Design Drilling Etching Loading Soldering Test
Well before the boards are manufactured, they must be designed. Engineers first develop circuits as prototypes, and when the circuit is established, they create the PC board pattern in software so all parts are accounted for and efficiently connected. The parts list and PC board patterns are sent to the factory where the boards will be put together.
The manufacturing process begins with a technician loading a batch of raw PC boards into an automatic drilling machine. The boards are typically made of glass-epoxy with a copper foil bonded to one or both sides. Company name, part designations and other information are silk-screened on the board in a prior step, usually in white. Holes are drilled to mount parts that will be added later.
Patterning
The board's copper side is printed with a circuit pattern either photographically or by silk-screening. It is a printed with a chemically resistant ink, so it's called "resist."
The board is dipped in a corrosive solution, dissolving the exposed copper. The copper protected by the resist pattern remains. The patterns left by etching are called the circuit board traces; they connect the electronic components. The resist is washed or scrubbed off, leaving clean, shiny copper.
Parts are placed on the board by a variety of methods. For high-volume manufacturing, automatic machines place the parts. In low-volume operations, the parts are hand-loaded, though some parts are less amenable to automatic placement and must be put in by hand even in high-volume situations.
Solder paste is applied through a stencil, coating parts on the component side of the board. The boards are run through an oven, melting the solder paste and fixing the components to the board. The board is carried horizontally on a conveyor, skimming the surface of a liquid solder (tin-lead or other alloy) bath. This plates the copper traces and makes connections between the traces and the parts.
The board is inspected and run through electronic tests to make sure it is working right. A technician connects the board to a test fixture and puts it through its paces. A pre-test may be run to check boards before parts are loaded; that way, flawed boards may be discarded more cheaply.
