Wettability of electroplated Ni-P in under bump metallurgy with Sn-Ag-Cu solder

Abstract

Nickel plating has been used as the under bump metallurgy (UBM) in the microelectronics industry. In this study, the electroplating process was demonstrated to be agood alternative approach to produce the Ni-P layer as UBM. The wettability of several commercial solder pastes, such as Sn-3.5Ag, Sn37Pb, and Sn-3Ag-0.5Cu solder, on electroplated Ni-P with various phosphorous contents (7 wt.%, 10 wt.%, and 13 wt.%) was investigated. The role of phosphorus in the wettability was probed. The surface morphology and surface roughness in electroplated Ni-P was observed with the aid of both field emission scanning electron microscope (SEM) and atomic force microscope (AFM). The correlation between wettability and phosphorus contents in electroplated Ni-P was evaluated. As the phosphorous contents increased, the surface morphology of the Ni-P deposit was smoother and surface roughness of Ni-P became smaller. The improvement of surface morphology and surface roughness enhanced the wettability of electroplated Ni-P. The interfacial reaction between lead-free solder and electroplating Ni-P UBM was also investigated.

Optimal phosphorous content selection for the soldering reaction of Ni-P under bump metallization with Sn-Ag-Cu solder

“…With different phosphoric acid (H 3 PO 3 ) additions, the various phosphorous contents of Ni-P deposit were evaluated (7 wt.%, 10 wt.%, and 13 wt.%). 13 After deposition, the electroplated Ni-P layer specimen ( was immediately immersed in deionized water for 2 min. and then dried with alcohol.…”

“…2c and d, the thickness of both (Ni,Cu) 3 Sn 4 and P-rich layer apparently increased. It was reported 13,[17][18][19]22 that a Ni-Sn-P phase formed on the P-rich layer caused the spalling of Ni 3 Sn 4 IMC to solder matrix. The spalling of Ni 3 Sn 4 IMCs in the tin-based lead-free solder/Ni-P UBM system raises a reliability problem.…”

“…The nickel based UBM, instead of Cu, has been widely used because of the rapid reaction of Sn with the Cu as well as the spalling problem associated with Cu-Sn intermetallic compounds (IMCs). [3][4][5][6][7][8][9][10][11][12][13] Recently, because of its cost effectiveness, the electroless nickel process has become an alternative method for depositing Ni. However, a Ni-Sn-P phase formed between IMCs and Ni-P UBM causes IMCs to be spalled into the solder matrix, resulting in a reliability concern.…”

“…22 It is argued that the formation of Ni-Sn-P is significantly dependent on the phosphorous content of Ni-P UBM. 13,22 Therefore, the phosphorous content selection for Ni-P as an UBM is a critical issue.…”

Electrical characteristics for Sn-Ag-Cu solder bump with Ti/Ni/Cu under-bump metallization after temperature cycling tests

“…The interfacial microstructure and IMC formation for different types of solders have been reported. [11][12][13][14][15][16][17] Nevertheless, data on the variation of electrical properties in solder joints were limited in the literature. The purpose of this work was to investigate the electrical characteristics of Sn-Ag-Cu solder bump with Ti/Ni/Cu UBM after the thermal cycle test.…”