Growth Mechanism Of Intermetallic Compounds Research Articles

Microstructural evaluation of interfacial intermetallic compounds between Sn58Bi and ENEPIG

BackgroundLow carbonization and Restriction of Hazardous Substances (RoHS) regulations have promoted the development of low-temperature lead-free solder. The solder and substrate are critical entities of joint connections. MethodsSn58Bi has been considered a promising low-temperature solder. Electroless nickel/electroless palladium/immersion gold (ENEPIG) is a good surface finish that prevents solder joints from oxidizing and extends the shelf life of the substrates. In this study, the interfacial reactions between the Sn58Bi solder and ENEPIG surface finish were systematically analyzed. Findings(Au,Pd,Ni)(Sn,Bi)4 was observed after reflow at 160 °C. Au and Pd dissolved into solder rapidly in the beginning. NiSn4 and Ni3Sn4 with small amounts of Au and Pd dissolution formed at the interface after aging. The morphology of NiSn4 evolved from block-like to needle-shaped and finally to a layered configuration as the aging temperature and time increase. Ni3Sn4 was observed between NiSn4 and substrate above 100 °C. This study established the growth mechanism of intermetallic compounds (IMCs) in the reaction between Sn58Bi and ENEPIG for low-carbon emitting processes.

Solid/solid state interfacial reactions in the lead-free solders/Cu- 2.3%wt. Fe alloy (C194) couples

BackgroundLead-free solders (LFSs) involve incorporating trace elements into Sn, resulting in alloys like Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and Sn-0.7 wt.% Cu (SC). These solder have similar properities to Sn-Pb solders. C194, renowned for its exceptional corrosion resistance, high strength, and good weldability, serves as a preferred lead-frame material in electronic packaging. In this study, we investigated the solid/solid state interfacial reactions between the LFS and Cu-2.3 wt.% Fe alloy (C194). MethodsThree LFS including Sn, SAC, and SC were first reflowed with C194 to form the LFS/C194 couple. Then the LSF/C194 couples were aged at 125–175 ℃ for 100–2000 h. Significant findingsThe results revealed that only the (Cu, Fe)6Sn5 phase was formed in the Sn/C194 couple aged at 125 ℃. At higher temperatures and longer aging times, the (Cu, Fe)3Sn phase was formed in all three couples. The Fe addition into Cu could inhibit the (Cu, Fe)3Sn phase growth. Kirkendall voids in this study occur more frequently with the increase in aging temperatures and times, but the intensity varies in each system. Meanwhile, the thickness of total intermetallic compound (IMC) was increased with the increase in aging times and temperatures in these three couples. The IMC growth mechanism is diffusion controlled in all LFSs/C194 couples.

Phase Equilibria of the Ag-Al-Au Ternary System and Interfacial Reactions in the Au-xAg/Al Couples at 450 °C.

The phase equilibria of the Ag-Al-Au ternary system and the solid-state reaction couple for the Au-xAg/Al system were investigated isothermally at 450 °C. By investigating the Ag-Al-Au ternary system and its isothermal section, this study aims to provide a clearer understanding of the phase stability and interfacial reactions between different phases. This information is crucial for designing materials and processes in electronic packaging, with the potential to reduce costs and improve reliability. There were seven single-phase regions, thirteen two-phase regions, and six three-phase regions, with no ternary intermetallic compound (IMC) formed in the isothermal section of the Ag-Al-Au ternary system. When the Au-25 wt.% Ag/Al couple was aged at 450 °C for 240-1500 h, the AuAl2, Au2Al, and Au4Al phases formed at the interface. When the Ag contents increased to 50 and 75 wt.%, the Ag2Al, AuAl2, and Au4Al phases formed at the interface. When the aging time increased from 240 h to 1500 h, the total IMC thickness in all Au-xAg/Al couples became thicker, but the types of IMCs formed at the interface did not change. The total IMC thickness also increased with the increase in the Ag content. When the Ag content was greater than 25 wt.%, the Au2Al phase was converted into the Ag2Al phase. The IMC growth mechanism in all of the couples followed a reaction-controlled process.

