In PCBA processing, two common soldering methods are the Reflow soldering process and the Wave soldering process. So in PCBA processing, what is the role of reflow soldering, what is the role of wave soldering, and what is the difference between them?
table of Contents:
1. Introduction to reflow soldering
2. Introduction to wave soldering
3. The difference between wave soldering and reflow soldering
1. Introduction to reflow soldering
Reflow soldering technology is not unfamiliar in the field of electronic manufacturing. The components on the various boards used in our computers are soldered to the circuit board through this process. There is a heating circuit inside this equipment to heat air or nitrogen. After heating to a high enough temperature, blow it to the circuit board where the component has been attached so that the solder on both sides of the component will melt and be bonded to the motherboard. The advantage of this process is that the temperature is easy to control, oxidation can be avoided during the welding process, and the manufacturing cost is easier to control.
Reflow soldering process technology background
Due to the continuous miniaturization of electronic product PCB boards, chip components have appeared, and traditional soldering methods can no longer meet the needs. At first, only the reflow soldering process was used in the assembly of hybrid integrated circuit boards, and most of the components to be assembled and soldered were chip capacitors, chip inductors, mounted transistors, and diodes. With the development of the whole technology of PCB SMT process becoming more and more perfect, a variety of chip components (SMC) and mount devices (SMD) appear, as part of the placement technology, reflow soldering process technology and equipment have also been correspondingly developed, and its application is increasing. Widely used in almost all fields of electronic products.
Reflow soldering process
The reflow soldering process is a surface-mounted board, and its process is more complicated, which can be divided into two types: single-sided mounting and double-sided mounting.
Pre-coated solder paste → SMT (divided into manual placement and automatic machine placement) → Reflow soldering → Inspection and electrical test
Pre-coated solder paste on A side → SMT (divided into manual placement and automatic machine placement) → Reflow soldering → Pre-coated solder paste on side B → SMT (divided into manual placement and automatic machine placement) → Reflow soldering → Inspection and electrical test
2. Introduction to wave soldering
Wave soldering is to make the soldering surface of the plug-in board directly contact the high-temperature liquid tin to achieve the purpose of soldering. The high-temperature liquid tin maintains an inclined plane, and a special device makes the liquid tin form a wave-like phenomenon, so it is called “wave soldering.” The main material is solder bars.
Wave soldering process
The wave soldering process refers to the melted solder (lead-tin alloy) sprayed into the solder wave crest required by design through an electric pump or an electromagnetic pump. It can also be formed by injecting nitrogen into the solder pool so that the components are pre-installed. The printed circuit board realizes the soft soldering of the mechanical and electrical connection between the solder end of the component or the pin and the printed board pad through the solder wave.
After the circuit board enters the wave soldering machine through the conveyor belt, it will pass through a certain form of flux coating device, where the flux is applied to the circuit board by wave, foaming, or spraying. Since most fluxes must reach and maintain an activation temperature during soldering to ensure complete wetting of the solder joints, the circuit board must pass through a preheating zone before entering the wave trough. The preheating after the flux coating can gradually increase the temperature of the PCB and activate the flux. This process can also reduce the thermal shock generated when the assembly enters the wave crest. It can also be used to evaporate all the moisture that may be absorbed or the carrier solvent that dilutes the flux. If these things are not removed, they will boil at the peak of the wave and cause the solder to splash or generate steam to stay in the solder to form hollow Solder joints or blisters. In addition, due to the larger heat capacity of double-sided and multi-layer boards, they require a higher preheating temperature than single-sided boards.
At present, wave soldering machines basically use thermal radiation for preheating. The most commonly used wave soldering preheating methods include forced hot air convection, electric heating plate convection, electric heating rod heating, and infrared heating. Among these methods, forced hot air convection is generally considered to be the most effective heat transfer method for wave soldering machines in most processes. After preheating, the circuit board is welded with a single wave (λ wave) or double wave (spoiler wave and λ wave). For perforated components, a single wave is sufficient. When the circuit board enters the wave crest, the direction of solder flow is opposite to the traveling direction of the board, which can generate eddy currents around the component pins. This is like a kind of scrubbing, which removes all the flux and the residue of the oxide film on it, and wetting is formed when the solder joint reaches the wetting temperature.
For hybrid technology assemblies, turbulence waves are generally used in front of the lambda wave. This wave is relatively narrow and has a high vertical pressure when disturbed, which allows the solder to penetrate well between the compact pin and the surface mount component (SMD) pad, and then use the lambda wave to complete the formation of the solder joint. Before any assessment of future equipment and suppliers, it is necessary to determine all the technical specifications of the board to be soldered with wave crest because these can determine the performance of the required machine.
3.The difference between the Wave soldering process and the Reflow soldering process
The reflow soldering process is to remelt the solder paste pre-distributed on the printed board pad to realize the mechanical and electrical connection between the solder end of the surface mount component or the pin and the printed board pad.
Wave soldering has a new soldering process with people’s awareness of environmental protection. In the past, the tin-lead alloy was used, but lead is a heavy metal that can cause great harm to the human body. So now there is the production of lead technology. It uses *tin-silver-copper alloy and special flux, and the welding temperature requires higher and higher preheating temperature. It is also necessary to set up a cooling zone workstation after the PCB board passes through the welding zone. This is to prevent thermal shock. On the other hand, if there is ICT, it will affect the detection.
Wave soldering can basically be interpreted as: it is different from reflow soldering for the soldering of slightly larger and smaller components. However, reflow soldering heats the board and components, which is actually to liquefy the solder paste that was originally brushed on. , In order to achieve the purpose of connecting the components with the board.
1. Reflow soldering passes through the preheating zone, reflowing zone, and cooling zone. In addition, wave soldering is suitable for manual boards and dispensing boards, and all components are required to be heat-resistant. The surface of the wave must not have components that used to be solder paste in the PCB smt process. The solder pasteboard in the PCB smt process can only be used. Reflow soldering, not wave soldering.
2, Wave soldering process is to melt the tin bar into a liquid through the tin bath, use the motor to stir to form a wave so that the PCB and the parts are welded together, generally used in the soldering of the hand plug-in and the glue board in the PCB smt process. Reflow soldering is mainly used in the SMT industry. It uses hot air or other heat radiation to melt the solder paste printed on the PCB and solder the parts.
3. The process is different: wave soldering must first spray flux and then go through preheating, soldering, and cooling zones.
Wave soldering is mainly used for soldering plug-ins; reflow soldering is mainly used for soldering chip components.
1. Wave soldering is to melt the tin bar into a liquid through a tin bath and use the motor to stir to form a wave so that the PCB and the parts can be welded together. It is generally used for the soldering of hand plug-ins and the glue board of SMT. The Reflow soldering process is mainly used in the SMT industry. It uses hot air or other heat radiation to melt the solder paste printed on the PCB and solder the parts.
2. Different processes: The wave soldering process must spray flux first and then go through preheating, welding, and cooling zones. The reflow soldering passes through the preheating zone, reflowing zone, and cooling zone. In addition, wave soldering is suitable for manual boards and dispensing boards, and all components are required to be heat-resistant. The surface of the wave must not have components that used to be SMT solder paste. The solder pasteboard in the PCB smt process can only be reflow soldered. Do not use wave soldering.