Research On Machining Process And Equipment Of Resistance Spot Welding For Sn-coated Copper

With the increase of integration and frequency,reduction of feature size in electronic products,the thermal failure and degradation of electronic components have become more prominent.The problem of heat dissipation has become a major issue that restricts the development of electronic devices.Although copper has a wide range of applications in heat dissipation due to its excellent heat dissipation performance,research on micro-electronic device,especially,small active cooling devices with complex flow paths inside multi-layered hollows,is currently still at the bottleneck stage in China.If the application of heat dissipation in microelectronic devices can be achieved by welding copper,it can break the foreign technology blockade against China and achieve considerable economic benefits.Because of its short heating time,heat concentration and high production efficiency,resistance spot welding has outstanding advantages in welding small and thin copper.Conducting in-depth research and optimizing process parameters to promote the application of copper in heat dissipation of microelectronic products is of great significance.In view of the difficulty of copper-copper welding,adding a Sn-coated layer to the surface of copper was used in this thesis to improve its weldability.This thesis focused on resistance spot welding on Sn-coated copper process,established experimental platform for resistance spot welding,including designing electrode and relevant clamps,choosing type of power supply and pressure mechanism.This paper introduced a method of measuring diameters of the inside spot welds to take place of measuring that of nuggets directly.And analysis about welding defects occurring in the process of experiment was done,“bumps”included,which had never been referred to in other papers before.It could be thought that because the contact resistance between electrodes and working pieces was uneven,and this caused burning problems of electrodes.In addition,the spot welds were so small that it was difficult for the heat to dissipate.Experiments were done on pure copper and Sn-coated copper by making comparisons among spot welds on morphologies and tensile-shear force.It showed that pure copper spot welds were all broken in the form of interfacial fracture,which did not meet the requirement of mechanical property for welding,while Sn-coated copper spot welds significantly excelled pure copper spot welds both on the aspects of morphologies and tensile-shear force.Single-factor experiments were performed on Sn-coated copper to study the influence of various factors on the quality of the spot welds,with preheat current,welding current,preheat time,welding time,electrode force and holding time being its study factors and with surface morphology,nugget diameter and tensile-shear force of the spot welds being the evaluation standard of the quality of the spot welds.It showed that preheat current,preheat time and holding time had significant influence on the welding quality of spot welds besides welding current,welding time and electrode force.Orthogonal experimental method was used to optimize welding parameters,and a standard orthogonal table(L₂₅（5⁶）)was adopted to conduct experiments to obtain optimal experimental parameters and analyze the degree of influence each factor had on the welding quality of spot welds.It showed that the significance in nugget diameter was welding current>welding time>preheat time>holding time>preheat current>electrode force and in shear force was current>welding time>holding time>electrode force>preheat time>preheat current.And the optimal parameters were when the preheat current was 1000A,welding current was 2200A,preheat time was 14ms,welding time was 10ms,electrode force was 8kgf and holding time was 100ms,under which parameters,the spot welds had good appearance and higher strength.And the tensile-shear force was as high as 319.413N.