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The purpose of this paper is to investigate the effect of typical morphologies of Au-Sn IMCs (intermetallic compounds) at the interfaces of solder and pads on shear properties of laser reflowed micro-solder joints.

Sn-2.0Ag-0.75Cu-3.0Bi (SnAgCuBi) solder balls (120 μm in diameter), pads with 0.1, 0.5, 0.9 or 4.0 μm thickness of Au surface finish, and different laser input energies were utilized to fabricate micro-solder joints with Au-Sn IMCs having different typical morphologies. The joints were performed by a shear test through a DAGE bond test system. Fracture surfaces of the joints were analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometry to identify fracture modes and locations.

Morphologies of Au-Sn IMCs would affect shear properties of the joints remarkably. When needle-like AuSn4 IMCs formed at the interfaces of solder and pads, almost entire surfaces presented the manner of ductile fracture. Moreover, shear forces of this kind of solder joints were higher than those of joints without Au-Sn IMCs or with a nearly continuous/continuous Au-Sn IMCs layer. The reason was that the shear performance of the solder joints with needle-like AuSn4 IMCs was enhanced by an interlocking effect between solder and needle-like AuSn4 IMCs. As a nearly continuous or continuous Au-Sn IMCs layer formed, the fracture surfaces presented more character of brittle than ductile fracture. However, if an Au layer still remained under Au-Sn IMCs, the shear performance of the joints would be enhanced.

The results in this study can be used to optimize microstructures and shear properties of laser reflowed micro-solder joints.

This paper aims to investigate the creep properties of the bulks of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints from 298 to 358 K. The creep constitutive modelling was developed. Meanwhile, the creep mechanism of the bulks of Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints was discussed.

The creep properties of the bulks of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints from 298 to 358 K were investigated using the nanoindentation method.

The results of the experiments showed that the indentation depth and area increased with increasing temperatures. At the test temperature of 298-358 K, the creep strain rate of the bulks of the micro solder joints increases with the rising of the tested temperature. The values of creep stress exponent and activation energy calculated for the bulks of Cu/Sn-Ag-Cu-Bi-Ni/Cu micro solder joints were reasonably close to the published data. At the tested temperatures, dislocation climb took place and the dislocation climb motion was controlled by the dislocation pipe mechanism, and the second-phase particles enhancement mechanism played a very important role.

This study provides the creep properties of low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu solder joints at different temperatures. The creep constitutive modelling has been developed for low-Ag Cu/Sn-Ag-Cu-Bi-Ni/Cu solder joints.

The purpose of this paper is to investigate the laser soldering of fine pitch quad flat package (QFP) devices using lead‐free solders and solder joint reliability during thermal cycling.

QFP devices were selected as the test vehicles and were soldered with four alloy types, Sn37Pb, Sn3.5Ag, Sn3.8Ag0.7Cu and Sn3.8Ag0.7Cu0.03Ce. The experimental samples were QFP‐256 devices with lead‐free solder paste on the printed circuit boards. The packages were dried for 24 h at 125°C prior to reflow soldering. Soldering experiments on the QFP devices were carried out with an infrared (IR) reflow soldering oven and a diode laser (DL) soldering system. Reflow soldering was performed at peak temperatures of 210°C (SnPb), 240°C (SnAgCu and SnAgCuCe) and 250°C (SnAg), as determined on the boards. Pull testing was adopted to evaluate the tensile strength of the four solders using an STR–1000 micro‐joint strength tester.

The tensile force of the QFP micro‐joints increased as laser intensity increased when it was less than an “optimal” value. The maximum tensile force of the QFP micro‐joints was gained when the laser intensity had increased to 2,165, 2,127, 2,165 and 2,064 W/cm², depending on the alloy used. The thermal fatigue performance of three lead‐free solder joints, SnAgCuCe, SnAgCu and SnAg, was determined to be superior to that of the eutectic SnPb alloy. After soldering without thermal cycling tests, the fracture morphology of soldered joints exhibited characteristic toughness fracture with both of the soldering methods. After 700 thermal cycles, the fracture mechanism was also toughness fracture, nevertheless, the dimples became large. The fracture morphology of the soldered joints subjected to 1,500 thermal cycles indicated brittle intergranular fracture on the fracture surface and no intense plastic deformation appeared before fracture with IR soldering. For DL soldering, the pull fracture model of the SnAgCuCe was completely ductile in the soldered joint with 1,500 thermal cycles.

