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Mechanical and Electromigration Reliability Evaluation of Various Lead-Free Binary/Ternary Solder Ball on Electroplated Ni/Au under Bump Metallurgy in Wafer Level Package
Keywords: WLP(Wafer Level Package), Electroplated nickel/gold, Reliability
Recently, WLP is becoming the main stream as a package type in case of low I/O pin device in consumer product. Of WLP Structures, the compatibility between UBM material and lead-free solder alloy respectively is the most important issue in respect to mechanical and electromigration reliability related to IMC growth and behavior. The mechanical and electromigration reliability of the two kinds of WLP(Wafer Level Package) using Sn1.2Ag0.5Cu and Sn3.0Ag0.5Cu on electroplated Ni/Au and ENIG(Electroless Nickel Immersion Gold) finished FR-4 substrate have been Investigated by employing TC (Thermal Cycling), HTS (High Temperature Storage) and Electromigration. Duing BST (Ball Shear Test) in HTS test, it was found that both of them came out a mixture mode of bulk solder and IMC layer. Inter-metallic area exposed during fracture was about 10% of solder area. EDX results on the fractured area shows elements of Sn & Ni & Cu indicating that fracture has started to show off at IMC layer. We will keep on evaluating HTS till 2000hrs. In electromigration test, We are doing a evaluation under condition 150in temperature and 0.6 x 104 A/ in current density.for both Sn1.2Ag0.5Cu and Sn3.0Ag0.5Cu. Currently, there is no failure until 400 hrs in case of Sn3.0Ag0.5Cu, and there is no failure until 200 hrs in case of Sn1.2Ag0.5Cu. We will additionally conduct a electromigration evaluation in range from 103 to 104 A/cm2 at current density.
Yun-Mook Park, Research Engineer
NEPES Corporation
Cheongwon-Gun, Chungbuk 363-883,
Republic of Korea

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