Electroless nickel/copper plating as a new bump metallization

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A comparative study of solid/solid interfacial reactions of electroless Ni-P (15at.%P) with lead-free solders, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu and pure Sn,, was carried out by performing thermal aging at 150oC up to 1000 h. For pure Sn and Sn-3.5Ag solder, three distinctive layers, Ni3Sn4, SnNiP and Ni3P, were observed in between the solder and electroless Ni-P; while for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders, two distinctive layers, (CuNi)6Sn5 and Ni3P, were observed. The differences in morphology and growth kinetics of the intermetallic compounds (IMCs) at the interfaces between electroless Ni-P and lead-free solders were investigated, as well as the growth kinetics of the P-enriched layers underneath the interfacial IMC layers. With increasing aging time, the coarsening of interfacial Ni3Sn4 IMC grains for pure Sn and Sn-3.5Ag solder was significantly greater than that of the interfacial (CuNi)6Sn5 IMC grains for Sn-0.7Cu and Sn-3.8Ag-0.7Cu solders. Furthermore, the Ni content in interfacial (CuNi)6Sn5 phase slightly increased during aging. A small addition of Cu (0.7 wt.%) resulted in differences in the type, morphology and growth kinetics of interfacial IMCs. By comparing the metallurgical aspects and growth kinetics of the interfacial IMCs and the underneath P-enriched layers, the role of initial Cu and Ag in lead-free solders is better understood

Section: Introductionmentioning

confidence: 99%

Morphology and growth kinetics of intermetallic compounds in solid-state interfacial reaction of electroless Ni-P with Sn-based lead-free solders

Huang

Loeher

Manessis

et al. 2006

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“…[1][2][3] During reflow soldering, the Au layer of ENIG dissolves into the molten solder, exposing the underlying Ni-P layer to the molten solder. Thereafter, Ni, Sn, and Cu react to form interfacial intermetallic compounds (IMCs), either (Cu,Ni) 6 Sn 5 or (Ni,Cu) 3 Sn 4 depending on the Cu content in the Sn-Ag-Cu (SAC) solder.…”

Section: Introductionmentioning

confidence: 99%

Effect of Ni-P Plating Temperature on Growth of Interfacial Intermetallic Compound in Electroless Nickel Immersion Gold/Sn-Ag-Cu Solder Joints

Seo

Kim

et al. 2017

The growth of interfacial intermetallic compound and the brittle fracture behavior of Sn-3.0Ag-0.5-Cu solder (SAC305) joints on electroless nickel immersion gold (ENIG) surface finish have been investigated using Ni-P plating solution at temperatures from 75°C to 85°C and fixed pH of 4.5. SAC305 solder balls with diameter of 450 lm were mounted on the prepared ENIG-finished Cu pads and reflowed with peak temperature of 250°C. The interfacial intermetallic compound (IMC) thickness after reflow decreased with increasing Ni-P plating temperature. After 800 h of thermal aging, the IMC thickness of the sample prepared at 85°C was higher than for that prepared at 75°C. Scanning electron microscopy of the Ni-P surface after removal of the Au layer revealed a nodular structure on the Ni-P surface. The nodule size of the Ni-P decreased with increasing Ni-P plating temperature. The Cu content near the IMC layer increased to 0.6 wt.%, higher than the original Cu content of 0.5 wt.%, indicating that Cu diffused from the Cu pad to the solder ball through the Ni-P layer at a rate depending on the nodule size. The sample prepared at 75°C with thicker interfacial IMC showed greater high-speed shear strength than the sample prepared at 85°C. Brittle fracture increased with decreasing Ni-P plating temperature.

“…[1][2][3] Due to the low resistivity of Cu, the conventional Al pad playing the role of conductor is replaced by a Cu pad in the Au/EN/Cu structure in current flip chip devices. 4 The oxidation of Cu could be avoided on account of the fact that the surface is covered by an under bump metallurgy (UBM) layer.…”

Section: Introductionmentioning

confidence: 99%

Diffusion behavior of Cu in Cu/electroless Ni and Cu/electroless Ni/Sn-37Pb solder joints in flip chip technology

Hsu

Duh

2006

For Cu pads used as under bump metallization (UBM) in flip chip technology, the diffusion behavior of Cu in the metallization layer is an important issue. In this study, isothermal interdiffusion experiments were performed at 240°C for different times with solid-solid and liquid-solid diffusion couples assembled in Cu/electroless-Ni (Ni-10 wt.% P) and Cu/electroless Ni (Ni-10 wt.% P)/ Sn-37Pb joints. The diffusion structure and concentration profiles were examined by scanning electron microscopy and electron microprobe analysis. The interdiffusion fluxes of Cu, Ni and P were calculated from the concentration profiles with the aid of Matano plane evaluation. The values ofJ Cu ,J Ni , and J P decreased with increasing annealing time. The average effective interdiffusion coefficients on the order of 10 À14 cm 2 /s were also evaluated within the diffusion zone. The amounts of Cu dissolved in the intermetallic compounds (IMCs) Ni 3 Sn 4 and Ni 3 P that precipitate after annealing the Cu/electroless Ni/ Sn-37Pb joints were about 0.25 at.% and 0.5 at.%, respectively. For the short period of annealing, it appears that the presence of electroless Ni (EN) with the Sn-Pb soldering reaction assisted the diffusion of Cu through the EN layer.