Brown ambitions, black humor: Three lessons from a PVD coating misstep

Discover how a PVD coating project aiming for a dark brown finish unraveled into unexpected complexity. Learn key lessons about color matching in PVD, reactive sputtering, and thin film process optimization.

When PVD Coating development gets complicated

Have you ever embarked on a PVD coating development project that seemed simple—only to uncover layers of hidden complexity?

Some time ago, our team faced this exact situation: tasked with creating a novel dark brown PVD coating for faucet taps, targeting a precise CIELab colour value of 44-7-7.

In L*a*b* color space:

• L* measures lightness (0–100)

• a* spans green-to-red hues

• b* spans blue-to-yellow hues

Our goal was clear: deliver a rich, deep brown with moderate red and yellow undertones, within just ten days. But scientific realities quickly steered us into a far more complicated journey.

The technical setup: new PVD equipment, new challenges

We used a Physical Vapor Deposition (PVD) coater, new to our team, equipped with cylindrical sputtering cathodes and round arc sources. For those new to PVD:

• Sputtering: Bombards a solid target with ions to eject atoms that deposit onto the substrate.

• Arc evaporation: Uses an electrical arc to vaporize material into a plasma for deposition.

By combining sputtering and arc evaporation, we aimed to produce a robust, uniform brown coating.

Substrate:

The parts were made from electroplated Zamak, a zinc-based casting alloy. Electroplating (likely nickel or chromium) gave the Zamak a corrosion-resistant surface and smoothness ideal for PVD thin films.

The Problem:

Our early PVD coating trials revealed a major issue—the brown color was consistently too light. Something was wrong in our process, and we needed to find it fast.

Diagnosing the thin film process: A battle of variables

Through in-depth troubleshooting, we identified multiple critical issues:

1. Faulty gas distribution

In reactive PVD sputtering, gases like nitrogen or oxygen are introduced to form compounds (nitrides or oxides) that define properties such as color and hardness.

Precise gas control depends on Mass Flow Controllers (MFCs)—but ours were miscalibrated!

For example:

• An MFC set for argon but calibrated for nitrogen will skew the chamber atmosphere.

• Result: Incorrect partial pressures, faulty stoichiometry, and the wrong coating color.

Using Gencoa OPTIX, a real-time process monitoring tool, we discovered that one MFC was calibrated for the wrong gas type entirely.

This mistake prevented us from forming the dense, dark compound-rich layers we needed for the desired optical absorbance.

Gencoas OPTIX mounted at the door of the coating equipment

2. Material and substrate interactions

Electroplated Zamak behaves differently under PVD conditions compared to stainless steel or brass. Factors like surface roughness, outgassing, and layer adhesion influenced the coating thickness and final appearance.

Three lessons from a PVD colour matching failure

After navigating these challenges, we distilled three hard-earned lessons about thin film coating development:

1. Trust your scientific intuition

When results don’t match expectations—such as lighter PVD coatings despite “calibrated” processes—question assumptions. Think critically about variables like:

• Gas flow accuracy

• Cathode condition

• Substrate surface chemistry

Scientific skepticism is your best tool for diagnosing complex problems.

2. Prioritize rigorous experimentation

Fast timelines tempt shortcutting R&D. Resist!

Systematically vary parameters like gas ratios, substrate temperature, and deposition rates to map the process window fully. Skipping steps increases failure risk exponentially.

3. Embrace the iterative nature of innovation

No coating project succeeds on the first trial—especially color-critical PVD coatings.

Allow room for iteration, process recalibration, and equipment fine-tuning. Our original ten-day estimate dramatically underestimated the complexity of PVD process optimization.

Collaboration: The key to problem solving in PVD coating projects

Solving the brown color challenge wasn’t a solo effort.

It took collaboration across our internal team and the customer’s experts, combining insights on:

• MFC recalibration

• Gas tuning

• Coating rate adjustments

By fostering open communication and mutual trust, we ultimately achieved a darker, richer brown coating—and deepened our collective expertise.