User Guide

ME910G1 HW Design Guide
1VV0301593 Rev.7 Page 74 of 98 2021-02-02
transfer for FR-4 PCBs is to add thermal vias - plated through-holes (PTH) between the
conductive layers. Vias are created by drilling holes and copper plating them, in the same
way that a PTH or via is used for electrical interconnections between layers. A series of
plated through-hole thermal vias, should be located in the GND area underneath Telit
module of the PCB to provide a thermal connection from the PCB GND to additional metal
layers of the PCB.
The application PCB layout should include plated through-hole thermal vias for efficient
heat dissipation from the Telit module into the PCB. One of the following thermal via types
should be used:
• Open plated through-hole vias that will provide lower PCB fabrication costs but
may fill with solder.
• Plugged and capped plated through-hole vias that will provide higher PCB
fabrication costs but will not fill with solder.
Telit recommends creating areas of 10 mil (0.254-mm) vias arranged on a 25 mil (0.635-
mm) rectilinear matrix. The reason for this choice is the combination of cost,
performance and manufacturability. According to several PCB manufacturers, 10-mil
holes and 25-mil spacing are reasonable and repeatable production choice.
A uniform metal plating thickness on the PCB will ensure reliable, high Telit module
solder assembly yield.
Stencil
A silk-screen process will be required for the deposition of solder paste to the PCB, for
reflow of the Telit module to the PCB. The silk-screen process requires the use of an
aperture based metal stencil where solder paste is transferred through the apertures
onto the solder pads of the application PCB. To minimize solder voids and ensure
maximum electrical and thermal connectivity of the module to the PCB, large pads,
solder volume, and solder straining must be considered in the stencil design. The design
and fabrication of the stencil determines the quality of the solder paste deposition onto
the PCB and the resulting solder joint after reflow. The primary stencil parameters are
aperture size, thickness, and fabrication method. The stencil should be made from
stainless steel and the apertures layout can be the same of the recommended footprint
(1:1). The recommended thickness shall be 127 um (5 mil). A stencil thickness of 152 µm
(6 mil) can be used as well.