Can Kovar Be Laser Welded? A Complete Guide to Laser Welding Kovar Alloy

Introduction

If you work in hermetic packaging, aerospace electronics, or photonics, you already know Kovar. This nickel-cobalt-iron alloy is the backbone of countless glass-to-metal seals, feedthroughs, and precision enclosures. But when it comes to joining Kovar components—whether sealing a lid to a housing or attaching a flange to a feedthrough—the question inevitably arises: can Kovar be laser welded?

The short answer is yes. Kovar can absolutely be laser welded, and in fact, laser welding is one of the most effective methods for joining this alloy in precision applications. However—and this is where experience matters—successful Kovar laser welding requires careful control of parameters, proper joint design, and meticulous surface preparation. Get those right, and you'll produce strong, hermetic welds with minimal distortion. Get them wrong, and you'll be chasing cracks, porosity, and oxidation issues.

In this guide, I'll walk through everything we've learned at KELTRYN about laser welding Kovar: the material's unique properties, the challenges you'll face, recommended laser types and parameters, joint design considerations, and practical tips for achieving reliable, repeatable welds. Whether you're a design engineer specifying welded assemblies or a manufacturing engineer setting up a production line, this article will give you the technical foundation you need.

What Is Kovar (ASTM F15)?

Before diving into welding specifics, let's make sure we're on the same page about the material itself.

Kovar is a controlled-expansion alloy composed of approximately 29% nickel, 17% cobalt, and the balance iron. Its defining characteristic is a coefficient of thermal expansion (CTE) that closely matches borosilicate glass and alumina ceramics across a wide temperature range—typically from room temperature up to about 450°C. This unique property makes Kovar the material of choice for hermetic seals where metal components must be joined to glass or ceramic without developing stress fractures during thermal cycling.

You'll encounter Kovar under several designations depending on your region and industry:

ASTM F15 — the standard specification
K-100 or Alloy K — common trade names
K94610 — UNS designation
Nilo K or Dilver P — international equivalents

Kovar is available in a variety of forms, including rod, sheet, strip, stampings, and machined parts. In our shop at KELTRYN, we regularly machine Kovar into housings, lids, caps, sealing rings, flanges, and frames for hermetic packaging applications. Many of these components are subsequently laser welded by our customers or their contract manufacturers.

One thing to note: Kovar is often supplied with a nickel plating or gold plating, particularly for electronic applications. As we'll discuss later, this plating can significantly affect weldability.

Can Kovar Be Laser Welded? Yes — Here's How It Works

So, can Kovar be laser welded? Absolutely. In fact, Kovar is considered one of the more laser-weldable alloys in the precision metals family, particularly when compared to materials like aluminum or copper that present reflectivity challenges.

Laser welding works well for Kovar for several reasons:

Localized heat input. Laser welding delivers energy precisely where it's needed, creating a small, focused melt zone. This minimizes the heat-affected zone (HAZ) and reduces thermal distortion—critical when you're trying to maintain tight dimensional tolerances on thin-wall enclosures or sealing surfaces.

Preservation of expansion properties. Because the heat input is localized and rapid, the bulk of the Kovar component never reaches temperatures that would alter its metallurgical structure or expansion characteristics. This is essential for parts that must maintain their CTE match with glass or ceramic seals.

Precision and repeatability. Modern laser welding systems offer exceptional control over pulse energy, duration, and focal position. This makes it possible to develop a "recipe" for a specific joint configuration and reproduce it thousands of times with minimal variation.

The scientific literature supports this. Research by Fadhali and colleagues (published in 2010) on laser welding of Kovar for photonic packaging demonstrated that optimized power density—on the order of 10⁵ W/cm²—produces excellent weld width-to-depth ratios with a minimal heat-affected zone. The key takeaway from this and similar studies is that Kovar responds predictably to laser energy when parameters are properly selected.

In practice, we see laser welding used extensively for:

Hermetic sealing of electronic packages and enclosures
Photonic device packaging (laser diode modules, fiber optic assemblies)
Sensor housings and feedthroughs
Glass-to-metal seal assemblies where Kovar components must be joined to other Kovar parts

Key Challenges When Laser Welding Kovar

While Kovar is weldable, it's not without its challenges. Understanding these issues upfront will save you significant time and scrap.

