Two common soldering methods in PCB: reflow soldering and wave soldering

There are two common soldering methods in PCBA processing: reflow soldering and wave soldering.

What is the function of reflow soldering, and what is the function of wave soldering? What is the difference between them?

1. Reflow soldering

Reflow soldering is the process of temporarily soldering using solder paste (a viscous mixture of powdered solder and flux) or connecting thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state to form a permanent solder joint. Heating can be accomplished by passing the assembly through a reflow oven or infrared lamp, or by soldering a single joint [unconventional] with a desoldering hot air pen.

Reflow soldering process: printed solder paste > placement components > reflow soldering >cleaning.

Common PCB Assembly line configuration

(1) Surface Mount Technology (SMT) Machine:
The SMT machine is a critical piece of equipment in automated assembly lines, used for accurately mounting surface-mount components (such as resistors, capacitors, and integrated circuits) onto PCBs. The precision and speed of the SMT machine directly impact assembly efficiency and product quality.

(2) Reflow Oven:

The reflow oven is used to heat PCBs after components are mounted, melting the solder paste and securing the components to the PCB. Precise temperature control and airflow adjustment in the reflow oven are crucial for soldering quality.

(3) Wave Soldering Machine:
The wave soldering machine is designed for through-hole component soldering. By passing the PCB over a wave of molten solder, component leads are tinned and secured to the PCB. The quality and efficiency of wave soldering are important factors in the assembly line configuration.

(4) Automated Optical Inspection (AOI) Equipment:
AOI equipment is used for real-time inspection of PCBs during assembly, ensuring the quality of component placement and soldering. By employing high-precision cameras and image processing technology, AOI can quickly identify soldering defects, component misalignments, and other issues.

(5) Manual Insertion Line:
For larger through-hole components, a manual insertion line is typically required. In this process, operators manually insert components into the designated positions on the PCB. This method is suitable for large or specially shaped components.

(6) Testing Equipment:
Testing equipment is used to conduct functional tests on assembled PCBs, ensuring all components operate correctly and the circuit connections are proper. Testing devices include functional testers and in-circuit testers.

(7)Cleaning and Packaging Equipment:
Cleaning equipment removes residues and flux from PCBs to ensure product quality. Packaging equipment is used to package tested and qualified PCBs for transportation and storage.

2. Wave soldering

Wave soldering is a batch soldering process used to printed circuit boards. The board passes through a molten solder disk where the pump produces a solder surge that looks like a standing wave. When the board is in contact with the wave, the component is soldered to the board. Wave soldering is used for through-hole printed circuit assembly and surface mounting. In the latter case, the parts are glued to the surface of the printed circuit board (PCB) by placement equipment prior to passing through the molten solder wave. Wave soldering is mainly used to solder through-hole components.

Wave soldering process: DIP>flux>preheating>wave soldering>cutting foot>check.

Through hole PCB soldering principle

The principle of PCB through-hole soldering involves melting solder at high temperatures to join metal surfaces. Under the action of flux, the oxide layers and contaminants on the metal surfaces are cleaned. The molten solder then wets the cleaned metal surfaces, undergoes diffusion, dissolves, and forms a metallurgical bond. A metallurgical intermetallic layer (weld seam) is created between the solder and the soldered metal surfaces, which solidifies upon cooling to form solder joints.

3. The difference between wave soldering and reflow soldering

(1) Wave soldering is a solder that can solder components;
Reflow soldering is a high-temperature hot air that forms a reflowed molten solder and solders components.

(2) During the reflow soldering process, there is solder on the PCB before the furnace, and only the applied solder paste is melted and soldered after soldering;
During the wave soldering process, there is no solder on the PCB in front of the furnace, the solder wave generated by the soldering machine applied the solder on the pads to be soldered to complete the soldering.

(3) Reflow soldering is suitable for SMD electronic components, and wave soldering is suitable for pin electronic components.