Photonic Curing and Soldering Ultra-fast Fabrication of Printed Electronics AIPIA Conference, Utrecht November 19 th, 215 Rob Hendriks Research Engineer
Presentation overview Introduction Photonic Curing Working principle Process optimization Photonic Soldering Reflow versus photonic Process study Simulation Summary PulseForge 13 Photonic Curing system Research and Development 2
Introduction NovaCentrix Enabling printed electronics Partnership model to drive technology PulseForge Tools Photonic curing equipment Sheet-to-sheet and Roll-to-roll SimPulse temperature simulation Highly advanced photonic curing systems Metalon Conductive Inks Silver, copper, copper oxide, etc. Nanopowders Silver, aluminum, metal oxide, etc. Copper oxide reduction ink 3
Introduction Smart Packaging & Printed electronics Smart packaging can be used to prevent wastage of food products Smart labels should be relative inexpensive compared to the product Roll-to-roll compatible fabrication methods are required Etched copper & Packaged chips Printed conductive inks & Bare die chips 4
Introduction Sintering Merging particles via atomic diffusion Fraction of bulk melting temperature Metal nanoparticle inks are suited for conductive structures on polymer films Curing of conductive inks Sintered Ag nanoparticles 1) Solvent evaporation: Densification and packing of particles 2) Breaking shells: Degradation/melting of polymer stabilizers 3) Sintering particles: Atomic diffusion, grain growth Solvent evaporation Breaking shells Sintering particles 5
Resistance (Ω) Temperature ( C) Introduction Oven curing on polymer / paper substrates Slow heating of the ink and substrate through convection Typical processing conductions: 12-15 C for 2 minutes Oven curing not suited for roll-to-roll production 1 1 1 16 14 12 1 1 1 1 1 8 6 4 1 1 2 1 2 3 4 5 6 7 8 9 1 Time (seconds) FIB-SEM cross-sectional image of a curing silver ink 6
Normailized absorption (emission) Photonic Curing Photonic curing working principle Selective heating of the ink through light absorption High intensity and short light pulses rapidly heat up the ink ( 25 C) Typical pulse lengths:.2 2 ms 1,9,8,7,6,5,4,3,2,1 PET film Ag nanoparticles Lamp emission 25 35 45 55 65 75 Wavelength (nm) Absortion / emission spectrums Temperature modeling 2 millisecond pulse 7
Photonic Curing Wrong temperature profiles Too long above the glass transition temperature of the substrate Short and high intensity pulses on wet ink Too high peak temperatures at the ink / substrate interface Shell formation Short pulses on wet ink 5 x 5 x SEM, 1 x Exploding bubbles Too fast heating Ablation (pre-dried ink) Too high peak temperature 8
Temperature C) Photonic Curing Optimal temperature profile Highest conductivity, best topology, shortest time 3 25 2 Photonic flash curing PulseForge equipment T melt 15 1 5 IR dyring, continuous illumination T g 1 2 3 4 5 6 7 Time (seconds) Pulse modulation, SimPulse Solvent evaporation Breaking shells Sintering particles 9
Photonic Curing Roll-to-roll processing of RFID antennas Modulated pulse (5 micro-pulses) to control temperature profile Operating at 33 m/min, longer pre-drying enables even higher speeds 1
Photonic Curing PulseForge equipment PulseForge 12 / 13: Research and Development (S2S) PulseForge 32 / 33: Development and Production (R2R) Full compatibilty Pulse settings Sheet-to-sheet (PulseForge 13) Roll-to-roll production (PulseForge 32) 11
Photonic Curing: Process optimization SimPulse: Temperature profile simulation Design your stack Shape the pulse Desired temperature profile Very fast for optimizing process conditions Stack design - Add up to 6 layers - Define thickness Materials - Database - Physical properties - Add your own Boundary conditions - Convection, heat sink Simulation time: - Fraction of a second 12
Temperature ( C) Photonic Curing: Process optimization Temperature / Resistance probe High temperature, high sensitivity, high speed: 4, S/s, > 5 C Close-up Conductive ink Insulation Temperature probe Glass 2 Double 4-point measurement 18 16 14 12 1 8 T( C) = 1.11194 R(Ω) - 465.77 R² =.99998 6 4 Probe 2 Temperature sensor (RTD) 42 44 46 48 5 52 54 56 58 6 Resistance (Ω) Temperature / Resistance probe Probe characterization 13
Resistance (Ω) Temperature ( C) Photonic Curing: Process optimization Temperature / Resistance measurements The measured temperature profile shows similar results as SimPulse Pulse modulation is a necessity for process control 1 PChem PSI-211: 2.5 µm thick 32 1 28 1 24 1 2 1 16 1 12 1 8 1 4 1 5 1 15 2 25 3 35 4 Time (milliseconds) Measuring setup in PulseForge 13 14
Temperature ( C) Photonic Soldering Reflow versus Photonic Soldering Typical temperature profile for reflow soldering: > 2 C for 5 minutes Reflow is not possible with temperature sensitive substrates Reflow soldering Photonic soldering 22 2 18 16 14 12 1 8 6 4 2 5 1 15 2 25 3 35 4 45 5 Time (milliseconds) 5 minutes 6, times faster 5 milliseconds 15
