Sn Intermetallic Compounds Research Articles

Effects of la addition on microstructure and mechanical properties of SN–58BI solders joints with osp pads

Rapid whisker growth was significantly alleviated in a Sn–58Bi alloy doped with 0·5 wt-%La. Experimental results showed that many thin, plate form intermetallic phases appeared in the solder matrix. The absence of tin whiskers was correlated to the shape effect of RE containing intermetallic plates. After reflowing, Cu6Sn5 intermetallic compounds appeared at the solder/pad interfaces of Sn–58Bi and Sn–58Bi–0·5La packages with OSP pads, which grow linearly during the aging at 75 and 100°C for various times ranging from 100 to 1000 h. In addition, the interfacial intermetallics layers in Sn–58Bi–0·5La solder joints were also observed thinner than those in undoped Sn–58Bi joints. However, RE containing interfacial intermetallic compounds in Sn–58Bi–0·5La solder joints led to lower bonding strengths in both ball shear tests (0·4 mm s−1) and high speed ball shear tests (2000 mm s−1). All the reflowed and aged solder joints of both packages were ruptured through the solder balls indicating brittle characteristic.On a réduit significativement la croissance rapide de barbe dans un alliage de Sn–58Bi dopé avec 0·5% en poids de La. Les résultats expérimentaux ont montré que plusieurs phases intermétalliques fines en forme de plaque apparaissaient dans la matrice du métal d’apport. On a corrélé l’absence de barbes d’étain aux effets de la forme des plaques intermétalliques contenant de la terre rare. Après la refusion, les composés intermétalliques de Cu6Sn5 apparaissaient à l’interface du métal d’apport et des pastilles des paquets de Sn–58Bi et de Sn–58Bi–0·5La avec pastilles d’OSP, lesquels s’accroissent linéairement lors du vieillissement à 75 et à 100°C pour des durées variées allant de 100 à 1000 heures. De plus, on a observé que les couches intermétalliques de l’interface dans les joints à brasure tendre de Sn–58Bi–0·5La étaient plus minces que celles des joints non dopés de Sn–58Bi. Cependant, les composés intermétalliques de l’interface contenant de la terre rare dans les joints à brasure tendre de Sn–58Bi–0·5La menaient à des résistances de cohésion plus faibles tant dans les épreuves de cisaillement de bille (0·4 mm s−1) que dans les épreuves de cisaillement de bille à haute vitesse (2000 mm s−1). Tous les joints à brasure tendre avec refusion et vieillissement des deux paquets se fracturaient à travers les billes de soudure, indiquant une caractéristique fragile.

Phase transformation and grain orientation of Cu–Sn intermetallic compounds during low temperature bonding process

The interconnection lengths between the stacked chips in three-dimensional (3D) package are a few of microns, hence the solder joints for the stacked chips joining are mainly composed by intermetallic compounds (IMCs) after reflow processes. To evaluate the phase transformation of Cu–Sn IMCs in the small interconnection joints, the Cu/Sn/Cu structures were bonded with different bonding times at various temperatures in argon gas atmosphere in this study. Scanning electron microscope and energy-dispersive X-ray were used to observe the joint interfacial microstructures and electron back scattering diffraction was used to identify the grain orientations in the joints. Scalloped Cu6Sn5 grains were found to be initially formed on the Cu substrates at the early stage. A lot of small Cu6Sn5 grains formed on the surfaces of the big scallop Cu6Sn5 grains. Those small grains gradually grew up to merge into the big Cu6Sn5 grains. With longer reflow time, the Cu6Sn5 grains initiated at both side of Cu substrate continued to grow up and started to contact with each other. Meantime, the different Cu6Sn5 grains with different grain orientations have merged into some bigger grains. The Cu3Sn grains formed between Cu6Sn5 layers and Cu substrates have further developed at the expense of the depletion of Cu6Sn5. Most of columnar Cu3Sn grains were vertical to Cu substrate surface and their grain sizes were 1–5 μm. With 960 min at 300 °C, the pure Cu3Sn IMC joint has formed. The Cu3Sn grains in IMC joint had different grain orientations and a contact line was observed in the middle of the Cu3Sn IMC joint.

