Iron-nickel controlled expansion alloys (CE Alloys) have had a long history of uses in electrical and electronic applications.
Temperature-compensating devices make use of the gradual and reversible change in magnetism of alloys containing about 30% of nickel, over the operating temperature range of a device.
Invar 36 (UNS K93600)
36% nickel-iron, has the lowest thermal expansion of any alloy from room temperature to about 230℃. Traditionally, Invar 36 has been used for the low expansion side of thermostatic bimetals, in liquefied gas tanks and pipelines, and in radar components. More applications today are in measuring and control instruments, jigs and fixtures, aircraft, missile, and electronic defense control components – all where utmost operational accuracy requires minimum dimensional change over the system’s operating temperature range.
Kovar (UNS K94610)
A nickel-iron-cobalt alloy containing approximately 29% nickel and 17% cobalt. Its thermal expansion characteristics match those of borosilicate glasses and alumina type ceramics. It is manufactured to a close chemistry range, yielding repeatable properties which make it eminently suitable for glass-to-metal seals in mass production applications, or where reliability is of paramount importance.
Alloy 42-6 (UNS K94760)
containing 42% nickel, 6% chromium, balance iron, develops a tight green oxide film during wet hydrogen annealing and finds applications in relatively large glass seals and vacuum tight windows.
Alloy 46 (UNS K94600)
It has been used extensively for sealing metalized ceramic and as terminal bands for vitreous enameled resistors.
Alloy 42 (UNS K94100)
Alloy 42 is widely used for high reliability ceramic Cer-DIP and plastic-packaged device where the worldwide availability and combination of properties and advantages this alloy has are important:
- high yield strength and modulus of elasticity – to minimize bent leads.
- high stress relaxation temperature – to maintain strength and stiffness during soldering, burn-in, and service.
- high strength developed through could work alone – no intermetallic compounds which could be harmful to soldering.
- closest match to thermal expansion of alumina, beryllia and vitreous glass – avoids cracks in soldered joints.
- plateability – can be plated, striped or spot-plated with nickel, copper or lead-tin solder, as well as gold or silver.
- weldability – can be joined by resistance, ultrasonic electron-beam, laser welds and by termo-compression bonding.
- cladding – Alloy 42 can be clad or inlayed with copper, aluminum or precious metals.
Chip and board designs, component densities, external cooling systems and thermal conductivity of the ceramic or epoxy package usually have more effect on junction and average die temperatures than the thermal conductivity of the lead frame material alone.