Oxidation and Discoloration

Kovar's iron and cobalt content makes it prone to oxidation at elevated temperatures. During laser welding, the intense heat in the weld zone can cause rapid oxidation, resulting in discoloration and, in severe cases, compromised weld integrity.

The solution: Use an inert shielding gas—argon or nitrogen—to protect the weld pool and the surrounding area. The shielding gas should flow over the weld zone both during and immediately after welding to prevent oxidation while the material is still hot. For critical applications, consider a trailing shield or a custom gas nozzle designed to provide coverage over the cooling weld bead.

If discoloration does occur, post-weld cleaning or pickling may be necessary, particularly if the part has cosmetic requirements or if corrosion performance is a concern.

Cracking and Porosity

Hot cracking is a risk when welding Kovar, particularly if you're using overly aggressive parameters or if joint fit-up is poor. The alloy's composition makes it susceptible to solidification cracking under certain conditions.

Porosity is another common issue. It typically results from trapped gas or contamination in the weld zone. Even trace amounts of hydrocarbons from fingerprints, machining fluids, or cleaning solvents can vaporize during welding and become trapped in the solidifying weld pool.

The solution: Use pulse shaping to control the thermal cycle and reduce crack susceptibility. Ensure proper joint fit-up—gaps should be minimal and consistent. Most importantly, maintain scrupulous cleanliness throughout the process.

Contamination Sensitivity

I cannot overstate this: Kovar is extremely sensitive to contamination. Small amounts of oil, grease, or residue can cause porosity, poor fusion, or weld defects that compromise hermeticity.

If your Kovar parts are plated—gold or nickel plating is common—the plating can also affect weldability. Gold, in particular, can form brittle intermetallics in the weld zone. In many cases, you'll need to strip or locally remove plating in the weld area before welding.

The solution: Implement a rigorous pre-weld cleaning protocol. Solvent cleaning with acetone or isopropyl alcohol, ultrasonic cleaning, or mild abrasive cleaning are all effective—but the key is consistency. Every part must go through the same cleaning process before welding.

Heat-Affected Zone Management

Excessive heat input can alter Kovar's expansion behavior in the HAZ, potentially degrading hermeticity in glass-to-metal seal assemblies. If the Kovar adjacent to a glass seal is heated too much during welding, the local CTE can shift, leading to stress fractures in the glass during thermal cycling.

The solution: Use short pulse durations and tightly focused beams to minimize the HAZ. Research has shown that optimizing pulse energy and peak power density allows you to achieve full penetration welds while keeping the HAZ to a minimum. This is where working with an experienced welding engineer pays dividends—they'll know how to balance penetration requirements against HAZ constraints.

Recommended Laser Types and Parameters for Kovar

The type of laser you choose will depend on your application, material thickness, and production requirements. Here's a breakdown of the most common options for Kovar welding.

Pulsed Nd:YAG Lasers

Pulsed Nd:YAG lasers are the workhorse for precision Kovar welding, particularly for thin sections and hermetic seals. These lasers deliver energy in discrete pulses, allowing precise control over heat input.

Typical parameters:

Power density: approximately 10⁵ W/cm²
Pulse duration: 1–10 milliseconds
Energy per pulse: tuned to material thickness (typically 1–10 J)

The pulsed nature of these lasers allows the weld pool to solidify between pulses, reducing heat buildup and minimizing the HAZ. This makes them ideal for thin-wall enclosures, lid sealing, and other applications where thermal management is critical.

Fiber Lasers

Fiber lasers have gained significant popularity in recent years due to their high beam quality, efficiency, and reliability. They offer excellent results for both Kovar-to-Kovar and Kovar-to-steel welds.

Fiber lasers can operate in both conduction mode (for shallow, wide welds) and keyhole mode (for deeper penetration). The choice depends on your material thickness and joint configuration. For most Kovar applications—typically under 3 mm thickness—conduction mode welding with a fiber laser provides excellent results with minimal distortion.

