Behr Hella Thermo Control (BHTC) of Lippstadt, Germany, manufactures automotive interior components. As the demand for smarter cars increases, BHTC encountered a new automotive interior challenge: optical bonding of automotive smart surfaces. The challenge of optical bonding led to a working relationship with Precision Valve and Automotive (PVA) of Cohoes, NY, to meet BHTC’s production and flexibility needs.

The original optically bonded smart surface technology was implemented in aviation and military sectors on large screens with limited variation. The production of these components was low-volume and less aesthetically complicated than the emerging automotive screens being produced today. The trend shows an increase in smart surface use across many consumer products. Televisions, washing machines, gas pumps, and refrigerators all have smart surfaces integrated into their designs.

Automobiles — even basic models — will soon include at least one display, and may include five or more. As the auto industry adopts smart surface technology, the demands on smart surfaces increase. Robust display assemblies with moisture, shock, and even head impact regulations are integration necessities. Screens need to be glare-free, with a wide viewing angle and vivid lighting, as well as being dimmable for night use. These parameters lead the auto industry to optical bonding as a required process, not an upgrade. With this kind of market demand, BHTC was faced with the decision to buy smart surfaces already bonded from another vendor and incorporate them into their product, or pursue the intimidating field of optical bonding themselves.

The primary steps in atmospheric optical bonding are plasma treatment, dam and seal (optional), LOCA fill dispense, bond and tack cure, and final cure.

Smart Surface Manufacturing

An automotive smart surface is made up of an image generator (TFT or OLED, for example), touch sensor, and a decorative lens. When optically bonded, these components are assembled through a process that applies the bonding adhesive, correctly positions the smart surface components, and then cures the adhesive. Optically bonding the smart surfaces enables them to meet the rigorous demands of the automotive industry and increases the life of the product. Optical bonding requires precise hydraulic management and preparation, which most experienced automation companies are hesitant to branch into.

To complicate matters further, the automotive industry also demands creative aesthetic integration with product model variation. An ideal solution would also have scalable deployment for ramping of production volumes, with initial volumes as low as 40,000 pieces per year quickly increasing to one million pieces or more per year in any given manufacturing facility. As an example, those one million pieces may be made up of ten different display models, each requiring 100,000 pieces per year. The variety of challenges continues to grow. BHTC needed easy-to-deploy, ramp-up, ramp-down, liquid optically clear adhesive (LOCA) bonding equipment that can handle a variety of products on the same production line, including curved and multi-display assemblies.

BHTC made the decision to produce the best smart surface product possible, and ownership of the optical bonding process was a clear requirement. BHTC began to investigate possible and practical solutions for optical bonding in 2013. The two primary types of optical bonding available are vacuum or atmospheric. With the many restrictions of working in a vacuum, atmospheric bonding has several advantages. Price, lead time, product variability, maximum product size, ramp up, and ramp down are all areas where atmospheric bonding is the clear choice.

Atmospheric optical bonding is unique because it does not require sensitive slit coaters, expensive vacuum chambers, or large batch-style autoclaves, causing large quantities of work in process. Instead, more basic in-line equipment can be used. The primary steps in atmospheric optical bonding include plasma treatment, dam and seal (optional), LOCA fill dispense, bond and tack cure, and final cure.

The DeltaBond 17 is located in the BHTC Class 6 cleanroom. This facility features atmospheric in-line optical bonding, where the bonding application takes place robotically.

Each step can be completed in small dedicated cells with in-line conveyance linking each upstream cell to each downstream cell, similar to industry-proven surface mount technology (SMT) lines. In addition, atmospheric optical bonding allows for single-piece-flow lean manufacturing that is well paired with automotive Takt times. These discrete process steps can be combined or separated conveniently to balance Takt time and capital expense requirements. Looking ahead, automotive interior designs will demand multi-display and curved smart surfaces, making slit coating and vacuum chamber sizes impractical. Current and future flexibility needs caused BHTC to focus their strategy on the atmospheric optical bonding process.

The Optical Bonding Process

PVA was approached by BHTC in 2013 to explore a custom optical bonding process. PVA worked with BHTC to achieve their vision. BHTC is inventing components for the display assembly such as the TFT, backlight, polarizers, touch sensors, and decorative lenses. Even touchless force feedback and gesture control are being introduced to the market by BHTC. Evaluation equipment from PVA was installed at the BHTC headquarters in Germany in early 2014. With this equipment, the company was able to develop their own expertise, ideas, and IP in this process. BHTC quickly had a need to move toward high-volume production equipment in late 2015.

The request for a high-volume automation line was expressed as a production rate, a wish list of features, and product tolerance requirements. PVA developed a tailored production line that fit the specialized needs and standards of BHTC. PVA integrated cure-in-place technology to eliminate the need for lengthy post-bond curing and reduce the number of waste parts generated through incorrect product handling. Cure-in-place also reduces the amount of dispensing equipment needed and, consequently, reduces the overall cycle time of the product, which helped to meet BHTC’s production rate. With PVA’s Bond Manager software that allows the user to develop bond sequences, different bond patterns can be tried and adjusted to create the fastest bond time while balancing high yield.

With these tools, BHTC was able to quickly design and test many unique techniques. PVA’s software also makes it possible to run several different smart surface designs on the same production line. The BHTC line was also equipped with PVA’s fluid flow camera, which is used when teaching bonds, to ensure the wet-out of the material is correctly paced, and all of the air is pushed out as the bond occurs. BHTC has the ability to modify their current layout going forward to increase production or produce new or different parts with only minor tooling changes.

This article was written by Alex Giordano, System Design Engineer at Precision Valve & Automation in Cohoes, NY. For more information, visit here.