楔焊金丝的强韧性及微观组织

Strength,Toughness and Microstructure of Wedge Bonding Gold Wire

采用双束电子显微镜和单纤维拉力测试仪对楔焊金丝和高纯金丝的微观组织和力学性能进行表征,利用有限元数值计算方法模拟拉拔过程中楔焊金丝的轴向、径向及表面应力分布,探索微量元素对高纯金的强化机制。结果表明:经单向深度拉拔,楔焊金丝的纵截面晶粒呈细长纤维状,沿径向分布均匀,有明显的[111]丝织构,晶粒在拉拔过程中发生了转变,晶界的取向差角度分布呈“双峰”特征,小角度晶界所占比例较高。而高纯金丝的纵截面晶粒沿径向方向差别较大,芯部呈细长纤维状,边缘由细小的等轴晶组成,沿[001]方向择优生长。楔焊金丝比高纯金丝的抗拉强度提高了250 MPa,再结晶温度提高了100℃,最大延伸率达到25%,具有良好的拉伸断裂韧性。楔焊金丝在拉拔过程中沿径向方向应力分布不均匀,芯部的轴向压应力和表面残余应力要低于高纯金丝。镍和镧复合添加到金基体中产生晶格畸变,阻碍位错滑移和晶界滑动,通过固溶强化、细晶强化和加工硬化获得适合楔焊用的强韧性。

Wedge bonding gold wire was a new type of rare,fine metal wire,mainly used to connect chips and chips,chips and circuit substrate in microwave components. It was the key basic material of military electronic components in weapons and equipment. In order to improve the combat ability of weapons and equipment,microwave components are developing in the direction of miniaturization,multi-function and high intelligence,and higher requirements were put forward for high strength and high toughness of wedge bonding gold wire. The wedge bonding process was the comprehensive action of force,electric and heat. In the process of pressure welding,arc forming,and breaking,gold wire bears many kinds of stress,such as tensile,compression,and bending. Therefore,the strength and toughness of wedge bonding gold wire were studied. This paper studied the microstructure,tensile deformation behavior and stress distribution of wedge bonding gold wire and high purity gold wire in the drawing process. The composition of wedge bonding gold wire was as follows:10×10^(-6)~60×10^(-6)nickel and 5×10^(-6)~25×10^(-6)lanthanum were added to 99.999% high pure gold. The electronegativity and atomic radius of nickel,lanthanum and gold varied greatly. According to the Lausch theory,the metal wire had a good solid solution strengthening effect. The control sample was 99.999% high purity gold wire. Focused ion beam technology(FIB)was used to cut the longitudinal section of wedge bonding gold wire and high purity gold wire,and the microstructure was observed by scanning electron microscope(SEM). Texture and orientation difference were analyzed by electron backscatter diffraction(EBSD). The tensile strength and elongation of wedge bonding gold wire and high purity gold wire were measured using a single-fiber tensile tester.The axial,radial and surface stresses of wedge bonding gold wire during drawing were simulated by finite element numerical calculation method. The strengthening mechanism of trace elements for high pure gold was explored. The results showed that grains of wedge bonding gold wire in the longitudinal section were long and thin fibrous after unidirectional depth drawing. The grain size was 0.18~1.56 μm and evenly distributed along the radial direction. Wedge bonding gold wire had an obvious[111]silk texture along the tensile direction. During the drawing process,the grain rotated from the[001]orientation to the[111]orientation of the ingot. The grain size and shape of the high purity gold wire varied greatly in the radial direction. The grain at the core was slender and fibrous,and the grain at the edge was composed of fine equiaxed grains. The minimum grain size was only 0.45 μm,and the maximum grain size was 8.5 μm,and the grain grew preferentially along the[001]direction. Both high purity gold wire and wedge bonding gold wire had a large number of grain boundary orientation difference distribution in the two ranges of 10°~22° and 52°~61°. The angle distribution of orientation difference showed a "double peak",while the random orientation difference had a peak value of 40°~50°. The large angle grain boundary of high purity gold wire was higher,while the small angle grain boundary of wedge bonding gold wire was higher. Compared with high purity gold wire,the tensile strength of wedge bonding gold wire was increased by 250 MPa,the recrystallization temperature was increased by 100 ℃,the maximum elongation reached 25%,and the tensile fracture toughness was about twice that of high purity gold wire. In the process of drawing,the stress of wedge bonding gold wire surface was distributed evenly along the radial direction,resulting in tensile stress. Wedge bonding gold wire was subjected to axial,radial and circumferential compression stress at the edge of the wire in the contact area with the drawing die,while the core was subjected to axial and radial tensile stress. After the gold wire was released from the die,the axial stress distribution was gradient along the radial direction of the gold wire. The tensile stress at the most edge was the largest,and the axial compressive stress at the core was generated. The edge of the gold wire produced less radial tensile stress,while the core part produced less radial compressive stress. The radial stress of wedge bonding gold wire was similar to that of high purity gold wire,but the stress value and residual stress of axial stress core were obviously lower than that of high purity gold wire.The addition of nickel and lanthanum to the gold matrix could cause lattice distortion,hindered dislocation slip and grain boundary slip,and improved the strength and toughness of the gold wire through solid solution strengthening,fine grain strengthening and work hardening. The weld joint appearance and tail wire length of the wedge bonding gold wire after arc forming met the requirements of use.The arc was stable and did not collapse. The arc pick breaking tension was high,and environmental adaptability was good.