Wave Soldering: Exploring the Process and Technology in Depth

Introduction

Wave soldering is a highly efficient soldering method that plays a pivotal role in the assembly process of hundreds of electronic components onto Printed Circuit Boards (PCBs). Developed by the German inventor Albert Hanson, this technique has revolutionized the manufacturing industry by simplifying and automating the soldering process. This article delves deeper into the intricacies of wave soldering, providing a comprehensive understanding of its principles, steps, equipment, and its advantages and disadvantages in modern PCB assembly.

The Historical Context

To appreciate the significance of wave soldering, it is essential to acknowledge its historical context. Soldering, as a method of joining metals, has been practiced since the discovery of tin, a crucial component of soldering paste. However, the advent of PCBs brought about new challenges in soldering numerous electronic components onto a single board efficiently. This challenge prompted Albert Hanson to pioneer the concept of a multi-layered flat structure, which included an insulating layer and foil conductors.

Hanson’s innovative approach also introduced the concept of drilling holes in the board, akin to the through-hole assembly technique used for mounting Dual In-Line Package (DIP) components today. This development led to manufacturing components in through-hole DIP packages, making it more convenient to apply solder paste to the entire board at once. Thus, the foundation for wave soldering was laid, where an entire board is exposed to a wave of molten solder.

Wave Soldering Process Steps

The wave soldering process comprises five fundamental steps: solder melting, component cleaning, PCB placement, soldering, and cleaning. Each step plays a crucial role in ensuring the quality and reliability of the solder joints.

Step 1: Solder Melting

Central to the wave soldering process is the precise control of the solder reservoir’s temperature, typically ranging from 180 to 450°C, depending on the solder type and machine model. This temperature control is paramount, as it ensures the solder reaches its optimal state, guaranteeing purity and effectiveness. Maintaining accurate temperature control is critical for achieving consistency, smoothness, and superior soldering results throughout the process.

Step 2: Components Cleaning

During this critical step, components undergo meticulous cleaning to remove any oxide layers. The presence of oxide layers can compromise soldering quality, making it imperative to address them promptly. To aid in this cleaning process and enhance solder wetting, a specialized chemical called flux is utilized. PCB flux is a well-engineered blend of base materials and activators designed to remove oxides from metal surfaces and promote superior solder wetting.

Step 3: PCB Placement

Precise positioning and securing of components onto the circuit board are essential in this step. Assembled boards are carefully placed within the machine, ensuring precise alignment with the conveyor belt at a 0° angle. Sturdy metal clasps hold the circuit board securely in place throughout the soldering process, ensuring optimal soldering results by maintaining the board’s position and alignment.

Step 4: Soldering

This phase is the heart of the soldering process, where the objective of effectively soldering the PCB components onto the circuit board is achieved. The conveyor belt steadily propels the board forward, bringing it closer to the solder pan. Controlling the conveyor belt’s speed is crucial, as a slow and deliberate movement allows excess solder to flow back into the solder bath. This deliberate pace promotes thorough solder coverage, ensuring secure and reliable connections.

Step 5: Cleaning

The final step focuses on the cleaning and refinement of the product. A meticulous cleaning procedure is employed to ensure the circuit board is free from residual flux. Various solvents and deionized water are used to wash the board thoroughly, removing any remaining flux residues. Isopropyl alcohol, due to its affordability and non-toxic nature, is a commonly preferred solvent for this task.

Working Principle of Wave Soldering Systems

Selecting the right PCBA service provider is crucial, as different projects may have varying requirements. Understanding the equipment capabilities of the chosen provider is essential. For projects involving Surface Mount Technology (SMT) assembly, it is vital to assess the reflow equipment. Pay attention to the number of temperature zones available in their reflow machines. When dealing with through-hole components, inquire if the PCBA company offers fully automatic assembly capabilities.

Key Components of Wave Soldering Systems

Flux Sprayer：The spray fluxing system is pivotal in the PCB assembly process. It accurately applies wave soldering flux to the designated areas, primarily targeting the plated holes of the circuit board. Additionally, it ensures precise flux application regardless of the board’s width, thickness, or hole diameter. A high-quality fluxing system is designed to excel in achieving these objectives, promoting proper solder wetting and ensuring robust solder joints.

Preheating Pad：While wave soldering can be performed without preheating, it significantly impacts the process duration. Preheating enhances flux activity by evaporating the solvent component, increasing flux effectiveness and promoting reliable solder joint formation. Furthermore, preheating minimizes the formation of solder balls, prevents thermal impact on the PCB, and facilitates the soldering of Dual In-Line Package (DIP) components.

Pump：The linear motor pump in wave soldering devices incorporates multiple pumping channels arranged in a parallel and spaced configuration. This design ensures uniform pumping performance and consistent pressure distribution, resulting in a homogeneous solder wave. The precise configuration and alignment of the pumping channels eliminate chaotic solder movement, contributing to a smooth and controlled solder wave.

Pros and Cons of Wave Soldering

Advantages:

1. Lead-Free Compliance: Wave soldering is suitable for high-quality lead-free PCB assembly, ensuring compliance with RoHS regulations while improving production efficiency.
2. No Masking Required: Unlike some soldering methods, wave soldering does not require masking off areas of the circuit board that do not need soldering, saving time in the process.
3. Cost-Effective: Wave soldering often offers cost advantages compared to other soldering techniques.
4. Parameter Adjustability: Modern equipment allows for precise adjustments, ensuring consistent and reliable results.
5. Energy Efficiency: Stepper motor-driven spraying and adjustable tin spraying mouth design result in 25% less power and auxiliary material consumption year over year.
6. Precise Control: Closed-loop control of the transport system, precise preheating, and welding time control contribute to high-quality solder joints.
7. Minimal Tin Dross Oxidation: Near the crest of a flat-flow wave, very little tin dross oxidation occurs, leading to flawless solder joints.

Disadvantages:

1. Limited Applicability to SMD Components: Wave soldering is better suited for through-hole components with larger lead spacing, making it challenging to achieve reliable solder connections with Surface Mount Device (SMD) components.
2. Potential Component Damage: SMD components, particularly temperature-sensitive ICs, can be susceptible to damage when exposed to high temperatures during wave soldering, potentially leading to functionality issues or permanent damage.
3. Dominance of SMT: As electronic components continue to shrink in size, Surface Mount Technology (SMT) dominates the industry due to its efficiency in handling smaller components.

Conclusion

Wave soldering, a technology born out of the necessity to streamline PCB assembly, has evolved into a highly efficient and precise soldering method. Understanding its principles, steps, and the role of equipment components is essential for achieving consistent and reliable soldering results. While wave soldering has its advantages, particularly in lead-free compliance and cost-effectiveness, it may not be suitable for all types of components, especially the smaller and more densely packed Surface Mount Device (SMD) components. As technology continues to advance, the PCB assembly industry will adapt to meet the demands of miniaturization and precision soldering.