164 research outputs found

    Effect of Intermetallic Growth on Durability of High Temperature Solders (SnAg, SAC305, SAC+Mn, SnAg+Cu Nano) in Thermal and Vibration Environments

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    The RoHS ban of lead from electronics has pushed the industry to find lead free alternatives. In high temperature environments, high lead solders have typically been used. A suitable lead free replacement alloy is required. In this study quad flat packages (QFP) and 2512 chip resistors soldered with commercially available Sn3.5Ag and SAC305, and experimental SAC+Mn and SnAg+Cu Nano alloys on ENIG finished copper were subjected to three tests. Isothermal aging at 185°C for up to 1000 hours and at 200°C for up to 500 hours were performed to measure the interfacial intermetallic thickness, assess intermetallic compounds, and view the microstructure. A durability assessment was performed featuring thermal cycling ranges of -40 to 185°C and -40 to 200°C intermixed with 50G vibration cycling to determine the most durable solder alloy. Failure analysis was performed to understand the durability results. Finally, shear testing was performed to determine a correlation between shear strength and durability. The results show SAC305 is the most reliable solder under these conditions

    Characterization of Transient Heating in Power Electronic Devices and its Implications for Die Attached Reliability

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    Military and commercial interest in the use of power electronics for applications requiring extreme operating conditions and/or placement in extreme environments is driving research to identify and develop packaging technologies that can withstand these conditions. Specifically, there is an interest in the development of packaging technology than can function reliably under transient high power loading conditions. This thesis addresses the unique packaging considerations required for this type of application, with a focus on the implications on the durability of the die attach layer. Simulations of the thermal conditions experienced at the die attach layer for different power pulse magnitudes and durations are presented. A test apparatus and experimental test plan for studying the reliability of die attach materials under high power transient loading is discussed. Studies conducted to validate the test apparatus and characterize die attach reliability are described along with recommendations for further investigation of the reliability issues associated with high power, transient loading conditions

    Lead-Free Solder Pull-Off Stress Comparison of a Novel Bump Pull Method with Conventional Hot/Cold Bump Pull Methods

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    A novel method for directly testing the adhesion strength of three lead-free solders was developed and compared with conventional methods. The Isotraction Bump Pull method utilizes a combination of favorable qualities of the Cold and Hot Bump Pull tests. Solder bumps were generated onto copper printed circuit board substrates using an in-house-fabricated solder bump-on-demand generator. The method uses polymer epoxy to encapsulate solder bumps under uniform tractions, and tested under tension for pull-off stresses. Maximum pull-off stresses for the novel method are: 18MPa (Sn-3.5Ag), 16MPa (SAC 305) and 22MPa (Sn-0.7Cu) and fall at the low end in the literature comparisons. It is suggested that since the copper substrates used in the current work were untreated, that the lower pull-off stress values resulted. Energy Dispersive X-Ray Spectrometry of the newly created faces after fracture shows that brittle fracture of the Intermetallic Compound layer was the mode of failure

    Time integration damage model for Sn3.5Ag solder interconnect in power electronic module

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    In this study, existing damage evolution models in the literature for solder layer in microelectronics have been reviewed. A two dimensional approximate semi-analytic time integration damage indicator model for Sn3.5Ag material solder interconnect in power electronic module has been proposed. The proposed time dependent damage model is dependent on the inelastic strain, the accumulated damage at previous time step and the temperature. The strains were approximated semi-analytically. A numerical modelling methodology combined with the data from public domain for crack initiation and crack propagation of Sn3.5Ag solder layer has been adopted to extract the parameter values of the proposed damage model. The proposed model has advantages over fatigue lifetime models as it instantaneously predicts the damage over time for any loading history. The damage model was compared with Ansys FEA tool based damage prediction using Coffin Manson and Paris law fatigue models. The predicted damage value by the model is slightly higher than those models. Furthermore, this damage model does not need a time consuming numerical simulation evaluating the damage model variables, which is an advantag

    COMPARISON OF INTERCONNECT FAILURES OF ELECTRONIC COMPONENTS MOUNTED ON FR-4 BOARDS WITH SN37PB AND SN3.0AG0.5CU SOLDERS UNDER RAPID LOADING CONDITIONS.

