The fatigue-induced solder joint failure of surface mounted electronic devices has become one of the most critical reliability issues in electronic packaging industry. Prediction of the shape of solder joints has drawn special attention to the related development and engineering applications. Numerous solder joint models, based on energy minimization principle and analytical methods, have been proposed and developed. The methods are extensively utilized to the shape design of solder joint. However, it is important to find a suitable method to real applications. Herein, a series of experiments with different geometric parameters of SAC405 solder joints were carried out and the results were compared with the prediction by Surface Evolver Program. The changes of geometric shape with respect to different parameters of solder joint were also discussed. The influence of the geometric parameters, such as volume of solder joint, package weight, solder surface tension, and gravity force to the shape of solder joint were investigated. Two experiments with SAC405 solder balls were carried out. One is to observe the different reflowed geometry shape of solder balls with various volumes, and another is to observe the different reflowed geometry shape of solder balls with various loadings on them. The results show that the models made by Surface Evolver program are very similar to the real shapes observed by experiments, and the differences are between -3% ~ 6.5%. Thus, the results show that the predicted shapes are satisfactorily suitable. Finally, the predicted models by Surface Evolver program were also put into the ANSYS program, and preceded the fatigue life prediction due to thermal cycling tests. The comparison of the effect on fatigue life with respect to different geometry shapes is illustrated. The results show the shape of solder ball due to high loadings is better than that in thermal cycling tests.

This study aims to investigate the thermal fatigue life of the solder ball.Generally, the fatigue of the solder ball results from thermal cyclic loading in different thermal expansion coefficiency of the material in the IC package. To analyze the equivalent stress and the equivalent strain distributions of the solder ball under loading, an analysis software ANSYS was adopted in this study. To stimulate viscoplastic (creep and plastic) property of the solder ball, the Anand model was adopted. From the modified Coffin-Manson equation and the viscoplastic strain range, the fatigue life of the solder ball was obtained finally. The causes of the fatigue life of the solder ball in this study were attributed to many factors, such as the solider ball¡¦s geometry, substrate thickness, different material properties, change of pad diameter, etc. Finally, the researcher found the increasing solder joint reliability methods and supplied the improving solder joint data for the design engineer.

Abstract In the interest of improving reliability, electrical monitoring methods were utilized to observe the degradation of electronics interconnections while simultaneously characterizing accelerated testing-induced changes in test structures by means of optical examination, X-ray, scanning acoustic microscopy and scanning electron microscopy. To improve the accuracy of lifetime prediction for the PCSB interconnections investigated in this work, a modified Engelmaier’s solder joint lifetime prediction model was recalibrated. The results show that with most of the presented lead-free (SAC387, SAC405, SAC-In) solder and structure combinations with a large global thermal mismatch (ΔCTE > 10 ppm/°C), lifetime was adequate in the presented TCT ranges of 0‒100 °C and −40‒125 °C, while the amount of non-preferred crack types, i.e. ceramic cracks, was minimized. Degradation of interconnections was characterized using RF measurements both during TCT and intermittently during TCT breaks. A grounded coplanar waveguide was arranged either in a straight back-to-back configuration or together with a filter module with a passband at 22‒24 GHz—both with two transitions—and characterized during cycling breaks up to 25 GHz and 30 GHz, respectively. Besides off-cycle measurements, in-cycle measurements were done on an antenna structure with an in-band at 10‒11 GHz, up to 14 GHz. The