The paper usefully investigates the influence of laser intensity on the tensile strength of different soldered joints and the solder joint reliability during thermal cycling.

This paper aims to assess precise correlations between intermetallic compounds (IMCs) microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using thermal shock (TS) tests.

This paper uses 200-µm pitch silicon flip chips with nickel (Ni) pads and stand-off height of approximately 60 µm, assembled on substrates with copper (Cu) pads. After assembly, the samples were subjected to air-to-air thermal shock testing from 55 to 125 per cent. The transfer time was less than 5 s, and the dwell time at each temperature extreme was 15 min. To investigate the microstructure evolution and crack growth, two samples were removed from the thermal shock chamber at 0, 400, 1,200, 2,000, 5,800 and 7,000 cycles.

The results showed that one (Cu, Ni)₆Sn₅/(Ni, Cu)₃Sn₄ dual-layer structure formed at the Ni pad interface of chip side dominates the micro-joints failure. This is because substantial (Ni, Cu)₃Sn₄ grain boundaries provide a preferential pathway for the catastrophic crack growth. Other IMCs microstructure evolutions that cause the prevalent joints failure as previously reported, i.e. thickened interfacial (Cu, Ni)₆Sn₅ and Ni₃P layer, and coarsened IMCs inside the solder matrix, only contributed to the occurrence of fine cracks. Moreover, the typical interfacial IMCs spalling triggered by thermally induced stress did not take place in this study, showing a positive impact in the micro-joint reliability.

As sustained trends toward multi-functionality and miniaturization of microelectronic devices, the joints size is required to be constantly scaled down in advanced packages. This arises a fact that the reliability of small-size joints is more sensitive to the IMCs because of their high volume proportion and greatly complicated microstructure evolutions. This paper evaluated precise correlations between IMCs microstructure evolutions and the reliability of micro-joints with a Cu/SAC305solder/Ni structure using TS tests. It found that one (Cu, Ni)₆Sn₅/(Ni, Cu)₃Sn₄ dual-layer structure formed at the Ni pad interface dominate the micro-joints failure, whereas other IMCs microstructure evolutions that cause the prevalent joints failure exhibited nearly negligible effects.

The purpose of this paper is to investigate oxidation and the Au‐Sn reaction of laser reflowed (LR) micro‐solder joints when different protective atmospheres were applied.

A N2 atmosphere at room temperature, 60°C, 100°C and 130°C, or an air atmosphere at room temperature were utilized in this study. The solder balls were composed of Sn‐2.0Ag‐0.75Cu‐3.0Bi, and 120 μm in diameter. The surface finish of one pad of the joints was 4.0 μm Au/0.1 μm NiFe/0.01 μm Ta, another pad was made of Cu plated with 3.0 μm Au. The laser reflow process time was controlled to within 10 ms. Auger Electron Spectroscopy (AES) was used to identify the oxidation condition of LR solder joints with or without protection from a N2 atmosphere at room temperature. The appearance and cross‐sections of the joints protected by a N2 atmosphere at different temperatures were evaluated using SEM analysis.

Oxidation of LR solder joints from an air atmosphere was extremely severe, and the surfaces of solder were rough as compared with joints protected by a N2 atmosphere. Au‐rich phases and needle‐like AuSn4 intermetallic compounds (IMCs) formed at the interfaces of the solder and the pads. As the temperature of the N2 atmosphere was increased above 100°C, almost all of the Au‐rich phases disappeared. More needle‐like AuSn4 IMCs formed at the interfaces, as compared with that in joints protected by a N2 atmosphere at room temperature and 60°C. In addition, the orientation of the IMCs had clearly changed.

