Ionizing Radiation Effects on Copperclad Polyimide

Copperclad polyimide is used as flexible printed circuit boards [1] and in beam-tape assembly processing for semiconductor devices [2]. Beam-tape bonding on semiconductor devices has been in general practice since the early \´70s With the advent of the General Electric "Mini-Mod,"® numerous systems of beam tape have been employed as interconnects from the silicon device to either package or substrate. It is obvious that the massbond technique (wherein all leads are attached to the semiconductor chip with a single process) has an advantage in production speed. The real advantages, however, are in the realm of performance. Tape bonding provides a level of impedance at least one-fourth that of a comparable wire-bonded product [3]. Additionally, since the area of cross section is greater than that of wire leads and the materials employed have higher thermal conductance, power dissipation is greatly enhanced. Flexible PCBs or "flex-print" are employed extensively in the computer industry. Polyimide layers are being used for dual layer metal/dielectric insulators [4]. This paper addresses the effects of ionizing radiation on the copperclad polyimide interconnection systems. The driving force behind these experiments was a packaging problem, i.e., too many components and interconnections for the available volume if standard PCB techniques were used. The product was an underwater radiation-hard TV camera for inspecting piping in nuclear power reactors.