AN1902 Freescale Semiconductor / Motorola, AN1902 Datasheet - Page 28

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

Freescale Semiconductor, Inc.
AN1902/D
flag size ratio, longer bonding wires may be required for the QFN than for the same
device in a leaded package or BGA. In these cases, the RLC performance may be
poorer for the QFN package. Therefore, it should not be assumed that the QFN will
provide better electrical performance for all devices as the die size and bonding wire
length must be considered.
Another advantage of the QFN package with regard to electrical performance is that
the wires may be bonded to the exposed center pad, allowing better grounding com-
pared to traditional leaded and BGA packages.
Electrical modeling has been performed to simulate the RLC performance of the 7x7
mm, 48-lead 0.5mm pitch QFN package [14].
Figure 28
shows the package and wire
SPICE model used for the simulation. SPICE stands for “Simulation Program with
Integrated Circuit Emphasis.” It’s a simulation tool used to design circuits.
WIRE
LEAD
N01R
N01C
N01O
N01I
N01W
System Board
R01 WB
L01WB
R01
L01
C01
BD_ GND
Figure 28 SPICE Model
The simulations yielded self inductance values for the QFN package leads of 1.04 to
-11
1.05 x 10
H compared to similarly obtained values for TQFP leads of 1.11 to 1.39 x
-9
10
H (4), fully two orders of magnitude lower for the QFN.
Figure 29
compares self-inductance values of the two packages including the contri-
butions from both bonding wire and lead. The bonding wire is assumed to be approxi-
mately the same length in the two packages. In the case of the QFN, the contribution
to inductance of the leads is negligible, and the only significant contribution to induc-
tance is that of the bonding wire. The average value for the TQFP package is 3.27nH,
while that for the QFN is 2.06nH, a 37% decrease.
28
Quad Flat Pack No-Lead (QFN)
MOTOROLA
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