Continuous-Wave (CW) Lasers

For thicker Kovar sections—say, 2 mm and above—continuous-wave lasers can provide deeper penetration than pulsed lasers. The trade-off is increased heat input, which means you'll need tighter control of shielding gas and may see a larger HAZ.

CW lasers are less common for precision Kovar welding but can be the right choice for certain structural applications or when welding thicker flanges or housings.

Process Control Tips

Regardless of laser type, successful Kovar welding comes down to process control. Here are some practical tips we've learned:

Develop a welding "recipe." Document your parameters—laser power, pulse duration, frequency, travel speed, focal position, shielding gas flow rate—and standardize them for each joint configuration. This ensures repeatability across production runs.

Monitor focal position carefully. The focal position relative to the workpiece surface has a dramatic effect on weld width and depth. A change of even 0.5 mm can mean the difference between a good weld and a failed one.

Consider automation. Seam tracking and vision systems can help maintain consistent weld quality, particularly for complex geometries or long weld paths. If you're producing high volumes, automated welding with real-time monitoring is worth the investment.

Joint Designs for Laser Welding Kovar

The joint design you choose will significantly impact weld quality and process reliability. Here are the most common configurations for Kovar laser welding.

Butt Joint

Butt joints are ideal for thin-wall Kovar enclosures and feedthroughs where you need to join two edges together. The key challenge is achieving precise edge alignment—gaps between the mating surfaces should be minimal (ideally less than 10% of material thickness).

For butt joints, the laser beam is directed at the seam, and the weld forms along the joint line. This configuration provides good penetration and a clean weld profile when fit-up is proper.

Lap Joint

Lap joints are common for lid sealing in hermetic packages. The lid overlaps the housing wall, and the laser welds through the top layer into the bottom layer.

For Kovar lap joints, you'll typically use a penetration weld through the top layer. The challenge is ensuring full fusion between the layers without excessive heat input that could damage components inside the package. Pulsed lasers excel here, as the short pulses allow you to control penetration depth precisely.

Fillet Joint

Fillet joints provide good mechanical strength for structural or hybrid assemblies. In this configuration, the laser creates a weld bead at the intersection of two components meeting at an angle.

Fillet welds on Kovar require adequate joint access for the laser beam. You'll need to consider the beam angle and ensure the focal point can reach the joint root effectively.

Fixturing and Fit-Up

Kovar's rigidity is actually an advantage here—it holds tolerances well, and tight fit-up is achievable with precision machining. However, tooling must be designed to prevent distortion during welding.

For high-reliability parts, consider vacuum baking before welding. This process—typically performed at 400–600°C—removes absorbed gases from the Kovar that could otherwise cause porosity in the weld. It's an extra step, but for mission-critical hermetic applications, it's often worth the added cost and cycle time.

Surface Preparation and Pre-Weld Treatment

I've mentioned cleanliness several times, but it deserves its own section because it's that important.

Cleaning: All surfaces in the weld zone must be free of organic residue. Acetone or isopropyl alcohol wipedowns are standard, but ultrasonic cleaning in a suitable solvent is more thorough and more repeatable. For parts that have been machined, make sure cutting fluids have been completely removed.

Plating considerations: If your Kovar parts are gold-plated, you'll need to remove the plating in the weld zone. Gold forms brittle intermetallics with iron and nickel that can cause cracking. Nickel plating, depending on thickness, may be weldable, but it changes the weld characteristics—you'll need to qualify the process with the plated material to ensure acceptable results.

Degassing: For hermetic applications, vacuum baking at 400–600°C removes hydrogen and other absorbed gases from the Kovar. This is particularly important when welding enclosures that will contain sensitive electronic components—outgassing after sealing can contaminate the internal environment.

Storage: After cleaning and preparation, parts should be stored in clean, dry containers. Even brief exposure to ambient shop conditions can re-contaminate surfaces. If parts won't be welded immediately, consider storing them in sealed bags with desiccant.

Kovar-to-Kovar vs. Kovar-to-Other Metals

While Kovar-to-Kovar welding is the most common scenario, you may occasionally need to join Kovar to other metals. Here's what you should know.

