Low mass power tape specifications

Requirements

Modularity
Length
High Voltage
Low Voltage
Sensing and control
Additional requirements

Design

Basic design considerations
Tape design
Tape construction
Tape properties

Resistivity and voltage drop
Material
Space and routing
Transmission line properties

Under development:

Production
Quality control and testing

Requirements index

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

Modularity:

basic modularity given by the SCT power distribution philosophy

each module served individually => 1 tape per module

barrel: 6 tapes (half-stave) - 1 harness: module <-> PPB1 <-> PPB2
forward: 2-3 tapes PPF0 <-> PPF1, 5-6 tapes PPF1 <-> PPF2

each harness shielded individually, shields connected at PP1

Length:

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

barrel

0.8 - 1.6 m module to PP1
4.6 m PP1 to PP2 (?)

forward

1.3 - 3.1 m PP0 to PP1
2.1 m PP1 to PP2 (?)

High Voltage

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

V_max = 500 V (HV component rating)
I_max = 5 mA

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):

I_cc_max = 1.3 A (prel.)
V_cc_nominal = 3.5 V

digital (ABCD + opto CMOS)

I_dd_max = 1.0 A (prel.)
V_dd_nominal = 4 V

PIN bias

V_max = 10 V
I_max = 2 mA

VECSEL drivers

V_max = 6.6 V
I_max = 10 mA

Sensing and control

Sensing

temperature on module (2 on barrel)
V_cc, V_dd and respective returns at module connector

Control

SELECT for clock (opto redundancy scheme)

V_nominal = 4.0 V
I_max = 1 mA

RESET module

V_nominal = 4.0 V
I_max = 1 mA

all lines but RESET carry DC levels

Additional requirements

Maximize conductivity

minimize V drop to stay under V_max = 5.5 V under any scenario
minimize power dissipation

Minimize material in sensitive region

minimize radiation length
minimize interaction length

importance of material grows towards interaction point !

Minimize space

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

from gap in-between LAr electronic boxes (ID X-sect 3500 cm²)
in-between tile nooses under mu-chambers (ID X-sect 5300 cm²)

Transmission line properties

maximize coupling capacitance (RF filter)
minimize inductance (loop)

Radiation hardness up to

100 kGy ionizing radiation
2.x 10¹⁴n/cm²(1 MeV neutron NIEL equivalent)

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

HV
HV_ret
V_cc_sense
A_gnd_sense
V_dd_sense
D_gnd_sense
TEMP_1
TEMP_2 (barrel only)
PIN_bias
ILED_a
ILED_b
SELECT
RESET

12(13 in barrel) narrow tracks

high current - wide tracks

V_cc
A_gnd
V_dd
D_gnd

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

Al(Cu)/Kapton FPC laminate with PU glue
glue
glue/Kapton coverlayer

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

inner part - "thin" low-mass tape

bottom to top

25 um Kapton/25 um PU glue/50 um Al laminate (GTS prod. # 660210AL)
25 um glue (GTS prod. # 102100)
25 um Kapton/25 um PU glue/50 um Al laminate (GTS prod. # 660210AL)
25 um glue/12.5 um Kapton coverlayer (GTS prod. # 322190)

outer part - "thick" low-mass tape

bottom to top

50 um Kapton/25 um PU glue/70 um Cu laminate (GTS prod. # 760220ED)
25 um glue (GTS prod. # 102100)
50 um Kapton/25 um PU glue/70 um Cu laminate (GTS prod. # 760220ED)
25 um glue/12.5 um Kapton (GTS prod. # 322190)

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

Ni minimal layer thickness: 1.3 um
Au maximal layer thickness: 0.8 um

Tape Properties index

Resistivity

of 4.5 mm power lines

250 mOhm/m round trip (thin)
110 mOhm/m round trip (thick)

of 0.5 mm lines

2.24 Ohm/m round trip (thin)
0.97 Ohm/m round trip (thick)

all values with nominal values for Al and Cu resistivity,

Al : 2.8 uOhm.cm
Cu: 1.7 uOhm.cm

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

view voltage drop table for baseline SCT power distribution

Material

input:

X₀(Cu) = 1.43 cm
X₀(Al) = 8.9 cm
X₀(Kapton) = 35 cm; all glues assumed ~kapton

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

thin: 21 mm * (25(K) + 25(G) + 25(G) + 25(K) + 25(G) + 25(G) + 12.5(K)) um = 3.4 x 10^-2 cm^-2
thick: 21 mm * (50(K) + 25(G) + 25(G) + 50(K) + 25(G) + 25(G) + 12.5(K)) um = 4.5 x 10^-2 cm^-2

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

single thin tape
X₁/ X₀= (S/X₀ (Al}) + S/X₀ ({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/X₀ (Cu}) + S/X₀ ({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 * X₁/ (2.pi * r) = 0.78 % X₀(this should be the maximum)

at cryostat wall (1056 cables, r = 1150 mm) X = 1056 * X₁/ (2.pi * r) = 0.35 % X₀

at end of forward cylinder (988 cables, r = 590 mm) X = 988 * X₁/ (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 35^o (barrel) or 13^o (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 * X₁/ (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)

2.1 * 0.02625 = 0.055 cm² (thin)
2.1 * 0.03525 = 0.074 cm² (thick)

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

minimal bending radius: 10 x tape thickness (IPC-2223 5.2.4.2.)

r_min = 3. mm (thin)
r_min = 4. mm (thick)

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

result:

r = 5 mm O.K.
r = 2 mm O.K.
r = 0.75 mm

30 bends O.K.
50 bends 1 broken line
100 bends 3 broken lines

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

1.9 nF/m (thin)
1.4 nF/m (thick)

inductance: L / l = u₀ d / w

20. nH/m (thin)
28. nH/m (thick)

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

Polishing

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: