Effect of Chemistry on Viscoelastic Properties of Moulding Compounds
ABSTRACT The present state-of-the-art in simulation of stresses in electronic packages is to model the moudling compound as a viscoelastic material. That means that stresses during packaging and subsequent thermomechanical loading are allowed to relax partially. Such an approach was seen to improve thermomechanical predictions considerably compared to the previously used temperature dependent elastic models. Therefore viscoelastic simulations are now becoming the standard for the modelling of packaging stresses and viscoelastic characterization of new moulding compound materials is now routinely being performed by most of the companies involved with packaging of electronic components. A problem is, however, that the viscoelastic data of moulding compounds turns out to be quite sensitive to variations in the compound chemistry and that this chemistry may vary slightly from batch to batch. Since these variations do not have a large effect on the room temperature properties (like the modulus) they often remain undetected by the standard quality tests. In order to anticipate to these problems it is desirable to develop a fundamental understanding of what parameters influence the viscoelastic properties of thermosets. A quantitative model, such as will be presented in this paper, has the additional advantage that it can be used for the selection of moulding compounds with optimized viscoelastic properties.
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ABSTRACT: The creep behaviour of Sn96.5Ag3.5- and Sn95.5Ag3.8Cu0.7-solder was studied specifically for its dependence on technological and environmental factors. The technological factors considered were typical cooling rates and pad metallizations for solder joints in electronic packaging. The environmental factors included microstructural changes as a result of thermal aging of solder joints. Creep experiments were conducted on three types of specimens—flip–chip joints, PCB solder joints and bulk specimens. flip–chip specimens were altered through the selection of various under bump metallizations (Cu vs. NiAu), cooling rates (40 K/min vs. 120 K/min), and thermal storage (24 h, 168 h, and 1176 h at 125 °C). PCB solder joints were studied by using a copper pin soldered into a thru-hole connection on a printed circuit board having a NiAu metallization. Bulk specimens contained the pure alloys. The creep behaviour of the SnAg and SnAgCu solders varied in dependence of specimen type, pad metallization and aging condition. Constitutive models for SnAg and SnAgCu solders as they depend on the reviewed factors are provided.Microelectronics Reliability. 01/2007;
Conference Proceeding: Viscoelastic characterization of fast curing moulding compounds[show abstract] [hide abstract]
ABSTRACT: Thermoset resins are well known as materials for high performance applications such as in the microelectronics. Examples are moulding compounds, underfill materials, coatings, adhesives, etc. A problem is however that the curing process induces thermal and reaction shrinkage, which leads to residual stresses and warpage. The polymer behavior is highly time, temperature and cure dependent and spans the entire range from liquid to solid state during processing. In order to be able to reduce and to prevent these stresses and warpage, the compound selection and the curing procedure should be optimized within the design process. For this, the polymer material behavior should be understood in advance, which in turn requires adequate modeling and characterization during cure. This paper deals with characterization and analysis of the viscoelastic properties of underfill and molding compounds. The focus is on the determination of the most useful method to find the viscoelastic properties of fast curing materials during the cure process.Thermal, Mechanical and Multi-Physics Simulation and Experiments in Micro-Electronics and Micro-Systems, 2005. EuroSimE 2005. Proceedings of the 6th International Conference on; 05/2005
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ABSTRACT: Particle-filled polymers are widely used in electronic industries. From microscale view, cure-induced residual stress can be generated not only by the external constraints but also by the constraint effect among the particles. In this paper, a three-dimensional micromechanical finite element method (FEM) model has been setup for a silica particle filled epoxy. In the micromechanical model, the epoxy matrix is modeled with a previously developed cure-dependent viscoelastic constitutive model, whereas the silica particles are modeled as elastic with high stiffness. Cure shrinkage is applied to the matrix as an initial strain for each time increment. The cure-dependent viscoelastic properties were obtained from shear and tension-compression dynamical mechanical analysis measurements. Cure shrinkage and reaction kinetics were characterized with online density measurement and differential scanning calorimeter measurements, respectively. In order to simulate a partly constrained object, the micromechanical model is coupled with a macromodel FEM analysis. The displacements from the macromodel are used as boundary conditions for the micromodel. The effect of external constraints on the generation of the micro stresses is studied by using the boundary conditions related to different external constrained states.IEEE Transactions on Components and Packaging Technologies 01/2005; · 0.94 Impact Factor