IPC-7351C Pin 1 Polarity Marking

Great question!

There are 3 different silkscreen polarity markers:

1. Leads extend from the component
2. Leads under the component
3. Chip and Molded Body 2-pin component

When the terminal leads extend beyond the body of the component package the silkscreen polarity marker is a Line that runs the full length of the pad and is visible after assembly.

When the terminal leads are under the component package (BGA, LGA, CGA, PQFN, PSON, DFN, etc.) the silkscreen polarity is removal of silkscreen. This is because the placement courtyard on "Bottom Only" terminals hugs the component package and there is no room to place a visible silkscreen polarity marker that is located inside the placement courtyard (not enough room). Note: the full silkscreen outline component boundary is shown and where the silkscreen is missing, that's pin 1. Intended for high density part placement.

The Chip and Molded Body 2-pin component the silkscreen polarity wraps around pin 1 (or Cathode) and is visible after assembly. Where non-polarized Chip and Molded Body only have parallel side component  silkscreen lines that map to the package length.

The Silkscreen Pin 1 Dot is only there because some people asked for it.

You can turn the Silkscreen Dot off in the "Drafting > Silkscreen" preferences by changing the value to 0 (zero). This is applicable for any outline that you don't want.

Our CAD tool, Pulsonix, has an automatic feature that clips the silkscreen automatically over solder mask clearances on the CAM output to prevent silkscreen over pads.

I only raise this because on every PCB Libraries footprint that I've generated since they added back in the silkscreen "dot" I've found the majority of dots on any board are automatically "clipped".

Since you then have a PCB with dots on some components but maybe not on other components of the same type in a more dense area it doesn't make sense to use them as an after-assembly aide for checking.

The assembler should never be using the silkscreen to generate assembly data prior to assembly anyway - I make that clear in all my documentation.  That's what the assembly drawing is for.

Just my tuppence half-pennies worth.

There is an unanswered question above for you Tom - 5th post in this thread.

Also, now when I create a new user preferences file with the preference of a 0.0 pin 1, then close PCBLE, then open PCBLE, and look at the preferences, its back to 0.40.  It will not go away, although it remembers my user suffix choice.  There seems to be no way to create a UserPreferences.dat with no pin 1 on the silkscreen.  Can you hear me screaming?

I talked to Jeff, and it is confirmed that there is a bug saving silkscreen settings in the User Preferences file.