Bump Bonding Development By: Bert Harrop Princeton University 12-2008

PRISM Technical Support Staff: Facility: Princeton Institute for the Science and Technology of Materials (PRISM) 5000 sq/ft Class 100/100 Cleanroom Micro/Nano Fabrication Laboratory The lab has a complete range of thin-film formation techniques available, such as plasma-enhanced chemical vapor deposition, thermal and electron-beam evaporators, sputterers, and high-temperature diffusion and oxidation. Another strength of the lab is pattern transfer by plasma, with five reactors dedicated to etching a wide range of thin films. The recent focus on nanopatterning capabilities prompted an installation of the state-of-the-art laser writer, nanoimprinter, and a modern electron beam writer. PRISM Technical Support Staff: Prism has a full technical support staff of fabrication Engineers that provide industry insight on the latest in micro/nano fabrication. 2

Metal’s Deposition Photo-Lithography 3 3

Diamond after TiW UBM application Titanium Tungsten Under Bump Pixel Metalization (UBM Lift-off Process) Equipment: Karl Suss’s MA-6 (2.0mW/Cm) Angstrom Engineering’s Metal Sputterer Pattern diamond (Photolithography) Sputter TiW 800-1000Å Liftoff Mask Anneal Diamond after TiW UBM application 4

Karl Suss’s MA-6 Angstrom Engineering’s Metal Sputterer 5

Indium Bump Prep During the spinning of photo-resist on a sample, there is a build-up of resist, concave meniscus, that occurs at the diamond edges. In order to get the best resolution using contact lithography, it is necessary to have intimate contact between the diamond and the photo-mask. We eliminated this edge bead on the 4.5mm diamond by placing a silicon frame around it leaving the build up on the sacrificial frame edge, that is removed prior to imaging, rather than on the diamond. 6

6-in Headway Spinners 7

Thick Photo-resist Diamond Lithography This is a 2 layer thick photo-resist liftoff process. The first layer is a flood exposed layer which allows the mask to be removed easily after indium has been evaporated onto the diamonds surface. The second layer is the patterned layer creating the opening where the indium will be deposited. Photoresist: ROHM SPR-220-4.5 1st Layer (8-9um) 2nd Layer(6-7um) 8

Indium Bumped Diamond Indium Bump Evaporation Equipment: Edwards/E306A Evaporator Coating System Deposit 7-10um of Indium Liftoff Photo-resist Mask Indium Bumped Diamond 9

Edwards/E306A Indium Evaporator Coating System TePla M4L O2 Plasma Etcher/Asher 10

1st Run of Indium Bumped Diamond Sensors ~80% Bump yield Sensor – PLT_17 PLT_17 ROC 11

2nd Run of Indium Bumped Diamond Sensors ~99% Bump Yield Sensor – PLT_21 PLT_22 ROC 12

Bumped Diamond Bumped ROC Bump Bond Diamond to ROC Equipment: Research Devices M8A (Flip Chip Bonder) Calibrate using glass die as per system instructions achieving ≤ 2um accuracy. Load Diamond bonding profile into the bonder (5Kg @ 30ºC). Align the respective contact bumps (X, Y, Z, Roll, & Pitch) of Diamond and ROC Run/Bond profile Bumped Diamond Bumped ROC 13

Research Devices M8A Kulike & Soffa 1470 Wire Bonder Flip Chip Bonder 14

Bump Bonded Diamond & ROC 15

Plane Assembly Mounting of the Hybrid Flex to the Hybrid Backer Board Place the woven glass hybrid backer board onto the bottom of the alignment fixture. Place the preformed epoxy sheet onto the fixtures alignment edge mark. Place the hybrid flex circuit over both the backer and epoxy. Place the alignment fixture top over the alignment dowels onto the top of hybrid epoxy stack and bake @ 100ºC for 15mins. Remove and cool. Inspect. Mounting of the ROC/Diamond to the Flex Hybrid/Backer Board With the hybrid flex assembly on the alignment fixture place the epoxy mask over it and screen the epoxy onto the hybrid assembly. This will leave a 75um layer of epoxy onto the flex where the ROC/diamond will be placed. Using a ceramic tweezer and a stereo boom microscope place the ROC/diamond onto the flex aligning the two vias along the x axis, and four along y. They define the top, left corner of the chip. (Microscope assisted placement accuracy ~ 50-75um) 3) Allow for the epoxy to set overnight before wire-bond and potting. 16

Wire bonding and Potting Place the hybrid assembly onto the bonding stage into the bonding chuck. Place the K-n-S 1470 auto bonder into semi-automatic mode and load the the PLT macro. Place the crosshairs onto ROC pad #1 lower left corner and enter the XY0 location This is also your ref point #1. Place the crosshairs onto ROC pad#35 (opposite end pad) and enter that location as ref point #2. Place your crosshairs onto Hybrid Flex pad #1 and enter that location as ref point #3. Place your crosshairs onto Hybrid Flex pad #35 and enter that location as ref point #4. Single step using the enter key and place all 35 wires. Draw a syringe of potting epoxy across the wire bonds and let set overnight. 17