Laminate-Based Technologies for Multichip Modules

Abstract

Subsystems based upon ICs wire bonded directly to printed wiring boards, have been important constituents of electronic products since the early 1970s. The density of these early systems was quite low and frequently did not connect many unpackaged die. Systems built with this process were said to be based upon chip-on-board (COB) technology. The term multichip module (MCM) has been widely used since the mid-1970s, but was not applied to modules based upon PWBs until the end of the 1980s. In the most common phraseology, the term MCM-L has come to imply an IC assembly comprised of multiple wire bonded die on a PWB. Other types of connection technologies, TAB and flip chip also are practiced in MCM-L systems, but COB assemblies have been the most common. COB involves the use of wire bonding and epoxy glob-top encapsulation, which are usually the lowest cost connection and sealing methods. These systems have typically been tested and burned in at the module level, and defective units are disposable. Higher cost, higher performance die often must be tested and burned-in prior to assembly, and the system cost forces planning for MCM repair. These higher performance die often have higher I/O counts, driving a higher module interconnect density than with the lower cost, disposable modules. Thus, COB modules have developed into a subset of MCM-L, where the modules are disposable and built with untested die. The range of MCM-L technologies has widened considerably in the areas of the materials and methods of substrate fabrication, and in the types of die connection to the board.