The design of low-temperature solder alloys and the comparison of mechanical performance of solder joints on ENIG and ENEPIG interface

In recent years, in order to adapt to the trend of low-temperature assembly and integration, low-temperature hybrid solders with multiple elements added to the tin solder matrix have been investigated. In this regard, the morphology and size of intermetallic compounds (IMCs) are altered by adding some alloying elements, and the strength of solder joints is improved to some extent. Different pad surface treatments affect the growth of IMC, which leads to various failure modes in interconnect solder joints. Therefore, it is necessary to study the interfacial reaction, microstructure and mechanical properties of hybrid solder and different metal pads to explore the growth mechanism of IMC and the failure modes of solder joints. In this paper, mixed Sn–3Ag-0.5Cu/Sn–58Bi low-temperature solder joints on Au/Ni/Cu (ENIG) and Au/Pd/Ni/Cu (ENEPIG) substrates are investigated. The results show that the addition of palladium element can change the IMC morphology, refine the grain size of the hybrid solder joints, and affect the fracture failure mode of the solder joints under shear force. The average shear strength is significantly higher than that of solder joints with ENIG surfaces under different process parameters. Thermodynamic calculations of enthalpy change and the effect of Jackson's parameter α value on IMC morphology are also investigated in this paper. The addition of palladium elements increases the α value and is more favorable to the formation of columnar grains. This provides guidance for the grain growth of IMC in hybrid solder joints with added alloying elements.

Interfacial reactions in the Sn-9.0 wt.% Zn/Cu-Ti alloy (C1990 HP) couple

PurposeThe purpose of this study was to examine the influence of adding a small amount of Ti to a Cu-based alloy, specifically the commercial Hyper Titanium Copper alloy (C1990 HP), which contains Cu-3.28 wt.% Ti, on its interfacial reaction with Sn-9.0 wt.% Zn (SnZn) solder, using the liquid/solid reaction couple technique.Design/methodology/approachThe SnZn/C1990 HP couples were subjected to a reaction temperature of 240–270°C for a duration of 0.5–5 h. The resulting reaction couple was characterized using a scanning electron microscope, energy dispersive spectrometer, electron probe microanalyzer and X-ray diffractometer.FindingsIt was observed that the scallop-shaped CuZn5 and planar Cu5Zn8 phases were formed in almost all SnZn/C1990 HP couples. With increased reaction duration and temperature, the Cu-rich intermetallic compound (IMC)-Cu5Zn8 phase became a dominant IMC formed at the interface. The total thickness of the IMCs was increased with the increase in the reaction duration and temperature. The IMC growth obeyed the parabolic law, and the IMC growth mechanism was diffusion controlled. The activation energy of the SnZn/C1990 HP couple was 64.71 kJ/mol.Originality/valueThis article presents an analysis of the IMC thickness in each sample using ImageJ software, followed by kinetic analysis using Origin software at various reaction temperatures of SnZn/C1990 HP in liquid/solid couples. The study also includes detailed reports on the morphology, interface composition and X-ray diffraction analysis, as well as the activation energy. The findings can serve as a valuable reference for electronic packaging companies that utilize C1990 HP substrates.

Investigation of the Sn-0.7 wt.% Cu Solder Reacting with C194, Alloy 25, and C1990 HP Substrates

Cu-based alloys are one of the most promising substrates to enhance the performance of lead-frame materials. In the present study, the interfacial reactions in the Sn-0.7 wt.% Cu (SC) lead-free solder reacting with Cu-3.3 wt.% Fe (C194), Cu-2.0 wt.% Be (Alloy 25), and Cu-3.3 wt.% Ti (C1990 HP) were investigated. The material underwent a liquid–solid interface reaction, and the reaction time was 0.5 to a few hours at the reaction temperatures of 240 °C, 255 °C, and 270 °C. The morphology, composition, growth rate, and growth mechanism of the intermetallic compounds (IMCs) formed at the interface were investigated in this study. The results showed that the reaction couples of SC/C194, SC/Alloy 25, and SC/C1990 HP formed IMCs, which were the [(Cu, Fe)6Sn5 and (Cu, Fe)3Sn], [(Cu, Be)3Sn and (Cu, Be)6Sn5], and [Cu6Sn5] phases, respectively. Finally, the IMC growth mechanism for the SC/C194, SC/Alloy 25, and SC/C1990 HP couples displayed reaction control, grain boundary diffusion control, and diffusion control, respectively.

