Next Generation Low Stress Plastic Cavity Package for Sensor Applications

A new cavity packaging technology has been developed to replace ceramic packages for stress sensitive device applications. High volume sensor applications such as inertial sensors, gyroscopes and pressure sensors require next generation packaging technology, with improved performance and a lower cost structure versus ceramic.. Requirements of this new generation of packaging technology include: applying minimum stresses to the devices, maintaining high levels of reliability, the ability to tailor critical properties of the package, the ability to incorporate other potential elements in the package, and, at the same time providing lower cost structures than traditional ceramic packages. In addition, there is a need for this new generation of cavity packages to utilize the existing high volume and low cost assembly infrastructure which has been developed for plastic packaging.

This paper discusses the design and performance of an air cavity plastic package made from proprietary thermoplastic materials, which allows for improved performance over ceramic packages, at much lower cost. The characteristics of the package include: cavity package in a state-of-the-art Quad Flat No-lead (QFN) format, exposed die pad using a cooper leadframe, a thermoplastic material whose CTE match that of the copper leadframe and PCB to which it is mounted, dielectric constant less than 4.00, very linear mechanical properties of the material over a wide temperature range (no Tg) low moisture absorption, and two lid sealing technologies (B-stage epoxy and ultrasonic welding). In addition the package is manufactured in an array using reel-to-reel injection molding, and singulated into strips, so that they can be assembled utilizing high speed assembly equipment. The materials (polymers and leadframe plating) are all compatible with lead free soldering and will meet the latest generation of environmental standards (RoHs directive--Europe and JGOSSI Initiative - Japan)

This paper reports results of this package incorporating a state-of-the-art MEMs structure. Specifically we will discuss design for assembly, material properties, package.