committed a v3 candidate for 3042 and 3052 cards. For the details on the mounting holes, this is preliminary as long as we're not done with the changed mounting situation.
I've again spent too much time in finally not finding any decent source for M2 screws w/ wafer head (or broad-head) in 2 mm length beside more or less random eb*y stores in CN. The very few exceptions selling 'laptop screws' believe that they trade gold, and hence their ridiculous prices.
During search, some more M.2 mounting options came across:
- some propagate a stand-off with inner and outer thread; their outer thread is 2.5mm long. They'd always scratch a plated hole, except you wide the hole and use a nut. - This was the only finding for that type of SMT mounts' drawing w/ measures on it, but some are strange there: e.g. the inner thread is likely not 3.0mm... (i-o-threads-spacer.jpg)
- the clip anchor is obviously not made of conductive material, and covers parts of the RF mounting terminals on the card. (ngff-clip-anchor.jpg)
- for the UDOO SBC, a very simple mounting kit gets sold (udoo-mounting-kit-pk.png) which consists of two generic metric screws w different legth, and each two spacer, nuts and washer.
Neither of those are especially elegant for out use case, only the last option is something we could consider.
One change we should do anyway as it would allow to mount double-sided cards, is to change to the 2,45mm card offset (insted of now 1,45mm): PC-SIG spec states those two default heights, manufacturer hence offer them. In our case, the 2,45mm-TE-type with B key would be 2199230-3 for the M.2 connector (instead of 2199119-3), and respective stand-off is SM3ZS067U410-NUT1. This is only a two-liner BoM change. - This change would also ease the wafer-head screw procurement situation, as only one M2x2mm is needed per PCBA, the 2nd can be an easier-to-source M2x3; also 2x M2x2,5 is then possible.
If the overall number of needed wafer-head M2 in 2mm is halved with that change to one per PCBA, we again could think of source them from a random eb*y seller...
Some retailer use normal DIN 7985 M2 screws in 2mm on top side even w/o a washer (screw head diam is nom. 4mm on M2 DIN7985). While this likely works, they are of course not broad-head of wafer-head screws, the latter with very low-profile head. Higher heads give less mounting freedom for the MHF4 pigtails. - But such screw would be perfectly sane on bottom side, even better with washer.
