Procedure Name:

# [Assembly of F-disks]{.underline}

Requirements:

CMM training (at least one person with training must be present)

Dzero Approval list:

Luda Rychnikova

Jorge Montes

Hans Jostlein

Wearing clean room attire, including face masks whenever working near
open silicon.

Major Steps:

A. Touch probing the Cooling Ring

B. System Setup, Optical

C. Wedge Installation on Post-Side

D. Wedge Alignment

E. Wedge Testing

F. Transfer of Ring to Bat Fixture

G. System Setup on N- Side

H. Wedge Installation on N-Side

I. Replacement of single Wedges on either Side

# Introduction

The Dzero Silicon Tracker consists of three types of detector
sub-assemblies: Barrels, F-Disks, and H-disks.

F-disks come in four types, which differ in their mounting features.
Type A F-disks will get mated to barrels, via their 6 posts.

Type B, C, and D F-disks are combined into (2) triplets, which are
formed by mounting them to one another.

The procedure here is not much affected by F-disk type, and covers all
types of F-disks. It mentions testing of individual wedges during F-disk
assembly. It does not cover the mating of F-disks to barrels, the
assembly of 3-disk end modules, or the installation of those
subassemblies into the Silicon support trough.

# Definitions

Alignment balls are 3 mm dia ruby balls, mounted on little Be stems
around the periphery of the cooling channel, located in the gap between
adjacent wedges. One ball is left off, because it would be at the bottom
of the trough where it cannot be easily touch probed

Bat Fixture Named after the way bats sleep, hanging from branches: A
fixture designed to allow wedge installation and removal on both Disk
faces without re-mounting the F-disk

Be Cooling Ring is a ring with a cooling water channel, nozzles,
alignment holes, and threaded holes for studs

F-disk is an assembly of a Be cooling ring involving 6 or 12 posts, 5 or
6 alignment balls, and 12 wedges.

Posts are CFC mounting features, which get glued to the Be cooling ring
prior to the start of this procedure. The free ends of the posts engage
the device that the disk will be mounted to, and define the reference
system to which the wedges must be aligned. For Type A disks, the face
of the ring with posts is called "P-side", the opposite one "N-side"
(for "no posts"). The P-side faces the barrel and hence the collision
point. We'll use the same convention, i.e. the P-side toward the
collision point (negative z-axis) , and the N-side away from the
collision point (toward positive z-axis) to ease keeping track of the
coordinate system while installing.

Steel fixture is a precision fixture consisting of a bottom and top
plate. The fixture is used for installing mounting hardware and balls,
and bottom plate of this fixture is also for the initial wedge
installation on the post side. This work is not covered in the present
procedure.

Studs are small Ti threaded rods, screwed into the Be Cooling ring and
secured with Locktite. They come in two different lengths. The radially
inner ones are 2-headed, and somewhat longer than the radially outer
ones, which stick out only to one face of the Be cooling ring Wedge
holes are oversized to permit lateral shifting for precision alignment.
A radial clearance of 5 mils is nominally provided. It can be reduced by
machining errors and stud leaning angles.

System Main Coordinate The main coordinate system (as available on the
Dzero web site) has the z-axis pointing away from the collision point.
The x-axis is horizontal, and the y-axis up, such as to form a right
handed system. For type A F-disks, the x-axis coincides with the
symmetry line of Wedge #1 (called W1). Wedges are numbered (regardless
of what face they are mounted on) by going in the positive rotation
sense from the x-axis. Posts are named like the wedge they are nearest
(and opposite) to, e.g. P2,P4,P6,P8,P10. Balls are named after a wedge
near them, e.g. B1,B3,B5,B7,B11. Ball B9 is not installed (at least on
type A's).

Systems Note that all coordinate systems are "2-dimensional", in the
sense that the system z-axis is normal to a plane 6 vertical (z)
measurements at 6 locations near the post bases (P-side) or future wedge
centers (on the N-side).

Transfer Fixture aids in transferring the F-disk assembly from the steel
fixture to the bat fixture after the first 6 wedges have been installed.
It is a simple tool to hold the bat fixture on edge to allow access to
both its faces.

