Specifications
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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 39.
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 40.