MicroLeadFrame

Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON (small-outline no leads), is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB.Flat no-lead packages include an exposed thermal pad to improve heat transfer out of the IC (into the PCB). Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package, and a ball grid array.

The figure shows the cross section of a Flat No lead package with a lead frame and wire bonding. There are two types of body designs, punch singulation and saw singulation. Saw singulation cuts a large set of packages in parts. In punch singulation, a single package is moulded into shape. The cross section shows a saw-singulated body with an attached thermal head pad. The lead frame is made of copper alloy and a thermally conductive adhesive is used for attaching the silicon die to the thermal pad. The silicon die is electrically connected to the lead frame by 1-2 mil diameter gold wires.

The pads of a saw-singulated package can either be completely under the package, or they can fold around the edge of the package.

Two types of QFN packages are common: air-cavity QFNs, with an air cavity designed into the package, and plastic-moulded QFNs with air in the package minimized.

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