October 30, 2013
LG
DRAFT
Ladder replacement on PXL Sectors
Included in the original PXL detector design requirements is the capability to be built into the mechanical design and tooling to allow for the replacement of damaged ladders on a PXL sector. This operation had not been tested in the actual assembly process until now. We report on the actual process required to carry out this operation and the successful replacement of a ladder in position 4 (out 3). This is the most difficult ladder to replace due to the overhang of the ladder in position 3 (out2). The replacement of the ladder in position 1 (in1) is trivial.
During the construction of the first PXL sector, one ladder (in positions 1 (in1) was damaged by handling when bond wires were crushed. Additionally, the ladder in position 4 (out3) also developed a hot sensor after the sector assembly. This provided the opportunity to test the ladder removal and replacement process. This process is described below.
Removal of ladders
Using a thin mini-spatula we separated the ladder from the sector tube by inserting the mini-spatula under the ladder (starting at the driver board end) and sliding it along the length of the ladder. This freed the ladder from the sector tube.
Figure 1 insertion of the mini-spatula into the bond gap between the driver board section and the sector tube.
Figure 2 sliding the mini-spatula along the bond gap, releasing the damaged ladder.
Removal of silicon adhesive
After the ladders were removed, the remaining adhesive on the sector tube was removed by inserting the mini-spatula between the silicon adhesive and the sector tube. The adhesive separates cleanly from the sector tube.
Figure 3 adhesive left on the sector tube in position 4 (out3).
Figure 4 removal of the silicon adhesive left on the sector tube.
Preparation for installation of the replacement ladder
The ladder installation fixturing is too high in the normal ladder assembly configuration and the aluminum support flange behind the ladder hits the installed ladder edge in position 3 (out2). To install the new ladder without stressing the ladder edge in position 3 we lowered the spring backed pins that keep the ladder holding fixture above the sector tube holding fixture. This allowed us to slip the new ladder into the existing space and lower the ladder into the correct position in the standard assembly procedure.
Figure 5 lowering the height at which the ladder is held by adjusting the spring pins.
At this point, the ladder is installed and the standard sector assembly procedure can be resumed.
Comments
The silicon adhesive worked exactly as designed and removal of the ladders and the adhesive was relatively easy.
The ladders were intended to be removed “destructively” but it appears that we may be able to remove partially functional ladders intact. We are currently testing the ladder with one hot sensor that was removed. If it is still functional, it can be used as a testing ladder.
The ladder removal and replacement process is now validated.