Data Sheet

W M B T 0 1 ( - s , - s c ) D a t a s h e e t
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lead free process technique when SMT processing to prevent the reduction of the
reliability of module welding technique which may be caused by the usage of lead
production process technique.
Note：the lead BGA solder ball has low melting point（183℃），the lead-free BGA
solder ball has high melting point（217℃-221℃）。When the temperature rises to 183
℃, the solder paste is melting; When the temperature rises to 220℃, lead free BGA
solder ball starts to melt, and it is in the state of coexistence of solid and liquid. If lead
technology is used and the furnace starts cooling, the original welding surface
structure of BGA elements is damaged, and a new alloyed layer of the welding surface
cannot be formed. This may lead to lead free BGA solder joint failure during reflow,
which results in pseudo solder joints and other reliability issues in further.
4.2 SMT stencil Design
Ladder stencil is recommended. Stencil opening design requirements are as
follows:
4.2.1 The PIN area of the module is recommended to be thickened. For modules
with different PCB thickness, the thickened solder paste is shown in the following
table. The thickening position should be kept at least 1mm apart from other parts.
Number
Module PCB
thickness
Thickness of the
steel mesh
Note
1
0.8mm
0.15mm ladder
If there is a precise IC pad
around the module, it is not
recommended to exceed
0.15mm step thickness. The
amount of solder paste can be
increased by using the square
of the epitaxial steel mesh
2
1.0mm
0.18mm ladder
3
1.2mm
0.25mm ladder
4
1.6mm
0.30mm ladder
4.2.2 Opening width: 55%-65% of PCB PIN foot pad Pitch (centre-to-centre
spacing)
(Since the actual width of the motherboard pad is not ensured, the opening width
is determined by pitch.)
4.2.3 Opening length: based on PCB PIN foot, cutting 0.1-0.2mm towards inside,
and extending 0.5-0.8mm towards outside. Outer extension pads maintain at least
0.25mm safety spacing with other elements. Cutting module pad opening if not
enough space is left. Opening should be round corners.