There are two types of conductive adhesives used to connect electrodes and external circuits: ① thermal drying type; ② thermal curing type Q thermal curing type conductive adhesive is usually epoxy type, and its curing temperature is about 90 15 (TC. Hope to develop in the future The low temperature curing conductive adhesive is around 7080T. The drying temperature of thermal drying conductive adhesive is mainly 120T, and the temperature is lower than 120T can also be used, but considering the viscosity change and clogging of the printing process, it is better to use 1201 of.
The properties of conductive adhesive used in screen printing. The basic characteristics require printing viscosity, curing conditions, line resistance, and adhesion to the substrate. In addition, depending on the application, various requirements such as hardness and bending resistance are required. In addition to the basic characteristics of the conductive adhesive for resistive touch screens, it also needs some characteristics that match the ITO film.
Because the top electrode of the resistive touch screen uses ITO film, its curing temperature should be lower than 150 feet, and the most ideal temperature is below 120 feet. Recently, thin film substrates with lower heat resistance than PET have been used, requiring a lower curing temperature. The most suitable material is AF4820, which can be cured at 90T. Since the bottom electrode is formed on the glass substrate, it is not necessary to perform a low-temperature process. However, recently, ITO films have also been used in the bottom electrode. It can be seen that the possibility of using conductive adhesives that can be cured at low temperatures will increase in the future.
In resistive touch screens, it is extremely important to improve the adhesion between the ITO film and the conductive adhesive, that is, to improve the stability of the contact resistance between the conductive adhesive and the ITO film. In resistive touch screens, changes in the contact resistance between the conductive adhesive and the ITO film will directly cause misoperation.
The change in contact resistance and its deviation has a great influence on the performance of the touch screen. It maintains the conductivity in the Z-axis direction and reduces the residual stress of the ITO film. The sensitivity of the conductive adhesive is extremely strict.
Compared with the previous conductive adhesive, AF5000 is specially designed to solve the contact resistance with ITO film. To be sure, its contact resistance with various ITO films is relatively stable. Therefore, the matching between the conductive adhesive and the ITO film is an important factor in the selection of the conductive adhesive. In the touch screen, the ITO film determines the optical characteristics of the product, so it is necessary to choose a conductive adhesive that matches the ITO film. Prior to this, the substrates with ITO film were generally PET. Considering the optical properties and surface characteristics of the substrates, the use of materials such as polycarbonate (PC) for substrates has gradually increased. The author believes that an important factor in selecting conductive adhesive materials is the matching performance of the material and the ITO film.
The adhesion of conductive adhesive is a simple method to evaluate the matching of conductive adhesive and ITO film.
As the curing conditions of the conductive adhesive and ITO film change, the adhesion also changes. In addition, the peeled part is not only the interface between the conductive film and the ITO film, but also the interface between the ITO film and the substrate in some cases. So pay attention when evaluating. Shows the results of the adhesion test after the insulating layer is formed on the conductive adhesive. Although the adhesion of the conductive adhesive alone is very good, its adhesion will be reduced when the insulating layer is formed on the conductive adhesive. Some examples have confirmed that the use of an insulating layer will affect the adhesion of the conductive adhesive to the ITO film.
