Key Technology And Experimentation Of Gold Stud Bump Manufacture Orienting Electronic Packaging

With the development of integrated chip technology, the functions of chips become more and more powerful and the amount of I/O become more and more. However the packaging areas become less and less, the thickness of chips become thinner and thinner and the pith between pins become smaller and smaller. Traditional flip chip packages use the solder bumps which include lead to realize interconnection. Along with the implement of green manufacture and the advantages of conductivity and thermal conductivity of gold compared to solder. The technology of gold bump interconnection will become a better method of flip chip packages. However, the foreign technology is forbidden for our country, and the core parts of high speed shearing wire technology have been kept secret all the while. The domestic research of gold bump shearing wire is blank. Supported by the National Natural Science Foundation of China under grand No. 50725518, this paper focuses on the process of Electric Flame Off (EFO) and EFO parameters affected the length of Heat Affected Zone (HAZ) on the process of manufacture of gold bump. Also it investigates the process parameters affected the shearing wire and does relative experiments based on the model of numerical simulation.For improving the precision of shearing wire, first, the process of EFO has been investigated on firing gold wire to form the gold ball. On the analysis of this paper, EFO model between gold wire and EFO wand is established. Based on this discharge model, through calculating the conservation equations of mass, momentum and energy, the density distribution of charged particles are obtained on the process of discharge. Also the current and electron temperature with time development between discharge gap and heat transfer to the gold wire through plasma are calculated simultaneously. For the sake of the more precision results, the body fitted coordinate system is introduced, and the shape of gold wire is close to the real shape on the calculation. The analysis of EFO process can provide theoretic foundation for the investigation of EFO parameters affected the gold wire HAZ.For the investigation that EFO parameters affected HAZ, the mathematical model of heat transfer on the gold wire melting to the Free Air Ball (FAB) is established. Thermal transferred to the gold wire is calculated according to various EFO current and time. And the magnitude of thermal determines the size of FAB and determines the strength and length of HAZ. The results indicate that with the increase of EFO current, the length of HAZ decreases if the same size FAB is manufactured. And if the EFO current is equal, with the increase of EFO current, the diameter of FAB increases and the length of HAZ increases. Thus, the shorter HAZ correspond to the bigger EFO current and smaller EFO current.The position of shearing wire is on the joint between gold ball and gold wire. For the better investigation of theory of shearing wire, the solidification process of gold ball is simulated using finite element analysis software. The results indicate that the columnar grains initiates from the unmelted wire end and then grow downwards radially to the free end of the gold ball during solidification. As no nucleation is required, the initial solidification simply adopts and extends the crystal structure of the adjacent solid with which it is in contact and the columnar grain comprises a subset of the solid crystal orientation. The orientation of the columnar grains is mainly controlled by the heat flow direction. During solidification, the principal way to lose heat in the molten ball is conduction through the wire.For the research of stress and strain of gold wire on the shearing wire process, the simulations of ball bonding and shearing wire have been done using finite element simulation software ANSYS/LS-DYNA. The results indicate that the gold wire does not affected on the ball bonding process, that is, the character of HAZ is unchangeable. On the shearing wire process, the maximum stress point is not the joint between capillary and gold wire, and it is on the foreside of contact point which is the failure point of plastic distortion. At the same time, by adjusting various parameters affecting shearing wire, optimized parameter window of shearing wire process can be obtained.Finally, the experiments of the manufacture of FAB and shearing wire process have been done. The results show that, for the gold wire of 25.4μm diameter, the diameter, the degree of circle, the degree of symmetry and surface qualities are best when the EFO current is above 25mA and the diameter is 50.8μm. For the different shearing velocities and shearing positions, the capillary can cut the gold wire primely and the coplanarity is very good. It indicates that the shearing velocity and shearing position have a litter influence on shearing wire. The gold stud bump of good coplanarity can be manufactured on condition that the ball bonding is good and the movement of capillary keeps consistent, and it validate the feasibility of finite element simulation of capillary shearing wire.