Pengawalan pertumbuhan sebatian antara logam sambungan pateri-papan litar bercetak menggunakan salutan nikel

Bahan aloi pateri dalam kumpulan Sn-Ag-Cu (SAC) merupakan bahan pematerian yang bebas plumbum digunakan secara meluas dalam industri elektronik. Antarasambungan pateri bertindak untuk menghubungkan komponen elektronik pada papan litar bercetak (PCB). PCB memainkan peranan yang penting dalam tindak balas pematerian dan mikrostruktur antarasambungan pateri-substrat seterusnya mempengaruhi kebolehharapan suatu sambungan pateri. Pes pateri Sn0.3Ag0.7Cu (SAC0307) dipaterikan pada tiga jenis PCB iaitu PCB tanpa salutan (PCB/Cu) sebagai sampel kawalan, PCB dengan salutan timah (PCB/Sn) dan PCB dengan salutan nikel (PCB/Ni). Kajian ini bertujuan untuk mengkaji kesan salutan permukaan PCB ke atas pertumbuhan sebatian antara logam (IMC) selepas uji kaji penuaan sesuhu yang berbeza selama 1000 jam. Keputusan menunjukkan purata ketebalan lapisan IMC ~ 5.7 μm serta kadar pertumbuhan lapisan IMC yang paling rendah adalah selari dengan tenaga pengaktifan tertinggi dengan salutan Ni iaitu 41 kJ/mol berbanding PCB/Cu dan PCB/Sn. Ini bermakna salutan Ni pada PCB mampu mengawal pertumbuhan IMC sehingga lebih kurang 40% berbanding salutan Sn dan tanpa salutan

FE IMPACTS ON SOLDER JOINT PROPERTIES IN MICROELECTRONIC ASSEMBLY

Master'sMASTER OF SCIENC

Thermo-mechanical reliability studies of lead-free solder interconnects

N/ASolder interconnections, also known as solder joints, are the weakest link in electronics packaging. Reliability of these miniature joints is of utmost interest - especially in safety-critical applications in the automotive, medical, aerospace, power grid and oil and drilling sectors. Studies have shown that these joints' critical thermal and mechanical loading culminate in accelerated creep, fatigue, and a combination of these joints' induced failures. The ball grid array (BGA) components being an integral part of many electronic modules functioning in mission-critical systems. This study investigates the response of solder joints in BGA to crucial reliability influencing parameters derived from creep, visco-plastic and fatigue damage of the joints. These are the plastic strain, shear strain, plastic shear strain, creep energy density, strain energy density, deformation, equivalent (Von-Mises) stress etc. The parameters' obtained magnitudes are inputted into established life prediction models – Coffin-Manson, Engelmaier, Solomon (Low cycle fatigue) and Syed (Accumulated creep energy density) – to determine several BGA assemblies' fatigue lives. The joints are subjected to thermal, mechanical and random vibration loadings. The finite element analysis (FEA) is employed in a commercial software package to model and simulate the responses of the solder joints of the representative assemblies' finite element models. As the magnitude and rate of degradation of solder joints in the BGA significantly depend on the composition of the solder alloys used to assembly the BGA on the printed circuit board, this research studies the response of various mainstream lead-free Sn-Ag-Cu (SAC) solders (SAC305, SAC387, SAC396 and SAC405) and benchmarked those with lead-based eutectic solder (Sn63Pb37). In the creep response study, the effects of thermal ageing and temperature cycling on these solder alloys' behaviours are explored. The results show superior creep properties for SAC405 and SAC396 lead-free solder alloys. The lead-free SAC405 solder joint is the most effective solder under thermal cycling condition, and the SAC396 solder joint is the most effective solder under isothermal ageing operation. The finding shows that SAC405 and SAC396 solders accumulated the minimum magnitudes of stress, strain rate, deformation rate and strain energy density than any other solder considered in this study. The hysteresis loops show that lead-free SAC405 has the lowest dissipated energy per cycle. Thus the highest fatigue life, followed by eutectic lead-based Sn63Pb37 solder. The solder with the highest dissipated energy per cycle was lead-free SAC305, SAC387 and SAC396 solder alloys. In the thermal fatigue life prediction research, four different lead-free (SAC305, SAC387, SAC396 and SAC405) and one eutectic lead-based (Sn63Pb37) solder alloys are defined against their thermal fatigue lives (TFLs) to predict their mean-time-to-failure for preventive maintenance advice. Five finite elements (FE) models of the assemblies of the BGAs with the different solder alloy compositions and properties are created with SolidWorks. The models are subjected to standard IEC 60749-25 temperature cycling in ANSYS 19.0 mechanical package environment. SAC405 joints have the highest predicted TFL of circa 13.2 years, while SAC387 joints have the least life of circa 1.4 years. The predicted lives are inversely proportional to the magnitude of the areas of stress-strain hysteresis loops of the solder joints. The prediction models are significantly consistent in predicted magnitudes across the solder joints irrespective of the damage parameters used. Several failure modes drive solder joints and damage mechanics from the research and understand an essential variation in the models' predicted values. This investigation presents a method of managing preventive maintenance time of BGA electronic components in mission-critical systems. It recommends developing a novel life prediction model based on a combination of the damage parameters for enhanced prediction. The FEA random vibration simulation test results showed that different solder alloys have a comparable performance during random vibration testing. The fatigue life result shows that SAC405 and SAC396 have the highest fatigue lives before being prone to failure. As a result of the FEA simulation outcomes with the application of Coffin-Manson's empirical formula, the author can predict the fatigue life of solder joint alloys to a higher degree of accuracy of average ~93% in an actual service environment such as the one experienced under-the-hood of an automobile and aerospace. Therefore, it is concluded that the combination of FEA simulation and empirical formulas employed in this study could be used in the computation and prediction of the fatigue life of solder joint alloys when subjected to random vibration. Based on the thermal and mechanical responses of lead-free SAC405 and SAC396 solder alloys, they are recommended as a suitable replacement of lead-based eutectic Sn63Pb37 solder alloy for improved device thermo-mechanical operations when subjected to random vibration (non-deterministic vibration). The FEA simulation studies' outcomes are validated using experimental and analytical-based reviews in published and peer-reviewed literature.N/

