SMT Reflow Soldering Technology: Overview, Selection, Evaluation, and Brand Comparison
Jan 04, 2026
(III) Equipment Performance Evaluation
V. Comparison of Different Brands of SMT Reflow Soldering Machines
2. HELLER (USA)
3. REHM (Germany)
4. BTU (USA)
(II) Domestic well-known brands
I. Introduction
In the field of modern electronics manufacturing, Surface Mount Technology (SMT) plays an extremely important role. SMT is a circuit assembly technology that directly mounts leadless or short-leaded surface mount components (SMC/SMD) onto the surface of a printed circuit board (PCB) or other substrate, and then solders them using methods such as reflow soldering or wave soldering. Reflow soldering, as a critical link in the SMT process, directly affects the performance and lifespan of electronic products. It achieves the mechanical and electrical connection between the solder terminals or leads of surface mount components and the solder pads of the printed circuit board by remelting the paste-like solder paste pre-applied to the solder pads. Due to the widespread application and continuous development of electronic products, in-depth research and rational application of SMT reflow soldering technology are of great significance.
II. SMT Reflow Soldering Process and Principles
(I) Working Process The SMT reflow soldering process includes four main zones.
Preheating Zone In the preheating zone, the PCB and components are preheated, and the solvent and gases in the solder paste are evaporated. During this process, the flux wets the solder pads, component terminals, and leads, and the solder paste softens and collapses, covering the solder pads to isolate oxygen. According to relevant research, when processing temperature-sensitive components, the setting of the preheating zone can effectively prevent component damage caused by sudden high temperatures.
Soaking Zone (Activation Zone) The function of the soaking zone is to fully preheat the PCB and components, preventing the solder paste from splashing due to sudden high-temperature melting, thus avoiding poor soldering.
Soldering Zone In the soldering zone, the solder in the solder paste melts the metal powder and wets the solder pads and component terminals and leads. The liquid solder surface appears in a concave form and generates suction, placing the components above the concave solder, and then cooling and solidifying to complete the soldering. Cooling Zone The cooling zone allows the solder joints to solidify and crystallize, resulting in bright solder joints, but at the same time, the solder joints begin to oxidize upon contact with air. Reflow soldering technology plays a decisive role in the quality and reliability of solder joints, which in turn directly affects the performance and lifespan of electronic products, and is crucial in different SMT production stages. For example, in mobile phone motherboard manufacturing, poor reflow soldering can lead to problems such as poor mobile phone signal transmission.
III. Key Factors in SMT Reflow Soldering Equipment Selection
(I) Production Scale and Capacity Requirements
Small-scale production: For small-scale production with low product output, high flexibility in welding equipment is required, and relatively low equipment prices are preferable. For example, small electronic equipment repair shops or small studios engaged in simple electronic product development may find small reflow soldering equipment sufficient. Such small equipment may have fewer temperature zones and relatively lower production efficiency, but the investment cost is also low.
Large-scale production: In large-scale production, it is necessary to ensure continuous and stable production of a large number of products, such as large electronic product manufacturing companies producing computer motherboards and mobile phone motherboards. At this time, the capacity of the equipment should be the main consideration. Large multi-zone reflow soldering equipment has strong thermal compensation capabilities. Regardless of the number of PCBs in the furnace or the thickness of the fixtures, the furnace temperature fluctuations are very small, ensuring a constant furnace temperature, thereby ensuring the efficiency and consistency of product quality in large-scale production. However, this type of equipment is usually more expensive.
(II) Product Size and Shape Adaptability
Small-sized and regularly shaped products: If the product is small in size and regular in shape, the requirements for the furnace size and conveying device of the reflow soldering equipment are relatively low.
Large-sized or irregularly shaped products: If the product is large in size (such as a large industrial control board) or has a special irregular shape, the furnace of the equipment needs to have enough space to accommodate the product, and there must be a suitable conveying device (such as a mesh belt or guide rail) to ensure that the product can smoothly pass through the various temperature zones of the reflow soldering process. Some equipment uses two-stage hardened narrow guide rails, which can be adjusted synchronously with three lead screws at the front, middle, and back, adapting to products of different sizes, while reducing the impact of deformation caused by thermal expansion on the product; other equipment uses widened protruding guide rails, which can reduce the impact of heat absorption and release from the guide rails on the temperature of both sides of the PCB, completely eliminating the possibility of jamming, which is better suited for products of different sizes and shapes.
