Basic steps for PCB manufacturing process
PCB manufacturing process develops rapidly. Different types and different requirements of printed circuit board adopt different crafts, but the basic craft process is the same.Generally, it has to go through the process of film plate making, graphic transfer, chemical etching, through hole and copper foil processing, welding and soldering resistance.
PCB manufacturing process can be divided into the following four steps:
PCB manufacturing first step: film plate making
1.Draw the base drawings
Most of the base drawings are drawn by the designer, but printed circuit board manufacturers need to check and modify them in order to ensure the quality of PCB processing. If it not meet the requirements, they need to draw again.
To make a photographic plate by drawing base drawings that the layout size should be consistent with the PCB size.
PCB manufacturing step 2: graphics transfer
Transfer the PCB printed circuit graphics to the copper clad plate, called printed circuit board graphics transfer.There are many PCB graphics transfer methods, commonly used screen printing and photochemical method.
Screen printing is similar to t and mimeograph which is attached to a layer of paint or film, and then according to technical requirements printed circuit diagram made of hollow graphics.Screen printing is an ancient printing craft with simple operation and low cost;which can be achieved by manual, semi-automatic or automatic silk screen printing machine.
Step 3 of PCB fabrication: optical method
(1) direct photosensitive method
The process is as follows: surface treatment of copper clad plate一 coating sensitive adhesive一exposure一 developing一fixing film一 one repairing plate.Repairing plate is the work must be done before etching, can repair burr, broken wire, sand holes, etc.
(2) photosensitive dry film method
The process is the same as the direct photosensitive method, but instead of using sensitive adhesive, a film is used as the photosensitive material.
(3) chemical etching
It is the usage of chemical methods to remove unnecessary copper foil on the board, leaving the composition of the graphics pads, printed wires and symbols.
Step 4: pass hole and copper foil processing
Metallized hole is to deposit copper on the hole wall through the two sides of the wire or welding plate, so that the original non-metallic hole wall metallization, also known as copper precipitation.This is an essential process in both duplex and multilayer PCBS
In actual production, a series of processes are required, such as drilling一degreasing一 coarsening, leaching cleaning fluid一hole wall activation一copper precipitation一electroplating and thickening.
The quality of the metallization hole is crucial to the double-sided printed circuit board, so it must be inspected to ensure that the metal layer is uniform, complete and reliably connected to the copper foil.The immersed copper fills the whole hole to reduce the area occupied by the hole and increase the density.
In order to improve printed circuit board conductivity, weld ability, abrasion resistance, extend the service life of PCB and improve electrical reliability, the copper foil of printed circuit board is often coated with metal.Commonly used coating materials are gold, silver and lead tin alloy.
Step 5: soldering and soldering resistance treatment
PCB after surface metal coating, according to different requirement can do welding or welding treatment.The solder ability can be improved by applying flux.In the high-density lead-tin alloy plate, in order to protect the plate surface and ensure the accuracy of welding, the soldering mask can be added on the plate surface to make the welding plate exposed. Other parts are under the soldering mask layer.
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