What Is Wave Soldering?

Introduction

In the fields of electronics manufacturing and SMT, the assembly quality of PCBs directly determines the lifespan and reliability of the end product. Although Surface Mount Technology dominates modern high-density electronic products, Through-Hole Technology (THT) remains indispensable when dealing with high-power components, connectors, capacitors, and pin-type components that require high mechanical strength.

Wave soldering machine is an automated soldering process that creates a continuous and stable liquid wave of molten solder, allowing the soldered surface of the PCB to come into contact with the solder and rapidly complete batch solder joint connections. It is commonly used for the efficient assembly of through-hole components (THT), short-lead through-hole components, and certain mixed-assembly PCBs combining SMT and THT components.

It is important to emphasize that wave soldering is not simply a matter of "dipping the PCB in solder." In actual production, soldering quality is influenced by the combined effects of multiple process parameters, including the uniformity of flux application, the activation temperature in the preheating zone, the wave height and flow rate, the solder alloy temperature, the conveyor angular velocity, and the thermal design of the PCB underside. This article will provide an in-depth analysis of the working principles, process flow, and differences between wave soldering and reflow soldering oven, and offer a selection guide based on technical parameters.

What Is Wave Soldering?

1. Definition of Wave Soldering Machine

Wave soldering refers to the process of using an electric or electromagnetic pump to spray molten, liquid solder (such as lead-free tin alloys) into a specific wave-like pattern. When a PCB assembled with components passes through this wave at a specific angle and conveyor speed, the pads on the underside of the PCB and the component leads are heated and wetted by the solder; after leaving the wave and cooling, a strong electrical and mechanical connection is formed.

The core value of a wave soldering system lies in its continuous automation and high efficiency. By sequencing flux application, PCB preheating, and dual wave soldering zones along the same conveyor track, the system achieves high consistency in batch soldering of components.

2. For which types of PCBs is wave soldering primarily used?

Wave soldering is primarily used in the manufacturing of the following types of PCBs:

• Through-hole component (THT) PCBs: Traditional electronic devices, power modules, home appliance control boards, etc.
• Short-lead through-hole component PCBs: Assembly of pin-type components that require no lead trimming or only minimal lead shortening.
• SMT + THT mixed-assembly PCBs: SMT surface-mount components (such as 0805 and 0603 resistors, capacitors, and SOP ICs) are placed via dispensing on the bottom layer, while THT components are inserted on the top layer; the entire assembly is soldered in a single wave soldering pass.
• High-reliability PCB soldering in bulk: Industrial-grade control boards requiring high through-hole fill rates.

How Does Wave Soldering Work?

Wave soldering equipment consists of multiple process stages. The PCB, held by titanium claws or secured to a carrier, is transported along a predetermined route via a chain conveyor system to complete continuous soldering.

1. PCB Entry into the Wave Soldering Machine

The PCB is fed into the machine by an inlet transfer device at a preset angle (typically 4°–7°). Titanium alloy grippers (titanium grippers) clamp the PCB's edges and transport it at a constant speed (e.g., 0–1.2 m/min) through each functional zone; the angle is designed to facilitate the drainage of excess flux and solder.

2. Flux Spraying

Prior to soldering, flux is atomized inside the spray chamber using compressed air and evenly sprayed onto the underside of the PCB.

• Key functions of flux:
• Removes oxidation layers from the surfaces of PCB copper foil pads and component leads.
• Prevents secondary oxidation of the solder and copper surfaces at high temperatures.
• Reduces the surface tension of molten solder, improving wetting performance.
• Key Control Points: The amount of flux must be precise. Insufficient application can easily lead to cold solder joints or solder bridges; excessive application can result in residue contaminating equipment and reducing the board's insulation resistance.

3. PCB Preheating

After flux application, the PCB immediately enters the preheating zone.

Main objectives of preheating:

• Activate the flux: Enable the chemical activators in the flux to fully exert their deoxidizing effect at a specific temperature.
• Evaporate volatiles: Vaporize the solvents in the flux to prevent boiling, spattering, or porosity when the PCB enters the 250°C solder pot.
• Reduce thermal shock: Preheat the entire PCB and components to 90°C–130°C to minimize PCB warping and thermal cracking damage to components caused by rapid heating.

4. PCB Passes Through the First and Second Wave Peaks

Modern lead-free wave soldering generally employs double-wave technology:

First Wave

• Characteristics and Function: Narrow wave amplitude, high flow velocity, and strong impact force.
• Issues Addressed: The high-velocity solder penetrates deeply into dense pin gaps, overcoming solder defects such as missed solder joints and cold solder joints caused by bubbles or the component shadow effect.