Nucleation and growth of intermetallic compounds on the prefabricated Cu6Sn5 layer

In the 3D advanced packaging process, solder joints undergo multiple reflows and the intermetallic compounds will continue to grow on the Cu6Sn5 layer. However, the nucleation and growth mechanism of intermetallic compounds on the Cu6Sn5 layer is not clear. In this paper, the Cu6Sn5 layer was prefabricated on (001) Cu and the reaction between the prefabricated Cu6Sn5 layer and the Sn-based solder under the influence of solder composition was investigated. Results show that when the prefabricated Cu6Sn5 layer has a preferred orientation, the orientation can be retained after reflowing. When the orientation of the prefabricated Cu6Sn5 layer is randomly distributed, small Cu6Sn5 grains nucleate on the surface of the prefabricated Cu6Sn5 layer and grow along the <0001> crystal direction. Besides, the addition of Ag is beneficial to the heritability of orientation and inhibits the nucleation of small Cu6Sn5 grains on the surface of the prefabricated Cu6Sn5 layer.

A new insight on the diffusion growth mechanism of intermetallic compounds in Al-Er system

The diffusion growth of intermetallic compounds in Al-Er alloys are closely related to the properties of the alloys. The current work aims at explaining the dominance of Al3Er in the Al-Er alloys precipitation phases and the interface thin layer phenomenon by diffusion couple technique, estimating the parabolic growth constant and diffusion activation energy of intermetallic compound in Al-Er diffusion couples to provide theoretical guidance for the design of new Al-Er alloys. In this work, Al-Er diffusion couples were successfully prepared by casting-cladding method in the atmosphere. The growth of Al-Er intermetallic compounds at diffusion couple interface during annealing were observed and recorded by High-Temperature Laser-Scanning Confocal Microscopy at 673, 698, 723 and 748 K respectively. The results show that the growth characteristics of Al-Er intermetallic compounds were accord with layer-terraced growth during annealing. The thickness of intermetallic compound was linear with the square root of time at experimental temperature. The intermetallic compound layer was composed of Al3Er and a very thin AlEr phase. The parabolic growth constants of Al3Er phase at 673, 698, 723 and 748 K were 1.017 × 10−14, 1.609 × 10−14, 3.111 × 10−14 and 4.76 × 10−14 respectively. The activation energy of Al3Er phase was (88.4 ± 5.3) kJ/mol and the pre-exponential factor was 7.126 × 10−8 m2/s.

Study of microstructure and mechanical properties of Cu/In-45Cu/SiC joints connected by ultrasonic-assisted TLP

With the application of the third-generation semiconductor SiC in high-power, high-current-density devices, the service temperature of electronic devices is getting higher and higher, and the traditional soldering materials and technologies are facing many technical problems, making it difficult to achieve the goal of “low-temperature connection and high-temperature service.” In this paper, a new type of In45Cu composite solder paste was developed to address this problem, and all-Cu2In IMC can be obtained at a service temperature of 600 °C by using ultrasonic-assisted TLP at 260 °C. In this paper, the effects of ultrasonic action time on the microstructure evolution, shear strength, and growth mechanism of intermetallic compounds (IMCs) of the joints were investigated. The results showed that the cavitation effect and acoustic flow effect of ultrasound accelerated the reaction between liquid In and Cu particles, and when the ultrasound action time was 30 s, all In and Cu particles in the joint were transformed into Cu2In, and the shear strength of the joint was 19.69 MPa, at which time the joint was dense due to the expansion of the volume of Cu2In, which eliminated the voids caused by the volume shrinkage of Cu11In9, making it possible for the electronic device to serve for a long time at high temperature.

