Buy Kovar Plating Services (Au/Ni) Manufacturers & Factories

Why Kovar (ASTM F15) Requires specialized Gold over Nickel (Au/Ni) Surface Finishes

Kovar (composed of approximately 29% Nickel, 17% Cobalt, and the remaining balance Iron) is engineered specifically to exhibit a coefficient of thermal expansion (CTE) that matches borosilicate glasses and alumina ceramic materials. At ambient temperatures up to $400^\circ\text{C}$, Kovar acts as the ideal structural backbone for glass-to-metal seals (GTMS) and ceramic-to-metal designs. However, the high content of iron in Kovar makes it exceptionally susceptible to atmospheric corrosion and oxidation during thermal cycles.

To address these oxidation challenges and ensure absolute solderability and wire bonding capacity, manufacturers deploy high-performance Au/Ni (Gold over Nickel) plating services. The coating configuration utilizes a highly specialized two-stage barrier system:

• Nickel Underplate (Diffusion Barrier): A critical deposit of electrolytic or electroless nickel is applied directly to the activated Kovar substrate. This layer blocks the outward solid-state diffusion of Iron and Cobalt into the outer gold surface. Without a properly executed nickel barrier, iron atoms migrate quickly to the surface, creating highly oxidized compounds that destroy solder wettability and weaken bond wires.
• Gold Outer Layer (Noble Finish): A layer of high-purity gold (commonly conforming to ASTM B488 standards) is applied to provide superior anti-oxidation performance, excellent electrical conductivity for high-frequency RF transmission, and reliable eutectic soldering interfaces (e.g., Au-Sn or Pb-Sn).

Precision Pre-Treatment & Electroplating Control Protocols

Plating gold and nickel onto Kovar is not a simple dipping process. The Fe-Ni-Co substrate naturally forms a persistent passive oxide scale which must be engineered out before successful coating can happen. Any residue, microscopic grain boundary imperfection, or carbon inclusion from the machining stage will result in disastrous blistering during downstream soldering processes.

Step 1: Ultrasonic Clean & Thermal Decarburization

Kovar parts first undergo immersion in organic solvents combined with ultrasonic excitation to completely strip residual manufacturing fluids. Following degreasing, parts undergo a critical thermal decarburization step in dry hydrogen or high-vacuum ovens at temperatures exceeding $900^\circ\text{C}$. This eliminates surface carbon that might otherwise lead to micro-voiding during glass-to-metal seal fusion.

Step 2: Micro-Etching & Activation

An acid activation bath using optimized hydrochloric or sulfuric acid mixtures dissolves the persistent chromium and iron oxides, leaving a clean, highly active metallic lattice exposed. A nickel strike is immediately applied to safeguard this active state and ensure maximum atomic bonding.

Step 3: Nickel Underplating & Internal Stress Control

Using highly controlled Nickel Sulfamate chemistry, we deposit an extremely ductile nickel layer. We continuously monitor the pH, surface tension, and concentration of active metals within the bath to control internal tensile stresses. Low internal stress is imperative to prevent cracking when the package experiences thermal shock in space or high-power industrial environments.

Step 4: High-Purity Gold Deposition

Our gold electroplating line deposits pure, soft gold (min. 99.9% purity) for high-end optical packages, or cobalt/nickel-alloyed hard gold where mechanical wear resistance is needed. The process parameters are dialed in to maintain a sub-micron uniform depth across complex configurations, preventing regional variations that could cause signal degradation at millimeter-wave frequencies.

Step 5: Rigorous Quality Verification & Adhesion Testing

To conform to high-reliability military and aerospace requirements, our plated components undergo rigorous quality screening:

• Thermal Adhesion Bake Test (ASTM B571): Components are heated to $400^\circ\text{C}$ in an air furnace for 30 minutes, followed by rapid quenching. Zero blistering or peeling at the Au/Ni/Kovar interface must occur.
• XRF Non-Destructive Thickness Audit: X-Ray Fluorescence spectroscopy measures the absolute plating thickness at various points across the geometry, ensuring compliance with strict drawings.
• Helium Leak Verification: Micro-leak tests prove our hermetically plated components reliably maintain vacuum integrity under pressures down to $1 \times 10^{-9} \text{ atm cc/s}$.