MICROMANUFACTURING 2009, APRIL 1-2, MINNEAPOLIS, MN LASER TRANSMISSION MICROJOINING TECHNOLOGY FOR PACKAGING OF MEMS R. Patwa 1, H. J. Herfurth 1, S. Heinemann 1, Golam Newaz 2 1 Fraunhofer USA, Center for, 46025 Port Street, Plymouth, MI 48170, USA 2 Wayne State University, Detroit, MI 48232, USA
Outline Introduction - Fraunhofer CLT Laser Transmission Microjoining Applications Joining Dissimilar Materials Results Process Characterization Joining Similar Materials Conclusions
Key Competencies at Fraunhofer CLT Unbiased Applied R&D in: Process Development (from Chips to Ships) Consulting to Production Validation Special Optics Engineering of Advanced Lasers - Diode Lasers - Fiber Lasers Unique Turn-Key Systems
Outline Introduction - Fraunhofer CLT Laser Transmission Microjoining Applications Joining Dissimilar Materials Results Process Characterization Joining Similar Materials Conclusions
Biomedical Applications Next-generation retinal Source: California prosthesis Institute of Technology Glass MEMS Device Cochlear Implant to restore partial hearing Challenges Hermetic sealing Localized bonding Silicon base Long term stability Source: Advanced Bionics, Corp. Biocompatibility Housing of MEMS / Hermetic sealing
Laser Transmission Joining Principle During laser transmission microjoining process - The laser radiation is transmitted through the partially transparent top material. It is absorbed at the surface of the bottom material. The laser radiation is converted into heat energy directly at the interface. Schematic of the sample undergoing the bonding process Schematic of sample in fixture
Different Joining Methods Simultaneous Quasi-simultaneous Mask
Basic Joint Designs laser beam transparent material absorbing material transparent material laser beam absorbing material laser beam laser beam transparent material absorbing material transparent material absorbing material
Laser Sources Laser Transmission Joining Setup cw Yb- doped fiber laser (JDSU) Wavelength : 1110 nm Maximum Power : 25 W Fiber Size : 9 µm Laser optic cw Diode laser (Fraunhofer) Wavelength : 808 nm Maximum Power : 27 W Fiber Size : 800 µm Sample Fixture cw Nd:YAG laser (Trumpf) Wavelength : 1064 nm Maximum Power : 1000 W Fiber Size : 600 µm
Material Combination Matrix Transparent Absorbing Imidex Teflon PEBAX PVDF Polyurethane PEEK Borosilicate glass PA PMMA Nitinol X X Chromium coating X X Stainless steel X X X Titanium X X X Silicon X Titanium coated glass X X X ABS X PA X Metal - Polymer Ceramic Metal/Ceramic Polymer - Polymer
Measured Laser Power (W) Optical Properties of Materials 8 7 6 5 Polymer Cover glass + Imidex Cover glass + PEEK No Cover glass & No Polymer Glass 4 3 2 Absorption ( ), 1 0 Transmissivity of Imidex with cover glass = 79.8 % Transmissivity of PEEK with cover glass = 80.9 % 0 2 4 6 8 Applied Laser Power (W) Transmission ( ) Silicon
Laser Power (W) Laser power [W] Process Optimization Process parameter window is determined to optimize bond formation process. Metal-Polymer Glass-Silicon 12 45 10 8 40 6 4 2 0 10 100 1000 10000 100000 (Log) Speed (mm/min) no effect Imidex changes color Weak Bond Bond Strong Bond Very Strong Bond Burned 35 good bond no bond 30 temporarily bonded partially melted completely melted 25 50 150 250 350 450 550 Speed [mm/min]
Outline Introduction - Fraunhofer CLT Laser Transmission Microjoining Applications Joining Dissimilar Materials Results Process Characterization Joining Similar Materials Conclusions
Metal-Polymer Bonding Chromium - PEEK Titanium - Imidex View Nitinol - PEEK Titanium - PVDF As is bond surface top view Nitinol - Imidex Chromium - Imidex Titanium - Polyurethane
Metal-Polymer Bonding Bond line Titanium coated glass/ Imidex bond Stainless steel/pebax bond
