The Complete Guide to Gold Plating on Kovar: Process, Benefits, and Applications

What is Kovar? Understanding the Substrate

If you work in hermetic packaging, semiconductor equipment, or aerospace electronics, you already know the name. But let’s take a moment to define exactly what we’re dealing with.

Kovar is a nickel-cobalt ferrous alloy — typically around 29% nickel, 17% cobalt, and the balance iron — that was developed for one very specific purpose: to match the thermal expansion characteristics of borosilicate glass and certain ceramics. When a metal and a glass or ceramic are sealed together at high temperatures and then cooled, any mismatch in their coefficients of thermal expansion (CTE) will cause stress, cracking, or outright failure of the seal. Kovar solves that problem by expanding and contracting at nearly the same rate as the mating material.

So, to answer the common query directly: what type of metal is Kovar? It is a controlled-expansion iron-nickel-cobalt alloy, often specified under ASTM F15, and it is the industry workhorse for glass-to-metal and ceramic-to-metal hermetic seals. You’ll find it in transistor housings, diode packages, feedthroughs, connector shells, and the carrier plates that hold sensitive electronic assemblies.

But here’s the catch: raw Kovar has a natural tendency to oxidize. When exposed to elevated temperatures or aggressive environments, it forms a surface oxide layer that compromises solderability, wire bondability, and corrosion resistance. That’s precisely why surface finishing — specifically gold plating — is not a luxury but a requirement for most high-reliability applications.

Established Benefits of Gold Electrodeposition on Kovar

Gold plating on Kovar isn’t just about making parts look good — though it does that too. It’s about transforming an already remarkable substrate into something that performs flawlessly under demanding conditions.

Here’s what a quality gold finish brings to the table:

Exceptional corrosion resistance. Gold is one of the most chemically inert metals available. A continuous gold layer protects the Kovar substrate from atmospheric oxidation, moisture ingress, and the corrosive attack of industrial or marine environments. This is critical for components that may sit in storage for years before deployment — think defense spares or medical device inventory.

Superior electrical conductivity. Gold offers excellent electrical conductivity and low contact resistance. For RF connectors, microwave packages, and high-frequency interconnects, that means minimal signal loss and reliable performance over the life of the component.

High solderability and wire bondability. This is arguably the most important benefit for our industry. Gold-plated surfaces wet readily with tin-lead, lead-free, and gold-tin solders. They also provide an ideal surface for thermosonic wire bonding — whether you’re bonding gold or aluminum wire. Without that finish, Kovar’s oxide layer would make consistent, repeatable bonds nearly impossible.

Reliable brazing and die attachment. Gold-plated Kovar also supports eutectic die attachment and brazing processes used in hermetic package assembly. The gold layer ensures uniform wetting and strong, void-free joints.

Oxidation resistance during storage and handling. Between manufacturing and final assembly, components may be handled, stored, and shipped multiple times. A gold finish keeps the surface stable and ready for subsequent processing steps without the need for aggressive cleaning or activation.

In short: gold plating takes Kovar from a metallurgically clever but surface-challenged alloy to a fully engineered solution for mission-critical electronics.

The Kovar Plating Process: A Step-by-Step Guide

Gold plating on Kovar is not a single-step operation. It requires careful surface preparation, a mandatory nickel underplate, and then the gold layer itself. Each step has a purpose, and skipping or shortchanging any of them will compromise the final result.

Surface Treatment and Preparation

The first step is everything. Kovar surfaces arrive at the plater with oxides, machining oils, fingerprints, and microscopic debris. Any of these contaminants will prevent proper adhesion of subsequent layers.

The cleaning process typically begins with alkaline degreasing to remove organic soils. This is followed by acid pickling or etching to strip the native oxide layer and activate the surface. For components that have been heat-treated — many Kovar parts are brazed or annealed before plating — more aggressive oxide removal may be required.

At KELTRYN, we often see parts that have undergone photochemical etching or precision chemical machining to create intricate features in carrier plates and sealing frames before they ever reach the plater. These processes can leave behind residues or micro-roughened surfaces that need careful attention during the pre-plate cleaning sequence. The plater must know what processes the part has been through to select the right cleaning chemistry.

The Crucial Nickel Underplating Step

Here’s a question we hear frequently: Can you gold plate Kovar directly? Technically, yes, but you absolutely should not.

