Experimental and modelling analysis on the performance of anisotropic conductive films as used in electronics packaging

The aim of this research is to understand the failure modes and mechanisms of adhesive materials used to flip-chip bond a silicon die onto a polyimide substrate. The bonding material investigated in this research is called Anisotropic Conductive Film (ACF). This is a promising interconnection material and has gained extensive interest in the electronics packaging industry. Both the experimental and finite element analysis (FEA) methods were used in order to investigate the behaviour of the ACF materials when subjected to certain manufacturing and environmental testing conditions. The manufacturing condition investigated was a subsequent solder reflow process on an ACF flip-chip bonded device. The environmental testing condition investigated was the moisture test. For the manufacturing condition, both experimental and modelling results demonstrate the impact of a subsequent reflow process on the behaviour of the ACF joint. Typical failures observed after this process were cracks at the pad/particle interface. This failure mode was more sever with a higher peak reflow temperature. This was also found using FEA where high tensile stresses were predicted in these regions. FEA modelling was also used to help identify the mechanisms leading to these failures. This is primarily due to the Coefficient of Thermal Expansion (CTE) miss-match in the materials and the elastic/plastic deformation behaviour of the conductive particle. Important design variables that can minimise these failures are the Young’s Modulus and CTE of the adhesive and the height of the hump on the die. For the environmental testing condition, an autoclave test at 121°C, 100%RH and pressure of 2atm was used. More than 85% of the ACF joints failed during the first 24 hours of testing. The failure mode observed was cracking along the interface between the adhesive and substrate and pad. A macro-micro modelling approach was used to help identify the mechanisms leading to these failures. It was found that most of the damage is caused by moisture diffusion and associated swelling. Important design variables that will help minimise this mode of failure are: Coefficient of Moisture Expansion (CME) and Young’s Modulus of the adhesive and the height of the bump on the die

The multidimensional dependence of halo bias in the eye of a machine: a tale of halo structure, assembly and environment

We develop a novel approach in exploring the joint dependence of halo bias on multiple halo properties using Gaussian process regression. Using a $\Lambda$CDM $N$-body simulation, we carry out a comprehensive study of the joint bias dependence on halo structure, formation history and environment. We show that the bias is a multivariate function of halo properties that falls into three regimes. For massive haloes, halo mass explains the majority of bias variation. For early-forming haloes, bias depends sensitively on the recent mass accretion history. For low-mass and late-forming haloes, bias depends more on the structure of a halo such as its shape and spin. Our framework enables us to convincingly prove that $V_\mathrm{max}/V_\mathrm{vir}$ is a lossy proxy of formation time for bias modelling, whereas the mass, spin, shape and formation time variables are non-redundant with respect to each other. Combining mass and formation time largely accounts for the mass accretion history dependence of bias. Combining all the internal halo properties fully accounts for the density profile dependence inside haloes, and predicts the clustering variation of individual haloes to a $20\%$ level at $\sim 10\mathrm{Mpc}h^{-1}$. When an environmental density is measured outside $1\mathrm{Mpc}h^{-1}$ from the halo centre, it outperforms and largely accounts for the bias dependence on the internal halo structure, explaining the bias variation above a level of $30\%$.Comment: MNRAS accepte

Modelling the impact of conformal coating penetration on QFN reliability

The impact of conformal coating penetration on the solder joints' thermal fatigue reliability in QFNs was studied using computational modeling techniques. 3D finite element models were developed with consideration of realistic solder joint shape and the actual coating profile. Thermal mechanical simulations were carried out for three cycles under accelerated thermal test conditions of -25 to 100°C, 10 minutes ramp and 10 minutes dwell. The inelastic strain energy density accumulated over one temperature cycle was used as an indicator for solder damage in the QFNs under the applied thermal cycling load. The impact of coating penetration level on the solder damage in QFNs was investigated for two types of coatings with different properties. The results show that coating penetrated underneath the package has significant impact on the solder joint damage in QFNs and the level of this impact depends on the coating properties and penetration level. When coating penetration level decreases, damage in the solder joint does not always decrease. In order to prevent coating penetration underneath the package, an edgebond adhesive was applied on the edge of the QFN assemblies prior to the application of the conformal coating. The modelling results show that using edgebond adhesive can reduce the solder joint damage in the investigated QFNs and thus improve their thermal fatigue reliability. When edgebond adhesive is used, the impact of conformal coating on the reliability of solder joints in QFNs is significantly reduced