Second Wave

• Characteristics and Function: Wide, flat wave surface with a slow, stable flow rate.
• Issues Addressed: Provides smooth secondary wetting for the heated solder joints, effectively correcting defects such as spikes and bridges left by the first wave, resulting in smooth and full solder joints.

5. Cooling and Soldering Completion

After leaving the wave, the PCB enters the cooling section. A moderate cooling rate promotes rapid solidification of the solder and prevents the formation of an excessively thick intermetallic compound (IMC) layer between copper and tin, thereby producing qualified solder joints with high mechanical strength and excellent fatigue resistance.

What is the complete process flow for wave soldering?

The complete standard process sequence for wave soldering is as follows:

PCB Loading ---> Flux Spraying ---> Preheating Zone Activation ---> First Wave (Agitation) ---> Second Wave (Smoothing) ---> Cooling and Solidification ---> PCB Unloading/Inspection

1. Why does wave soldering require strict control of the transfer speed?

The transfer speed directly determines the dwell time of the PCB in each temperature zone and the contact time with the solder.

• Excessively fast speed: Insufficient preheating time prevents the flux from activating, subjects the PCB to thermal shock, and results in contact time in the solder wave of less than 2 seconds, which can easily lead to issues such as cold solder joints, thin solder coverage, and low via fill rates.
• Too slow: The PCB remains in the high-temperature solder wave for too long, which can easily lead to thermal warping of the board, yellowing of the substrate, thermal damage to components, and copper wicking at solder joints.
• Standard control range: Industrial-grade equipment typically maintains a stable speed of 0.8–1.2 m/min to keep the dwell time within the optimal process window of 3–5 seconds.

What is the difference between wave soldering and reflow soldering?

In SMT placement and PCB assembly, wave soldering machine and reflow soldering oven are two core automated soldering processes. The fundamental differences between them are as follows:

When to Choose Wave Soldering?

The PCB contains a large number of through-hole components, connectors, electrolytic capacitors, relays, etc.

Power supply and industrial control products that require high mechanical strength and complete solder filling of through-holes (PTH).

When to Choose Reflow Soldering?

PCBs consisting almost entirely of high-density SMT components (e.g., cell phone motherboards, graphics cards, servo drives).

Can Mixed-Assembly PCBs Use Both Reflow and Wave Soldering Simultaneously?

Yes, and this is the most common production combination in EMS (Electronic Manufacturing Services) facilities.

• Phase 1 (SMT top side): Solder paste printing → Component placement → Reflow soldering.
• Phase 2 (DIP bottom side and through-holes): Flip the board for dispensing/inserting THT components → Wave soldering.

What key parameters should be considered when purchasing a wave soldering machine?

1. Maximum PCB Width

This determines the equipment's processing limits. It must match the factory's current and future planned PCB specifications. For example, the NeoDen ND250 supports a maximum PCB width of 250 mm and is specifically designed for small-to-medium-sized boards and high-precision mixed-assembly boards.

2. Preheating Length and Sections

Lead-free solder has a high melting point (e.g., SAC305 has a melting point of approximately 217°C–221°C), requiring the equipment to have strong preheating capabilities. The longer the preheating zone and the greater the number of sections (e.g., 800 mm with 2 independently temperature-controlled sections), the more uniform the heat distribution across the PCB, which better ensures soldering consistency at high transfer speeds.

3. Wave Type & Height

A double-wave configuration is recommended for lead-free processes. Additionally, the wave height must be precisely adjustable (e.g., up to 12 mm) to accommodate different lead lengths and carrier thicknesses.

4. Transfer Speed Range

A drive system capable of stepless speed adjustment from 0–1.2 m/min-or even a wider range-provides engineers with greater flexibility for debugging temperature profiles.

5. Temperature Control System

The solder pot and preheating zone should employ a PID + SSR (Solid-State Relay) closed-loop control mode. PID provides real-time correction for temperature fluctuations, ensuring the solder pot temperature control accuracy remains within ±1°C and preventing solder overheating and oxidation or solder bridging caused by excessively low temperatures.

What production scenarios is the NeoDen ND250 wave soldering machine suitable for?

As a control-class machine specifically designed by NeoDen for small-to-medium batch production, prototype development, and cost-effective SMT/DIP production lines, the NeoDen ND250 touchscreen dual-wave soldering machine achieves an excellent balance between size, energy consumption, and soldering performance.

