Key points of single-layer capacitive touch design
Summary: Various methods of reducing costs have been proposed, including the use of plastic or acrylic instead of glass, or the use of film instead of glass, the original double-layer structure is hard squeezed inside the single-layer structure and so on. In the end, the two final methods of using the Sensor on the protective glass (Touch on Lens) and in the LCD (in-cell) are pitted against each other. Various methods of reducing costs have been proposed, including the use of plastic or acrylic instead of glass, or the use of film instead of glass, the original double-layer structure is hard squeezed inside the single-layer structure and so on. In the end, the two final methods of using the Sensor on the protective glass (Touch on Lens) and in the LCD (in-cell) are pitted against each other.
In recent years, the touch wave set off in mobile devices has become an uncontrollable fire. Touch has become a part of life, and looking forward to the future, the trend is irresistible. From small size mobile phones, medium size tablet computers, NB, to large size TVS, home appliances, etc., will be penetrated by touch, and the scale of touch industry will become larger and larger. According to the latest publication of DisplaySearch touch panel market analysis report pointed out that in 2011, the global touch panel output value will reach 13.4 billion US dollars, of which two-thirds of the touch panel used in mobile phones is expected to reach 868 million pieces, the rest of the fastest growing is the tablet more than 72 million pieces, about 3 to 4 billion US dollars of output value.
Reduce costs! High yield of Touch on Lens
Just think about 13.4 billion US dollars is equivalent to 380 billion Taiwan dollars, if someone can come up with a way to reduce the cost by 50%, you can create 190 billion Taiwan dollars of profit, if the cost is reduced by 80%, you can create 300 billion Taiwan dollars of profit, and every year is growing, the above profits believe that people are hard to see, of course, the industry is no exception, Various methods of reducing costs have been proposed, including the use of plastic or acrylic instead of glass, or the use of film instead of glass, the original double-layer structure is hard squeezed inside the single-layer structure and so on. In the end, the Sensor is done on the protective glass (Touch on Lens) and the two final methods in the LCD (in-cell) showdown, the two methods in the material cost is almost no difference, but in the production cost and yield there is a big difference, and these differences will form the key to the outcome.
However, to achieve single-layer capacitive Touch on the protective glass (Touch on Lens), there are those requirements and considerations, the following are a few key points:
Design points of single-layer capacitive Touch on protective glass (Touch on Lens)
● Only a single layer of protective glass can complete the touch function.
●Sensor is made on the protective glass.
● It is best to be a real single-layer structure, without a three-dimensional span bridge structure.
● Minimum production procedures
● Thinnest and lightest construction
● Best optical effect
● Minimum material cost
● The lowest production equipment cost investment
● Maximum output capacity of touch panel
Basically three-dimensional span structure, is the main cause of poor production yield, will increase a lot of production procedures and costs, and increase difficulties in LCD fit, these are the pain in the hearts of manufacturers, of course, some highly skilled manufacturers also have a relative competitive advantage, but once the technical bottleneck is overcome will cause touch panel production quickly into maturity, Also due to the reduction of the technical threshold, a large number of latecomers joined, forming a Red Sea competition situation.
Because the single-layer structure minimizes the production process, laser etching and printing technology can be introduced, and has the opportunity to replace the yellow process, which can reduce chemical pollution, save water resources, and meet the requirements of environmental protection, but the manufacturer is most happy to see the significant reduction in the cost of production equipment, after all, the equipment of the yellow process is quite expensive. The laser etching and printing technology is relatively low, and the production environment requirements are lower than the yellow process, but the weakness of laser etching is that the output capacity is not as high as the yellow process, the loss of equipment must also be carefully considered, the cost of screen printing is determined by the loss caused by the blockage of the screen can be controlled, in summary, the single-layer structure creates the diversity of the process. The competitiveness of manufacturers has also evolved from simple equipment investment to complex production portfolios, becoming more flexible.
