The Perfect Footprint from PCB Libraries

[Tom Yunghans]

Hi Robert,

I just watched the video you did with Tom Hausherr at PCB Libraries. I have been a little frustrated over how difficult it is to find two people that agree on how a footprint should be designed. I like the approach Tom seems to be using; a mix of IPC guidelines but with feedback from the industry. However, I was a little surprised at the response he gave to your question about what happens when the manufacturers recommended footprint doesn't match with the IPC guidelines (at the 1:05 mark of the video). He seemed to suggest that in that case, you should use the manufacturers recommendation, as he stated that the manufacturers do a lot of testing on their recommended footprint.

My experience is that you can almost always find a manufacturers recommended footprint. The problem gets a more difficult with small passives (e.g. resistors, caps) where you can use parts from multiple vendors with different footprint recommendations. I have also observed that the manufacturer's recommendation rarely matches exactly with the footprint recommendations from others or Altium's IPC footprint generator.

I was surprised by his response, because if we should always use the manufacturer's recommendation, why would we need to use the software from his company?

Your thoughts?

Here is the link to the video: https://www.youtube.com/watch?v=cMxXea16Hxc

Thanks,

Tom Yunghans

[qdrives]

I totally agree. I used footprints that were specified by the manufacturer and the assembly company stated the the footprint pads were to big. PCB libraries would use smaller pads too.
The problem is that about everything has pro's and con's. Do you want perfect aligned components: small pads. Do you want to hand solder: use large pads.

I like Tom. He backs (most) up with arguments.

If you want that everyone is in agreement, you cannot work in the electronics world. There are to many points of view on solder mask (expansion), paste mask (expansion), pads sizes. Partly fueled by the various options: solder mask color and imaging technique, stencil thickness, paste type, etc. The devil is also in the detail - solder balls forming depending on the shape of the stencil opening (see https://smtnet.com/library/files/upl...Guidelines.pdf )

[robertferanec]

Initialy:
- I almost always use recommended footprint if it exists
- I have used PCB Libraries in the times when we needed to get footprints quickly

Then:
We always print the footprints, compare them with the real components and if needed we adjust them (and it doesn't matter if they are recommended or IPC)

About footprint compatibility between different manufacturers for the same component type - often we use the biggest one, so as many options as possible can fit.