Barry,
Regarding the mechanical feature and a 3-place dimension that you are
speaking of --
Can you describe what is dimensioned? Is the dimension between a board edge
and a hole? Is it between a hole and another hole? Is it relative to the
thickness of the board? If it to a hole, what is the tolerance on the hole?
All these mechanical features will have varying tolerances based on the
manufacturer's fabrication processes, which may or may not conform w/ IPC
standards.
If you are trying to design around this "tolerance-less" dimension that
you've mentioned, it's designer (or documenter) has indeed done you a grave
disservice! Every mechanical feature will have a manufacturing tolerance and
in order to design around it, it must be specified w/ documentation.
Now you've got to go back to the board vendor. Get in touch with the
production supervisor and get a guaranteed tolerance in writing to design
around. Keep it in your job history file, and forward a copy to your
customer and request that it gets added to the formal documentation.
-- Kelly
Kelly Dack
Sr. Pcb Dsnr
IGT (International Game Technologies)
Reno, NV
-----Original Message-----
From: Barry Gallegos [mailto:[log in to unmask]]
Sent: Thursday, June 05, 2003 7:35 AM
To: [log in to unmask]
Subject: [DC] IPC PCB Dimensioning standard
Good morning,
My Name is Barry and I have been asked to locate some information. As I have
had great
experiences with TechNet, I thought I would Give the Designer Council a Try.
So here goes.
I ask for some input on the following Message that I received this morning.
We have an issue on a customer drawing, where the customer calls out
dimensioning on their data, to 3 decimal places, but do not provide a
tolerance table or tolerance indication at all. The exact method the
customer used to call-out dimensions on their drawing is: 250Mils or 530Mils
for example. The pcb shop that built these is saying that, in the absence of
having a tolerance call-out, they default to IPC standard tolerance. The
customer service person at the pcb shop, cannot tell me which standard he is
referring to, nor can he tell me what that default IPC standard tolerance
might be. We do not have the 2221 IPC design standard nor do I know if it
would cover this issue. We have issue with the dimensions of these pcbs we
received, including hole positions.
Can you find out what the IPC default tolerance is for dimensioning of pcbs,
in the absence of having a specific tolerance call-out?
Barry Gallegos
Western Electronics
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