Characters of multicomponent lead-free solders

In the process of electronic packaging, such as flip chip technology, under bump metallization (UBM) can be consumed gradually by solder during soldering. Then dissolution of Ni, Au and Cu from UBM into the solder may change the original solder to a multicomponent one especially under the trend of miniaturization. It is quite necessary to evaluate the properties of the multicomponent solders that have new composition after soldering. In this study, the microstructure, thermal and mechanical properties of five types of multicomponent lead-free solders, i.e. Sn–2Cu–0.5Ni, Sn–2Cu–0.5Ni–0.5Au, Sn–3.5Ag–0.5Ni, Sn–3.5Ag–1Cu–0.5Ni and Sn–3.5Ag–2Cu–0.5Ni (all in wt% unless specified otherwise) were investigated. Comparison with eutectic Sn–0.7Cu, Sn–3.5Ag and Sn–3.5Ag–0.7Cu solders was made. There was no obvious difference of the melting point between the multicomponent lead-free solders and the eutectic ones. For Sn–2Cu–0.5Ni solder, Cu6Sn5 and (Cu,Ni)6Sn5 intermetallic compounds (IMCs) formed. In the case of Sn–2Cu–0.5Ni–0.5Au, besides (Cu,Ni)6Sn5, (Cu,Au)6Sn5 and (Cu,Ni,Au)6Sn5 were also observed. The IMCs formed in Sn–3.5Ag–0.5Ni solder were Ag3Sn and Ni3Sn4. In both Sn–3.5Ag–1Cu–0.5Ni and Sn–3.5Ag–2Cu–0.5Ni solders, Ag3Sn and (Cu,Ni)6Sn5 were detected. The mechanism for the formation of the IMCs was discussed. Tensile test was also conducted. The fractography indicated that all of the multicomponent lead-free solders exhibited a ductile rupture.

Evolution of microstructure, thermal and creep properties of Ni-doped Sn–0.5Ag–0.7Cu low-Ag solder alloys for electronic applications

For development of lead-free solder for advance electrical components, the correlation of microstructure with thermal and creep properties of novel Ni-doped Sn–0.5Ag–0.7Cu (SAC (0507)) lead free solders has been investigated. Results showed that addition of 0.05Ni into the lead-free SAC (0507) solder led to the microstructural refinement, more uniform distribution of the Ag3Sn, (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. However, the SAC (0507)–0.1Ni alloy has relatively high fraction of the primary β-Sn phase and the IMCs appeared coarse within the matrix compared with the other examined alloys. DSC results showed that the addition of Ni did not produce any significant effect on the melting behavior. Interestingly, 0.05wt.% Ni addition exhibited a drastically reduced undercooling to be 6.3°C. In terms of creep behavior, the SAC (0507)–0.05Ni gave the highest creep resistance due to the fine dispersion of IMCs. Furthermore, 0.05wt.% Ni addition can evidently increase the creep–rupture life, about 2.0 times greater than that of the baseline SAC (0507) and approximately 5.0 times better than that of SAC (0507)–0.1Ni solder. Meanwhile, the SAC (0507)–0.1Ni alloy shows lower creep resistance which is mainly attributable to smaller volume fraction of the precipitate phases. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.

Comparison of spreading behaviour and interfacial microstructure in Sn–0·7Cu, Sn–0·3Ag–0·7Cu and Sn–2·5Ag–0·5Cu lead free solder alloys on Fe–42Ni substrate

In the present work, spreading behaviour and development of interfacial microstructure in Sn–0·7Cu, Sn–0·3Ag–0·7Cu and Sn–2·5Ag–0·5Cu lead free solder alloys on Fe–42Ni substrates having two different surface textures were investigated. Smooth textured surfaces yielded better wettability than rough surfaces particularly for Sn–0·7Cu solder alloy. Wettability of Sn–0·7Cu solder on rough textured surfaces was found to be poor compared to other solder alloys. Spreading of Sn–0·7Cu solder on substrate surface showed longer viscous regime, Sn–2·5Ag–0·5Cu solder exhibited shortest viscous regime. Sn–0·3Ag–0·7 solder showed intermediate behaviour. Sn–Cu solder alloy exhibited needle and coarse shaped (Cu,Ni)6Sn5 intermetallics at the interface and in the matrix of the solder alloy on smooth substrate, whereas on rough substrate, formation of only coarse shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) was observed. For Sn–0·3Ag–0·7Cu solder alloy, Fe–Ni–Sn and FeSn2 IMCs identified at the interface. (Cu,Ni)6/Sn5 IMCs were found to be less coarser than as observed at Sn–0·7Cu/substrate interface. Sn–2·5Ag–0·5Cu alloy exhibited (Cu,Ni)3Sn4 and (Cu,Ni)6 Sn5 IMCs at the interface and in the bulk of solder alloy.

