0.25mm-Thick CCD Packaging for the Dark Energy Survey Camera Array Page: 1 of 10
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FERMILAB-CONF-06-156-E
0.25mm-Thick CCD Packaging for the
Dark Energy Survey Camera Array
Greg Deryloa, H. Thomas Diehla, Juan Estradaa
aFermi National Accelerator Laboratory, Box 500, Batavia, IL, USA 60510
ABSTRACT
The Dark Energy Survey Camera focal plane array will consist of 62 2k x 4k CCDs with a pixel size of 15 microns and
a silicon thickness of 250 microns for use at wavelengths between 400 and 1000 nm. Bare CCD die will be received
from the Lawrence Berkeley National Laboratory (LBNL). At the Fermi National Accelerator Laboratory, the bare die
will be packaged into a custom back-side-illuminated module design. Cold probe data from LBNL will be used to
select the CCDs to be packaged. The module design utilizes an aluminum nitride readout board and spacer and an Invar
foot. A module flatness of 3 microns over small (1 sqcm) areas and less than 10 microns over neighboring areas on a
CCD are required for uniform images over the focal plane. A confocal chromatic inspection system is being developed
to precisely measure flatness over a grid up to 300 x 300 mm. This system will be utilized to inspect not only room-
temperature modules, but also cold individual modules and partial arrays through flat dewar windows.
Keywords: CCD, packaging
1. INTRODUCTION
The Dark Energy Survey (DES) proposes to build a new camera with a 2.2 deg. diameter field of view for the 4 m
Blanco telescope at the Cerro-Tololo International Observatory. The camera will use fully-depleted high-resistivity
CCDs2 developed at LBNL. These 2k x 4k devices have 15 micron pixels and are 250 microns thick for greatly-
improved efficiency at 800-1100 nm. A focal plane array of 62 CCD modules will be constructed, resulting in a
520 megapixel image. A four-side-buttable, back-side-illuminated module design is undergoing development at the
Fermi National Accelerator Laboratory (FNAL). In order to minimize the loss of coverage area within the survey array,
a gap of 0.5 mm is planned between adjacent modules. Factors that influenced the initial package design concept
include:
" LBNL 2k x 4k high-resistivity CCDs for use between 400-1000 nm
o CCD size = 63.4 mm x 33.3 mm x 250 microns thick
" CCD flatness:
o On 1 sqcm scales within a CCD, the mean height variation should be < 3 microns
o For adjacent 1 sqcm areas within a CCD, the difference in mean heights should be < 10 microns
o Entire CCD surface within 25 microns of the mean focal plane
" Operation in vacuum at about 150 K
" Installation onto the focal plane support plate without shimming
" Easy to install and replace
Early packaging effort has emphasized construction of simple pictureframe-style modules. Six different pictureframe
types have been assembled, allowing testing of three different CCD sizes in either front- or back-side-illuminated
configurations. All six pictureframe types are shown in Figure 1. In addition to four 2k x 4k sensors, each silicon wafer
contains a 2k x 2k sensor, which is intended for use in separate guide, focus and alignment modules, and four 1k x 512
sensors, which are not intended for use in the camera but which are being utilized during development testing. Three
different pictureframe readout card types were fabricated, with window opening sizes and trace layouts corresponding
to the three different sensor sizes*. The module's readout connectors are assembled onto the board from different sides
The two smaller sizes were adapted from the 2k x 4k pictureframe board, which was designed by LBNL for the SNAP program.
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Derylo, Greg; Diehl, H. Thomas & Estrada, Juan. 0.25mm-Thick CCD Packaging for the Dark Energy Survey Camera Array, article, 2006-06~; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc887388/m1/1/: accessed May 30, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.