Fabrication of a miniaturized dewar module Available to Purchase

A miniaturized dewar module required three joints between Kovar and Stainless Steel 304. There is a heat sensitive glass feed-through adjacent to the joints through which 72 lead wires radially protrude from a circuit inside. The welds were required to sustain high acceleration, and expected to have leak rate less than 10^–12 atm.cc.s⁻¹ of Helium. Following a parametric study, laser welding was successfully done. However during the welding, glass-feed-through adjacent to a joint developed cracks. Analytically discounting possible thermal shock and resonance cracking of the glass feed-through, the cracking problem has been attributed to an acoustically driven pressure wave. Which might have been initiated by the associated periodic instant vaporization of the surface during laser welding. Reflection of such a wave from the interface, where acoustic impedance mismatch occurs e.g., glass-metal, generates tensile stresses, which results in the cracking of the glass. The problem had been solved by introducing a micro-discontinuity in the propagation path of the wave. Theoretical rationalization of the cracking problem and its solution is presented and discussed here.