Physical dimensions
The thickness of the daughterboard must be 1.6mm thick.
Overall size is 18 x 16.5 mm, with screw holes placed 14 x 12.5 mm apart.
Corner radius is 2.0 mm.
Please allow for PCB manufacturing tolerances (i.e. 0.2-0.3mm) to fit against the case.
Screws and contact
Screws should be of M2 size, and at minimum long enough to clear the 1.6mm PCB substrate.
Head diameter should be less than or equal to 4mm.
Lift the screw zones compared to the rest of the daughterboard area if using a metal chassis, so the metal case does not make flush contact against the entirety of the daughterboard.
Only the screws and screw pads should make direct contact against the case; failure to do so may result in short circuit, and will most definitely not put the EMI suppression and chassis grounding circuits into proper function.
Cable considerations
A one-to-one JST-SH 4 pin cable is used to connect the daughterboard to the mainboard.
Make sure that the cable is properly one-to-one; a cable which inverts the pinout will result in reverse voltage applied to the main PCB resulting in its destruction.
One good option for testing and low quantity boards is the Sparkfun Qwiic cables; these are confirmed functional and compatible with the Unified USB Daughterboard series.
Digikey carries both the "correct" and "incorrect" variants of the JST cables in various lengths; before ordering, check the specification/drawing PDF for the item and verify that the cable is of the correct type.
The correct type is the 4-wire variant of the "Socket to Socket, Reversed" type cables listed here.
Do make sure that there is enough clearance for the cable to insert into the port on both PCBs.
Also, allocate enough space for the cable to fit; for example, dig a channel from the daughterboard to the mainboard's connector for the cable to fit in.
Modelling
A 3D STEP model of the daughterboard can be found here.
Simply insert into your case model and align for easy dimension checking.
Example implementation model
A 3D model of an example implementation can be found here.
The example implementation without the daughterboard in place.
Lifted screw points allow case-to-db screw pad contact while having a gap to the rest of the PCB.
A cable channel exits from the JST connector area and stairsteps upwards after bending towards the mainboard connector.
The example implementation with the daughterboard in place.
A cross-section showing the 1mm thick case wall and 0.25mm gap between the USB connector face and inner wall face.
As long as the total distance from the USB connector face to the exterior wall face does not exceed around 1.8mm, the implementation will work fine.
