Title: LSST detector components and assemblies: Metrology issues
1LSST detector components and assembliesMetrology
issues
- Peter Z. Takacs
- Brookhaven National Laboratory
- 23 March 2005
- LSST Camera Project Meeting
- SLAC
This research was sponsored (in part) by the U.S.
Department of Energy under Contract No.
DE-AC02-98CH10886.
2Detector Metrology Issues
- Focal plane flatness requirements - from proposal
draft doc 2/9/05 - Measure over temperature range and at various
angular attitudes - What does it take to insure these requirements
are met?
1 µm 0.000040 2.5 µm 0.0001 1 ?
0.6 µm
3Example of what could happen
- Several microns of bow and twist possible in
detector surface
4FPA Metrology Error Budget
- Goal - Focal plane planarity 10 µm PV over 64cm
dia. area - Maintain planarity at -100C and at 45 tilt
attitude angle. - FPA comprised of
- CCD modules
- Raft plates
- Raft assemblies
- Integrating structure
- Adjustable kinematic mounts
- Other items hanging from raft assemblies
- Specified tolerances
- CCD module planarity 5µm PV
- Raft plate planarity and parallelism 1.0µm
- Raft assembly planarity 6.5µm PV
- Integrating structure planarity 1.0µm,
attitude deflection 1.0µm - Measurements on individual components and
subassemblies required to insure final tolerances
5FPA component structures
5 µm
1 µm
1 µm
6CCD module metrology
Require non-contact measurement methods
- PMI Interferometer for surface flatness -
aperture 60mm - White-light micro PMI for edge height
discontinuity - Gauge block reference for absolute height
- Vendor guarantee on absolute height (?)
PMI ? Phase Measuring Interferometer
7CCD module metrology considerations
- 201 live individual sensor modules
- Planarity 5µm over 40x40 mm2 area
- Datum plane defined by shoulders on 3 pins
- Absolute height (piston) and tilt relative to
datum is important - General case is warped CCD surface --gt not flat
- Do we believe vendor???
- Warping and distortion after cryo test cycles?
- Height measurement requires non-contact optical
method - Use gauge block as absolute standard
- White-light micro PMI needed for comparison
measurement - Conventional PMI required for non-contact 2D
topography measurement - Useful for in-situ measurement through dewar
window during cryotesting
8Raft plate metrology
- Area 120 x 120 mm2
- Measure before any items assembled onto it
- Thickness tolerance 1µm
Unknowns Kinematic mount configuration - impact
on thickness tolerance??? Measure plate with
kinematic mount assembled?
9Raft plate metrology considerations
- Raft construction - 120 x 120 mm2
- Double-sided plates, top surface lapped plano to
1µm - Thickness secondary issue. Adjust with kinematic
mounts? - Is 1µm PV parallelism tolerance too tight?
- Insure planarity - want no bowing or twisting
- Changes vs. time and temperature -- causes
deformation - Measure surface 2D topography
- Easiest method by conventional PMI -- 200mm
aperture - Require top surface to be specular reflector --
lapped smooth - Full aperture in one measurement - short time
- Contact probe if non-specular surface -- discrete
points - Need CMM with lt 1µm accuracy
- Not good for in-situ cryotesting
- Takes time for complete surface measurement
10Raft assembly metrology
- Flat and coplanar 6.5 µm PV
- Absolute height with kinematic mounts attached,
ZR - Distortion at cryo temperatures and off-normal
attitudes - Surface deformation of modules after assembly -
torque effects from pins
11Raft assembly metrology considerations
- CCD module mounting pins - force and torque
transmission into surface - Easy with 200mm PMI
- Kinematic mount static height adjustment
- Need to know absolute height of detector plane
above IS surface - Require dummy IS reference surface during
assembly - Gauge block standard with micro PMI for absolute
edge heights - Edge discontinuity between modules ? height
ambiguity - Requires white light PMI
- Full aperture (200mm) PMI for dynamic surface
distortions - Configure for viewing through dewar window and at
45
12FPA Integrating Structure metrology
Nominal max OD 1 meter
- Planarity tolerance 1 µm PV
- Interface to raft assemblies through kinematic
mounts - Map topography of interface surfaces
- Measure distortion vs. temperature and attitude
- Testing with unassembled raft plates installed???
- Requires BIG interferometer
13FPA metrology
- Assemble rafts onto IS
- Edge height continuity
- Dynamic distortion vs. attitude and temperature
- Monitor changes over time
- Full aperture measurement requires steerable
750mm dia aperture PMI
14Major optical instrumentation required
- White-light micro PMI
- Eliminates edge height ambiguity
- Microscope-based system
- ADE Phase Shift MicroXAM w/200mm stage
- 200mm aperture PMI
- Add beam steering for attitude testing
- (Fisba stock item, on order)
- 750mm aperture white-light Fizeau PMI
- with variable optical delay line
- 4D Technology concept with Jim Burge, UofA
15FPA instrumentation issues
- 200mm aperture Twyman-Green PMI interferometer
- Available from Fisba, currently on order, 110K
- Customize for variable attitude, variable
stand-off distance - White-light micro PMI
- FOV 3.3x2.5mm2 at 2.5x magnification
- Essential for edge discontinuity problem
- Available from several sources, start at 55K,
87K as shown - Large aperture (750mm) white-light Fizeau
interferometer - Remote sensing of module problems within FPA
- New concept, licensed by Zeiss to 4D Technology
- Will require significant development work,
collaboration with Jim Burge, UofA - Cost TBD
- Surface plates for clean room workstations
- Gauge blocks
- Fixtures for cryotesting and variable attitude
testing
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