TABLE OF CONTENTS The packaging industry has focused on lower-cost alternatives for MEMS, SAW filters, and BAW filters for applications that demand high performance. These packages are currently hermetically sealed with a metal lid through welding. A lower-cost near-hermetic solution has been developed with a raw bulk silicon lid [51] and epoxy.
This approach also reduces the package height, which is a critical factor for SiP packages. The previous ceramic packages with a metal lid are too tall for today's low-profile SiP modules, although they have been used for SiP modules employing a 1.1-mm overmold in applications that allow for a larger height. However, the metal lid causes reliability issues for the SiP package, since the overmold material does not adhere well to the metal lid, which causes voids and overmold cracking during reliability testing. In some cases, the metal lid would be ground for better adhesion of the overmold.
The silicon lid avoids these reliability issues, since the overmold adheres well to the silicon. Any metallization on the silicon is within the cavity of the SAW, BAW, or MEMS die. It is not exposed to the overmold.
The two approaches are to add a polyimide buildup layer on the die or to add a frame. The die fabricator incurs the cost of multiple polyimide buildup layers, whereas the packaging manufacturer incurs the cost of the frame and assembly. More expensive and slower die placement equipment is required to accurately position the frame. The frame could include epoxy on the...
