AN1902 Freescale Semiconductor / Motorola, AN1902 Datasheet - Page 10

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

AN1902/D
10
For general guidelines, the PCB pad should be long enough to accommodate the larg-
est package pad. The PCB pad should extend past the exterior package edge for the
solder fillet to form. Motorola recommends this value to be approximately 0.15mm
(external to the package).
4.1.2.2 PCB Thermal Pad Guidelines
The exposed pad (EP) on many QFN packages dissipates heat from the actual
device. The thermal path between the package and the PCB is important for the long
term survival of the device. The PCB EP area will be slightly smaller than the package
EP. The PCB EP is still a large solderable area. The stencil opening for the EP region
should be segmented in several smaller areas (as explained in Section 4.2). The PCB
EP region itself can also be segmented, matching the stencil pattern. If this is the
case, the spacing between segments should be 0.15mm or more.
4.1.2.3 Solder Mask Opening for PCB Area
The solder mask opening around the PCB pads can be as large as the spacing
between pads (see
der mask and the solder mask can lift off from the PCB. A potential solution is not to
have solder mask along the pad-to-pad spacing and only have the “toes” of the pads
covered with solder mask for better PCB strength.
Table 4 Spacing Between Maximum Package Pad and Maximum Exposed Pad
Freescale Semiconductor, Inc.
32 QFN 0.50mm
32 QFN 0.65mm
48 QFN 0.50mm
44 QFN 0.65mm
QFN Package
For More Information On This Product,
Quad Flat Pack No-Lead (QFN)
Go to: www.freescale.com
Figure 12 Pad and Solder Mask with Thin Webbing
Figure
Maximum Pad
12). The area in between the pads may be too thin for sol-
0.50mm
0.75mm
0.50mm
0.75mm
Exposed Pad
Maximum
3.25mm
4.85mm
6.25mm
6.85mm
Spacing in
between
0.37mm
0.32mm
0.37mm
0.32mm
MOTOROLA