Thermal and thermo-mechanical performance of voided lead-free solder thermal interface materials for chip-scale packaged power device

The need to maximise thermal performance of electronic devices coupled with the continuing trends on miniaturization of electronic packages require innovative package designs for power devices and modules such as Electronic Control Unit (ECU). Chip scale packaging (CSP) technology offer promising solution for packaging power electronics. This is as a result of the technology’s relatively improved thermal performance and inherent size advantage. In CSP technology, heat removal from the device could be enhanced through the backside of the chip. Heat dissipating units such as heat spreader and/or heat sink can be attached to the backside (reverse side) of the heat generating silicon die (via TIM) in an effort to improve the surface area available for heat dissipation. TIMs are used to mechanically couple the heat generating chip to a heat sinking device and more crucially to enhance thermal transfer across the interface. Extensive review shows that solder thermal interface materials (STIMs) apparently offer better thermal performance than comparable state-of-the-art commercial polymer-based TIMs and thus a preferable choice in packaging power devices. Nonetheless, voiding remains a major reliability concern of STIMs. This is coupled with the fact that solder joints are generally prone to fatigue failures under thermal cyclic loading. Unfortunately, the occurrence of solder voids is almost unavoidable during manufacturing process and is even predominant in lead (Pb)-free solder joints. The impacts of these voids on the thermal and mechanical performance of solder joints are not clearly understood and scarcely available in literature especially with regards to STIMs (large area solder joints). Hence, this work aims to investigate STIM and the influence of voids on the thermo-mechanical and thermal performance of STIM. As previous results suggest that factors such as the location, configuration (spatial arrangement) and size of voids play vital roles on the exact effect of voids, extensive three dimensional (3D) finite element modelling is employed to elucidate the precise effect of these void features on a Pb-free STIM selected after thermo-mechanical fatigue test of standard Pb-free solder alloys. Finite element analysis (FEA) results show that solder voids configuration, size and location are all vital parameters in evaluating the mechanical and thermal impacts of voids. Depending on the location, configuration and size of voids; solder voids can either influence the initiation or propagation of damage in the STIM layer or the location of hot spot on the heat generating chip. Experimental techniques are further employed to compare and correlate levels of voiding and shear strength for representative Pb-free solders. Experimental results also suggest that void size, location and configuration may have an influence on the mechanical durability of solder joints. The findings of this research work would be of interest to electronic packaging engineers especially in the automotive sector and have been disseminated through publications in peer reviewed journals and presentations in international conferences

A Finite Element approach to understanding constitutive elasto-plastic, visco-plastic behaviour in lead free micro-electronic BGA structures