Wedges are assemblies of a double-sided trapezoidal Si sensor with HDI's
on both side. The HDI's are laminated to a Be plate which is mounted on
the cooling channel with 4 Al nuts engaging 4 studs. Thermal contact is
via grease.

# A. Touch Probing the Cooling Ring

The cooling ring is mounted on the Steel fixture base plate for
installation of posts and alignment balls (not part of this procedure).
This is done on the Lab C Zeiss UMC 850, normally.

When complete, the posts and alignment balls are measured by touch
probe. Before the measurement, the ring is removed and the ball cups are
taken out. The ring is then re-installed with its 6 spring loaded
clamps.

For each post, the engagement cylindrical end (4mm dia) is measured.

A best fit system is established based on the six post ends. This is
done by fitting a grand circle through the six post end centers, to
establish the origin. The clocking is selected to provide an average
post azimuthal error of zero degrees.

After a rotation of 22.5000 degrees to go to the main coordinate system,
the alignment ball coordinates are expressed in the Main system.

The balls are the "transfer standard" for the reference system, because
they can be measured accurately by touch and optically, and are visible
form both faces of the disk. The will also be used to position the
F-disks in the mounting trough, eventually.

Although stud holes were already measured before studs were inserted, at
this time most studs on the P-face are also measured to assure adequate
clearance for wedge alignment.

Hazards: Ring damage from handling.

Hazard Level: Low, due to the sturdiness of the rings, their proximity
to the steel fixture, and the fact that spare rings exist.

Hazard Control: Operator care, and protective cover whenever unattended.

QA Issues: Standard CMM procedures, including verification of "forms",
diameters as expected, and observed deviations from expected locations.

Documentation: CMM printout kept with Ring traveler (Joe Howell). Copy
goes into F-disk assembly binder (Luda R.)

# 

# B. System Setup, Optical

The use of the RT05 turn table has been shown to create errors of the
order of 10 to 25 microns, which are not understood. Avoiding actual
rotations (while using software rotations as needed) has eliminated the
problem. The unavailability of actual rotations causes an overhead in
system setup of about 30 minutes when installing more than one pair of
wedges in one day.

The steel fixture with the bare Be cooling channel on it is mounted on
the RT05 turn table of the Zeiss UPMC 850 in Lab D (normally). The CMM
is equipped with optics. The current RAM optics will be replaced with a
Nikon setup to improve standoff distance, magnification, and
illumination. However, the present RAM optics yields adequate accuracy.

The RT05 is turned until the symmetry axis for that pair of wedges to be
installed is reasonably well aligned with the machine x-axis. This is to
make sure that the targets on the silicon sensors are well aligned with
the cross hair of the camera, for optimum accuracy. Note that the RT05
is re-aligned for the next pair of wedges, and the system re-created
from scratch.

The system is created in these steps:

a\. A preliminary system is created by leveling a z-plane through 6
elevation points on the surface of the Be ring. For the P-side these are
taken near the foot of each post. For the N-side they are taken near the
center of each wedge to be installed. An x-axis is created, with the
origin not too far from the ring center.

b\. The five alignment balls are measured as circles. The measurements
are done, for convenience, in software rotated systems, and later
recalled in the preliminary system. Their x and y coordinates are then
entered manually into an old laptop computer, located at the CMM. The
computer has a spread sheet that fits the optical ball coordinates to
the values obtained earlier by touch probing, as expressed in the Main
system. The fit results in a rotation angle and x- and y offsets.

c\. The angle and offsets are entered into the CMM to create the Main
system. The ball data are recalled in the new system , and compared with
expectations from the spread sheet analysis. This guards against typing
errors. After the fit, optical ball coordinates agree typically to much
better than 5 microns with the touch results, individually.

d\. A software rotation is made to the wedge pair to be installed.

Hazards: Ring damage from handling, e.g. breaking posts by CMM
mis-drive. Cable tail damage, e.g. during bend-back needed to reveal
alignment balls

Hazard Level: Low, because the posts can be re-installed if damaged.

