In this essay, we will look at the PCB assembly(PCBA) process steps that lead to a completed product. the pricess is also the standard ones that apply to other manufacturers for reference.
Application of solder paste – In automated assembly, a solder stencil is held in place on the board while an applicator applies solder paste in precise amounts exactly where it is needed. The stencil is a thin sheet of metal with holes in it, making sure solder paste is only applied to the parts of the PCB where components will sit. The solder paste is a mix of solder (tiny balls of metal) and flux (a chemical that helps the metal melt and bond to the surface better).
Pick and Place (SMT) – Once the solder is applied, the board moves to the pick and place (PNP) machine. This machine automatically orients the board and places components onto the solder paste using preprogrammed locations. With surface mount technology (SMT), components are soldered only to the surface of the board. Today, the majority of non-connector components are mounted with SMT because PNP machines are extremely fast and accurate.
- Reflow soldering – After the components are placed, the board is moved to the reflow oven. The oven gradually heats the board to melt the solder paste to create a permanent connection between components and boards, then cools the board in an equally controlled manner to prevent damage from shock.
Inspection and Quality Assurance – Errors in the previous process can result in components that are not connected, shorts in the board, or misaligned components. Inspections ensures errors and found and corrected as quickly as possible, preventing costly delays. The are several inspection methods, including hands-on inspection by a person, automatic optical inspection that relies on image recognition, and even x-ray inspection to look through components that may block an inspector’s view.
Insert Through-Hole Components – Depending on the board, it may require through-hole technology (THT) components in addition to SMT components. Certain items, such as headers and larger components, are only available in THT. Since the leads for these components are run through holes in the board, the soldering paste can’t be used as it would simply run through the holes without adhering. Instead, THT uses wave soldering. Here a machine creates a wave of solder in a pan which washes over the bottom of the board and solders all the pins on the bottom of the board at once.
Final Inspection and Functional Testing – Once all soldering is completed, the PCB is put through its paces and tested under the normal conditions in which it will operate. This is the most important PCB assembly process step and ensures only quality boards are delivered to the client.