On the study of morphological characteristics and growth mechanism of intermetallic compounds in ultrasonically fabricated Cu–Sn solder joints

On the study of morphological characteristics and growth mechanism of intermetallic compounds in ultrasonically fabricated Cu–Sn solder joints

Interfacial Reactions in Lead-Free Solder/Cu-2.0Be (Alloy 25) Couples

The interfacial reactions between lead-free solders Sn, Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and Sn-9 wt.% Zn (SZ), and Cu-2.0 wt.% Be (Alloy 25) were investigated using the liquid/solid couple technique. The couples were reacted at 240–270°C for 0.5–10 h. The results revealed that only the scallop-shaped (Cu, Be)6Sn5 phase was formed at 240°C for 0.5–2 h in the Sn/Alloy 25 couple. At a longer time (> 4 h) or higher temperature (255°C and 270°C), the (Cu, Be)3Sn phase was observed at the interface. In the SAC/Alloy 25 couple, the results were similar to that in the Sn/Alloy 25 couples. Only the scallop-shaped (Cu, Be, Ag)6Sn5 phase was formed for the short reaction time or at lower reaction temperature. With increasing reaction times and temperatures, both the (Cu, Be, Ag)6Sn5 and (Cu, Be, Ag)3Sn phases were observed at the SAC/Alloy 25 interface. In the SZ/Alloy 25 couple, the (Cu, Sn)Zn5 and (Cu, Sn)5Zn8 phases were observed. Of these three couples, the intermetallic compound (IMC) thickness obeyed the parabolic law, and the IMC growth mechanism was diffusion-controlled.

Study on Electromigration Effects and IMC Formation on Cu–Sn Films Due to Current Stress and Temperature

In this study, the effects of electromigration on a solder/copper substrate due to temperature and current density stress were investigated. The copper–tin (Cu–Sn) film samples were subjected under a fixed current and various heating conditions (130 °C and 180 °C) and current densities (different cross-sectional areas). The micro-structural changes and intermetallic compound (IMC) formation were observed, and failure phenomena (brittle cracks, voids, bumps, etc.) on the structures of samples were discussed. The results showed that the IMC thickness increased as the temperature and current density increased. Moreover, it was found that the higher the temperature and current density was, the greater the defects that were observed. By adjusting the designs of sample structures, the stress from the current density can be decreased, resulting in reduced failure phenomena, such as signal delay, distortion, and short circuiting after long-term use of the material components. A detailed IMC growth mechanism and defect formation were also closely studied and discussed.

Interlayer Material Design Reducing Transient Liquid Phase Bonding Time

Power semiconductors require a large bonding area for die attachment. For this purpose, transient liquid phase bonding (TLPB) was applied using fabricated interlayers, namely Sn–3Cu and Sn–10Cu, to study the intermetallic compound (IMC) formation, and the results were compared with those obtained with a pure-Sn interlayer. The Sn–3Cu and Sn–10Cu interlayers exhibited primary IMC fraction of 0.06 and 0.24, respectively, before the TLPB. For a Cu/interlayer/Cu sandwich structure, the TLPB was applied at 250 °C over various time periods (1–4 h). A reduction in the bonding time was more significant for a Sn–10Cu interlayer with a larger amount of primary IMCs than for the Sn–3Cu interlayer. The time exponent of the IMC fraction with respect to the bonding time was approximately 0.3 for all interlayers. This implies that the IMC growth mechanism is governed by a liquid channel or wet grain boundary diffusion. The nearly constant fraction and increasing size of the primary IMCs produced during the TLPB indicate that the primary IMCs coalesced during this process. The primary IMCs preferentially coalesced with the interface IMCs produced during the TLPB when they had the same crystalline orientation.

