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CHAPTER 5

IMPROVEMENT OF CURRENT EFFICIENCY AND

HARDNESS IN PULSE REVERSE PLATING

5.1 INTRODUCTION

The preliminary investigation is done using pulse plating on PCB.

Here Pulse Reversal technique is tried for plating on do uble sided PCB. It

should be noted that not much of research is being carried until 1990. Pulse

reversal technique is absolute new technique to be employed on PCB using

silver.

The electrochemical deposition of pulse reverse current plating

plays a new role on Printed circuit Boards. As the name suggests, Pulse

reverse is the direction of the current that alternates so that the sample acts as

both cathode and anode. Pulse reverse plating helps in obtaining an improved

quality deposit such as reduced grain size, increased conductivity and reduced

porosity.

Pulse reversal plating makes it possible to improve the material

distribution, by dissolving "unwanted" metals during the anodic periods. This

type of pulse plating also has a dramatic influence on the crystalline structure

of the coating and is known to be able to reduce internal stress of the

deposits . As the size of the holes on the printed circuit boards is decreased

and the thickness of the boards is increased, it becomes more and more

difficult to deposit enough silver in the holes. Using pulse reversal plating it

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is possible to improve the material distribution, by dissolving previously

plated silver in high current density regions during the anodic periods.

Figure 5.1 Pulse Reverse Current Waveform

Pulse reverse current waveform with the five parameters

highlighted:

(a) cathodic current intensity amplitude,

(b) cathodic pulse duration on time,

(c) anodic current intensity amplitude,

(d) anodic pulse duration on time, and

(e) off-time of the pulse

All the above five parameters can be controlled in pulse reversal

plating. Since the controlling parameters increase, the ability to obtain grain

of desired size also increases.

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The introduction of PRC, in PCB manufacturing, eliminates the

passive layer formation on the copper anode. The distribution of the

electroplated metal is improved when PCB becomes temporarily anodic. The

use of pulse reverse current reduces the non uniform plating and thereby it

forms a diffusion causing the silver to dissolve easily ,thus leading to a more

uniform deposit.

5.2 EXPERIMENTAL SET UP

The same set up that is used for pulse plating is used for pulse

reversal plating. The only difference is that here small number of additives are

added to bath .These additives ensure that the uniform coating is obtained

In chapter 4, the pulse plating set up is discussed .The same setup

with the bath of silver cyanide and potassium cyanide is used. Here anode and

cathode is kept constant during the complete experiment is carried out.

The PH value is checked and it is 11.76 which is ideal condition for

plating of silver. The room temperature is checked and it is maintained at the

value of 28 degree centigrade since the background conditions play a major

role in pulse reverse plating technique.

5.3 PROCEDURE FOR OBTAINING PULSE REVERSE

PLATING

Pulse reverse waveform is obtained by making ON time and OFF

time work within the given direction time. During this time the values are set

for Forward ON time, Forward OFF time, Forward time duration ,Reverse

time duration, Reverse ON time and Reverse off time. All the above said

values are set on the displayed meter using keyboard and then the plating is

carried.

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To operate the Pulse reversal plating the following steps are carried

out

In the CONTROL Panel of the rectifier, Press the PULSE

TIMING Key

Select SET REVERSE Duration using the arrow keys and the

value namely 15 is set and the value is entered.

Select SET REVERSE ON TIME and enter the value namely

10 and the value is entered.

Select SET REVERSE OFF TIME and enter the value 5 and

the value is entered

Now it will show the main menu. It displays the duty cycle that

is applied for the plating

It is observed that the Forward duty cycle and reverse duty cycle

is one and the same.

Now the current value and voltage values are entered by using

the arrow keys near the AMPS and VOLTS

Now the Effective value is displayed in the main screen.

Similarly on pressing the ENTER key it will display the

Average forward output values and average reverse output

values.

OPR key is pressed to turn on the Unit’s output.

