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Engineering Design ReviewEngineering Design Review
RPC - BAKELITERPC - BAKELITE
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3.1 THE MATERIAL
We have investigated and measured three main physical parameters of the bakelite:
• the volume resistivity as a function of Temperature and Humidity• the average roughness Ra
• the relative dielectric constant r as a function of the input frequency
We also have investigated how the factory parameters are related to the sheets resistivity value.
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Quality Control
Factory Main Parameters:
• Type of Paper• Flow• Resin• Volatile• Heating Temperature• Pressing Temperature• Resin Reactivity
How muchthe resin spreadsout on the paper foil
Percentage of resin
in the paperResinResin
Percentage of additives VolatileVolatile
GOES
GOES
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RESISTIVITY MEASURE
Needs good electrical contact between electrodes and bakelite
We have tried several options for the contact - among other:• sponge with water• antistatic foam (with and without water)• conductive gel• conductive rubber
• Brass Electrodes• Upper 5 cm • Lower 10 cm for guard ring option
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How to measure ~ 1010 - 1011 cm
R = 10 or 100 k
= k V0/(V/R)
k = geometrical factor(98.17)
V0 = 500 Volts
V0
VR
Constant pressure (3 atm) on the electrodesby means of pistons
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V0
VRR
HV distribution: CAEN SY 127
Reading through Nat. Inst. FIELDPOINT FP-100
or through a 617 Keithley programmable
electrometer (via gpbi )
and LabView 5.0
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Conductive rubber vs cloth and water for 3 bakelite samples
V1 C
or
V2 C
(m
V)
VR (mV) Normalisation factor to water : 0.25
VR/V1C VR/V2C V1C/V2C
V0
VRR
V0
V1CR
V0
V2CR
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Resistivity measurements at the factory0
prot
otyp
e
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View of the pistons driven by a manual air valve0
prot
otyp
e
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The manual switch for the serial read-out0
prot
otyp
e
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Aging Studies
``Natural’’ Aging • vs Temperature• vs Humidity• vs Time
``Radiation” Aging• gamma irradiation• neutron irradiation
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Resistivity at 20 C and Humidity
1,90
1,95
2,00
2,05
2,10
2,15
2,20
1 5 9 13 17 21 25 29 33 37 41 45 49 53
n. of measures (1 meas/15 minutes)
44,0
45,0
46,0
47,0
48,0
49,0
50,0
51,0
52,0
53,0
x 11)cm
H (%)
Resistivity vs Humidity
We have normalized at 20 C first
Temperature and Humidity
21,0
21,2
21,4
21,6
21,8
22,0
22,2
22,4
22,6
1 5 9
13
17
21
25
29
33
37
41
45
49
53
n. of measur. (1 measure/15 minutes)
44,0
45,0
46,0
47,0
48,0
49,0
50,0
51,0
52,0
53,0
TEMPERATURE
HUMIDITY
Max % variation ~ 7%with a
max H = 5 %
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Resistivity and Humidity
1,45
1,50
1,55
1,60
1,65
1,70
1,75
1 5 9 13
17
21
25
29
33
37
41
45
49
53
n. of measures (1 measure/15 minutes)
44,0
45,0
46,0
47,0
48,0
49,0
50,0
51,0
52,0
53,0
(
x 10
11)
cm
H (%)
Without temperature correction
= (1/ ) (d / d T)
Max % variation ~ 10%
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In all our data a temperature normalised value is usually given at T=20 C following this curve.
Temperature Normalisation
Multiplying factoran effective valuehas to be multiplied forto obtain at T=20 C
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Resistivity as a function of temperature
Note also the ``inertia” of the bakelite in following the temperature change
Resistivity and Temperature
1,45
1,50
1,55
1,60
1,65
1,70
1,751 5 9 13 17 21 25 29 33 37 41 45 49 53
N. of measures (1 pt /15 minutes)
21,0
21,2
21,4
21,6
21,8
22,0
22,2
22,4
22,6
(
x 10
11)
cm
T (C)
Here temp starts to decrease
while
is stillconstant
Then also startsto increase
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Resistivity measurement made by ATLAS group
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Comparison with ATLAS measurements on a subsample of the pre-production set
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Results on preproduction samples
We have measured the resistivity of some 130 bakelite panels in different places and in different conditions to check their behaviour in a medium time range. The following plots refer to foils of different sizes and for melamine and/or phenolic plates
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Resistivity (at T=20 C) for Melamine foils. Size :160 cm x 320 cm
At the factory
At General Technicaafter 2 months
panels on the pallets
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Resistivity (at T=20 C) for Phenolic foils. Size :130 cm x 320 cm
At the factory
At General Technicaafter 2 months
panels on the pallets
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Dielectric behaviour of the bakelite as a function of the input frequency signal
tg
Rp
Cp
rRp
Cp
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Resistivity as a function of the input frequency
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SystematicAutomatic measurement of the resistivity of a bakelite sampleas a function of the time.SETUP: • a piston with conductive rubber is continuously measuring theresistivity of a bakelite sample• after a predetermined set of measurements the piston moves up fora fixed time and back down on the sample for the next cycle of measures.• reading through FIELDPOINT FP-100 interface driven byLabView.• Number of cycles, number of measures within a cycle, time betweencycles and time between measurements are supplied by the user• Automating reading of Temperature and Humidity
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Normalised rho at T=20
0,90
0,92
0,94
0,96
0,98
1,00
1,02
1,04
1 24 47 70 93 116
139
162
185
208
231
254
277
300
323
346
369
392
415
438
461
484
507
530
553
576
599
622
645
668
691
714
737
760
783
Time (A.U.)
No
rmal
ised
Rh
o 2
0
44
45
46
47
48
49
50
51
52
53
54
Hu
mid
ity
(%)
Normalised rho at T=20
Humidity
Systematic: 800 cycles of measures, 10 measures/cycle, 10 sec after each measure (~ 26 hours).The resistivity (at T=20 C) of a phenolic sample as a function of time is normalised to the first value and plotted (left scale). The recorded value of the humidity is also shown (right scale)
H=47.5 %
H= 53 %
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Nornalised Rho at T=20
0
50
100
150
200
250
300
350
400
450
0,92 0,94 0,96 0,98 1 1,02 1,04 1,06
Normalised Rho
Nornalised Rho at T=20
Histogram distribution from the previous plot
22
22,2
22,4
22,6
22,8
23
23,2
23,4
1 50 99 148 197246 295 344 393 442491 540 589 638 687 736785
4445464748495051525354
Temperature (C)
Humidity (%)
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rho20 normalised and humidity
0,92
0,94
0,96
0,98
1,00
1,02
1,04
1,06
1,08
1 10 19 28 37 46 55 64 73 82 91 100
109
118
127
136
145
154
163
172
181
190
199
208
217
226
235
244
253
262
271
280
289
time (A.U.)
No
rm.
Rh
o a
t 20
44
44,5
45
45,5
46
46,5
47
Hu
mid
ity
(%)
normalised
humidity
Another example (melamine) for which instead the humidity has changed onlyfrom 45 % to 46.5 % (only 294 cycles)
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-20
0
20
40
60
80
100
120
0,94 0,96 0,98 1 1,02 1,04 1,06 1,08 1,1
Histogram distribution of the previous plot.
23,0
23,2
23,4
23,6
23,8
24,0
24,2
1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289
Temperature
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Roughness QualityQualitative view of the surface of the new improved bakelite. The pixel matrix greyscale of a micropictrue of the bakelite surface is shown
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Automatic Station for Resistivity measurement
• mechanics and controls• electronics and DAQ
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