induction sealing glass

Induction sealing glass to enclose resistors with high frequency induction heating system

Objective Provide a hermetic seal of glass enclosed resistor to a lead
Material Resistor Kovar rings, 0.1 inch (0.254cm) diameter Glass tube slightly larger than 0.1 inch (0.254cm) diameter, 0.5 (1.27) inch length
Metal lead
Temperature 900 ºF (482) ºC
Frequency 324 kHz
Equipment • DW-UHF-6kW-III induction heating system, equipped with a remote workhead containing two (2) 1.5 μF capacitors (for a total of 0.75 μF).
• An induction heating coil designed and developed specifically for this application.
Process A three turn concentrator plate coil is used to heat the Kovar ring for 500 milliseconds. This causes the glass to melt and seal one side of the resistor. The resistor is then turned over
and the process is repeated to seal the other side using a second Kovar ring.
Results/Benefits Induction heating provides precise, consistent heat to very small parts resulting in repeatable, quality seals.
By heating with medium frequency, arcing (which occurs at high frequencies) is avoided.