(III) Adaptability to Welding Materials
Solder paste: Solder paste is an important welding material in the reflow soldering process, consisting of a uniform mixture of alloy powder (particles) and a paste-like flux carrier. The reflow soldering equipment must be compatible with different types of solder paste (such as leaded and lead-free), different component ratios, different alloy particle shapes and sizes, and different viscosities. For example, in the soldering of some high-precision, narrow-pitch electronic products, solder paste with alloy powder particle shapes suitable for narrow-pitch soldering is required. In this case, the reflow soldering equipment must ensure the effectiveness of this solder paste during the soldering process. In addition, solder paste is generally stored in refrigeration, and the lid should only be opened after it has returned to room temperature. Special attention should be paid to avoiding moisture ingress into the solder paste due to temperature differences, and the equipment must also consider these requirements for solder paste usage conditions.
Other soldering materials: In addition to solder paste, other soldering materials such as solder balls and solder wires are also used in some special SMT processes, and the equipment must be able to adapt to the soldering requirements of these different soldering materials.
(IV) Temperature Control Accuracy
The temperature in the preheating zone plays a crucial role in all areas of the reflow soldering process. In the preheating zone, if the temperature rises too quickly (exceeding 4°C/s is usually considered too fast), the circuit board and components may be damaged by thermal shock; if it is too slow, the solvent will not evaporate sufficiently, affecting the soldering quality. A typical heating rate of 2°C/s is more suitable.
Reflow zone: In the reflow zone, the temperature needs to reach above the melting point of the solder paste. Different solder pastes have different melting points (e.g., leaded and lead-free solder pastes have different melting points), requiring the equipment to accurately control the temperature to the appropriate peak temperature. Cooling zone: In the cooling zone, cooling needs to be done as quickly as possible (e.g., for leaded soldering, the temperature drop slope should be less than 4 degrees per second), and the equipment must be able to control the cooling efficiency to obtain bright, well-shaped solder joints with a low contact angle. The uniformity of the air temperature in the equipment is also very important. If the temperature difference between each point in each temperature zone is greater than 5°C, then determining the production curve will be more difficult, and it may even be impossible to measure a suitable temperature curve for production. In addition, a large temperature difference between the set temperature and the actual measured temperature on the PCB indicates low heat transfer efficiency, which affects product quality and increases power consumption. This should be a key consideration in equipment selection. For example, some excellent equipment uses 8MM imported American aluminum plates with heat storage rectification technology to achieve high-precision control of air temperature ≤ ±1.5°C. (V) Equipment Maintainability
Good maintainability includes ease of cleaning and maintenance, such as the effectiveness of the flux recovery system. Equipment with flux recovery ports in each temperature zone and at the front and rear exits can keep the furnace clean, saving maintenance time.
Troubleshooting: The rationality of the equipment's structural design is also crucial for troubleshooting. If the internal mechanical structure (such as chains, guide rails, etc.) is prone to wear or deformation, it will not only affect normal production but also increase maintenance costs and difficulty. In addition, easily damaged parts that are easy to replace and have a certain degree of standardization are also very important for equipment maintenance.
IV. SMT Reflow Soldering Evaluation Indicators and Methods
(I) Appearance Evaluation Indicators and Detection Methods
Solder Joint Shape: A normal solder joint should be crescent-shaped, with good solder flow, a complete and smooth, bright surface. A universal projector or 10x magnifying glass can be used for inspection. If the solder joint shape is irregular, such as exhibiting spikes or flatness, it may be caused by factors such as the temperature profile or solder paste quantity during the reflow soldering process.
Short Circuit: Check for any accidental connections between solder joints; bridging is a soldering defect that can cause short circuits. A magnifying glass or other tools can be used for inspection. Bridging may be caused by excessive solder paste, poor temperature control, etc. Wetting State: The solder should completely cover the solder pad and the soldered part of the lead, with a contact angle preferably less than 20° (usually less than 30° is the standard, and the maximum should not exceed 60°). If the contact angle is too large, it indicates poor wetting, which may be due to incomplete removal of the oxide layer (flux failure or poor surface treatment before soldering), insufficient temperature, etc.
(II) Electrical Performance Detection Indicators and Methods
Conductivity Detection: This item checks whether the circuit connected by the solder joint is conducting properly, and whether there are factors such as tiny cracks, tin erosion of extremely fine wires, and rosin adhesion that lead to poor conductivity. Professional electrical testing instruments can be used to measure electrical parameters such as resistance between two points without power. Abnormal resistance values may indicate poor conductivity.
Component Thermal Damage Detection: This item checks whether components fail due to overheating during the soldering process, or whether components are corroded or deteriorated due to decomposition gases from the flux. The method typically involves testing the product under load conditions by applying power and monitoring the performance parameters of the components during operation, such as whether the power increases abnormally or the current fluctuates abnormally. By comparing these observations with the normal operating parameter range of the components, it can be determined whether thermal damage has occurred. For example, if a power amplifier shows a significant increase in power after soldering, it may indicate that the high temperature or prolonged soldering time during the reflow soldering process has damaged the internal circuitry.
