Low mass power tape specifications

Requirements Design

Under development:

Quality control and testing

Requirements                                                                    index

carry HV, power, sensing and control levels from PP2  to detector modules


basic modularity given by the SCT power distribution philosophy

each module served individually => 1 tape per module

each harness shielded individually, shields connected at PP1


based on Technical Design Report, PP2 in-between LAr electronic boxes



High Voltage

according to SCT Bias Voltage Power  Specification V2.03 (draft)

Low Voltage

according to ATLAS SCT Low Voltage Power  Specification V2.0 (draft)

DMILL process limit for ABCD chip: V_max = 5.5 V (on chip)

analog (ABCD bipolar FE):

digital (ABCD + opto CMOS) PIN bias VECSEL drivers

Sensing and control



SELECT for clock (opto redundancy scheme)

RESET module all lines but RESET carry DC levels

Additional requirements

Maximize conductivity Minimize material in sensitive region importance of material grows towards interaction point !

Minimize space

severe space constraints all way through ATLAS detector
identified hot spots (so far)

Transmission line properties Radiation hardness up to

Design                                                                          index

Basic design considerations

long but simple, two-layer flexible circuit design with conductor/KAPTON laminates

IPC standards for flexible printed circuits taken as design guidelines
caveat: no IPC standards exist for aluminium flexes

0.5 mm track and gap grid chosen to match 1 mm pitch, (25 mil = 0.635 mm felt too risky)

Tape design                                                                     index

group lines into

low current - minimal 0.5 mm tracks

         12(13 in barrel) narrow tracks

high current - wide tracks

         4 wide tracks

group track in two layers with matching supplies and returns for RF filtering and minimal loops

obey IPC-2223 specification for HV separation (500 V -> 2.5 mm)

take 50 um Al as conductor for inner part up to PP1 (4x smaller X0 than Cu for same conductivity)
take 70 um Cu as conductor for outer part (> 2x better conductivity than 50 um Al)

21 mm tape width compatible with on-barrel engineering constraints

9 mm remain for power lines, shared equally between digital and analog

keep same design also for outer part

view  barrel design  and  forward design

Tape construction                                                                         index

basic material from GTS Ltd. (holder of ISO 9001 )

matched product line

PU glue tested by CERN-TIS for radiation hardness, Kapton specified radiation hard

inner part - "thin" low-mass tape

bottom to top

outer part - "thick" low-mass tape

bottom to top

tape ends chemicaly Ni/Au plated for contact/soldering according to IPC-6013 Class 3

Tape Properties                                                                         index


of 4.5 mm power lines

of 0.5 mm lines

all values with nominal values for Al and Cu resistivity,

GTS sheet resistance spec for Al 2.5 - 2.7 uOhm.cm (?)

view  voltage drop table  for baseline SCT power distribution



The width of all conductors is

4*4.5 + 13(12)*0.5 = 24.5(24) mm (in brackets forward cables without the TEMP2 line)

X-section of plastic

Radiation length seen at perpendicular impact for one cable (w - width over which the material is spread)

single thin tape
X1 / X0 = (S/X (Al}) + S/X ({plastic})) / w = (1.23(1.20) mm2 / 89 mm + 3.4 mm2 / 350 mm) / w =  (0.014 + 0.010) mm / w
= 0.024 mm / w

single thick tape
X1 / X0 = (S/X (Cu}) + S/X ({plastic})) / w = (1.72(1.68) mm2 / 14.3 mm + 3.4 mm2 / 350 mm) / w =  (0.0120(0.118) + 0.010) mm / w
= 0.130(0.128) mm / w

thin cable

  • spread over cable  (w = 21 mm) X = 0.114 % X0
  • spread over module (w = 60 mm) X = 0.040 % X0
  • end of stave over module (6 cables) X = 0.24 % X0
  • outer barrel radius (1056 cables, r = 520 mm)  X = 1056 * X/ (2.pi * r) = 0.78 % X0 (this should be the maximum)
  • at cryostat wall (1056 cables, r = 1150 mm)  X = 1056 * X/ (2.pi * r) = 0.35 % X0
  • at end of forward cylinder (988 cables, r = 590 mm)  X = 988 * X/ (2.pi * r) = 0.64 % X0 (maximum in forward)
  • Beware of fast conclusions from these numbers ! In the worst case, tapes are traversed twice and at an angle of 35o (barrel) or 13o (forward).
    The worst-case material estimate in thin low-mass tapes seen by particles is therfefore 2.7 % X0  in the barrel and 3.5 % X0  in the forward.

    thick cable

  • spread over cable  (w = 21 mm) X = 0.619(0.610) % X0
  • spread over cryostat bore (1056 barrel cables, r = 1150 mm) X = 1056 * X/ (2.pi * r) = 1.90 % X0
  • on cryostat face (1056 barrel + 988 forward cables, r = 1200 mm) X = (1056 * 0.130 + 988 * 0.128)  / (2.pi * r) = 3.49 % X0 (maximum)
  • Space and routing

    X-sections, nominal thickness (measured somewhat smaller)

    envelopes, shielding (50 um foil per harness) & packing factors (1.2) not taken into account

    minimal bending radius: 10 x tape thickness (IPC-2223

    thin tape (no IPC for Al !) tested: bending over a mandrel (r = 5, 2, 0.75 mm), 100 180o bends, repetition 1 Hz


    Al tape safe, if IPC recommendations followed

    Transmission line properties

    eps (Kapton) = 3.5
    eps (glue) = eps (Kapton)

    capacitance: C / l = eps * eps0 * w / d

    inductance: L / l = u0 d / w

    for comparison: flat (TP) ribbon cables: C/l  typically 50 pF/m, L/l  700 nH/m

    Production                                                                         index

    Production is with a standard photolithographic process adapted to the size of the circuits.

    Mask production

    Laminate polishing

    Photo-resist lamination

    Photo-resist exposure

    Photo-resist development

    Conductor etching

    Photo-resist stripping


    Ni/Au deposition

    Laminate/glue/laminate/coverlay pressing

    Tape cutting

    Quality control and testing                                           index

    Production steps are carried out according to production sheets of the producer (available in Slovenian). Quality control actions for separate steps are as follows:

    Mask production

    Laminate polishing

    Photo-resist lamination

    Photo-resist exposure

    Photo-resist development

    Conductor etching

    Photo-resist stripping


    Ni/Au deposition

    Laminate/glue/laminate/coverlay pressing

    Tape cutting