Kovar to Stainless Steel (e.g., 304)

This is a feasible and relatively common combination. Research has demonstrated good interaction between Kovar and stainless steel when welded with Nd:YAG lasers. The similar melting points and compatible metallurgies make this a practical joint.

The main concern is the difference in thermal expansion coefficients between Kovar and stainless steel. This can create residual stresses at the joint, particularly if the assembly will experience thermal cycling. For hermetic applications, careful joint design and potentially a stress-relief heat treatment may be necessary.

Kovar to Copper or Aluminum

These combinations are difficult and generally not recommended for laser welding. The challenges include:

Significant differences in melting points
High reflectivity of copper and aluminum at typical laser wavelengths
Formation of brittle intermetallic compounds

If you must join Kovar to copper or aluminum, consider alternative approaches such as brazing or using an interlayer material that can accommodate the metallurgical mismatch.

Kovar to Ceramic or Glass

Laser welding is not applicable for direct Kovar-to-ceramic or Kovar-to-glass joints. Instead, these are made using glass-to-metal sealing or brazing processes. Kovar's expansion match with borosilicate glass and alumina ceramics makes it the preferred metal for these hybrid seals—the components are joined by heating the assembly to fuse the glass or braze material, not by welding.

Common Applications and Industries

Laser-welded Kovar components appear across a wide range of high-reliability applications.

Hermetic Sealing for Electronics

Laser-welded Kovar enclosures protect sensitive electronic components from moisture, gases, and contaminants. The hermetic seal created by laser welding is reliable and repeatable, making it the process of choice for many electronic packaging applications.

Aerospace and Defense

Kovar connectors, housings, and feedthroughs are found throughout avionics, sensors, and RF components. The alloy's reliability under thermal stress and its compatibility with glass and ceramic seals make it indispensable in these demanding environments.

Medical Devices

Implantable and diagnostic equipment often requires biocompatible, hermetically sealed packages. Laser-welded Kovar provides the reliability and cleanliness these applications demand.

Photonics and Optical Packaging

Laser welding of Kovar is extensively used in photonics for laser diode modules and fiber optic assemblies. The precision and minimal heat input of laser welding are essential when packaging delicate optical components.

Testing and Quality Assurance

For mission-critical applications, you can't just weld and ship. Comprehensive testing ensures weld integrity and hermeticity.

Visual Inspection

Every weld should undergo visual inspection for cracks, porosity, discoloration, or incomplete fusion. While not sufficient on its own, visual inspection catches gross defects that would fail more sophisticated testing.

Helium Leak Testing

Helium leak testing is the standard method for verifying hermeticity of Kovar laser welds. The welded component is placed in a test chamber, helium is introduced on one side, and a mass spectrometer detects any helium that penetrates the weld. Leak rates below 1×10⁻⁸ atm·cc/s are typically required for hermetic packages.

Metallurgical Cross-Sectioning

For process qualification, metallurgical cross-sectioning provides valuable insight into weld quality. The weld is cut, polished, and etched to reveal its internal structure, allowing evaluation of weld depth, width, and HAZ characteristics. This is destructive testing, so it's typically performed on sample parts rather than production units.

Mechanical Testing

Pull or shear tests validate joint strength, particularly for load-bearing parts. These tests confirm that the weld has adequate mechanical properties for the intended application.

Common Defects and How to Prevent Them

Even with careful process control, defects can occur. Here's a quick reference for common issues and their solutions.

Cracks: Reduce energy input, preheat thick sections, and avoid rapid quenching. If cracking persists, evaluate your joint design and consider whether the fit-up is causing stress concentrations.

Porosity: Ensure surfaces are scrupulously clean, improve shielding gas flow, and reduce travel speed to allow gases to escape the weld pool.

Oxidation: Increase gas coverage, use trailing shields, or weld in a glovebox for critical parts. Check that your shielding gas flow rate is adequate and that the nozzle is positioned correctly.

Incomplete penetration: Increase pulse energy or adjust focal position. Verify that your parameter "recipe" matches the actual material thickness.

