Similar to the creation of any product, there are several steps and processes that need to be executed in order to come up with the perfect finished printed circuit board. Likewise, it is most important that the stages are each seamlessly integrated to ensure overall product quality.
There must be a constant relay of information throughout each stage of PCB assembly from the very first input to the last output. This practice helps to lessen the amount of problems that will be encountered in later stages since each small issue can be resolved as soon as it is detected.
The assembly process
In a nutshell, the main stages in PCB assembly are applying solder paste, picking out components, placing components, soldering, and the final inspection and product testing. Not one of these processes can be removed from the line-up and meticulous monitoring must be observed to ensure quality output.
Nowadays, most PCB assembly make use of surface mount technology or SMT. The processes enumerated below likewise entail the use of components that are compatible with surface mount technology.
Printing solder paste
Unlike the application of conventional paste or glue, solder paste is deposited onto the circuit board in a way that is similar to printer’s ink. However, the solder paste is not runny or completely liquid in form. Instead, it is composed of small solder grains mixed together with flux.
The specific areas on the printed circuit board where solder must be added are commonly referred to as component pads or solder pads. A solder screen is used to designate where the solder will be deposited. This special screen is created from the same mold and files as the actual printed circuit board. This ensures that the two parts will be perfectly aligned and that the solder will only be placed on the designated areas in the right concentrations.
Picking and Placing Components
In order to ensure precision in the PCB assembly, the placement of the printed circuit board components are performed by a special machine designed to handle surface mount technology. The design information is already programmed into the machine to simplify the process of picking out and placing each component.
In addition, printed circuit boards that need components on both sides and those that need to undergo wave soldering require the use of a glue dispenser in order to hold everything in place.
Nevertheless, the glue does make future repairs more difficult to perform. For this reason, certain types of glue are made to degrade over time.
Reflow soldering is a process that melts that solder paste and permanently connects that component joints. Throughout the entire process, a controlled temperature is applied across the surface of the board. Reflow refers to the fact that the solder is heated to a certain temperature that will make the solder alloy melt or flow.
Cropping and Insertion
To ensure that the component leads fit the board, they will need to be measured and cropped if necessary. Leads that are too long will not fit securely, while leads that are too short will not be able to form a strong solder joint.
After the leads pass through the through-holes, jigs are used to hold the leads in place. Bending the ends of the leads can also lessen the stress on the component parts.
After the individual components have been placed onto the board, the entire piece must then undergo a soldering process to seal the bond. Wave soldering was a popular type of soldering used in the past although it is not commonly used for boards that use surface mount technology. Nowadays, reflow soldering is the technique of choice.
After undergoing the soldering process, the printed circuit boards must then undergo a final inspection. Automatic optical inspection machines and x-rays are used to detect loose solder balls, shorts, poor joints, solder bridges, and misplaced components.
Prior to leaving the factory, each finished board must be tested at the end of the PCB assembly process. Any boards that do not pass the company’s strict quality standards are immediately rejected and disposed of.
In order to provide this overview, the entire printed circuit board assembly was considerably simplified and summarized. The whole process itself is extremely exhaustive and detailed. Manufacturers are constantly expected to uphold high product standards and defects must be minimized if not completely eliminated. For this reason, precision machinery is often preferred over manual labor.
Today, there are normally over a hundred individual components and joints that can be found on each printed circuit board. This only means that the manufacturers have even greater pressures placed on them when it comes to ensuring quality. After all, the proper execution of each stage and process will dictate whether the products themselves will be created and perform as intended.