Reflow soldering and wave soldering are two common soldering methods for electronic products in the production process of electronic products. The main differences between them are: wave soldering is used for soldering plug-in circuit board, and reflow soldering is used for soldering SMT chip circuit board. Next, GrandSeed technology and Dachu share the difference between reflow soldering and wave soldering.

Video comparison of reflow and wave soldering

SMT reflow line work video

Wave soldering video

Comparison of product pictures of reflow welder and wave soldering machine

Picture of reflow welder

Pictures of wave soldering machine

Introduction of SMT reflow soldering process

SMT products have the advantages of compact structure, small volume, vibration resistance, shock resistance, high frequency characteristics and high production efficiency. SMT has played an important role in PCB assembly process.

The typical surface mounting process is divided into three steps: applying solder paste, mounting components and reflow soldering

Step 1: apply solder paste

The purpose is to evenly apply appropriate amount of solder paste on the PCB pad, so as to ensure that the solder pad corresponding to the chip components and PCB has good electrical connection and sufficient mechanical strength during reflow soldering.

Solder paste is made of alloy powder, paste flux and some additives, which has fixed viscosity and good contact characteristics. At room temperature, because the solder paste has a certain viscosity, electronic components can be pasted on the PCB pad. Generally, the components will not move when the tilt angle is not too large and there is no external force collision. When the solder paste is heated to a certain temperature, the alloy powder in the solder paste melts and flows again, and the liquid solder soaks the solder end of the components and the PCB pad, After cooling, the solder end and pad of the components are interconnected by solder, forming electrical and mechanical solder joint.

Solder paste is applied on the pad by special equipment, including GSD automatic printing machine, GSD semi-automatic printing machine, manual printing station, semi-automatic solder paste distributor, GSD solder paste mixer auxiliary equipment, etc.

The typical surface mounting process is divided into three steps: applying solder paste, mounting components and reflow soldering

Step 1: apply solder paste

The purpose is to evenly apply appropriate amount of solder paste on the PCB pad, so as to ensure that the solder pad corresponding to the chip components and PCB has good electrical connection and sufficient mechanical strength during reflow soldering.

Solder paste is made of alloy powder, paste flux and some additives, which has fixed viscosity and good contact characteristics. At room temperature, because the solder paste has a certain viscosity, electronic components can be pasted on the PCB pad. Generally, the components will not move when the tilt angle is not too large and there is no external force collision. When the solder paste is heated to a certain temperature, the alloy powder in the solder paste melts and flows again, and the liquid solder soaks the solder end of the components and the PCB pad, After cooling, the solder end and pad of the components are interconnected by solder, forming electrical and mechanical solder joint.

Solder paste is applied on the pad by special equipment, including GSD automatic printing machine, GSD semi-automatic printing machine, manual printing station, semi-automatic solder paste distributor, GSD solder paste mixer auxiliary equipment, etc.

The typical surface mounting process is divided into three steps: applying solder paste, mounting components and reflow soldering

Step 1: apply solder paste

The purpose is to evenly apply appropriate amount of solder paste on the PCB pad, so as to ensure that the solder pad corresponding to the chip components and PCB has good electrical connection and sufficient mechanical strength during reflow soldering.

Solder paste is made of alloy powder, paste flux and some additives, which has fixed viscosity and good contact characteristics. At room temperature, because the solder paste has a certain viscosity, electronic components can be pasted on the PCB pad. Generally, the components will not move when the tilt angle is not too large and there is no external force collision. When the solder paste is heated to a certain temperature, the alloy powder in the solder paste melts and flows again, and the liquid solder soaks the solder end of the components and the PCB pad, After cooling, the solder end and pad of the components are interconnected by solder, forming electrical and mechanical solder joint.

Solder paste is applied on the pad by special equipment, including GSD automatic printing machine, GSD semi-automatic printing machine, manual printing station, semi-automatic solder paste distributor, GSD solder paste mixer auxiliary equipment, etc.

When the PCB enters the preheating temperature range of 140 ℃ ~ 160 ℃, the solvent and gas in the solder paste evaporate. At the same time, the flux in the solder paste moistens the pad, the solder ends and pins of components, and the solder paste softens and collapses, covering the pad, isolating the pad and pins of components from oxygen; Then, when entering the welding area, the temperature rises rapidly at the standard heating rate of 2-3 ℃ per second, so that the solder paste reaches the melting state. The liquid solder is wetted, diffused, diffused and refluxed on the PCB pad, component solder end and pin to form metal compound on the bonding interface, forming solder joint; After the PCB enters the cooling zone, the solder joint solidifies.

Reflow soldering method introduction: different reflow soldering has different advantages, and the technological process is also different

Infrared reflow soldering: high radiation heat conduction efficiency, large temperature gradient, easy to control the temperature curve, easy to control the upper and lower temperature of PCB during double-sided soldering. Shadow effect, uneven temperature, easy to cause components or PCB local burn out

Hot air reflow welding: uniform convection conduction temperature, good welding quality. The temperature gradient is not easy to control

Forced hot air reflow welding: combined with the advantages of infrared and hot air stove, it can get excellent welding effect when welding products. Forced hot air reflow welding can be divided into two kinds according to its production capacity

1. Temperature zone type equipment: it is suitable for mass production, PCB board is placed on the walking belt, and it needs to pass through several fixed temperature zones in sequence. If the temperature zone is too small, there will be temperature jump phenomenon, which is not suitable for high-density assembly board welding. And it's bulky and consumes a lot of power.

