Ag3Sn Growth Research Articles

Nucleation and growth of Ag3Sn in Sn-Ag and Sn-Ag-Cu solder alloys

Nucleation and growth of Ag3Sn in Sn-Ag and Sn-Ag-Cu solder alloys

Asymmetry of interface reactions in Ag-Sn thin film couples—In-situ synchrotron radiation study

Synchrotron radiation grazing incidence X-ray diffraction was used to study in situ the asymmetry of the interface reactions and the first phase formation at interfaces prepared by Ag evaporation onto Sn thin films (Ag/Sn case) and by Sn evaporation onto Ag thin films (Sn/Ag case). The ordered Ag3Sn phase forms first on both types of interfaces, in agreement with empirical thermodynamic criteria. Interface asymmetry is observed in the growth mode of the Ag3Sn phase, the reaction constant for Ag3Sn formation, the delay time for the appearance of the Ag3Sn phase, and in the grain-size growth kinetics. At the Ag/Sn interfaces, Ag3Sn growth is predominantly interface controlled and forms almost instantaneously, whereas at the Sn/Ag interfaces, it is diffusion controlled and appears 2 min after the beginning of the Sn deposition. The reaction constant for Ag3Sn formation at the Ag/Sn interface (k =0.22 ± 0.02 nm/s) is much larger than the reaction constant at the Sn/Ag interface (k ≪ 0.09 nm/s). The differences in the interface reactions are attributed to the larger diffusion coefficient of Ag in Ag3Sn (DAg = 3.9 ± 0.2 × 10−17 m2/s), compared to the diffusion coefficient of Sn in Ag3Sn (DSn = 6.2 ± 0.1 × 10−19 m2/s), estimated from the in situ X-ray diffraction data. The second intermetallic phase (Ag4Sn), existing in the Ag-Sn system, forms only in the presence of excess Ag atoms at the Sn/Ag interface (realized only after the complete consumption of the Sn bottom layers), because the Ag4Sn phase has a higher nucleation barrier ΔG* and a lower growth rate than the Ag3Sn phase.

Growth of an Ag3Sn Intermetallic Compound Layer Within Photovoltaic Module Ribbon Solder Joints

In this study, the characteristics of growing an intermetallic compound(IMC) layer at solder joint in photovoltaic (PV) ribbon solder joint were investigated through the thermal ageing test. Also, the growth rate of IMC in the ribbon solder joint, which depend on the temperature and time, was predicted through the ageing test. That the ageing test were performed under three different conditions: 90 °C, 120 °C and 150 °C. Also, we prepare the two type solder composition(60Sn40Pb, 62Sn2Ag36Pb) to analyze Ag addition effect in solder to forming IMC layer. Following testing, the IMC layer formed Ag3Sn in Ag sintered layer by Sn diffusion phenomena at high temperature. The thickness of Ag3Sn in solder joint was measured by cross-section images during the thermal ageing test. The Ag3Sn IMC layer was filled in sintered Ag layer in 70 h under the harshest conditions of 150 °C and 750 h at 120 °C. The Ag3Sn thicknesses were calculated to activation energies forming IMC layer in solder joints. The results, the Ag3Sn growth rates under the various temperatures were predicted for long-term reliability of PV modules.

Relation of silver electrode solderability to intermetallic compound growth rate

The reliability of crystalline silicon (c-Si) photovoltaic modules has a strong dependence on the silver (Ag) electrode solderability. To achieve desirable soldering, the reaction that occurs between Ag electrode and solder (Sn/Pb alloy) need to be comprehensively understood and elaborately controlled. In this article, the correlation of Ag electrode soldering states with intermetallic compound (Ag3Sn) growth was discussed. It was found that the reaction dynamics of Ag electrode and solder was closely associated with the glass frit in Ag paste. Here taken for exemplification were three kinds of V–B–Si oxide glass frit, which led to diverse soldering states for the Ag electrode, e.g. inveracious soldering, appropriate soldering and over-soldering, owing to their different affection on the Ag3Sn growth rate. The effect of glass frit on the Ag3Sn growth was addressed from the aspects of glass phase transition temperature, distribution of glass phase in electrode, and reaction between glass and solder. In addition, it was also demonstrated that the amount of glass frit added in Ag paste might impose significant affection on the solderability of the sintered electrode.

