Electronic – Help me decode this mechanical drawing of an SD card PCB layout

drawingmechanicalpcb

I'm trying to understand this mechanical drawing so I can create a layout for it in gEDA PCB.

Specifically on page 4. I've already managed to place GND 1 and GND 2; those were fairly simple to work out. But GND 3 confuses me, because it's apparent from close inspection of the drawing that it doesn't quite line up with GND 1 and the offset doesn't appear to be given. The same is true for GND 4 which doesn't quite line up.

Also on a semi-related note it is unclear whether the pins are in the order as they are on the SD card or if they are numbered arbitrarily – that is, does pin 1 correspond to pin 1 on the SD card?

While this isn't strictly electronics, I think it passes as an appropriate question because it is an electronic connector and it requires a PCB layout.

Best Answer

If an offset isn't given from the center-line or some other point, it should be symmetrical about the c.l. (always has been in my experience). So 4.7 mm between the inside of GND3/GND4 would mean they are each 2.35 mm away from the c.l., likewise with the 8.3 mm outer to outer.

The pins appear to correspond to the SD card pinout I looked up. It appears backwards on the footprint because the actual SD terminals would be on the right side, but the contacts lead to the left to connect to the board.