Phenomena of electroless Ni-P and intermetallic-compound stripping and dissolving in Sn-Bi and Sn-Pb solder joints with Au/EN/Cu metallization

Self Cite

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.

Section: Introductionmentioning

confidence: 99%

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

Lin

Duh

Chiou

2006

Self Cite

“…1,2 For flip-chip assembly in advanced packaging, a Au/Ni/Cu structure has been used as the wetting layer of the under-bump metallurgy system. 3,4 However, Au normally reacts with the Sn-based solder and generates a continuous brittle (Au,Ni)Sn 4 phase at the solder/pad interface, and this continuous intermetallic compound can reduce the interface shear strength and lead to the embrittlement of the solder joints. 5 Eutectic Sn-0.9Cu solder is one of the popular Pb-free solders because of its advantages of low cost, high shear strength, good creep resistance, and longer thermal fatigue life.…”

Section: Introductionmentioning

confidence: 99%

Reflow and burn-in of a Sn-20In-0.8Cu ball grid array package with a Au/Ni/Cu pad

Chiang

Chang

Chuang

2004

The intermetallic compounds formed after reflow and burn-in testing of a Sn20In-0.8Cu solder ball grid array (BGA) package are investigated. Along with the formation of the Cu 6 (Sn 0.78 In 0.22 ) 5 precipitates (IM1) in the solder matrix, scallop-shaped intermetallic compounds (IM2) with a compositional mixture of Cu 6 (Sn 0.87 In 0.13 ) 5 and Ni 3 (Sn 0.87 In 0.13 ) 4 appear at the interfaces between the solder balls and Au/Ni/Cu pads. A significant number of intermetallic particles (IM3), with a composition of (Au 0.80 Cu 0.20 )(In 0.33 Sn 0.67 ) 2 , can also be found in the solder matrix. After aging at 115°C for 750 h, an additional intermetallic compound layer (IM4) with a composition of (Ni 0.91 Cu 0.09 ) 3 (Sn 0.77 In 0.23 ) 2 is formed at the interface between IM2 and the Ni layer. The ball shear strength of the Sn-20In-0.8Cu BGA solder after reflow is 4.5 N and will rise to maximum values after aging at 75°C and 115°C for 100 h. With a further increase of the aging time at both temperatures, the joint strengths exhibit a tendency to decline linearly at about 1.7 ϫ 10 -3 N/h.

“…For joints of Sn-Bi/Ni-based UBM, previous studies concerning wettability, 11 IMC stripping and dissolving, 12 and metallurgical reaction after annealing 13 have been conducted. The purpose of this study was to investigate the interfacial reaction between eutectic Sn-Bi solder and Ni-based UBMs during aging at 110°C and 130°C and the corresponding microstructural evolution in the joint.…”

Section: Introductionmentioning

confidence: 99%

Compound formation for electroplated Ni and electroless Ni in the under-bump metallurgy with Sn-58Bi solder during aging

Young

Duh

Jang

2003

Self Cite

The Ni-based under-bump metallurgies (UBMs) are of interest because they have a slower reaction rate with Sn-rich solders compared to Cu-based UBMs. In this study, several UBM schemes using Ni as the diffusion barrier are investigated. Joints of Sn-58Bi/Au/electroless nickel (EN)/Cu/Al 2 O 3 and Sn-58Bi/Au/electroplated nickel/Cu/Al 2 O 3 were aged at 110°C and 130°C for 1-25 days to study the interfacial reaction and microstructural evolution. The Sn-Bi solder reacts with the Ni-based multimetallization and forms the ternary Sn-Ni-Bi intermetallic compound (IMC) during aging at 110°C. Compositions of ternary IMC were (78-80)at.%Sn-(12-16)at.%Ni-(5-8)at.%Bi in joints of Sn-58Bi/Au/Ni-5.5wt.%P/Cu, Sn-58Bi/Au/Ni-12wt.%P/Cu, and Sn-58Bi/Au/Ni/Cu. Elevated aging at 130°C accelerates the IMC growth rate and results in the formation of (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 adjacent to the ternary Sn-Ni-Bi IMC for the Sn-58Bi/Au/Ni-12wt.%P/Cu and Sn-58Bi/Au/Ni/Cu joints, respectively. The Cu content in the (Cu,Ni) 6 Sn 5 IMC is six times that in (Ni,Cu) 3 Sn 4 . Electroplated Ni fails to prevent Cu diffusion toward the Ni/solder interface as compared to EN-based joints. Cracks are observed in the Sn-58Bi/Au/Ni-5.5wt.%P/Cu/Al 2 O 3 joint aged at 130°C for 25 days. It is more favorable to employ Ni-12wt.%P for the Sn-58Bi/Au/EN/Cu joint. Electroless nickel, with the higher P content of 12 wt.%, is a more effective diffusion barrier during aging. In addition, P enrichment occurs near the interface of the EN/solder, and the degree of P enrichment is enhanced with aging time. The Au(Sn,Bi) 4 , with pyramidal and cubic shape, is observed in the Sn-58Bi/