Search results

To investigate effects of the thermal history on intermetallic thickness and morphology and on the resulting shear strength of the ball attachment for a variety of BGA components.

In this study, a variety of BGA components with balls made of Pb‐free Sn‐Ag‐Cu (SAC) 305, Sn‐Pb eutectic and high‐temperature 90Pb‐10Sn alloys, were subjected to different thermal histories, including up to ten reflow cycles, and aged at 125°C from 24 to 336 h. The intermetallic thickness and morphology after these thermal events were then examined under optical and scanning electronic microscopes. Ball shearing tests were conducted to investigate effects of the thermal history and intermetallic thickness and morphology on shearing strength of these solder balls.

The results show that effects directly from intermetallic layers may or may not be detectable; and the shear strength of solder balls is largely dependent on the solder alloy and its microstructure. Shear strength increases are observed after multiple reflow cycles and ageing at elevated temperature for the two Pb‐bearing alloys, while the SAC305 lead‐free alloy shows slight reductions in both strength and ductility after thermal exposure.

Presented results can be used for estimation of reliability for electronic assemblies subjected to multiple rework and repair operations, which expose sensitive components, such as BGAs, to elevated temperatures.

It is believed that a sound understanding of the effects of intermetallic morphology and thickness on reliability of BGA solder balls can lead to more intelligent choice of soldering processes, as well as to rework/repair process optimisation and to establishing their operational limits.

The purpose of this paper is to investigate effects of the multiple rework of ball grid array (BGA) components on mechanical strength of BGA balls, as well as any possible intermetallic (IMC) embrittlement, and obtain data correlated with possible estimation on the maximum permitted limits of BGA rework.

In this paper, mechanical strength of BGA components assemblies with multiple numbers of rework operations was evaluated. Mechanical evaluation was conducted using BGA ball shear tests and four‐point bending tests of BGA assemblies. Test samples were prepared under the following conditions: virgin, one, two, three and five BGA reworks. Failure mechanism was evaluated using cross‐section and SEM analysis.

The results show that both ball shearing tests and four‐point bending tests indicates that strength of BGA solder ball itself was not reduced significantly after repair/rework operation from one to five cycles. The IMC structure layer after rework is a mixture of IMC, Sn‐rich and Pb‐rich phases. This mixture layers with thickness even more than 10 μm in thickness does not show reduction of strength of BGA solder balls and do not cause premature embrittlement. However, the bonding strength of the copper pads to the laminates is reduced with rework/repair operation, with the great reduction coming from the first and second rework operation.

In general, the industry recommends two rework cycles for BGA components on the same spot. This study indicates that further rework (up to five) causes little degradation, therefore there is room to increase the total rework cycle limit beyond recommended two for plastic BGA components.

Presented test results shows that in most cases industry overestimates risks associated with increased embritlement of the BGA solder joints due to the intermetallics growth after multiple BGA rework operations. Strength reduction of BGA assemblies is mostly associated with reduction of bonding strength of the copper pads to the laminates is reduced with rework/repair operation and number of reworks could be increased in most cases.

This study aims to offer an image-based robust edge detection system that can estimate, identify, locate and label surface flaws during manufacturing for real-time surface issue diagnostics. Of great concern, this methodology extrapolates surface defect information from scanning electron microscopy (SEM) images of composite fracture surfaces. This study predicts changes in topological intensity of composite fracture surfaces and display them as real-time surface intensity values for the first time.

This work, however, introduces a novel robust edge detection method – based image processing – as it is shown to be effective in locating defects, as measured by SEM images of composite fracture surfaces created using additive manufacturing (AM). SEM images, obtained in this study, are related to previous study considering the fracture surfaces of reinforced thermoset composites created via the AM method. These SEM images are of two types: fracture surface of AM of carbon fiber reinforced thermoset composites and fracture surface of AM of syntactic foam reinforced thermoset composites. Initially, MATLAB environment is used for analyzing the SEM images; the technique used, as well as the validity are explained more in the methodology section.

The robust surface defect inspection approach used herein is found to be capable of predicting, identifying, localizing and labeling surface defects during production, allowing for real-time surface issue diagnosis. Further, this work makes it possible to use image processing and analysis of these surfaces to anticipate fluctuations in the topological intensity of the fracture surfaces of composites and represent them as values of surface intensity in real time.

Rising worldwide company rivalry requires a fast, accurate component failure diagnostic method. To create an efficient feature set, a surface defect inspection system must identify product flaws in real time. Thus, this study proposed an image-based robust edge detection system – based on MATLAB environment – that is capable of estimating, identifying, locating and labeling surface faults during production. This paves the way for an extensive set of high-quality tools for dealing with a wide range of problems associated with digital image processing in composites. As a result, the ability to define methodologies and rapidly prototype prospective solutions typically minimizes the cost and time required to implement a successful system during the design phase of an image processing system.

The purpose of this paper is to investigate the microstructural development of SnAgCu solder joints under different loading conditions (isothermal storage, thermal cycling and vibration).

The observed microstructural changes have been studied with respect to grain growth and grain refinement, crack formation and crack growth. The growth kinetics of the intermetallic phases encountered as particles in the bulk as well as a reaction layer on the copper pad, were studied in the temperature range of 125‐175°C.

Dynamic recrystallisation of the tin matrix leads to a change in the diffusion controlled growth mechanism, which causes an increase of the particle growth rate compared to isothermal storage. Thus, these grain boundaries are separated forcibly by crack growth during thermal cycling. This stress causes intergranular cracks while vibration stress induces transgranular cracks.