STDBY key is used to turn OFF the output.

Calculate the TOTAL ON TIME and TOTAL OFF TIME in

reverse current. Sometimes it is observed that the number of cycles of

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forward and reverse may not be same. In this experimental analysis there are

only even number of forward and reverse cycles. So that experimental

calculation becomes accurate.

5.4 FORMULAE

The formulae used for pulse reverse plating is as below.

PARAMETER MATHEMATICAL EXPRESSION

Frequency f=(1/b+d+e)

Average Current Intensity Id=(axb+cxd)/(b+d+e)

Current ratio R=c/a

OFF time Toff =e

Positive Duty Cycle ?+ =b/(b+d+e)

Negative duty Cycle ?-=d/(b+d+e)

ON duty Cycle ? on=(b+d)/(b+d+e)

5.5 DUTY CYCLE FOR REVERSE PLATING TECHNIQUE

It is necessary to calculate the duty cycle for pulse reverse

waveforms .Period is the total ON +OFF time .It can also be defined as the

period of the time from the beginning point of the waveform to the point

where the waveform begins to repeat. This is one period. With periodic

reverse there are 3 possible periods.

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There are 3 possible periods.

1 Forward ON +OFF

2 Reverse ON+OFF

3 Forward+Reverse

Now the Total ON time is calculated. The Total ON time is divided

by the sum of the Time (Fwd) + sum of the Time (Rev).This is called as

effective duty cycle and it is multiplied by the peak current to obtain the

average current. From the ampere time preset the plating thickness is

determined.While electroplating it is also observed that if the current

efficiency is close to 100% the material deposition will be equal to current

distribution.

5.6 DESIGN OF EXPERIMENTS (DOE)

The design of experiment (DOE) is a series of steps that follows a

sequence for the experiment to yield an improved performance. It contains 3

phases .They are Planning phase, conducting phase and analysis phase. Here

the experiment is planned in such a way that it yields positive experimental

results. This attitude is possible when the planning phase is done properly by

taking into consideration various variables that plays major role in obtaining

the results. Positive information indicates which factors lead to improved

performance.

Here the combination of variables namely Reverse duration time,

Forward duration time, Forward ON time, Forward OFF time ,Reverse ON

time and Reverse OFF time play a major role in determining the

characteristic of plating on Printed Circuit Board. The aim is to execute an

effectively designed experiment.

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5.7 OPTIMIZATION TECHNIQUE

In the plating of printed Circuit Board using reverse plating 5

variables influence the performance of the plating. The technique of defining

and investigating all possible conditions in an experiment involving multiple

factors is called as design of experiments.

Parameter design is the key step in the pulse reverse plating

method.

5.7.1 Determination of Current Density of the Bath using Hull Cell

Apparatus

The Hull cell is nothing but a miniature plating tank where a test

panel is used as the cathode and is placed at a diagonal to the anodes so that it

experiences very high current density at one end and very low current density

at the other.

Current density for silver plating of the bath using Hull Cell

Apparatus is given by

i = I (5.1-5.24 log X) (4.7)

X= distance from high current density end of panel in cm for pulse

plating =4.4 cm

I= applied current = 1 ampere

i = i (5.1 – 5.24 log (4.4)) (4.8)

i = (5.1 – 3.37169) (4.9)

i = 1.7283 ampere/dm2 = The current density of the bath for Pulse

reverse plating.