Nickel substrate covered with a Sn-based protection bi-layer as a photoanode substrate for dye-sensitized solar cells

Ni is a metallic substrate commonly used in microelectronic and opto-electronic devices due to its high stability, cost-efficiency and flexibility. Up to now, Ni has not yet been used as the substrate for the photoanode in dye-sensitized solar cell (DSSC) because the formation of p-type Ni oxide hinders the electron transfer from n-type TiO2 mesoporous film to Ni substrate. In this paper, a Sn-based protection bi-layer coating on the Ni foil successfully turns Ni into a good photoanode substrate in DSSC. A Sn layer is initially electroplated onto the Ni surface to prevent its oxidation. The Sn layer is then transformed into a bi-layer of SnO2 and Ni–Sn intermetallic compound after high-temperature TiO2 sintering. Unlike the p-type Ni oxide layer, the top n-type SnO2 layer enables the electron transfer from the TiO2 mesoporous film to the conductive Ni substrate because its energy level of conduction band well matches that of TiO2. In addition, the interfacial Ni–Sn intermetallic compound is a good electrical conductor which facilitates the electron transfer. By carefully controlling the plating current density and time, a 1.2-μm-thick Sn layer with a smooth surface morphology is formed and is recognized as the best protection layer over the Ni substrate. The energy conversion efficiency of the resultant DSSC achieves 4.422% with a short-circuit current density of 10mA/cm2, an open-circuit voltage of 0.643V, and fill factor of 0.689 under AM 1.5 back-side illumination.

Investigation of microstructure and mechanical properties of novel Sn–0.5Ag–0.7Cu solders containing small amount of Ni

This work investigates the effects of small additions (0.05 and 0.1wt.%) of Ni on the microstructure and mechanical properties of low Ag content Sn–0.5Ag–0.7Cu (SAC (0507)) lead-free solder alloy. The addition of 0.05Ni resulted in the microstructural refinement, uniform distribution of the Ag3Sn and (Cu,Ni)6Sn5 intermetallic compounds (IMCs) and small primary β-Sn grains. This apparently enhances the mechanical strength and microhardness. However, the addition of 0.1Ni leads to the formation of relatively high fraction of the primary β-Sn phase and the IMCs appeared abrasive within the matrix. As a result, the SAC (0507)–0.1Ni solder exhibits low tensile strength, microhardness and large elongation, which produce a soft and highly compliant bulk solder. In addition, the strength of all studied alloys increases with increasing strain rate and decreasing testing temperature, showing strong strain rate and temperature dependence. Based on the obtained stress exponents and activation energies, it is proposed that the dominant deformation mechanism in SAC (0507) solders is dislocation climb over the whole temperature range investigated.

Bondability of Cu wire on Cu substrate with Sn plating by ultrasonic

This study evaluated both the joint strength of copper wire on a copper substrate with tin plating and the joint reliability of copper wire bonding after heat treatment. The suitable tin thickness and bonding conditions, which are stage temperature, wire bonding power and bonding time, were chosen by the peel test after copper wire bonding. Tin thickness of 10 m showed a high bonding rate under the conditions of stage temperature 373 K, bonding power 500–700 mW and bonding time 30 50 ms. Before heat treatment, the peel strength of the copper wire on the copper substrate with tin plating conditions was weaker than that of gold wire on a gold substrate. After heat treatment for more than 70 h at 298 K, the peel strength of the copper wire became higher than that of the gold wire and twice as high as the initial bonding strength. The tin layer remained between the copper wire and copper substrate before heat treatment. When the samples were held at 298 K, tin reacted with copper and turned into a Cu–Sn intermetallic compound. Upon completion of this reaction at 298 K for over 70 h, the soft tin layer between the copper wire and copper substrate disappeared. Therefore, the peel strength of copper wire after heat treatment increased. These results were observed by scanning electron microscope images of the interface between the copper wire and copper substrate before and after heat treatment.

