Ag-Zn Intermetallic Compounds Research Articles

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 Ag on the Microstructure of Sn-8.5Zn-xAg-0.01Al-0.1Ga Solders Under High-Temperature and High-Humidity Conditions

The effect of Ag on the microstructure and thermal behavior of Sn-Zn and Sn-8.5Zn-xAg-0.01Al-0.1Ga solders (x from 0.1 wt.% to 1 wt.%) under high-temperature/relative humidity conditions (85°C/85% RH) for various exposure times was investigated. Scanning electron microscopy (SEM) studies revealed that, in all the investigated solders, the primary α-Zn phases were surrounded by eutectic β-Sn/α-Zn phases, in which fine Zn platelets were dispersed in the β-Sn matrix. SEM micrographs revealed that increase of the Ag content to 1 wt.% resulted in coarsening of the dendritic plates and diminished the Sn-9Zn eutectic phase in the microstructure. Differential scanning calorimetry (DSC) studies revealed that the melting temperature of Sn-8.5Zn-xAg-0.01Al-0.1Ga solder decreased from 199.6°C to 199.2°C with increase of the Ag content in the solder alloy. Both ZnO and SnO2 along with Ag-Zn intermetallic compound (IMC) were formed on the surface when Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solder was exposed to high-temperature/high-humidity conditions (85°C/85% RH) for 100 h. The thickness of the ZnO phase increased as the Ag content and exposure time were increased. Sn whiskers of various shapes and lengths varying from 2 μm to 5 μm were extruded from the surface when the investigated five-element solder with Ag content varying from 0.5 wt.% to 1 wt.% was exposed to similar temperature/humidity conditions for 250 h. The length and density of the whiskers increased with further increase of the exposure time to 500 h and the Ag content in the solder to 1 wt.%. The Sn whisker growth was driven by the compressive stress in the solder, which was generated due to the volume expansion caused by ZnO and Ag-Zn intermetallic compound formation at the grain boundaries of Sn.

Development of a lead‐free solder: Sn‐4.0Bi‐3.7Ag‐0.9Zn

PurposeThe purpose of this paper is to study the relationship between microstructure and mechanical properties of Sn‐4.0Bi‐3.7Ag‐0.9Zn (in wt%) solder, and the structural evolution of the soldered interfaces.Design/methodology/approachThe solder was prepared by a vacuum arc furnace. Scanning electron microscopy (SEM) and X‐ray diffraction were used to identify the microstructure and composition. The melting temperature, microhardness and tensile strength were measured. Solder joints were prepared by reflowing at 250°C for 1 min in a vacuum oven and the soldered interfaces were observed by using SEM.FindingsThe microstructure of the slowly cooled Sn‐4.0Bi‐3.7Ag‐0.9Zn specimen is composed of bulk Ag3Sn, AgZn intermetallic compounds (IMCs), Bi precipitates and a β‐Sn phase. The developed solder exhibits good comprehensive properties, such as low‐melting temperature, high microhardness and ultimate tensile strength. A complicated IMC layer forms at the interface with Cu pads and it turns into a thinner Ni3Sn4 layer with Ni/Cu substrates.Originality/valueThe paper shows how a high performance, lead‐free solder was developed.

Effects of Ag on Properties of Sn-9Zn Lead-Free Solder

Abstract The influences of different Ag contents on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ag plays an important role not only in the solderability and the structure of the solder, but also in the mechanical property of the soldered joint. In particular, adding 0.3% (mass fraction) Ag can improve the oxidation resistance of the solder, so the solderability of the solder is significantly improved. Sn-9Zn-0.3Ag shows finer and more uniform microstructure than Sn-9Zn. Results also indicate that when the content of Ag is 0.3%, the best mechanical property of the soldered joint can be obtained, and the fracture micrographs show that plenty of small and uniform dimples are found on the soldered joints fractures. Some Cu-Zn and Ag-Zn intermetallic compounds appear at the bottom of dimples when the content of Ag is up to 1%, and the mechanical property of the soldered joint is reduced.

