Assemic Invited Session Papers

Method for Overcoming the Unwanted Displacements of an Electro-Thermally Actuated Microgripper

Abstract

Thermal microactuators are based on the principle of material deformation due to heat generated by Joule effect. As a class of microactuators, the microgrippers are promising tools for manipulation of micro and nano - scaled objects. The designs of two models of SU-8 microgrippers electro-thermally actuated are described. A simple design for an electro-thermaly actuated polymeric microgripper is compared with an improved design using a pair of heaters on both sides of the microgripper. We demonstrated that it is possible to reduce the unwanted out of plane displacement, the second model capable of being more stable to the out of plane deflection, generated by the stress, when a voltage is applied. Electro-thermo-mechanical simulations based on finite element method were performed for each of the model in order to make a comparison between the results. Preliminary results on the fabrication of the last model, using a surface micromachining technique and an SU-8 polymer as functional material are presented.

Keywords: microgripper, SU-8 polymer, thermal actuation, FEM simulation

A Simple Bonding Process of SU-8 to Glass to Seal a Microfluidic Device

Abstract

This paper describes a simple process of adhesive bonding between a glass lid and a SU-8 microfluidic device. The bonding is made by applying pressure, between 1.24 MPa – 3.72 MPa, and heat, above the SU-8 glass transition temperature (Tg). The advantages of this process are low cost, simplicity and no need of extra adhesive material, which could block microchannels and inlets. The SU-8 microchannels are fabricated on a glass substrate by UV photolithography. The resist thickness is 30 μm and the smallest channels are 5 μm in width. The bonding process was performed using a simple uniaxial press, a torque wrench and a convection oven as an alternative to the complex and expensive bonding machines with a vacuum chamber and alignment tools. To identify a suitable bonding temperature, a Tg of 175°C for the patterned SU-8 was obtained by Dynamic Mechanical Analysis (DMA). The bonding strength was 1.15MPa, measured by a pull-out test, and a bonding area of 90% was achieved, which was observed by visual inspection. It was also investigated the effect of an O2 plasma cleaning process on the bonding quality.

Keywords: SU-8, adhesive bonding, microfluidic device

ASSEMIC: Research Advances in Microhandling and Assembly – “Special ASSEMIC Session”

Abstract

Few technical fields are so multidisciplinary and present so challenging demands as microtechnologies. The Research and Training Network “Advanced Methods and Tools for Handling and Assembly in Microtechnology” (ASSEMIC) addresses this research field at a European scale. ASSEMIC brings together a consortium of 14 participants, focusing their efforts in microhandling and microassembly. This paper summarizes some of the latest results achieved in this project.

Keywords: microhandling, microassembly

A Concept of Collision Prevention during Micro Assembly in a SEM Chamber

Abstract

This paper presents a concept for avoiding collisions during micro assembly processes in the camber of a Scanning Electron Microscope (SEM). Focus is the phase of approaching of a micro-gripper to the specimen holder and the phase of picking up the micro-components that are positioned on it. Although the 3D position of the gripper tips should be known exactly the current design of equipment in the SEN chamber does not allow an assesment of the position in the z-direction. This uncertainty of relative positions causes a high risk that tips of micro-crippers break if colliding with the speciment holder as the operator has no information about the distance. Keywords: collision avoidance, micro assembly, SEM

Technologies for Microassembly: Selected Methods

Abstract

This paper presents three different Microassembly examples. The first part of the paper presents a solution based on a laser system, next a contact-less microdispensing system and finally an innovative hot air stream joining system. One of the most remarkable differences between these methods is the different material requirements: meanwhile the laser system requires that one of the joint components is optically transparent, the other two systems do not have this constraint but require compatibility between glue and parts.

Keywords: microassembly, laser, dispensing, joining

Preliminary Experiments for the Fabrication of Thermally Actuated Bimorph Cantilever arrays on non-silicon wafers with vertical interconnects

Abstract

This paper describes the first steps for the fabrication of low-cost cantilever arrays, developed at RAL, on nonsilicon polymer substrates with vertical interconnects, produced at Profactor. The deflection and actuation of these cantilevers is based on the bimorph thermal actuation principle. The fabrication of the cantilever arrays requires many process steps which are presented in this article. The first one is the planarization between the via-holes interconnects with a uniform layer. This was achieved by spin coating of a thick (~58μm) SU-8 layer. Next, two thin metal layers of Cr (500Ǻ) and Au (1000Ǻ) were thermally deposited and patterned, using UV lithography with a mask alignment process and wet etching. The following step was the coating of a 1μm structural Au layer, in which the deposited layer had a very poor adhesion. Alternative procedures were explored to overcome this problem in the future. Modifications of the photo masks design and the substrates will be carried out to make the RAL microcantilevers technology more compatible with Profactor substrates.

Keywords: bimorph cantilever, vertical interconnect, epoxy glass fibre, FR4