Hazard Control: Program testing on steel disk and Ring #1, operator
care, and protective cover whenever unattended. Care in handling cable
tails (if any).

QA Issues: Standard CMM procedures, including verification of "forms",
diameters as expected, and observed deviations from expected locations.

Documentation: CMM printout goes into F-disk assembly binder (Luda R.).
F-Disk assembly log book entry (Luda R.)

# 

# C. Wedge Installation on Post-Side

Wedge selection: As determined by the detector selection committee

Wedge transport:: Wedges stay in their boxes until ready to install..

Wedge installation: From 1 to 6 wedges can be installed at any one time.

Grease application: Three narrow (2 mm wide) strips of 2 mil (total
thickness) Kapton tape are placed for each wedge location. One strip is
along the wedge symmetry line, the other two are outside the studs for
this wedge. The strips are used to level the grease for uniform and
controlled thickness. This is done by applying the grease by hand, based
on operator judgment, and leveling with a Stanley utility knife blade
that rides on two of the strips. The blades are not long enough to cover
the whole width at once, and also the studs make it quite hard to do a
full width leveling.

Any excess grease that has been pushed to the ring's edges can be taken
off with a Q-tip. If the amount of grease was insufficient, which can be
readily seen, grease is added and the leveling repeated. The Kapton
strips are now pulled up.

Wedge placement: Wedges are removed form their storage boxes. This is
tricky because fingers are close to the sensor and wire bonds, and loose
hardware (clamp parts, nuts) can fall on the sensor and break it. It has
also been observed that the clearance over the holding studs is so tight
that wedges must be lifted parallel, or they will jam.

Wedges are now lowered over the 4 studs. This can be done by holding the
wedges very lightly by their cable tails. When all 4 studs are engaged,
the wedge does not fall off. Four aluminum nuts are now brought in with
a nut driver. The driver is best held horizontally so that the nut won't
fall out. After contacting the end of the stud, the driver can be tilted
to the vertical and the nut spun on. The four nuts are gently tightened
and backed off to be almost totally free to allow edge alignment by
shifting it sideways.

Documentation: F-Disk assembly log book entry (Luda R.)

Wedge disposition (e.g. "installed on ring \# 1, location W7, on
3/26/2000, by Luda R) is marked both on the box, the F-disk assembly log
book, and the CMM printout

# D. Wedge Alignment

The installation CMM program is designed to move repeatedly between two
fiducials on the wedge to be installed. The alignment strategy depends
on which fiducials are available.

For production assembly, we expect to use the two fiducials on the
center line, one near the inner tip(the "inner fiducial"), and the other
one under the sensor wire bonds (the "outer fiducial"). A gap will be
left in the encapsulant to provide an undistorted view of that fiducial.
The bond wires above it are out of focus and do not seem to impair
alignment accuracy significantly. This procedure describes only the
strategy appropriate for these two fiducials.

The wedge has three degrees of freedom, i.e. two offsets and a rotation.
The wedge is mounted with the x-axis coincident with its symmetry line,
and the y-axis through the ring center at right angles to x.

We have found it useful to set first the y of the outer fiducial. This
is done by shifting the wedge, using a small screw driver pushing the Be
plate in azimuthal direction, using the ring as a fulcrum. Not much
force is required, and it is easy to control the motion.

Next the y of the inner fiducial, and the X of the outer fiducials can
be set together. The strategy is to tighten slightly one of the stud
nuts, and to use it as a hinge. For instance, for a pure x-motion, one
makes half the correction using a stud at positive y, and the other half
using a stud at negative y. This will leave y at the inner fiducial
unchanged (one is watching the inner fiducial while doing this). Other
combinations of stud selection and move distance can be found to cure
inner-y and x-offsets by compound motions.

Under normal circumstance, a wedge can be aligned to 2 microns or so
within 15 minutes. Note that the 2 micron number refers only to this
step, and is by no means the final placement accuracy in the detector.

Hazards:

Wedge breakage, by hand touch, tool drop, CMM error.