NeoDen ND250 Wave Soldering Machine

• Control System: Mitsubishi PLC + Touch Screen
• Soldering Zone Configuration: Double Wave (12 mm)
• Preheating System: 800 mm / 2-section PID+SSR independent control
• Maximum Board Width: 250 mm / Speed 0–1.2 m/min
• Solder Pot Capacity: 200 kg corrosion-resistant titanium alloy solder pot

Advantages of the NeoDen ND250's Dual-Wave Process

The dual-wave system featured in the NeoDen ND250 effectively eliminates common defects in lead-free soldering:

The first wave generates powerful liquid agitation, allowing the solder to rapidly rise and fill the through-holes in the PCB on the ND250's guide rails, eliminating air gaps between high-density pins.

The second wave smooths the solder joints with a stable, flat wave of 12 mm, breaks off excess solder strands, prevents solder bridging, and ensures compliance with IPC-A-610 solder joint standards.

Automation and Intelligent Control of the ND250

Mitsubishi PLC + HMI: The control core utilizes an industrial-grade Mitsubishi PLC, combined with intuitive touchscreen operation, to enable parameter adjustment, alarm monitoring, and real-time display of preheating temperature curves.

Precision Spray System: A 5.2L high-capacity flux tank paired with a pneumatic atomizing nozzle supports stroke and range settings, significantly reducing flux consumption while keeping the board surface clean.

How to Choose the Right Wave Soldering Machine for Your Needs?

When selecting a model, "more expensive" does not necessarily mean "better"; rather, a comprehensive assessment based on your factory's actual conditions is required:

1. Select Based on PCB Dimensions

[ ] Maximum Width: Confirm whether the product's maximum width falls within the equipment's capacity range (e.g., the ND250 supports ≤250 mm).

[ ] Clamping Method: Confirm the clamping accuracy of the titanium claws and the maximum PCB thickness.

2. Select Based on PCB Component Type and Density

[ ] Pure through-hole or mixed assembly: For mixed assemblies or high-density components, it is strongly recommended to opt for a dual-wave + high-power preheating model.

[ ] Lead-free process support: It is essential to confirm that the solder pot liner is made of corrosion-resistant material (e.g., titanium alloy) to accommodate high-copper/high-tin lead-free alloys.

3. Selection Based on Production Capacity Requirements

[ ] Preheating Length: High line speeds (>1.0 m/min) require a longer preheating section (>1000 mm). For small to medium batches, an 800-mm preheating zone offers excellent value for money.

[ ] Solder pot capacity: A 200 kg capacity ensures stable thermal capacity while effectively reducing initial solder loading costs and power consumption.

4. Selection Based on Factory Infrastructure

Verify environmental and utility connections before purchasing:

[ ] Power requirements: Three-phase 380 V industrial power; confirm the equipment's total power and operating power.

[ ] Air Supply Configuration: Flux spraying requires stable, dry industrial compressed air.

[ ] Exhaust System: Wave soldering generates volatile flux gases; the factory must be equipped with a dedicated exhaust duct.

Frequently Asked Questions About Wave Soldering

Q1: What is wave soldering?

A: Wave soldering is an automated process that uses a pump to spray molten solder into a stable wave, allowing the solder to contact the pads on the underside of a moving PCB as it passes through, thereby completing batch soldering in a single pass.

Q2: What types of PCBs is wave soldering primarily used for?

A: It is primarily used for batch soldering of through-hole components (THT), short-lead through-hole components, and mixed-assembly PCBs containing both SMT and THT components.

Q3: Why does wave soldering use two waves?

A: The first wave has strong flushing power and is used to address missed solder joints and solder leakage in densely packed pin configurations; the second wave is used to refine the shape of the solder joints, eliminating solder spikes and bridging.

Q4: What key parameters should be considered when purchasing a wave soldering machine?

A: Key considerations include maximum PCB width, preheating zone length and sections, wave type and height, conveyor speed range, tin bath capacity, and PID temperature control accuracy.

Q5: What is the maximum PCB width supported by the NeoDen ND250?

A: The NeoDen ND250 supports PCBs up to 250 mm in width for feed-through soldering.

Conclusion

As a core automated soldering technology in the electronics manufacturing industry, wave soldering plays a decisive role in quality control for through-hole and mixed-assembly PCB production. Understanding the working principles of wave soldering, as well as the process logic behind preheat zone activation and dual-wave technology, is essential for selecting and effectively utilizing wave soldering equipment.

Evaluate Your Wave Soldering Solution

If you are planning a new SMT/DIP production line or need to evaluate the most suitable wave soldering equipment based on your PCB dimensions and component types:

[View NeoDen ND250 Product Details]

[Get a Custom Quote for Wave Soldering Equipment]