In the context of microsystems technology, the electronic package represents all the elements responsible for the protection and interaction with the environment of integrated circuits. A typical reliability issue of electronic packages is the decohesion between the encapsulant material, the Epoxy Molding Compound (EMC), and the metallic lead frame on which the semiconductor chip is mounted. The EMC is a composite material, with a thermoset resin as matrix and silica microspheres as filler. The present computational study is aimed at understanding the influence on mechanical and adhesive macroscopic properties of its microstructure, in order to improve the reliability of electronic devices. Firstly, the geometry of the matrix-filler system is virtually reproduced using Statistical Volume Elements (SVEs) characterized by a random distribution of spherical particles, whose diameters are optimized to best represent the volume fraction and size distribution of the filler in commercial EMCs. The obtained geometry is compared with micrographs of EMC cross-sections. The elastic modulus, Poisson’s ratio, and yield stress of the neat polymeric matrix are obtained from experimental data about the EMC trough an inverse homogenization algorithm, in which finite element analyses of the SVE are performed iteratively. Then, it is investigated the effect of varying the particles volume fraction and size distribution. Finally, the microstructural effects on adhesion are studied with micro-scale models of the lead frame-matrix-filler system, accounting for the lead frame-matrix adhesion with a cohesive zone model. The global displacement and stresses are used to compute an effective traction-separation law. The effects of filler content, substrate roughness, and intrinsic adhesive properties on the global behavior are observed. The present results give insights about the microscale properties of EMCs and their effects on adhesive properties. They also allow the usage of a homogeneous description of the EMC in computational models at the package level, without explicitly modeling the underlying microstructure.
Nel contesto della tecnologia dei microsistemi, il package consta negli elementi responsabili della protezione ed interazione con l’ambiente dei circuiti integrati. Una tipica problematica per la loro affidabilità è la decoesione tra l’incapsulante, l’Epoxy Molding Compound (EMC), e il lead frame su cui si assembla il chip. L’EMC è un materiale composito, con una matrice di resina termoindurente ed una carica di microsfere di silice. Questo studio computazionale è atto a comprendere l’influenza della sua microstruttura sulle proprietà meccaniche e di adesione, per migliorare l’affidabilità dei dispositivi elettronici. In primo luogo, la geometria del sistema matrice-carica è riprodotta virtualmente usando elementi di volume statistici (EVS) con una distribuzione casuale di particelle sferiche, i cui diametri sono ottimizzati per rappresentare la frazione volumetrica e la granulometria della carica di EMC commerciali. La geometria è comparata con micrografie in sezione di un EMC. Il modulo di Young, Coefficiente di Poisson, e sforzo di snervamento della resina polimerica pura sono ottenuti da dati sperimentali sull’EMC attraverso un algoritmo di omogenizzazione inversa, in cui analisi agli elementi finiti degli EVS sono effettuate iterativamente. In seguito, si analizza l’effetto di variazioni in frazione volumetrica e granulometria delle particelle. Successivamente, si studiano gli effetti della microstruttura sull’adesione tramite modelli alla micro-scala del sistema lead frame-matrice-carica, descrivendo l’adesione tra matrice e substrato metallico tramite un modello di zona coesiva. Sforzi e deformazioni globali sono utilizzati per calcolare una legge trazione-separazione efficace. Si osservano quindi gli effetti del contenuto di carica, rugosità del substrato e proprietà adesive intrinseche sul comportamento macroscopico.
Micromechanical investigation of lead frame : Epoxy Molding Compound adhesion
Della Porta, Alessandro
2021/2022
Abstract
In the context of microsystems technology, the electronic package represents all the elements responsible for the protection and interaction with the environment of integrated circuits. A typical reliability issue of electronic packages is the decohesion between the encapsulant material, the Epoxy Molding Compound (EMC), and the metallic lead frame on which the semiconductor chip is mounted. The EMC is a composite material, with a thermoset resin as matrix and silica microspheres as filler. The present computational study is aimed at understanding the influence on mechanical and adhesive macroscopic properties of its microstructure, in order to improve the reliability of electronic devices. Firstly, the geometry of the matrix-filler system is virtually reproduced using Statistical Volume Elements (SVEs) characterized by a random distribution of spherical particles, whose diameters are optimized to best represent the volume fraction and size distribution of the filler in commercial EMCs. The obtained geometry is compared with micrographs of EMC cross-sections. The elastic modulus, Poisson’s ratio, and yield stress of the neat polymeric matrix are obtained from experimental data about the EMC trough an inverse homogenization algorithm, in which finite element analyses of the SVE are performed iteratively. Then, it is investigated the effect of varying the particles volume fraction and size distribution. Finally, the microstructural effects on adhesion are studied with micro-scale models of the lead frame-matrix-filler system, accounting for the lead frame-matrix adhesion with a cohesive zone model. The global displacement and stresses are used to compute an effective traction-separation law. The effects of filler content, substrate roughness, and intrinsic adhesive properties on the global behavior are observed. The present results give insights about the microscale properties of EMCs and their effects on adhesive properties. They also allow the usage of a homogeneous description of the EMC in computational models at the package level, without explicitly modeling the underlying microstructure.File | Dimensione | Formato | |
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2022_12_DellaPorta_THESIS.pdf
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2022_12_DellaPorta_SUMMARY.pdf
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https://hdl.handle.net/10589/196765