Improved strength of Ni and Zn-doped Sn–2.0Ag–0.5Cu lead-free solder alloys under controlled processing parameters

The Sn–Ag–Cu (SAC) solders with low Ag or Cu content have been identified as promising candidates to replace the traditional Sn–Pb solder for flip-chip interconnects. The changes in microstructure, microhardness and mechanical properties associated with the alloying of Ni and Zn to the Sn–2.0Ag–0.5Cu(SAC205) solders were explored in this work. Furthermore, correlations between the mechanical behavior and controlled processing parameters such as temperature, strain and strain rate were analyzed and established. Microstructure analysis showed that additions of Ni and Zn to SAC(205) alloy not only suppressed the formation of brittle Ag3Sn IMC phase but also refined the large β-Sn dendrites, and promoted the formation of new (Cu,Ni)6Sn5 and Cu5Zn8 intermetallic compounds (IMCs) in the SAC(205) solder. Besides, the IMC particles were uniformly distributed in the β-Sn matrix. Accordingly, the mechanical properties, the microhardness and total elongation of Ni and Zn-doped SAC(205) solders were significantly improved. Both the yield strength (YS) and ultimate tensile strength (UTS) were observed to increase with increasing strain rates and decreasing temperature. This behavior was attributed to the competing effects of work hardening and dynamic recovery processes. The Zn-doped solder consistently displayed the highest mechanical properties and ductility due to the formation of hard Cu5Zn8 IMC particles and the refinement of β-Sn grain size, which could provide more obstacles for dislocation pile up in the adjacent grains.

The Wiedemann–Franz–Lorenz relation for lead-free solder and intermetallic materials

Lead-free solders are replacing lead-rich solders in the electronics industry. Due to the limitation of available experimental data for thermal conductivity of lead-free solder and intermetallic compound (IMC) materials, the Wiedemann–Franz–Lorenz (WFL) relation is presented in this paper as a possible solution to predict thermal conductivity with known electrical conductivity. The method is based upon the fact that heat and electrical transport both involve free electrons. The thermal and electrical conductivities of Cu, Ni, Sn and different Sn-rich lead-free solder and IMC materials are studied by employing the WFL relation. Generally, analysis of the experimental data shows that the WFL relation is obeyed in both solder alloy and IMC materials, especially matching close to the relation for Sn, with a positive deviation from the theoretical Lorenz number. Thus, with the available electrical conductivity data, the thermal conductivity of solder and IMC materials can be obtained based on the proper WFL relation, and vice versa. A coupled thermal–electrical three-dimensional finite element analysis is performed to study the behavior of lead-free solder/IMC interconnects. Solder and IMC material properties predicted using the WFL relation are adopted in the computational model. By applying the WFL relation, the number of experiments required to determine the material properties for different lead-free solder/IMC interconnects can be significantly reduced, which can lead to pronounced savings of time and cost.

Enhanced electromigration reliability via Ag nanoparticles modified eutectic Sn–58Bi solder joint

A comprehensive study on the effect of Ag nanoparticles doping on the electromigration related microstructure evolution in Sn---58Bi solders is reported. Doped Sn---58Bi solders were prepared by mechanically dispersing Ag nanoparticles additive in Sn---58Bi solders. The interfacial morphologies of the undoped and doped Sn---58Bi solders under a direct current of 2.5 A (103 A/cm2) at 75 °C temperature with Cu pads and Au/Ni/Cu pad on daisy chain type ball grid array substrates for up to 20 days, were analysed. Unlike the undoped solder, there is no obvious formation of Bi-rich IMC growth on the anode side. The Cu---Sn and Au---Sn intermetallic compounds were formed on the Cu and Au pad, respectively, near the cathode and anode interface after the first reflow. Ag3Sn particles were found dispersed in the solder matrix, which behaved like barriers, blocking the diffusion of metal atoms during current stressing. In addition, during the shear test, fracture occurred at the intermetallic compound interface showing a ductile fracture mode. In the solder ball region of Sn---58Bi solder joint, β-Sn matrix with a refined microstructure and nano Ag intermetallic compound were observed, which resulted in an increase in the shear strength, due to a second phase dispersion strengthening mechanism.