Resistance (Ω) Photodiode (V) Photonic Soldering Proof of Principle The bare die chip is soldered, but it jumps during heating What is the temperature within the stack during photonic soldering? 1 1 Channel 1 Channel 2 Photodiode,9,8 Bare die chip 1 1 Jumping chip,7,6 1,5 1 4 ms, 4.6 J/cm 2 1 Pre-dried 1 Soldered,1 Pulse,1-1 -8-6 -4-2 2 4 6 8 1 12 14 16 18 2 Time (milliseconds),4,3,2,1 Substrate: Polyimide 125 µm Bond pad: Copper 18 µm Solder paste: NC-56-LF ~ 2 µm Chip: IZM41.1 2 µm 16
Photonic Soldering: Process study Blow off & Flipped chips With photonic soldering there is a high change of blowing off the chip Too high chip temperature causes rapid gas generation within the solder The temperature profile should be properly controlled Chip blow off (IZM28) Flipped chip, partially soldered 17
Photonic Soldering: Process study Photonic Soldering probe The temperature probes are 18 x 18 µm 2 in size Designed for a IZM41.1 chip: 1 mm 2, 5 µm pitch, 25 µm bumps Temp / Resistance probe Microscope image of the bond pad (back) 18
Photonic Soldering: Process study Stack build-up Substrate: Borosilicate glass 7 µm Temperature probe: Metal.4 µm photolitho Conductive track: DuPont 525 6 µm screen printed Buffer layer: DuPont Exp. paste 16 µm stencil printed Solder paste: NC-56-LF, type 6 2 µm stencil printed Bare die chip: IZM41.1 2 µm pick&place Bond pad Cross-section (FIB-SEM) Solder paste, without chip 19
Resistance (Ω) Temperature ( C) Photonic Soldering: Process study Experimental data After placing the chip, pre-drying at 95 C for 2 minutes Pulse settings: 5 ms, 3.4 J/cm 2 1 24 21 1 18 15 1 12 9,1 6,1 5 ms, 3.4 J/cm 2 Pulse 5 1 15 2 25 3 Time (milliseconds) 3 Photonic soldered IZM41.1 2
Photonic Soldering: Simulation Stack build-up A 3D model of the stack is developed to predict soldering behavior The solder paste has temperature dependent material properties Between every layer there is a decomposition layer to simulate blow-off P pulse * Abs chip P pulse * Abs ink P pulse * Abs glass Chip (2 µm) Pre-dried Soldered Solder paste (2 µm) Buffer layer (16 µm) Conductive ink (6 µm) Glass (7 µm) Limited heat sinking to substrate Strong heat sinking to substrate 21
Temperature ( C) Curing degree (-) Photonic Soldering: Simulation Temperature dependent material properties (irreversible) Soldering behavior is defined by three parameters: Activation temperature (T act. ), Effective curing time (t eff ), Accelerated Curing Factor (ACF) Thermal conductivity (heat sinking) increases with the curing degree 4 35 T decomposition 1 dt c t c 3 ACF 25 2 15 T activation Curing profile 1 t effective 5 5 1 15 2 Time (milliseconds) Effective time (s) 22
Photonic Soldering: Simulation Temperature profile & Soldering behaviour Soldering parameters: T act. : 18 C, t eff. : 1 ms, ACF: 2 Thermal conductivity of the bump: 1 6 W/mK, pre-dried soldered Temperature Soldering 23
Resistance (Ω) Temperature ( C) Average curing degree (-) Temperature ( C) Photonic Soldering: Simulation Validation A good fit between experimental and simulated data was found Peak temperature of the chip is 35 C, which is close to ablation Model can be used to predict soldering behavior various chips sizes 1 24 1 Curing Probe Track Chip 4 1 21 18 15,9,8,7,6 36 32 28 24 1 12,5 2,1 9 6 3,4,3,2,1 16 12 8 4,1 5 1 15 2 25 Time (milliseconds) 5 1 15 2 Time (milliseconds) 24
Curing degree (-) Temperature ( C) Photonic Soldering: Simulation Geometry dependency Significant influence of the chip geometry on the soldering behavior Thicker chip Higher fluence Larger chip Lower fluence The pulse settings need to be tuned for the chip geometry 1 Curing Probe Track Chip 4 1 Curing Probe Track Chip 6 1 Curing Probe Track Chip 4,9,8,7,6 36 32 28 24,9,8,7,6 54 48 42 36,9,8,7,6 35 3 25,5 2,5 3,5 2,4,3,2,1 16 12 8 4,4,3,2,1 decomposition 24 18 12 6,4,3,2,1 15 1 5 5 1 15 2 Time (milliseconds) 5 1 15 2 Time (milliseconds) 5 1 15 2 Time (milliseconds) 4 µm thick chip 2 mm 2, 2 µm thick chip 2 mm 2, 4 µm thick chip 25
Summary Photonic Curing Fast method for achieving highly conductive structures Printed (flexo, inkjet, screen, etc.) to fully cured within seconds Two stage processing for limited substrate deformation Photonic Soldering Enables soldering on temperature sensitive substrates (PET, paper) Highly efficient and roll-to-roll compatible 3D simulation is necessary to understand process (in progress) PulseForge equipment State-of-the-art photonic curing equipment Enables roll-to-roll production of printed electronics 26
Acknowledgements Holst Centre Gari Arutinov, Daan van den Ende (Philips), Guy Bex, Eric Rubingh, Robert Abbel, Pit Teunissen, Pim Groen, Jeroen van den Brand Modelling Erica Coenen (TNO) Software and Data acquisition Henk Steijvers (TNO) Temperature probes Tom Geuns (Philips) 27
Thank you Rob Hendriks Research Engineer Ph: +31 ()4 42429 rob.hendriks@novacentrix.com Harald Moder Merconics Ph: +49 173 5627425 haraldmoder@merconics.com 28