Printed Circuit Board Assembly
What is Printed Circuit Board Assembly?
Printed circuit board assembly (PCBA) is the process of placing all of the electronic components on a printed circuit board. A printed circuit board (PCB) is a laminated sandwich structure of conductive and insulating layers. PCBs have two complementary functions:
Assemble electronic components in designated locations on the outer layers by means of soldering.
Provide reliable electrical connections between the component's terminals.
Each layer of the board is designed with an artwork pattern of conductors — similar to wires on a flat surface — that provides electrical connections on that layer. Another manufacturing process adds vias, plated through-holes that allow interconnections between layers.
PCBAs mechanically support electronic components using conductive pads in the shape designed to accept the component's terminals. The components are electrically connected using traces etched from one or more sheet layers of Copper. Components are generally soldered onto the board for both electrical and mechanical attachment. PCBAs are used in nearly all electronic products and many electrical products.
How Does Printed Circuit Board Assembly Work?
Printed circuit board assemblies can have different layering configurations:
Single-sided - One Copper layer
Double-sided - Two Copper layers on both sides of one substrate layer
Multi-layer - Outer and inner layers of Copper, alternating with layers of substrate
Multi-layer PCBAs allow for higher component density, because circuit traces on the inner layers would otherwise take up surface space between components. However, multilayer PCBAs make repair, analysis, and field modification of circuits more difficult and often impractical.
In assembly, the bare board is populated (or "stuffed") with electronic components to form a functional printed circuit board assembly (PCBA). Components can be assembled via through-hole or surface mount technology:
Through-hole Technology: Component leads are inserted into holes surrounded by conductive pads. The holes keep the components in place, before they are soldered for permanent placement and connectivity.
Surface-mount Technology (SMT): Components placed onto the board so that the pins line up with conductive pads or land on the surfaces of the PCBA. Solder paste that was previously applied to the pads holds the components in place temporarily. If SMT components are applied to both sides of the board, the bottom side components are glued to the board — then soldered in place permanently.
A variety of soldering techniques are used to assemble components in a PCBA. High-volume assembly typically occurs on a pick-and-place machine, with bulk wave soldering for through-hole parts or reflow ovens for SMT components and/or through-hole parts. For low-volume PCBAs, skilled technicians can hand-solder tiny components under a microscope using tweezers and a fine-tip soldering iron. Selective soldering may be used for delicate parts. Through-hole and SMT construction are often combined in a single assembly because some required components are only compatible with one of the techniques.
After the PCBA has been populated, it may be tested in a variety of ways:
Power Off - Visual inspection, automated optical inspection, analog signature analysis, or power-off testing
Power On - In-circuit testing with physical measurements such as voltage, or functional testing ("Does the PCBA do what it's supposed to?")
When boards fail a test, technicians may desolder and replace failed components — a process known as rework.
Advantages of Printed Circuit Board Assembly
Printed circuit board assemblies are used in nearly every electronic product. Industrial PCBA processes offer several advantages, such as:
Functional reliability and repeatability
Lower-cost, efficient production of critical electronics
Ease of integration and testing
Advanced performance in a compact envelope
Eliminate loose connections and connectivity issues