Continuous Wire-Feeding Laser Soldering Process for PCB Liquid Crystal Modules (18 Solder Joints)

Continuous Wire-Feeding Laser Soldering Process for PCB Liquid Crystal Modules (18 Solder Joints)

I. Introduction

Illustration of PCB Liquid Crystal Module

In the field of electronic device manufacturing, the soldering quality of PCB (Printed Circuit Board) liquid crystal modules is critical to product performance. As electronic products trend toward miniaturization and high performance, traditional soldering technologies increasingly reveal limitations when addressing dense solder joints and high-precision requirements.

Laser soldering technology, with its advantages of high energy density, exceptional precision, and minimal heat-affected zones, has emerged as the ideal solution for PCB liquid crystal module soldering. In particular, the continuous wire-feeding laser soldering process enables efficient and stable completion of multiple solder joints, meeting the demands of large-scale production.

This paper provides an in-depth exploration of the technical key points, process parameter optimization, and quality control methods for the 18-solder-joint continuous wire-feeding laser soldering process in PCB liquid crystal modules.

II. Principle of Continuous Wire-Feeding Laser Soldering

Continuous wire-feeding laser soldering utilizes a high-energy-density laser beam as the heat source, which irradiates the soldering area of the PCB liquid crystal module. The laser energy is rapidly absorbed by the material, causing the temperature in the soldering zone to rise sharply until reaching the melting point of the solder wire. Under the action of the wire-feeding mechanism, the solder wire is continuously fed into the soldering area, where it melts and fills the joint, forming a metallurgical bond with the base material. This process enables sequential soldering of all 18 joints.

Compared to conventional soldering methods, laser soldering offers:

• Highly concentrated energy (106–108 W/cm² power density)

• Rapid heating (up to 103–104 °C/s heating rate)

• Minimal heat-affected zone (typically <200μm)

These characteristics significantly reduce thermal damage to surrounding components, making the technology particularly suitable for heat-sensitive precision electronics like PCB liquid crystal modules.

Continuous Wire-Feeding Laser Soldering Process Diagram

III. Welding Equipment Composition and Key Components

1. Laser Generator
Provides high-energy-density laser beams for welding, where parameters such as power stability and beam quality directly affect welding results. For continuous welding of 18 solder joints on PCB liquid crystal modules, a laser generator with moderate power and excellent beam mode must be selected to ensure fast and uniform melting of solder wire.

2. Wire Feeding Mechanism
Precisely controls the feed speed and quantity of solder wire to ensure stable supply during the welding process. The response speed and accuracy of the wire feeding mechanism significantly impact solder joint quality. When continuously welding 18 solder joints, it is essential to synchronize the wire feed speed with the laser welding speed to avoid:

• Solder wire accumulation (due to excessive feeding)

• Insufficient solder filling (due to slow feeding)

3. Welding Worktable
Designed to carry PCB liquid crystal modules, it must feature high-precision positioning and motion control capabilities. During welding, the worktable moves precisely along a preset path to ensure the laser beam accurately irradiates each solder joint, enabling orderly welding of all 18 joints. Additionally, the worktable's stability is critical to prevent vibration-induced quality issues during welding.

Songsheng Optoelectronics Constant-Temperature Laser Soldering System Diagram

Vision Positioning System: Utilizing cameras and other visual equipment, the system acquires real-time positional data of PCB liquid crystal modules to achieve precise identification and positioning of solder joints. Prior to welding, the vision positioning system rapidly calibrates module positions to ensure absolute accuracy of the initial welding points. During the welding process, it monitors solder joint quality in real-time and dynamically adjusts welding parameters, thereby enhancing welding consistency and reliability.

IV. Process Parameter Optimization

Laser Power
Laser power determines the energy input during welding and is a critical parameter affecting welding quality. Insufficient power prevents complete melting of the solder wire, leading to weak joints or cold soldering. Excessive power may cause over-melting of the base material, burn-through, or even damage to the liquid crystal module. For continuous wire-feed laser soldering of 18 joints, the appropriate laser power range should be determined experimentally based on solder wire material, diameter, and PCB thickness, with stable power maintained throughout the process.

Welding Speed
Welding speed must coordinate with laser power as both parameters jointly affect heat input and joint formation. Excessive speed results in incomplete wire melting and insufficient joint filling, while insufficient speed causes excessive heat accumulation and an expanded heat-affected zone that may compromise nearby components. Practical welding requires optimization of speed considering joint quantity, distribution, and production efficiency requirements to ensure consistent quality across all 18 joints.

