Footprints with rounded rectangle pads & correct initial rotation, generated from Library Expert

[Robin-Whittle]

I just completed my first KiCad design, which was also my first SMT PCB. My notes on how I did it are at:

http://www.firstpr.com.au/kicad/kicad-design-for-manufacture/

I was able to create footprints which I believe meet one of the two industry standards for centroid and initial rotation. Therefore, the data in the .pos file, which is used to drive the pick-and-place machines for automated SMT assembly should require little or no manual adjustment by the PCB assembly company. I haven’t tried this yet. There is a program VisualPlace:

https://www.compuphase.com/visualplace/visualplace_en.htm

which should enable me to check this data.

My SMT footprints with rectangular pads use rounded rectangles (I was using a late November Windows nightly), with pad dimensions according to the forthcoming IPC-7351C standard.

Both these aspects of my footprints were only possible (without huge amounts of manual effort) by using and modifying the files exported from the free version of Library Expert, from http://pcblibraries.com .

There are a lot of things to get right, starting with schematic symbols in the library, their fields, footprints in the library and all the details of the fields in the PCB’s placed footprints (components).

The use of various layers needs to be carefully considered, and I have adopted the approach suggested in this forum by Mars_Warrior and Joan Sparky: to use the ECO1.User layer for a box outline of each SMT component, with text there for each component’s value. The intention is that this layer will be used to create an image or print-out to be used as a guide for manual and automated assembly.

In my case, I use a program (kicad-pcb-value) so I can set some alternative text in a field in a schematic component, and have that text used for the “value” value in the netlist used by Pcbnew - and this is what controls the text in the ECO1.User layer.

There’s a lot on this page, so you might want to scan over it first - I doubt anyone will read the whole thing.

Of possible interest to many people is my chart of how I use the layers, how this relates to the layers in the Library Expert exported footprints - and how they relate to the layers inside Library Expert itself:

http://www.firstpr.com.au/kicad/kicad-design-for-manufacture/#chartlayers

• Robin

[bobc]

Looks like a very comprehensive write-up, perusing it now!

One quick question, if you derived your footprints from PCB LIbraries’ data, does their license agreement permit you to re-distribute them?

[Robin-Whittle]

The text has remained unchanged from earlier versions going back to May 2017. The EULA for the latest version of Library Expert is here:

https://www.pcblibraries.com/Downloads/FPX!Library_Expert_2017-22_Lite.asp

I discuss licensing restrictions here: http://www.firstpr.com.au/kicad/kicad-design-for-manufacture/#libexpeula and as far as I can see, there is nothing which prohibits sharing the generated footprints, or any footprints derived from them. The closest I could find to a restriction such as this is:

Lite version output files may be altered, but removal or alteration of the auto-inserted “PCB Libraries” meta data from any output files is a violation of this Agreement.

However, the exported footprint files contain no such text.

[bobc]

FPX data files and Library Expert output data is not to be sold or re-distributed (other than with a PCB design project), unless you obtain a Distribution of Content (DoC) License from PCB Libraries. The DoC is currently available (starting at $50,000 per year) per output format type supported by the Library Expert.

That seems to cover this case. It seems that if you distribute the part data, you must also distribute your project files. I guess you didn’t pay for the DoC license, not cheap!