Microstructure evolution during electromigration in eutectic SnPb solder bumps

2004 ◽  
Vol 19 (8) ◽  
pp. 2394-2401 ◽  
Author(s):  
C.M. Lu ◽  
T.L. Shao ◽  
C.J. Yang ◽  
Chih Chen
Keyword(s):  
Failure Mechanism ◽  
Microstructural Evolution ◽  
Microstructure Evolution ◽  
Under Bump Metallization ◽  
Current Stressing ◽  
Solder Bumps ◽  
Snpb Solder ◽  
Cathode Substrate ◽  
Anode Substrate ◽  
Eutectic Snpb

A technique has been developed to facilitate analysis of the microstructural evolution of solder bumps after current stressing. Eutectic SnPb solders were connected to under-bump metallization (UBM) of Ti/Cr-Cu/Cu and pad metallization of Cu/Ni/Au. It was found that the Cu6Sn5 compounds on the cathode/chip side dissolved after the current stressing by 5 × 103 A/cm2 at 150 °C for 218 h. However, on the anode/chip side, they were transformed into (Nix,Cu1-x)3Sn4 in the center region of the UBM, and they were converted into (Cuy,Ni1-y)6Sn5 on the periphery of the UBM. For both cathode/substrate and anode/substrate ends, (Cuy,Ni1-y)6Sn5 compounds were transformed into (Nix,Cu1-x)3Sn4. In addition, the bumps failed at cathode/chip end due to serious damage of the UBM and the Al pad. A failure mechanism induced by electromigration is proposed in this paper.

Microstructural Evolution During Electromigration in Eutectic SnAg Solder Bumps

2005 ◽  
Vol 20 (9) ◽  
pp. 2432-2442 ◽  
Author(s):  
Y.H. Chen ◽  
T.L. Shao ◽  
P.C. Liu ◽  
Chih Chen ◽  
T. Chou
Keyword(s):  
Microstructural Evolution ◽  
Current Density ◽  
Electron Flow ◽  
Under Bump Metallization ◽  
Substrate Side ◽  
Current Stressing ◽  
Solder Bumps ◽  
Cathode Substrate ◽  
Snag Solder ◽  
A Current

Microstructural changes induced by electromigration were studied in eutectic SnAg solder bumps jointed to under-bump metallization (UBM) of Ti/Cr–Cu/Cu and pad metallization of Cu/Ni/Au. Intermetallic compounds (IMCs) and phase transformations were observed during a current stress of 1 × 104 A/cm2 at 150 °C. On the cathode/substrate side, some of the (Cuy,Ni1−y)6Sn5 transformed into (Nix,Cu1−x)3Sn4 due to depletion of Cu atoms caused by the electron flow. It is found that both the cathode/chip and anode/chip ends could be failure sites. On the cathode/chip side, the UBM dissolved after current stressing for 22 h, and failure may occur due to depletion of solder. On the anode/chip side, a large amount of (Cuy,Ni1−y)6Sn5 or (Nix,Cu1−x)3Sn4 IMCs grew at the low-current-density area due to the migration of Ni and Cu atoms from the substrate side, which may be responsible for the electromigration failure at this end.

Measurement of electromigration activation energy in eutectic SnPb and SnAg flip-chip solder joints with Cu and Ni under-bump metallization

2010 ◽  
Vol 25 (9) ◽  
pp. 1847-1853 ◽  
Author(s):  
Hsiao-Yun Chen ◽  
Chih Chen
Keyword(s):  
Activation Energy ◽  
Flip Chip ◽  
Void Formation ◽  
Under Bump Metallization ◽  
Solder Bumps ◽  
Snpb Solder ◽  
Snag Solder ◽  
Temperature Coefficient Of Resistivity ◽  
Eutectic Snpb ◽  
Real Temperature

Electromigration activation energy is measured by a built-in sensor that detects the real temperature during current stressing. Activation energy can be accurately determined by calibrating the temperature using the temperature coefficient of resistivity of an Al trace. The activation energies for eutectic SnAg and SnPb solder bumps are measured on Cu under-bump metallization (UBM) as 1.06 and 0.87 eV, respectively. The activation energy mainly depends on the formation of Cu–Sn intermetallic compounds. On the other hand, the activation energy for eutectic SnAg solder bumps with Cu–Ni UBM is measured as 0.84 eV, which is mainly related to void formation in the solder.