Effect of addition of Ce in Sn–30Zn solder on the structure and properties of the Mg/Al-brazed joint

AZ31B Mg alloy and 6061 Al alloy are joined using low-temperature soldering with Sn–30Zn–xCe solder alloy. The effect of Ce content in Sn–30Zn–xCe solders on microstructure evolution and mechanical properties of the different brazed joints are investigated. The experimental results show that adding appropriate amount of Ce into Sn–30Zn solder is conducive to decreasing the amount of Mg2Sn intermetallic compounds and increasing the amount of Al–Sn–Zn solid solutions in the soldering zone of the brazed joint, which restricts the drawback of the formation of hard and brittle Mg2Sn intermetallic compounds and enhances the mechanical property of soldered joint. The average shear strength of the Mg/Sn–30Zn–0.05Ce/Al-brazed joint can reach 77.48 MPa. Results also indicate that the excessive content of Ce leads to the formation of some Ce–Zn and Ce–Sn intermetallic compounds in soldering zone and subsequently decreases the strength of soldered joint.

Effect of a Pd sacrifice layer on the interfacial reaction in Sn-3.5Ag/Pd/Cu

The effect of a Pd layer on the interfacial reaction in Sn-3.5Ag/Pd/Cu was studied by varying the thickness of the Pd layer. The formation of PdSn4, (Pd1−xCux)Sn4, and (Cu1−yPdy)6Sn5 intermetallic compounds (IMCs), along with CuSn IMCs, was observed. The Sn-3.5Ag/Pd/Cu structure did not suppress the growth of the (Cu1−yPdy)6Sn5 IMCs, but the growth of Cu3Sn IMCs was inhibited by the presence of a 200- to 600-nm-thick Pd layer.

Morphologies and grain orientations of Cu–Sn intermetallic compounds in Sn3.0Ag0.5Cu/Cu solder joints

Morphologies and grain orientations of Cu6Sn5 and Cu3Sn intermetallic compounds (IMCs) at the interface of Sn3.5Ag0.5Cu lead-free solder alloy and copper substrates were investigated by Electron Backscatter Diffraction (EBSD) technology combined with Scanning Electron Microscopy (SEM). Scalloped Cu6Sn5, Cu6Sn5 planes and six-prism shaped Cu6Sn5 IMCs were observed at the interface after 48h of soldering at 250°C. Moreover, Cu6Sn5 planes emerged in pairs on top and beside the scalloped Cu6Sn5, and two adjacent Cu6Sn5 planes were with an angle of 120°. Cu3Sn and scalloped Cu6Sn5 IMCs had preferred orientations, and they were Cu6Sn5 (0001)∥substrate surface, and Cu3Sn (1¯00) and (100)∥substrate surface.

Characterization of IMC layer and its effect on thermomechanical fatigue life of Sn–3.8Ag–0.7Cu solder joints

Intermetallic compound (IMC) growth was investigated under isothermal aging condition at 125°C for up to 500h. The evolution in the IMC morphology and microstructure were observed at four aging time conditions for 0, 120, 260 and 500h, respectively. Solid state IMC growth thickness measurements were determined from scanning electron microscope (SEM) observations for Cu–Sn and Cu–Ni–Sn IMC systems. The Young’s modulus and hardness of the IMCs were determined by nanoindentation tests. A finite element analysis (FEA) was carried out to model the effect of the IMC layer on the solder joint thermal fatigue life. The nanoindentation mechanical properties of Cu6Sn5 and CuNiSn IMCs were modeled with different IMC thicknesses in the FEA simulation to study the effect of the IMC growth on the fatigue life of the solder joint. It was shown that the IMC layer reduces the fatigue life of the solder joints and thick IMC layer results in a lower fatigue life. In addition, thermal cycling test and analysis for plastic ball grid array (PBGA) package with Sn–3.8Ag–0.7Cu Pb-free solder joints was performed. The mean-time-to-failure (MTTF) for the PBGA solder joints was determined, which was used for validating the FEA simulation results.

Evaluation of the microstructure and whisker growth in Sn–Zn–Ga solder with Pr content

Abstract

Suppressing the growth of Cu–Sn intermetallic compounds in Ni/Sn–Ag–Cu/Cu–Zn solder joints during thermal aging