(III) Equipment Performance Evaluation
1 Temperature Control Performance Evaluation
1) Temperature Uniformity: This examines the temperature difference between different points in each temperature zone of the reflow soldering machine. If the temperature difference is large (e.g., greater than 5°C), determining a suitable production curve becomes difficult, and it may be impossible to find a temperature curve suitable for production. For example, some equipment has large temperature zones, and different heating and air circulation methods can lead to uneven temperature distribution within the zone. Traditional infrared radiation reflow soldering, which relies solely on infrared heat sources for heating, results in different heat absorption rates for different materials and colors. Without hot air assistance, this can easily cause temperature differences within the temperature zone.
2) Temperature Difference between Set Temperature and Actual Measured Temperature on the PCB: This represents the heat transfer efficiency and is a comprehensive reflection of product quality and power consumption. If the heat transfer efficiency is poor, the set temperature in the soldering zone needs to be higher, and it may even be necessary to increase the number of soldering zones. Higher temperature settings can significantly damage components, affecting their lifespan and increasing heat loss. For example, some older reflow soldering equipment, due to aging heating systems and sensors, shows a large difference between the set temperature and the actual temperature on the PCB.
3) Thermal Compensation Capability: During mass production, PCBs and components carry away a large amount of heat. The ability of the reflow soldering machine to quickly provide sufficient heat to maintain a constant furnace temperature is crucial. For example, high-efficiency reflow soldering machines show very little temperature fluctuation regardless of the number of PCBs in the furnace or the thickness of the fixtures, allowing for lower alarm temperature settings; while low-efficiency reflow soldering machines require higher alarm temperature settings (typically 5-10°C on the market), otherwise the reflow soldering machine will frequently trigger alarms, preventing continuous production and affecting productivity.
4) Cooling Efficiency: This refers to the cooling rate in the cooling zone and the temperature of the PCB board at the reflow soldering machine's exit. The temperature of the PCB board at the exit should usually be less than 70°C to facilitate the board handling process. If the cooling speed is insufficient, it will result in poor solder joint solidification, potentially leading to poor solder joint appearance and mechanical properties. For example, some equipment has low cooling efficiency due to insufficient power of the cooling device.
5) Temperature drop caused by gaps between temperature zones. Severe temperature fluctuations in reflow soldering can cause significant thermal shock to the PCB board in the furnace, easily leading to delamination of the PCB and copper foil, resulting in quality problems. The maximum temperature difference achievable between preheating zones and between the preheating zone and the reflow zone, without temperature fluctuations, reflects the equipment's ability to control the temperature gradient. A large temperature difference is a guarantee for the production of double-sided surface mount products and can accommodate the production of higher-demand products.
2. Mechanical Performance Evaluation
1) Flux Recovery System: If the equipment has flux recovery ports in each temperature zone and at the front and rear exits, it can keep the furnace clean and save maintenance time. For example, some advanced equipment has special designs in the flux recovery system, making flux recovery efficient and preventing residue in the furnace.
2) Other Mechanical Components: The performance of other mechanical components such as rectifier plates, guide rails, chains, and air duct structures is also very important. Good rectifier plates can improve thermal efficiency; if the guide rails use appropriate size and materials and are reasonably designed (e.g., some equipment uses two-stage hardened narrow guide rails with unified mold installation, and front, middle, and rear three-screw synchronous width adjustment), it can improve thermal efficiency, reduce deformation, and avoid jamming; the quality and wear resistance of the chain affect equipment stability; air duct structures, such as equipment using 8MM American imported aluminum plates with heat storage rectification technology, can achieve air temperature of ≤±1.5°C, high thermal efficiency, fast thermal compensation, and more uniform temperature distribution, with smaller temperature deviations at various points on the PCB surface.
V. Comparison of Different Brands of SMT Reflow Soldering Machines
(I) Internationally Renowned Brands
1 Kurtz Ersa (Germany)
1) Company Overview: Founded in 1779 in Germany, it is a global supplier of large-scale electronic assembly SMT welding equipment and tools, with a profound historical background and technological accumulation. 2) Application Areas: Their products are used in various high-end manufacturing industries, including aerospace, 5G communication, autonomous driving, industrial control, and artificial intelligence. They are a core supplier to many well-known companies worldwide, providing customized solutions for their production processes. For example, in the aerospace field, where the reliability of electronic products is extremely high, their reflow soldering equipment can meet the requirements for high-reliability solder joints.
3) Product Features: They are a technology leader in selective wave soldering and reflow soldering equipment, capable of handling complex soldering needs in high-end manufacturing.
2. HELLER (USA)
1) Company Overview: Founded in 1960 in the United States, specializing in thermal process solutions for SMT, electronic assembly, power device assembly, and advanced semiconductor packaging industries.
