LASOR research supported under DARPA/MTO DoD-N Program Award Number W911NF Packaging Emily F. Burmeister, Walter Yuen, Henrik N. Poulsen, John P. Mack, John E. Bowers, Daniel J. Blumenthal

DOD-N PI Review, November 6-7, Santa Barbara, CA2 Buffer Packaging First package has been completed successfully. Largest challenge - fiber affix. However reasonable coupling efficiencies to spot size converters were achieved (-3.9 dB, -4.7 dB, -6.2 dB, and -7.4 dB) for the four ports of the first package.

DOD-N PI Review, November 6-7, Santa Barbara, CA3 Buffer Assembly Order Assembly order is critical 1. Chip on carrier, wirebonds (AuSn 2. Carrier on submount (In solder 3. Fan-out boards to package (In solder 4. Surface mount thermistor (Ag 5. Submount to TEC and TEC to package (epoxy or _ ˚C) 6. Solder TEC leads to fan-out board 7. Wirebond to fan-out boards and package pins (100 ˚C) 8. Bring chip to operating conditions and perform fiber attach using UV-curing low-shrink epoxy

DOD-N PI Review, November 6-7, Santa Barbara, CA4 Buffer Packaging Innovations and Challenges Innovations  Detachable wall allows for easier fiber manipulation and attach  Fiber assemblies have not been implemented in the first package, but should allow for easier fiber alignment as well and more strain relief. Challenges  Achieving the right heights for fiber epoxying is difficult Epoxying the fiber directly to the carrier can be too little height difference. 100 micron additional height difference provided by submount is too much.

DOD-N PI Review, November 6-7, Santa Barbara, CA5 A Super Cooler for High Heat Flux and Localized Heating Applications W. W. Yuen J. P. Tu Department of Mechanical Engineering University of California, Santa Barbara, Calif

DOD-N PI Review, November 6-7, Santa Barbara, CA6 Gene Tu and Walter Yuen Passive Hybrid Super-Cooler Motivation Goals: To allow operation of a high power device at room temperature (20 ˚C) without the use of a thermoelectric cooler; thus saving overall power consumption The passive cooler should be able to dissipate up to 2 W by natural convection. With internal fins, we anticipate that it can dissipate 5 W or more.

DOD-N PI Review, November 6-7, Santa Barbara, CA77 Package Selected for the Current Study

DOD-N PI Review, November 6-7, Santa Barbara, CA88 Numerical Modeling To assess the effect of replacing a “supporting” packaging material (Kovar, k = 17.3 W/m-K,  = 4.6e-6 m 2 /s) with Carbon Foam (k = 135 W/m-K,  = 3.59e-4 m 2 /s) InGaAsP (Active region) InP AlN Kovar TE-cooler Side view 0.1mm 2mm AuSn solder (280 o C) AuSn solder (280 o C) 5 microns 5mm Keep 20 o C Assuming 1W, 1.5W, and 2W heat flux InSnPb solder (95 o C) Top view 5.5mm 5.8mm 0.5mm 5.5mm 20mm

DOD-N PI Review, November 6-7, Santa Barbara, CA99 Use of Carbon Foam to Enhance Cooling Replacing Kovar with Carbon Foam completely or with a “cold finger” configuration

DOD-N PI Review, November 6-7, Santa Barbara, CA10 Preliminary Results (Numerical) Detail of the “cold finger” configuration

DOD-N PI Review, November 6-7, Santa Barbara, CA11 Numerical Simulation Steady State Result (Power = 5W, Q = 200 W/cm 2, TEC on (2V))

DOD-N PI Review, November 6-7, Santa Barbara, CA12DOD-N PI Review, November 6-7, Santa Barbara, CA12 Design of a Super Cooler Passive Hybrid Super-Cooler Structure AlN, Kovar and Carbon/carbon foam will be brazed together to minimize thermal resistance Foam will be saturated with liquid (water) and the wicking effect to ensure liquid re-circulation (heat pipe effect) Operating At room temperature (20 ۫ C) Interior evacuated to low pressure so water will boil at less than 40 C Expect to dissipate up to 2W by nature convection (with no thermoelectric cooler) With external fins, expect to dissipate up to 5W

DOD-N PI Review, November 6-7, Santa Barbara, CA13DOD-N PI Review, November 6-7, Santa Barbara, CA13 Design of a Super Cooler Copper Cover Dimension D = 1.18 in. L = 2.13 in. Thickness of Carbon Foam Shell d = 0.16 in.

DOD-N PI Review, November 6-7, Santa Barbara, CA14 Experimental Setup Heater Super Cooler Electrical Connection to Power Supply Reflecting Mirror

DOD-N PI Review, November 6-7, Santa Barbara, CA15 Experimental Setup Infrared Camera

DOD-N PI Review, November 6-7, Santa Barbara, CA16 Test Conditions for a 30-sec Run Heating Data Heating area: 0.5 mm x 5 mm Resistance: 25 Ohm Input Voltage 10 Volt Input Power 4 Watts Input Flux 160 W/cm 2 Heating Duration 30 sec.

DOD-N PI Review, November 6-7, Santa Barbara, CA17 Initial Temperature Rise, 0 < t < 5 sec,  t = 0.25 sec. Gene Tu and Walter Yuen Passive Cooler Experiment: Temperature Rise Huge power output from heater leads to a fast rise, but begins to level off.

DOD-N PI Review, November 6-7, Santa Barbara, CA18 Temperature Transient, 5 < t < 30 sec,  t = 2.5 sec. Gene Tu and Walter Yuen Passive Cooler Experiment: 4 Watt Heater Can observe that temperature levels off below 40 ˚C.

DOD-N PI Review, November 6-7, Santa Barbara, CA19 End of Heating Period, 30 < t < 32 sec,  t = 0.1 sec. Gene Tu and Walter Yuen Passive Cooler Experiment: Cool Down After heater is turned off, temperature drops quickly, demonstrating that the passive cooler may be especially useful for pulsed operation.

DOD-N PI Review, November 6-7, Santa Barbara, CA20 30-sec.vs. 60-sec Run

DOD-N PI Review, November 6-7, Santa Barbara, CA21 Summary and Future Works Heat Transfer Capability of Super Cooler More data on operations under Steady State Periodic Heating Pulse Effect of heater orientation and forced convection Fundamental Work on Two-Phase Heat Transfer in Carbon Foam Boiling characteristic, wetting characteristics on carbon foam What is the critical heat flux, i.e. heat transfer limit More basic understanding on the fundamental heat transfer and fluid mechanics Fabrication issues Add fin to external surface to enhance natural convection Brazing between carbon foam with other electronic packages (e.g. materials other than AlN, Copper and Kovar)