Microstructure evolution in Cu pillar/eutectic SnPb solder system during isothermal annealing

2009 ◽  
Vol 15 (5) ◽  
pp. 815-818 ◽  
Author(s):  
Byoung-Joon Kim ◽  
Gi-Tae Lim ◽  
Jaedong Kim ◽  
Kiwook Lee ◽  
Young-Bae Park ◽  
...  
Keyword(s):  
Microstructure Evolution ◽  
Isothermal Annealing ◽  
Cu Pillar ◽  
Snpb Solder ◽  
Eutectic Snpb

Interfacial stability of eutectic SnPb solder and composite 60Pb40Sn solder on Cu/Ni(V)/Ti under-bump metallization

2007 ◽  
Vol 22 (3) ◽  
pp. 735-741 ◽  
Author(s):  
Albert T. Wu ◽  
F. Hua
Keyword(s):  
Sacrificial Layer ◽  
Under Bump Metallization ◽  
Worst Case ◽  
Die Attach ◽  
Snpb Solder ◽  
Cu Film ◽  
Kirkendall Voids ◽  
The Stability ◽  
Cu Thin Film ◽  
Eutectic Snpb

Eutectic SnPb solder has been widely used in packaging for several decades. The stability of the interface between solder and under-bump metallization (UBM) is an important issue that has led to many studies. Even though Ni atoms dissolve much slower into SnPb solder than Cu, the intermetallic compound, Ni3Sn4, which forms when eutectic SnPb solder reacts with Ni(V)/Ti UBM, is not stable on Ti layer, creates V-rich zone, and causes spalling. To prevent the phenomenon, and the resulting reduction of mechanical reliability in solder joints, we propose the addition of a layer of Cu thin film to serve as a sacrificial layer. Both eutectic SnPb solder and composite solder (high-Pb solder with eutectic SnPb solder) were studied in severe reflow conditions to simulate the worst case of die attach and later reflow process. Cu film first was consumed completely to form a compound. Due to lower interfacial energy between Cu6Sn5 and Ni(V), the interface was stable and no spalling occurred. However, the same thickness of Cu was insufficient to prevent Ni from diffusing into solder or compound. Not only diffusion of Ni atoms was observed; Sn atoms also diffused into the Ni(V) layer. The Sn–Ni reaction caused the interface between the compound and Ni(V) to retreat into the Ni(V) layer. The compound was not stable at the interface, and spalling could be seen. Due to the interdiffusion of Ni and Sn, many Kirkendall voids were also observed at both side of the interface.

scholarly journals Cross interactions on interfacial compound formation of solder bumps and metallization layers during reflow

2004 ◽  
Vol 19 (12) ◽  
pp. 3654-3664 ◽  
Author(s):  
T.L. Shao ◽  
T.S. Chen ◽  
Y.M. Huang ◽  
Chih Chen
Keyword(s):  
Flip Chip ◽  
Driving Forces ◽  
The Other ◽  
Compound Formation ◽  
Bump Height ◽  
Performance Requirements ◽  
Substrate Side ◽  
Solder Bumps ◽  
Snpb Solder ◽  
Eutectic Snpb

While the dimension of solder bumps keeps shrinking to meet higher performance requirements, the formation of interfacial compounds may be affected more profoundly by the other side of metallization layer due to a smaller bump height. In this study, cross interactions on the formation of intermetallic compounds (IMCs) were investigated in eutectic SnPb, SnAg3.5, SnAg3.8Cu0.7, and SnSb5 solders jointed to Cu/Cr–Cu/Ti on the chip side and Au/Ni metallization on the substrate side. It is found that the Cu atoms on the chip side diffused to the substrate side to form (Cux,Ni1−x)6Sn5 or (Niy,Cu1−y)3Sn4 for the four solders during the reflow for joining flip chip packages. For the SnPb solder, Au atoms were observed on the chip side after the reflow, yet few Ni atoms were detected on the chip side. In addition, for SnAg3.5 and SnSn5 solders, the Ni atoms on the substrate side migrated to the chip side during the reflow to change binary Cu6Sn5 into ternary (Cux,Ni1−x)6Sn5 IMCs, in which the Ni weighed approximately 21%. Furthermore, it is intriguing that no Ni atoms were detected on the chip side of the SnAg3.8Cu0.7 joint. The possible driving forces responsible for the diffusion of Au, Ni, and Cu atoms are discussed in this paper.

Microstructure Studies of Under Bump Metallization Systems Using Transmission Electron Microscopy

2002 ◽  
Author(s):  
Chih-Hang Tung ◽  
Poi-Siong Teo ◽  
Marvin C.Y. Lo ◽  
George T.T. Sheng
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Sample Preparation ◽  
Under Bump Metallization ◽  
Interface Reactions ◽  
Bonding System ◽  
Transmission Electron ◽  
Snpb Solder ◽  
Ball Bonding ◽  
Eutectic Snpb

Abstract In this study, the interface reactions between eutectic SnPb solder and two Ni-based UBM systems are reported, namely the sputtered Cu/Ni(V)/Al and the electroless Au/Ni(P) systems. Comparisons are made to the conventional Au/Al ball bonding system in terms of microstructure evolution, and metallurgical stability. TEM sample preparation is critical in this analysis. The capability of TEM in UBM microstructure studies is demonstrated.