The paper adds insight into microstructural changes of lead‐free solder joints during long‐term ageing, thermal cycling and vibration fatigue.

The purpose of this paper is to study the effect of copper concentration in near‐eutectic liquid SAC solders on their thermophysical properties: viscosity, surface tension, density; as well as wetting behavior on copper substrates at 523 K.

Viscosity, surface tension, and density were studied over a broad range of temperatures with the recently developed Roach‐Henein method. The obtained results were compared with the data from modified capillary, maximum bubble pressure, wetting balance and dilatometric measurements. Wetting angles measured with wetting balance method were compared with the results of sessile drop measurements.

The results obtained indicate that increasing concentration of copper in the alloy results in higher density, surface tension and viscosity, but differences resulting from copper concentration on wettability are relatively small. At 523 K, the density is: 7.097, 7.186, 7.232 g cm⁻³, the surface tension is: 538.1, 553.5, 556.7 m Nm⁻¹, the viscosity is: 2.173, 2.227, 2.467 mPas, respectively, for alloys containing 0.41, 1.01 and 1.61 wt% of Cu. Wetting angles on copper substrates are similar within a margin of error for all compositions. The results of present study are compared with the available literature data and a relatively good agreement is observed.

This paper provides the data of thermophysical properties of widely‐used SAC solders including viscosity, of which there is little data in the literature. It is confirmed that the increased copper concentration increases viscosity, yet this effect is small and does not correlate with the wetting behavior.

As a literature review article, the purpose of this paper is to highlight the intricate interaction and correlation between the interconnection microstructure and the failure mechanism. It is therefore critical to summarize all the challenges in understanding solder solidification of interconnections.

Literature review.

Solidification of solder interconnections is therefore critical because it is the process during which the solder interconnection is formed. The as‐solidified microstructure serves as the starting point for all failure modes. Because of the miniaturization of electronics, the interconnection size decreases continuously, already to such a range that solder solidification takes place remarkably differently from the bulk ingot, on which solidification studies have been focused for decades. There are many challenges in understanding the solidification of tiny solder interconnections, including the complex metallurgical system, dynamic solder composition, supercooling and actual solidification temperature, localized temperature field, diverse interfacial IMC formation, and so on, warranting further research investment on solder solidification.

This paper provides a critical overview of the concerns in solidification study for lead‐free solder interconnection. It is probably an article initiating more attention towards solidification topics.

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.

This paper aims to discuss the effect of surface treatment on the wettability between copper and a lead-free solder paste. The industrial applications of laser technologies are increasing constantly. A specific laser treatment can modify the surface energy of copper and affect the wetting properties.

The surfaces of copper plates were treated using an Nd:YAG laser with varying laser powers. After laser surface treatment, wetting experiments were performed between the copper plates and SAC305 lead-free solder paste. The effect of laser treatment on copper surface was analysed using optical microscopy and scanning electron microscopy (SEM).

The experimental results showed that the wetting contact angles changed with the variation in laser power. Furthermore, it means that the surface energy of copper plates was changed by the laser treatment. The results demonstrated that the contact angles also changed when a different soldering paste was used.

Previous laser surface treatment can be a possible way to optimize the wettability between solders and substrates and to increase the quality of the soldered joints.

The increased use recently of area‐array technology in electronic packaging has similarly increased the importance of predicting the thermal distribution of area‐array solder interconnection. As the interconnection technology for flip chip package is getting finer and smaller, it is extremely difficult to obtain the accurate values of thermal stresses by direct experimental measurements. Different types of solder bumps used for interconnection would also influence the thermal distribution within the package. Because the solder balls are too small for direct measurement of their stresses, finite element method (FEM) was used for obtaining the stresses instead.

This paper will discuss the results of the thermal stress distribution using numerical method via ABAQUS software. The variation of the thermal stress distribution with the temperature gradient model was evaluated to study the effects of the different material thermal conductivity of solder bumps used. A detailed 2D finite element model was constructed to perform 2D plain strain elastoplastic analysis to predict areas of high stress.

It is found that thermal distribution of solder bumps starts to propagate from the top region to the bottom region of the solder balls. Other than that, thermal stress effect increases in parallel with the increasing of the temperature. The simulation results shows that leaded solder balls, SnPb have higher maximum thermal stress level compared to lead‐free SAC solder balls.

The paper describes combination of stress with thermal loading correlation on a flip chip model. The work also shows how the different thermal conductivity on solder balls influences the thermal induced stress on the flip chip package.

The purpose of this paper is to investigate the effect of Sb (0, 0.2 and 2 wt.%) on wetting performance of lead-free solder of near eutectic Sn-Cu micro-alloyed with Ni and Ge.

The melting characteristic of the lead-free alloys was studied using differential scanning calorimetry. Wettability was examined using wetting balance test for two liquid fluxes, water based and alcohol based in two temperatures 265°C and 277°C. Also, contact angle was measured using sessile drop test.

It is shown that 0.2 wt.% Sb reduces the melting temperature and pasty range. Moreover, the addition of 0.2 wt.% Sb improves wetting behavior for alcohol-based flux. It is also demonstrated that the effect of Sb on meniscus height in wetting balance test and contact angle in sessile drop test follows the trend of wetting performance.

It is found that adding 0.2 wt.% Sb improves the wettability of Ni-Ge micro-alloyed Sn-Cu solder; however, higher concentration of Sb does not benefit the alloy.