Interfacial Reactions and Joint Strengths of Sn-xZn Solders with Immersion Ag UBM

The solder joint microstructures of immersion Ag with Sn-xZn (x = 0 wt.%, 1 wt.%, 5 wt.%, and 9 wt.%) solders were analyzed and correlated with their drop impact reliability. Addition of 1 wt.% Zn to Sn did not change the interface microstructure and was only marginally effective. In comparison, the addition of 5 wt.% or 9 wt.% Zn formed layers of AgZn 3 /Ag 5 Zn 8 at the solder joint interface, which increased drop reliability significantly. Under extensive aging, Ag-Zn intermetallic compounds (IMCs) transformed into Cu 5 Zn 8 and Ag 3 Sn, and the drop impact resistance at the solder joints deteriorated up to a point. The beneficial role of Zn on immersion Ag pads was ascribed to the formation of Ag-Zn IMC layers, which were fairly resistant to the drop impact, and to the suppression of the brittle Cu 6 Sn 5 phase at the joint interface.

Solderability and intermetallic compounds formation of Sn-9Zn-xAg lead-free solders wetted on Cu substrate

The eutectic Sn-9Zn alloy was doped with Ag (0 wt.%-1 wt.%) to form Sn-9Zn-xAg lead-free solder alloys. The effect of the addition of Ag on the microstructure and solderability of this alloy was investigated and intermetallic compounds (IMCs) formed at the solder/Cu interface were also examined in this study. The results show that, due to the addition of Ag, the microstructure of the solder changes. When the quantity of Ag is lower than 0.3 wt.%, the needle-like Zn-rich phase decreases gradually. However, when the quantity of Ag is 0.5 wt.%-1 wt.%, Ag-Zn intermetallic compounds appear in the solder. In particular, adding 0.3 wt.% Ag improves the wetting behavior due to the better oxidation resistance of the Sn-9Zn solder. The addition of an excessive amount of Ag will deteriorate the wetting property because the glutinosity and fluidity of Sn-9Zn-(0.5, 1)Ag solder decrease. The results also indicate that the addition of Ag to the Sn-Zn solder leads to the precipitation of e-AgZn3 from the liquid solder on preformed interfacial intermetallics (Cu5Zn8). The peripheral AgZn3, nodular on the Cu5Zn8 IMCs layer, is likely to be generated by a peritectic reaction L + γ-Ag5Zn8 → ɛ-AgZn3 and the following crystallization of AgZn3.

Investigation of small Sn–3.5Ag–0.5Cu additions on the microstructure and properties of Sn–8Zn–3Bi solder on Au/Ni/Cu pads

Abstract The formation of intermetallic compounds and the shear strength of Sn–Zn–Bi solder alloys with various (0, 1, 3, 5 and 7 wt%) weight percentages of Sn–Ag–Cu were investigated on Au/Ni metallized Cu pads depending on the number of reflow cycles. In Sn–Zn–Bi solder joints, scallop-shaped AuZn3 intermetallic compound (IMC) particles were found at the interfaces and in the solder ball regions, fine Bi- and needle-shaped Zn-rich phase were observed in the Sn matrix. After Sn–Ag–Cu additions, an additional Ag–Zn intermetallic compound layer was adhered to the top surface of the AuZn3 layer at the interface and fine spherical-shaped AgZn3 intermetallic compound particles were detected in the solder ball regions together with Bi- and Zn-rich phase volumes. After the addition of Sn–Ag–Cu, the shear strength of Sn–Zn–Bi solder joints increased due to the formation of the fine AgZn3 intermetallic compound particles. The shear strengths of Sn–Zn–Bi and Sn–Zn–Bi/7 wt% Sn–Ag–Cu solder joints after one reflow cycle were about 44.5 and 53.1 MPa, respectively and their shear strengths after eight reflow cycles were about 43.4 and 51.6 MPa, respectively.

Effects of Ag on microstructures, wettabilities of Sn–9Zn–xAg solders as well as mechanical properties of soldered joints

The microstructures, wettabilities and mechanical properties of Sn–9Zn–xAg (x = 0, 0.1, 0.3, 0.5, 1 wt%) lead-free solders were investigated, respectively in this paper. Results show that, when the quantity of Ag added to the solder is 0.3 wt%, the microstructure of the solder becomes finer and more uniform than Sn–9Zn, and when the quantity of Ag is exceeded 0.3 wt% (upto 0.5–1 wt%), the AgZn3 intermetallic compounds appear in the solder. In particular, adding 0.3 wt% Ag improves the wettability due to the better oxidation resistance of the Sn–9Zn–0.3Ag solder. Results also indicate that adding 0.3 wt% Ag to the solder enhances mechanical property of soldered joint, at which the fracture micrographs show that plenty of small and uniform dimples could be observed on the Sn–9Zn–0.3Ag soldered joints fractures. When the content of Ag is upto 1 wt%, some Cu–Zn and Ag–Zn intermetallic compounds appear on the bottom of dimples, and the mechanical property of the soldered joint decreases.