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    Electronic circuit boards can experience rapid loading through shock or vibration events during their lives; these events can happen in transportation, manufacture, or in field conditions. Due to the lead-free migration, it is necessary to evaluate how this rapid loading affects the durability of a leading lead free solder alternative (Sn3.0Ag0.5Cu) assemblies as compared with traditional eutectic lead based solder Sn37Pb assemblies. A literature review showed that there is little agreement on the fatigue behavior of Sn37Pb solder assemblies and Sn3.0Ag0.5Cu solder assemblies subjected to rapid loading. To evaluate the failure behavior of Sn37Pb and Sn3.0Ag0.5Cu solder assemblies under rapid loading conditions, leadless chip resistors (LCR), ball grid arrays (BGA), small outline integrated circuits (SOIC), and small outline transistors (SOT) were subjected to four point bend tests via a servo-hydraulic testing machine at printed wiring board (PWB) strain rates greater than 0.1/s. The PWB strain was the metric used to evaluate the failures. The PBGAs and LCRs were examined with both Sn37Pb and Sn3.0Ag0.5Cu solders. There was no significant difference found in the resulting test data for the behavior of the two solder assembly types in the high cycle fatigue regime. PBGA assemblies with both solders were also evaluated at a higher strain rate, approximately 1/s, using drop testing. There was no discernable difference found between the assemblies as well as no difference in the failure rate of the PBGAs at this higher strain rate. The PWB strain was converted to an equivalent solder stress index using finite element analysis. This equivalent stress index value was used to compare the results from the LCR and BGA testing for Sn37Pb and Sn3.0Ag0.5Cu. Independently generated BGA data that differed with respect to many testing variables was adjusted and incorporated to this comparison. The resulting plot did not show any significant differences between the behaviors of the two solder assemblies under rapid loading outside of the ultra low cycle fatigue regime, where the assemblies with Sn37Pb solder outperformed the assemblies with SnAgCu solder

    Modeling the SAC microstructure evolution under thermal, thermomechanical and electrical constraints

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    Développement d’un procédé d’électrodéposition séquentielle pour fabrication des microbilles à haute densité

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    Aujourd’hui l’industrie des semiconducteurs aborde une époque requérant le couplage de l’innovation au niveau de l'assemblage avec la mise à l’échelle des dispositifs. Cette dernière n’est plus l’élément clé qui propulse l’évolution technologique à cause de l’énorme investissement requis vis-à-vis sa rentabilité qui devient de plus en plus limitée. Avec la réorientation de l’intérêt de la majorité des acteurs vers l’innovation au niveau des assemblages, cette thèse s’inscrit dans un contexte d’amélioration de la fiabilité des assemblages de larges puces renversées pour le calul haute performance à travers le développement des microbilles de brasures à faible coût et de métallurgie optimisée. Des microbilles de brasure à faible coût et hétérogènes sont proposées comme une approche simple qui présente des bénéfices métallurgiques et économiques. D’une part, l’électrodéposition séquentielle des couches de Sn et Ag pures au lieu d’alliage est réalisée à un faible coût d’acquisition et avec une simplicité de maintenance. D’une autre part, la même installation d’électrodéposition de Sn et Ag purs peut servir à la fabrication d’une multitude de brasures avec différentes teneurs en Ag. Malgré le besoin d’une standardisation des procédés de fabrication des microbilles, les motivations citées précédemment peuvent constituer un facteur d’attraction pour l’industrie afin de l’adopter comme alternative à l’électrodéposition conventionnelle des alliages. En plus de son faible coût, l’approche de fabrication des microbilles par électrodéposition séquentielle amène une flexibilité métallurgique avec l’utilisation d’une barrière qui limite la diffusion d’Ag. Cette dernière résulte en une microbille de brasure unique, qui peut à la fois i) avoir une structure hétérogène avec une faible teneur en Ag dont la ductilité élevée est maintenue à proximité des couches fragiles de la métallisation de la puce lors des étapes de l’assemblage; ii) avoir une forme en pilier dont des bénéfices sont similaires à ceux du pilier en Cu en évitant les effets néfastes de sa rigidité sur les couches du BEOL. Les différentes étapes de fabrication des microbilles de brasure ont été développées en se limitant à des procédés qui peuvent être intégrés facilement dans un environnement de production industrielle. La manipulation de la métallurgie des joints de brasure a été réalisée avec succès en démontrant une structure hétérogène unique de brasure dans un assemblage de puces renversées

    Intermetallic growth of SAC237 solder paste reinforced with MWCNT

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    The formation of intermetallic compound (IMC) layer at the interfaces of pad finishes has been studied. The growth of IMC layer as a reflow process and its properties were also discussed. In this study, solder alloy SAC237 (Sn: 99 wt.%, Ag: 0.3 wt.%, Cu: 0.7 wt.%), reinforced with 0.01 wt.% Multi-Walled Carbon Nanotubes (MWCNTs), was mixed to form a composite solder paste and soldered on Electroless Nickel Immersion Gold (ENIG) and Immersion Tin (ImSn) pad finishes. Reflow process was conducted in oven with specific reflow profile. The growth and properties of IMC layer were analysed using optical microscope with image analyser. Results showed that the thickness of IMC layer for ENIG and ImSn were 1.49 and 2.51 µm, respectively. Floating IMC and voids within the solder bulk and IMC layer were also identified in the samples. In addition, the measured wetting angle for ENIG and ImSn were 16.21° and 34.32°, respectively
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