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This paper aims to establish a method to optimize reflow profiles and achieve high reliability of solder joints on the basis of the heating factor, Q_η, a measure of the reflow profile related to reliability of reflow processed products.

The focus of the paper is on how to realize the optimal range of Q_η, since there is no need to pay particular attention to the shape of a reflow profile when performing a heating factor‐based optimization. The coldest point on the printed circuit board assembly (PCA), which experiences the minimum heating factor (Q_η^min) during the reflow process, was used to set the lower limit of the optimal range (Q_η^L). If Q_η^min approaches Q_η^L and the temperature difference across the PCA is minimized, then the solder joints on the PCA will all experience heating factors within the optimal range, ensuring high quality reflow soldering. Establishing an initial reflow profile may be performed using profiling software. The resultant oven recipe may then be used as the reference recipe by which to apply the heating factor‐based optimization. A combinatorial parameter, H_t, is defined to represent the temperature settings of all the top heating zones within the heating section of the reflow oven. The relative difference between H_t and each top heating zone temperature setting is derived from the reference recipe, and H_t is then adjusted to achieve Q_η^L for Q_η^min. This is achieved by using a least squares estimation method to build a regression model for Q_η^min versus H_t.

Experiments and regression analysis have demonstrated that Q_η^min varied linearly with H_t, with α denoting its slope. With a measured Q_η^min in response to the reference setup after the first run of a PCA, H_t should be increased by ((Q_η^L−Q_η^min)/α) to attain Q_η^L in the second run. Thereby, a suitable reflow process recipe can be obtained with only two reflow runs where Q_η^min is close to Q_η^L.

The optimal range of heating factor for lead‐free solder pastes is currently unknown, and the method to establish the required oven recipe for achieving a required reflow profile requires further exploration.

Provides a methodology for reducing the risk of process‐related reliability issues in lead‐free soldering.

Q_η^L can be fairly quickly achieved for Q_η^min with the approach established in this paper, facilitating the formation of solder joints with high reliability during the reflow soldering process.

This paper aims to investigate the microstructural evolution rules of the intermetallic compound (IMC) layers in high‐density solder interconnects with reduced stand‐off heights (SOH).

Cu/Sn/Cu solder joints with 100, 50, 20 and 10 μm SOH were prepared by the same reflow process and isothermally aged at 150°C. The IMC microstructural evolution was observed using scanning electron microscopy.

The whole IMC layer (Cu₃Sn + Cu₆Sn₅) grew faster in the solder joints with lower SOH because of the thinner IMC layer before aging. Also, the IMC proportion increased more rapidly in solder joints with the lower SOH. In all solder joints with different SOH, the growth rates of the Cu₃Sn (ϵ) layers were similar, and slowed down with increasing aging time. The Cu₆Sn₅ (η) was consumed by the Cu₃Sn (ϵ) growth at the beginning of the aging stage; while it turned to thickening after a period of aging. Finally, the Cu₆Sn₅ thickness was similar in all the solder joints. It is inferred that the thickness ratio of Cu₃Sn to Cu₆Sn₅ would maintain a dynamic balance in the subsequent aging. Based on the diffusion flux ratio of Cu to Sn at the ϵ/η interface, a model has been established to explain the microstructural evolution of IMC layers in high‐density solder interconnects with reduced SOH. In the model, interfacial reactions are mainly supposed to occur at the ϵ/η interface.

The findings provide electronic packaging reliability engineers with an insight into IMC microstructural evolution in high‐density solder interconnects with reduced SOH.

The purpose of this paper is to identify the solder joint with optimal mechanical properties among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni solder joints.

Solder joints with the same specimen shape were prepared by reflow. The microstructures were observed and analyzed by scanning electron microscopy and tensile testing was carried out to investigate the mechanical properties.

The mechanical properties of solder joint correlate closely with the intermetallic compounds (IMC) layer structure and the dissociative IMC particles in the solder bulk. Under the influence of the opposite Cu bar, the Cu/Sn/Ni has a duplex IMC layer structure at the Ni side, involving a thin Ni‐Cu‐Sn IMC layer and a faceted (Cu,Ni)₆Sn₅ layer. The mechanical connection of the duplex IMC layers is weak due to the pores in the layers. The Cu/Sn/Ni fractures in the IMC layers in a brittle mode under tensile testing. Comparatively, the Ni/Sn/Ni also has duplex Ni₃Sn₄ layers, and they connect firmly with each other. The tensile fracture of the Ni/Sn/Ni occurs in the solder bulk in a ductile mode, as well as for the Cu/Sn/Cu. Compared with the Cu/Sn/Cu solder bulk, the solder bulk of the Ni/Sn/Ni and the Cu/Sn/Ni have higher ultimate tensile strengths, because the strengthening effect of the dissociative Ni₃Sn₄ and (Cu,Ni)₆Sn₅ particles on the solder bulk is stronger than that of the Cu₆Sn₅ particles. Among Cu/Sn/Cu, Ni/Sn/Ni and Cu/Sn/Ni, Ni/Sn/Ni has the optimal mechanical properties.

The paper offers insights into the significant influence of base material matching on the microstructure and mechanical properties of solder joints.

The purpose of this paper is to investigate the effect of stand‐off height (SOH) on the microstructure and mechanical behaviour of the solder joints in high density interconnection.

