Nanosecond Photography of Shock-Induced Elastic Ripples

When electronic circuitry is exposed to a shock wave of nuclear origin, intense acoustic agitation occurs within each of the components. Obviously, each component must be exceedingly strong mechanically in order to withstand such conditions. Our work primarily concerns survival of transistors and integrated circuits. In these devices there is a tendency for elastic or plastic surface ripples to develop on the headers or flatpacks. These ripples previously were quite difficult to record, although they were known to be the primary cause for cracking of transistor chips or microcapacitors from their substrates. However, we now have a system for photographing such motions on polished surfaces. This system is based on incoherent (or geometrical) optics, and thus does not require the use of a massive optically stable bench. Up to 130 frames may be taken in 6.5 μsec at a rate of 50 nsec/frame. It is possible to observe disturbances as small as 100 μm wide by .1 μm high, and group velocity may be as fast as 5 x 109 μm/sec. For illustration, in this article we present photographs of ripples on a transistor header which has been subjected to a shock wave generated by a pulsed electron beam.