User's Manual

Page 44
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Charpt 4. Module Mounting Issues
Frey M1 modules have been designed with an easy integration into SMT processes in mind.
Some module mounting issues are discussed in more detail in the sections below.
Please note that Frey M1 modules are specified for one soldering cycle only. Once removed
from the application, the module will very likely be destroyed and cannot be soldered onto
another application. Please also note that the modules are not sealed and should therefore
not be subjected to any post SMT wash or to any environments where condensation could
occur.
4.1. Solder Paste
A variety of solder paste types can be used to realize connections to external applications.
Soldering using lead free eutectic SnAgCu alloy can be done without any special restrictions,
because of its maximum allowed temperature of 245°C.
ENIG finish of the modules soldering pads ensures good wetting properties even after 12
month of storage.
However, there are some restrictions that should be noted before selecting the solder paste:
Due to the fact that the top side of the modules is assembled using standard eutectic SnAgCu
alloy, no higher melting alloys should be used (even though remelting of top side solder joints
also happens with eutectic SnAgCu).
Higher temperatures mean more stress to materials than lower temperatures: Increasing the
reflow temperature increases the growth of intermetallics, especially if the temperature lies
above the melting point of that alloy. Large intermetallics are commonly considered a
reliability risk. They should therefore be kept as small as possible.
4.2. Stencil Printing
4.2.1. General Stencil Considerations
The higher the stand off formed by the solder paste volume, the better the reliability for land
grid array (=LGA) based connections. The solder paste volume in a stencil printing process is
formed by aperture size (area) and stencil height:
VolumeSolder paste = AreaAperture x HeightStencil