The results may provide a guide for controlling oxidation and the Au‐Sn reaction of micro‐solder joints during the LR process, and improving the properties of joints between solder and pads with Au surface finishes, by regulating the protective atmosphere.

The purpose of this paper is to study the temperature cycling reliability of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu micro solder joints compared with Sn-5Sb/Cu and SAC305/Cu micro solder joints, which has important engineering and theoretical significance for the research of micro solder joint reliability. This paper also aims to provide guidance for the selection of solder for third-generation semiconductor power device packaging.

The shear strength, plasticity, bulk solder hardness and creep performance of three kinds of micro solder joints before and after temperature cycling were studied by nanoindentation and micro shear experiments. Scanning electron microscopy and energy dispersive spectrometry were used to analyze the fracture mode, fracture position and compound composition of the solder joints.

The bulk solder hardnesses and shear strengths of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were higher than those of Sn-5Sb/Cu and SAC305/Cu solder joints before and after temperature cycling. The indentation depth, creep displacement and creep rate of bulk solders of Sn-5Sb-0.5Cu-0.1Ni-0.5Ag/Cu solder joints were the smallest compared with those of Sn-5Sb/Cu and SAC305/Cu solder joints after the same number of cycles. In addition, the fracture mode and fracture position of the micro solder joints changed before and after temperature cycling.

A new type of solder was developed with excellent temperature cycling performance.

To study the behaviour of voids in PBGA solder joints and their influence on the lifetime of lead‐free solder joints.

The behaviour of voids was studied using micro via and land pad PWBs, PBGA components, and by measuring voids in the solder joints. The lifetimes of solder joints were tested using accelerated temperature tests.

Number of factors affecting the solder joint lifetimes were found. The voids were discovered to have a significantly large influence on the solder joints.

The findings can be used to achieve better soldering results, methods, and designs.

In this paper, the effect and the behaviour of voids were studied profoundly. The findings can be valuable to researchers and process personnel.

Solder bumps for chip interconnections are downsizing from current approximately 100 µm to the expected 1 µm in future. As a result, the Cu-Ni cross-interaction in Cu/Solder/Ni solder joints will be more complicated and then strongly influence the growth of the intermetallic compounds (IMCs). Thus, it is critical to understand the fundamental aspects of interfacial reaction in micro solder joints. This paper aims to reveal the effect mechanism of reflow temperature and solder size on the interfacial reaction in Cu/Solder/Ni solder joints.

The Cu-Ni cross-interaction in the Cu/Sn/Ni micro solder joints with 50 and 100 µm solder sizes at 250°C and 300°C were observed, respectively. The line-type interconnects were soaked in silicone oil, and the temperature of the line-type interconnects was 250 ± 3°C and 300 ± 3°C, which were monitored by a fine K-type thermocouple, and followed by an isothermal aging process at various times. After aging, the specimens were removed from the silicone oil and cooled in the air to room temperature.

The major interfacial reaction product on both interfaces was (Cu,Ni)₆Sn₅, and the asymmetric growth of (Cu,Ni)₆Sn₅, evidenced by the thickness of (Cu,Ni)₆Sn₅ IMCs at the Sn/Ni interface was always larger than that at the Sn/Cu interface, resulted from the directional migration of Cu atoms toward the Sn/Ni interface under Cu concentration gradient. The morphology of (Cu,Ni)₆Sn₅ IMC at Sn/Cu interface was columnlike at 250°C, and which changed from columnlike to scallop with large aspect ratio at 300°C, while that at Sn/Ni interface gradually evolved from needlelike to the mixture of needlelike and layered at 250°C, and which evolved from needlelike to scallop with large aspect ratio at 300°C. The evolution of morphology of (Cu,Ni)₆Sn₅ is attributed to the content of Ni. Furthermore, the results indicate that the Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.

The asymmetric growth of (Cu,Ni)₆Sn₅ in the Cu/Sn/Ni micro solder joints, evidenced by the thickness of (Cu,Ni)₆Sn₅ IMCs at the Sn/Ni interface, was always larger than that at the Sn/Cu interface. The morphology evolution of (Cu,Ni)₆Sn₅ IMC at both interfaces was attributed to the content of Ni. The Cu-Ni cross-interaction was stronger with small solder size and relatively low temperature in the Cu/Sn/Ni micro solder joints.