The solution is a nickel barrier layer between the Kovar substrate and the gold finish. This is typically applied as either:

• Bi-nickel plating — a duplex system with a semi-bright nickel layer followed by a bright nickel layer. This provides a dense, leveling barrier with good ductility.
• Electroless nickel-phosphorus coating — a chemically deposited nickel layer that offers uniform thickness even on complex geometries, along with excellent corrosion protection.

The nickel layer serves multiple functions. It blocks diffusion of cobalt and iron into the gold. It provides a hard, wear-resistant foundation. And it creates a surface that promotes strong adhesion for the gold layer.

For Kovar specifically, the nickel underplate is not optional. It is the difference between a gold finish that performs for decades and one that fails within months.

Gold Plating (Electroplating vs. Electroless)

Once the nickel underplate is in place and inspected, the gold layer is applied.

Electrolytic gold plating is the standard method for most Kovar components. The part is immersed in a gold electrolyte solution, and an electric current drives gold ions onto the surface. This process allows precise control over thickness and produces a dense, pure gold deposit. Depending on the formulation, you can produce either:

• Soft gold (pure gold, 99.99%) — used where wire bonding and compression bonding are required. Soft gold deforms easily, which is ideal for thermosonic bonding.
• Hard gold (alloyed with cobalt or nickel) — used where wear resistance and durability are priorities, such as contact surfaces and edge connectors.

Electroless gold plating (immersion or autocatalytic) is sometimes used for specific applications. Immersion gold, for example, deposits a very thin layer via a displacement reaction. It is not suitable as a standalone finish over nickel for high-reliability applications because it is thin and can be porous. Autocatalytic electroless gold is thicker but still generally used only when the part geometry makes electrolytic plating impractical.

For most Kovar components — carrier plates, housings, lids, sealing rings — electrolytic gold over a nickel underplate is the industry standard.

Key Applications and Industries for Gold-Plated Kovar

Carrier Plates and Glass-to-Metal Seals

A carrier plate is a flat Kovar substrate that supports semiconductor devices, optoelectronic components, or hybrid circuits during assembly and in final service. These plates often require precision-machined cavities, registration features, and mounting holes. Gold-plated Kovar is the ideal material because it provides:

• A CTE match to the ceramic or glass substrates being mounted
• A solderable and bondable surface for die attach and wire bonding
• Long-term corrosion resistance in sealed or semi-sealed environments

Gold-plated Kovar is also essential for glass-sealed connectors and hermetic packages. The Kovar-to-glass seal provides the hermetic barrier, while the gold plating ensures that the external and internal leads can be soldered or bonded reliably.

Aerospace and Defense

In aerospace and defense electronics, there is zero tolerance for field failure. Components may face extreme temperature cycling, vibration, humidity, and decades of storage. Gold-plated Kovar is used extensively for:

• Mission-critical electronic contacts
• Heat-treated contact strips
• Hermetic sensor housings
• Connector shells and feedthroughs
• RF and microwave packages

When a failure could mean losing a satellite or compromising a missile guidance system, the reliability provided by a properly plated Kovar substrate is non-negotiable.

Telecommunications and Microelectronics

The telecommunications industry pushes the boundaries of frequency and power density. Gold-plated Kovar components appear in:

• High-frequency microwave packages
• RF connectors and adapters
• Semiconductor housings and transistor bases
• Optoelectronic transceiver packages

The combination of CTE matching, electrical performance, and solderability makes gold-plated Kovar the go-to choice for these demanding applications.

Medical Devices

Implantable medical devices and diagnostic instruments require materials that are biocompatible, corrosion-resistant, and capable of forming hermetic seals that will last for decades inside the human body. Gold-plated Kovar meets those requirements.

Applications include:

• Implantable pulse generator housings
• Sensor feedthroughs for diagnostic catheters
• Hermetic enclosures for hearing aids and neurostimulators

The gold finish provides a biocompatible surface, while the Kovar substrate enables reliable glass-to-metal sealing.

Quality Control and Plating Specifications

Industry Specifications for Kovar Plating

If you are sourcing gold-plated Kovar components, you need to be familiar with the governing specifications. The two most important are:

• MIL-DTL-45204 — the U.S. military specification for electrodeposited gold plating. It defines thickness classes, purity requirements, and quality assurance testing.
• ASTM B488 — the ASTM standard for electrodeposited gold coatings on metallic substrates. It covers thickness grades, types (hard vs. soft), and quality requirements.

