AN1902 Freescale Semiconductor / Motorola, AN1902 Datasheet - Page 5

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

4.0 PRINTED CIRCUIT BOARD (PCB) LEVEL GUIDELINES
MOTOROLA
4.1 PCB Design Guideline
The PCB design guidelines are separated in two sections: Motorola MAP QFN Spe-
cific Guidelines and Robust Design Guideline. Two separate Motorola sites evaluated
the QFN package. One concentrating on MAP style QFN and the other using both
MAP and punch singulated QFN package styles. As explained in Section Package
Dimensioning, part interchangeability becomes important with multiple QFN suppliers.
The Robust Design Guideline Section may not be optimal for one specific QFN sup-
plier, but it takes into consideration both MAP and non-MAP QFN styles with good
manufacturing yield and solder joint reliability.
4.1.1 Motorola MAP QFN Specific Guidelines [2]
4.1.1.1 Perimeter Pad Design Guidelines
The perimeter pad guideline specific to Motorola MAP style QFN is provided in this
section. Since it is harder to prevent solder bridging in smaller pitch packages, the
evaluation was performed using 0.5mm pitch MAP QFN. There are two approaches in
PCB pad designs, namely Non-Solder Mask Defined Pad (NSMD) and Solder Masked
Defined Pad (SMD).
The NSMD has an opening that is larger than the copper pad. The PCB pad area is
controlled by the size of the copper pad. Since the copper pad etching process is
rather capable and stable, smaller size copper pad can be defined accurately. As QFN
is a fine pitch and small outline package, it is recommended to use the NSMD method
to define the perimeter pad on the PCB. The clearance around the copper pad and
solder mask should be 75µm nominal to account for the registration tolerance of the
solder mask.
Freescale Semiconductor, Inc.
For More Information On This Product,
Quad Flat Pack No-Lead (QFN)
Go to: www.freescale.com
Figure 6 Motorola MAP Style QFN Process Flow
AN1902/D
5