Note: Hermetically sealing glass-enclosed resistors

Objective:

Provide a hermetic seal of glass enclosed resistor to a lead 

End Product:

Resistor

Equipment:

Ambrell 7.5 kW induction heating system, equipped with a remote workhead containing two 1.5 μF capacitors for a total of 0.75 μF
An induction heating coil designed and developed specifically for this application

Materials:

Resistor
Kovar rings, 0.1 in (0.254 cm) diameter
Glass tube slightly larger than 0.1 in (0.254 cm) diameter,
0.5 in (1.27 mm) length
Metal lead

Temperature:

900 °F (482) °C

Frequency:

Testing:

A three-turn concentrator plate coil is used to heat the Kovar ring for 500 ms. 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.

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.  
Hermetically sealing glass-enclosed resistors

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