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Table 5.1 The Various Experimental Data Given to the Rectifier for

Pulse Reverse Plating of Double Sided Printed Circuit

Board

DoE

Reverseduration

(milliseconds)

ReverseON

time(milliseconds)

ReverseOFFtime(milli

seconds)

Forwardduration

time(milli

seconds)

ForwardON time

(milliseconds)

ForwardOFFTime(milli

seconds)1 -20 15 5 30 20 102 -30 20 10 20 15 53 -20 5 15 30 20 104 -20 5 15 30 10 205 -30 25 5 40 30 106 -40 30 10 30 25 57 -30 5 25 40 10 308 -30 5 25 40 30 109 -40 30 10 30 20 1010 -40 30 10 20 30 1011 -40 20 20 30 15 512 -40 15 5 30 5 1513 -40 10 30 20 15 514 -40 10 30 20 5 1515 -30 10 20 20 15 516 -20 10 10 30 15 517 -50 40 10 40 30 1018 -40 30 10 50 40 1019 -50 10 40 40 30 1020 -50 10 10 40 10 2021 -50 20 30 40 30 1022 -50 30 20 40 20 10

Ireverse = 1amps and Vreverse= 10 volts , (DoE = Design of Experiment)

Table 5.1 shows the various experimental data given to the pulse reverse plating setup. The values are designed in such a way that it yields high current efficiency and hardness to the plated printedcircuit board. The

difference between pulse plating and pulse reverse plating is that with pulse plating there will be only one ON +OFF cycle but in reverse pulse plating technique there will be several ON + OFF cycles. If the ON time is in

opposite direction then it is equal to OFF time. While calculating not only one

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ON time is taken for calculation but all ON time of the whole period is taken for calculation .From Table 5.1 it is observed that No forward ON time is in

negative direction

Table 5.2 The Experimental Data Obtained for Various Pulse Duty

Cycles of 10% to 100%

DoE

Forwardduty Cycle

(fDC) inpercentage

Effective forward duty cycle (efDC)

in percentage

Reverse duty cycle (rDC) in

percentage

Effectivereverse duty

cycle (erDC) in percentage

EffectivePlating

Current

1 66.7 40 75 30 -0.3

2 75 30 66 40 -0.4

3 66.7 40 25 10 -0.1

4 66.7 40 25 10 -0.1

5 75 50 100 33.3 -0.3

6 83.3 35.7 75 42.9 -0.4

7 25 14.3 16.7 7.1 -0.1

8 75 42.9 16.7 7.1 -0.1

9 66.7 28.6 75 42.9 -0.4

10 100 33.3 75 50 -0.5

11 83.3 35.7 50 28.6 -0.3

12 33.3 14.3 75 42.9 -0.4

13 75 25 25 16.7 -0.2

14 25 8.3 25 16.7 -0.2

15 75 30 33.3 20 -0.2

16 83.3 50 50 20 -0.2

17 75 33.3 80 44.4 -0.4

18 80 44.4 75 33.3 -0.3

19 75 33.3 20 11.1 -0.1

20 50 22.2 60 33.3 -0.3

21 75 33.3 40 22.2 -0.2

22 75 33.3 60 33.3 -0.3

Ireverse = 1amps and Vreverse= 10 volts ,(DoE = Design of Experiment) RTC =600 sec .

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From Table 5.2 for the DOE the respective fDC and efDC is

calculated. The fDC is the duty cycle of the settings during the forward time

of the waveform. The efDC is the duty cycle of the forward time relative to

the overall waveform. rDC is the reverse duty cycle of the settings during the

reverse time of the waveform. erDC is the effective duty cycle of the reverse

time relative to the overall waveform .

Since there are continuous forward and reverse pulses in Pulse

reverse plating technique, it will lead to coarse deposits at the first cycle ,then

the reverse current will dissolve the excess of silver deposited , the following

forward cycle will plate the silver without any dog boned deposits.

Thus reverse cycle leads to better efficiency when compared to

pulse plating and DC plating. But there is a disadvantage that the RTC (Real

Time Cycle) maintained is at higher rate when pulse reverse plating is carried

.

