Ultrasonic Spraying Optimization of Solder Joint Performance

Research on Optimizing Electronic Solder Joint Performance Using Ultrasonic Spraying to Modify Substrates

As electronic packaging technology iterates towards higher precision and stability, the quality and lifespan of interconnect solder joints in electronic devices have become core factors restricting equipment reliability. Lead-free solders have become the industry mainstream due to their environmental friendliness and stable performance, and the technology of optimizing solder properties through powder doping is also becoming increasingly mature. However, simply improving the solder itself is no longer sufficient to meet the welding requirements under complex working conditions such as high temperature and high stress. Therefore, innovating welding processes and optimizing substrate interface performance have become key research directions for improving the overall quality of solder joints.

Currently, external field welding technologies such as magnetic field-assisted and ultrasonic-assisted welding are widely used in production, which can effectively refine solder joint grains and optimize microstructure. However, these technologies only change the solidification state of the solder and do not improve the interface characteristics of the substrate, resulting in a significant bottleneck in performance improvement. To overcome this limitation, the industry has begun to explore the integration of substrate surface modification and welding technology, and ultrasonic spraying technology, with its advantages of uniform coating and strong controllability, has become a high-quality solution for interface modification. This study investigated the effects of different spraying durations on the microstructure, wettability, and mechanical properties of composite solder joints by depositing a nickel coating on a copper substrate using ultrasonic spraying. The aim was to screen for optimal process parameters and provide theoretical support for high-performance electronic soldering technology applications.

This study used a composite lead-free solder and a copper substrate as the core materials. A nickel-modified coating was prepared on the polished copper substrate surface using ultrasonic spraying. Six different spraying durations (0, 5, 10, 20, 40, and 60 minutes) were set to control the nickel particle coverage on the substrate surface. Throughout the experiment, the spraying rate, temperature, and robotic arm motion parameters were kept constant, with only the spraying duration being varied to ensure a single variable. After substrate modification, soldering was performed at a constant temperature of 250℃. Standard samples were prepared through cleaning, polishing, and etching processes. Subsequently, the wettability, microstructure, intermetallic compound layer characteristics, and mechanical properties of the solder joints were systematically tested.

The experimental results show a positive correlation between spraying duration and the nickel particle coverage on the substrate. During short-duration spraying, nickel particles are sparsely distributed, failing to form a continuous coating. With increasing spraying time, the nickel coating becomes increasingly dense and uniform; after 60 minutes of spraying, the nickel coverage of the substrate reaches 80%, essentially achieving full surface coverage. Nickel modification of the substrate significantly improves solder wetting performance. Trace amounts of nickel reduce solder surface tension, weaken the copper-tin interface, and promote solder spread. The 20-minute sprayed sample exhibited the largest solder spread area and smallest contact angle, demonstrating the best wetting effect. However, excessively long spraying times lead to nickel particle agglomeration, hindering solder flow and reducing wettability.

Microstructural analysis shows that the nickel coating effectively optimizes the internal phase composition and grain distribution of the solder joint. Unmodified substrate solder joints exhibit problems such as coarse intermetallic compound grains and uneven bismuth phase distribution. Appropriate amounts of nickel can replace some copper atoms, generating higher-performance composite intermetallic compounds while refining bismuth phase grains, resulting in a more uniform distribution of all phases. Regarding the interface structure, a reasonable nickel spraying process can suppress excessive growth of the intermetallic compound layer and refine the interface grains. The compound layer thickness of the 20-minute sprayed sample decreased by 16%, and the grain size decreased by 9%, resulting in a smoother and denser interface structure. However, exceeding the spraying time limit leads to excessive nickel causing localized agglomeration, resulting in a thicker compound layer, coarser grains, and structural defects.

The mechanical property test results closely match the microstructure changes. The shear strength and Vickers hardness of the solder joints both show a trend of first increasing and then decreasing with increasing spraying time. The solder joints modified by 20-minute spraying exhibit the best mechanical properties, with shear strength and Vickers hardness increasing by 10% and 11%, respectively, compared to the unmodified solder joints. The composite intermetallic compound formed by an appropriate amount of nickel can hinder grain dislocation movement through dispersion strengthening, and the refined microstructure can also improve the interfacial bonding strength, allowing the solder joint to exhibit excellent toughness fracture characteristics. However, structural defects caused by excessive nickel can become crack initiation points, significantly reducing the stability and load-bearing capacity of the solder joint.

In summary, ultrasonic spraying nickel modification can effectively optimize the overall performance of copper-based composite solder joints. Spraying time is the core parameter for controlling coating coverage, microstructure, and mechanical properties. Appropriate nickel coating modification can improve solder wettability, refine interface structure, and enhance solder joint mechanical properties. Spraying time of 20 minutes was the optimal process parameter for this experiment. This study confirms the feasibility of substrate interface modification technology and provides an important reference for the development of high-precision, high-reliability soldering processes for high-end electronic packaging.

About Cheersonic

Cheersonic is the leading developer and manufacturer of ultrasonic coating systems for applying precise, thin film coatings to protect, strengthen or smooth surfaces on parts and components for the microelectronics/electronics, alternative energy, medical and industrial markets, including specialized glass applications in construction and automotive.

Our coating solutions are environmentally-friendly, efficient and highly reliable, and enable dramatic reductions in overspray, savings in raw material, water and energy usage and provide improved process repeatability, transfer efficiency, high uniformity and reduced emissions.

Chinese Website: Cheersonic Provides Professional Coating Solutions