Dependence of Palladium Thickness on the Lead-free Soldering Reaction and Mechanical Reliability

• Main Authors: Wei-Hsiang Wu, 巫維翔
• Other Authors: Cheng-En Ho
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/76279542886913511569

博士 === 元智大學 === 化學工程與材料科學學系 === 101 === Recently, lead-free soldering activities in global electronic industry have pushed PCB and chip carrier board manufacturers to seek a more adequate surface finish for soldering with lead-free alloys, so as to advance the mechanical strength of each joint and the overall reliability of the package. Traditionally, electroless nickel/immersion gold (ENIG) process has been widely accepted for depositing a viable surface finish over the Cu, providing a reliable soldering and wire-bonding pads in the high-end devices applications. However, the galvanic hyper-corrosion of the electroless nickel induced by the sequent gold plating process will cause the so-called “black pad”, which embrittles the interfacial strength and deteriorates the overall reliability of one package. This reliability concern becomes even more serious due to continuously increased input/output (I/O) terminal numbers in miniaturized package sizes, producing a larger number of solder joints with smaller joint sizes. In order to solve this problem completely, modifications to the ENIG by plating one additional Pd(P) layer between Au/Ni(P) in advance, preventing the gold plating bath to contact with the Ni directly, are being considered and adopted by industry. This study concentrates on the solderability between Sn-Ag-Cu lead-free solders and the Au/Pd(P)/Ni(P) surface finish with various Pd(P) thicknesses. We found that the interfacial reactions and mechanical reliability of Sn-3Ag-0.5Cu/Au/Pd(P)/Ni(P) strongly depended of Pd(P) thickness.