results show that the signal response was initially affected at some frequencies as short-duration (< 1 s) glitches in the monitored signal when measured during cycling in 0‒100 °C TCT. Later on the degradation could be observed in the whole frequency band as TCT was continued. Development of the semi-empirical lifetime prediction model for PCSB interconnections showed the temperature range dependency of the correction term to be a second order polynomial instead of a logarithmic one. For components with PCSB BGA, promising prediction results were achieved which differed from the realized lifetime by less than 0.5% at best. / Tiivistelmä Elektroniikkaliitosten rikkoontumisen seurantaan tarkoitettuja sähköisiä monitorointimenetelmiä kehitettiin samanaikaisesti karakterisoimalla testauksella liitoksiin aikaansaatuja muutoksia optisesti, akustisella mikroskoopilla sekä röntgen- ja pyyhkäisyelektronimikroskoopeilla. Liitosten eliniän ennustamiseen soveltuva muokattu Engelmaierin malli kalibroitiin PCSB-liitosten elinikäennusteen tarkkuuden parantamiseksi. Tulosten perusteella useimmille tässä työssä käytetyille lyijyttömille (SAC387, SAC405, SAC-In) juotteille ja suuren termisen epäsovituksen (ΔCTE > 10 ppm/°C) rakenneyhdistelmille eliniät lämpösyklaustesteissä 0‒100 °C ja −40‒125 °C alueilla olivat riittävät ja haitallisimpien murtumien, eli keraamimurtumien, määrä saatiin minimoiduksi. RF-mittauksia käytettiin liitosten vikaantumisen seurantaan sekä lämpösyklauksen aikana että syklausten välillä. Maadoitettua koplanaarista aaltojohtoa käytettiin joko suoraan perättäiskytkennässä tai suodatinmoduulin kanssa, jonka päästökaista oli 22–24 GHz. Rakenteet karakterisoitiin syklausten välillä 25 GHz ja 30 GHz asti tässä järjestyksessä. Näiden mittausten lisäksi 10–11 GHz kaistalla toimivaa antennirakennetta karakterisoitiin syklauksen aikana 14 GHz asti. Tulokset osoittavat, että signaalivasteen muutos ilmenee aluksi joillakin taajuuksilla lyhyinä, alle 1 s mittaisina häiriöpiikkeinä, 0‒100 °C syklauksen aikana. Syklauksen edetessä vasteen huononeminen havaitaan myöhemmin koko mittausalueella. Puolikokeellista elinikäennustemallia tarkasteltaessa havaittiin, että PCSB-liitosten lämpötila-alueesta riippuvia korjauskertoimia kuvasivat logaritmisen riippuvuuden sijaan parhaiten toisen asteen polynomifunktiot. PCSB BGA ‒rakenteille saadun ennusteen ja toteutuneen eliniän välinen ero oli pienimmillään alle 0.5 %.

Abstract Electronic devices are subjected to various usage environments, wherein stresses are induced to components and their interconnections. The level of stress affects the interval of failure occurrences. When the stress level and aging characteristics of sub-material parts are known, the failure occurrence can be predicted. However, the predictions are based on uncertainties and a practical method to help to assess the component interconnection reliability is needed. In this thesis a novel method to utilize the accelerated stress test data for the hazard rate estimates is introduced. The hazard rate expectations of the interconnection elements are presented as interconnection failures in time (i-FIT) figures that can be used as a part of the conventional product reliability estimates. The method utilizes second level reliability test results for a packaging type specific failure occurrence estimates. Furthermore, the results can be used as such in the component packaging reliability estimates. Moreover, a novel method to estimate the interconnection failures in terms of costs is presented. In this novel method the interconnection elements are dealt as cost elements. It is also shown that the costs of the interconnection failures could be very high, if the stress-strength characteristics of the interconnection system are wrongly chosen. The lead-free manufacturing has emphasized the thermal compatibility of the materials of the component, the solder and the Printed Wiring Board. Improper materials for Area Array components will result as excessive component warping during the reflow, as is shown in this thesis. A novel method for estimating the amount of component warping during the lead-free reflow is introduced. In this thesis, a method to predict the second level interconnection hazard rate is introduced. The method utilizes the