The QFN packages come with a die that is surrounded by a lead frame. The lead frame is made up of a copper alloy with a matt tin coating.
The die and the frame are usually connected to each other using wire bonding. Copper/gold is usually preferred for wire bonding. Some manufacturers use flip-chip technology for this interconnection. The flip-chip technique offers better electrical performance compared to the conventional one.
The metalized terminal pads are located at the bottom surface. These terminal pads are present along the four edges of the bottom surface and provide electrical interconnections to the PCB.
The bottom side of the package consists of an exposed pad. This pad provides an efficient heat path to the PCB. The exposed pad enables ground connection as well. The QFN package is soldered to the circuit board at the exposed pad. The die attach is the epoxy material used to fix the die to the exposed pad.
For thermal management in PCBs, check out 12 PCB Thermal Management Techniques to Reduce PCB Heating.
The following are some of the properties of standard QFN packages:
- 0.35mm to 2.10mm maximum seated height (standard: 0.85 mm)
- Terminal plating of Ni-Pd-Au and Sn
- Halogen-free and lead-free
- RoHS, ELV, and REACH compliance
What are the advantages of QFN package?
·Quad flat no-lead packages come in lightweight and are easy to handle.
·These packages are available in a thin profile and a small form factor.
·The bond wires that are used to connect the die and frame are short.
·The lead inductance of these packages is low.
·They are ideal for applications that require good heat dissipation.
·These packages are easily available at a low cost.
What are the main types of QFN package?
Based on the method of molding, the QFN packages are classified into punch-type and sawn-type packages.
In punch-type singulation, the package is molded in the single mold cavity format and is separated using a punch tool. This means that only a single package is molded into shape using this method.
These packages are molded using the mold array process (MAP). This method involves cutting a large set of packages into parts. A final saw process helps to separate the sawn-type packages into individual packages.