LBNL CCD Packaging“Yale Mount” Mechanical Analysis

Dan Cheng

LBNL

4/19/2003 Dan Cheng 2

First Guess for SNAP

1.4mm thick AlN substrate with 200m via’s, not under bumps or CCD

CCD, 200m thickGold bump (flattened wire bond bump)applied in house

Underfill with Epotek301-2 glue at 60oC

Gold platedInvar

Connector mounted to Invarwith spring loaded pins against AlN

AlN circuits from COORS

Bumps on AlN appliedat 4” wafer size levelthen diced

No success yet in wafer scale bump bonds with AlN…dicing leaves large chips on edges

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Yale CCD Mount

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Solid Model Geometry (Pro/E)

Rear View

Front View

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Quarter-Symmetry Solid Model

CCD(200 microns thick) Substrate

(1.5-mm thick AlNOr 2-mm thick Si)

EA9361 Epoxy(250 microns thick)

Molybdenum Base(~5-mm thick)

EPO-TEK 301-2(50 microns thick)

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Finite Element Mesh

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FEA Notes

• Quarter-symmetry model

— Approximately 80,000 elements

• Symmetric boundary constraints

— X- and Y- symmetry planes fixed, allowed to “slide”

— Z-symmetry plane about square hole fixed in Z-direction

• Most material properties are temperature-dependent

— With the exception of some Young’s Modulus numbers

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FEA Assumptions

• Mounting holes

— Assumed constraints—see previous slide

• Did not model Gold/Indium bump bonds

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FEA Notes

• Ran four cases

— Case 1: AlN Substrate, Square hole

— Case 2: Si Substrate, Square hole

— Case 3: AlN Substrate, Square hole w/Fillets

— Case 4: Si Substrate, Square hole w/Fillets

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FEA Epo-Tek Stress Contour Plot

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FEA AlN Substrate Results

Case 1, ALN Substrate, Square Hole

Max Z Displacement 24 microns At corner edge

Max VM Stress 347 MPa

~50 ksi

Corner of square hole in Moly

CCD Max Stress 26 MPa

3.7 ksi

Max. Substrate Stress

51 MPa

7.4 ksi

EA9361 Joint 37 MPa

5.4 ksi

Closer to 18-20 Mpa average (2.7 ksi)

Epo-Tek 301-2 Joint 7.5 MPa

1.1 ksi

Bending shear*

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FEA Si Substrate Results

Case 2, ALN Substrate, Square Hole

Max Z Displacement 28 microns At corner edge

Max VM Stress 325 MPa

~47 ksi

Corner of square hole in Moly

CCD Max Stress 17 MPa

2.5 ksi

Max. Substrate Stress

64 MPa

9.3 ksi

EA9361 Joint 36 MPa

5.4 ksi

Closer to 18-20 Mpa average (2.7 ksi)

Epo-Tek 301-2 Joint 6.6 MPa

.9 ksi

Bending shear

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FEA AlN Substrate Results #2

Case 3, ALN Substrate, Square Hole with Fillets

Max Z Displacement 25 microns At corner edge

Max VM Stress 305 MPa

~43 ksi

Corner of square hole in Moly

CCD Max Stress 25 MPa

3.5 ksi

Max. Substrate Stress

50 MPa

7.4 ksi

EA9361 Joint 34 MPa

4.9 ksi

Closer to 18-20 Mpa average (2.7 ksi)

Epo-Tek 301-2 Joint 7.4 MPa

1 ksi

Bending shear*

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FEA Si Substrate Results #2

Case 4, ALN Substrate, Square Hole with Fillets

Max Z Displacement 30 microns At corner edge

Max VM Stress 276 MPa

~40 ksi

Corner of square hole in Moly

CCD Max Stress 15 MPa

2.2 ksi

Max. Substrate Stress

64 MPa

9.3 ksi

EA9361 Joint 35 MPa

5.4 ksi

Closer to 18-20 Mpa average (2.7 ksi)

Epo-Tek 301-2 Joint 6.6 MPa

.9 ksi

Bending shear

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FEA Summary

• Some material properties need to be defined at operating temperature (140 K)

• Current design shows critical Epo-Tek joint at above Yield Stress of 926 psi (may change with model)