How to make PCB step by step?
The PCB production process is developing rapidly. Different types and requirements of PCB adopt different processes, but the basic process flow of PCB manufacturing is the same. Generally, it has to go through the process of film plate making, graphics transfer, chemical etching, vias and copper foil treatment, flux and solder resist treatment, etc.
In the PCB production process, different processes can roughly divide into the following four steps:
The first step in PCB production is film plate making
1．Draw a basemap
Most of the basemaps drawn by designers. And PCB manufacturers must check and modify these basemaps in order to ensure the quality of printed circuit board processing. If they do not meet the requirements, they need to redraw.
2．Photographic plate making
Use the drawn board-making basemaps for photographic plate-making, and the layout size should be the same as the PCB size.
The process of PCB photographic board making is roughly the same as that of ordinary photography. And can divide into: film cutting-exposure-development-fixing-washing-drying-revision. Before performing photography, check the correctness of the basemaps, especially the basemaps that have been placed for a long time.
Before exposure, the focal length should adjust, and the phase version of the double-sided panel should keep the focal length of the two shots on the front and back consistent. The phase version needs to revise after it is dry.
The second step of PCB production graphics transfer
Transferring the PCB printed circuit graphics on the phase version to the copper clad plate called PCB graphics transfer. There are many methods for transferring PCB graphics. The commonly used methods are screen leakage printing method and photochemical method.
Screen leakage printing is similar to a mimeograph, that is, a layer of paint or film is attached to the screen. And then the printed circuit diagram made into a hollow pattern according to the technical requirements. Performing screen leakage printing is an ancient process of printing circuit boards with simple operation and low cost. It can achieve by manual, semi-automatic or automatic screen printing machines.The steps for manual screen leakage printing are：
1) Position the copper clad plate on the base plate, and place the printed material in the frame of the fixed wire mesh.
2) Scrape the embossing material with a rubber sheet so that the wire mesh is in direct contact with the copper clad plate. And the composition of the pattern is formed on the copper clad plate.
3) Then dry and repair the version.
The third step of pcb production optical method
(1) Direct photosensitive method
The process is: PCB copper clad laminate surface treatment, one coating of photosensitive adhesive, one exposure, one development, one solid film and one revision. Revision is a work that must do before etching, and burrs, disconnections, sand holes, etc. can repaire.
(2) Photosensitive dry film method
The process is the same as the direct photosensitive method, except that a photosensitive adhesive is not use, but a film used as the photosensitive material. This kind of film composed of three layers of polyester film, photosensitive film and polyethylene film. The photosensitive film sandwiched in the middle. The outer protective film removed when used, and the photosensitive film attached to the copper clad plate by a film laminating machine.
(3) Chemical etching
It uses chemical methods to remove unwanted copper foil from the board, leaving behind the pads, printed wires and symbols that make up the graphics. Commonly used etching solutions are acidic copper chloride, alkaline copper chloride, ferric chloride, etc.
The fourth step of PCB production, vias and copper foil treatment
A metallized hole is to deposit copper on the wall of the hole that penetrates the wire or pad on both sides. So that the original non-metallic hole wall is metallized, also known as submerged copper. In double-sided and multi-layer PCBs, this is an essential process.
In actual production, it must go through a series of processes such as drilling, degreasing, roughening, immersion in cleaning solution, hole wall activation, chemical copper immersion, electroplating, and thickening before it can complete.
The quality of the metallized holes is essential to the double-sided PCB. So it must check, and the metal layer is required to be uniform, complete, and reliably connecte to the copper foil. In the surface-mounted high-density board, this metallized hole adopts the blind hole method (submerged copper fills the entire hole) to reduce the area occupiy by the vias and increase the density.
In order to improve the conductivity, weldability, wear resistance, decoration, extend the service life of PCB printed circuits. And improve electrical reliability, metal coating is often carry out on the copper foil of PCB. Commonly used coating materials are gold, silver and lead-tin alloys.
The fifth step of PCB production, flux and solder resist treatment
After the PCB coated with surface metal, it can flux-soldere or solder resist treatment according to different needs. Coating flux can improve weldability; on high-density lead-tin alloy plates. In order to protect the board surface and ensure the accuracy of welding, flux can add to the PCB board surface to expose the pad, and other parts are under the solder resist layer. Solder resist coatings divide into two types: heat-curable and light-curable, and the color is dark green or light green.