Precision Kovar Alloy Bar

Updated: 2026-07-19

Overview

Precision Kovar alloy rods are engineered metallic components primarily composed of nickel, cobalt, and iron. Developed in the 1930s by Westinghouse Electric Corporation, Kovar exhibits a thermal expansion coefficient nearly identical to borosilicate glass (≈5.1×10⁻⁶/°C between 30-200°C), making it indispensable in hermetic sealing applications. The alloy's controlled expansion properties stem from its unique composition (typically 29% Ni, 17% Co, 54% Fe). Precision rods are manufactured through vacuum induction melting followed by cold drawing or machining to achieve tight dimensional tolerances (often within ±0.01mm).

Structure and Working Principle

Kovar rods derive their functionality from face-centered cubic (FCC) crystal structure, which remains stable across a wide temperature range. The alloy's thermal expansion curve closely mirrors that of glass up to its Curie temperature (≈435°C), beyond which magnetic properties change. In operation, the rod maintains dimensional harmony with adjoining glass or ceramic components during thermal cycling. This prevents stress fractures in applications like microwave tube envelopes or optoelectronic packages. The material's yield strength (typically 275-350 MPa) ensures mechanical stability under assembly stresses.

Key Features

1. Thermal Matching: CTE of 4.7-5.8×10⁻⁶/°C (30-200°C) matches common sealing glasses. 2. Hermetic Performance: Forms oxide layers that bond chemically with glass during sealing processes. 3. Machinability: Can be precision-turned or ground, though requires carbide tools due to work-hardening tendencies. Additional advantages include good electrical conductivity (≈4.9% IACS) and resistance to hydrogen embrittlement. Modern variants may include trace additions of manganese (0.3-0.5%) to enhance oxidation resistance during high-temperature sealing operations.

Application Areas

The primary application is in electronic packaging, particularly for: - IC and MEMS device headers - Microwave and X-ray tube components - Laser diode housings - Satellite feedthrough assemblies In aerospace, Kovar rods serve in fuel sensors and thermal management systems. Emerging uses include quantum computing hardware where ultra-stable mounts are required. The medical industry employs them in MRI equipment and implantable device packaging.

Maintenance and Precautions

Storage: Keep in vacuum-sealed bags with desiccant to prevent surface oxidation. Relative humidity should remain below 40%. Machining: Use flood cooling with sulfur-free cutting fluids. Recommended speeds: 30-50 SFM for turning, 500-800 RPM for drilling (varies by diameter). Annealing: For stress relief, heat to 750-850°C in hydrogen atmosphere followed by slow cooling (≤100°C/min). Avoid temperatures above 900°C to prevent grain growth.

B2B Procurement Guide

Technical Specifications to Verify: 1. ASTM F15 compliance for composition 2. CTE certification across your operating temperature range 3. Surface finish requirements (Ra ≤0.8μm for glass sealing) Supplier Evaluation: - Request mill test reports with spectrographic analysis - Assess capability for custom diameters (standard range: 1mm-50mm) - Lead time negotiation: 4-8 weeks typical for precision-ground stock Bulk discounts commonly apply for orders exceeding 500kg. Consider MOQ requirements (often 10-25kg per diameter).