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Table 5.3 The Experimental Values Namely Frequency, Average

Current Intensity, Positive Duty Cycle, Negative Duty Cycle

and ON Duty Cycle RTC =600 sec

DoEFrequency

(Hertz)

Averagecurrentintensity

(mA)

CurrentRatio

Positiveduty cycle

(%)

Negativedutycycle

(%)

On duty cycle(%)

1 25 22.5 0.667 40 37.5 87.5

2 22 20 1.5 33 44.4 77.7

3 25 17.5 0.667 50 12.5 62.5

4 33 13.3 0.667 33 16.6 50

5 16.6 32.5 0.75 50 41.6 91.7

6 15.4 30 1.33 38.5 46.2 84.6

7 25 13.75 0.75 25 12.5 37.5

8 16 22.5 0.75 50 8.3 58.33

9 16 30 1.33 33 50 83.3

10 14.3 25.7 2 43 42.8 85.7

11 18.2 22.7 1.33 27.3 36.36 63.6

12 40 30 1.33 20 60 80

13 18.2 12.7 2 27.3 18.2 27.3

14 22 11.1 2 11.1 22.2 33.3

15 22 13.3 1.5 33.3 22.2 55.5

16 28.6 18.57 0.667 42.8 28.6 71.4

17 12.5 40 1.25 37.5 50 87.5

18 12.5 40 0.8 50 37.5 87.5

19 12.5 21.25 1.25 37.5 12.5 50

20 33 30 1.25 33.3 33 66.7

21 12.5 27.5 1.25 37.5 25 66.7

22 14.3 32.85 1.25 28.6 42.9 71.4

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Table 5.3 Diplays the frequency that is used during pulse reverse

plating technique. Frequency depends mainly on the cathodic pulse duration

ON time, anodic pulse duration ON time and OFF time of the pulse. Average

current intensity is high when the ON time is higher both in positive and

negative direction. It plays the role obtaining the grain of the desired size

.Current ratio is high when the cathodic intensity amplitude is low and the

anodic intensity amplitude is high. Positive duty cycle is high when the

forward ON time is high.

Negative duty cycle is high when the reverse ON time is high. It is

observed that the ON duty cycle is high when the reverse ON time and OFF

time are high.

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Table 5.4 The Experimental Data Obtained after Pulse Reverse

Plating Namely Current Effici ency and Hardness

DoE

Averagecurrentintensity

(mA)

AveragecurrentDensity

mA/ mm2

Theoreticalweight(grams)

ExperimentalWeight(grams)

Currentefficiency

(%)

Hardness(VHN)

1 22.5 54.87805 0.0150 0.0146 97.2 76.4

2 20 48.78049 0.0134 0.012392.3

73.2

3 17.5 42.68293 0.0117 0.0103 88.4 76.24 13.3 32.43902 0.0089 0.0050 56.2 82.2

5 32.5 79.26829 0.0218 0.01813 83.2 70.46 30 73.17073 0.0201 0.0162 80.6 68.2

7 13.75 33.53659 0.0092 0.00547 59.4 76.1

8 22.5 54.87805 0.0150 0.0146 97.2 70.8

9 30 73.17073 0.0201 0.0162 80.7 68.1

10 25.7 62.68293 0.0172 0.01625 94.3 68.111 22.7 55.36585 0.0152 0.01496 98.3 71.2

12 30 73.17073 0.0201 0.0162 80.6 87.3

13 12.7 30.97561 0.0085 0.00402 47.3 70.114 11.1 27.07317 0.00744 Poor deposit

15 13.3 32.43902 0.00892 0.00501 56.2 73.1

16 18.57 45.29268 0.01245 0.01128 90.6 78.2

17 40 97.56098 0.02683 Burnt deposit18 40 97.56098 0.02683 Burnt deposit

19 21.25 51.82927 0.01425 0.01347 94.5 65.3

20 30 73.17073 0.02012 0.0162 80.7 82.221 27.5 67.07317 0.01844 0.01663 90.2 65.3

22 32.85 80.12195 0.02203 0.01833 83.2 66.3Average Current Density =Average current flowing per 0.41mm2

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Table 5.4 concentrates only on the DOE that gives desired plating

thickness. All other DOE are neglected since DOE 17,18 gives burnt deposits

and DOE 14 gives poor deposit in the film deposited. Micro hardness

measurements are made for pulse reversal technique .The current density is

also calculated. Different pulse reversal waveforms produced different

coatings ranging from dull white to bright white colour.

