Exploring the Differences Between Reflow Soldering and Wave Soldering in PCB Assembly

In PCB assembly processing, wave soldering and reflow soldering are two common soldering processes, but the choice of soldering method varies depending on the scenario. What is the difference between these two welding processes?

Principles and Applications of Wave Soldering

Wave soldering is a batch PCB soldering process mainly used for soldering through-hole devices (THD). The wave soldering process consists of four steps: flux spraying, pre-coating, wave soldering, and cooling.

1.Flux is primarily used to remove oxides from the board, which results in lower surface tension, enhanced heat transmittance, and a smoother soldering process.

2. Preheating: The PCB passes through a thermal channel for preheating and activation of flux.

3. Wave soldering: As the temperature rises, the solder paste transforms into a liquid, creating a wave that allows the components to be securely bonded to the board.

4. Cooling: The wave soldering process follows the temperature curve. During the wave soldering stage, as the temperature reaches its peak, it subsequently decreases in what is known as the cooling zone.

Wave Soldering progress

Advantages and Disadvantages of wave soldering:

Advantage

Fast Welding Speed: Wave soldering is suitable for soldering large-scale, high-density electronic components because of its rapid welding speed.

Stable welding quality: The solder joints are strong and reliable, making them suitable for applications with high welding quality requirements, such as the military industry, aerospace, and other fields.

Suitable for high-reliability connections: Ideal for applications that require highly reliable connections and electrical performance.

Shortcoming

Thermal Stress Effects: Welding-induced thermal stress may affect sensitive components.

Challenges with Soldering Complex PCBs: Wave soldering may not be ideal for intricate PCBs due to the requirement of exposing the entire board to a wave of molten solder.

Principles and Applications of Reflow Soldering

Reflow soldering is a common process used to connect electronic components to PCBs. The principle involves assembling PCBs and components pre-coated with solder paste, and then using high-temperature hot air or hot plates to melt the solder paste. This process forms solder joints, completing the soldering process. Reflow soldering can achieve efficient mass production, is suitable for SMT (surface mount technology) processes, and is widely used in the manufacturing of various electronic products.

The processing flow can be divided into two types: single-sided mounting and double-sided mounting.

Single-sided mounting involves pre-coating solder paste, mounting side A, reflow soldering, and power-on testing.

Double-sided mounting: Pre-coat the A-side with solder paste → Surface Mount Technology (SMT) → Reflow soldering → Apply solder paste to the B-side → Reflow soldering → Power-on inspection

With double side mounting, top and bottom sides doesn’t use same solder paste. Solder paste with higher reflow temperature goes on the first layer. After assembly and reflow of first layer is finished, second layer uses solder paste that melts on lower temperature point. This technique or trick is used to accomplish the effect that first layer doesn’t get melted while second one is being soldered.

Advantage

Fast welding speed: Reflow soldering offers high production efficiency and is suitable for mass production.

Stable welding quality: By accurately controlling the temperature curve and welding process, stable welding quality can be achieved.

Strong adaptability: Suitable for various types of electronic assembly, including small electronic equipment, SMT assembly, and welding of precision components.

High-density component welding: This process enables the welding of high-density components, enhancing the reliability and performance of the product.

Shortcoming

High equipment cost: Special equipment and process control are required, leading to high costs.

High-temperature control requirements: Precise control of parameters such as temperature curve and welding atmosphere is necessary.

Thermal Sensitivity: Some components may be sensitive to heat, posing a risk of thermal damage.

Comparison between reflow soldering and wave soldering

Welding Process

Applicability

Wave soldering is suitable for soldering large-scale, high-density electronic components, such as power boards and motherboards. It is typically used in applications that require highly reliable connections and electrical performance.

wave soldering

Reflow soldering is suitable for various types of electronic assembly, including small electronic devices, SMT assembly, and soldering of precision components. It allows for more flexible production since the application of solder paste can adapt to a variety of PCB designs and component arrangements.

Reflow soldering

Welding Temperature

Wave soldering typically involves higher soldering temperatures because it requires exposing the entire PCB to waves of molten solder. This can cause thermal stress on some sensitive electronic components.

Reflow soldering temperatures are typically lower because only the solder paste and solder joints need to be heated to the melting point. This helps reduce thermal damage to components.

Control and Precision

Wave soldering is generally easier to control because soldering parameters, such as the temperature and speed of the solder wave, can be adjusted more accurately.

Reflow soldering: The control of reflow soldering is more complex because the speed of heating and cooling needs to be considered, as well as the thermal sensitivity of different components. Requires more complex equipment and control systems

In summary, reflow soldering and wave soldering are two commonly used soldering technologies in industrial electronics manufacturing, each with unique advantages and applications. In practical applications, choosing suitable welding methods according to specific requirements and component characteristics can enhance production efficiency and welding quality.