Kovar and Invar are two highly regarded materials in the manufacturing industry, particularly for creating sensitive electronic equipment. While both are known for their low thermal expansion and high strength, they each offer distinct advantages that make them suited for specific applications. Recognizing the distinctions among these substances can assist you in deciding which is most suitable for your requirements.
What is Kovar?
Kovar, also known as ASTM F15, is a nickel-cobalt ferrous alloy renowned for its compatibility with borosilicate glass due to its similar coefficient of thermal expansion. This property makes Kovar an excellent choice for sealed electronic components, such as metal-ceramic packages. Additionally, Kovar offers outstanding machinability, allowing it to be developed into complex shapes with tight tolerances. It also provides good thermal shock and chemical corrosion resistance, making it ideal for applications like electrical housings and optical reflectors.
Applications of Kovar:
- Electronic packages
- Vacuum-sealed devices
- Airtight containers
- Transistors
- Ceramic mountings
When considering Kovar for your project, keep in mind that Kovar plates are often used in manufacturing processes that require precise and durable components. These plates are particularly valued for their stability and resistance in demanding environments.
What is Invar?
Invar is an iron-nickel alloy composed of nearly equal amounts of nickel and iron. It is best known for its negligible coefficient of thermal expansion, which makes it an excellent choice for applications that demand high precision and stability across a wide range of temperatures. Invar’s properties make it ideal for scientific instruments, clocks, and other precision devices where thermal expansion could cause significant errors.
Applications of Invar:
- Scientific instruments
- Precision optical devices
- Telescope mirrors
- Interferometers
- Electronic devices
Differences Between Kovar and Invar
Physical Properties:
- Thermal Expansion: Kovar has a thermal expansion coefficient of 4.57 x 10^-6 m/mK, closely matching that of borosilicate glass, making it suitable for glass-to-metal seals. In contrast, Invar has a much lower coefficient of 1.2 x 10^-6 m/mK, making it excellent for applications where thermal stability is critical.
- Density and Melting Point: Kovar’s melting point is 1430°C, and its density is 8800 kg/m³, while Invar’s is slightly lower, at 1425°C and at 8100 kg/m³.
- Magnetic Properties: Kovar and Invar are ferromagnetic but differ in magnetic behaviour. Kovar exhibits a strong magnetic response, whereas Invar is magnetically soft, meaning it has lower coercivity and hysteresis.
Processing:
- Machinability: Kovar is relatively easy to machine using oil-based lubricants and water-soluble cutting fluids. It can be formed through cold or hot rolling, pressing, and forging. Invar, on the other hand, is more challenging to use due to its hardness and toughness. It often requires precise control during forming methods like spinning or stamping to maintain dimensional stability.
OUR KOVAR AND INVAR PRODUCTS
Cost:
- Price: Generally, Kovar is more cost-effective than Invar. Invar’s precise composition and manufacturing process contribute to its higher price. However, the cost difference may be justified depending on the application’s specific requirements.
Conclusion
Kovar and Invar offer unique properties suitable for different industrial applications. Kovar’s low thermal expansion and minimal outgassing make it an excellent choice for electronic packages, vacuum-sealed devices, and other applications where these properties are crucial. In contrast, Invar’s exceptional thermal stability makes it the material of choice for precision optical devices and scientific instruments.
When deciding between Kovar and Invar, consider your application’s specific needs, including physical properties, processing methods, and cost. By doing so, you can select the material that best meets your requirements, ensuring optimal performance and longevity in your project.
