Ultrasonic Ni-sprayed Cu Substrates
Effect of ultrasonic Ni-sprayed Cu substrates on the microstructures and properties of composite interconnection joints
With the rapid development of the electronic packaging industry, the optimization of lead-free solder performance has become a research hotspot. The traditional way of improving solder performance by doping particles is no longer sufficient to meet high-end production needs. The existing ultrasonic and magnetic field assisted welding technologies can only optimize the microstructure of solder joints and cannot achieve performance breakthroughs at the substrate level. Therefore, this article combines ultrasonic spraying and welding technology to explore the effects of different nickel spraying durations on the microstructure and mechanical properties of Sn58Bi/SAC105 composite solder joints modified copper substrates, providing theoretical support for optimizing surface treatment technology for electronic packaging.
This study used ultrasonic spraying equipment to perform nickel spraying treatment on copper substrates for different durations, preparing multiple groups of modified substrates and using unmodified copper substrates as controls. After unifying the experimental process parameters and completing the processes of composite solder mixing, substrate spraying, welding sample preparation, corrosion polishing, etc., the wetting properties, microstructure, intermetallic compound (IMC) layer structure, and mechanical properties of the solder joints were systematically tested using scanning electron microscopy, contact angle measuring instruments, shear testing machines, and other equipment.
The experimental results show that the duration of nickel spraying is positively correlated with the nickel particle coverage on the substrate surface, and the nickel particle coverage can reach 80% after 60 minutes of spraying. Moderate nickel modification can effectively improve the wettability of solder, reduce the surface tension of solder, promote solder spreading, and the solder spreading area reaches its peak after 20 minutes of spraying. Microstructure analysis shows that nickel atoms can replace copper atoms at the interface, promote the precipitation of (Cu, Ni) ₆ Sn ₅ grains, hinder dislocation movement through pinning effect, and refine the dispersed Bi phase, making the internal structure of the solder joint more uniform.
In terms of interface structure, nickel modification can suppress excessive growth of IMC layer, refine grain size, and improve the traditional fan-shaped non-uniform structure. When sprayed for 20 minutes, the thickness of the IMC layer decreased by 16%, the grain size decreased by 9%, and the interface bonding became denser. Mechanical performance tests have confirmed that moderate nickel modification can significantly improve the performance of solder joints. After 20 minutes, the modified solder joints have a shear strength of 38.42 MPa and a Vickers hardness of 21.43 HV, which are 10% and 11% higher than unmodified substrate solder joints, respectively. However, prolonged spraying can cause nickel particles to agglomerate, leading to coarsening of the IMC layer, uneven microstructure, and degradation of solder joint performance.
In summary, moderate ultrasonic nickel spraying modified copper substrates can optimize the performance of composite solder joints from the interface structure and microstructure levels, with 20 minutes being the optimal spraying process. This process effectively addresses the shortcomings of traditional welding techniques and provides important references for optimizing and applying efficient and highly reliable welding processes for 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.
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