It is observed from the readings that the dull white refers to the

coating with the hardness and current efficiency being low. When the same

specimen obtains bright white it states that the current efficiency and hardness

is high. This high hardness is obtained in the cases when the forward duty

cycle is high and the reverse duty cycle is low. Since the forward cycle adds

up coating to the specimen and the reverse plating dissolves the metal added

up to the specimen. In order to obtain high current efficiency always the

forward duty cycle is kept high and the reverse duty cycle is kept low. This is

possible by having the forward ON time being greater than the reverse ON

time and also the forward OFF cycle is kept lower than the reverse OFF cycle.

It is observed that as the average current intensity increase the

deposition of silver also increases .

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Figure 5.2 DOE Plotted for Forward ON Time and Reverse ON Time

5.7.2 Inference of DOE Plotted for Forward ON Time and

Reverse ON Time

Figure 5.2 shows the various values of DOE being plotted to

various forward ON time and Reverse ON time. Since the aim is to obtain

high current efficiency readings with high reverse ON time and Low forward

ON time is not considered .Such readings lead to poor deposits .So

concentration is done on readings with high Forward ON time and Low

reverse ON time.

More number of readings are plotted for forward ON time of 30 and

less number of readings after 30 .This graph eventually proves the

consistency of readings taken to obtain better current efficiency.

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Figure 5.3 DOE Plotted for Forward OFF Time and Reverse OFF

Time

5.7.3 Inference of DOE Plotted for Forward OFF Time and

Reverse OFF Time

From Figure 5.3 it is observed that many values are taken for reverse OFF

time being high and forward OFF time being low. Only few values are

considered for high forward OFF time and low reverse OFF time.

From the figure it is analysed that many readings are taken for forward OFF

time of 10 and less number of readings after 30.Similarly more number of

readings are taken below 30 and less number of readings are taken after the

reverse OFF time of 30.The main reason behind designing of Experiment in

this way is to analyse and determine the deposit characteristics with good

reliability.

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Figure 5.4 DOE Plotted for Effective Forward Duty Cycle (efDC) in

Percentage and Effective Reverse Duty Cycle (erDC) in

Percentage

5.7.4 Inference of DOE Plotted for Effective Forward Duty

Cycle (efDC) in Percentage and Effective Reverse Duty Cycle

(erDC) in Percentage

Figure 5.4 shows DOE plotted for effective forward Duty cycle and

effective reverse duty cycle. There are more DOEs with high effective

forward duty cycle and low effective reverse duty cycle.It is observed that

there are many plots of effective forward duty cycle after the value of 30 and

less number of effective forward duty cycles below 30.It is observed that the

reverse cycles have significant influence on the distribution of silver due to its

mass transport properties.

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5.8 X-RAY DIFFRACTOMETER TEST

The pulse reverse plated specimen is tested for XRD .The sample

n.o with DOE1 and DOE11 ,which contain the highest current efficiency are

examined. From figure 5.5 it is observed that the metal coated is silver and it

is proved from the JCPDS N.O:87-0598.The structure of the metal deposited

is hexagonal in nature.

Figure 5.5 XRD Graph for the Specimen of DOE 1

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Table 5.5 Strongest 2 Peaks of XRD of DOE 1

No.Peakno.

2Theta

(deg)

D

(A)I/I1

FWHM

(deg)

Intensity

(counts)IntegratedInt(counts)

1 2 51.6827 2.08603 100 0.17290 300 2925

2 5 59.0600 1.81482 3 0.13000 10 116

From Table 5.5 the 2 theta value is determined .It has the highest

intensity counts.