Distortion: Use clamping fixtures to hold parts in position, and minimize heat input with pulsed lasers. Consider welding in alternating segments to balance thermal stresses.

Frequently Asked Questions (FAQ)

What is the thickest material a laser welder can weld?

Modern high-power fiber lasers can weld steel up to approximately 20–25 mm in a single pass. However, for Kovar in precision applications, the practical thickness for laser welding is typically under 3 mm. Thicker Kovar sections may require multiple passes or alternative processes like electron beam welding. If you're working with thicker Kovar, consult with a welding engineer to determine the best approach.

What two metals cannot be welded together?

Some metal combinations are extremely difficult or impossible to weld due to the formation of brittle intermetallic compounds or vastly different melting points. Common examples include aluminum to steel and copper to titanium. For Kovar specifically, welding to copper or aluminum is very challenging. Kovar welds well with itself and similar alloys, but dissimilar metal joints require careful evaluation—sometimes brazing or mechanical joining is a better solution.

What materials can be laser welded?

Laser welding is suitable for a wide range of materials, including stainless steel, low-carbon steel, titanium, nickel alloys, and Kovar. Some aluminum and copper alloys can be laser welded with specialized lasers (e.g., green or blue wavelength lasers that are better absorbed by these reflective metals). Plastics and ceramics are not typically laser welded using conventional processes.

What are the downsides of laser welding?

Laser welding has several limitations to consider:

High equipment cost: Industrial laser welding systems represent a significant capital investment.
Precise fit-up required: Laser welding tolerates minimal gaps—parts must be machined and fixtured to tight tolerances.
Rapid cooling: The fast thermal cycle can crack sensitive alloys, including some steels and aluminum alloys.
Shielding gas requirements: Most metals require inert shielding gas to prevent oxidation.

For Kovar specifically, the main drawbacks are oxidation sensitivity and the need for careful parameter control. However, with proper process development, these challenges are manageable.

Conclusion

So, can Kovar be laser welded? Absolutely—and it's one of the most reliable methods available for joining this critical alloy. The key to success lies in understanding Kovar's unique characteristics and designing your process accordingly.

From our experience at KELTRYN, the most successful Kovar laser welding operations share several traits:

Meticulous attention to cleanliness — every part is cleaned and handled with care
Well-designed joints with tight fit-up and proper fixturing
Optimized parameters developed through testing and documented in welding "recipes"
Effective shielding gas coverage to prevent oxidation
Comprehensive quality assurance including leak testing and metallurgical evaluation

If you're developing a Kovar welding process for hermetic or mission-critical applications, I strongly encourage you to partner with experienced professionals. The learning curve is real, and the cost of failed welds—in both materials and schedule—far exceeds the cost of getting it right the first time.

At KELTRYN, we specialize in precision-machined Kovar components designed for laser welding and hermetic sealing. We understand how our machined parts will perform in your welding process, and we design our components with weldability in mind—controlling burrs, maintaining tight tolerances on sealing surfaces, and ensuring material traceability.

If you're working on a Kovar project and need precision-machined components—housings, lids, caps, sealing rings, flanges, frames, or custom parts—we'd love to help. Our team provides practical manufacturability feedback, clear communication, and reliable delivery from prototype through production.

Contact KELTRYN today to discuss your Kovar machining needs. Send us your drawings or CAD models, and we'll provide engineering feedback and a quotation for your project.

Additional Resources

For further reading on Kovar laser welding and related topics, I recommend the following resources:

EB Industries — technical articles on hermetic sealing and laser welding
Accumet Materials — Kovar material properties and specifications
Prekovar — Kovar machining and fabrication resources
Academic research papers on Kovar laser welding (searchable via OSTI or university repositories, including work by Fadhali et al.)

If you'd like design guidelines for Kovar components intended for laser welding, or a checklist for qualifying your welding process, reach out to our engineering team—we're happy to share what we've learned.

Ready to discuss your Kovar project? Contact KELTRYN for expert consultation, prototyping support, or production machining. We're here to help you turn your designs into precision components that perform flawlessly in the most demanding applications.