Statistical analysis of the impact of refinishing process on leaded components

Refinishing process such as Hot Solder Dip (HSD) process can be used to prevent tin whisker growth in microelectronics components by replacing the lead-free finishes with conventional tin–lead coatings. In some applications, it is also used to ensure reliable solder joints by replacing contaminated finishes and lead-free alloys with tin–lead to result in a homogeneous solder joint with tin–lead paste. In this paper, the impact of a HSD refinishing process on leaded components was statistically studied by comparing the electrical test data of refinished samples with those not-refinished. The likely damage from the component refinishing was thought to be the degradation of package integrity through thermo-mechanical stressing. This might be detectable as a microscopic leakage current if moisture could be encouraged into any open areas. Ten types of leaded components were selected and samples for each type of the component were allocated into 2 lots, one for refinishing and one used as a control. 150 cycles −65/150 °C thermal cycling followed by 500 h 85%RH/85 °C humidity test was applied to all the samples (both refinished and not-refinished) to amplify any incipient failure points and accelerate moisture ingress into the package. Electrical test was then carried out to measure any small changes in current under zero and reverse bias conditions. In the end, a data reduction process in conjunction with a statistical hypothesis test was used to analyze the electrical test data. The results showed that there was no significant difference between the measured currents of refinished and not-refinished post-aged samples. Therefore it was concluded that the refinishing process did not have a significant impact on the tested components. This conclusion was further strengthened by other experimental test results such as CSAM images

Prognostic and health management for engineering systems: a review of the data-driven approach and algorithms

Prognostics and health management (PHM) has become an important component of many engineering systems and products, where algorithms are used to detect anomalies, diagnose faults and predict remaining useful lifetime (RUL). PHM can provide many advantages to users and maintainers. Although primary goals are to ensure the safety, provide state of the health and estimate RUL of the components and systems, there are also financial benefits such as operational and maintenance cost reductions and extended lifetime. This study aims at reviewing the current status of algorithms and methods used to underpin different existing PHM approaches. The focus is on providing a structured and comprehensive classification of the existing state-of-the-art PHM approaches, data-driven approaches and algorithms

Computer simulation of the reliability of wire bonds and ribbon bonds in power electronics modules

Aluminium wires are widely used in power electronics modules to connect power semiconductor devices and other parts of the module electrically. Recently, other interconnect techniques have been proposed such as ribbon bond to improve the reliability, performance and reduce costs of power modules. The reliability of ribbon bond technique for an IGBT power module under power cycling is compared with that of conventional wire bond in this study using electro-thermal nonlinear Finite Element Analysis. The results showed that a single ribbon of 2000μm x 200μm will replace three wire bonds of 400μm in diameter to achieve a similar module temperature distribution under same power load. Using the equivalent plastic strain increment per cycle, it is seen that the ribbon bond is more reliable than the wire bonds. The impact of neglecting joule heat in the wire/ribbon bonds during power cycling simulation has also been investigated

Key Findings: 2013 ATRS Global Airport Performance Benchmarking Project

The ATRS Global Airport Benchmarking Project measures and compares the performance of several important aspects of airport operations: Productivity and efficiency, unit costs and cost competitiveness, financial results and airport charges. The report also examines the relationships between various performance measures and airport characteristics as well as management strategies in order to provide a better understanding of observed differences in airport performance. This report includes 195 airports and 26 airport groups of various sizes and ownership forms in Asia Pacific, Europe and North America. This presentation highlights key findings on efficiency and cost

(*Review Article) The Impact of Digital Transformation on Enterprise Accounting

Digital transformation represents a significant trend within the accounting domain, exerting a profound influence on conventional accounting processes, financial reporting, and decision-support capabilities. Primarily, it has revolutionized the accounting process by integrating sophisticated digital technologies and tools, enabling real-time data collection and processing, and thereby enhancing the efficiency and accuracy of accounting tasks. Secondly, digital transformation has played a pivotal role in expediting and refining the production and dissemination of financial reports, rendering financial statements faster and more precise, while also bolstering the disclosure and transparency of financial information. Furthermore, it has elevated the capacity of accounting decision support by furnishing management with profound business insights and decision-making aid through data analysis and visualization tools.Notwithstanding its merits, digital transformation faces certain implementation challenges in the accounting realm. Technical barriers, data integration, organizational structure, and cultural factors necessitate careful consideration and resolution. Additionally, digital transformation introduces data quality and security risks, compelling enterprises to ensure data accuracy, security, and compliance with pertinent laws and regulations.In order to adapt to the transformative influence of digitalization, accounting personnel must continuously acquire and update skills, cultivating proficiency in data analysis, data science, and digital tools. Concurrently, enterprises must prioritize the establishment of a conducive organizational culture and change management practices to ensure the successful implementation and effective operation of digital transformation. While digital transformation opens up numerous opportunities in the accounting sector, it must surmount challenges to achieve sustainable development and advancement within the field