second level reliability test data in the life time predictions of the component solder joints. The resulted hazard rates can be used as a part of product field performance estimates. Also, the effect of the process variation and the material properties on the lead-free solder joint reliability is introduced. / Tiivistelmä Elektronisen laitteen materiaalien yhteensopivuus ja käyttöympäristö määrittävät sen kokemat rasitukset. Laitteen komponentteihin tai niiden liitoksiin kohdistuvat rasitukset aiheuttavat lopulta laitteen vikaantumisen. Vikaantumisten taajuuteen vaikuttavat paitsi rasituksen taso ja tyyppi, myös laitteen materiaalien ominaisuudet. Todellinen vikaantumistaajuus perustuu kuitenkin muihinkin parametreihin, mistä johtuen vikaantumisennusteet voivat olla epätarkkoja. Tästä syystä käytännölliselle liitosten vikaantumisen arviointimenetelmälle on tarve. Tässä väitöskirjassa esitellään uusi komponenttien juotosliitosten arviointimenetelmä, jonka avulla voidaan muuntaa kiihdytetyn rasitustestauksen tulos vikaantumistaajuusarvioksi laitteen todellisessa käyttöympäristössä. Menelmässä hyödynnetään levytason rasitustestauksen tuloksia komponenttien kotelotyyppikohtaisiin vikaantumisennusteisiin. Menetelmää voidaan käyttää sellaisenaan arvioitaessa komponenttikoteloiden luotettavuutta todellisissa rasitus- tai tuoteympäristöissä. Väitöskirjassa esitellään myös uusi menetelmä vikaantuneiden liitosten kustannusten määrittämiseen, mikä auttaa myös uuden liitosteknologian kokonaiskustannusten arvioimisessa. Lisäksi väitöskirjatyössä osoitetaan, että liitosvikojen aiheuttamat kustannukset voivat olla erittäin korkeita, mikäli juotosliitoksiin kohdistuvat rasitukset ylittävät liitosten suunnitellun kestävyyden. Elektroniikan lyijyttömän valmistamisen myötä komponenttien, juotteen ja piirilevyn materiaalien yhteensopivuus korostuu. Väitöskirjatyössä osoitetaan, että yhteensopimattomien materiaalien käyttäminen komponenteissa voi johtaa komponentin liialliseen taipumaan kuumakonvektiojuottamisen aikana. Lisäksi esitellään menetelmä komponentin taipuman arvioimiseksi lämpötilan funktiona. Tässä väitöskirjassa esitellään uusi menetelmä, jolla voidaan arvioida komponenttien juotosliitosten vikaantumista ja vikaantumisen vaikutusta tuotteiden kokonaiskustannuksiin. Menetelmä perustuu kiihdytetyn rasitustestauksen tuloksiin, joita voidaan käyttää juotosliitosten vikaantumisten arvioimiseen tuotteen todellisissa käyttöolosuhteissa. Lisäksi väitöskirjatyössä on arvioitu juotosmateriaalin ja juotosaluemitoituksen vaikutusta juotosliitosten luotettavuuteen.

Standard crystalline silicon photovoltaic (PV) modules are designed to continuously convert solar energy into electricity for 25 years. However, the continual generation of electricity by the PV modules throughout their designed service life has been a concern. The key challenge has been the untimely fatigue failure of solder interconnections of solar cells in the modules due to accelerated thermo-mechanical degradation. The goal of this research is to provide adequate information for proper design of solar cell solder joint against fatigue failure through the study of cyclic thermo-mechanical stresses and strains in the joint. This is carried-out through finite element analysis (FEA) using ANSYS software to develop the solar cell assembly geometric models followed by simulations. Appropriate material constitutive model for solder alloy is employed to predict number of cycles to failure of solder joint, hence predicting its fatigue life. The results obtained from this study indicate that intermetallic compound thickness (TIMC); solder joint thickness (TSJ) and width (WSJ) have significant impacts on fatigue life of solder joint. The impacts of TIMC and TSJ are such that as the thicknesses increases solder joint fatigue life decreases. Conversely, as solder joint width (WSJ) increases, fatigue life increases. Furthermore, optimization of the joint is carried-out towards thermo-mechanical reliability improvement. Analysis of results shows the design with optimal parameter setting to be: TIMC -2.5μm, TSJ -20μm and WSJ -1000μm. In addition, the optimized model has 16,264 cycles to failure which is 18.82% more than the expected 13,688 cycles to failure of a PV module designed to last for 25 years.

