AN1902 Freescale Semiconductor / Motorola, AN1902 Datasheet - Page 6

• Manufacturer Part Number: AN1902
• Description: Quad Flat Pack No-Lead (QFN)
• Manufacturer: Freescale Semiconductor / Motorola

AN1902/D
6
4.1.1.2 PCB Thermal Pad Guidelines
The QFN package, with its exposed die pad soldered to the PCB, has a good thermal
path to the board. The thermal performance of the package is greatly influenced by
the PCB design. The PCB thermal pad should be Solder Mask Defined (SMD). The
pad area is controlled by the size of the solder mask opening. The size of the thermal
pad land pattern should be equal to the exposed pad of the QFN. Finally, the solder
mask opening should overlap the edges of the PCB thermal pad land by at least 65µm
on all four sides.
4.1.1.3 Spacing Between Lead and Thermal Pad
The design of the pattern and the size of the thermal pad depend heavily on the ther-
mal characteristic and power dissipation of the specific product. In general the size of
the thermal pad should be as close to the exposed pad of the package as possible,
provided that there is no bridging between the thermal pad and the perimeter lead
pads. In the evaluation, the size of the thermal pad was kept constant to the exposed
pad and no bridging was found in all samples. The thermal pad size, therefore, can
be the size of the exposed pad in 4x4mm and 9x9mm QFN.
Freescale Semiconductor, Inc.
For More Information On This Product,
≥0.065 mm
Quad Flat Pack No-Lead (QFN)
75 µm
Go to: www.freescale.com
Figure 7 NSMD Design on MAP QFN Lead/Terminal
Figure 8 SMD Design on QFN Thermal Pad
≥0.065 mm
75 µm
MOTOROLA