A Multiplayer PCB (printed circuit board) is made of two or more printed circuits boards stacked together in a way that creates a reliable mutual connection between them.
Multilayer PCBs have at the very least three conductive layers. Two outside layers and the middle layer synthesized and encapsulated by the outer insulation. Because of their complex manufacturing methods, Multilayer PCB production is very exclusive and its price quiet high.
PCBs for basic electronic equipment comprise of 4 to 8 layers, while PCBs for more complex equipment can have anywhere from 8 to 40 layers. In PCBs, the number of layers on a multilayer PCB is recognized as the number of separate conductor patterns. This is usually when an even number and includes the two outer layers.
Multilayer PCB Manufacturing
Engineers/designers create a layout using the Computer Aided Design (CAD system) which uses their own internal data format and that is later extended into a Gerber File. The Gerber Files provides the information for the copper tracking layers needed as well as the solder mask and all other options for the board.
Upon confirmation from the designer, Photo tools are created using a Photo plotter which ultimately gives PCBs an image. This image enables the machines to print the inner layers the right way with an epoxy resin and laminate. It also comprises of glass fiber which has copper foil pre-bonded to each side of the resin.
A powerful alkaline solution is later used to dissolve or etch the inner layers to remove the unwanted copper as needed. This renders the inner core areas of the multilayer PCB complete. Later the required holes are punched in to meet and line up the inner layers to the outer layers. This process is called the Register Punch and (AOI) Automatic Optical Inspection.
When the required holes have been created, all the layers are assembled together and then starts the drilling of the PCB. The holes for leaded components are drilled as well as through the holes that attach the copper layers together. To find the target holes, an X-Ray drill is used.
The next stage involves plating by applying a chemical deposition of a very thin layer of copper to cover the inside of the holes drilled. Before that, the outer layers are imaged to make certain that there arent any short circuits in the board. Later, the boards are electroplated with copper. They are checked to make sure that the electrical connection is good.
After that the outer layers are dissolved or etched to remove any excess and unwanted copper. To make sure that the required copper is not damaged, the surface area is coated with tin as a protective barrier. Later the solder mask is printed on each side of the board to guard the copper surface. This is also done to prevent the solder from short-circuiting during the assembly.
All multilayer boards are electrically tested with a flying probe tester to make sure that there arent any open circuits or faulty areas. Finally the PCBs are cut out as per the need of the customer.
Each step of PCB fabrication has to be handled very carefully by experts, which is why you should only choose a professional PCB manufacturing company, like Super PCB for the job. Super PCB specializes in both rigid and flex PCBs and also offers PCB prototype services.