Scaling effect on Ag3Sn growth behaviours in micro-joints for flip chip assemblies

ABSTRACTThe scaling effect on Ag3Sn growth behaviours in Sn–3.0Ag–0.5Cu (SAC305) micro-joints of flip chip assemblies was investigated using thermal shock (TS) tests. After assembly reflow, the large plate-like Ag3Sn compounds only emerged from the Cu interface of small joints, which was strongly related with a higher local Ag concentration in the remaining solder. During TS cycling, the growth of Ag3Sn grains exhibited comparatively more pronounced growth in the solder matrix of small joints, due to the stronger strain-enhanced coarsening induced by more cycle stress and strain. Coarsening kinetic models based on TS experiments were employed to predict Ag3Sn growth, the kinetic constants N were determined to clarify the correlation of the joints scaling and Ag3Sn coarsening in depth.

Growth kinetic of Ag3Sn intermetallic compound in micro-scale Pb-free solder alloys under a temperature gradient

The interfacial reaction of Ag3Sn intermetallic compounds (IMCs) in micro-scale Ag/SnAg/Ag sandwich structure was investigated under a temperature gradient of 168.9 °C/cm at 260 °C. In contrast to a symmetrical growth of Ag3Sn at both interfaces under isothermally annealed at 260 °C, the asymmetric growth of Ag3Sn IMCs at both interfaces was observed under a temperature gradient; the growth rate of Ag3Sn at colder interface was faster than that at hot side because of temperature gradient induced Ag atoms diffusion from the hot end toward the cold end. In addition, the findings indicate two-stage growth behavior of Ag3Sn IMC under a temperature gradient. The growth kinetic analysis suggests that the chemical potential gradient controls the thickness change of Ag3Sn at stage I (0–10 min) whereas force driving thermomigration becomes dominant at stage II (10–30 min). The molar heat of transport (Q*) of Ag in Sn in molten-state was calculated as 14.9 kJ/mol.

Suitable Thicknesses of Base Metal and Interlayer, and Evolution of Phases for Ag/Sn/Ag Transient liquid-phase Joints Used for Power Die Attachment

Real Si insulated gate bipolar transistors with conventional Ni/Ag metallization and dummy Si chips with thickened Ni/Ag metallization have both been bonded, at 250°C for 0 min, 40 min, and 640 min, to Ag foil electroplated with 2.7 µm and 6.8 µm thick Sn as an interlayer. On the basis of characterization of the microstructure of the resulting joints, suitable thicknesses are suggested for the Ag base metal and the Sn interlayer for Ag/Sn/Ag transient liquid-phase (TLP) joints used for power die attachment. The diffusivities of Ag and Sn in the ξAg phase were also obtained. In combination with the kinetic constants of Ag3Sn growth and diffusivities of Ag and Sn in Ag reported in the literature, the diffusivities of Ag and Sn in the ξAg phase were also used to simulate and predict diffusion-controlled growth and evolution of the phases in Ag/Sn/Ag TLP joints during extended bonding and in service.

Optimization of Ag Composition in Cu Pillar Bumps with Sn-xAg Solders

In order to minimize the large plate growth of Ag3Sn intermetallic compounds (IMCs) adversely affecting the mechanical behavior and reducing the reliability of solder joints, the Ag content of less than 3wt% has been suggested in ball grid array (BGA) Sn-Ag solders. The suggestion (< 3wt% Ag in the solders) is invalid in small solder bumps, and moreover there is no available guideline of the Ag content in the small Sn-Ag solders. In this study, the optimum level of Ag content in small Sn-Ag Cu pillar bumps (CPBs) of less than 50um in diameter was investigated to suppress the large plate growth of Ag3Sn. Since the undercooling of Sn-Ag solders increases with a decrease of solder ball size, the Ag3Sn IMCs are more prone to become largely plate-like in small solders. Actually, in small Sn-Ag CPBs, the large plate growth of Ag3Sn was observed on the top surface of solder bumps even though the Ag content was less than 3.0wt%. For suppression of Ag3Sn plates in Sn-Ag CPBs, two ways were suggested; increasing the cooling rate of the reflow profile and reducing the Ag content in the solders. Reducing the Ag content was effective on reducing the large plate growth of Ag3Sn, while a high cooling rate was not effective. Through the thermal analysis and thermodynamic calculations, the optimized Ag content in Sn-Ag CPBs of less than 50um was suggested, and the large plate growth of Ag3Sn was effectively reduced within the suggested Ag content.

