Technologies for Microassembly: Selected Methods 4M 2007 Conference 3-5 October 2007, Borovets, Bulgaria. ASSEMIC Invited Session
Micro-joining by hot gas stream Laser based micro-assembly system Contactless microdispensing system
Micro-joining by hot gas stream Development of a micro-assembly system based on hot air stream joining (TU Vienna - ISAS) Gas supply - low production costs - simplicity of use - possibilty for integration into existing production lines - applicability for different materials combinations Compressor Heating tube Nozzle Hot gas stream Substrate with µ-part
Laser based micro-assembly system Development of an advanced laser based Pick and Join tool and of a microassembly system Innovative methods and processes for micro-welding of polymeric parts (Fraunhofer ILT) - new laser sources - innovative joining processes - high flexibility and processing speed - increased robustness - high accuracy
Contactless microdispensing system Ana Almansa (Profactor Research & Solutions GmbH) Fratila, Bou, Palfinger, Mann (Profactor R&S), Möst (PICO Dosiertechnik) PROFACTOR Research and Solutions GmbH A-2444 Seibersdorf, Austria, Forschungszentrum Tel. +43 50 550-0, Fax +43 50 550-2204 www.profactor.at
Outline Introduction Adhesive Dispensing processes and principles Description of PROFACTOR measuring set-up First results Conclusions
Introduction
Dispensing processes- Brief introduction Microdispensing: key process in many production processes Packaging, automotive, (typically automatic dispensing) Lower volume, craft based industries, (frequently manual dispensing from a cartridge using e.g. sealant gun or tool) Electronics and Microsystems (challenging task due requirement for very high precision at high production rates) Different types of adhesive processes Contact / contactless dispensing Single component / Multicomponent adhesive Distinct fluid properties (anisotropic, thermally conductive, IR curing.) Wide range of applications Dispensing of lubricant Adhesive processes Colour, lack, dot marking Dispensing of cleaning fluids and reactive substances Surface coating Sealing, protection, isolation Source: PICO Dosiertechnik GmbH
Typical problems with dot dispensing Tailing typical needle dispensing problem Tombstoning a component rises at one side during cure because of uneven forces in the adhesive result of an inaccurate dispense, poorly designed process, or improperly handled materials. Stringing break up of the adhesive between nozzle and substrate Consequence of too hight ejection speed for the viscosity/cohesive strength of adhesive. No dispense due to insufficient force next dot due to have twice nominal size) Popcorning Result of air or moisture getting into the adhesive and popping out during the curing stage usually results from improper handling of fluid or using out of date material Satellites frequent in high speed dispensing may be caused by air bubbles Source: www.maths.bris.ac.uk Satellite Drop formation SourceSMT magazine (4/2001) Tailing
Description of PROFACTOR Contactless Microdispensing System measuring set-up
Prototype implemented Dispensing machine DV-100 Picodostec system Contactless dispensing mode Viscosity range: 50-200.000 mpas Minimum dispensing time from 10 µs XY Micropositioning Table travel distance from 250 mm High accuracy Glass plate for enabling through view USB Camera 1024x768px, 8bit Optic 2 different telecentric objectives Area Pixel Size Exposure time T50/1.0 5/3.75mm 5µm 10ms T107/0.33 15/11.25mm 15µm 5ms
PROFACTOR Microdispensing measuring set-up Light difusion for enhanced light homogeneity XY Micropositioning stage integrating glass plate for enabling through view PICODOS contactless Microdispensing unit System Control and image processing Software Drop array dispensing glass plate Circular light source mounted for optimal illumination incidence angle Camera and telecentric objective Microdispensing control unit and interface Hardware
The PICODOS Microdispensing unit The dispensing valve is actuated by two piezoactuators onto a rod, with a ceramic sealing ball attached to its end Piezoactuator frequencies of up to 1000 Hz enable dispensing amounts of down to approx. 2nl are possible PICODos dispensing valve Contactless dispensing with distance of up to several centimeters (single drops or continuous flux) The dispensing valve integrates a heating element which allows to control the temperature of the fluid within the needle valve (e.g. to change viscosity or attain operating working temperature)
Microdispensing process control The hardware developed enables remote computer control of the dispensing system and integrates galvanic isolation through 8x Optical coupling device between the computer and dispensing unit circuit (3.8 to 24 Volt)
Image processing method A challenge for image processing: Vision based analysis of transparent drops through a glass plate Border Contrast by a total reflection light on the drop surface. Sharp edge at the border of the drop Tailing primary beams
Image processing Method Imaging Manual Threshold Fill Holes Dilate and Erode Dilate and Erode Convolute Illumination optimized typical Intensity profile
Analysis of the drops The questions The answers X,Y central position Has the drop been adequately dispensed? Are the drops homogeneous? Are the drops displaced from the target position? Are there existing satellite drops? Are the drops too large or too small? Are there detectable faults in the adhesive or dispensing process? What is the process repeatability? Perimeter & diameter Number of holes Area Ratio of equivalent ellipse Ratio of equivalent radius Excentricity: Outer inner radius Presence and number of satellite drops Statistic values
System control software and user interface System control and user interface developed in NI LabView Automatic control of positioning table and dispensing unit Automatic or user driven vision based analysis of the drops Data exportable as excel table High degree of configurability
First results
First tests Experimental conditions First experiments where done with oil- providing particularly challenging conditions due to: Low viscosity Transparency Difficulty to dispense Variability
Results of first experiments Formation of air bubbles The temperature increase failed to solve the problem Air bubbles only disappeared after few minutes The problem was solved by new optimization of measurement set-up and program Dynamic evolution of the drops due to low viscosity and fluid properties (the area increased with time) Effect was successfully measured and recorded by PROFACTOR measuring system Satellites were formed Effect was detected by the measuring system and could be corrected after readjustment of dispensing parameters
Conclusions
Conclusions Profactor has developed in cooperation with PICO Dosiertechnik an automated system for measurement and characterization of dispensed microdrops The system has a high degree of flexibility and configurability, in order to be easily adapted to difference process conditions, fulfilling the needs of the customer. Further work is planned, in order to enable on-line measurement and integration in closed-loop dispensing processes
Acknowledgements This work was made possible thanks to the partial support of the European Commission through the Marie Curie Actions in the 6th Framework Programme and to the main support and strong contribution of the company PICO Dosiertechnik GmbH.
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