A computer-aided, spatially-selective protection technique for multichip module and chip-on-board devices

Abstract

The use of a precise computer-controlled dispensing system to fashion medium-modulus, very thin silicone dams around the interconnection area of IC devices is described. The computer-controlled capability greatly facilitates changing circuit layouts and designs. An inner dam confines the gel to a desired area and to a sufficient height above the ICs. An outer dam confines the hard shell encapsulant while creating a structural wall of required width and height, permitting overcoating of the inner gel area. The flexible placement of dams eliminates the need for expensive molds and larger-cavity molded dams that are not optimum for the configuration. In addition, some data are presented to determine some of the parameters needed to provide adequate device protection. This technique of flexible dam positioning permits telecommunication circuit prototypes to be fabricated, such as a high-data-rate (155-Mb/s) circuit, on a single unit basis. This technique could find important applications in rapid prototyping.<>