Cu/Sn/Cu solder joints with 100, 50, 20 and 10 μm SOH are prepared using a reflow process. The microstructures and compositions of solder joints are observed and analyzed by scanning electron microscopy. Tensile testing is carried out to investigate the mechanical properties of the solder joints.

The SOH has a significant effect on the microstructure and mechanical behaviour of Cu/Sn/Cu solder joints. The thickness of the intermetallic compound (IMC) decreases with the reducing SOH; however, their corresponding IMC proportion increases. Meanwhile, the Cu concentration in the solder bulk experiences a marked increase, and the dissolved Cu exists in the forms of a solid solution and Cu‐rich particles at the grain boundary. Because of the higher strain rate and more dissolved Cu in the solder bulk with the reducing SOH, the ultimate tensile strength of solder joints is enhanced. When the SOH reduces to 10 μm, there is only one grain in height in the bulk, and a fracture in the IMC layer occurs. According to the mass balance of substance, a model is established to semi‐quantitatively calculate the consumed Cu thickness, and it is found that the consumed Cu thickness decreases with the reducing SOH.

The paper offers insights into the microstructural and mechanical property changes of the solder joints with the reducing SOH.

The purpose of this paper is to investigate the thermal fatigue behavior of a single Sn-3.0Ag-0.5Cu (SAC) lead-free and 63Sn-37Pb (SnPb) solder joint treated by rapidly alternating heating and cooling cycles.

With the application of electromagnetic-induced heating, the specimen was heated and cooled, controlled with a system that uses a fuzzy logic algorithm. The microstructure and morphology of the interface between the solder ball and Cu substrate was observed using scanning electron microscopy. The intermetallic compounds and the solder bump surface were analyzed by energy-dispersive X-ray spectroscopy and X-ray diffraction, respectively.

The experimental results showed that rapid thermal cycling had an evident influence on the surface and interfacial microstructure of a single solder joint. The experiment revealed that microcracks originate and propagate on the superficial oxide of the solder bump after rapid thermal cycling.

Analysis, based on finite element modeling and metal thermal fatigue mechanism, determined that the rimous cracks can be explained by the heat deformation theory and the function of temperature distribution in materials physics.

The purpose of this paper is to present a novel reflow profile optimization method using mechanical reliability estimation of micro‐ball grid array (μBGA) solder joints, based on the heating factor, Q_η is introduced, where the coupling effect of reflow temperature and time on the mechanical reliability of μBGA joints is considered.

The method presented is actualized through vibration fatigue tests. First, a two‐parameter Weibull distribution is used to model the collected data of vibration fatigue lifetime for different Q_η. After that, two explicit functions are deduced in a unified mathematic expression form, which give an intuitionistic description of the mean time to failure and reliability of solder joints against induced variable Q_η, thus revealing definitely the effect of Q_η on the mechanical fatigue lifetime of solder joints suffering from cyclic vibration loading. Finally, for a specified reliability goal, how to choose proper Q_η values, based an improved Golden Section Search arithmetic, is discussed.

Numerical analysis and calculation are performed. The results show that the solder joints made at Q_η near 510 have higher mechanical reliability, and those reflowed farther away this optimal value have less reliability.

This paper presents a useful and applicable solution to achieve reflow profile optimization and process control for a quantitative mechanical reliability estimation of μBGA solder joints.

The purpose of this paper is to present the development of cumulative rainfall deficit (CRD) indices for corn in Shandong Province, China, based on high-resolution weather (county, 1980-2011) and yield data (township, 1989-2010) for five counties in Tai’an prefecture.

A survey with farming households is undertaken to obtain local corn prices and production costs to compute the sum insured. CRD indices are developed for five corn-growth phases. Rainfall is spatially interpolated to derive indices for areas that are outside a 25 km radius from weather stations. To lower basis risk, triggers and exits of the payout functions are statistically determined rather than relying on water requirement levels.

The results show that rainfall deficits in the main corn-growth phases explain yield reductions to a satisfying degree, except for the emergence phase. Correlation coefficients between payouts of the CRD indices and yield reductions reach 0.86-0.96 and underline the performance of the indices with low basis risk. The exception is SA-Xintai (correlation 0.71) where a total rainfall deficit index performs better (0.87). Risk premium rates range from 5.6 percent (Daiyue) to 12.2 percent (SA-Xintai) and adequately reflect the drought risk.

This paper suggests that rainfall deficit indices can be used in the future to complement existing indemnity-based insurance products that do not cover drought for corn in Shandong or for CRD indices to operate as a new insurance product.

Stereolithography (SL) is a kind of rapid prototyping technology which uses the laminate manufacturing to fabricate parts. With the development of RP, some new RP processes have boomed rapidly. Compact prototyping system (CPS) is a kind of novel stereolithography method which utilizes conventional UV light as the light source. After transmitting by optic fiber and focusing through lens set, the light is intensified and can be used to cure the photopolymer. Compared with the laser SL prototyping apparatus, this apparatus has unique characteristics on its driving system and light path system. Discusses the characteristics and corresponding consequences of the driving system and light path system, and analyzes the light energy distribution and the corresponding line shapes. Since each layer is constructed from a serial of lines, the scanning parameters, especially scanning speed and hatch gap, will influence the overall light intensity which determines the layer thickness, section shape and ultimately the prototyping accuracy. The driving system, due to the non‐uniform moving speeds, could cause the shape error of the lines. A light shutter, keeping the light only illuminating on resin surface within given curing areas, is employed to solve this deficiency.