The color rendering of the full-color and rich ink is of course an important factor to measure the quality of the panel keys, but the more important factor to measure the quality and performance of the panel keys is its conduction function and the reliability of the conductive circuit. Even if the panel button panel layer has the best color design, color reproducibility and color rendering of the ink, if the conduction function of the switch and the reliability of the conductive circuit are lost, everything is in vain. The conduction function of the panel keys and the reliability of the conductive circuit depend on the use of functional inks and other treatment measures. Functional inks used in panel keys mainly include conductive silver paste, conductive carbon paste and insulating ink.
The conduction function of the panel buttons and the reliability of the circuit are not only related to the quality of the functional ink, but also closely related to the correctness and rationality of the circuit design in the manufacturing process, and the screen production and printing methods. The thickness control of the photosensitive material (photosensitive adhesive or photosensitive film film), too thick photosensitive film layer will cause waste of expensive functional ink and increase manufacturing cost; while too thin photosensitive film layer will significantly increase the circuit The resistance value seriously affects the conductivity of the panel keys.
Carbon paste ink is a one-liquid type thermosetting ink. After film-forming and curing, it can protect copper foil and conduct current. It has good electrical conductivity and low impedance; it is not easy to oxidize, has stable performance, and is resistant to acid, alkali and chemical solvents. Erosion: It has the characteristics of strong wear resistance, wear resistance and thermal shock resistance. The commonly used models of carbon paste inks are CH8 from Japan's Shijo Company. The shielding layer of the panel keys is also realized with carbon paste as functional ink. The role of the shielding layer:
1. Safely discharge possible harmful static electricity to avoid damage to sensitive electronic components.
2. Shielded panel keys are protected from radio frequency interference and electromagnetic interference from the surrounding environment.
3. Reduce or eliminate the radiation of radio frequency interference and electromagnetic interference by means of reflection or absorption. The effectiveness and performance of a shield depends on the properties and construction of the shield material, as well as on the frequency and distance of the shield source. EMI shielding is commonly used in electronic equipment in medical equipment, telecommunications and military industries. The importance of shielding is especially important as these devices incorporate modern radiating and anti-jamming components.
Silver paste ink is a one-liquid ink mainly composed of ultra-fine silver powder and thermoplastic resin. It can be used on most substrates and has strong adhesion and covering power. Low temperature cure, controlled conductivity and very low resistance. The mainstream silver paste inks are Korean Changxing Paragon 910A and domestic Yingshang SH8301 series.
The printing material for switching circuit printing is mostly viscous paste silver paste, which is a method of screen printing and a common material for processing electronic components. However, since most of the silver pastes belong to the high-temperature sintering reduction type, the silver pastes used in the panel key circuits must use low-temperature curing silver pastes due to the limitation of the temperature resistance of the substrate. There are currently many types of silver pastes for printed panel key circuits, and the performance and quality are also very different. The performance of silver pastes should be evaluated from the aspects of resistivity, solid content, particle size of metal particles, bonding strength, and curing temperature. , then select. Since the silver paste is expensive and its quality is related to the electrical properties of the panel buttons, it should be selected carefully.
Since the viscosity of the silver paste is thicker than that of ordinary ink, and it also contains metal solid components, care should be taken to re-scrape lightly when scratching. The existence of various solvents and additives in the conductive silver paste has a certain influence on the resistivity. To release them from the conductive circuit, they mainly rely on hot air drying to volatilize them. The drying temperature is generally controlled at 85 ℃ ~ 90 ℃, and the temperature is kept constant for 40 minutes under hot air. Practice has proved that the resistance value of an incompletely dried conductive pattern is often dozens of times higher than that of a completely dried pattern.
Therefore, dry quality is also a major aspect of panel key quality. The author has a deep experience in the Zhengzhou silk printing factory where I have worked for many years. In addition, on the metal silver contacts of the switch, a protective layer of conductive carbon paste should be screen-printed, and the characteristics of carbon paste should be used to facilitate the rapid separation of the contacts after they are closed, improve the wear resistance of the switch contacts, and ensure that the switch contacts The points are capable of withstanding millions of contacts, protecting the underlying metallic silver contacts from oxidation. Carbon paste is a non-metallic substance. The dense carbon coating can prevent the metal silver from contacting the narrow gas and hinder the migration of silver ions, thus effectively protecting the stability of the electrical performance of the switch circuit. When the carbon coating acts on the lead socket, it can be beneficial to Insertion and extraction of lead wires and connection terminals.
Insulating ink, which plays an insulating role, is usually green. In the field of circuit board PCB manufacturing, a layer of green on the surface of many PCB printed circuit boards is also an insulating ink. In the panel key panel manufacturing industry, the models that use the more mainstream insulating inks include In15 from Japan's Shijo Company.
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