Screen printing is a printing method that uses a plate (screen mask) that uses a “screen mesh,” which is woven with synthetic fibers such as polyester or metal fibers such as stainless steel. It is a type of “stencil printing,” which prints on target objects by passing ink through the mesh of a screen mask. Due to the many kinds of target objects on which it can print, it is even said that screen printing can be used on all materials other than “water” and “air.” In recent years, in line with the advancement of developments to enable the printing of extra fine line, its application to the electronics field, which requires ultra-fine processing (printing), has attracted attention.
(1)A screen mesh is stretched across an aluminum or wooden frame that matches the size of the printed object
(2)A photosensitive material that hardens by ultraviolet light is coated on the screen mesh
(3)The parts to be printed such as the characters and illustrations are masked with a positive film (masking), and it is exposed to ultraviolet light (exposure)
(4)When the printing object from (3) is flushed with water, the photosensitive material of the part that wasn't exposed to ultraviolet light and didn't harden is washed away, and the mesh part is exposed
(5)Once the printing object from (4) is dried and inspected, the screen mask is complete
(6)The completed screen mask is placed on top of the target object to be printed (hereinafter “the object”)
(7)When the ink is spread across over the screen mask, the hole portions of the mesh that are not blocked by photosensitive material are filled with ink
(8)The ink is pressed against the object with a squeegee from the edge of the screen mask
(9)As a result of the plate that has been pressed by a squeegee coming into contact → being released from the object, the ink filled in the hole portions of the mesh is copied to the object (called snap-off). This completes the printing on the object
Screen printing does not limit its target printing object due to a simple principle it uses, which is to print by pushing out ink from a screen mesh. It can print on a variety of objects, including paper, cloth, plastic, metal and glass.
Many different types of screen mesh, photosensitive material and ink are used in screen printing, and by selecting an optimal combination of these, screen printing can make printed materials such as advertisements that appeal visually as well as printed objects such as electronic components that emphasize functionality.
Amid an ever increasing need for price reduction, miniaturization and weight saving in the electronics industry in recent years, a technology called printed electronics is gathering attention.
Printed electronics is a technology that forms electronic circuits, devices and the like by using printing technology. Although printed electronics employs various printing methods, such as offset printing, gravure printing and ink jet printing, screen printing is particularly a method that is frequently used due to its characteristic of “being able to be used on many kinds of material.”
Screen printing can be used regardless of the printing object, so it can even be used on base materials that are slightly uneven. In addition, any ink can be used as long as it is in paste form, so the ink components can be designed and selected relatively freely.
Screen printing can be said to be a printing method that meets the needs in the manufacturing of electrical and electronic components, as seen in how it has enabled the printing of fine wiring to the degree of just 10μm (the diameter of a single human hair is 60 to 80μm) through technological advancements in recent years.
Forms the path for electric current (wiring) by screen printing
Protective resist printing
Protects the parts other than the part that connects the components by using screen printing (resist)
Forms symbols by screen printing to make it possible to discern the part type
Broadly speaking, there are two methods of coating the photosensitive material on the screen mesh.
This is a method of directly coating the photosensitive material on the screen by using a type of trays called bucket, a coating machinery or the like. Its advantages are the rich variations of photosensitive materials that can be used as well as the high durability after printing. On the other hand, it has disadvantages such as being difficult to coat uniformly and the contours being prone to bleeding.
This is a method of using a photosensitive film that has been coated in advance with photosensitive material.
After performing the plate making procedures (3) and (4) on the photosensitive film, the photosensitive film that exposes only the patterned portion is pasted on the screen mesh to copy the photosensitive material on the plate. The screen plate is complete once only the film is peeled off.
While the indirect method has advantages such as having less bleeding and easier procedures compared to the direct method, it also has disadvantages such as low durability of the plate and requiring preparation of supplies for post-exposure development, including hydrogen peroxide solution and hot water.
A film that has been coated with photosensitive material in advance is pasted on a screen by using liquid photosensitive material or water, and after it is dried, the film is peeled off and the emulsion film is copied on the screen. Then, plate making procedures (3) and (4) are performed. This method retains the simplicity and thickness accuracy of the indirect method and it is superior in durability to the direct method.