At 10:36 AM 5/20/2002 -0700, Brooks,Bill wrote:
>Okay, I'll jump in... The PCB fab house can do what ever it wants to make
>the board.....YOUR FAB DRAWING allows your company to ACCEPT/REJECT it if it
>does not meet your standards.

Yes. Another reason not to specify as-drilled sizes. It is a lot harder to 

>  Tolerances need to be specified for
>inspection. The FAB Drawing is the control document that protects your
>company. If you think of it that way you will not go wrong.

There are still plenty of ways to go wrong.

Note that Protel does not generate, in its .Legend table, tolerances. These 
will need to be specified separately, for a formal drawing.

>So, making a board without a FAB drawing is do-able, but it leaves your
>company no recourse to reject whatever they ship unless you have some
>accept/reject criteria specified for the material they ship to you, IN
>WRITING. That is usually defined in the Fab Drawing.

Yes, the criteria could be defined in the Fab Drawing, but they could also 
be defined in a purchase order or attached document, which might refer to 
an industry standard.

In the absence of a fabrication drawing, there is still protection for the 
buying company. First of all, the company will typically have the magic 
wand of simply not paying for bad boards. To keep its credit rating, it 
will, of course, need to formally document for the vendor its reasons for 
not paying. If a PCB does not meet generally-accepted standards in the 
industry, the common-law position would be, I'd think, that the customer 
would not have to pay. If, for example, there is a track on the Gerber and 
it is missing on the PCB, or vice-versa, that is clearly a manufacturer 
error unless the customer has approved a modification.

The most common cause, in my experience, of serious disputes is where a 
fabricator failed to catch a relatively obvious customer error. This is, in 
fact, the customer's fault, and would still be a problem even if there is 
the most formal fab drawing in the world.

Informal board purchasing is not all that unsafe UNLESS and UNTIL the 
quantities get large or the boards are very complex, i.e., very expensive 
to make individually. Most board vendors will bend over backwards to please 
customers, if there is any reasonable basis for the customer's complaint. 
Not all, but most, and you want to find out about the companies that won't!

If a customer error caused a batch of boards to be useless, and it was an 
error that the fabricator might have caught in a decent inspection, a good 
fabricator is likely to make some compromise to lessen the customer's pain.

Still, it doesn't take much to add critical information to the drill 
drawing to make it into at least a rough fab drawing. Perhaps some of us 
will make available standard fab drawings that they use.... If some are 
sent to me, I'll put them up on the protel-users web space.

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