This work deals research of the reliability of leed-free solder joints. It summarizes the basic knowledge of lead-free solder alloys, soldering and testing process, the soldered joints. The work is done selecting the most important factors entering into the soldering process. The method of the DOE sought the optimal combination of factors, which would correspond to the highest quality solder joints.

Sn-based solder alloys are extensively used in electronic devices to form interconnects between different components to provide mechanical support and electrical path. The formation of a reliable solder interconnects fundamentally relies on the metallurgic reaction between the molten solder and solid pad metallization in reflowing. The resultant IMC layer at the solder/pad metallization interface can grow continuously during service or aging at an elevated temperature, uplifting the proportion of IMCs in the entire solder joint. However, the essential mechanical properties of interfacial IMC (i.e. Cu6Sn5, Cu3Sn) layers, such as Young s modulus and hardness, are drastically different in comparison with Sn-based solder and substrate. Therefore, the increasing fraction of interfacial IMCs in the solder joint can lead to significant deformation incompatibility under exterior load, which becomes an important reliability concern in the uses of solder joints for electronic interconnects. In the past decades, extensive research works were implemented and reported regarding the growth of interfacial IMC layers and its effect on the mechanical integrity of solder joints. But, the following fundamental issues in terms of mechanical and microstructural evolution in the uses of solder joints still remain unclear, demanding further research to elaborate: (1) The protrusion of IMCs: Though the growth of interfacial IMC layers along the diffusion direction in solder joints were studied extensively, the growth of IMCs perpendicular to the diffusion direction were reported in only a few papers without any further detailed investigation. This phenomena can crucially govern the long-term reliability of solder interconnects, in particular, in the applications that require a robust microstructural integrity from a solder joint. (2) Fracture behaviour of interfacial IMC layers: The fracture behaviour of interfacial IMC layers is a vital factor in determining the failure mechanism of solder joints, but this was scarcely investigated due to numerous challenges to enable a potential in-situ micro-scale tests. It is therefore highly imperative to carry out such study in order to reveal the fracture behaviour of interfacial IMC layers which can eventually provide better understanding of the influence of interfacial IMC layers on the mechanical integrity of solder joints. (3) Volume shrinkage: The volume shrinkage (or solder joint collapse) induced by the growth of interfacial IMC layers was frequently ascribed as one of the main causes of the degradation of mechanical reliability during aging due to the potentially resulted voids and residual stress at the solder/substrate interface. However, very few experimental works on the characterisation of such type of volume shrinkage can be found in literatures, primarily due to the difficulties of observing the small dimensional changes that can be encountered in the course of IMCs growth. (4) Residual stress: The residual stress within solder joints is another key factor that contributes to the failure of solder joints under external loads. However, the stress evolution in solder joints as aging progresses and the potential correlation between the residual stress and the growth of interfacial IMC layers is yet to be fully understood, as stress/strain status can fundamentally alter the course of total failure of a solder joint. (5) Crack initiation and propagation in solder joints: Modelling on the mechanical behaviour of solder joints is often undertaken primarily on the stress distribution within solder joints, for instance, under a given external loading. But there is lack of utilising numerical analysis to simulate the crack initiation and propagation within solder joints, thus the effect of interfacial IMC layers on the fracture behaviour of the solder joints can be elaborated in further details. In this thesis, the growth of interfacial IMCs in parallel and perpendicular to the interdiffusion direction in the Sn99Cu1/Cu solder joints after aging was investigated and followed by observation with SEM, with an intention of correlating the growth of IMCs along these two directions with aging durations based on the measured thickness of IMC layer and height of perpendicular IMCs. The mechanism of the protrusion of IMCs and the mutual effect between the