Silicon-Glass Joining Material Silicon (Top), Borosilicate Glass (Bottom) Diode laser 30 W, 60 mm/min Nd:YAG laser 35 W, 200 mm/min Fiber laser Spot Bond
laser power [ W ] Laser power [ W ] Temperature Control for Plastic Welding signal processor 25 600 optical fibre temperature detector laser beam L L T focussing lens filter laser power detector 20 15 10 5 0 0 0 50 100 25 distance [ mm ] 500 400 300 200 100 600 temperature [ C] temperature radiation L T focussing lens workpiece 20 15 10 5 500 400 300 200 100 temperature [ C] Custom optic for temperature control 0 0 0 50 100 distance [ mm ] Diode laser; 5 m/min
Load (grams) Failure Load (N) Joint Characterization Failure Load Limit Metal-Polymer Polymer-Polymer 6000 Nitinol/Imidex 1400 5000 Chromium/Imidex Chromium/PEEK Nitinol/PEEK 1200 4000 Titanium/Imidex 1000 3000 2000 800 1000 600 Thickness - 3.1mm Thickness - 2.4mm 0 0 0.2 0.4 0.6 0.8 1 Displacement (mm) Thickness - 1.9mm 400 0.0 1.0 2.0 3.0 4.0 Speed (m/min)
Pull Strength (N/mm2) Maximum Pull Strength (N/mm2) Joint Characterization Shear Pull Strength Nitinol/PEEK Metal-Polymer 20 15 15 10 10 5 5 0 3 4 5 6 7 8 9 10 Laser Power (W) 0 Nitinol/Imidex Nitinol/PEEK Chromium/PEEK Chromium/Imidex Titanium/Imidex
Failure Load (N/mm 2 ) Joint Characterization Degradation in Cerebrospinal fluid (CSF) Material combination: Glass: Pyrex 7740 Ti-coated Imidex: 0.177 mm thick 25 20 15 10 Laser: Fiber laser 5 0 0 2 4 6 8 10 12 14 Weeks in CSF Solution at 37 o C Average failure load as bonded: 21.5 N/mm 2
Joint Characterization Pressure Testing Sample Titanium: 3 mm x 5 mm; hole diameter = 1 mm Imidex: O. D. 2 mm Pressure test setup Result Burst pressure: 80 bar Tensile strength: 8 N/mm 2
Joint Characterization He-Leak Testing Polyimide to Titanium Substrate: 2.6 x 10-6 Std. cc/sec/cm 2 Bond: 3.4 x 10-6 Std. cc/sec/cm 2 Leak rate slightly higher Helium Vacuum Laser Bond Helium detector/ Mass spectrometer Laser: Fiber laser Power: 4.2 W Speed: 100 mm/min
Joint Characterization SEM Analysis
Joint Characterization XPS Analysis Material combination: Imidex/Titanium Bond Lines Titanium Surface XPS Signal Collection Area C1S lines Ti2p lines
Competing Technologies Laser Micro-joining Advantages - Highly localized - Precise bond lines - Heat affected zone (HAZ) confined to very small volume of material - Encapsulation design flexibility Ultrasonic Welding Advantages - Lower initial equipment cost Adhesive Bonding Advantages - Good for area bonds - Non-contact process
Outline Introduction - Fraunhofer CLT Laser Transmission Microjoining Applications Joining Dissimilar Materials Results Process Characterization Joining Similar Materials Conclusions
Glass-to-Glass Welding Material: Glass wafer (Pyrex 7740) Thickness: 0.5 mm Laser: Pulsed CO 2 (Rofin SC x10) Power: Speed: 65 W >25.0 m/min Multiple scans Butt Joint (33 W, 100 mm/min) Cross-section
Glass-to-Glass Welding 0.25 mm T - Joint Fillet Edge Joint Fillet Edge Joint 0.25 mm Cross-section Cross-section
Conclusions Laser transmission microjoining of similar and dissimilar material combinations has been successfully achieved. The results demonstrate the similarities and differences between the different material systems and underscored the importance of laser microjoining technology for such applications. This study provides a database of novel joining combinations that can be commercialized for industrial applications. This technology clearly exhibits a high potential for laser joining processes to address the increasing demand for packaging applications.
Thank you for your attention! CONTACT- Rahul Patwa rpatwa@clt.fraunhofer.com www.clt.fraunhofer.com Fraunhofer Center for 46025 Port Street Plymouth, Michigan 48170