
:)
Bill
James Head wrote:
> For rigid boards, IPC-2222, section 9.2.1.2, table 9.2 lists minimum
non-plated hole tolerance ranges, and section 9.2.2.2 has plated hole
tolerances, given in table 9.5.
>
> Regards,
>
> James
>
> James Head BEng CID MIIE MIET
> Senior PCB CAD Engineer
> Crowcon Detection Systems Limited
> 2 Blacklands Way
> Abingdon Business Park
> ABINGDON
> OX14 1DY
>
> Telephone: +44 (0) 1235 557700 extension (9) 289
> Fax: 07092024504
> Email: [log in to unmask]
>
>
>
> -----Original Message-----
> From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Tracy Norton
> Sent: 30 September 2009 17:36
> To: [log in to unmask]
> Subject: [DC] drill tolerance
>
> I just got caught in an embarrassing situation. A client pointed out
> that I don't have drill tolerance specified on my fab notes, and wants
> it added AND referred to the specific IPC standard
> I looked back at all my work as far back as to '98...and there's no
> drill dia tolerance callout!
> All I need is pointed to specific standard so I can research it and
add
> to notes
> Thanks!
> Tracy Norton
>
>
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