Growth characterization of intermetallic compounds at the Cu/Al solid state interface

Cu/Al cold-rolled composite plates were annealed in the temperature range of 573∼773 K. The growth mechanism of intermetallic compounds formed at the Cu/Al solid-state interface was analyzed from the point of view of diffusion kinetics. After annealing, the interfacial reaction layer of the sample consisted of three kinds of intermetallic compound: Al2Cu adjacent to Al, Al4Cu9 adjacent to Cu and AlCu between Al2Cu and Al4Cu9. The formation sequence of the intermetallic layers was Al2Cu, Al4Cu9, and AlCu. The results show that the growth of Al2Cu, Al4Cu9 and AlCu layer were governed by reaction-controlled mechanism in the previous period and by diffusion-controlled mechanism in the latter period in the annealing temperature range of 573 to 773 K, and the higher annealing temperature, the earlier the reaction-controlled stage ends for three kinds of intermetallic compound.

Investigation of the interfacial reactions between Sn-3.0 wt%Ag-0.5 wt%Cu solder and Cu[sbnd]Ti alloy (C1990HP)

The interfacial reactions between Sn-3.0 wt%Ag-0.5 wt%Cu (SAC) solder and CuTi alloy (C1990HP) using the solid/liquid reaction couple technique reflowed at 240, 255, and 270 °C for 10 min to 20 h was first investigated. The results revealed that the Cu6Sn5 phase and the precipitated Ti2Sn3 and Ag3Sn phases with a small grain size were formed and no Cu3Sn phase was observed in the SAC/C1990HP couple when the reflowing time was longer than 30 min. In addition, the Ti2Sn3 phase was observed among the upper the Cu6Sn5 phase. Comparing the SAC/Cu reaction couple, the thicker intermetallic compound (IMC) layers were observed in the SAC/C1990HP reaction couple. It was also shown that the massive spalling of the Cu6Sn5 phase in the SAC/C1990HP reaction couple for the prolonged reflowing time. Meanwhile, the Sn-rich layer was observed between the upper and lower Cu6Sn5 phases. When the reaction temperatures and times were increased, the small grain of the Cu6Sn5 phase was merged and ripened each other, and then spread over to the SAC solder. The hexagonal prism-shaped Cu6Sn5 phase was found when the Cu6Sn5 layer detached at the SAC/C1990HP interface. The IMC growth mechanism was diffusion controlled.

Modelling intermetallic phase growth during high-power ultrasonic welding of copper and aluminum

An analytical model was developed to understand the rapid growth mechanism of intermetallic compounds (IMC) interlayer in high-power ultrasonic welding process. The analytic solution was derived for the relationships among welding time, interface temperature and vacancy concentration. The effectiveness of this model was tested by comparing the predicted thickness with the experimental value for high-power ultrasonic welding of copper and aluminium at various amplitudes. The consistency of the comparison demonstrates the accuracy of the model has been improved by considering the dynamic change process of vacancy concentration. Besides, the effects of vibration amplitude and resistance heat on the increasing of the intermetallic thickness have been investigated independently. The results show that the additional heat source could significantly promote the process of ultrasonic welding.

Effects of Static Heat and Dynamic Current on Al/Zn∙Cu/Sn Solder/Ag Interfaces of Sn Photovoltaic Al-Ribbon Modules

This present study applied Cu∙Zn/Al ribbon in place of a traditional Cu ribbon to a photovoltaic (PV) ribbon. A hot-dipped and an electroplated Sn PV ribbon reflowed onto an Ag electrode on a Si solar cell and estimated the feasibility of the tested module (Ag/Solder/Cu∙Zn/Al). After bias-aging, a bias-induced thermal diffusion and an electromigration promoted the growth of intermetallic compounds (IMCs) (Cu6Sn5, Ag3Sn). To simulate a photo-generated current in the series connection of solar cells, an electron with Ag-direction (electron flows from Ag to Al) and Al-direction (electron flows from Al to Ag) was passed through the Al/Zn∙Cu/Solder/Ag structure to clarify the growth mechanism of IMCs. An increase in resistance of the Ag-direction-biased module was higher than that of the Al-direction biased one due to the intense growth of Cu6Sn5 and Ag3Sn IMCs. The coated solder of the electroplated PV ribbon was less than that of the hot-dipped one, and thus decreased the growth reaction of IMCs and the cost of PV ribbon.

