PCB Tech - The most basic steps of PCB copy board manufacturing

The manufacturing process of PCB copy board has developed rapidly. Different types and different requirements of PCB adopt different processes, but the basic process flow is the same. Generally, it has to go through the processes of film plate making, pattern transfer, chemical etching, via and copper foil treatment, soldering and solder mask treatment.

The PCB copy board production process can be roughly divided into the following four steps:

The first step of making PCB copy board

1. Draw a base map

Most of the base maps are drawn by designers. In order to ensure the quality of printed board processing, PCB manufacturers must check and modify these base maps. If they do not meet the requirements, they need to be redrawn.

2. Photoengraving

Use the drawn base drawing of the board to make a photo plate. The size of the layout should be the same as that of the PCB.

PCB photographic plate making process is roughly the same as that of ordinary photography, which can be divided into: film cutting-exposure-development-fixing-water washing-drying-retouching. Before performing photography, check the correctness of the base map, especially the base map that has been placed for a long time.

Before exposure, the focal length should be adjusted, and the double-panel photographic plate should keep the same two focal lengths of the front and back of the camera; after the photographic plate is dry, it needs to be revised.

The second step of PCB production graphics transfer

Transfer the PCB printed circuit pattern on the phase plate to the copper clad board, which is called PCB pattern transfer. There are many methods of PCB pattern transfer, and the commonly used methods are the silk screen printing method and the photochemical method.

1. Screen leakage

The screen printing is similar to the mimeograph, which is to attach a layer of paint or glue to the screen, and then make the printed circuit diagram into a hollow pattern according to the technical requirements. Performing screen printing is an ancient printing process with simple operation and low cost; it can be realized by manual, semi-automatic or automatic screen printing machines. The steps for manual screen printing are as follows:

1) Position the copper clad board on the bottom plate, and place the printed material in the frame of the fixed screen.

2) Scrape the embossing material with a rubber plate, make the screen and the copper clad laminate directly contact, then a composition pattern will be formed on the copper clad laminate.

3) Then dry and revise.

The third optical method of PCB production

(1) Direct photosensitive method

The process is as follows: surface treatment of copper clad laminate, coating of photosensitive glue, exposure, development, solid film, and revision. Revision is the work that must be done before etching. Burrs, broken wires, sand holes, etc. can be repaired.

(2) Photosensitive dry film method

The process is the same as the direct photosensitive method, but instead of using photosensitive glue, a thin film is used as the photosensitive material. This film is composed of three layers of materials: polyester film, photosensitive film and polyethylene film. The photosensitive film is sandwiched in the middle. The protective film of the outer layer is removed during use, and the photosensitive film is pasted on the copper-clad board using a film laminator.

(3) Chemical etching

It is the use of chemical methods to remove unnecessary copper foil on the board, leaving behind the pads, printed wires and symbols that make up the pattern. Commonly used etching solutions include acid copper chloride, alkaline copper chloride, ferric chloride, etc.

The fourth step of PCB production, via and copper foil processing

1. Metallized hole

Metalized hole is to deposit copper on the hole wall that penetrates the wires or pads on both sides, so that the original non-metallic hole wall is metalized, also called sinking copper. In double-sided and multilayer PCBs, this is an indispensable process.

The actual production has to go through a series of processes such as drilling, degreasing, roughening, immersion cleaning solution, hole wall activation, electroless copper plating, electroplating, and thickening.

The quality of metallized holes is very important for double-sided PCBs. Therefore, they must be inspected. The metal layer is required to be uniform and complete, and the connection to the copper foil is reliable. In the surface-mounted high-density board, this metallized hole adopts the blind hole method (the sinking copper fills the entire hole) to reduce the area occupied by the via hole and increase the density.

2. Metal coating

In order to improve the conductivity, solderability, wear resistance, decoration, and prolong the service life of the PCB, and improve the electrical reliability of the PCB printed circuit, metal coating is often carried out on the copper foil of the PCB. Commonly used coating materials include gold, silver and lead-tin alloys.

The fifth step of PCB production soldering assistance and solder mask treatment

After the PCB copy board is coated with metal on the surface, it can be treated with flux or solder mask according to different needs. Applying flux can improve the solderability; and on high-density lead-tin alloy boards, in order to protect the board surface and ensure the accuracy of soldering, solder resist can be added on the board surface to expose the pads and other parts are Under the solder mask. There are two types of solder resist coatings: heat curing type and light curing type. The color is dark green or light green.