Principles of Graphic Transfer Technology （Exposure- DES）
Under a certain temperature and pressure, a dry film is attached to the board surface, and then the negative film is used for alignment, and finally the ultraviolet light is irradiated on the exposure machine. Ultraviolet light penetrates the pattern transfer medium (negative film) and the photosensitive material (dry film) undergoes a photochemical reaction, which changes the chemical structure of the polymer or between the polymer, resulting in a change in the physical properties of the photosensitive polymer, and its chemical activity Poor. The unirradiated chemical reaction does not occur, the activity remains unchanged, and the chemical activity of the reaction part is low. Using this feature, the conductive pattern is formed by dissolving or peeling.
Inner Image Transfer
Outer Image Transfer
Dry film
The photosensitive material medium is composed of three layers of polyester film base, photoresist film and polyethylene protective film. The base is the carrier of the photoresist film, which keeps the dry resist film with good dimensional stability and can also protect the resist film from abrasion; the photoresist film is composed of photosensitive resist resin; Acrylic or polyethylene film is a protective layer covering the other side of the resist layer.
Negative film & Posotive film
Negative film and positive film are the graphic transfer medium. And the negative film is usually used on inner layer, while the positive film is used on outer layer.
Exposure
Development- Etching- Strip (DES)
Etching
PCB etching is to remove non-circuit copper from the circuit board to achieve the desired circuit pattern.
Acid etching
Through the developing section, under the action of the developer, the film that has not been irradiated by light is dissolved, and the exposed copper is etched away under the action of the acid etching solution through the etching section, and finally through the film removal section. Under the action, the film is removed to expose the inner circuit pattern.
Alkaline etching
Under the action of lye, the film is removed to expose the copper surface to be etched. In the etching tank, copper reacts with copper ions to produce cuprous, which achieves the etching effect. In the tin stripping tank, nitric acid reacts with the tin surface to remove the tin plating. Layer, exposing the copper surface of the circuit pad.
The alkaline method is a fast process. The parameters of this process must be strictly adhered to, because the solvent will damage the circuit board if it is exposed for a long time. This process must be well controlled.
The entire process is carried out in a conveyor-type high-pressure spray chamber, where the PCB is exposed to the renewed etchant spray. The important parameters to be considered during the PCB etching process are the speed of panel movement, the spray of chemicals and the amount of copper to be etched away. This ensures that the etching process evenly completes the straight side walls.
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