1. PCBA processing encompasses the entire journey of creating a finished electronic device, following a comprehensive series of steps such as PCB patterning, SMT patch processing, DIP soldering, quality inspection, testing, and assembly. Various assembly methods exist.
2. One, single-layer mixed
Typically, single-layer PCBs are used for assembly. Single-layer mixed assembly entails distributing SMT patches and DIP components on opposite sides of the PCB. The soldering surface is on one side, while the patch surface occupies the other. This assembly method employs single-layer PCBs along with wave soldering techniques. There are actually two methods of assembly:
(1) Laying first, then inserting: SMC/SMD components are mounted on the B side of the PCB, followed by crimping THC components on the A side.
(2) First inserting, then pasting: THC components are crimped on the A side first, and then SMD components are installed on the B side.
3. Two, mixed on both sides
The commonly used circuit boards for this type of PCBA processing are double-sided PCBs. SMT patches and DIP components can be mixed and placed on the same side or on both sides of the PCB. In this assembly method, there is also a distinction between laying components first and then sticking SMC/SMD later. Typically, the choice depends on the type of SMC/SMD and the size of the PCB, with the first paste method often being preferred. Two common assembly methods in this category include:
(1) SMT and DIP components coexist on the same side: SMT patch components and DIP components are located on the same side of the PCB; DIP components may appear on one or both sides. Typically, SMC/SMD is placed first, followed by DIP components.
(2) DIP components with SMT components on one or both sides: Surface mount integrated circuits (SMIC) and THT components are positioned on side A of the PCB, while SMC and small outline transistors (SOT) are found on side B.
(3) Complete surface assembly
The assembled circuit boards processed in this type of PCBA are single-layer and double-sided PCBs, containing only SMT components without THT components. As electronic devices have not yet fully transitioned to SMT at this stage, such assembly methods are rare in specific applications. There are two assembly types:
(1) Single-layer surface assembly.
(2) Double-sided surface assembly.
The characteristics of surface mount components in PCBA processing include:
1. On SMT component electrodes, some solder ends lack leads entirely, while others have very short leads; the distance between adjacent electrodes is significantly smaller than the lead spacing, with integrated circuit pins sometimes reduced to 0.3 mm; at the same integration level, SMT components occupy less area, with chip resistances and capacitances down to 0.6 mm and 0.3 mm.
2. SMT components are directly mounted on the surface of the printed circuit board, with electrodes soldered to pads on the same side. This design eliminates pads around through holes, significantly increasing wiring density.
3. During PCBA processing, surface mount technology not only influences the area occupied by wiring on the PCB but also affects the electrical characteristics of devices and components. The absence of leads or the use of short leads minimizes parasitic capacitance and inductance, thereby enhancing high-frequency performance, which is advantageous for increasing circuit frequency and speed.
4. The simple shape and robust structure, along with close proximity to the surface, improve reliability and impact resistance. During assembly, there is no lead bending or trimming required. When manufacturing the printed circuit board, the dimensions and shapes of the through holes for component placement are standardized and minimized, enabling automated placement with high efficiency, reliability, and low overall costs for mass production.
5. Traditionally in PCBA processing, surface mount components feature no leads or very short leads. These surface components can endure higher temperatures, although the pins or ends of SMT components may tolerate lower temperatures during soldering.
