Template Based Assembly for Solid State Cooling

This paper presents a fully dry assembly method to obtain densely packed arrays of parts from 400-800μm in size. This approach shows promise for enabling formation of a module of n and p type materials optimized for micro scale thermoelectric cooling performance. INTRODUCTION Inertial force (mass of the assembled parts) plays a critical role for part alignment and orienting in a dry microassembly process [1]. However, when the parts get smaller, adhesion force and friction force become significant compared to inertial force and cause failures [1]. This paper: (1) presents a novel fully dry self-assembly process with a cross scaled feasibility study for small parts; (2) defines three major kinetic states for stochastic part manipulation; (3) utilizes the surface energy gap caused by differences in roughness with dynamic annealing to achieve face orienting and parallel self-assembly; no specific part features [1] or hydrophobic coatings [2] are necessary. This fully dry assembly process is capable of (1) high-density parts arrangement and packing within a single batch; (2) multi-batch assembly; (3) the possible unique orienting with specific template design and dynamic annealing. A comparison of different dry and semi-dry microassembly technologies is shown in Figure 1. MATERIALS AND SETUP Figure 2 shows a schematic diagram and photo of the experimental setup for dry assembly. Both double and single side polished Si dummy parts are tested on the smooth and rough templates. All parts are square and ~120μm thick with five size scales (width =150, 200, 400, 600, 800μm). They are made from polished SOI wafers with DRIE. The template for each part has 20μm clearance and 55μm depth to facilitate the assembly. The template is mounted with an antistatic cylinder and driven vertically by a coil motor under a range of frequencies (from 200 to 1000Hz). The antistatic cylinder confines parts on top of the template without inducing extra electrostatic charge into the process. The assembly process has three steps (Figure 3) for achieving high density of part assembly. First, using the competition among template trapping potential energy, part kinetic energy and surface energy between solid-solid Fig. 1: A comparison of different dry and semi-dry assemblies. Fully dry self-assembly process Semi-dry self-assembly process This work (800μm square) single-batch Ref. [1] single batch Ref. [4] single batch Ref. [2] single batch Ref. [2] multi-batch This work (400μm square) single-batch Template (a) Camera 1 (b) Camera 2 Parts