Numerical study of paste-bridge transfer process for laser induced high-viscosity silver paste

Abstract

Laser-induced forward transfer (LIFT) is promising for solar-cell metallization and electronic printing due to its low dependence on paste viscosity and nozzle-free process. In this paper, the transfer process and morphological characteristics for LIFT of high-viscosity silver paste were studied through simulations and experiments. The shear-thinning rheological properties were considered using the fitted Carreau model. Variations of paste protrusion with single pulse energy and time were obtained from the high-speed imaging. The evolution of initial pressure that induces the paste protrusion was solved inversely and quantitatively expressed by a polynomial function. The internal pressure should be sufficiently larger than 40 MPa to induce the effective transfer. In the simulation, the induced bubble undergoes a non-spherical transition from mushroom to pea-pod and capsule shapes due to constraints from surrounding paste and substrate. The deposition morphology formed by the induced mushroom-shaped bubble shows high printing precision with thin width (<30 μm) and large height (∼10 μm). The simulated diameter and height of transferred single voxel agree with those from experimental measurement. It can gain insight into the transfer dynamics of high-viscosity pastes and provide process optimization for precision printing of voxels by LIFT.