This paper presents a novel low-temperature process that combines high-aspect-ratio polymer structures with electroless copper plating to create laterally compliant MEMS structures. These structures are evaluated as IC-package interconnects that can lead to reliable, low-cost and high-performance nano wafer-level packaging. High-aspect-ratio low CTE polyimide structures with low stress, high toughness and strength were fabricated using plasma etching, This dry etching process was tuned to yield a wall angle above 80 degrees leading to an aspect ratio higher than 4. The etching process also leads to roughened sidewalls for selective electroless plating on the sidewalls of the polymer structures. Simulations of these fabricated structures show tremendous reduction in the stresses at the interfaces and superior reliability as IC-package nano interconnects. Metal-coated polymer structures from MEMS fabrication techniques can provide low-cost high-performance solutions for wafer-level-packaging.

High aspect ratio metal-polymer composite structures for nano interconnects

This paper gives a bibliographical review of the finite element methods (FEMs) applied to the analysis and simulation of adhesive bonding, soldering and brazing. The bibliography is an addendum to the Finite element analysis and simulation of adhesive bonding, soldering and brazing: a bibliography (1976–96) published in the 1997 Modelling Simul. Mater. Sci. Eng. 5 159–85. The added bibliography at the end of this article contains 867 references to papers and conference proceedings on the subject that were published in 1996–2002. The following topics are included: adhesive bonding—stress analysis of adhesive bonding in general, stress analysis and design of specific bonded joints, fracture mechanics and fatigue analysis, destructive and non-destructive evaluation of bonds, and other topics; soldering—thermal stresses and deformation analysis of solder joints, fracture mechanics aspects and fatigue analysis of solder joints, solder joint reliability; and brazing—finite element analysis and simulations.

https://iopscience.iop.org/article/10.1088/0965-0393/10/6/304/pdf

Finite element analysis and simulation of adhesive bonding, soldering and brazing—an addendum: a bibliography (1996–2002)

This work deals with the selection and evaluation of candidate materials as a future base substrate for SOP. New composite materials using advanced fiber clothes and fillers were fabricated and tested to evaluate the increase in performance compared to conventional glass-epoxy substrates (FR-4). Composites built with advanced carbon-cloth having a negative thermal expansion coefficient (CTE) yielded a composite CTE of <3 ppm//spl deg/C. The composites have 2-3 times higher modulus than conventional FR-4. In order to evaluate materials with further higher modulus, metal matrix composites Al/SiC with low CTE of 7 ppm//spl deg/C and high modulus of 220 GPa were also considered. The thermomechanical reliability of the electrical interconnections was evaluated after assembling flip-chips on three different substrates by subjecting test vehicles to thermal shock treatments. The failure modes in different substrates were analyzed with optical microscopy. The stresses in the solder joints and dielectric layer were also estimated with analytical and finite element models (FEM).

Selection and evaluation of materials for future system-on-package (SOP) substrate

Fine-pitch ball grid arrays (BGAs) and underfills have been used in benign office environments and wireless applications for a number of years, however their reliability in harsh environments is not well understood. In this work, the design guidelines development effort for deployment of fine-pitch ball-grid array packages in the harsh environments have been presented. Guidelines are targeted toward government contractors, OEMs, and third party contract manufacturers who intend to select part architectures and board designs based on specified mission requirements. The guidelines are intended as an aid for understanding the sensitivity of component reliability to geometry, package architecture, material properties and board attributes in different thermal environments in order to quantitatively evaluate the impact of these parameters on the component reliability. The intent is to develop a tool for doing tradeoffs between geometry, materials and quantitatively evaluating the impact on reliability. Sensitivity relations for geometry, materials, and architectures based on statistical models and failure mechanics based closed form models have been developed. Convergence between statistical model sensitivities and failure mechanics based sensitivities has been demonstrated. Predictions of sensitivities have been validated against experimental test data.

Thermo-mechanical reliability tradeoffs for deployment of area array packages in harsh environments

Fine-Pitch BGAs and underfills have been used in benign office environments and wireless applications for a number of years, however their reliability in harsh environments is not well understood. In this work, the design guidelines development effort for deployment of fine-pitch ball-grid array packages in the harsh environments have been presented. Guidelines are targeted towards government contractors, OEMs, and 3rd party contract manufacturers who intend to select part architectures and board designs based on specified mission requirements. The guidelines are intended as an aid for understanding the sensitivity of component reliability to geometry, package architecture, material properties and board attributes in different thermal environments in order to quantitatively evaluate the impact of these parameters on the component reliability. The intent is to develop a tool for doing trade-offs between geometry, materials and quantitatively evaluating the impact on reliability. Sensitivity relations for geometry, materials, and architectures based on statistical models and failure mechanics based closed form models have been developed. Convergence between statistical model sensitivities and failure mechanics based sensitivities has been demonstrated. Predictions of sensitivities have been validated against experimental test data.

Thermal reliability considerations for Deployment of area array packages in harsh environments

Analytical thermomechanical models have been developed in order to calculate the thermally induced stresses in leadless solder interconnection systems. Two different analytical models are highlighted: the peripheral and area array thermomechanical model which describe the thermally induced stresses for two components connected to each other with a peripheral, respectively, area array of joints. The analytical models are based on structural mechanics and have the ability to characterize the nature and estimate the magnitude of the joint stresses. Using these models, structural design optimization of interconnection systems can be performed very quickly in order to reduce time consuming experiments and finite element simulations. It is found that the largest stresses in the solder joints of flip chip assemblies are at the top and bottom surface of the connection and that they are especially caused by bending moments subjected to the joints. Comparisons with finite element simulations have proved a good accuracy of the thermomechanical models.

J. Bergmans

Papers

Thermomechanical models for leadless solder interconnections in flip chip assemblies