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PCB specs

PCB specs. Single-strip defects. The issue. We have observed some defects in the readout strips (metallic) in a number of boards delivered by ELTOS for the MMSW chambers (as presented by Fabian Kuger , e.g., in the Würzburg Meeting) Defects are Interconnected lines (shorts)

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PCB specs

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  1. PCB specs Single-strip defects Joerg Wotschack

  2. The issue • We have observed some defects in the readout strips (metallic) in a number of boards delivered by ELTOS for the MMSW chambers (as presented by Fabian Kuger, e.g., in the Würzburg Meeting) • Defects are • Interconnected lines (shorts) • Interrupted lines (resulting in partly dead strips) • Questions • How many defects of each type can we accept? • Shall we specify limits for these defects in the specs for the PCB producers and, if yes, which? Joerg Wotschack

  3. QC on PCBs • Besides systematic dimension deviations local defects on the PCBs are a QC issue: Repaired lines are straight, width variations are small Defect: Interconnected strips Damaged strip, huge width variation Strip is broken  dead channel Joerg Wotschack

  4. Considerations for the discussion • Tracks from the IP have inclinations between 7 and 35 degrees • Typical cluster sizes (track projection onto readout strips) are 10 – 28 mm or 3(4) to 8(10) strips. • A missing or interconnected strip will lead to a missing or wrong strip signal and thus to a larger position error • Comparable effects are created by the pillars (1% inefficiency) • Proposal: accept defects at a similar level as the inefficiency created by the pillars • ≤10 interconnected lines (shorts) as long as they are distributed; minimum distance between defects: 10 strips • ≤ 10 interrupted lines/PCB (1024 channels) as long as they are distributed; minimum distance between defects: 10 strips • The sum of interconnects and shorts: ≤10/PCB; minimum distance between defects: 10 strips Joerg Wotschack

  5. What to do with defects • Quality control to detect defects • Accept defects as long as below threshold? • Record defects; do not do anything further • Repair, where possible (e.g., shorts) • Centrally (e.g. CERN) • Construction site • Ask for repair (where possible) in PCB industry? • Extra costs? Joerg Wotschack

  6. What to write into specs? • No limits, but ask PCB industry to deliver a protocol with each PCB listing the number and address of defect strips • Define max number of defects (as specified above) • Accept repairs ? • Require repairs ? Joerg Wotschack

  7. What about spares? • How many PCBs of each type do we want to order? Minimum is 64 PCBs of each type • To cope with defects • To allow for selection of PCBs • To allow for accidents during panel construction • Is it cheaper to accept defects and to produce 10–20% more boards? • Option on re-processing after full delivery Joerg Wotschack

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