Understanding a PCB Assembly
There is some confusion about the definition of a printed circuit board assembly. Most people may simply call these printed circuit boards, or PCBs. However, PCB really only refers to the actual board. When all of the components have been attached and wired together, that produces a printed circuit board assembly. The assembly is a product that actually functions. In order to understand this, it might be helpful to read a short summary of how components get mounted on a PCB board to form the assembly.
How Are Printed Circuit Boards Assembled?
There are two basic ways that the components are attached to the board: • Through-hole: The leads of the components are inserted into holes that are already set into the board. • Surface-mount: In this type of assembly, the components are mounted onto pads on the board.
In either case, the parts are permanently attached to the board with by soldering them there at temperatures hot enough to make metal molten. Most complex boards actually may make use of both types of mounting. Some components are only available with mounting packages for one of the other type of mounting.
Surface vs. Through-Hole Mounting of PCB Components
There are also advantages and disadvantages to each kind of mounting. Designers have to consider the strength they need from the connections and the available space on the board. Of course, the main consideration might be the style of mounting available for certain components that are needed for the final assembly. This is a short comparison of the two types of component mounting: • Through-hole mounting is more robust, and it is usually considered for parts that might endure more physical stress. However, it makes boards more expensive because these holes have to be precisely drilled. Typically, parts that need holes drilled also take up more space.
• Surface-mounted parts usually take up less space on a board, and this might be considered for some complex designs. This is a newer method that has parts with small tabs on them that can get soldered right to the surface. It's cheaper, but it is not likely to be as durable.