Selection of glass VS plastic panel carrier
To produce single-layer capacitive touch panels, there are three levels of issues to consider, the first is the choice of carrier. That is, the material of the protective layer should choose glass or plastic (acrylic), the hardness of glass, optical properties and touch sensitivity are better than plastic, however, plastic wins in good construction, not easy to break, high safety, in the author’s point of view, glass is suitable for small and medium-sized panels such as mobile phones and tablet computers, and plastic is suitable for large size. The reason is that the safety issue is a priority, and the plastic can be made into a film directly attached to the LCD, the success rate of lamination is very high, on the contrary, the success rate of glass lamination is greatly reduced, and the larger the glass area, the higher the probability of rupture, the optical penetration rate of glass or plastic can reach 90% under the single-layer structure, so there is little difference in optical characteristics. However, plastic is an organic substance, the number of molecules is large, the light will be diffused through the phenomenon, will affect the resolution of the screen display, such as iPhone 4 using 400 dpi resolution when using plastic touch panel, the screen display resolution looks like 200 dpi, will lose the value of 400 dpi. However, the large-size display panel will not use a high resolution such as 400 dpi, which is less affected by the light diffraction of plastic materials.
Performance is very different Sensor pattern selection knowledge
The second factor to consider is the Sensor pattern. Previously, the double-layer mutual capacitive touch panel used by Apple adopted the X and Y axis interlocking matrix structure, which is the method used by the most people at present. Then, someone proposed the method of squeezing the double-layer structure into the single-layer structure, which is the common diamond span bridge structure at present. In order to reduce costs, some people began to adopt the technology used in the early self-capacitive touch button in mainland China. The structure of the triangular one-dimensional slide rail is arranged into a plane, which becomes the earliest version of the single-layer capacitive touch panel. There are also improved methods using mutual capacitive. However, whether self-capacitive or mutual capacitive, these two methods are simple but have the shortcomings of insufficient resolution. Can not be used in large size, currently most commonly used in the 3.5 inch touch panel, according to some industry said that this single-layer capacitive touch panel in the use of low-cost mobile phones is really a lot, but also let many panel factories in Taiwan, touch IC design companies, actively invested in this market.
The single-layer touch technology of All Points was proposed as early as in 2004 when Apple applied for the invention of the touch panel (US 7,663,607B2), but the scope of the application did not include the All Points structure, and the structure of X and Y axes was the main body. In fact, many early Keyboard structures also use the structure of All Points, All Points is also the most original structure of multi-touch, because each Point is an independent detection point, so the total number of All Points is the maximum number of multi-touch, for example, If the touch panel composed of 10 rows X 10 columns equivalent to 100 Points can allow 100 fingers to touch each of the 100 points at the same time, the multi-touch that we now recognize is the X and Y axis matrix mutual capacitive touch panel used by Apple. In fact, it is evolved from All Points, in recent years, the promotion of All Points structure is indispensable to IDT’s PureTouch, because it can produce ultra-low-cost touch panels, it is said that the mainland’s e-book manufacturers have adopted.
As for the ultra-low touch panel price from where? No matter the method used by IDT or the previous single-layer triangle Pattern, the cost can be effectively reduced by more than 40%. Combined with the Sensor made on Cover lens, the cost can be effectively reduced by 60-70%. Why is such a large cost reduction method not used in mainstream products? Smart phones and tablet computers have not been adopted by well-known manufacturers, the reason is that the above two methods can not be used in large and medium-sized touch panels, the longer the triangle pattern is pulled, the larger the error will be, the worse the resolution will be, and IDT All Points of the method more than five inches when the center of the point can not be traced out. Therefore, the way of All Points is limited by the space of the line, to increase the space of the line, it is necessary to increase the sensitivity of the touch and SNR ratio to have a chance of success, so the smaller the size of the touch panel using the above two methods the better the effect, according to this reasoning in the low price of small size of the touch device should have a lot of these two methods.