another modular focal plane: part 1 – sub-modules

Another Modular Focal Plane:Another Modular Focal Plane:Part 1 – Sub-modulesPart 1 – Sub-modules

Bruce C. Bigelow

University of Michigan

Department of Physics

5/17/04

2

Focal Plane Sub-modulesFocal Plane Sub-modules

Motivations: install/remove single detectors from “front” of FP assemble detectors in modules of 3 x 3

simplify assembly, integration, and test reduce part counts, simplify part design simplify part fabrication individual module thermal control (Vis vs. IR) optimize materials for detector packages (CTE)

local, discrete control of focal plane surface height minimize mechanical mass minimize thermal time constants minimize gravity deflections for ground testing maximize resonant frequencies

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Focal Plane Sub-modulesFocal Plane Sub-modules

Requirements: final focal plane flatness: +/- 25 microns support different optimal temperatures for Vis and IR detector temperature stability +/- 1K high stiffness – high first resonance

4

Focal Plane Sub-modulesFocal Plane Sub-modules

This talk: sub-module designs sub-module FEA

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IR sub-moduleIR sub-module

Rockwell H2RG package

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IR sub-moduleIR sub-module

Rockwell H2RG package with filter and frame

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IR sub-moduleIR sub-module

Rockwell H2RG package on moly MZT sub-plate

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IR sub-moduleIR sub-module

Rockwell H2RG 3 x 3 sub array

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IR sub-moduleIR sub-module

3 x 3 sub array with flexure mounts

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IR sub-moduleIR sub-module

Sub-array with CRICs, flex circuits, connectors, local IR electronics (cold), sub-plate heater

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IR sub-moduleIR sub-module

Finished IR module with aperture mask

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CCD sub-moduleCCD sub-module

Finished CCD module with aperture mask

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Sub-module FEASub-module FEA

FE Analyses: Static analysis – gravity deflections

package mass modeled by doubling sub-plate density moly packages and sub-plate, invar flexures omit package cutouts, mounting holes, etc. focal plane axis vertical and horizontal

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Sub-module static FEASub-module static FEA

(meters)

Sub-module, Gy, Y deflection = 1.1 microns

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Sub-module static FEASub-module static FEA

(meters)

Sub-module, Gy, Z deflection = +/- 0.3 microns

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Sub-module static FEASub-module static FEA

(meters)

Sub-module, Gz, max. Z deflection = 0.8 microns

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Sub-module FEASub-module FEA

FE Analyses: Dynamic analysis - vibration modes and frequencies

package mass modeled by doubling sub-plate density omit package cutouts, mounting holes, etc.

First resonance = 528 Hz for Invar/Invar case First resonance = 630 Hz for Moly/Invar case

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Sub-module dynamic FEASub-module dynamic FEA

Moly sub-plate and Invar flexures – first mode

Mode/Freq.

1. 630

2. 630

3. 654

4. 1289

5. 1376

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Sub-module dynamic FEASub-module dynamic FEA

Moly MZT sub-plate and flexures – third mode

Mode/Freq.

1. 630

2. 630

3. 654

4. 1289

5. 1376

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Sub-module thermal FEASub-module thermal FEA

Thermal analysis – stress and distortion omit package cutouts, mounting holes, etc. omit package mass, stiffness -160 K temperature shift static, isothermal analysis no effort yet to optimize flexure design no effort yet to optimize stiffness of sub-plate

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Sub-module thermal FEASub-module thermal FEA

Elements:

Purple = Invar

Red = Moly

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Sub-module thermal FEASub-module thermal FEA

Purple = invar

Red = molyMax stress at Invar/Moly joint (not realistic), 86.8 MPa (12,557 Psi), (Invar yield ~ 250 MPa)

(Pascals)

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Sub-module thermal FEASub-module thermal FEA

Purple = invar

Red = molyShrinkage of Invar vs. Moly in X direction, +/- 50 microns

(meters)

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Sub-module thermal FEASub-module thermal FEA

Purple = invar

Red = molyShrinkage of Invar vs. Moly in X directionSub-plate displacement in Z direction – 15 microns

(meters)

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Sub-module thermal FEASub-module thermal FEA

Purple = invar

Red = molyShrinkage of Invar vs. Moly in X directionSub-plate displacement in Z direction – 15 microns

(meters)

Distortion of mounting surface ~2 micron

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FP sub-modulesFP sub-modules

Conclusions: sub-module designs for Vis and IR developed

• detector packages

• filters with mounts

• sub-plates

• sub-plate mounting flexures

• electrical connectors, junction boxes FEA demonstrates stiffness, high resonant freq. FEA demonstrates acceptable thermal performance