The
Quad Flat No Leads
package, or QFN,
is
a very small square-shaped or rectangular surface-mount plastic package with no leads.
It is basically a quad flat package, except for
the absence of leads
protruding from its sides.
Metal pads or lands around the
periphery of the bottom of the QFN package serve as electrical connection points to
the outside world.
Because the QFN has no leads and has shorter bond wire lengths, it
exhibits less inductance than leaded packages and therefore provides a
higher electrical performance.
The QFN package also includes an exposed thermal pad at the package
bottom to facilitate heat dissipation from the die.
The QFN
package has two common types: the 'plastic-molded QFN' and the
'air-cavity QFN'. Of these two, the plastic-molded QFN is less
expensive because of a simpler body structure consisting of just a lead
frame encapsulated by plastic. The air-cavity QFN, on the other
hand, has a cavity inside the package body and requires a third part: a
ceramic or plastic lid to seal the package. The air-cavity QFN,
however, allows device operation at much higher frequencies: 20-25 GHz
vs. the 2-3 GHz possible with the plastic-molded QFN.
The QFN package may also be classified
according to its assembly process: either as cavity-molded punch-singulated
QFN or
as array-molded saw-singulated QFN.
The body sizes of typical QFN's range
from 3 mm. square to 12 mm. square. The standard QFN pad pitch
(distance between pads) is
0.5 mm.
Table 1. Properties of
Some Examples of QFN's
|
Part Number |
No. of Pads |
Body
Size |
Body Thickness |
Pad Pitch |
|
QFN-16 |
16 |
3 mm x 3 mm |
0.9 mm |
0.5 mm |
|
QFN-24 |
24 |
4 mm x 4 mm |
0.9 mm |
0.5 mm |
|
QFN-32 |
32 |
5 mm x 5 mm |
0.9 mm |
0.5 mm |
|
QFN-44 |
32 |
5 mm x 5 mm |
0.9 mm |
0.5 mm |
|
QFN-50 |
50 |
5 mm x 10 mm |
1.0 mm |
0.5 mm |
|
QFN-72 |
72 |
10 mm x 10 mm |
0.9 mm |
0.5 mm |