This work investigates the non-linear elasto-plastic and visco-plastic behaviour of lead free solder material and soldered joints. Specifically, Finite Element (FE) tools were used to better understand the deformations within Ball Grid Array solder joints (BGA), and numerical and analytical methods were developed to quantify the identified constituent deformations. FE material models were based on the same empirical constitutive models (elastic, plastic and creep) used in analytical calculations. The current work recognises the large number of factors influencing material behaviour which has led to a wide range of published material properties for near eutectic SnAgCu alloys. The work discovered that the deformation within the BGA was more complex than is generally assumed in the literature. It was shown that shear deformation of the solder ball could account for less than 5% of total measured displacement in BGA samples. Shear displacement and rotation of the solder balls relative to the substrate are sensitive to the substrate orthotropic properties and substrate geometry (relative to solder volume and array pattern). The FE modelling was used to derive orthotropic FR4 properties independently using published data. An elastic modulus for Sn3.8Ag0.7Cu was measured using homologous temperatures below 0.3. Suggested values of Abaqus-specific creep parameters m and f (not found in literature) for Sn3.8Ag0.7Cu have been validated with published data. Basic verification against simple analytical calculations has given a better understanding of the components of overall specimen displacement that is normally missing from empirical validation alone. A combined approach of numerical and analytical modelling of BGAs, and mechanical tests, is recommended to harmonise published work, exploit new material data and for more informed analysis of new configurationsEPSRC-funded PhD studentshi

Investigation into Solder Joint Failure in Portable Electronics Subjected to Drop Impact