growth of IMCs along these two directions was also discussed. The tensile fracture behaviour of interfacial Cu6Sn5 and Cu3Sn layers at the Sn99Cu1/Cu interface was characterised by implementing cantilever bending tests on micro Cu6Sn5 and Cu3Sn pillars prepared by focused ion beam (FIB). The fracture stress and strain were evaluated by finite element modelling using Abaqus. The tensile fracture mechanism of both Cu6Sn5 and Cu3Sn can then be proposed and discussed based on the observed fracture surface of the micro IMC pillars. The volume shrinkage of solder joints induced by the growth of interfacial IMC layers in parallel to the interdiffusion direction in solder joint was also studied by specifically designed specimens, to enable the collapse of the solder joint to be estimated by surface profiling with Zygo Newview after increased durations of aging. Finite element modelling was also carried out to understand the residual stress potentially induced due to the volume shrinkage. The volume shrinkage in solder joints is likely to be subjected to the constraint from both the attached solder and substrate, which can lead to the build-up of residual stress at the solder/Cu interface. Depth-controlled nanoindentation tests were therefore carried out in the Sn99Cu1 solder, interfacial Cu6Sn5 layer, Cu3Sn layer and Cu with Vickers indenter after aging. The residual stress was then evaluated in the correlation with aging durations, different interlayers and the locations in the solder joint. Finally, finite element models incorporated with factors that may contribute to the failure of solder joints, including microstructure of solder joints, residual stress and the fracture of interfacial IMC, were built using Abaqus to reveal the effect of these factors on the fracture behaviour of solder joints under applied load. The effect of growth of IMC layer during aging on the fracture behaviour was then discussed to provide a better understanding of the degradation of mechanical integrity of solder joints due to aging. The results from this thesis can facilitate the understanding of the influence of interfacial IMC layers on the mechanical behaviour of solder joints due to long-term exposure to high temperatures.

L'objectif principal de cette thèse est l'étude de la fiabilité des cartes électroniques. Ces cartes sont utilisées dans plusieurs domaines, tels que l’industrie automobile, l’aéronautique, les télécommunications, le secteur médical, ..., etc. Elles assurent toutes les fonctions nécessaires au bon fonctionnement d’un système électronique. Les cartes électroniques subissent diverses sollicitations (mécaniques, électriques et thermiques) durant la manipulation et la mise en service. Ces sollicitations sont dues aux chutes, aux vibrations et aux variations de température. Elles peuvent causer la rupture des joints de brasage des composants électroniques. Cette rupture entraine la défaillance du système électronique complet. Les objectifs de ce travail sont: - Développer un modèle numérique pour la simulation du drop-test d’une carte électronique ; - Prédire la durée de vie en fatigue des joints de brasure en tenant compte des incertitudes des diverses variables ; - Développer une méthode d’optimisation fiabiliste pour déterminer la géométrie optimale qui assure un niveau cible de fiabilité d’une carte électronique ; - Application d’une nouvelle méthode hybride d’optimisation pour déterminer la géométrie optimale d’une carte électronique et d’un joint de brasure. Cette thèse a donné lieu à deux publications dans une revue indexée, et deux projets de publication et quatre communications dans des manifestations internationales. / The main objective of this thesis is to study the electronics’ cards reliability. These cards are used in many fields, such as automotive, aerospace, telecommunications, medical. They provide all necessary electronic functions for well functioning of an electronic system. Electronic cards are undergoing various extreme stresses (mechanical, electrical, and thermal) when handling and commissioning. These stresses are due to drops, vibration and temperature variations. They may cause solder joints failures’ of electronic components. This may causes the failure of the entire electronic system. The objectives of this work are: To develop a numerical model to simulate the drop test of an electronic card; To predict the fatigue life of solder joints in uncertain environment of the variables; To develop a reliability-optimization method to determine the optimal geometry providing a targeted reliability level of an electronic card; To apply a new hybrid optimization method in order to determine the optimal geometry both of an electronic card and a solder joint.

