Develop/Etching/Strip Process 

Before work starts on a multi-layer printed circuit board. the areas that will become the traces, pads, and metal ground put down with laser direct imaging (LDI).On top of a copper laminate, a dry film has existed.Laser direct imaging lets light shine on parts of the board that match the pattern on the PCB.Any parts of the board that are not exposed will develop, leaving the film as an etch barrier.The rest of the film is an etch barrier that will remove off the copper to make the copper circuitry.The layers checked for flaws by an automated optical inspection before lamination. Fixed any mistakes, like possible shorts or opens.

Oxide and Layers

After etching, the inner layers of a PCB are treated with oxide to strengthen the bond. Then, heat and a hydraulic press to glue together layers of prepreg and copper foil. Prepreg is a material made of fiberglass with an epoxy resin that melts when heated and pressed. This glues the layers together to make a “PCB sandwich.”

Drilling

In order for signals to travel from one layer of a multilayer PCB to the next. holes drilled or lasered into them to create vias that connect the layers. Drilling performed on two or three panels at a time, depending on the type of through employed. Through electroless copper deposition. these holes plated with copper to aid in the transmission of electrical signals. 

Dry Film and Electroless Copper Deposition

Chemical and mechanical techniques remove resin and debris after drilling holes. After removal, a thin copper coating applied to all exposed panels . to create a metallic base for electroplating. Dry film put to the copper panel’s outer layers . and laser direct imaged to create a conductive pattern. similar to the develop/etch/strip method.

Electroplating, Stripping, and Etching

The panel put into a copper plating bath with sulfuric acid and copper sulfate. The conductive pattern and drill holes are now visible. As more electricity flows through it. copper deposited on the conductive surface of the board until it is about 1 mil thick. The board is then removed and placed into a tin bath that acts as an etching barrier.

As the plating completed, the dry film is removed and the bare copper not covered by tin etched away. leaving only the traces, pads, and other patterns on the board. The remaining tin is then chemically stripped. leaving only the copper in the precise area.

Solder Mask, Silkscreen, and Surface Finish

A solder mask is a thin layer of polymer that shields the copper traces . that printed onto the board from oxidation. It also prevents solder bridges – when accidental joins form between two wires. reducing the functionality of a printed circuit board.

At this point, producers choose a solder mask color. usually green for its high contrast and trace visibility. which aids fault inspection during PCB prototyping. Darker solder mask colors absorb heat, making them unsuitable for high-temperature applications.

Once the solder mask deposited component reference designators. and extra board marks silkscreened onto the PCB. Oven-baking the circuit board cures the solder mask and silkscreened ink.

Assembly Preparation, Inspection, and Testing

After completion of the PCB fabrication process. the final boards subjected to a series of inspections. and testing to confirm their functionality prior to assembly or shipment. Any PCBs that fail the test are discarded.