A printed wiring board is the framework used for many modern electronic components. These boards are typically green in color with several styles of electrical components and computer chips attached. A printed wiring board has an extremely high reliability coupled with a very low cost. As a result, these boards are common in everything from cellphones, to children’s toys to automobiles.
All printed wiring boards are made of a non-conductive material called a substrate. This material is the base of the board. It needs to be light, strong and completely non-conductive. Most boards are made of a combination of man-made materials, such as polyester or fiberglass, mixed with various plastics.
The next step in creating a printed wiring board is laying on the conductive tracks. In order to do this, most companies cover the entire surface of the board with a copper alloy. After the board is covered, any unwanted material is taken off. Other manufactures lay the circuit pathways directly on the board, but this process is more complex and expensive, so it is rarely used.
In order to remove the unwanted copper, one of three techniques is typically used. Milling the board works like most industrial milling, a specialized machine scrapes off the unwanted substance down to extremely precise specifications. With screen etching, the copper that stays behind is protected, either physically or with specialized inks, and the rest of the copper is etched off. Photoengraving is the third method and is similar to screen etching. The materials and protectants have different properties, but the process is the same.
At this point, holes are drilled into the substrate of the printed wiring board. Some of these holes are used as anchor points for mounting the board or electrical components. Other holes have rivets inserted; these rings allow electrical signals to move from one side of the board to the other. After the holes are drilled, the board is covered in a variety of sealants and protectants.
The final step in assembling these boards is the connection of electrical components. Some components are threaded through holes and secured on the underside of the board. Others are placed on non-conductive pads and work entirely on one side. Typically, machines make mass production printed wiring boards. In smaller batch jobs, or when dealing with extremely small components, it isn’t unusual for a printed wiring board to be made by hand.
After the board is assembled, it is put through an automated test. Testing machines flood the board with electricity and verify that all the connected equipment is powered as it should be. This process will also highlight any potential short circuits or broken pathways.