Layout Recommendations; Solder Mask - Sierra Wireless AirPrime HL Series Customer Process Manuallines

Customer Process Guidelines
4.2.3.

Layout Recommendations

Sierra Wireless' layout recommendations include:
 A ground area under the AirPrime Snap-in Socket. This ground area should be a whole area
of copper with proper ground vias to provide a good grounding system between the
application and the embedded module, and improved thermal dissipation. It should be
covered by solder resist on the non-soldered area.
The ground vias may be micro-vias, filled or unfilled. Through-holes can be used between
each of the 64 ground pads (under the solder resist).
 The antenna pad and its track should be adapted according to RF constraints, based on
customer layout. Refer to each corresponding Product Technical Specification for more
details.
 There shouldn't be any SIGNAL trace or hole/micro-via under the AirPrime module.
 Leave a component-free area of 0.5 mm around the Snap-in Socket body (27.4x28.4 mm) for
accessing the surrounding components.
4.3.

Solder Mask

The pads on the printed circuit board are either Solder Mask Defined (SMD) or Non Solder Mask
Defined (NSMD).
Since the copper etching process has tighter control than solder masking process, NSMD pads are
preferred over SMD pads.
Moreover, NSMD pads with solder mask opening larger than the metal pad size also improve the
reliability of solder joints, as this limits the stress concentration at the solder-to-mask corner interface.
For external pads, the solder mask opening should be 100 µm to 150 µm larger than the pad, resulting
in 50 µm to 75 µm clearance between the copper pad and solder mask. This allows for solder mask
registration tolerances, depending on the PCB fabricator's capabilities.
For ground pads, SMD should be used if a copper ground area is under the AirPrime module.
Recommended solder mask thickness on the top copper is 10 to 30 µm.
4115102 Rev 6.0
SMT Assembly Process
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