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Eagle smd-ipc.lbr footprints not quite right?

gandrewstone

Maybe I'm reading something wrong, but I think that certain footprints may be slightly off so I'd like a second opinion.

 

smd-ipc.lbr claims that it is based on IPC-SM-782.  I'm looking at that document from here:  https://www.pcb-3d.com/wordpress/wp-content/uploads/ipc-sm-782a_amendment_1_and_2.pdf

 

I'm working off of page 73 in the Surface Mount Design and Land Pattern Standard Chapter section 5.0 Land pattern dimensions.

 

When I read Figure 3, it looks like they've used the label "X" for the vertical pad size and "Y" for the horizontal size.  That's unintuitive... but the figure very clearly marks the dimensions.  And my drawn pads don't match up with smd-ipc.lbr for the 0603 part -- they match perfectly when the X and Y are transposed, so perhaps the smd-ipc.lbr author got confused with the X and Y labelling.

 

Can someone check my reading of this doc?

 

A lot of the other resistor footprints in smd-ipc.lbr are slightly different than this doc as well but not clearly transposed.  As we all know from experience, there is quite a bit of fudge in the pads of SMT resistors, which is probably why these footprints are generally working.  However, the doc is supposed to be the "best" (that is, providing the best yields) land pattern, so if fixing smd-ipc.lbr stops a few tombstones in everybody's runs that would be a worthy goal I think.  ... Or maybe the doc is obsolete and the smd-ipc dimensions are what is currently considered "best"?

 

Regards,

Andrew

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  • 0

    Hi Andrew ,

     

    This image shows a footprint, that is correct drawn.

    But it could be shown rotated in this document.

     

    Normally the X direction is horizontal, Y is vertical.
    The rectangle is drawn like this, but is turned to the right on the head.

    In addition, the second rectangle is in the distance, together it gives the whole footprint of the component.

    !! There are also footprints where the dimensions of the Y-side are longer than the X-side. !!
    You always have to check this, otherwise the component footprint will be drawn with the wrong direction of rotation.

    The best way to draw the components from the data sheets of the component manufacturers.

    If the component manufacturer optimally adheres to this IPC standards, this is an advantage and makes it easier to draw the plans in CAD.

     

    One can also help one by comparing the consideration with a house:
    "Where's the front?" - The front is where the front door is ".
    So you can now easily turn in 3D and always have the front page in the mental image, even if this front door is shown behind and mirrored.

    Seen from above, from below, no matter, you always have the door in the mental field of vision, and each mirrored and rotated.

    But the reference always leaves the front with the right side drawn door.
    But ! the side of the house wall, the front where the door is, can be much shorter than the house wall side to the rear. (X is smaller than Y)

     

    Best Regards

    Gerald

    ---

Reply
  • 0

    Hi Andrew ,

     

    This image shows a footprint, that is correct drawn.

    But it could be shown rotated in this document.

     

    Normally the X direction is horizontal, Y is vertical.
    The rectangle is drawn like this, but is turned to the right on the head.

    In addition, the second rectangle is in the distance, together it gives the whole footprint of the component.

    !! There are also footprints where the dimensions of the Y-side are longer than the X-side. !!
    You always have to check this, otherwise the component footprint will be drawn with the wrong direction of rotation.

    The best way to draw the components from the data sheets of the component manufacturers.

    If the component manufacturer optimally adheres to this IPC standards, this is an advantage and makes it easier to draw the plans in CAD.

     

    One can also help one by comparing the consideration with a house:
    "Where's the front?" - The front is where the front door is ".
    So you can now easily turn in 3D and always have the front page in the mental image, even if this front door is shown behind and mirrored.

    Seen from above, from below, no matter, you always have the door in the mental field of vision, and each mirrored and rotated.

    But the reference always leaves the front with the right side drawn door.
    But ! the side of the house wall, the front where the door is, can be much shorter than the house wall side to the rear. (X is smaller than Y)

     

    Best Regards

    Gerald

    ---

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