Effects of composition and cooling rate on the microstructure of Sn–3.7Ag–0.9Zn–Bi solders

The effects of Bi addition, of less than 3 wt.%, and applied cooling rate on the solidified microstructure of the eutectic Sn–3.7Ag–0.9Zn (weight percent, hereafter) solder were investigated. As observed by microstructural analysis, the increase of Bi content favors the separation of the β-Sn and AgZn intermetallic compounds (IMCs) in the eutectic Sn–Ag–Zn solder. And there are some Bi precipitates formed along with the primary β-Sn dendrites as the concentration of Bi exceeds 2%. As the applied cooling rate increases, the microstructure of the Sn–3.7Ag–0.9Zn–Bi solder is refined, and the segregation of Bi is restrained. By increasing the amount of Bi, the microhardness of the solder increases.

Effects of Thermal Aging on Microstructure and Microhardness of Sn-3.7Ag-0.9Zn-1In Solder

The structural stability of Sn-3.7wt.%Ag-0.9wt.%Zn-1wt.%In solder was explored by thermal aging at 473 K. According to the microstructural observations, the high cooling rate (about 10 2 K/s) applied to the water-cooled specimens prompted the formation of β-Sn dendrites and inhibited the formation of the AgZn phase. After annealing for 20 h and 50 h, the corresponding microstructure changed significantly, especially the morphology of the intermetallic compounds (IMCs) in the slowly cooled solder. IMC particles grew in order to minimize the system energy. In addition, β-Sn dendrites grew coarser as the IMCs segregated along their grain boundaries in the water-cooled solder. Furthermore, the Ag-Zn IMCs were suppressed in the water-cooled Sn-Ag-Zn-In solder. It is suggested that coarsening of the microstructure led to significant softening during annealing of the investigated Sn-Ag-Zn-In alloys.

Effect of Zn Addition on Interfacial Reactions Between Sn-4Ag Solder and Ag Substrates

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.

Phase equilibria of the Sn–Zn–Ag system and interfacial reactions in Sn–Zn/Ag couples

The phase equilibria of the Sn–Zn–Ag ternary system and interfacial reactions between Sn–Zn alloys and Ag were experimentally investigated at a specific temperature. Ternary Sn–Zn–Ag alloys were prepared and annealed at 260 °C to determine the Sn–Zn–Ag ternary system isothermal section. The experimental results reveal that no ternary compound was formed, and noticeable Zn solubility was observed in the Ag 4Sn phase. Three Ag–Zn intermetallic compounds, AgZn 3, Ag 5Zn 8 and AgZn, were formed on the Sn–9Zn/Ag interface at 260 °C. As the Zn content was gradually decreased in the Sn–Zn alloy, the intermetallic compound microstructures changed. If the Zn content was less than 2 wt% in the Sn–Zn alloy, Ag–Sn IMCs were then formed on the Ag surface and massive spalling of Ag–Zn IMC layers occurred from the Ag–Sn IMC surface.

Effect of the addition of In on the microstructural formation of Sn–Ag–Zn lead-free solder

Abstract The effect of addition of In, up to 1 wt.%, on the formation of intermetallic compounds (IMCs) in the solidified Sn–3.7%Ag–0.9%Zn lead-free solder was investigated. As observed by microstructural analysis, the typical structure of Sn–Ag–Zn solder is composed of β-Sn phase and mixed granules of Ag 3 Sn and AgZn IMCs. After alloying with In, it evolves into a mixture of randomly distributed rods and granules of Ag 3 Sn and AgZn. Clearly, the addition of In into the explored Sn–Ag–Zn solder promotes the formation of rod-like IMCs for the reason that the growth competition of the Ag 3 Sn and AgZn IMCs was destroyed by the selective adsorption of In atoms on a certain preferable crystalline planes of the separated IMCs. The change in the morphology of the formed IMCs leads to a great difference in the mechanical performances, for example, the measured microhardness of the investigated solders evolves from 16.95 HV to 21.35 HV with the increase of In content.