Ph.DDOCTOR OF PHILOSOPH

Métodos alternativos de fixação para componentes de circuitos impressos

The growing demand for innovation and the ever-shorter product lifespan result in a great amount and diversity of waste disposal at dumps and landfills. One of the fastest growing waste types nowadays is e-waste. Consequently, Printed Circuit Boards (PCBs), which are the basis of the electronic industry, have become a serious social problem and a threat to the environment. Wasted PCBs recycling processes, therefore, have been extensively investigated. These processes can be quite complex and expensive since the recycling of PCBs involves a variety of materials and components that are not easily separated. Recently, there has been a change in the way PCBs are fixed. The traditional Sn-Pb solder has been substituted for a Lead-Free solder in an attempt to minimize the toxic composition of the first. Nevertheless, this substitution has not solved the problem of component separation for future reuse and/or recycling. The present work aims at developing and testing possible alternative fixing methods for the components in printed circuits without the use of a metallic solder in order to facilitate its subsequent recycling process. The first step was the study of the components and materials present in PCBs with emphasis on the types of solders used and the required fixing properties. Then, new fixing methods were proposed, followed by the development of prototypes and tests. These initial tests were undertaken in a laboratory at the Vilanova i La Geltrú Campus, Universitat Politècnica de Catalunya (UPC) in Spain. At this stage, the main objective was to test the initially chosen proposal for further studies. The final tests, comparing the ultimate proposal with boards that employ commercially conventional fixing systems were done at Instituto Tecnológico em Ensaios e Segurança Funcional (Itt Fuse), Universidade do Vale do Rio dos Sinos (UNISINOS) in Brazil. The final prototype version was assembled by a PCB company to ensure its reliability. Thermal cycling, vibration and salt-spray tests were conducted with continuity and inspection x-ray visual analysis both during and after the tests. The tests showed that, for the type of product proposed (reliability category product class 1), norm IPC-A-600G (IPC, 2004), the ultimate proposal for a Concept board fulfilled all functioning requirements when compared to the traditional Sn-Pb and the Lead-Free systems. Thus, results point at potential further studies on the environmental impact of this alternative type of PCB.Con la creciente demanda de innovación y la reducción gradual de la vida útil de los productos, éstos generan residuos y, en consecuencia, aumentan enormemente el volumen de basureros y rellenos sanitarios. En la actualidad, uno de los segmentos de tal volumen son los residuos tecnológicos. Esto se refleja en las placas de circuito impreso (PCIs), base de la industria electrónica, y las transforma en un grave problema social y una amenaza para el medio ambiente. El descarte de este tipo de residuos se hace difícil y su reciclaje, complejo y costoso, por causa de la diversidad de materiales y componentes existentes, y su difícil separación. Actualmente, las PCIs presentan problemas de fijación, donde se utiliza soldadura tradicional de Sn-Pb y que se pretende reemplazar por diversas aleaciones sin plomo (Leadfree). El objetivo de esta sustitución es minimizar el problema da Sn-Pb considerada tóxica; sin embargo, no altera el problema de separación de componentes para posterior reutilización o reciclaje. En el presente trabajo, se desarrollaron y caracterizaron métodos de fijación alternativos para componentes de circuitos impresos, con el fin de diseñar y evaluar un sistema de fijación exento de soldadura metálica, para facilitar el posterior reciclaje. Entonces, se estudiaron los diversos componentes y materiales existentes en PCIs, con énfasis en los tipos de soldadura utilizados, donde se investigaron las propiedades necesarias para la fijación. Luego, se presentaron las propuestas de nuevas formas de fijación de componentes, se elaboraron prototipos y se realizaron las evaluaciones correspondientes. La evaluación inicial se llevó a cabo en los laboratorios del Campus Vilanova i la Geltrú, da la UPC (Universitat Politècnica de Catalunya), España, donde se buscaba verificar el funcionamiento de la propuesta inicial elegida, para dar continuación al trabajo. La evaluación final incluye la comparación de la propuesta final con placas que utilizan sistemas comerciales convencionales de fijación, y se ejecutó en el Itt Fuse (Instituto Tecnológico em Ensaios e Segurança Funcional) da UNISINOS (Universidade do Vale do Rio dos Sinos). El prototipo definitivo, de la propuesta, lo fabricó y lo ensambló una empresa de ensamblado de PCIs, para mayor confiabilidad. Se realizaron ensayos de ciclado térmico, vibración y niebla salina, así como análisis visual y de continuidad, e inspección por rayos X, antes, durante y después de cada ensayo. Los resultados mostraron que, para el tipo de producto propuesto (categoría de confiabilidad producto clase 1), norma IPC-A-600G (IPC, 2004), la propuesta final de la placa Conceito, cumplió con los requisitos de funcionamiento de la placa, en comparación con los sistemas tradicionales de Sn-Pb y Lead-free. De esta forma, está demostrado el potencial para continuar con estudios futuros, con énfasis en el impacto ambiental de las PCIs.Com a crescente demanda por inovação e o fato dos produtos apresentarem cada vez mais uma vida útil reduzida, estes geram resíduos e aumentam enormemente o volume dos lixões e aterros sanitários. Um dos segmentos de grande volume atualmente é o resíduo tecnológico. Isto reflete nas placas de circuito impresso (PCIs) que são a base da indústria eletrônica, que as torna em um grave problema social e uma ameaça ao meio ambiente. Esse tipo de resíduo é de difícil descarte, tendo em vista que sua reciclagem é complexa e cara, devido à diversidade de materiais e componentes existentes e sua difícil separação. As PCIs apresentam recentemente um problema de fixação, que está migrando da solda tradicional Sn-Pb para diversas ligas sem chumbo (Lead-Free). Esta substituição tenta minimizar o problema da solda Sn-Pb considerada tóxica; porém não altera o problema da separação dos componentes, para posterior reutilização e/ou reciclagem. No presente trabalho buscou-se o desenvolvimento e caracterização de métodos alternativos de fixação para componentes de circuitos impressos, com o objetivo de projetar e testar um sistema de fixação sem a utilização da solda metálica, para facilitar assim a reciclagem posterior deste tipo de produto. Para isso, estudaram-se os componentes e materiais existentes em PCIs, com foco nos tipos de solda utilizados, onde investigou-se as propriedades requeridas para fixação. Após, foram propostas novas formas de fixação dos componentes, realizaram-se protótipos e testes. Os testes iniciais foram realizados no laboratório do Campus Vilanova i la Geltrú, da UPC (Universitat Politècnica de Catalunya), Espanha, onde buscou-se testar o funcionamento inicial da proposta escolhida para continuação do trabalho. Os testes finais, comparando a proposta final em relação às placas com sistemas comerciais convencionais de fixação, foram realizados no Itt Fuse (Instituto Tecnológico em Ensaios e Segurança Funcional) da UNISINOS (Universidade do Vale do Rio dos Sinos). O protótipo definitivo, da proposta foi obtido e montado por uma empresa de montagem de PCI’s para maior confiabilidade. Foram realizados testes de ciclagem térmica, vibração e névoa salina, tendo sido realizadas análises visuais, de continuidade e inspeção por raios X, antes, durante e após os testes. Os testes demonstraram que, para o tipo de produto proposto (categoria de confiabilidade produto classe 1), norma IPC-A-600G (IPC, 2004), a proposta final de placa Conceito atendeu os requisitos de funcionamento da placa, comparando com os sistemas tradicionais Sn-Pb e Lead-free. Isso demonstra potencial para seguir com mais estudos relacionados, tendo como foco o impacto ambiental dessas placas de circuito impresso