Plastic Air Cavity QFN Coupled with an Innovative Ultrasonic Lid Process Achieves True Hermetic Performance

摘要

Devices such as Image Sensors,MEMS,and HB-LEDs are increasingly designed into automobiles and require greater package reliability particularly in high temperature,high humidity conditions. As a result,hermetic performance is becoming more important in today’s packaging requirements. Traditional plastic transfer molded packages are mature,low cost packages but not a viable solution because of poor moisture absorption and other material related issues such as stress and non-linear properties. Similarly,plastic air cavity packages have never met true MIL 883 reliability,because of exposed leak paths at the lead frame-polymer interface and poor lid seal methods that fail to achieve hermetic levels. Hermetic package choices have been limited to ceramic packages which require specific lid attach processes – low melt glass,and seam weld. Nevertheless,high modulus,low CTE,limited flexibility and high costs have led companies to search for other alternatives. There has been a clear need for greater flexibility and improved packaging solutions that achieve hermetic performance.rn By combining a unique new material technology,package design and an innovative processing,a plastic air cavity QFN has been developed to achieve hermetic fine leak performance,5x10~-8 atm cc/s He. This capability is the first in the industry. This paper will discuss material development based on Liquid Crystal Polymer derivatives,controlling mechanical properties such as CTE,key design features and an innovative ultrasonic lid process that enable a hermetic plastic package. Performance and reliability data will be presented on 8mmx8mm QFN’s that meet fine leak requirements and serve as the package solution for hermetic,high reliability applications.