Adherence to these specifications matters because they define not just the final product but the process controls needed to achieve it. Thickness tolerances, purity requirements, and adhesion testing are all spelled out. A reputable plating partner will be certified to these standards and will provide certification documentation with every lot.

Analytical Lab Testing and Inspection

You cannot assume a plating job is good just because it looks shiny. Verification requires analytical testing. A qualified plating facility will offer or coordinate:

• X-ray fluorescence (XRF) testing — to measure gold and nickel thickness non-destructively and verify composition.
• Thermal shock testing — to ensure the plating survives the temperature excursions typical of soldering, brazing, and service.
• Solderability testing — to confirm that the gold surface wets properly with the specified solder alloys.
• Adhesion testing — to verify that the gold and nickel layers are firmly bonded to the Kovar substrate.
• Porosity testing — to detect any discontinuities in the gold layer that could compromise corrosion resistance.

At KELTRYN, we routinely coordinate with our plating partners to ensure that every batch of components meets the required specifications. We also review plating reports and certifications before parts ship to our customers.

Frequently Asked Questions (PAA)

Does gold electroplating wear off?

Yes, gold electroplating can wear over time, but the rate of wear depends heavily on the application and the plating specification. A thin soft gold layer (e.g., 2–5 microinches) used for wire bonding is not designed for repeated mechanical contact. A thicker hard gold layer (e.g., 30–50 microinches) alloyed with cobalt or nickel is intended for contact surfaces and will withstand significant wear.

Equally important is the quality of the nickel underplate. If the nickel is properly applied and the gold is dense and pore-free, the overall system will perform far better than a poorly plated part with the same gold thickness. For applications involving sliding contact or repeated mating cycles, specify hard gold and work with your plater to determine the appropriate thickness.

How much does it cost to gold plate something?

Gold plating costs are driven by several factors:

• Surface area — larger parts require more gold.
• Gold thickness — thicker deposits cost more because gold is expensive.
• Current market price of gold — this fluctuates daily and directly impacts plating quotes.
• Batch volume — larger production runs spread the setup and tooling costs over more parts.
• Part complexity — intricate geometries may require special fixturing and more careful process control.

As a rough rule, gold plating is quoted per square inch of surface area per microinch of thickness, plus process charges. For a precise estimate, you need to provide your plater with the part geometry, the required gold thickness, and the applicable specification.

How much does it cost to plate rose gold?

Rose gold is created by alloying gold with copper, which changes both the color and the properties of the deposit. In industrial applications — especially on Kovar substrates for hermetic packaging — rose gold is essentially never used. The copper content would compromise corrosion resistance, solderability, and wire bondability. Rose gold is a decorative finish, not an engineering finish.

If you are asking because you have a decorative application, the cost will be similar to standard gold plating, with slight variations based on the specific alloy formulation and the additional process control required. But for Kovar components in high-reliability applications, stick with pure or hard gold.

Choosing the Right Plating Partner for Kovar Substrates

Gold plating on Kovar is not a commodity service. It requires an understanding of the metallurgy of the substrate, the purpose of the nickel barrier, and the performance requirements of the final application. The right plating partner will:

• Understand the nuances of Kovar surface preparation
• Have experience with MIL-DTL-45204 and ASTM B488 requirements
• Provide full documentation and traceability for every lot
• Coordinate with your machining partner to ensure parts arrive clean and ready for plating
• Communicate openly about thickness requirements, process limitations, and cost drivers

At KELTRYN, we don’t just machine Kovar components — we help our customers navigate the entire manufacturing journey, including surface finishing. We work with trusted, qualified plating suppliers who understand the demands of hermetic packaging and high-reliability electronics. We review drawings for plating compatibility before machining, we coordinate logistics between machining and plating, and we verify that finished parts meet your specifications.

If you are developing a Kovar component that requires gold plating — whether it’s a custom housing, a carrier plate, a sealing ring, or a complex precision frame — we’d like to help. Send us your drawings, your material requirements, and your performance expectations. We’ll provide practical manufacturability feedback, clear communication, and a reliable path from prototype to production.

Contact KELTRYN today to discuss your Kovar machining and plating requirements. Our team is ready to support your next high-reliability project with precision machining, material expertise, and a partner who understands what it takes to succeed.