This study aims to investigate the interfacial reactions and cross-interaction of Ni/Sn–3.0Ag–0.5Cu/Cu–xZn (Ni/SAC/Cu–xZn; x = 0, 15, and 30 wt.%) solder joints. In comparison with the Ni/SAC/Cu solder joint, Ni/SAC/Cu–15Zn and Ni/SAC/Cu–30Zn solder joints revealed thinner Cu6Sn5-based intermetallic compounds (IMCs) at both Ni/SAC and SAC/Cu–Zn interfaces after aging at 150 °C for 40 days. (Cu,Ni)6(Sn,Zn)5/(Cu,Ni)6Sn5 dual-phase formed at the Ni side, while (Cu,Ni)6(Sn,Zn)5 single-phase at the Cu–Zn side. Interestingly, the interfacial IMCs grew very slowly, and no void formed in these Zn-contained solder joints during the heating process. Also, the dissolved Zn in the solder alloy reduced the elemental cross-interaction between Ni and Cu–Zn substrates. The noticeable thermal stability of Ni/SAC/Cu–Zn solder joints is attributed to the Zn redistribution retarding the reaction of Ni, Cu and Sn. Phase formation and IMCs suppression mechanisms in Ni/SAC/Cu–Zn solder joints were probed and discussed.

Impact crack propagation through the dual-phased (Cu,Ni)6Sn5 layer in Sn–Ag–Cu/Ni solder joints

The interfacial reactions of the Sn–3Ag–0.75Cu/Au/Ni solder joint before and after aging were investigated. The dual-phased (Cu,Ni)6Sn5 with high (20.6at.%) and low Ni (5.7at.%) contents formed at the Sn–Ag–Cu/Ni interface, represented as H-(Cu,Ni)6Sn5 and L-(Cu,Ni)6Sn5, respectively. By employing high-speed impact test, the impact fracture morphology reveals that the H-(Cu,Ni)6Sn5/L-(Cu,Ni)6Sn5 interface facilitates the crack nucleation within the intermetallic compound (IMC). The indentation data shows that bulk H-(Cu,Ni)6Sn5 exhibits distinctly higher hardness and lower fracture toughness than bulk L-(Cu,Ni)6Sn5. In correlating the impact fracture behavior and mechanical properties of H-(Cu,Ni)6Sn5 and L-(Cu,Ni)6Sn5, cracks tend to propagate through the H-(Cu,Ni)6Sn5 IMC due to the relatively low fracture toughness of H-(Cu,Ni)6Sn5. In addition, mechanisms for the formation of the dual-phased (Cu,Ni)6Sn5 IMC are discussed in details.

The performance and fracture mechanism of solder joints under mechanical reliability test

The drop resistance and fracture behavior of Sn–37Pb, Sn–3.0Ag–0.5Cu (SAC305), Sn–1.0Ag–0.5Cu (SAC105), and Sn–8.5Zn–0.5Ag–0.01Al–0.1Ga (SnZn-5e) solder ball joints under the board-level drop test (BLDT) and the ball impact test (BIT) were studied. The results show that the drop reliabilities in terms of the characteristic life ratio from the Weibul plot are SnZn-5e : Sn–37Pb:SAC105:SAC305=3.1:2.9:2.1:1. It was observed that failure of Sn–37Pb occurred at the eutectic tin–lead phase whereas it took place at the brittle interface between the (Cu,Ni)6Sn5 inter-metallic compound and Ni layer in SAC305. The failure of SAC105 was found to be located within the solder matrix as well as at the interface of the inter-metallic compound. The failure of SnZn-5e depends on the morphology of the interfacial inter-metallic compound. The failure modes of Sn–37Pb and SAC305 after the BIT were similar to those after the BLDT. The maximum impact force (Fmax) and the initial fracture energy (E) from the BIT can be used to evaluate the drop reliability of solder joints.

Interfacial reactions between SnAg1.0Ti and Ni metallization

The effect of Ti on the solid state reactions between Sn and Ni has been investigated in this work. Based on the experimental results the following statements can be made: Firstly, the presence of Ti does not have measurable effects on the thickness evolution of Ni3Sn4 during solid state annealing. Secondly, the results from long term heat treatments show that there is no marked solubility of Ti to Ni3Sn4. Rather Ti reacts with Sn to form large Ti2Sn3 platelets inside the solder matrix. The Sn-rich part of the Ni–Sn–Ti phase diagram was assessed in order to rationalize the experimental results. By utilizing this information, the absence of any marked effects of Ti on the growth of Ni–Sn intermetallic compounds (IMC) was analysed. As there is no solubility of Ti to SnAg solder or to Ni–Sn IMC’s, Ti cannot change activities of components in the solder nor influence the stability of the IMC layers. Hence, these results throw significant doubts over the concept of trying to influence the Ni–Sn IMC layer thickness or quality by Ti alloying.