Conventional transfer molding.
Encapsulation is a crucial step in the assembly of semiconductors. Basically, there are two major encapsulation techniques: transfer molding and potting or glob topping. Transfer molding is the method of choice for mass production. Aside from that, transfer molding produces higher-quality IC packages. Transfer molding equipment for electronic components consists of a press equipped with platens, one of which contains a chamber known as a pot, in which the molding material is placed and liquified by a combination of heat and pressure. A piston or plunger transfers the melt material into the cavities of the mold via a series of channels known as runners. The typical temperature of the molding process is around 175 °C (347 °F) and the pressure ranges from 3 to 100 bar.
Typical molding cycle:
- Lead frame loading into mold; a pre-heated lead frame with die and wire is loaded into the mold.
- Mold closure; the mold is typically closed under high pressure of 60-80 tons.
- Compound loading; the thermoset compound in pellet format is loaded into the pot.
- Plunger down (transfer cycle); pellets heat up in the pot and are pushed by plunger.
- Runner and cavity filled; the compound heats up when travelling through the runners and gates, and enters the cavity at molding temperature (175 °C (347 °F)).
- Compound curing; after the cavity is filled and has reached the set cure pressure, compound curing starts, typically lasting 30-90 seconds.
- Unloading lead frame; after curing is complete, the molded strips are unloaded from the mold and the culls, runners and gates will be removed.
- Mold cleaning; before loading new lead frames onto the mold, the mold is cleaned using a brush.