2) Application Areas: Provides solutions to global electronic manufacturers and advanced semiconductor packaging companies. Especially in the semiconductor industry, its reflow soldering equipment can meet the requirements for high-precision soldering. For example, for soldering the tiny pins of semiconductor chips, it can precisely control parameters such as temperature and soldering time to prevent chip damage while maintaining excellent soldering results.
3) Product Features: A market leader in reflow soldering furnace technology, flux-free reflow soldering technology, and curing furnace technology, and pioneered convection reflow soldering technology in the 1980s.
3. REHM (Germany)
1) Company Overview: Founded in 1990 in Germany, dedicated to providing efficient and energy-saving production equipment for the electronics and photovoltaic industries.
2) Application Areas: Established an Asian production base in Dongguan in 2007, providing comprehensive services to the Asian market, addressing the needs of the automotive electronics, consumer electronics, medical, and military electronics industries. For example, in the automotive electronics field, its reflow soldering equipment helps produce high-precision, high-reliability automotive electronic control units and other components.
3) Product Features: Products cover reflow soldering, vapor phase soldering, drying and protective coating systems, and various customized systems related to soldering, coating, and curing.
4. BTU (USA)
1) Company Overview: Founded in 1950 in the United States, mainly providing thermal processing equipment for the electronic manufacturing market and the alternative energy generation market. 2) The main products in the application field include various reflow ovens, atmospheric furnaces, drying ovens, etc. The equipment and technology are widely used in fields such as solar cell manufacturing, nuclear fuel, fuel cell manufacturing, printed circuit board assembly, and semiconductor packaging production. The sales and service network covers more than 30 countries and regions worldwide. For example, in solar cell manufacturing, it can meet the welding requirements of precision electronic components on solar panels, ensuring the normal power generation performance of the panels.
3) Product features: High brand recognition, reliable equipment performance, and a global sales and service network for convenient international customer support.
(II) Domestic well-known brands
Brands
1. Jintuo Co., Ltd. (Shenzhen, China)
1) Company Overview: Established in 2004, Jintuo is a Shenzhen GEM-listed company (stock code: 300400), and a supplier of intelligent equipment systems and advanced manufacturing systems integrating R&D, production, and sales.
2) Application Fields: Its products mainly include production and testing equipment for the electronics manufacturing industry, semiconductor equipment, and specialized equipment for the optoelectronic display industry, providing intelligent equipment and solutions for various electronic and optoelectronic products such as communications, mobile phones, automotive electronics, wearables, and semiconductors. For example, in mobile phone production, it can provide reflow soldering equipment suitable for welding various components such as mobile phone motherboards.
3) Product Features: As a domestic listed company, it has considerable R&D capabilities and can develop cost-effective equipment that meets the needs of the domestic market based on the requirements of domestic electronics manufacturing companies.
2. Nitto Technology (Hong Kong, China)
1) Company Overview: Founded in 1984, it is a core enterprise under Xincheng Technology Holdings.
2) Application Fields: It is committed to providing customers with complete solutions including intelligent equipment, MES manufacturing execution systems, and LOA data-driven information platforms. It has independently developed a series of products including reflow soldering, wave soldering, selective wave soldering, vertical furnaces, and printing machines. Its products are widely used in automotive electronics, electronic machinery, home appliances, and medical fields. For example, in circuit board soldering for home appliance production, its reflow soldering equipment can meet the efficiency and quality requirements for the production of a large number of home appliances.
3) Product Features: It can provide complete solutions, and in addition to the reflow soldering equipment itself, it can also provide corresponding software support for enterprise production management. In the domestic market, it has good adaptability to electronic production in different industries.
(III) Comprehensive Comparison of Domestic and International Brands
In terms of technology, internationally renowned brands (such as Kurtz Ersa from Germany and HELLER from the United States) often have a longer history of technological development and have certain technological advantages in some high-end welding technologies (such as semiconductor packaging welding technology and high-reliability welding requirements for aerospace). Although domestic brands (such as Jintuo Co., Ltd. and Nitto Technology) have developed rapidly in recent years and are gradually catching up in technology, they may still be slightly lacking in technological depth in extreme application scenarios. However, domestic brands are doing very well in meeting local needs (such as adapting to the production needs of a large number of domestic consumer electronics such as mobile phones and tablets). In terms of price, international brands are generally more expensive due to factors such as brand value and R&D costs. Domestic brands offer more competitive pricing, making them more attractive to cost-sensitive companies (such as small and medium-sized electronics manufacturers). For example, a small or medium-sized company producing ordinary consumer electronics might face significant budget pressure if it purchases international brand reflow soldering equipment, while domestic brands with equivalent functionality would be much cheaper. Regarding service, international brands' service networks are mainly concentrated in key regions and areas with a high concentration of high-end customers. After-sales service and support for remote areas or smaller orders may not be as timely. Domestic brands, on the other hand, often have a more extensive service network within China, enabling them to respond to and meet the needs of domestic customers more quickly.