Another Modular Focal Plane: Part 1 – Sub-modules Bruce C. Bigelow University of Michigan Department of Physics 5/17/04

2 Focal 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

3 Focal 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-modules This talk:  sub-module designs  sub-module FEA

5 IR sub-module Rockwell H2RG package

6 IR sub-module Rockwell H2RG package with filter and frame

7 IR sub-module Rockwell H2RG package on moly MZT sub-plate

8 IR sub-module Rockwell H2RG 3 x 3 sub array

9 IR sub-module 3 x 3 sub array with flexure mounts

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

11 IR sub-module Finished IR module with aperture mask

12 CCD sub-module Finished CCD module with aperture mask

13 Sub-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

14 Sub-module static FEA (meters) Sub-module, Gy, Y deflection = 1.1 microns

15 Sub-module static FEA (meters) Sub-module, Gy, Z deflection = +/- 0.3 microns

16 Sub-module static FEA (meters) Sub-module, Gz, max. Z deflection = 0.8 microns

17 Sub-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

18 Sub-module dynamic FEA Moly sub-plate and Invar flexures – first mode Mode/Freq

19 Sub-module dynamic FEA Moly MZT sub-plate and flexures – third mode Mode/Freq

20 Sub-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

21 Sub-module thermal FEA Elements: Purple = Invar Red = Moly

22 Sub-module thermal FEA Purple = invar Red = moly Max stress at Invar/Moly joint (not realistic), 86.8 MPa (12,557 Psi), (Invar yield ~ 250 MPa) (Pascals)

23 Sub-module thermal FEA Purple = invar Red = moly Shrinkage of Invar vs. Moly in X direction, +/- 50 microns (meters)

24 Sub-module thermal FEA Purple = invar Red = moly Shrinkage of Invar vs. Moly in X direction Sub-plate displacement in Z direction – 15 microns (meters)

25 Sub-module thermal FEA Purple = invar Red = moly Shrinkage of Invar vs. Moly in X direction Sub-plate displacement in Z direction – 15 microns (meters) Distortion of mounting surface ~2 micron

26 FP 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