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.

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.

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.

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.

Tensile fracture behaviors of solid-state-annealed eutectic SnPb and lead-free solder flip chip bumps

2004 ◽  
Vol 19 (6) ◽  
pp. 1826-1834 ◽  
Author(s):  
Jin-Wook Jang ◽  
Ananda P. De Silva ◽  
Jong-Kai Lin ◽  
Darrel R. Frear
Keyword(s):  
Solid State ◽  
Fracture Behavior ◽  
Flip Chip ◽  
Interfacial Fracture ◽  
Bulk Solder ◽  
Tensile Fracture ◽  
Solder Bumps ◽  
Snag Solder ◽  
Free Solder ◽  
Eutectic Snpb

The tensile fracture behavior for solid-state-annealed eutectic SnPb and lead-free solder flip chip bumps was examined. The annealing temperatures were in the range of 125–170 °C for 500 h. Prior to solid state annealing, the eutectic Sn–37Pb (SnPb) and Sn–0.7Cu (SnCu) solders showed fracture through the bulk solder. Brittle interfacial fracture occurred in the Sn–3.5Ag (SnAg) solder. After solid-state annealing, the fracture behavior changed dramatically. For eutectic SnPb solder, the fracture modes gradually changed from cohesive solder failure to interfacial fracture with increasing annealing temperature. The fracture mode of the SnCu solder showed greater change than the SnPb and SnCu solders. After annealing at 125 °C, the SnAg solder had a ductile taffy pull fracture, but an increase in temperature resulted in brittle interfacial fracture again. The SnCu solder maintained the same ductile taffy pull mode up to170 °C annealing, independent of the under bump metallization (UBM) type. Microstructure analysis showed that the interfacial fracture of the SnPb and SnAg solder bumps was ascribed to Pb-rich layer formation and Ag embrittlement at the interface, respectively. The bulk solder fracture of SnAg annealed at 125 °C appeared to be a transient phenomenon due to the abrupt breakdown of the hard lamella structure. The eutectic SnCu solder bumps had no significant change in the interfacial structure, except for interfacial intermetallic growth.

Electromigration Performance of Flip-Chips with Lead-Free Solder Bumps between 30 μm and 60 μm Diameter

2012 ◽  
Vol 2012 (1) ◽  
pp. 000891-000905 ◽  
Author(s):  
Rainer Dohle ◽  
Stefan Härter ◽  
Andreas Wirth ◽  
Jörg Goßler ◽  
Marek Gorywoda ◽  
...  
Keyword(s):  
Flip Chip ◽  
Failure Modes ◽  
Solder Bump ◽  
Void Formation ◽  
Lead Free ◽  
Large Temperature ◽  
Flip Chips ◽  
Solder Bumps ◽  
Current Densities

As the solder bump sizes continuously decrease with scaling of the geometries, current densities within individual solder bumps will increase along with higher operation temperatures of the dies. Since electromigration of flip-chip interconnects is highly affected by these factors and therefore an increasing reliability concern, long-term characterization of new interconnect developments needs to be done regarding the electromigration performance using accelerated life tests. Furthermore, a large temperature gradient exists across the solder interconnects, leading to thermomigration. In this study, a comprehensive overlook of the long-term reliability and analysis of the achieved electromigration performance of flip-chip test specimen will be given, supplemented by an in-depth material science analysis. In addition, the challenges to a better understanding of electromigration and thermomigration in ultra fine-pitch flip-chip solder joints are discussed. For all experiments, specially designed flip-chips with a pitch of 100 μm and solder bump diameters of 30–60 μm have been used [1]. Solder spheres can be made of every lead-free alloy (in our case SAC305) and are placed on a UBM which has been realized for our test chips in an electroless nickel process [2]. For the electromigration tests within this study, multiple combinations of individual current densities and temperatures were adapted to the respective solder sphere diameters. Online measurements over a time period up to 10,000 hours with separate daisy chain connections of each test coupon provide exact lifetime data during the electromigration tests. As failure modes have been identified: UBM consumption at the chip side or depletion of the Nickel layer at the substrate side, interfacial void formation at the cathode contact interface, and - to a much lesser degree - Kirkendall-like void formation at the anode side. A comparison between calculated life time data using Weibull distribution and lognormal distribution will be given.

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.

Experimental Study of Void Formation in Eutectic and Lead-Free Solder Bumps of Flip-Chip Assemblies

2005 ◽  
Vol 128 (3) ◽  
pp. 202-207 ◽  
Author(s):  
Daijiao Wang ◽  
Ronald L. Panton
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Flip Chip ◽  
Void Formation ◽  
Lead Free ◽  
Void Volume ◽  
Lead Free Solder ◽  
Solder Bumps ◽  
Free Solder ◽  
High Lead

This paper reports the experimental findings of void formation in eutectic and lead-free solder joints of flip-chip assemblies. A previous theory indicated that the formation of voids is determined by the direction of heating. The experiments were designed to examine the size and location of voids in the solder samples subject to different heat flux directions. A lead-free solder (Sn-3.5Ag-0.75Cu) and a eutectic solder (63Sn37Pb) were employed in the experiments. Previous experiments [Wang, D., and Panton, R. L., 2005, “Experimental Study of Void Formation in High-Lead Solder Joints of Flip-Chip Assemblies,” ASME J. Electron. Packag., 127(2), pp. 120–126; 2005, “Effect of Reversing Heat Flux Direction During Reflow on Void Formation in High-Lead Solder Bumps,” ASME J. Electron. Packag., 127(4), pp. 440–445] employed a high lead solder. 288 solder bumps were processed for each solder. Both eutectic and lead-free solder have shown fewer voids and much smaller void volume than those for high-lead solder. Compared with lead-free solder, eutectic solder has a slightly lower void volume and a lower percentage of defective bumps. For both eutectic and lead-free solders, irrespective of the cooling direction, heating solder samples from the top shows fewer defective bumps and smaller void volume. No significant effect on void formation for either eutectic or lead-free solder was found via reversing the heat flux direction during cooling. Unlike high-lead solder, small voids in eutectic or lead-free solder comprised 35-88% of the total void volume. The final distribution of voids shows a moderate agreement with thermocapillary theory, indicating the significance of the temperature gradient on the formation of voids.

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