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Abstract: The growth and morphology of the intermetallic compounds formed at the solder joint between the Sn–9Zn–2.5Ag lead-free solder and the Cu substrate have been investigated in this study. The planar Cu6Sn5 formed after soldering transforms to a scalloped Cu5Zn8 after aging at 180°C for 250h. However, the Cu5Zn8 decomposes and the scalloped Cu6Sn5 reforms at the interface close to the solder alloy after aging for 400h. The η′-Cu6Sn5 transforms to the η-Cu6Sn5 as aged at 180°C. The interdiffusion coefficient of Cu and Sn in the Cu6Sn5 is determined as 2.58×10−13 cm2 s−1, and that of Cu and Zn in the Cu5Zn8 layers is determined as 3.36×10−14 cm2 s−1 at 180°C, from the estimated thickness of the intermetallic compound (IMC). On the other hand, they are determined as 3.43×10−13 and 2.36×10−14 cm2 s−1, respectively, from the microbeam EDS analysis. [Copyright &y& Elsevier]

The enhancement of the wettability and solder joint reliability at the Sn–9Zn–0.5Ag solder alloy–Cu interface by Ag precoating has been investigated. The wettability of the Sn–9Zn–0.5Ag solder alloy–Cu interface has been improved by Ag precoating. The adhesion strength of the solder alloy–Ag precoated Cu interface increases from 4.11±0.56 to 6.92±0.85 MPa as dipped at 250 °C for 10 s. When the dipping time is prolonged from 10 to 30 s, the interfacial adhesion strength increases from 6.92±0.85 to 13.62±0.73 MPa. The interfacial adhesion strength is enhanced by the rod-like Cu–Zn intermetallic compound (IMC) formed close to the interface. The diffusion coefficients of Sn and Zn in the IMC layer are determined as 5.76×10−10 and 9.50×10−11 cm2/s at the Sn–9Zn–0.5Ag–Cu and Sn–9Zn–0.5Ag–Ag precoated Cu interfaces, respectively. [Copyright &y& Elsevier]

The intermetallic compounds formation and interfacial adhesion strength of the Sn–9Zn–0.5Ag lead-free solder alloy hot-dipped on Cu substrate have been investigated by pull-off test, X-ray diffractometry, optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive spectrometry. The intermetallic compounds of Ag3Sn, Cu6Sn5 and Cu5Zn8 were identified for Sn–9Zn–0.5Ag solder alloy–Cu, in which the thickness of Cu6Sn5 increased from 0.69±0.18 to 1.59±0.46 μm when the dipping time increased from 10 to 30 s. The interfacial adhesion strength increased from 3.21±0.73 to 4.11±0.56 MPa when the Ag content increased from 0 to 0.5 wt.% at the dipping temperature of 250 °C for 10 s. The interfacial adhesion strength of Sn–9Zn–0.5Ag alloy–Cu substrate also increased to 4.46±0.48 and 5.49±0.67 MPa when the dipping time increased to 20 and 30 s, respectively. The fracture path was observed at the Sn–9Zn–Cu5Zn8 interface, and within the Sn–9Zn–0.5Ag solder alloy. [Copyright &y& Elsevier]

The shrinking solder dimensions greatly impact the reliability of devices and increase entire failure modes. Limited solder volumes can be consumed completely and transformed into intermetallic compound (IMC) microbumps. Microvoids surface when microbumps are formed and may be attributed to a mismatch of the thermal expansion coefficient between the constituents. After thermal aging at 150 °C, the stress induced by the growth of IMCs relaxes and enhances propagation of the cracks along the middle of the bumps. The brittle nature of the IMC showed minimal resistance to cracks and incurred a failure mode. [ABSTRACT FROM AUTHOR]

Highlights: [•] Serious warpage of IGBT power module is induced from assembly processes. [•] A pre-bending substrate with a curve opposite the warp is proposed. [•] Design is validated by FEA and related actual measurements. [•] Increasing DBC thickness of Al2O3 layer reduces warps and bonded solder stresses. [•] A thicker base plate is suggested to reduce warping of the entire packaging structure. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of lead-free solders, Sn–8Zn–3Bi and Sn–9Zn–lAl, were used to mount passive components onto printed circuit boards via a re-flow soldering process. The samples were stored at 150°C for 200, 400, 600, 800, and 1100h. The microstructures of the samples after aged at 150°C for various times were characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and the analyzed of solder joint shear strengths. The joint strength between Sn–8Zn–3Bi and Cu pad was about 4.0±0.3kg, while the strength between Sn–9Zn–lAl and Cu pad had values of 2.6±0.1kg. Both kinds of solder joints exhibited reduced strengths with increasing aging times. After aging at 150°C for 1100h, the joints strengths of Sn-8Zn-3Bi and Sn–9Zn–lAl were 1.8±0.3 and 1.7±0.3kg, respectively. Both the Sn–8Zn–3Bi and Sn–9Zn–lAl joints showed brittle fracture behaviors. A flat layer of Cu5Zn8 intermetallic compound (IMC) was formed between Sn–8Zn–3Bi solder and Cu pad after reflow. When the aging time was increased to 400h, Zn-depletion and formation of Cu6Sn5 IMC were observed in the solders due to the interaction between the tin and zinc compounds. The interaction between Sn–9Zn–lAl solder and Cu pad had similar behavior, however, Cu6Sn5 IMC formed in Sn–9Zn–lAl solder when after aging at 150°C for 600h. As the aging time increased, both types of solders generated clear IMC spalling layers with large and continuous voids. Those voids substantially decreased the joint strength. [Copyright &y& Elsevier]

We report electromigration induced failure on lead-free micro bumps in three-dimensional integrated circuits samples with chip on chip configuration. Compared to flip chip solder joints, micro bumps of chip-on-chip samples exhibit better electromigration resistance and are able to withstand a higher current density. No exhibited electromigration-induced failure was observed when current density was below 2 × 104 A/cm2. A threshold current density to trigger electromigration in chip-on-chip samples was found to be 3.43 × 104 A/cm2. When current density was higher than 7.5 × 104 A/cm2 at an ambient temperature of 150 °C, no void propagation through whole bump opening was found; instead, electromigration induced voids were observed at the cathode side of Al trace. [ABSTRACT FROM AUTHOR]