The purpose of this paper is to propose a solution procedure to minimize/eliminate voiding and spattering defects in the assembly of 0201 chip components with micro via‐in pads and 95 wt.%Sn‐5 wt.%Sb solder alloy.

In total, four different micro via‐in pad designs were compared (via‐hole opening size): ultra small via‐in pads (d: 10 μm), small via‐in pads (d: 20 μm), and large via‐in pads (d: 60 μm), as well as designs with no via‐in pads and capped via‐in pads. Two process variables were also evaluated for the goal of achieving a high‐yield assembly solution in micro via‐in pad and lead‐free solder systems. Potential factors, such as the preheat conditions of the reflow profile and stencil aperture size, which might affect voiding and spattering in solder joints with micro via‐in pad, were investigated. Solder voiding frequency and size were also determined from X‐ray inspection and sample cross‐section analysis.

The results indicated that larger via‐holes were seen to create bigger voiding than smaller via‐holes. For smaller via‐holes, spattering is a greater problem than voiding in solder joints. Ultra small via‐in pads generated higher spattering compared to no via‐in pads and capped via‐in pads. Capped via‐in pads exhibited the best results in preventing voiding and flux spattering, and provided a wide process window for the selection of process parameters. It is also indicated that spattering was found to rapidly reduced with both increasing stencil opening size and use of reflow profile with long‐preheat conditions.

The findings provide certain process guidelines for surface‐mount assembly with via‐in pad substrate design. The strategy is to prevent voiding and spattering by adopting capped via‐in pads, if possible, when applying micro via with the 95 wt.%Sn‐5 wt.%Sb solder alloy system.

The purpose of this work is to explore the forms of intermetallic phase compounds (IMPCs) in Pt/In/Au and Pt/In/Ag joints by using isothermal solidification. This lead-free technique leads to formation of IMPCs having high-temperature stable joints for platinum-based micro-heater gas sensor fabricated on low temperature co-fired ceramic (LTCC) substrate.

Proposed task is to make an interconnection for Pt micro-heater electrode pad to the silver and gold thick-films printed on LTCC substrate. Both Pt/In/Au and Pt/In/Ag configured joints with different interactive areas prepared at 190 and 220°C to study temperature and contact surface area effects on ultimate tensile strength of the joints, for a 20 s reaction time, at 0.2 MPa applied pressure. Those delaminated joint interfaces studied under SEM, EDAX and XRD.

IMPCs identified through material analysis using diffraction analysis of XRD data are InPt3, AgIn2, AgPt, AgPt3, Au9In4 and other stoichiometric compounds. The interactive surface area between thick-films and temperature increment shows improvement in the formations of IMPCs and mechanical stability of joints. These IMPCs-based joints have improved the mechanical stability to the joints to sustain even at high operating temperatures. Elemental mapping of the weak joint contact interface shows unwanted oxide formations also reported. Physical inter-locking followed by the diffusion phenomenon on the silver substrate strengthen the interconnection has been noticed.

Inert gas environment creation inside the chamber to isolate the lead-free joint placed between heating stamp pads to avoid oxide formations at the interface while cooling which adds up to the cost of manufacturing. Most of the oxides at a joint-interface increase minute to moderate resistance with respect to the level of oxides took place. These oxides contributed heat certainly damage the micro-heater based gas sensors while functioning.

These isothermal solidification-based lead-free solder joints formation replace the existing lead-based packaging techniques. These lead-free interconnections on ceramic or LTCC substrate are reliable and durable, especially those designed to work for heavy-duty engines, even at severe environment conditions.

Platinum micro-heater-based gas sensors handles over a wide-range of temperatures about 300 to 500°C. The specific temperature level of different oxide films (SnO2) on the micro-heater is capable of detecting various specific gases. This feature of platinum based gas sensor demands durable and mechanically stable joints for continuous monitoring.