User's Manual
Bluegiga Technologies Oy
Page 58 of 71
11 Layout and Soldering Considerations
11.1 Soldering Recommendations
WT32 is compatible with industrial standard reflow profile for Pb-free solders. The reflow profile used is
dependent on the thermal mass of the entire populated PCB, heat transfer efficiency of the oven and
particular type of solder paste used. Consult the datasheet of particular solder paste for profile configurations.
Bluegiga Technologies will give following recommendations for soldering the module to ensure reliable solder
joint and operation of the module after soldering. Since the profile used is process and layout dependent, the
optimum profile should be studied case by case. Thus following recommendation should be taken as a
starting point guide.
o Refer to technical documentations of particular solder paste for profile configurations
o Avoid using more than one flow.
o Reliability of the solder joint and self-alignment of the component are dependent on the
solder volume. Minimum of 150m stencil thickness is recommended.
o Aperture size of the stencil should be 1:1 with the pad size.
A low residue, “no clean” solder paste should be used due to low mounted height of the component
11.2 Layout Guidelines
11.2.1 Audio Layout
Route audio lines as differential pairs. The positive and negative signals should run parallel and close to each
other until they are converted to single-ended signals. Use dedicated audio ground plane for entire audio
section.
11.2.2 Antenna Design
Do not place GND plane or any metal directly under the chip antenna of WT32. To avoid any excess parasitic
capacitance in the antenna feed line caused by the RF test pin on the bottom side of the module, the area
underneath the RF test pin should also be left free from copper. The chip antenna of WT32 requires GND
planes as shown in the Figure 37. The module should not be placed closer than 7 mm from a PCB corner and
the module should be placed to an edge of the PCB. Any metal in close proximity of the antenna will have an
effect on the antenna performance. Thus any metal should be placed as far from the antenna as possible. The
antenna of WT32 is high dielectric chip antenna and any surrounding dielectric material has only minor effect
(< 20 MHz) on the resonant frequency.
Avoid placing vias or any bare copper under the module. Since the module has several vias on the bottom
side, any via or bare copper under the module can cause a short circuit. Vias under the module are shown in
the Figure 38.