5.8.1 Inference of XRD Graph for the Specimen of DOE 1

There are 2 peaks with the highest intensity counts.The highest peak is pak

n.o 2 with the highest intensity count of 2925. The (h,k,l) value is found to be

104 and 105 where 104 is first order of reflection and 105

is second order of reflection. They are the values of adjacent planes. Pulse

reverse plating reduces the surface thickness and it fills the hole with good

ability. From the scherrer equation it is observed that the grain size is 8 nm

for DOE 1 .When the grain size is minimum it is obvious that the adhesion of

silver on to the PCB is going to be high.The reverse pulse dominates the

reverse action and it leads to surface uniformity. The forward and reverse

cycles influence the size of silver deposited .

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Figure 5.6 XRD Graph for the Sample of DOE 11

From Figure 5.6 the various peaks are obtained for the sample data.

Table 5.6 Strongest 3 Peaks of DOE 11

No.Peaks

no.2Theta(deg)

D(A)

I/I1FWHM

(deg)Intensity(counts)

IntegratedImt(counts)

1 108 51.675 2.08469 100 0.20160 90 978

2 130 59.3772 1.80600 42 0.16110 38 335

3 131 59.1217 1.79927 13 0.11000 12 73

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5.8.2 Inference of XRD Graph for the Specimen of DOE 11

It is observed from the table 5.6 that there are many peaks and the

strongest peak is obtained at the 2 theta value of 51.675 which has the greatest

intensity counts .When the theta value is substituted in scherrer equation the

grain size value obtained is equal to 7 nm. The metal coated is silver and it is

proved from the JCPDS N.O:87-0598.The structure of the metal deposited is

hexagonal in nature.

The (h,k,l) values are found to be 104 and 105 .They are the values

of adjacent planes. In all the graphs the adjacent planes are same referring it

to be the silver metal. Pulse reverse plating has a control of charge transfer

done on the silver characteristics.

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Table 5.7 Various Plating Techniques and their Corresponding Weight

and Efficiency(%)

S.NoPLATINGtechnique

WEIGHTDEPOSTED(grams)

EFFICIENCY(%)

1 DC 0.3329 87.1

2 PULSE 0.078 97.2

3PULSEREVERSE

0.01496 98.3

Table 5.7 shows that in pulse reverse plating there is minimum

amount of weight deposited for the maximum current efficiency 98.3% .The

amount of weight deposited is 0.01496.As far as weight deposited is

concerned pulse reverse plating is better than DC plating and Pulse plating .

Pulse reverse plating exhibits a maximum of 98.3%

efficiency.Thus manufacturers can prefer to pulse reverse plating when

compared to Pulse plating and DC plating if they require high current

efficiency.

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Figure 5.7 Hardness between DC Plating, Pulse Plating and Pulse

Reverse Plating

From Figure 5.7 it is observed that the highest hardness value is

obtained for pulse reverse plating of 87.1 VHN. Thus from the above graphs

it is observed that pulse reverse plating is better than the pulse plating and DC

plating technique. But it is a time taking process .In pulse plating RTC (real

time cycle) is maintained at 180 seconds but for pulse reverse plating it is

maintained at 600 seconds.

5.8.3 Inference of Hardness between DC Plating, Pulse Plating and

Pulse Reverse Plating

It is analysed that the highest hardness value of the plating leads to

longer life of the plated printed circuit board.When the hardness is higher

there will not be any embrittlement of the PCB. Moreover when the

components are attatched to the board using the silver plated holes they are

not detatched from the board easily.

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5.9 CORROSON TEST FOR PCB

The corrosion test is carried for PCB using salt spray test. Here the

PCB is exposed to a fine mist of 5% sodium chloride atmosphere. The onset

value indicates the minimum time required for the tarnishing effect to start.

