Under bump metallurgy study for Pb-free bumping

Jang, Seung‐Ho; Wolf, J.K.; Paik, Kyung‐Wook

doi:10.1007/s11664-002-0103-x

Cited by 11 publications

(5 citation statements)

References 33 publications

(26 reference statements)

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“…Among many Pb-free solder alloys, SnAg, SnAgCu, and SnCu alloys are promising candidates for replacing the Sn37Pb alloy. [1][2][3]5 However, proper Pb-free solder alloys compatible with electroless Ni-P UBM have not been well understood yet. Especially, because of Cu addition in the solder alloy, a typical NiSn binary reaction could change into a Cu-Ni-Sn ternary reaction at Ni/Sn-based solder interfaces.…”

Section: Introductionmentioning

confidence: 99%

Effects of Cu contents in Pb-free solder alloys on interfacial reactions and bump reliability of Pb-free solder bumps on electroless Ni-P under-bump metallurgy

Jeon

Paik

Ostmann

et al. 2005

Journal of Elec Materi

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Using the screen-printed solder-bumping technique on the electroless plated Ni-P under-bump metallurgy (UBM) is potentially a good method because of cost effectiveness. As SnAgCu Pb-free solders become popular, demands for understanding of interfacial reactions between electroless Ni-P UBMs and Cu-containing Pb-free solder bumps are increasing. It was found that typical Ni-Sn reactions between the electroless Ni-P UBM and Sn-based solders were substantially changed by adding small amounts of Cu in Sn-based Pb-free solder alloys. In Cu-containing solder bumps, the (Cu,Ni)(6)Sn-5 phase formed during initial reflow, followed by (Ni,Cu)(3)Sn-4 phase formation during further reflow and aging. The Sn3.5Ag solder bumps showed a much faster electroless Ni-P UBM consumption rate than Cu-containing solder bumps: Sn4.0Ag0.5Cu and Sn0.7Cu. The initial formation of the (Cu,Ni)(6)Sn-5 phase in SnAgCu and SnCu solders significantly reduced the consumption of the Ni-P UBM. The more Cu-containing solder showed slower consumption rate of the Ni-P UBM than the less Cu-containing solder below 300degreesC heat treatments. The growth rate of the (Cu,Ni)(6)Sn-5 intermetallic compound (IMC) should be determined by substitution of Ni atoms into the Cu sublattice in the solid (Cu,Ni)(6)Sn-5 IMC. The Cu contents in solder alloys only affected the total amount of the (Cu,Ni)(6)Sn-5 IMC. More Cu-containing solders were recommended to reduce consumption of the Ni-based UBM. In addition, bump shear strength and failure analysis were performed using bump shear test

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Section: Introductionmentioning

confidence: 99%

Effects of Cu contents in Pb-free solder alloys on interfacial reactions and bump reliability of Pb-free solder bumps on electroless Ni-P under-bump metallurgy

Jeon

Paik

Ostmann

et al. 2005

Journal of Elec Materi

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“…Once the adhesion layer is consumed, the intermetallic compounds ͑IMCs͒ formed at the interface are spalled off from the nonwettable layer and the joint become fragile. [7][8][9][10][11][12][13][14] Eutectic SnAg (T eut ϭ221°C) and eutectic SnAgCu (T eut ϭ217°C) have been recommended by National Electronic Manufacturing Initiative as a replacement of the SnPb solders in the chip joint process for the manufacturing of low cost, large volume consumer products. 4,15 At higher reflow temperature, these solders can dissolve higher amounts of Cu than the eutectic SnPb.…”

Section: Introductionmentioning

confidence: 99%

Effect of 0.5 wt % Cu addition in Sn–3.5%Ag solder on the dissolution rate of Cu metallization

Alam

Chan

2003

Journal of Applied Physics

103

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The dissolution of thin film under-bump-metallization ͑UBM͒ by molten solder has been one of the most serious processing problems in electronic packaging technology. Due to a higher melting temperature and a greater Sn content, a molten lead-free solder such as eutectic SnAg has a faster dissolution rate of thin film UBM than the eutectic SnPb. The work presented in this paper focuses on the role of 0.5 wt % Cu in the base Sn-3.5%Ag solder to reduce the dissolution of the Cu bond pad in ball grid array applications. We found that after 0.5 wt % Cu addition, the rate of dissolution of Cu in the molten Sn-3.5%Ag solder slows down dramatically. Systematic experimental work was carried out to understand the dissolution behavior of Cu by the molten Sn-3.5%Ag and Sn-3.5%Ag-0.5%Cu solders at 230-250°C, for different time periods ranging from 1 to 10 min. From the curves of consumed Cu thickness, it was concluded that 0.5 wt % Cu addition actually reduces the concentration gradient at the Cu metallization/molten solder interface which reduces the driving force of dissolution. During the dissolution, excess Cu was found to precipitate out due to heterogeneous nucleation and growth of Cu 6 Sn 5 at the solder melt/oxide interface. In turn, more Cu can be dissolved again. This process continues with time and leads to more dissolution of Cu from the bond pad than the amount expected from the solubility limit, but it occurs at a slower rate for the molten Sn-3.5%Ag-0.5%Cu solder.

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“…[9][10][11] Among the deposition methods, electrolytic plating is highly recommended for a fine-pitch and lead-free solder because of the stability of the process, the feasibility of fine pitch, and the low cost. [12][13][14][15][16][17][18] Evaporation is too expensive, even though it can deposit very fine-pitch solder bumps. Stencil printing has a much lower cost, but it is highly doubtful for fine-pitch bumping.…”

Section: Introductionmentioning

confidence: 99%

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

Kim

et al. 2004

Journal of Elec Materi

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Pure Ni, the Ni-Cu alloy, and pure Cu layers as the under bump metallurgy (UBM) for a flip-chip solder joint were deposited by electrolytic plating. For the pure Ni layer, residual stress can be controlled by adding a wetting agent and decreasing current density, and it is always under tensile stress. The Ni-Cu alloys of different Cu compositions from ϳ20wt.%Cu to 100wt.%Cu were deposited with varying current density in a single bath. The residual stress was a strong function of current density and Cu composition. Decreasing current density and increasing Cu content simultaneously causes the residual stress of the metal layers to sharply decrease. For the pure Cu layer, the stress is compressive. The Cu layer acts as a cushion layer for the UBM. The residual stress of the UBM strongly depends on the fraction of the Cu cushion layer. Interfacial reaction of the UBM with Sn-3.5 wt.% Ag was studied. As the Cu contents of Ni-Cu alloys increased, the dissolution rate increased. Several different intermetallic compounds (IMCs) were found. The lattice constants of alloys and the IMC increase with increasing Cu contents because the larger Cu atoms substitute for the smaller Ni atoms in the crystallites. The Cu content of the IMC are strongly dependent on the composition of the alloys. Ball shear tests were done with different metal-layer schemes. The failure occurs through the IMC and solder.

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Under bump metallurgy study for Pb-free bumping

Cited by 11 publications

References 33 publications

Effects of Cu contents in Pb-free solder alloys on interfacial reactions and bump reliability of Pb-free solder bumps on electroless Ni-P under-bump metallurgy

Effects of Cu contents in Pb-free solder alloys on interfacial reactions and bump reliability of Pb-free solder bumps on electroless Ni-P under-bump metallurgy

Effect of 0.5 wt % Cu addition in Sn–3.5%Ag solder on the dissolution rate of Cu metallization

Residual stress and interfacial reaction of the electroplated Ni-Cu alloy under bump metallurgy in the flip-chip solder joint

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