Let's use IPC-2221 and 2222.

2222 places the conductive feature locations in paragraph 9.1.5 for board
dimensions with x-y dimensions less than 300 mm: Preferred tolerance 0.3mm;
Standard tolerance 0.2mm and reduced yield at 0.10mm.

2221 places the hole location tolerance in table 9-3 Preferred tolerance
0.25mm; Standard tolerance 0.2mm and reduced yield at 0.15mm.

Caution: Your question seems simple but it is not. Dimensioning systems can
alter the meaning of tolerances. Figure 5-4 of 2221 and the associated text
discuss the problem. Tolerances can accumulate, the hole location tolerance
above is for the center of the hole, but the hole size has a tolerance as
well.

> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of Eric Christison
> Sent: Thursday, May 02, 2002 8:19 AM
> To: [log in to unmask]
> Subject: [TN] Some Advice on PCB tols required
>
>
> I wonder if some experts could refresh my memory on some PCB
> tolerances assuming materials and processes
> suitable for very high volume commercial quality PCB's.
>
> Imagine I have a rectangular board about 50 X 100 mm (2"X4") with
> four fixing holes - one in each corner
> and a set of pads somewhere in the middle of the board. Here's
> the features I'd like tols on:
>
> The tolerance on the fixing hole diameter.
>
> The tolerance on the position of the pad pattern to the fixing hole.
>
> The tolerance between individual pads in the pattern - assume
> each pad is 1mm wide by 2mm long.
>
>
> Thanks,
>
>
> --
> Eric Christison
> Mechanical Engineer
> STMicroelectronics
> 33 Pinkhill
> Edinburgh
> EH12 7BF
>
> Tel: (0)131 336 6165
> Fax: (0)131 336 6001
>
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