Investigations on Flip Chip Solder Bump and Under Bump Metal

• Main Authors: Chien-Tai Lin, 林建泰
• Other Authors: Kwang-Lung Lin
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/69863201748334421890

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 92 === Interactions between under bump metal and solder will affect the material property of solder bump. Therefore, the design and manufacturing of the UBM and solder bump should be conducted carefully. Amorphous Cu1-xTax and a new structure of under bump metal (Si/Ta/Cu1-xTax/Cu/Cu1-xTax/Cu/Solder) for flip chip were investigated. The investigation was also performed for the adhesive layers, diffusion barrier layers and wetting layers. Reliabilities of this new packaging structure were tested for different Pb content solders. Amorphous Cu1-xTax films were prepared by multi-targets sputtering depositions and were considered to be adhesive layers and diffusion barrier. The incorporation of Cu will greatly decrease the resistivity of Cu1-xTax. However, Cu3Si and TaSi2 were formed at the interface of Si/Cu1-xTax in the as-sputtered deposits. The adhesive strengths within the Si/Cu1-xTax/Cu were all above 6 kpsi for x=72~100. Annealing results in the growth of Cu3Si grains that degrades the characters of diffusion barrier. But the Cu1-xTax (x=87~100) is still effective as a diffusion barrier. Current densitiy and deposition time were the main factors investigated in the Cu electroplating process. The correlation between surface morphology, microstructure, electrical property of Cu plating and the experimental parameters were discussed. Sheet resistance and resistivity of the Cu plating will decrease with the increase of the Cu layer thickness. The surface roughness might not be the dominate parameter but the density of nodule boundary in the porous films would affect the electrical reisitivity of the electroplating Cu. The surface morphology of nodules affected by increasing deposition time and decreasing current density will enhance the XRD (111)/(200) peak intensity ratio and decrease sheet resistance and resistivity of electroplated Cu. Surface roughness of Cu layers and flux daubing methods of 63Sn-37Pn and Pb-free solders were investigated to understand the wetting behavior. The wetting behavior of de-ionized water was also investigated for reference. The contact angle of the de-ionized water drop decreased with the increase of Cu layer surface roughness. Daubing flux on both solder ball and Cu layer was beneficial to the cleaning of oxide and lower the contact angle. Contact angles of solders on Cu plating also decrease with the increase of Cu layer surface roughness. The Solid/Liquid and Solid/Solid interfacial interactions within Si/Ta/Cu1-xTax/Cu/Cu1-xTax/Cu/Sn-Pb multilayer and the shear strength of the solder bump were analyzed. After a reflow, the scallop-shape Cu6Sn5 IMC (Intermetallic Compound) was formed at the interface of Cu/63Sn-37Pb, and the layer-type Cu3Sn IMC was formed at the interface of Cu/95Pb-5Sn . With the increase in reflow time, the thickness of these two IMCs increased. After aging, the scallop-shape Cu6Sn5 IMCs near solders transformed into layer-type morphology, and that away from solders transformed into Cu3Sn. The thickness of the whole IMC layer increases with the aging time. However, the thickness of the Cu3Sn formed in Cu/95Pb-5Sn did not change with the increase in aging time. The shear fracture always happened within the solders (63Sn-37Pb and 95Pb-5Sn), and the shear strength is only determined by the solder. After multi-reflows, the shear strength drops down and a mixed-type fracture surface happened among the UBM, IMC and solder.