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Flex Cable Development

Flex Cable Development. The development of the flex cable for sensor readout and control is envisioned as a 4 stage process that involves the construction of 3 PCB test boards.

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Flex Cable Development

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  1. Flex Cable Development The development of the flex cable for sensor readout and control is envisioned as a 4 stage process that involves the construction of 3 PCB test boards. Since the goal is to have 10 functioning sensors on a ladder for all tests => Probe testing is required for the RDO cable development. • Stage 1 - Infrastructure development and testing stage. • Test PCB is FR-4 with Cu traces and contains structures that allow for the testing of various sensor infrastructure configurations. This stage is designed to evaluate. • LVDS clock multi-drop. • JTAG daisy chain. • Sensor and system bypass capacitor requirements. • Power and ground routing and stiffness. • Noise and cross-talk. • General operation. LBNL PIXEL IPHC 2009_06_LG

  2. Flex Cable Development (cont.) Use what we learn in stage 1 to develop: Stage 2 – Production prototype in FR-4 with Cu traces. Stage 3 – Production prototype in kapton with Cu traces. Stage 4 – Production cable in kapton with Al traces. • Making some assumptions about the testing results, We can generate a strawman final cable design with enough detail in the characteristics to evaluate the probable radiation length for Al and Cu conductor versions. • Assumptions: • Limit the conductor used for power and ground to what is required to give < 50 mV resistive drop for the full power path in the low mass region. • The signal list is as we have already defined and multi-drop of LVDS clock and daisy chaining of JTAG works. • That what we have learned from the infrastructure testing and later stages does not invalidate any other design choices made here. http://rnc.lbl.gov/hft/hardware/docs/Phase1/cable_power_gnd_trace_optimization.doc LBNL PIXEL IPHC 2009_06_LG

  3. Flex Cable Development (cont.) Number of traces and required width to route (without vias) With 17.5 um Cu trace equivalent thickness. Using industry standard 0.005” (125um) traces and spaces. Signal http://rnc.lbl.gov/hft/hardware/docs/Phase1/cable_power_gnd_trace_optimization.doc LBNL PIXEL IPHC 2009_06_LG 3

  4. Flex Cable Development (cont.) Number of traces and required width to route (without vias) With 17.5 um Cu trace equivalent thickness. Power W = 23.08 mm http://rnc.lbl.gov/hft/hardware/docs/Phase1/cable_power_gnd_trace_optimization.doc LBNL PIXEL IPHC 2009_06_LG 4

  5. Flex Cable Development (cont.) Recall the basic cable geomety Using standard flex PCB fabrication for the PCB we can use 5 mil spacing and 5 mil traces. We are attempting to fit the routing onto two sides of a 23.08 mm wide cable or 46.16 mm. The absolute minimum space required would be ~0.650” + 0.94” = 1.59” (40.4 mm). Designing a layout that fits into the required width for 0.005” t&s will be very challenging if it is even possible. We can optimize the conductor layer thickness and the trace size in the low mass region attempting to fit all required conductor into a 2 sided cable, we arrive at the following strawman design. LBNL PIXEL IPHC 2009_06_LG

  6. Flex Cable Development (cont.) Hybrid Copper / Aluminum conductor flex cable Side view (exaggerated vertical scale) Top View • 2 layer Al conductor cable in low mass region • 0.004” (100 um) traces and 0.004” (100 um) spaces • 70% fill factor • Conductor thickness in low mass region is 21 um (Cu) or 32 um (Al) • Minimum required conductor trace width 1.325” (33.65 mm) of 46.16 mm available. • Bond wire connection between Al and Cu cable sections. Low mass region calculated X0 for Cu conductor = 0.232 % Low mass region calculated X0 for Al conductor = 0.073 % LBNL PIXEL IPHC 2009_06_LG

  7. Flex Cable Development (cont.) • Compared to the standard 4 layer Al conductor cable construction; • Advantages • One 2-layer Al conductor cable – less reliance on Al conductor flex PCB fabrication process and less complex Al structure. • Lower radiation length than previous (not as well justified) estimate. • More layers and thus more complex structures in the driver region are possible (this may be needed). • Disadvantages • Wire bonding (or other high density connection technique) required for inter cable connection. • Cable will not be the same thickness everywhere – may complicate fixturing. • Non homogeneous CTE in cable. LBNL PIXEL IPHC 2009_06_LG 7 7

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