What is the basic principle of reflow soldering machine?

Introduction

In modern electronic products such as smartphones, automotive electronics, and smart home devices, surface mount technology (SMT) has become the mainstream assembly process. As a core component of the SMT process, reflow soldering directly determines the quality and reliability of component soldering on PCBs.

This article will provide an in-depth analysis of reflow soldering technology, covering its working principles, temperature curve design, equipment selection criteria, and solutions for common defects, helping beginners quickly establish a systematic understanding.

I. What is reflow soldering machine?

1. Basic definition

Reflow soldering oven refers to the process of connecting one or more electronic components to contact pads using solder paste (a mixture of solder and flux), then melting the solder through controlled heating to achieve permanent bonding. This can be performed using various heating methods such as reflow ovens, infrared heating lamps, or hot air guns.

2. Core Differences from Wave Soldering

3. Typical Application Scenarios

Consumer Electronics: Smartphone motherboards, wearable devices

Automotive Electronics: ECU control units, sensor modules

Industrial Equipment: Variable frequency drives, PLC controllers

Communication Equipment: 5G base station RF modules

II. The Four Core Stages of the Reflow Soldering machine Process

1. Preheat Zone

Temperature Range: Room Temperature → 150°C

Key Functions:

Gradually evaporate solvents and flux from the solder paste

Prevent PCB deformation due to thermal shock

Establish a uniform thermal foundation for subsequent temperature increases

Control Points: The temperature rise rate should be controlled at 1-3°C/s; too fast a rate may cause solder paste splatter

2. Soak Zone

Temperature Range: 150-180°C

Core Objectives:

Ensure uniform temperature across all PCB areas

Activate the flux and remove oxide from the pads

Prevent solder paste from forming balls during the reflow stage

Typical Issues: Insufficient soak time may result in incomplete flux activation, leading to cold solder joints

3. Reflow Zone

Peak Temperature: 210–245°C (lead-free solder paste)

Physical Changes:

Solder paste alloy powders melt into a liquid state

Form concave solder joints under surface tension

Flux residues decompose and evaporate

Key Metric: Liquid Time (Time Above Liquids, TAL) must be controlled between 30–90 seconds

4. Cooling Zone

Cooling Rate: 3–5°C/s (recommended value)

Importance:

Too rapid cooling can cause solder joint cracks

Too slow cooling increases intermetallic compound thickness (IMC)

Ideal result: Formation of bright, well-defined solder joints

III. Types of Reflow Soldering Machine and Selection Guidelines

1. Classification by Heating Method

2. Key Parameter Selection Criteria

Number of heating zones: 6–12 zones meet most requirements

Conveyor belt width: Standard widths are 300/400/500 mm

Temperature control accuracy: ±1°C is the industrial standard

Nitrogen consumption: Nitrogen furnaces require a gas flow meter

3. Intelligent trends

Modern reflow soldering equipment now integrates:

Automatic temperature curve optimization system

AOI (automatic optical inspection machine) linkage function

IoT remote monitoring and fault warning

IV. Key factors affecting soldering quality

1. Solder paste printer printing quality

Steel mesh aperture size error must be <±25μm

Solder paste coverage should reach 75%-85%

Common defects: collapse (Slump), missed printing

2. Temperature Curve Optimization

Ideal curve characteristics:

Temperature difference between zones ≤5℃

Peak temperature matches solder alloy melting point (Sn96.5Ag3.0Cu0.5 at 217-220℃)

Stable cooling slope

3. Environmental Control Parameters

Workshop humidity: 40-60% RH (to prevent static electricity and solder paste moisture absorption)

Air cleanliness: ISO Class 7 or above

Vibration control: Avoid conveyor belt vibration causing misalignment

V. Six Common Defects and Solutions

VI. Future Trends: Green Manufacturing and Intelligent Upgrades

Lead-free solder adoption: Under the RoHS directive, SAC305 (Sn96.5Ag3.0Cu0.5) now accounts for 85% of the market share

Micro-pitch welding technology: Supports precise welding of components with pitches below 0.3 mm

AI temperature control: Dynamically optimizes process parameters through machine learning

Energy-saving design: New insulation materials reduce energy consumption by 30%

Conclusion

Understanding the principles of reflow oven is the first step toward improving electronic manufacturing quality. Companies are advised to take the following actions:

• Establish standardized management processes
• Regularly use a furnace temperature tester to verify the curve
• Collaborate with equipment suppliers to develop customized process solutions

Quick facts about NeoDen

1) Established in 2010, 200 + employees, 27000+ Sq.m. factory.

2) NeoDen Products:Different Series PnP machines, NeoDen YY1, NeoDen4, NeoDen5, NeoDen K1830, NeoDen9, NeoDen N10P. Reflow Oven IN Series, as well as complete SMT Line includes all necessary SMT equipment.

3) Successful 10000+ customers across the globe.

4) 40+ Global Agents covered in Asia, Europe, America, Oceania and Africa.

5) R&D Center: 3 R&D departments with 25+ professional R&D engineers.

6) Listed with CE and got 70+ patents.

7) 30+ quality control and technical support engineers, 15+ senior international sales, for timely customer responding within 8 hours, and professional solutions providing within 24 hours.