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Research Papers

Lid-Integral Cold-Plate Topology: Integration, Performance, and Reliability

[+] Author and Article Information
Gerd Schlottig

IBM Research–Zurich,
Rüschlikon 8803, Switzerland
e-mail: erd@zurich.ibm.com

Marco de Fazio

Advanced System Technology,
ST Microelectronics,
Burlington, MA 01803

Werner Escher, Thomas Brunschwiler

IBM Research–Zurich,
Rüschlikon 8803, Switzerland

Paola Granatieri

Custom MEMS Division,
ST Microelectronics,
Agrate Brianza 20864, MB, Italy

Vijayeshwar D. Khanna

IBM Research–T.J. Watson Research Center,
Yorktown Heights, NY 10598

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 25, 2015; final manuscript received January 8, 2016; published online March 10, 2016. Assoc. Editor: Toru Ikeda.

J. Electron. Packag 138(1), 010906 (Mar 10, 2016) (7 pages) Paper No: EP-15-1094; doi: 10.1115/1.4032493 History: Received September 25, 2015; Revised January 08, 2016

We demonstrate the lid-integral silicon cold-plate topology as a way to bring liquid cooling closer to the heat source integrated circuit (IC). It allows us to eliminate one thermal interface material (TIM2), to establish and improve TIM1 during packaging, to use wafer-level processes, and to ease integration in first-level packaging. We describe the integration and analyze the reliability aspects of this package using modeling and test vehicles. To compare the impact of geometry, materials, and mechanical coupling on warpage, strains, and stresses, we simulate finite element models of five different topologies on an organic land-grid array (LGA) carrier. We measure the thermal performance in terms of thermal resistance from cold-plate base to inlet liquid and obtain 15 mm2 K/W at 30 kPa pressure drop across the package. We build two different topologies using silicon cold-plates and injection-molded lids. Gasket-attached cold-plates pass an 800 kPa pressure test, and direct-attached cold-plates fracture in the cold-plate. The results advise to use a compliant layer between cold-plate and manifold lid and promise a uniformly thick TIM1 layer in the Si–Si matched topology. The work shows the feasibility of composite lids with integrated silicon cold-plates in high heat flux applications.

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Figures

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Fig. 1

The difference between the lid-attached and lid-integral cold-plate topologies: vicinity to the heat source eliminates a thermal interface layer (TIM2)

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Fig. 2

Section through the assembled stack showing manifold on cold-plate on test vehicle (a), with a magnified die edgewith one access slit to the microchannel region (b), the corresponding magnification for the gasket design D1 (c), and a magnified microchannel detail recorded by scanning electron microscopy (SEM)

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Fig. 3

(a) Schematic of the quarter model, simplified sectional view, not to scale, measured in µm and (b) top view. The quarter is 25 mm wide.

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Fig. 4

Schematic showing manifold duct volume, side view with test vehicle position, top view with heat-exchanging area covered by the cold-plate, and the magnified microstructure of the cold-plate

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Fig. 5

Schematic of the silicon cold-plate fabrication: structuring and bonding of two 8 in. wafers

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Fig. 6

Overview photograph of the silicon cold-plate and SEM image of the pin fin structures in the microchannel layer seen through the access opening of the cold-plate

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Fig. 7

Heaters and temperature sensors on the test-vehicle die (21 × 25 mm2) that was bonded to the lid-integrated cold-plate

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Fig. 8

Schematic showing the test setup

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Fig. 9

Injection-molded manifold (top side, left) and the same with the integrated cold-plate (bottom side, center) and connectors as well as with an assembled test vehicle. The substrate edge length is 50 mm. Two of the four openings are intentionally closed by plugs here for processing reasons.

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Fig. 10

Pressure drop and thermal resistance Rth,cpbase-inlet plotted against volumetric coolant flow, as well as the thermal efficiency as the ratio of pump power to heater power

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Fig. 11

Results of TIM opening strains in percent of the initial layer thickness (a), bottom-side warpage (b), corner solder-ball peel stresses (c), tensile and compressive stresses in the silicon cold-plate and (d) plotted for the four load steps and three TIM types

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Fig. 12

Simulated lid warpage of the bare injection-molded PPS GF40 manifold and conventional ductless copper lids

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Fig. 13

Warpage results of the injection-molded manifold at 165 °C temperature for both regions: seal band and cold-plate attach area. The cold-plate area warpage is relevant between 12 and 38 mm.

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Fig. 14

Pressure test results and observed failure mode: fracture of the silicon cold-plate, including fracture through the glass-frit bond

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