What raw materials are used for PCB proofing?

The main raw materials commonly used in pavement proofing are: substrate, copper foil, PP, photosensitive material, solder mask and negative film. Let's introduce the related knowledge of these pcb raw materials to you.

1. substrate: except for some special purposes, ceramic materials are generally used as substrates, and organic insulating materials are generally used as substrates. We know that PCB is rigid and flexible. The corresponding organic insulating materials can be divided into thermosetting resin and thermoplastic polyester. Commonly used thermosetting resins are phenolic resin and epoxy resin; Commonly used thermoplastic polyesters are polyimide and polytetrafluoroethylene. The processing flow of pcb substrate is not explained here. Interested friends can check relevant information online.

2. Copper foil: At present, the metal foil covered on pcb is mostly copper foil made by rolling or electrolysis. The thickness of copper foil is generally 0.3 mil to 3 mil (0.25 oz/ft2 to 2 oz/ft2). The specific choice depends on the current-carrying current and etching accuracy. Copper foil has an influence on the quality of products, which is embodied in dents, pits and peeling strength on the surface of products.

3.PP: it is a second-class resin when making multilayer pcb, and it is an indispensable interlayer adhesive.

4. Photosensitive materials: generally divided into photoresist and photographic film, and according to the industry, divided into wet film and dry film. The wet film coating on copper clad laminate will change chemically under a certain wavelength of light, thus changing its solubility in developing solution (solvent). Wet film can be divided into photodegradable (positive film) and photopolymerizable (negative film). Photopolymerized resist can be dissolved in the developer before exposure, but the polymer converted into it after exposure is insoluble. In the developer; Photodegradation of resist is just the opposite, and the polymer produced by photosensitive can be dissolved in the developer. Dry film can also be divided into positive film and negative film, that is, the difference between photodegradation type and photopolymerization type, both of which are very sensitive to ultraviolet rays. Dry film may replace wet film in the future, because it can provide high-precision lines and etching.

5. Solder resist (ink): a kind of solder resist, which is an ordinary liquid photosensitive material and has no affinity for liquid solder. Under certain lighting conditions, it will change and harden. Ink comes in many colors. The most common color of solder mask is green. What is the specific reason? I have written (why are PCB boards mostly green? ) article. You can go and have a look if you are interested. I won't go into details here.

6. Negative film: similar to polyester film used in photography, it is a material that uses photosensitive materials to record image data. The contrast, sensitivity and resolution of film are quite high, but the photosensitive speed is low. In order to meet the requirements of fine lines and dimensional stability, glass can be used as the bottom plate.