Screen-printable black epoxy coatings offer a balanced solution for versatile and cost-effective optical systems

Black coatings are a vital component within optical applications such as telescopes, cameras, spectrometers, and laser systems—integral to their performance and efficiency—due to their ability to suppress scattered light and reduce optical reflections. These coatings, which are typically engineered with materials that exhibit high absorption across a broad spectral range, are applied to surfaces within optical systems to minimize unwanted light that can degrade image quality, measurement accuracy, and overall system performance.

Various types of black coatings exist, such as black anodized coatings, physical vapor deposition (PVD) black coatings, and carbon nanotube coatings. Each has specific advantages and disadvantages, depending on application requirements and where it sits on the spectral range. But when it comes to combining optical performance, high versatility, and cost-effectiveness, one type of black coating stands out: black epoxy coatings.

Black epoxy coating properties

A class of black epoxy coatings developed by DELO provides the following key features:

Thin layer application precision for smallest dimensions. The ability to apply layers of black epoxy coating at <10 µm allows for precise control over its thickness, which ensures optical components retain their dimensional tolerance. This is particularly important for systems where space constraints and optical path length are critical.

High optical density for effective scattered light suppression. With an optical density >4, these thin layers of coating can absorb more than 99.99% of incident light (see Figs. 1 and 2), which is crucial to minimize scattered light and enhance contrast for sensitive optical applications such as imaging systems, sensors, and spectroscopic instruments.

A matte surface reduces specular reflection. Its matte surface inherently reduces specular reflection, which is critical in optical systems where glare can degrade image quality or measurement accuracy. This helps ensure unwanted light is absorbed effectively for a clearer optical path.

Durability and adhesion enable long-term performance. Black epoxy coatings are known for their excellent adhesion to a wide range of substrates, including metals, glass, and plastics. This contributes to their longevity and resistance to delamination, even under challenging environmental conditions such as humidity, temperature fluctuations, and mechanical wear throughout its service life.

Versatility and compatibility for a wide range of applications. These coatings can be formulated to adhere to various materials, which makes them suitable for components fabricated from different substrates within the same optical system. This versatility simplifies logistics and reduces the need for multiple types of coatings.

Cost-effective with efficient application. Despite their high-performance characteristics, black epoxy coatings can be more cost-effective than higher-end alternatives like carbon nanotube coatings. Their application does not require specialized vacuum environments, which leads to reduced manufacturing complexities and, in turn, lower costs. Most materials comprise only one component and don’t require mixing before use. And a long material processing time of three days after defrosting makes them easy to handle and efficient to use.

Black epoxy coatings provide a balanced solution for applications that require maximum light suppression—without compromising component thickness or durability. They enable designers to achieve high optical performance within compact, durable systems, which makes them suitable for a wide array of optical technologies and their associated design challenges.

Screen printing opens door to greater production efficiency

The ability to structure black epoxy coatings through screen printing, along with low curing temperatures starting at 100°C, offers advantages for optical component manufacturing. These properties enhance coating versatility and adaptability within advanced optical systems. Among their key benefits:

High-volume manufacturing. Screen printing allows multiple components to be coated directly and simultaneously on large areas, such as on wafer- or panel-level. This enables high throughput and units per hour (UPH), thanks to the straightforward setup and operation of the screen-printing process. It is commonly used for industrial applications to apply coatings, inks, or pastes within a single process step—which makes it efficient for mass production.

In combination with short curing times and low temperatures (for example, 20 minutes at 100°C), screen-printable black epoxy coatings are suitable even for large-volume optical components.

Flexibility. Screen printing enables precise coating patterning to create detailed and complex geometries directly onto component surfaces. This is particularly beneficial for components that require selective light absorption or intricate designs, such as scattered light baffles, aperture masks, or light traps within optical systems.

The screen-printing process allows for customization and facilitates the inclusion of specific patterns or gradients within the coating layer. This further tailors optical properties to different parts of a component and adapts to their functional needs without requiring additional steps.

With curing temperatures starting at 100°C, black epoxy coatings can be applied to a wide range of substrates, including certain plastics or composites that may be sensitive to higher thermal processes. This reduces the risk of substrate warpage or degradation and expands the potential applications for these coatings.

In addition, low-temperature curing reduces overall energy consumption and the environmental impact of the coating process.

Screen printing is a widely accessible manufacturing process that can be easily integrated into existing production lines. Its simplicity and adaptability make it an attractive option for manufacturers who want to add or enhance capabilities without significantly reworking their operations.

Screen printing allows for scalability in production because it supports both small-scale prototyping and large-scale manufacturing with consistent quality and repeatability.

These practical benefits highlight reasons to use screen-printed black epoxy coatings for optical systems. By combining the precision and customization of screen printing with the material advantages conferred by low temperature curing, manufacturers can achieve high-performance optical components that meet demanding specifications across a broad range of applications, as a case study from one manufacturer shows.

Case study: Time-of-flight sensor by ESPROS

Black epoxy coatings present an advantageous solution to enhance the performance and manufacturability of time-of-flight (ToF) sensors. These sensors, which are increasingly used in a variety of applications like three-dimensional (3D) imaging, automotive LiDAR, and industrial automation, benefit significantly from coatings that improve optical performance while meeting stringent manufacturing and reliability standards. Black epoxy coatings excel in this sense for our customer ESPROS Photonics, a foundry, product, and technology solution provider for optoelectronics.

ESPROS Photonics is using black epoxy coatings for wafer-level application via screen printing them onto 8-inch wafers. Screen printing allows these coatings to be applied at the wafer level to ensure consistent thickness and uniformity across all dies (see Fig. 3), which is critical for maintaining consistent optical performance across all of ESPROS’ sensors. It also enables design flexibility to intricately pattern apertures directly on the wafer.

Other features ESPROS appreciates include the scalability of screen printing well suited for their high-volume manufacturing. It allows them to rapidly process wafers with minimal variability, which is ideal for mass-producing ToF sensors. It also streamlines production because integrating the coating process at wafer level simplifies the flow of manufacturing, which allows ESPROS to forego handling and assembly steps to enhance their throughput.

Using epoxy coatings minimizes waste, which subsequently lowers ESPROS’ material costs. The simplicity and speed of the screen-printing process also contribute to reduced labor and equipment costs compared to more complex coating methods.

Its material reliability enables standard compliance. DELO black epoxy coatings withstood ESPROS’ rigorous reliability testing, including reflow tests using JEDEC standards to ensure they maintain their performance—even during soldering processes common in electronic packaging.

DELO black epoxy coatings are designed to endure extreme environmental conditions, including temperature cycling and highly accelerated stress testing (HAST) for 96 hours at 130°C and 95% relative humidity. This ensures long-term reliability within ESPROS’ ToF sensors across applications ranging from consumer electronics to harsh industrial settings.

The robust nature of epoxy coatings provides excellent mechanical adhesion and resistance to delamination, which is essential for the durability and lifespan of ESPROS’ sensors (and was proven by successful peel tests following environmental testing).

Incorporating DELO black epoxy coatings into ToF sensor design provides ESPROS with benefits that align with the needs of modern manufacturing and application demands. These coatings improve optical performance through efficient scattered light management and support high-volume, cost-effective manufacturing strategies—ensuring reliability and durability through compliance with rigorous standards. Such advantages make black epoxy coatings a wise choice for enhancing the functionality and competency of ToF sensors and other optoelectronic systems.