At 04:53 PM 9/28/2010, you wrote:
For all those, that follow the discussion from here or vaguely
remember some other rotations:
Rick Collins wrote:
I had to go through all this some time ago and recently I wanted to
iron out all the difficulties so that the assembly house could use
my XYRS file (location and rotation data) directly without alteration.
That ended up being a fool's errand, but I did learn a few things.
IPC has a standard for this which everyone "seems" to use. For two
pin symmetrical parts, pin one is to the left. For IC type parts,
pin one is in the upper left quadrant for parts with pin one in a
corner or for parts where pin one is in the center of a side pin
one is on the upper most side. This is the zero degree rotation
point for the part. All rotations are counter-clockwise from this position.
on 2010-08-15 Rick wrote in thread 'Specification of Rotations for
Auto Assembly':
"I just found something that changes what I thought I knew. I have
a PDF of an IPC magazine from 2005 where they are touting a "leap
forward" in land pattern generation. An illustration showing pin 1
in the upper left for SOT components is what I used as my
reference. That and the post in the FreePCB forum of a normally
very reliable source. But I found a copy of IPC-7351 and it clearly
says that for SOT and most other IC parts, the original rotation is
with pin 1 in the LOWER left. That is what FreePCB does in the
library editor by default. "
This isn't Ricks fault: reading the 2005 IPC-7351 I can confirm
this, while the 2009 IPC-7351B says,
that pin 1 is in the upper left corner ;-)
Shall I comment on this ? I'll just use upper left...
I'm not sure what you are saying. Did you have a point you wanted to make?
I went through a very lengthy search for a rational basis for picking
a standard. Virtually no one seemed to actually know the source of
the standard they used or what anyone else was using. It seems like
the board fab and assembly business is full of cowboys who just want
to make the current project work rather than to figure out a system
that would help everyone. In the end I found that the incorrect
IPC-7351 that I found was an initial short form version from 2003,
limited to naming conventions and a brief listing of pin 1
orientations, not a full spec. I had also found some other materials
that had wrong information attributed to IPC-7351, but not official
(dated in 2003). The officially released standard came out after, in
February 2005, with the pin 1 orientation of all ICs either in the
top left or the top. Without knowing the whys, I can see that
IPC-7351 seems to be what is more supported than anything else. IPC
claims that IPC-7351 matches EIAJ/ANSI 481C. I have not found an
official copy of IPC-7351 that shows any other orientation than what
was stated. If you have an official copy of the released IPC-7351
spec that says pin 1 of ICs is anywhere other than top or top left, I
would like to see it.
Rick
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