Kovar,Alloy K,UNS K94610,E FORU

### **Kovar® / Alloy K / UNS K94610

** **Iron-Nickel-Cobalt Low Expansion Alloy for Glass-to-Metal Seals

** --- #### **1. Overview

** **Kovar**, also known as **Alloy K**, is a iron-nickel-cobalt alloy specifically designed to exhibit a thermal expansion coefficient that closely matches that of borosilicate hard glass and alumina ceramics. This unique property makes it ideal for creating reliable hermetic seals in electronic and semiconductor packages. Developed to solve the problem of thermal stress cracking in glass-to-metal seals, Kovar forms a strong, stable bond with glass during the sealing process, ensuring long-term reliability in critical applications. 

 --- #### **2. Chemical Composition (Weight %)

** The typical chemical composition of Kovar is outlined below. The balance is Iron (Fe). 

| Element | Content (%) | Key Function | 

| :--- | :--- | :--- | 

| **Iron (Fe)** | Balance | Base element providing the fundamental matrix. | 

| **Nickel (Ni)** | 28.5 - 29.5 | Controls thermal expansion characteristics to match glass. | 

| **Cobalt (Co)** | 16.8 - 17.8 | Fine-tunes thermal expansion and improves sealing properties. | 

| **Manganese (Mn)** | 0.20 - 0.50 | Improves hot workability and acts as a deoxidizer. | 

| **Silicon (Si)** | 0.20 max | Controlled to ensure proper glass wetting and adhesion. | 

| **Carbon (C)** | 0.02 max | Kept low to prevent gas formation during sealing. | 

| **Aluminum (Al)** | 0.10 max | Controlled to maintain surface quality for sealing. | 

| **Magnesium (Mg)** | 0.10 max | Improves oxide characteristics for bonding. | 

| **Zirconium (Zr)** | 0.10 max | Enhances high-temperature stability. | 

| **Sulfur (S)** | 0.015 max | Impurity, kept low to prevent hot shortness. | 

| **Phosphorus (P)** | 0.015 max | Impurity, controlled to maintain ductility. | 

 --- #### **3. Physical Properties** 

| Property | Value / Condition | 

| :--- | :--- | 

| **Density** | 8.36 g/cm³ (0.302 lb/in³) | 

| **Melting Range** | ~ 1450 °C (2640 °F) | 

| **Mean Coefficient of Thermal Expansion** | 20 - 400°C (68 - 752°F): **5.3 x 10⁻⁶/°C** (2.9 x 10⁻⁶/°F)
20 - 450°C (68 - 842°F): **5.5 x 10⁻⁶/°C** (3.1 x 10⁻⁶/°F) | 

| **Thermal Conductivity** | 17.3 W/m·K (120 Btu·in/hr·ft²·°F) at 20°C (68°F) | 

| **Specific Heat** | 439 J/kg·K (0.105 Btu/lb·°F) at 20°C (68°F) | 

| **Electrical Resistivity** | 0.49 μΩ·m at 20°C (68°F) | 

| **Modulus of Elasticity (Young's Modulus)** | 138 GPa (20.0 x 10⁶ psi) at 20°C (68°F) | 

| **Curie Temperature** | ~ 435 °C (815 °F) | 

| **Magnetic Permeability** | Magnetic below Curie temperature. | 

 --- #### **4. Mechanical Properties 

(Typical for Annealed Condition)** 

| Property | At Room Temperature | 

| :--- | :--- | 

| **Tensile Strength** | 517 MPa (75 ksi) | 

| **Yield Strength (0.2% Offset)** | 345 MPa (50 ksi) | 

| **Elongation (in 50 mm / 2 in)** | 30% | 

| **Hardness (Rockwell B)** | 65 - 80 HRB | 

 --- #### **5. International Standards

** Kovar is covered by the following international specifications: 

 *   **ASTM:**    

*   **F15:** Standard Specification for Iron-Nickel-Cobalt Sealing Alloy 

*   **AMS:**    

*   **AMS 7724:** Sheet, Strip, and Plate    

*   **AMS 7725:** Bar and Wire 

*   **UNS:** K94610 

*   **MIL:**   

 *   **MIL-I-23011:** Insulating Compound, Electrical (for Sealing) 

*   **ISO:**    

*   **ISO 17672:** Brazing - Filler metals 

*   **JIS:**    

*   **JIS C 2531:** Iron-nickel alloy for sealing use 

 --- #### **6. Product Applications

** Kovar is essential in applications requiring precise thermal expansion matching: 

 *   **Electronics & Semiconductor Packaging:

**    *   Transistor and IC packages    

*   Diode and rectifier housings    

*   Microwave and RF packages    

*   Ceramic chip carriers 

*   **Aerospace & Defense:

**    *   Hermetic connectors and feedthroughs    

*   Sensor packages    

*   Military electronic systems 

*   **Telecommunications:

**    *   Fiber optic components    

*   Laser diode packages    

*   Optoelectronic enclosures 

*   **Medical Devices:

**    *   Implantable medical device packages    

*   Pacemaker and defibrillator housings    

*   Medical sensor packaging 

*   **Power Electronics:

**    *   Power semiconductor packages    

*   High-reliability power modules 

 --- #### **7. Key Characteristics & Advantages

** *   **Controlled Thermal Expansion:

** Precisely matches borosilicate glass and ceramics (∼5.3 x 10⁻⁶/°C) 

*   **Excellent Glass Sealing Characteristics:** Forms strong, hermetic bonds with hard glass 

*   **Good Electrical Conductivity:** Suitable for electrical feedthrough applications 

*   **High Strength-to-Weight Ratio:** Provides structural integrity in miniature packages 

*   **Good Corrosion Resistance:** Withstands various environmental conditions 

*   **Excellent Fabricability:** Can be easily stamped, drawn, and machined 

*   **Reliable Performance:** Proven long-term reliability in critical applications 

*   **Consistent Quality:** Tight compositional control ensures reproducible performance 

 --- **Disclaimer:

** *Kovar® is a registered trademark of CRS Holdings, Inc., a subsidiary of Carpenter Technology Corporation. The values provided are typical and for informational purposes only. For critical applications, always consult the official material data sheets from the supplier and relevant design codes. Proper surface preparation and heat treatment are essential for achieving optimal glass-to-metal seals.*

Packing of Kovar,Alloy K,UNS K94610

Standard Packing: 

Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 1678 gallon liquid totes Special package is available on request.