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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 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.

3D chip stacking is a key technology for 3D integration in which two or more chips are stacked with vertical interconnections. In the case of multi chip stacking with fine pitch microbump connections, capillary dispensing presents big limitations in terms of cost and processability. The purpose of this paper is to describe the way in which wafer‐level underfill (WLUF) process development was carried out with particular emphasis on microbump height coplanarity, bonding pressure distribution and the alignment of the microbumps. A three factorial design of experiment (DOE) was also conducted to enhance the understanding of the factors impacting the WLUF process such as bonding pressure, temperature and time on reliability test.

B‐staged WLUF was laminated on an 8″ wafer with a 30 μm pitch bump structure of 8 μm Cu/5 μm Sn2.5Ag Pb‐free solder. After wafer dicing, the chip with the WLUF was assembled on a substrate chip with the same bump structure using a high accuracy bonder. The substrate chip had metalisation (wiring) to enable evaluation of the electrical characteristics of the bonded daisy chain chips as they varied with material bonding process conditions and reliability testing.

The WLUF bonding process development pertaining to the processability and reliability for the flip chip assembly using Cu/SnAg microbumps was successful in this work.

The development of a WLUF bonding process that offers reliability for flip chip assembly using Cu/SnAg microbumps has been presented in this work. The critical steps, such as alignment of the WLUF coated chip with the substrate chip and void elimination, which enable this technology to work were optimised.

Valuable concepts for flexible sheet metal assembly have come out of a student project which is now in its fourth year at the Cranfield Institute of Technology.

Optimization of the process parameters remains a challenging task in thermosonic wire bonding due to relatively poor understanding of the bonding mechanism. The purpose of this paper is to understand initial bond formation in thermosonic gold wire bonding on aluminium metallization pads and the effect of bonding time on the initiation of bonding.

A gold wire (20 μm diameter/99.99 per cent wt%) was bonded to aluminium metallization pads (1 μm thick) on a silicon chip using a commercial ball/wedge automatic bonder. Bonding parameters were selected specifically to produce underdeveloped ball bonds so that ball lift‐off occurred during looping process. The lift‐off footprints on the aluminium metallization pads and their evolution were carried out using optical microscopy and scanning electron microscopy. A model is proposed to elaborate the effect of bonding time on initiation of bonding.

The obtained results showed that metallurgical bonding initiated at the peripheral areas of the contact area situated along the direction of ultrasonic vibration. Those areas extended inwards with bonding time, eventually covering the entire contact area.

This paper describes how bond initiation and its evolution in thermosonic gold wire bonding on aluminium metallization is ascertained by observing lift‐off footprints. The understanding of bonding mechanism benefits the optimization of process parameters and improvement of bondability in thermosonic wire bonding.

The purpose of this paper is to numerically evaluate the reliability of SnAgCuCe solder joints compared with that of SnAgCu. A trace amount of the rare earth (RE) element Ce was added into SnAgCu solder in order to improve the reliability of lead‐free solder joints, which was evaluated based on finite element simulation and experiments.

A finite element method and an Anand constitutive model were employed to analyze the reliability of SnAgCuCe and SnAgCu solder joints in fine pitch quad flat packages under thermal cycling. The mechanical properties and reliability of solder joints were characterized by using thermal fatigue and creep tests, while the microstructure of the solder alloy and SnAgCu/SnAgCuCe solder joints were also investigated in the experimental procedure.

The simulation results indicated that SnAgCuCe solder joints had better reliability than SnAgCu. In addition, the experimental results accorded well with those of simulation, the thermal fatigue property and creep resistance of solder joints was increased by adding cerium. SnAgCuCe alloy can get its microstructure refinement improved and the thickness of the intermetallic compound layer at the solder/Cu interface decreased significantly compared to that of SnAgCu.

The findings provide certain guidelines to the reliability evaluation of solder joints when applying novel RE containing solder alloys in practical electronics industry applications. In the meantime, the reason for the superior reliability of SnAgCuCe solder joints can be explained from the property and microstructural point‐of‐view.

The purpose of this paper is to improve the properties of Sn−9Zn solder, so as to meet the requirements of industrial applications.

The effects of Praseodymium on property and Sn whisker growth under aging treatment in Sn−9Zn lead‐free solder were investigated.

The results indicate that with the addition of rare earth Pr, the wettability and mechanical properties of Sn−9Zn solder were improved. The best wettability and comprehensive property of soldered joint is obtained when the content of Pr is 0.08 wt.%. After aging treatment at 150°C for 360 h, the mechanical properties of Sn−9Zn−0.08Pr decreased but are still obviously higher than that of Sn−9Zn. Moreover, when the content of Pr reached 0.1 wt.%, plenty of Sn−Pr compounds were found in the Sn−9Zn solder. The inevitable oxidation of Sn−Pr compounds would cause a high stress accumulated within PrSn3 phases, which would be served as driving force to induce the Sn whisker sprout and growth after aging treatment at 150°C for 120 h to 360 h. Compared with the results in Sn−9Zn−0.5Ga−0.7Pr solder that Sn whisker observed until the addition of Pr reached 0.7 wt.%, it could be inferred that the addition of Ga may react against the sprout of Sn whisker.

It is found that the addition of Pr can improve the properties of solder and avoid Sn whisker growth in the right range and proper conditions. The cost of the solder with added Pr is limited to RMB 2 yuan/kg so it can be widely used in industry.

With the application and development of intelligent clothing and wearable technology, the term “micro-interaction” has gradually entered people’s lives. The paper aims to discuss this issue.

The paper takes the concept of “micro-interaction” as the design principle, starting from the consumer demand, combing the realization mode of the intelligent safety clothing in recent years, and finds out the existing problems in the design of the intelligent safety clothing.

Under the concept of micro-interaction, a new theoretical model has been proposed to study intelligent safety clothing. Finally, the paper also emphasizes the importance of the industrialization of the proposed model.

The paper proposes a new research and development mode for intelligent clothing in safety protection area which is a pioneering study and can be valuable for safety clothing manufacturers to produce more functional and attractive products.

The transistor circuit based on Moore's Law is approaching the performance limit. The three-dimensional integrated circuit (3-D IC) is an important way to implement More than Moore. The main problems in the development of 3-D IC are Joule heating and stress. The stresses and strains generated in 3-D ICs will affect the performance of electronic products, leading to various reliability issues. The intermetallic compound (IMC) joint materials and structures are the main factors affecting 3-D IC stress. The purpose of this paper is to optimize the design of the 3-D IC.

To optimize the design of 3-D IC, the numerical model of 3-D IC was established. The Taguchi experiment was designed to simulate the influence of IMC joint material, solder joint array and package size on 3-D IC stress.

The simulation results show that the solder joint array and IMC joint materials have great influence on the equivalent stress. Compared with the original design, the von Mises stress of the optimal design was reduced by 69.96 per cent, the signal-to-noise ratio (S/N) was increased by 10.46 dB and the fatigue life of the Sn-3.9Ag-0.6Cu solder joint was increased from 415 to 533 cycles, indicating that the reliability of the 3-D IC has been significantly improved.

It is necessary to study the material properties of the bonded structure since 3-D IC is a new packaging structure. Currently, there is no relevant research on the optimization design of solder joint array in 3-D IC. Therefore, the IMC joint material, the solder joint array, the chip thickness and the substrate thickness are selected as the control factors to analyze the influence of various factors on the 3-D IC stress and design. The orthogonal experiment is used to optimize the structure of the 3-D IC.