In this thesis, the main investigation is focused on the design and fabrication of Re-distribution(RDL) in Wafer Level Chip Scale Package(WLCSP). As bumping process capability becoming more and more popular, WLCSP will be the main package trend for IC with lower pin count. Due to the high performance analog devices should be met more restricted requirements for electrical conductivity and higher electrical current passing by, hence the thick plating Cu is chosen for RDL and under bump metallization(UBM) for WLCSP package to meet both electrical and reliability requirements. The experiments discussed herein include: photo exposure DOE, adhesion DOE between 2ND PI and RDL and contact resistance DOE after post etching treatment. From the DOE results, we obtain the results as follows: The exposure dosage optimized by using 1.5X original parameter that can fix the photo resist residue problem. The key to the adhesion between PI2 and RDL is the curing temperature. Lower curing temperature 375¢J/320¢J provides better adhesion. O2/ CF4 treatments effectively increase contact resistance. However, O2/Ar¡BAr and O2 work much better than O2/ CF4 in increasing the contact resistance after surface treatment. The completion of this study could give some suggestions to the manufacturers of application of RDL WLCSP, furthermore, it shorten the development period to enhance the mechanical and electrical performances of products.