The onset of blackish brown oxide formation on the PCB is 300 seconds for

Pulse plating ,340 seconds for Pulse Reverse Plating and 180seconds for DC

plating. The coating has been consumed by the corrosion reaction, and the

corrosion of the base metal begins. It is observed that for pulse plating the

value is more compared to DC plating. Hence the anti tarnishing behaviour is

dominant in pulse plating and pulse reverse Plating.

The arrival of pulse plating technique is going to make the DC

plating technique obsolete. Pulse plating plays a major role in today’s

electronics, automobile and jewellery industry as well. A reduction in grain

size is accompanied by an increase in grain boundaries and a consequent

increase in resistivi ty in nanocrystalline materials.

It is observed that pulse reverse plating is a powerful tool for

plating on printed circuit boards.

Table 5.8 Various PLATING Technique and

Corresponding Time for Corrosion

S.NoPLATING

techniqueTIME

TAKEN(seconds)

1 DC 180

2 PULSE 300

3 PULSE REVERSE 340

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Figure 5.8 Corrosion Test between DC Plating, Pulse Plating and Pulse

Reverse Plating .

From Figure 5.8 it is observed that the highest time taken for PCB

to be corroded value is obtained for pulse reverse plating of 340 seconds and

the least time to get corroded is obtained for DC plating which is 180 seconds.

5.9.1 Inference of Corrosion Test between DC Plating, Pulse

Plating and Pulse Reverse Plating.

It is analysed that the higher the time taken by the Printed

Circuit Board to become corroded higher the efficiency is the board because it

will not lead to any short circuit between the components and such a board is

also useful to be used at humid temperatures rather than the ordinary board.

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5.10 FINAL TEST ON PCB

Boards are tested for opens and shorts in the circuitry, in one of the

last steps of production. Boards are visually inspected to assure they meet our

customers’requirements, industry specifications and Advanced Circuits’

standards, as well as having the physical dimensions and hole sizes verified.

Even the smallest corrosion attack could be fatal for a micro component .

Finally a double sided PCB is manufactured with high grade electronic

components and superior quality raw material and highly superior plating

technology. This PCB is highly corrosion resistant.

` Today Pulse or Reverse Pulse Plating processes are mature in terms

of rectifier and chemistry reliability. Their main advantages are an

unsurpassed throwing power as well as an even metal distribution across the

board surface especially during pattern plating. Due to these properties cost

savings are significant particularly, in the area of final copper etch and solder

mask application.

After mounting the components on PCB is finished, a final check

is carried for the continuity track of the circuit. This part of job is to ensure

that the operation of this circuit will run smoothly.

The tools related with the checking parts is multimeter and the

continuity checking involve with every circuit tracks and the point of

soldering. By using the buzzer multimeter, it will alert the failed continuity.

117

5.11 SUMMARY OF FINDINGS FOR PULSE REVERSE

PLATING

From the tabulations obtained for various average current density it

is observed that the highest current efficiency is found for constant average

current density 55.36585 .DOE 11 has Reverse duration as 40seconds,

Reverse ON time as 20seconds reverse OFF time as 20 seconds, Forward

duration time as 30 seconds ,Forward ON time as 15 seconds and Forward

OFF time as 5 seconds. The maximum current efficiency obtained is

98.3.The maximum hardness obtained is at DOE12 and its value is 87.3but its

current efficiency is 80.3. So DOE11 is considered as optimal for plating .

Pulse reverse plating is better than the previous two techniques

namely DC plating and Pulse plating due to the following reasons.

Grain size is much smaller than pulse plating technique.

Anti tarnishing effect is high

It contains higher current efficiency and greater hardness than other

two techniques.

It contains less number of pores

There is a control of charge transfer done on the silver

characteristics.

When there is reverse current there is uniformity in deposition

properties because concentration gradient is developed at low

frequency.

The grain size influence the coercivity, relative permeability and

more importantly resistivity.

The reverse current leads to in depth deposition of the material with

uniformity.

Additional number of variables used help in control of anamolous

codeposition of particles