Discussion of Optically Clear Adhesives

Introduction

Optically Clear Adhesive (OCA) improves the brightness and contrast of a touch screen. It allows a clearer and more vivid user experience. With the level of integration today's mobile computing devices play in our daily lives, OCA helps enrich the user's interaction and engagement with their touch screen devices.

Thin-film-transistor liquid crystal display (TFT-LCD) technology replaced traditional cathode ray tube (CRT) as the primary leader of display technology approximately ten years ago. One of the key benefits of a TFT-LCD display is that screen size is very flexible, from small screens of 1" to very large screens of 100". This innovation created numerous new opportunities for screen design, impacting dimensions and end-use applications.

Multi-point projective capacitive touch panel technology was similarly developed about ten years ago. This technology characterizes the touch panel's precise positioning capability and very fast response times.

The combination of TFT-LCD display and multi-point projective capacity touch panel technology has been a revolutionary product introduction, specifically for mobile computing devices, taking the phone from a simple communication tool to allowing the ability to quickly and easily use handheld technology for hundreds of different applications.

One inherent problem with touch panel display technology is that light transmittance decays as incremental materials are stacked upon one another, degrading picture and screen quality. This is where Boyd's expertise in OCA brings the ideal solution. Optically Clear Adhesives help to solve transmittance problems by improving brightness and contrast in the touchscreen, providing the high quality image consumers demand.

Snell’s Law

How OCA Works

OCA Segments

OCA Converting Cleanliness Requirements

To meet the needs of ever-increasing visual experience improvements, the resolution of TFT-LCD displays continually climbs, like VGA (640 x 480), WXGA (1280 x 768), Full HD (1920 x 1080) and 4K2K (3840 x 2160). When resolution increases, display pixel density increases, meaning pixel size becomes smaller and smaller. A retina display has more than 300 pixels per inch (PPI) for smartphones or more than 260 PPI for tablets.

Smaller pixel size means more defined, critical and tighter particle contamination specifications. For example, no particle the size of 0,02 mm² or greater is allowed in a 10" retina display area.

Maintaining cleanliness is one of the most challenging tasks in OCA converting processes, especially with the ever-increasing contaminant specifications. In addition to requiring ultra clean room environments (Class 1000 or better), machine setup, line layout, temperature and humidity control, operating methods and dress code will directly impact the cleanliness of components to be assembled in a device display.

OCA Applications

The design engineer must consider all aspects of excitation sources present for a typical operating device, understand how the device's structural response influences these sources, and make wise design and component choices early in the design cycle to help avoid undesirable noise and vibration characteristics. Often design and manufacturing trade-offs must be made to meet both performance and cost targets.

Elimination of all noise and vibration problems at the source level is often impossible to achieve for a variety of reasons: precision components are cost prohibitive, it is difficult to control manufacturing variation and tolerance stack-up, or simply that these factors were not taken into consideration early in the design cycle when changes were possible. Therefore, some form of modification to the structural dynamics of the device is necessary, and the most attractive option is often some form of converted add-on countermeasure that can isolate the structural transmission of vibration, block or capture the radiated airborne noise, or damp the unwanted resonant amplification. Understanding the basic nature of a specific NVH condition is the starting point in knowing which types of treatments are most appropriate to consider.

The more detailed and nuanced activity then involves the optimization of these control devices as each must be tailored for the specifics of the structure at the frequency and temperature range of the application. Achieving this while also meeting other product requirements (like RoHS compliance, flammability ratings, and cost constraints, etc.) is the challenge facing today's product designer. In future White Papers, we will take a deeper dive into the optimization process of various converted noise and vibration solutions provided by Boyd.

Conclusion

The structure of a smartphone touch screen. One piece of OCA adheres the glass screen to the touch panel. The other piece of OCA adheres the LCM to the touch module.

With Class 100 to Class 100.000 cleanroom facilities, advanced rotary converting technologies and disciplined operations teams, Boyd offers OCA die-cut solutions for market segments and applications including:

• Smartphones (< 5”)
• Phablets (5 – 8”)
• e-Books (6 – 9”)
• Tablets (8 – 13”)

For your OCA challenges, engage Boyd early in the design cycle to ensure that the most functional and cost effective designs are in place prior to emergent situations at product launch.

Use Boyd’s years of experience and engineering support in concert with your engineering and technical expertise to ensure your OCA challenges are solved in a cost effective, leading edge way.