Mobility based 3D simulation of selective, viscoelastic polymer reflow using surface evolver

Abstract

This work demonstrates implementation of the main effects of viscoelastic thermal polymer reflow in an efficient energy and mobility based simulation. The concept is based on a finite-element, soap-film method using the free software surface evolver. Properties of a homogeneous 3D volume are thereby represented by a corresponding 2D surface. The simulation only requires the contact angle between polymer and substrate for infinite long reflow times, obtained from fingerprint experiments, and a mobility value as input. The mobility value is a measure for the polymer-chain mobility and is directly linked to the polymer viscosity. This concept allows for an accurate and fast treatment of the thermomechanically complex polymer behavior close to the glass transition. The simulation time scale is linearly related to the experimental time scale allowing for accelerated-time simulations. Simulation and experiment showed a very good agreement. As a generalized concept, the approach presented here can be used for fast and full 3D shape computation during any complex, energy driven geometry optimization process like polymer reflow, viscoelastic wetting or dewetting and droplet coagulation. This simulation may facilitate a faster uptake of grayscale reflow technologies for industrial processes. Supplementary material supports a quick grasp of the simulation approach.