Table of Contents
Kovar metal tubing is a specialized form of nickel-iron-cobalt alloy tubing known for its unique thermal expansion characteristics, which closely match that of glass and ceramics. This property makes Kovar ideal for glass-to-metal and ceramic-to-metal seals in electronic and vacuum applications. Kovar, designated under UNS K94610, is widely used in the aerospace, electronics, medical, and defense industries where tight dimensional stability and hermetic sealing are critical.
Composition of Kovar
Kovar is composed of controlled amounts of nickel, iron, and cobalt, along with trace elements to enhance its sealing properties. Its thermal expansion behavior is specifically engineered to match that of borosilicate glass.
| Element | Composition (%) |
|---|---|
| Nickel (Ni) | 29.0 |
| Cobalt (Co) | 17.0 |
| Iron (Fe) | Balance |
| Manganese (Mn) | 0.5 max |
| Silicon (Si) | 0.2 max |
| Carbon (C) | 0.02 max |
Thermal Expansion Properties
The most important feature of Kovar tubing is its controlled coefficient of thermal expansion (CTE), which matches the CTE of common glasses used in electronics and vacuum components. This makes it ideal for hermetic seals.
| Temperature Range (°C) | CTE (x10⁻⁶ /°C) |
|---|---|
| 20 – 300 | 5.0 |
| 20 – 400 | 5.5 |
| 20 – 500 | 6.0 |
Mechanical Properties of Kovar Tubing
Kovar tubing offers good mechanical strength and can be drawn into thin-walled sections without losing structural integrity. Below are its typical mechanical properties:
| Property | Value |
|---|---|
| Tensile Strength | 517 MPa |
| Yield Strength | 414 MPa |
| Elongation | 25% |
| Hardness (HRB) | 80–90 |
Applications of Kovar Tubing
Kovar tubing is used in precision components that require hermetic sealing, thermal stability, and magnetic compatibility. Common applications include:
- Electronic Packages: Transistor and diode enclosures requiring glass-to-metal seals
- Vacuum Devices: Tubes, feedthroughs, and sensor housings
- Aerospace Systems: Sealed components in navigation and communication instruments
- Medical Devices: Hermetically sealed implants and diagnostic equipment
Available Sizes and Standards
| Specification | Range |
|---|---|
| Outer Diameter | 0.5 mm to 25 mm |
| Wall Thickness | 0.1 mm to 2.0 mm |
| Standard | ASTM F15, UNS K94610 |
| Form | Seamless or welded tubing |
Processing and Handling
Kovar tubing is usually supplied in an annealed condition for ease of fabrication. It can be machined, laser-cut, welded, and drawn. Care must be taken to prevent contamination, especially before sealing to glass or ceramic. Heat treatment can restore ductility and help in dimensional stabilization before sealing.
FAQs
1. Why is Kovar tubing used in electronic packaging?
Kovar has a thermal expansion rate that closely matches glass and ceramics, allowing it to form reliable hermetic seals in transistor and diode packages, preventing gas and moisture intrusion.
2. Can Kovar tubing be welded?
Yes, Kovar can be welded using TIG or resistance welding techniques. It is essential to perform welding in a controlled environment to avoid oxidation or contamination.
3. What standards govern Kovar metal tubing?
Kovar tubing is standardized under ASTM F15 and UNS K94610. These standards specify the chemical composition, mechanical properties, and thermal characteristics required for high-performance applications.