Effect of Interfacial Reaction in Sn-Ag-Cu Solder Alloy with Ni Addition

Sn-Ag-Cu-Ni-Ge solder alloy has been developed to improve the mechanical properties of the Sn-Ag-Cu base solders and prevent oxidation of those solders. In this paper, an interfacial reaction and microstructure between the solder and a Cu electrode were investigated under heat exposure conditions. It was found that intermetallic compounds growth at the interface of the solder and the Cu electrode was greatly affected by amounts of added elements. Adding Ni in the solder can suppress the formation and growth of intermetallic compounds (IMCs) such as Cu-Sn and decreasing the amount of adding Ag in the solder can prevent the formation and growth of Ag3Sn. Moreover, it was found that there was an effect of suppress the growth of the Cu3Sn formed on the interface of Cu and (Cu,Ni)6Sn5 by adding Ni from analysis results of EDX and TEM.

Indium Addition on Intermetallic Compound Evolution in Tin-Silver Solder Bump

The formation of large Ag3Sn plate in Sn-Ag solder joint has restricted its application in lead-free electronic industry. There is a great interest for finding new approach to suppress the growth of Ag3Sn. In this paper, Sn-2.1Ag and Sn-1.8Ag-9.4In solder bumps are prepared by electroplating of Sn-Ag and indium in sequence. After reflow at 260 C for 30min with cooling rate 0.33 C/s, the phase composition, microstructure and undercooling of solder alloys are characterized by X-ray diffraction, Scanning electron microscopy and Differential scanning calorimeter, respectively. It is found that after indium addition, large Ag3Sn plate is substituted by Ag9In4 with irregular polygon morphology. It is also found that indium addition can significantly reduce the undercooling of -Sn, which promotes the solidification of -Sn and inhibits the growth of Ag9In4 during slow cooling. [doi:10.2320/matertrans.M2011058]

Kinetics of Ag 3Sn growth in Ag–Sn–Ag system during transient liquid phase soldering process

The kinetics of the interfacial reaction of a thin layer of Sn sandwiched between two pieces of Ag foil has been investigated at temperatures of 260 °C, 300 °C and 340 °C. A time dependence of the form t 1/ n with n = 3 was obtained for the kinetics of both the consumption of the Sn remaining and the thickening growth of the Ag 3Sn scallops formed between Sn and Ag. Such a result can be explained well using the model of grain boundary/molten channel-controlled growth of intermetallic compounds. In this case, the diffusion of Ag atoms through the molten channels existing between the previously formed Ag 3Sn scallops is the controlling mechanism for the kinetics. We also report here the derived kinetic constants including reaction constants and the associated activation energy for guiding the practical transient liquid phase soldering of the Ag–Sn–Ag system.

Development of a New Multi Layer Substrate Bonding Technology using Ag-Sn Liquid Phase Sintering Process (First Report) -Investigations of Diffusion Processes-

In order to construct the multi layers IVH (Interstitial Via Hole) structure with only one time hot pressing, we have developed the new diffusion bonding technology. In this paper, the sintering process of Ag-Sn mixed powders (Ag/Sn:65/35 mass%) between copper foils in IVH with hot vacuum pressing was investigated, and the effect of temperature on the respective diffusion reactions was discussed. Ag and Sn formed Ag3Sn up to 473 K with the solid diffusion reaction. At 483 K, Ag particles disappeared completely and the mixed compact consisted of Ag3Sn and excess Sn. Cu-Sn diffusion reaction between excess Sn and copper foil commenced at 493 K. Excess Sn was consumed completely below 573 K. The liquid phase of Sn contributed not only to Cu-Sn diffusion bonding but also to Ag3Sn sintering. As a result of hot pressing above 573 K, the mechanical properties were improved without large grain growth of Ag3Sn (about 4 μm).

A study of superimposed tin and silver films

The effects of film structure on the contact depression of the superconducting transition temperature for superimposed Sn and Ag films has been studied before and after annealing. The films were composed of a layer of 550 ± 50 Å Sn and a layer of Ag which varied from 20 to 385 Å (±30 Å). Experimental evidence has shown that the superimposed Sn and Ag films as deposited result in an inberdispersion of Ag 3Sn compound and Sn rather than a composite of single Sn and Ag films. The depression of transition temperature for such films is not due to a contact effect between two superimposed films but to a contact effect at the adjacent surface between the dispersed Ag 3Sn crystallites and the Sn matrix. Upon annealing of the superimposed films, grain growth and preferred orientation of the crystallites of Ag 3Sn and Sn were observed. The decrease in contact surface, due to the grain growth of Ag 3Sn, thus increases the transition temperatures of the superimposed films after annealing.