Effects of Electrical Current and External Stress on the Electromigration of Intermetallic Compounds Between the Flip-Chip Solder and Copper Substrate

This study investigated the effects of electric current and external stress on electromigration of intermetallic compounds (IMC) between solder and copper substrate. Different samples were tested under three different sets of conditions: (1) thermal aging only, (2) thermal aging with electric current ,where resistivity changes were measured using four-point probe measurements, (3) thermal aging with electric current and external stress provided using a four-point bending apparatus. The micro-structural changes in the samples were observed. The results were closely examined; particularly the coupling effect of electric current and external stress to elucidate the electromigration mechanism, as well as the formation of IMC in the samples. For thermal-aging-only samples, the IMC growth mechanism was controlled by grain boundary diffusion. Meanwhile, for thermal aging and applied electric current samples, the IMC growth mechanism was dominated by volume diffusion and interface reaction. Lastly, the IMC growth mechanism in the electric current and external stress group was dominated by grain boundary diffusion with grain growth. The results reveal that the external stress/strain and electric current play a significant role in the electromigration of copper-tin IMC. The samples exposed to tensile stress have reduced electromigration, while those subjected under compressive stress have enhanced electromigration.

Effect of Zn Addition on Interfacial Reactions Between Sn-Bi Solder and Cu Substrate

In this study, the effect of Zn (Zn = 1 wt.%, 3 wt.%, and 7 wt.%) additions to Sn-4Ag solder reacting with Ag substrates was investigated under solid-state and liquid-state conditions. The composition and microstructure of the intermetallic compounds (IMCs) significantly changed due to the introduction of different Zn contents. In the case of Sn-4Ag solder with 1 wt.% Zn, a continuous Ag-Sn IMC layer formed on the Ag substrates; discontinuous Ag-Zn layers and Sn-rich regions formed on the Ag substrates under liquid-state conditions when the Sn-4Ag solders contained 3 wt.% and 7 wt.% Zn. If 3 wt.% Zn was added to Sn-4Ag solder, the Ag-Sn IMC would be transformed into a Ag-Zn IMC with increasing aging time. Rough interfaces between the IMCs and the Ag substrates were observed in Sn-4Ag-7Zn/Ag joints after reflowing at 260� C for 15 min; however, the interfaces between the IMCs and the Ag substrates became smooth for Sn-4Ag-1Zn/Ag and Sn-4Ag-3Zn/Ag joints. The nonparabolic growth mechanism of IMCs was probed in the Sn-4Ag-3Zn/Ag joints during liquid-state reaction, and can be attributed to the detachment of IMCs. On the other hand, the effect of gravity was also taken into account to explain the formation of IMCs at the three different interfaces (bottom, top, and vertical) during the reflow procedure.

Effect of Cu–Sn intermetallic compound reactions on the Kirkendall void growth characteristics in Cu/Sn/Cu microbumps

Growth behaviors of intermetallic compounds (IMCs) and Kirkendall voids in Cu/Sn/Cu microbump were systematically investigated by an in-situ scanning electron microscope observation. Cu–Sn IMC total thickness increased linearly with the square root of the annealing time for 600 h at 150 °C, which could be separated as first and second IMC growth steps. Our results showed that the growth behavior of the first void matched the growth behavior of second Cu6Sn5, and that the growth behavior of the second void matched that of the second Cu3Sn. It could be confirmed that double-layer Kirkendall voids growth kinetics were closely related to the Cu–Sn IMC growth mechanism in the Cu/Sn/Cu microbump, which could seriously deteriorate the mechanical and electrical reliabilities of the fine-pitch microbump systems.