Wire bond damage by finger touch, nut driver contact, screw driver
contact

Hazard Level: High, due to work very close to the wedges

Hazard Control: Operator care, protective cover whenever unattended;
tails are gently pulled back and taped (away from the contact s) to the
fixture. Fingers are not used near wedges. Tool motions are deliberate
and slow. process is paused on any unexpected observation

QA Issues: Assure good focus, good target capture, repeat fiducial
measurement after tightening nuts.

Documentation: CMM printout goes into F-disk assembly binder (Luda R.).
F-Disk assembly log book entry (Luda R.)

# E. Wedge Testing

Wedges are tested individually for downloading and readout. This is done
at least after each group of six wedges is installed. takes place on the
CMM.

Hazards: Cable tail stresses

Hazard level: Moderate

QA Issues: Record keeping

Documentation: results summarized in F-disk assembly log.

Results go into wedge traveler (Michaele ?)

# F. Transfer of Ring to Bat Fixture

Ring needs to be removed from steel plate to allow wedge installation on
the N-side (Note that P-side installation can be done on the steel
fixture or on the Bat fixture).

The Bat fixture (a shaped aluminum plate) is clamped in the transfer
fixture (to be built; use a table-clamped vise for now).

The six clamps holding the F-disk to the steel plate are removed.

The ring is picked up by the posts, carefully avoiding stressing the
posts, and the post-ends are inserted into the holes of the Bat fixture.
They enter from the relieved side of each finger. Entry must be easy and
stress free. If there is a fit problem, the ring is returned to the
steel plate until the issue is resolved.

The next step takes two people. One person holds the ring by two posts
to assure that it doesn't fall out. The other person installs a washer
and a brass nut on two opposing post studs. At that point the ring is
secure. The remaining four washers and brass nuts are now installed. All
nuts are tightened with the torque limiting nut driver.

The bat fixture with the ring is now installed on the rotary table,
using these steps:

-remove the Steel base plate

-install the aluminum disk which will hold the bat fixture, using the
T-nuts and screws that used to hold the steel plate.

-install three 1/4-20 SS studs into the threaded holes of the Al base
plate. bottom ends of studs are flush with Al plate. Install counter-
nuts on top of Al plate, but do not tighten hard.

-install a nut one inch below top of each stud, as shelf for Bat fixture

-lower the Bat fixture over the 3 studs.

-install nuts on studs above the fixture

-Tighten counter nuts

-slide plexi cover over the three studs

-set desired elevation of Bat fixture using its pairs of nuts

Hazards:

Wedge breakage, by hand touch.

Ring can fall while small brass nuts are being installed

Transfer fixture may fail to hold the Bat fixture securely

Hazard Level: Moderate

Hazard Control: Operator care. Two operators required.. Tool motions are
deliberate and slow. Process is paused on any unexpected observation.
Cover installed when transfer is complete.

QA Issues: None

Documentation: F-Disk assembly log book entry (Luda R.)

# G. System Setup on N- Side

Select CMM system to have z-axis down.

Use the N-side program.

Test the program (quickly) while the plexi cover is in place.

System is set up on balls the same way it is done on the P-side.

Hazards, QA, documentation like on P-side.

# H. Wedge Installation on N-Side

Same as on P-side, except:

Clamp the auxiliary platform to the Bat fixture at site of wedge to be
installed. This provides a surface to work from when aligning the wedge.

Hazards, QA, documentation like on P-side.

# I. Replacement of single Wedges on either Side

This is always done on the Bat fixture.

Note that both sides of the ring are accessible without removing the
ring from the fixture; one simply "flips" the fixture on the three
mounting studs.

Wedge removal:

-remove (4) aluminum nuts

-pry Be plate from the ring, using very little force and lots of
patience

-remove the bulk of grease form the ring, using a Q-tip

-clean up at tape locations, using Q-tip wetted with a little alcohol

-install 3 strips of Kapton tape and proceed like normal wedge
installation and alignment.

Hazards, QA, documentation like those for wedge installation and
alignment above.