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

Abstract

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/

Interfacial reaction between Sn-Bi alloy and Ni substrate

“…This indicates that the growth of Ni 3 Sn 4 is controlled by a diffusion mechanism, in agreement with the literature. [9][10][11][12][13][14] Moreover, the average thickness of Ni 3 Sn 4 decreases with increasing Bi content (see Fig. 3).…”

“…Thus, the present work is consistent with previously reported experimental results. [9][10][11][12][13][14] In addition, it is of value to note if other phases can form at the interface. According to Fig.…”

“…Chen et al 10 investigated the interfacial reaction between solid Sn-Bi eutectic alloy and Ni substrate at different temperatures for various reaction times. Recently, Young et al 11 reported the interfacial reaction for electroplated Ni and electroless Ni with Sn-Bi eutectic alloy annealing at 418 and 453 K. In their work, [9][10][11][12][13][14] only Ni 3 Sn 4 was found as a product of the interfacial reaction at each reaction temperature for various reaction times. This seems unreasonable, as two IMCs exist in the Ni-Bi binary system (NiBi and NiBi 3 ) and three (Ni 3 Sn, Ni 3 Sn 2, Ni 3 Sn 4 ) in the Ni-Sn binary system according to the Ni-Bi and Ni-Sn binary phase diagram.…”

“…Several studies [9][10][11][12][13][14] have reported on the interfacial reaction between Sn-Bi eutectic alloy and Ni substrate. Kang et al 9 studied the interfacial reaction between liquid Sn-Bi eutectic alloy and Ni substrate at 443 K for 20 min.…”

An Investigation of Diffusion Barrier Characteristics of an Electroless Co(W,P) Layer to Lead-Free SnBi Solder

“…Alloy reactions between SnBi and EN or Cu layers and their barrier characteristics have been extensively studied. [8][9][10][11][12][13][14][15][16][17][18] Recently, electroless cobalt (Co) has attracted a lot of research interest due to its promising application as a diffusion barrier in Cu-ICs 19 and UBMs. [20][21][22][23] However, studies regarding the diffusion barrier characteristics of electroless Co layer/SnBi solder couples are lacking.…”