2. Temperature zone small desktop equipment: small and medium batch production, rapid development, in a fixed space, the temperature changes with time according to the set conditions, easy to operate. It is not suitable for mass production

Due to the reflow process has the characteristics of "reflow" and "self positioning effect", the reflow process has relatively loose requirements on the mounting accuracy, and it is easier to realize the high automation and high speed of welding. At the same time, because of the characteristics of reflow and self positioning effect, reflow soldering process has more stringent requirements on pad design, component standardization, component end and PCB quality, solder quality and process parameter setting.

Cleaning is a process of using physical action and chemical reaction to remove pollutants and impurities on the surface of the object to be cleaned. On the use of solvent cleaning or water cleaning, must go through the surface wetting, dissolution, emulsification, saponification, etc., and by applying different ways of mechanical force to peel the dirt from the surface of the surface assembly board, and then rinse or rinse clean, then blow dry, dry or natural dry.

Reflow soldering is a key process in SMT production. Reasonable temperature curve setting is the key to ensure the quality of reflow soldering. Improper temperature curve will lead to incomplete welding, false welding, component warping, too many solder balls and other welding defects, which will affect the product quality.

SMT is a comprehensive system engineering technology, which covers substrate, design, equipment, components, assembly process, production accessories and management. SMT equipment and SMT process require stable voltage on the operation site, prevent electromagnetic interference, prevent static electricity, have good lighting and exhaust emission facilities, have special requirements for the temperature, humidity and air cleanliness of the operation environment, and the operators should also receive professional technical training.

Introduction of wave soldering method

Wave soldering refers to the soldering that melts the solder (lead tin alloy) into the solder wave required by the design through the electric pump or electromagnetic pump, so that the printed circuit board with components in advance can pass through the solder wave to realize the mechanical and electrical connection between the solder end or pin of components and the pad of printed circuit board. The wave soldering machine is mainly composed of transport belt, flux adding area, preheating area and wave soldering furnace.

The surface of the wave surface is covered by oxide skin, which almost keeps static along the whole length of the solder wave. During the wave soldering process, the PCB contacts the front surface of the tin wave, the oxide skin breaks, and the tin wave in front of PCBA is pushed forward, which indicates that the whole oxide skin and PCB move at the same speed. When PCBA enters the front (a) of the wave surface, the solder joint of the wave welder is formed, The substrate and pins are heated, and before leaving the wave surface (b), the whole PCB is immersed in solder, which is bridged by solder. However, at the moment of leaving the end of the wave, a small amount of solder adheres to the pad due to the wetting force, and due to the surface tension, there will be a small shrinkage state with the lead as the center, At this time, the wetting force between solder and pad is greater than the cohesive force between two pads. As a result, a full and round solder joint will be formed, and the excess solder leaving the tail of the wave will fall back into the tin pot due to gravity.

Wave soldering process: insert the component into the corresponding component hole → precoat flux → pre dry (temperature 90-1000c, length 1-1.2m) → wave soldering (220-2400c) → cut off redundant plug-in pins → check.

The difference between wave soldering and reflow soldering is 1

Reflow soldering process is to re melt the paste solder which is pre distributed to the PCB pad to realize the mechanical and electrical soldering between the solder end or pin of surface assembly components and the PCB pad.

With the enhancement of people's awareness of environmental protection, wave soldering has a new welding process. In the past, tin lead alloy was used, but lead is a heavy metal, which is harmful to human body. So now there's the lead process. It uses * Sn Ag Cu alloy * and special flux, and requires higher welding temperature, higher preheating temperature. In addition, a cooling area workstation should be set up after the PCB passes through the welding area. This is to prevent thermal shock. On the other hand, if there is ICT, it will affect the detection

Wave soldering can be basically interpreted as soldering for slightly larger and relatively small components. The difference between wave soldering and reflow soldering is here. Reflow soldering heats up the board and components. In fact, it liquefies the original solder paste, so as to achieve the purpose of connecting the components and the board

1. Reflow soldering passes through preheating zone, reflow zone and cooling zone. In addition, wave soldering is suitable for hand inserted boards and spot glued boards, and all components are required to be heat-resistant. Components with SMT solder paste can not be used on the wave passing surface. SMT solder paste boards can only be reflow soldered, and wave soldering is not allowed.

2. 
   

2. Wave soldering is to dissolve the tin bar into liquid through the tin bath, and stir it with the motor to form a wave, so that PCB and parts can be welded together. It is generally used in hand plug-in welding and SMT glue board. Reflow soldering is mainly used in SMT industry, which melts the solder paste printed on PCB and welds the parts through hot air or other heat radiation conduction.

3. Different process: wave soldering should spray flux first, then preheat, weld and cool zone.

The difference between wave soldering and reflow soldering 2: wave soldering is mainly used for welding plug-ins; Reflow soldering is mainly used to solder SMD components

1. Wave soldering is to dissolve the tin bar into liquid through the tin bath, and use the motor to stir to form a wave, so that PCB and parts can be welded together. It is generally used in hand plug-in welding and SMT glue board. Reflow soldering is mainly used in SMT industry. It melts the solder paste printed on PCB and welds the parts by hot air or other heat radiation conduction.

2. Different process: spray flux first, then preheat, weld and cool zone. Reflow soldering passes through preheating zone, reflow zone and cooling zone. In addition, wave soldering is suitable for hand inserted boards and spot glued boards, and all components are required to be heat-resistant. Components with SMT solder paste can not be used on the surface of wave passing. SMT solder paste boards can only be reflow soldering, and wave soldering is not allowed.