Multilayer PCB Fabrication

The broad steps of multilayer PCB fabrication are as under:

Cutting

This process involves cutting the copper-clad board into smaller boards that can be made on the production line.

Graphic transfer

This step involves transferring the inner circuit pattern to the PCB board. This involves multiple processes such as inner layer sticking, exposure and development and etching.

Black Oxidation

This process helps to remove contaminants such as oil and impurities on the surface. It also helps to increase the specific area of the copper foil. The oxidized surface also isnt affected by moisture.

Pressing

The process of lamination involves bonding layers of circuits by means of B-stage prepeg. The discrete multilayer board is then pressed together with the adhesive sheet into the multilayer printed circuit board.

Mechanical Drilling

The use of a mechanical drill at high speed ensures through holes on the multilayer PCB.

Decontamination and sinking copper

The purpose of this process is to metallize the through hole. A three part process, this helps in decontamination, copper sinking and thickening.

Dry film and pattern plating

This process is similar to the inner layer graphics transfer as it uses photosensitive dry film to print circuit patterns on the board.

Wet film solder mask

The idea of adding the solder mask is to prevent short circuits between lines, insulation and resistance to harsh environment.

Printing

In this process, the screen for the printing plate is produced followed by printing character ink on the plate and finally drying of the ink.

Profiling

This involves separating the delivery graphics from the large panel. Many capacity parameters such as shape tolerance, inner corner size, safety distance between figure and edge of the board are considered.

Testing

Commonly used electrical testing includes needle bed test as well as flying probe test.

Immersion Tin

Electroless tin plating process uses chemical deposition to deposit tin on the PCB surface.

Final inspection

Largely this consist of the following methods: Optical Inspection – With AOI testing equipment, the machine scans the PCB and displays any defects.

Target Inspection Confirmation

This is a process of visual inspection that confirms or eliminates defects.

Visual inspection

This is menat to repair or scrap confirmed defects.

Packaging

There is a wide variety of packaging available including mositure-proof packaging, anti vibration packaging and more. Typicaly vaccum packaging is commonly used.