Wire Feed Speed
Wire feed speed must synchronize with laser power and welding speed to ensure proper melting and timely, accurate joint filling. Excessive feed speed causes wire accumulation and solder bumps, while insufficient speed creates underfilled joints. Calibration of the wire feed mechanism to identify the optimal speed matching other parameters is essential for achieving uniform and stable continuous soldering of 18 joints.

Defocus Amount
Defocus amount refers to the distance between the laser focal point and the welding surface. Proper defocusing creates ideal spot geometry and energy distribution for improved quality. Positive defocus produces larger spot size with lower energy density, suitable for thin materials. Negative defocus yields smaller spots with higher energy density for thicker materials. PCB liquid crystal module welding requires specific defocus adjustment for optimal results.

Songsheng Optoelectronics Laser Constant-Temperature Soldering System consists of a real-time temperature feedback system, CCD coaxial positioning system, and semiconductor laser. The innovative PID online temperature regulation feedback system effectively controls constant-temperature soldering, featuring real-time high-precision temperature control of the soldering target, ensuring superior soldering yield and precision. It is particularly suitable for temperature-sensitive high-precision soldering applications such as micro speakers/motors, connectors, electronic modules, camera modules, etc.

V. Welding Quality Control

Solder Joint Appearance Inspection
The shape, size, surface smoothness, and potential defects (e.g., solder bumps, porosity, cracks) of solder joints are examined through manual visual inspection or automated vision systems. Qualified solder joints should exhibit a regular hemispherical shape with smooth surfaces, proper transition to the base material, and no obvious defects. For continuous soldering of 18 joints, each must meet consistent appearance standards in compliance with product specifications.

Electrical Performance Testing
Completed PCB liquid crystal modules undergo electrical tests, including continuity checks, resistance measurements, and insulation performance verification. These tests identify potential cold solder joints, short circuits, or other connection issues, ensuring reliable module functionality in practical applications. As a critical quality control step, electrical testing directly reflects the impact of soldering on circuit performance.

Metallographic Analysis
Using metallurgical microscopes, the microstructure of solder joints is analyzed to evaluate metallurgical bonding quality, grain size, and morphology. High-quality joints exhibit uniform, dense structures with robust bonding layers between the base material and solder wire. This analysis provides in-depth insights into intrinsic soldering quality and supports process optimization.

Process Monitoring & Feedback
Real-time monitoring of temperature, laser power, wire feed speed, and other parameters is achieved via sensors, enabling dynamic adjustments through the control system. The system triggers alarms and corrective actions upon detecting abnormalities, ensuring stable and reliable soldering. Additionally, welding process data is recorded and analyzed to facilitate future process improvements.

VI. Common Problems and Solutions

Cold Solder Joint : Characterized by poor metallurgical bonding between the solder joint and base material, resulting in unreliable electrical connections. Possible causes include insufficient laser power, too short welding time, irregular wire feeding, or contaminated (oily/oxidized) workpiece surfaces. Solutions involve appropriately increasing laser power, extending welding time, inspecting the wire feeding mechanism, and cleaning the workpiece surface to ensure a clean welding area.

Solder Bumps : Refers to excessive solder accumulation around joints, mainly caused by too fast wire feeding speed, too slow welding speed, or excessive laser power. Adjusting the wire feeding speed, increasing welding speed, or reducing laser power to achieve balanced welding parameters can effectively prevent solder bump formation.

Porosity : Voids appearing inside or on the surface of solder joints, likely due to moisture or oil contamination on the solder wire or workpiece surface that vaporizes during welding but fails to escape in time. Thoroughly drying and cleaning the solder wire and workpiece before welding, and selecting appropriate process parameters such as moderately increasing welding speed, can help gas escape and reduce porosity.

Burn-through : Over-melting of base material forming perforations, mostly caused by excessive laser power or too slow welding speed. Reducing laser power, increasing welding speed, and adjusting parameters to appropriate ranges can prevent burn-through.

VII. Conclusion

The continuous wire-feeding laser soldering technology for 18 solder joints on PCB liquid crystal modules holds significant application value in modern electronics manufacturing. Through in-depth understanding of soldering principles, optimization of key welding equipment components, rational adjustment of process parameters, and implementation of effective quality control measures, common soldering issues can be resolved to achieve high-quality, high-efficiency soldering results.