Advances in Printing nano Cu and Using Existing Cu Based Manufacturing Processes Michael J. Carmody Chief Scientist, Intrinsiq Materials
Why Use Copper? Lower Cost than Silver. Print on Numerous Substrates. Reduce Electro migration - Reduce shorting of adjacent traces in fine line and pitch patterns. Equipment Agnostic. World is Tooled to Process Copper: Seamlessly Fits into Established Downstream Global Copper Based Manufacturing Processes (solder mask, soldering, plating, etc.). Objective: Show that copper can fit into time-tested and developing electronics manufacturing processes 2
IM Nanoparticle Production and Formulation Inks Rapid Prototyping Process flexibility Process control Fully instrumented Pilot Plant Annual capacity pastes/inks: ~1 tonne Analysis Extensive Scientific Testing facilities SEM / STEM / EDX Screen Pastes
Four Applications, Various Deposition Methods, Substrates, Sintering Methods, and PCB Processes Application Deposition Method Fluid Substrate Sintering Method Bulk Factor/Adhesion Automotive Lighting Screen Print Inkjet Print Paste LCP Formic Acid / Nitrogen 7X / 5B Cu Foil Slot Die Ink Kapton Pulse Forge 12X, 10 N/cm Wiring Harness Screen Print Paste PET Formic Acid / Nitrogen 7X / 5B 3D Conformal Parts Optomec AJ Ink Kapton Laser 4X / 5B
Molex ASEP Process Steps 1 2 3 4 5 6 7 8 9 10 11 1. Stamp 2. Mold 3. Surface Pattern 4. Print (Screen Print or Inkjet) 5. Sinter (Heller Industries) 6. Electroplate Cu and Sn 7. Soldermask 8. Solderpaste 9. Place Components and Reflow 10. Remove Electrical Connections and Test 11. Remove from Carrier and Final Assembly 5
Advantages of the Application Specific Electronics (ASEP) Process v Standard PCB Additive vs subtractive (saves 20 steps) Package Use Common Surface finishes like ENEPIG (Electroless Ni Electroless Pd and Immersion Au) can be used for wire bonding bare die, solderability, and connector interfaces. Uses far less water than standard PCB process 20 gallons/m^2 v 400 gallons/m^2 for standard boards Molded plastic can be recycled (instead of thrown in a landfill) Lower total cost
Automotive Testing 1. Multi-layer circuitry 2. Three dimensional feature capable 3. Integrated connector function 4. Integrated rigid PCB functions 5. Integrated flexible circuit functions 6. Thermal management features 7. High current carrying features can be integrated 8. Could be used to combine first and second level silicon packaging 9. Fully additively manufactured which minimizes water use 10. Hermetically sealed interfaces are inherently possible 11. Continuously flow manufactured which minimizes Accelerated Life Testing -Cycling from -40 C to 85 C over 1000 hours -All parts passed Under the Hood Testing (on the previous parts) -Temperature range extended to -40 C to 110 C -All parts passed labor cost 12. Highly automated manufacturing improves yields and reliability 13. Minimizes the need for secondary assembly through part integration 14. Validated for automotive under the hood applications (-40 to 110 C)
Process Flow for Ultra Thin Copper Foil Slot die coat Photonically Sinter Plate and Etch
14 Ave Peel as f(overlap Factor) Peel Strength (N/cm) 12 10 8 6 4 2 0 0 5 Overlap Factor10 15 20 We optimized peel strength as a function of Pulse Forge sintering parameters. Statistically, our best conditions averaged 9.5+/-0.6 N/cm for 18 samples. Conditions giving the best conductivity are not necessarily best for peel strength
Etching Results Etch results were excellent Very straight side walls due to very thin base copper to be etched. Profilometry graph and cross section pictures show very straight side walls. Very important for high speed and RF Designs.
Process Flow for Conformal 3D Printing Figure 2. Optomec AJ5X System, Tilt & Rotate Trunnion. 130 micron line width Optomec Jetting 808 nm Laser Test
Laser Sintering Copper on Kapton Not All Applications Need Bulk Copper Conductivity Resistivity (x bulk Cu) 14 12 10 8 6 4 2 0 0 200 400 600 800 Laser Power (mw) Resistance as a function of laser power at 5 mm/s scan speed 10 9 8 7 6 5 4 3 2 1 0 0 5 10 15 20 Scan Speed (mm/s) Resistance as a function of scan speed with laser power at 300 mw Resistivity (x bulk Cu) 12
Post Sinter Processing 5B ranking on Kapton according to ASTM3359 SnPb with flux Uniform wetting of pad Unlike Ag pads, no savaging of metal by the solder is observed
Flex Application: Strain Gauges Copper strain gauge Wheatstone Bridge Circuit diagram Cyclic bending over 28 mm diameter pipe (0.3% strain) More than 10,000 flexes without signal degradation 14
Traditional Cable Harness vs. Printed Copper on PET -Bulky, heavy and limited flex because of insulation -Labor intensive to manufacture -Lighter, fewer cable ties and fasteners and more flexible. Print only copper needed. -Process is very automated
Lightweight Cable Assembly on PET -1 wide X 3 long -Laminated with PET cover -10X Bulk Cu resistivity -Able to easily change digital tooling -Inexpensive materials -No changes to standard screen printing technology required Don Novotny: DNovotny@intrinsiqmaterials.com 16
Sintering in the Heller Conveyor Oven -190 C -7.5% Formic Acid in Nitrogen -Conveyed at 5 inches / minute Large area screen printing at Swansea University
A Screen Printed, Heller Sintered Prototype Circuit Intrinsiq Confidential
Conclusions Sintered Copper materials can be printed on low Tg Flexible Substrates, plated and etched using conventional PCB process common world wide. After sintering and common overcoating, copper survives solder reflow temperatures. Manufactured parts with Copper can survive large, real world temperature testing (1000 hrs) and bend cycles (10,000 cycles). A variety of sintering conditions were used. A variety of deposition methods were employed.
Special Thanks Nextflex Molex-Vic Zaderej NovaCentrix-Vahid Akhavan Optomec-Mike Renn and Matt Schrandt Heller Industries-Dave Heller & Michael Barnes Intrinsiq colleagues in the US and UK