how do I use fiducials anyway?

[Hrvspooner]

Reading a recent thread on fiducials, I have a question.

How do I use fiducials? I understand that they help the pick-n-place equipment
locate ics or to mark fixed locations on boards or panels. How, if I'm using
local fiducials, do I determine where to place the mark? How do I tell the
board house where the mark is relative to the body of the device?

Regards, Hrv.....

 

[Matthew Kendall]

"Hrvspooner" <hrvspooner@aol.com> wrote

Reading a recent thread on fiducials, I have a question.

How do I use fiducials? I understand that they help the pick-n-place
equipment locate ics or to mark fixed locations on boards or panels.
How, if I'm using local fiducials, do I determine where to place the
mark?

It doesn't matter exactly where they are so long as you know where they are;
you have enough of them; they are reasonably near the fine pitch component
in question; and the machine vision system can see them (i.e. they are not
obscured or obstructed by other components).

http://www.smema.org/ have some (brief) guidelines.

How do I tell the board house where the mark is relative to
the body of the device?

The same way you tell them everything else about how and what you want them
to do; on the assembly drawing. If you don't they will figure it out for
themselves by examining the PCB Gerber files.

(By board house I assume you mean the company that will assemble the
components on to the PCB. The PCB manufacturer doesn't care about fiducials,
they are just pads on the board like any other to him).