The effects of third alloying elements on the bulk Ag3Sn formation in slowly cooled Sn–3.5Ag lead-free solder

The effects of third alloying elements (Cu, In, Zn) on the formation of bulk Ag3Sn intermetallic compounds (IMCs) in slowly cooled Sn–3.5Ag lead-free solder were investigated by microstructural observation and thermal analysis technique. Microstructural observation shows that bulk Ag3Sn IMCs existed in the microstructure of slowly cooled Sn–3.5Ag, Sn–3.5Ag–0.75Cu and Sn–3.5Ag–1.5In alloys, while no bulk Ag3Sn IMCs formed in the slowly cooled Sn–3.5Ag–2.0Zn alloys. Thermal analysis results indicate that Ag preferably reacted with Zn to form Ag–Zn IMCs at high temperature rather than reacted with Sn to form Ag3Sn plate.

Effect of Cu addition on interfacial reaction between Sn–9Zn solder and Ag

The effect of Cu added eutectic Sn–9Zn solder reacting with the Ag substrate has been investigated in this study. Three Ag–Zn intermetallic compounds (IMCs), ∈–AgZn3, γ–Ag5Zn8, and ζ–AgZn, were formed on the Sn–9Zn/Ag interface at 260 °C. While Cu was gradually added to the Sn–9Zn alloy, microstructures of intermetallic compounds changed dramatically. The intermetallic compound microstructures became loose and Sn and Cu atoms in the Ag-Zn intermetallic compounds increased. If more than 3 wt% of Cu was added to the Sn-9Zn alloy, Ag-Sn intermetallic compounds were formed on the Ag surface and massive spalling of Ag–Zn IMC layers from the Ag surface occurred in a short reaction time.

Pasty Ranges and Latent Heat Release Modes for Sn-9Zn-<i>x</i>Ag Lead-free Solder Alloys

The pasty ranges and latent heat release modes of Sn-9Zn-xAg alloys, where x varies between 0.5 and 3.5, are examined in this study. The effects of alloy composition and cooling rate on the pasty range and latent heat release modes are also investigated. A Computer Aided-Cooling Curve Analysis (CA-CCA) technique is used to determine the pasty ranges and latent heat release modes for the alloys. To comply with the requirements of CA-CCA, the heat transfer conditions of the experimental setup must closely resemble of a lumped system, in which the alloy is cooled in a uniform fashion. To confirm this, two thermocouples are inserted into the crucible where the alloy is melted and subsequently resolidified. The crucible is used with and without a covering of insulating material to obtain different cooling rates. The temperature readings show that the heat transfer conditions in the experimental setup indeed meet the requirements of a lumped system. The solid fraction versus temperature relationship (f s -T) for the various alloy compositions and cooling rates are obtained from the temperature data through CA-CCA. The experimental results show that as the silver content of the Sn-9Zn-xAg alloy increases, the liquidus temperature rises and the pasty range broadens. The pasty range is approximately 2°C for 0.5Ag, 9°C for 1.5Ag, 14°C for 2.5Ag, and 18°C for 3.5Ag. As long as the silver content is below 0.5 mass%, silver has little effect on the microstructure, which is basically the eutectic Sn-9Zn and the f s -T relationship is nearly a vertical line. However, as the silver content exceeds 1.5 mass%, the formation of Ag-Zn intermetallic compounds becomes obvious. This causes the alloy composition to deviate from eutectic and to lean towards the tin side of the Sn-Zn phase diagram. This in turn causes the proportion of the primary tin phase to increase and that of the zinc-tin eutectic phase to decrease. This is reflected on the plot of the f s -T relationship by two distinct vertical regions. One corresponds to the primary tin phase and the other to the eutectic phase. As the silver content further increases, the effects of intermetallic compound formation become even more obvious. As an alternative to CA-CCA, Huang's model can be used to obtain a quantitative f s -T function. As the silver content increases, the primary solid fraction for Huang's model increases. As the cooling rate increases, the primary solid fraction and the nonlinearity factors n e and n p decrease.