User Guide

WE866C6 Hardware Design Guide
1VV0301658 Rev. 1 Page 46 of 58 2020-06-16
Recommendations for PCB pad surfaces:
Finish
Layer Thickness (um)
Properties
Electro-less Ni / Immersion Au
3 –7 / 0.05 – 0.15
good solder ability protection,
high shear force values
The PCB must be able to resist the higher temperatures which are occurring at the lead-
free process. This issue should be discussed with the PCB-supplier. Generally, the
wettability of tin-lead solder paste on the described surface plating is better compared to
lead-free solder paste.
It is not necessary to panel the application’s PCB, however in that case it is suggested to
use milled contours and predrilled board breakouts; scoring or v-cut solutions are not
recommended.
Stencil
Minimum stencil thickness recommended is 125um (5mil)
Solder Paste
We recommend using only “no clean” solder paste in order to avoid the cleaning of the
modules after assembly.
Cleaning
In general, cleaning the module mounted on the carrier board is not recommended.
• Residues between module and host board cannot be easily removed with any
cleaning method.
• Cleaning with water or any organic solvent can lead to capillary effects where the
cleaning solvent is absorbed into the gap between the module and the host board
or even leak inside the module (due to the gap between the module shield and PCB) .
The combination of soldering flux residues and encapsulated solvent could lead to
short circuits between conductive parts. The solvent could also damage the module
label.
• Ultrasonic cleaning could damage the module permanently. Especially for crystal
oscillators where the risk of damaging is very high.