AN1902 Freescale Semiconductor / Motorola, AN1902 Datasheet - Page 2

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

Freescale Semiconductor, Inc.
AN1902/D
Figure 1 QFN and QFN-EP Packages from Motorola SPS
3.2 Package Dimensioning
Available QFN packages range from 3.0 x 3.0 mm to 9.0 x 9.0mm in size. As the pack-
age size shrinks and the lead count increases, the dimensional tolerance and posi-
tioning accuracy affect subsequent processes. Special care must be taken when
preparing for test, especially in the test contactor cavity design and contactor pin loca-
tion. Further down the process, the PCB layout and stencil designs are critical to
ensure sufficient solder coverage between the package and the Printed Circuit Board
(PCB). When designing the PCB layout, refer to the Motorola case outline drawing to
obtain the package dimensions and tolerances.
Part interchangeability is a concern when primary and secondary QFN suppliers both
provide production parts. The optimized PCB layout of primary supplier may have
issues (manufacturing yield and/or solder joint life) with the secondary supplier, espe-
cially when two styles of the QFN packages are selected (See Section 3.3). When
more than one QFN source is expected, the PCB layout should be designed for
robustness. Additional information of this topic is provided in the PCB Design Guide-
lines Section PCB Design Guideline.
3.3 QFN Package Design
3.3.1 Cross Section
A typical QFN cross section, depicted in
Figure
2, illustrates a leadframe based pack-
age with wirebonding technology. The die is usually epoxy attached to die pad (or flag)
with an option for the die pad exposure (QFN-EP version) external to the package.
This option is denoted as “optional exposed heat sink” in
Figure
2. In most cases,
gold wire is used in wirebonding, ranging anywhere from 1.0mil to 2.0mils.
2
Quad Flat Pack No-Lead (QFN)
MOTOROLA
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