Hermetic Package for Optical MEMS

Abstract

This paper describes the design and fabrication of a hermetic LTCC package for an optical MEMS chip designed for space applications. The package ensured electrical and optical connections, mechanical positioning, atmosphere control, and finally low thermally induced stress on the MEMS during the final packaging operation. The package consisted of a 10-layer LTCC case with a recessed cavity for the MEMS chip, and a glass lid (with antireflection coating and thin-film metallization for soldering) for optical I/O. The chip was mechanically attached to the bottom of the cavity with a silicone adhesive, and electrically connected through gold wire bonds. The gold wire bonding pads were routed through the LTCC module to a MegArray BGA connector. Hermetic closure of the cavity was carried out by soldering the glass lid onto the case in a controlled atmosphere. The two main difficulties involved in such a package were the high electrical connection density (400 connections) and low-temperature hermetic sealing. LTCC design rules for small-pitch lines, thick- and thin-film materials selection, screen printing, lamination techniques, and soldering methods are described in this paper.