PCB footprint insertion origin

[Michael]

There are two reference points when a footprint is created: insertion
origin and "datum" (0,0).
There are two "special" points in a footprint: pin one center and
component center (not always clearly defined).
Is component center preferred insertion origin and datum location?
What are the pros and cons of alternatives?
Any relevant comment will be appreciated.
Thank you!
P.S.: we are using ORCAD layout and will move to ORCAD PCB editor

 

[[email protected]]

There are two reference points when a footprint is created: insertion
origin and "datum" (0,0).
There are two "special" points in a footprint: pin one center and
component center (not always clearly defined).
Is component center preferred insertion origin and datum location?
What are the pros and cons of alternatives?
Any relevant comment will be appreciated.
Thank you!
P.S.: we are using ORCAD layout and will move to ORCAD PCB editor

Are you referring to how the tool will generate a pick and place file?
It doesn't matter, eventually your assembler will translate to
whatever he wants for his particular tool.
Anyways, most PCB tools let you choose to what point the cursor sticks
to when placing on-screen, you can usually choose from centroid, 0,0,
pin 1 or user select (which can be any pin# or a x,y).

 

[Spehro Pefhany]

There are two reference points when a footprint is created: insertion
origin and "datum" (0,0).
There are two "special" points in a footprint: pin one center and
component center (not always clearly defined).
Is component center preferred insertion origin and datum location?
What are the pros and cons of alternatives?
Any relevant comment will be appreciated.
Thank you!
P.S.: we are using ORCAD layout and will move to ORCAD PCB editor

Probably depends on the component. I might want to place the center of
a coaxial jack on a precise center line, but not care much where (and
whether they were off-grid) the hard metric pin locations turn up on
my inch standard board. OTOH, for a part that does not have some
mechanical relationship with the outside world other than through the
padstacks, probably you'd rather use pin 1 or something like that.
Best regards,
Spehro Pefhany

 

[donald]

You don't solder a part down from the center of the silkscreen.

All parts should reference a real copper "foot print", not painted art work.

My .02

donald

 

[Michael]

Th reason I posted this question: some time ago we were asked by
assembly house to place origin and insertion origin in the middle (if
my memory serves me right). Now we are trying to clean up the
libraries and I started having doubts.....

 

[Martin Riddle]

Look at the IPC requirements. Most assembly shops use this standard.
Cheers

 

[donald]

Look at the IPC requirements. Most assembly shops use this standard.
Cheers

I have goggled for "IPC requirements", but I still do not understand
what IPC means.


Please elaborate a little more about IPC requirements.

Thank you

donald

 

[donald]

I have goggled for "IPC requirements", but I still do not understand
what IPC means.


Please elaborate a little more about IPC requirements.

Thank you

donald

Found it:

Institute of Interconnecting and Packaging Electronic Circuitry

I'll have to check this out.

thanks

donald

 

[Martin Riddle]

Found it:

Institute of Interconnecting and Packaging Electronic Circuitry

I'll have to check this out.

thanks

donald

Have a look here...
http://www.pcblibraries.com/

They have a std IPC-7531 land pattern calculator, SMT only but it should give you an idea....

Cheers

 

[qrk]

There are two reference points when a footprint is created: insertion
origin and "datum" (0,0).
There are two "special" points in a footprint: pin one center and
component center (not always clearly defined).
Is component center preferred insertion origin and datum location?
What are the pros and cons of alternatives?
Any relevant comment will be appreciated.
Thank you!
P.S.: we are using ORCAD layout and will move to ORCAD PCB editor

In Layout, you want to place the datum at the center of the part. This
is contrary to what Orcad wants you to do with the datum. Layout was
developed in the days of parts on 50 mil pitches. This will prevent
the component from being placed on a weird grid after you rotate it
and/or place it on the opposite side if the pads aren't on a multiple
of your placement grid. When the part gets placed on a weird grid, you
need to pick up the part and place it down again to get the part to
snap to the proper grid (you'll see the part jump to the new
location). This is a very annoying bug in Layout. Placing the datum on
the center of the part solves this issue. Layout, which was the
Massteck(sp??) router of yore, had a lot of issues with coordinate
translation and rotation. Back in the mid 90s, I got sick of moving
Layout projects back to PCAD to give proper pick & place coordinates
for bottom mounted parts. I figured out the translation/rotation math
and gave it to the Layout manager so they could post a work around
using Excel. They actually fixed the next release of the program. Boy,
folks think Layout is a bear to use these days, you should have seen
how horrible it was back then!

Always put the pick & place point at the center of the part for a
symmetrical part (like smt resistors). For odd parts where the body
isn't centered on the pads, I'll put the pick & place point on the
center of the body.

 

[Jim Thompson]

Found it:

Institute of Interconnecting and Packaging Electronic Circuitry

I'll have to check this out.

thanks

donald

But you're still the dummy one.



...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Tree Abusers, Because of the Bastards

 

[Joerg]

In Layout, you want to place the datum at the center of the part. This
is contrary to what Orcad wants you to do with the datum. Layout was
developed in the days of parts on 50 mil pitches. This will prevent
the component from being placed on a weird grid after you rotate it
and/or place it on the opposite side if the pads aren't on a multiple
of your placement grid. When the part gets placed on a weird grid, you
need to pick up the part and place it down again to get the part to
snap to the proper grid (you'll see the part jump to the new
location). This is a very annoying bug in Layout. Placing the datum on
the center of the part solves this issue. Layout, which was the
Massteck(sp??) router of yore, had a lot of issues with coordinate
translation and rotation. Back in the mid 90s, I got sick of moving
Layout projects back to PCAD to give proper pick & place coordinates
for bottom mounted parts. I figured out the translation/rotation math
and gave it to the Layout manager so they could post a work around
using Excel. They actually fixed the next release of the program. Boy,
folks think Layout is a bear to use these days, you should have seen
how horrible it was back then!

Maybe that's why everyone was using Autotrax back then