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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