Packaging Classes

Protection at the package level is provided by full hermetic, near-hermetic, and non hermetic packaging solutions. Full hermetic packages evolved from glass to metal and ceramic in the semiconductor/microcircuit world and are used in MEMS packaging schemes. The near-hermetic package is used where full hermetic seal is either not required or is driven by a specific product application. The non-hermetic plastic package is widely used in the microcircuit community for high volume low cost packaging. In a plastic package, the chip is typically attached to a metal leadframe by wire bonding followed by epoxy overmolding. The overmolding compound is a mix of solid epoxy resins, hardeners, fillers and additives that is heated to polymerize the material. This mold compound makes direct contact with the die, wire bonds and leadframe. This technique cannot be translated directly to MEMS without an intermediate protection solution such as capping the chip. Capped chips may then be packaged using this technique.

Protecting chips at the wafer-level is normally done through capping and a multi step partial packaging process. Caps are passive with no electrical paths and must allow access to chip bond pads. In this partial wafer level packaging the most common solution is to singulate caps first using a multi-step process and later singulate the MEMS wafer. To eliminate the extra steps of the multi step partial wafer level package, full wafer level packaging (WLP) involves incorporating the interconnect structure through the chip or cap. This allows the cap layer to be singulated during the MEMS sawing step. For applications requiring gas and fluid transport, the capping wafer level solutions have yet to be developed.

Date: 2015-02-28; view: 964