Development of Thermocompression Bonding for the Photodetector Top Seal for the LAPD Project

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1 Development of Thermocompression Bonding for the Photodetector Top Seal for the LAPD Project M.E. Kupfer, A.G. Raraz, and J.E. Indacochea GodParent Review Argonne National Laboratory October 22, 2010

2 Objectives Produce a seal between the window and the photodetector body sidewall that is vacuum tight and mechanically sound. Develop a reliable technique to produce seals with a lifetime of at least 10 years. The sealing temperature must be much lower than the maximum temperature that could damage the photocathode. Determine the short term stability of the selected sealant. Long term effects of aging.

3 Technical Approach Base materials: Side wall and top window (Borosilicate glass) Metal coated glass: Cr/In Other materials considered: Ag paste glass: Argonne NiCr coated glass (Fermi/Argonne) Sealing materials: In and In-based solders (52In/48Sn, In/3Ag) Rationale: Low temperature solders. Solders are oxidation resistant High plasticity and good wetting facilitate bonding between materials that may differ in CTE. Applications: gas tight joints of glass or quartz; in manufacturing of Vidicons.

4 Technical Approach Processing parameters: Temperature: 150 C Pressure: determined by cracking of either glass or frit bond. Time: the shortest possible but it will also depend on the applied pressure and temperature.

5 Solder Selection Advanced Materials & Processes/April 2005

6 Solder Selection and Aging RT Aging

7 Indium Sealing Schematic Two main steps Borofloat glass Compression Indium films Chromium films Borofloat glass Borofloat glass Borofloat glass Step 1 Step 2

8 Preliminary Efforts Summer 2010 Window-to-window samples

9 Heat-Press Setup Static Platen Heater

Cr/In Coated Samples: Window to Sidewall RT Compression

Joining glass members did not show a homogeneous coated

10 Cr/In Coated Samples: Window to Sidewall RT Compression Bonding Matting surfaces Sample did not bond after compression under a low applied force. On the window sample less spots were observed. Joining glass members did not show a homogeneous coated surface (agglomerates present) On the sidewall sample was observed flattened indium spots (due to shapes and shines differences)

Samples were rinsed in alcohol before observation.

11 Evaluation of coated samples: Cr/In coating -- Sample 1 Glass surface Coated surface ~ 250 nm Cr and ~ 650 nm In. Samples were rinsed in alcohol before observation. Surface imperfections (agglomerates) of irregular shape are observed. Pits are also observed. SEM analysis of agglomerates was done.

12 Cr/In Coated Samples Indium agglomerates in Cr coating

13 Window-to-window Samples: In-based Solders (50- m foils) Sample ID Date Coating Foil Pressure (psi) Temp (ºC) Time (min) WW-UC/48Sn/1000/22/5 9-Aug-10 Uncoated 52In-48Sn WW-UC/100In/1000/22/5 9-Aug-10 Uncoated 100In WW-Ag/100In/1000/100/5 9-Aug-10 Ag 100In WW-Ag/3Ag/1000/100/5 9-Aug-10 Ag 97In-3Ag WW-Ag/100In/1000/22/5 18-Aug-10 Ag 100In WW-Ag/100In/1000/150/5(M) 18-Aug-10 Ag 100In WW-Ag/100In/1000/150/5 18-Aug-10 Ag 100In

14 Silver Coated Samples Glass is revealed through these voids Uneven surface conditions (Polished)

15 Hermeticity

16 Bonding and Hermiticity tests: Tube samples Bonding parameters: - uncoated samples - 1 indium foil: (50 µm) psi (12.4 MPa) - 25 o C - 5 min

17 Window to Sidewall 1.25 Square Samples: Hermeticity Unpolished silver coated (Silver oxide on top of silver metal) Uncoated Details of surface morphology

2D 2D 2C 2C 2B 2B 2A 2A Dean s Flatness Data: Free Condition 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 0.001 0.001 2A 2A 0.000 0.000-0.001-0.001 0.001 2B 0.001 2B 0.000 0.000-0.001-0.001 0.001 2C 0.001 2C 0.000 0.000-0.001-0.001 0.001 2D 0.

18 2D 2D 2C 2C 2B 2B 2A 2A Dean s Flatness Data: Free Condition A 2A B B C C D D Points Points Equivalences: = 12.7 μm = 25.4 μm Zero - reference line The localized flatness data suggest that total height differences varies from 12.7 (sample 2A) μm to 38.1 μm (sample 2D) at this experimental conditions

19 Bonded Samples with One/Two foils 1 foil The silver paste coated bonded to an uncoated glass. Bonding with 1 foil shows more dullish appearance. 2 foils Dull spots (poor bonding, bad sealing) Sample 3A The uncoated samples after bonding show a shiny bonding area with dull spots too. Sample 2C

E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.

20 Leak Test (std cc/sec) Bonding of 1¼ x1¼ samples with two 50.0 m thick In foil: Hermeticity Baseline Leak Test: 1.25" Square samples (1200 psi, 100ºC, 15 minutes) 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 Ag Coated Uncoated Total Background Location 1 Location 2 Location 3 Ag paste Baseline Processing details: 1200 psi (8.3 MPa) / 100 C / 15 minutes in air; 2 foils (100 m) 1 width. Background = not reported No Ag paste

21 Bonding of 1 x1 Ag-coated samples with 100 m In: Hermeticity Background = 2.0 x 10-9 std. cc/s He Bonding Parameters Processing Time (min) psi (8.3 MPa) 110 o C Baseline 8 x 10-7 Max. Leakage 1 x 10-5 Baseline 3.3 x 10-6 Max. Leakage 3.6 x psi (8.3 MPa) 150 o C Baseline 5 x 10-8 Max. Leakage 8 x 10-7 Baseline 5 x 10-8 Max. Leakage 1.4 x 10-6 * Side wall cracked

22 Bonding of 1 x1 Ag-coated samples with 100 m In: Hermeticity

23 Bonding of 1 x1 Ag-coated samples with 100 m In: Hermeticity

test Issues: Surface homogeneity Thickness of deposit

24 Surface Appearance of Ag-coated samples Silver coated sidewall glass sample that cracked during bonding test Issues: Surface homogeneity Thickness of deposit Depositing parameters Silver coated window glass sample

25 Immediate Plans Determine maximum processing pressure: Need several 1 square samples with glass frit bottom seal to test. Tests will proceed using a conservative value: e.g. 75% and move up. Best if 8 x 8 glass with frit bottom tested. Decide on the most suitable tie layer for In sealing of photodetector. Layer must be: Uniform in thickness Smooth Establish optimum temperature and time based on new pressure in vacuum.

26 Immediate Plans (cont d) Continue with hermetic testing of new seals. Move into vacuum bonding fabrication of coated samples. Scale up experiments to 8 square tiles.

27 Equipment Considerations Vacuum chamber with hydraulic/pneumatic press. Heating devices: Induction Resistance Infrared Compatibility with other stages of manufacturing. At least 50 1 square samples with metal tie layer and indium coatings.

28 Fine Tuning of Process Parameters Temperature cannot exceed a value that can damage the photocathode 80ºC is a conservative limit to focus testing. Recall that the pressure to fracture the glass is affected by: Surface characteristics of glass, Uniformity of the metal coatings, and Size of the tile.

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