look like the customer got some tight request... (the board might be small
- however, choice of fr4 is strange in that case.  otherwise, no reason to
get so hang on the tolerance... we might talking about something else). 
of course, unless you deal with a newbie designer - never see a fab house
before... just a guess.
             jk
> IPC-2222A page 24 9.1.5 Conductive pattern Feature Location Tolerance.
> Table 9-3 is for the tolerance to be applied to the nominal dimensions
> chosen for the location of the lands, connector contacts, and conductors
> in relation to the datums. This tolerance includes tolerances for master
> pattern accuracy, material movement, layer registration and fixturing.
> It looks like the requested tolerances exceed Level C Producibility.
>
> Guy
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Lazzara
> Sent: Wednesday, August 05, 2015 10:34 AM
> To: [log in to unmask]
> Subject: Re: [TN] PCB length/width tolerance
>
> Scott, thanks for furthering the conversation.
>
> I have a client (OEM) who wants us (Board House) to fabricate a copper
> plane to within +/- 0.002" of the PCB edge of FR-4 laminate.
> I replied that the edge, per his print, allows a tolerance of +/- 0.005",
> making one tolerance incompatible with the other.
>
> He replied that he'd simply change the print tolerance for the PCB length
> and width to  +/- 0.002".
> When I replied that composite materials would neither punch nor CNC
> machine to that tolerance, he asked what the IPC comments were for board
> size tolerances.
>
> That seemed an easy-enough task. After-all, circuit board size tolerance
> is about as basic or fundamental as it gets for design and fabrication
> considerations. But in the absence of actual values from the IPC (such as
> those defined for hole size dia.) anyone can ask for anything on a print.
>
> Given that the IPC has geometric dimensioning and tolerance comments on
> virtually all other PCB features (machined, imaged or otherwise) I found
> the absence of same for board size tolerance surprising.
>
> So I figured I overlooked it, and asked for help.
>
> Thanks again -
>
> Robert "Bob" Lazzara, CIT
> Tel: (603) 318-3075
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Scott A. Bowles
> Sent: Wednesday, August 5, 2015 10:07 AM
> To: [log in to unmask]
> Subject: Re: [TN] PCB length/width tolerance
>
> Bob,
>
> Maybe you can clarify what is driving your question.  You state that the
> ±.016" seems liberal (and I agree) but this is our subjective opinion.
> Are you asking from a design/OEM perspective or manufacturing/supplier
> perspective? Section 3.4 of IPC-6012 states the printed board shall meet
> the dimensional requirements specified in the procurement documentation.
> However, if there truly isn't any requirement specified then you default
> to the applicable design series specifications. I would think it is very
> rare for a drawing to have no requirements, to not even have the "Unless
> Otherwise Specified" title block tolerances on sheet 1, which typically
> default to something along the values of three place decimals ±.005",
> two-place decimals ±.010".
>
> From a design perspective, IPC-2222A, paragraph 5.4.1 states the
> tolerances specified on the drawing shall accommodate the dimensions and
> tolerances of the mating part.
>
> I suggest clarifying the requirement before manufacturing product.
>
> Regards,
> Scott
>
>
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