Characterizing hidden solder joint shapes is essential for electronics reliability. Active thermography is a methodology to identify hidden defects inside an object by means of surface abnormal thermal response after applying a heat flux. This research focused on understanding, modeling, and predicting hidden solder joint shapes. An experimental model based on active thermography was used to understand how the solder joint shapes affect the surface thermal response (grand average cooling rate or GACR) of electronic multi cover PCB assemblies. Next, a numerical model simulated the active thermography technique, investigated technique limitations and extended technique applicability to characterize hidden solder joint shapes. Finally, a prediction model determined the optimum active thermography conditions to achieve an adequate hidden solder joint shape characterization. The experimental model determined that solder joint shape plays a higher role for visible than for hidden solder joints in the GACR; however, a MANOVA analysis proved that hidden solder joint shapes are significantly different when describe by the GACR. An artificial neural networks classifier proved that the distances between experimental solder joint shapes GACR must be larger than 0.12 to achieve 85% of accuracy classifying. The numerical model achieved minimum agreements of 95.27% and 86.64%, with the experimental temperatures and GACRs at the center of the PCB assembly top cover, respectively. The parametric analysis proved that solder joint shape discriminability is directly proportional to heat flux, but inversely proportional to covers number and heating time. In addition, the parametric analysis determined that active thermography is limited to five covers to discriminate among hidden solder joint shapes. A prediction model was developed based on the parametric numerical data to determine the appropriate amount of energy to discriminate among solder joint shapes for up to five covers. The degree of agreement between the prediction model and the experimental model was determined to be within a 90.6% for one and two covers. The prediction model is limited to only three solder joints, but these research principles can be applied to generate more realistic prediction models for large scale electronic assemblies like ball grid array assemblies having as much as 600 solder joints.

Today, Scania CV AB is facing challenging demands on functionality and performance within their vehicles. The electronics are increasing rapidly and to stay competitive on the market, concerns regarding reliability of electronic systems needs to be evaluated. Prognostics and health management (PHM) is a concept where reliability of, for example, electronic control units (ECUs) are assessed. It requires customized systems for each specific environment, due to different strains and stresses. One approach is to have canaries (components with reduced soldering mass) implemented into ECUs as an indication that something is about to happen. Another essential aspect is the continuous real-time data acquisition from sensors, that can be used for different algorithms and models, which could provide forecasts on remaining useful life (RUL) of the ECUs. An appliance is the big data acquisition, where a database will collect data from vehicles, which means that ECU data need be communicated differently than today. This is why this master thesis project investigated canaries on printed circuit boards (PCBs) when they were subjected to vibrations as well as thermal cycling (TC), which are common parameters within vehicles. The PCBs consisted of both lead (Sn-Pb) and lead-free (SAC305) soldering for material comparison, since a transition to lead-free electronics is happening. Several fatigue tests were performed to collect as much information as possible. For further advances towards a PHM implementation, thermal shock (TS) tests on ECUs were performed as well. The ECUs were shocked in a temperature cabinet while being in active state. The internal temperature sensor was communicated with via controller area network (CAN). Scania’s CAN program was used and the data was logged in a computer, which in turn was compared to the data from the surrounding thermocouples, placed in specific spots. The results that were achieved clearly showed that lead-free PCBs are much more sensitive to stresses (both vibrations and TC). It was also shown that canaries failed in a much higher extent than regular resistors. The real-time data acquisition from the ECU could successfully be managed, where continuous data was logged. Also, the TS tests showed how the correlation between sensors indifferent positions was. Finally, the results from these tasks were discussed for future work. One have to keep in mind that this is just the beginning of a many-years project within Scania. The results and progress within this master thesis project will hopefully be a step in the rightdirection.