ax5051 AXSEM, ax5051 Datasheet - Page 42

• Manufacturer Part Number: ax5051
• Description: Ax5051 Radio
• Manufacturer: AXSEM

42
QFN28 Package Information
8.3.
1.
Figure 7: PCB land and solder mask recommendations
2.
3.
8.4.
Stencil Design & Solder Paste Application
1.
2.
3.
4.
5.
Version 1.6
PCB land and solder masking recommendations are shown in Figure 7.
Thermal vias should be used on the PCB thermal pad (middle ground pad) to improve
thermal conductivity from the device to a copper ground plane area on the reverse side
of the printed circuit board. The number of vias depends on the package thermal
requirements, as determined by thermal simulation or actual testing.
Increasing the number of vias through the printed circuit board will improve the thermal
conductivity to the reverse side ground plane and external heat sink. In general, adding
more metal through the PC board under the IC will improve operational heat transfer,
but will require careful attention to uniform heating of the board during assembly.
Stainless steel stencils are recommended for solder paste application.
A stencil thickness of 0.125 – 0.150 mm (5 – 6 mils) is recommended for screening.
For the PCB thermal pad, solder paste should be printed on the PCB by designing a
stencil with an array of smaller openings that sum to 50% of the QFN exposed pad area.
Solder paste should be applied through an array of squares (or circles) as shown in Figure
8.
The aperture opening for the signal pads should be between 50-80% of the QFN pad
area as shown in Figure 9.
Optionally, for better solder paste release, the aperture walls should be trapezoidal and
the corners rounded.
QFN28 Recommended Pad Layout
Assembly Process
A = Clearance from PCB thermal pad to solder mask opening,
B =
C = Clearance from PCB land edge to solder mask opening to be
D = PCB land length = QFN solder pad length + 0.1mm
E =
0.0635 mm minimum
Clearance from edge of PCB thermal pad to PCB land, 0.2
mm minimum
as tight as possible to ensure that some solder mask remains
between PCB pads
PCB land width = QFN solder pad width + 0.1 mm
Datasheet AX5051