Early stage of material movements in eutectic SnPb solder joint undergoing current stressing at 150°C

2007 ◽  
Vol 91 (2) ◽  
pp. 021906 ◽  
Author(s):  
C. E. Ho ◽  
A. Lee ◽  
K. N. Subramanian ◽  
W. Liu
Keyword(s):  
Solder Joint ◽  
Early Stage ◽  
Current Stressing ◽  
Snpb Solder ◽  
Eutectic Snpb

Interface reactions and phase equilibrium between Ni/Cu under-bump metallization and eutectic SnPb flip-chip solder bumps

2003 ◽  
Vol 18 (4) ◽  
pp. 935-940 ◽  
Author(s):  
Chien-Sheng Huang ◽  
Jenq-Gong Duh
Keyword(s):  
Multilayer Structure ◽  
Electron Probe ◽  
Flip Chip ◽  
Electronics Packaging ◽  
Elemental Distribution ◽  
Under Bump Metallization ◽  
Interface Reactions ◽  
Solder Bumps ◽  
Different Thickness ◽  
Eutectic Snpb

Ni-based under-bump metallization (UBM) for flip-chip application is widely used in today's electronics packaging. In this study, electroplated Ni UBM with different thickness was used to evaluate the interfacial reaction during multiple reflow between Ni/Cu UBM and eutectic Sn–Pb solders in the 63Sn–37Pb/Ni/Cu/Ti/Si3N4/Si multilayer structure. During the first cycle of reflow, Cu atoms diffused through electroplated Ni and formed the intermetallic compound (IMC) (Ni1−x, Cux)3Sn4. After more than three times of reflow, Cu atoms further diffused through the boundaries of (Ni1−x, Cux)3Sn4 IMC and reacted with Ni and Sn to form another IMC of (Cu1-y, Niy)6Sn5. After detailed quantitative analysis by electron probe microanalysis, the values of y were evaluated to remain around 0.4; however, the values of x varied from 0.02 to 0.35. The elemental distribution of IMC in the interface of the joint assembly could be correlated to the Ni–Cu–Sn ternary equilibrium. In addition, the mechanism of (Cu1−y, Niy)6Sn5 formation was also probed.

Effects of electromigration on microstructural evolution of eutectic SnPb flip chip solder bumps

2006 ◽  
Vol 83 (11-12) ◽  
pp. 2391-2395 ◽  
Author(s):  
Dae-Gon Kim ◽  
Won-Chul Moon ◽  
Seung-Boo Jung
Keyword(s):  
Microstructural Evolution ◽  
Flip Chip ◽  
Solder Bumps ◽  
Eutectic Snpb

Damages and Microstructural Variation of High-lead and Eutectic SnPb Composite Flip Chip Solder Bumps Induced by Electromigration

2005 ◽  
Vol 20 (8) ◽  
pp. 2184-2193 ◽  
Author(s):  
Yeh-Hsiu Liu ◽  
Kwang-Lung Lin
Keyword(s):  
Flip Chip ◽  
Solder Bump ◽  
Electron Flow ◽  
Electron Probe Microanalyzer ◽  
Current Stressing ◽  
Solder Bumps ◽  
Underbump Metallization ◽  
Current Polarity ◽  
High Lead ◽  
Eutectic Snpb

The electromigration behavior of the high-lead and eutectic SnPb composite solder bumps was investigated at 150 °C with 5 × 103 A/cm2 current stressing for up to 1711 h. The diameter of the bumps was about 125 μm. The underbump metallization (UBM) on the chip side was sputtered Al/Ni(V)/Cu thin films, and the Cu pad on the board side was plated with electroless Ni/Au. It was observed that damages occurred in the joints in a downward electron flow (from chip side to the substrate side), while those joints having the opposite current polarity showed only minor changes. In the case of downward electron flow, electromigration damages were observed in the UBM and solder bumps. The vanadium in Ni(V) layer was broken under current stressing of 1711 h while it was still intact after current stressing of 1000 h. The electron probe microanalyzer (EPMA) elemental mapping clearly shows that the Al atoms in the trace migrated through the UBM into the solder bump during current stressing. Voids were found in the solder bump near the UBM/solder interface. The Sn-rich phases of the solder bumps showed gradual streaking and reorientation upon current stressing. This resulted in the formation of uniaxial Sn-rich phases in the middle of the solder bump, while the columnar and fibrous Sn-rich phases were formed in the surrounding regions. The formation mechanism of electromigration-induced damage to the UBM structure and solder bump were discussed.

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