Induction Heating for Glass-to-Metal Seals

Abstract

Making glass-to-metal seals using RF is actually quite easy, albeit empirical. Preliminary lab work to determine the approximate equipment requirements is both necessary and desirable. This can and should be done at the equipment manufacturer's lab. Choice of metal mass is critical so as to provide a sufficient heat sink. Metal part configuration also affects the interface heat transfer to the glass and, therefore, the glass flow or wetting. Properly done, capillary flow and fillet formation will prevent undesirable reentrant seal shapes with resultant undesirable stress concentrations. Ordinarily, metal chosen should possess physical characteristics (such as coefficient of expansion) which closely match the glass to be used. Cleaning procedures prior to preoxidieing of the metal transcend customary "routine" cleaning and so are very fussy, as is the oxidizing. Sealmet no. 4, 430-TI, and Kovar are the three most widely used metals in the electronics glass field. The induction heating (RF) process also lends itself to creation (cutting) of holes in glass prior to final terminal insertion. The holes can be used in their own right (as holes only) so long as cutting is followed by light glazing and stress relief (annealing) of the glass. Provision must exist to control and vary time and power input within reasonable limits in order to finally arrive at a condition of process control which will satisfy the needs of the end product.