Update SC-74 to use more permissive JEITA values
SC-74 is a JEITA standard package: https://www.jeita.or.jp/japanese/standard/book/ED-7500B/#target/page_no=39
As is often true, manufacturers use a stricter set of tolerances for their own parts (and SC-74 is double-confusing because it can go by other names like SOT-457 and SOT-23-6)
The values of the SC-74 in the generator are taken from this NXP datasheet: https://www.nxp.com/docs/en/package-information/SOT457.pdf (which calls it SOT-457):
This produces a footprint with slightly smaller pads. Below, red is NXP (current) and blue is the JEITA values (this MR):
The reason I think this is important is other SC_74-ish parts, like the Diodes Inc. SOT-23-6 (https://www.diodes.com/assets/Datasheets/MMDTA06.pdf) have a different set of dimensions and tolerances, which are still in-spec per JEITA SC-74, but not with the NXP part:
Where we see that the NXP (current, red) footprint has too-narrow pads, but the Diodes footprint has shorter heels:
Which means the current SC-74 footprint isn't quite suitable for the MMDTA06 part ( kicad-symbols!3913 (merged)).
And here we see the Diodes footprint (red) strictly fit within the JEITA footprint (blue, this MR):
There are only two symbols using the current footprint:
- NCR401U (NXP part)
- BCR430UW6 (a Diodes part - so it actually doesn't fit the current NXP land pattern)
And the PMN48XP has SC-74 in the description, but uses a non-generated TSOP-6 which doesn't quite match the datasheet land pattern either.
- Footprint implementaton MR: kicad-footprints!3390 (merged)
- Symbol update MR: kicad-symbols!4162 (merged)