Download Fabrication of Complex Circuit Using Electrochemical

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
Fabrication of Complex Circuit Using Electrochemical
Micromachining on Printed Circuit Board (PCB)
Singh Jitendra1, Jain V.K.2*, Ramkumar J.3
1
Mechanical Engineering Department, IIT Kanpur - 208016, [email protected]
2*
Mechanical Engineering Department, IIT Kanpur - 208016, [email protected]
3
Mechanical Engineering Department, IIT Kanpur - 208016, [email protected]
Abstract
Electrochemical micromachining (ECMM) is an advanced machining process for machining of electrically
conducting materials. In the present work, an experimental set-up for electrochemical micromachining (ECMM) is
used to fabricate complex circuits on printed circuit board (PCB) by using masking technique. Mask is made using
50 µm transparency sheet cut by laser beam. This mask is bonded on printed circuit board of cross section 35 mm X
35 mm by a water insoluble glue Araldite (epoxy adhesive). For the analysis of the data the channel width of the
circuit structure is measured with the help of photographs taken by using Dinolite capture and optical microscope.
For this purpose whole structure is divided into 4 regions, which have fifty eight points in which width has been
measured. For the analysis of the depth of a channel, a dial gauge having 1 µm least count is used to measure the
depth at different sections (or regions) as marked in the Figure. For this purpose, the whole structure is divided into
4 regions, which have twenty seven points. After all the experiments have been completed, the circuit is compared
with the main circuit which is fabricated by milling process and % error in the circuit is evaluated.
Keyword: Electrochemical micromachining, Printed circuit board, micromachining
1
Introduction
Due to the limited resources such as space, material and
energy, their efficient utilization is an important issue.
Miniaturization is becoming an important need of the
days. The term micromachining considers the miniature
features/structures/parts which are not easily visible
with naked eyes and have dimensions smaller than 1
mm (1 µm ≤ dimension ≤ 999 µm) [1]. Recent changes
in society demands have forced to introduce micro
parts, or macro parts with micro features into various
industries; for example, automobiles, aviation, space,
electronics and computers (printed circuit boards).
Making 3D structure by conventional machining is
difficult as compared to advanced machining processes.
Electrochemical micromachining (ECMM) process is an
advanced micromachining process for machining
electrically conductive materials. The process works on
the principle of Faraday’s laws of electrolysis, where
material is liberated from the work piece surface atom
by atom. ECMM process is just reverse of the
electroplating process where the objective is to deposit
the material. On applying potential across the tool and
work piece, positively charged ions are attracted
towards cathode and negatively charged ions are
attracted towards anode. The inverse shape of the tool is
produced on the work piece. Positive metal ions leave
the work piece and they form insoluble precipitate.
Following reactions take place at both the electrodes [1,
2].
At anode;
In the present case, M is copper and n (= 2) is valency
of the work piece material. The electrolyte accepts these
electrons resulting in a reduction reaction which can be
represented as
At cathode;
Thus, positive ions from the metal react with the
negative ions in the electrolyte, forming hydroxides and
thus the metal is dissolved forming a precipitate.
In solution;
Insoluble material and heat generated during machining
are removed by flowing electrolyte.
ECMM appears to be a promising micromachining
technology due to its advantages that include high
material removal rate (MRR), better precision and
control, low machining time, and no tool wear [3]. It has
been observed that the desired accuracy can be achieved
at higher frequency, medium electrolyte concentration
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Fabrication of Complex Circuit Using Electrochemical Micromachining on Printed Circuit Board (PCB)
(20 g/l), and average machining voltage (3 V) [4-7].
Smaller parts size with better machining accuracy are
produced ECMM by side insulation of tool [8]. Use of
short pulse voltage and passive electrolyte, higher
dimensional accuracy can be achieved [9]. ECMM
process is comparatively more environmental friendly
and high speed technology [10].
3
2
3.1 Adhesion between work piece and tool
Experimental set-up
A schematic diagram of experimental set-up is shown in
Fig. 1. Hyper 10 (Multi Process Micro Machine Tool by
Sinergy Nano systems) machine is used to carry out
experiments by electrochemical micromachining
process. The maximum travel ranges of the machine are
130 mm (X) x 75 mm (Y) x 80 mm (Z). Each axis has
positional accuracy of ±5 µm, repeatability of all sides
±1 µm and side straightness ±1 µm for all axes. Desired
interelectrode gap (IEG) is maintained by giving feed to
the motor by Z-axis controller. A perspex tray with
drain is mounted on X–Y table, and it also holds
electrolyte and reaction products
Fabrication of complex circuit and
performance evaluation
In this work, a complex circuit structure on printed
circuit board (PCB) is made by ECMM using masking
technique. Fabrication is not expensive and takes less
time as compared to other fabrication processes.
Adhesion of the mask (Fig. 2) to the work piece plays a
crucial role in fabrication of structure. If mask is not
properly glued to the work piece, electrolyte flows
between work piece and mask, and causes undercut. A
printed circuit board sheet having the size of 35 mm X
35 mm is used as a work piece (anode) by connecting it
to positive terminal of power supply and, another
copper plate having dimensions of 35 mm X 35 mm X 1
mm is used as a tool (cathode) by connecting it to the
negative terminal of power supply.
The mask is prepared from a thin transparent sheet
having thickness of 50 µm. Mask cutting is done by
using engraving technique with low power laser cutting
machine. Dimensions of the mask are shown in Fig. 2.
Maximum width of channel cut on the mask is 385 µ m.
The circuit has been divided in four different regions for
characterization purposes, Fig. 3.
All specified
dimensions are in mm
Figure 1: Schematic diagram of electrochemical
micromachining process
Components of multipurpose machine tool are
X, Y, and Z axes feed unit,
Working table,
ECM power supply unit,
Control unit,
Electrolyte flow control unit.
Table 1: ECMM parameters in Hyper 10
multipurpose machine tool
Parameter
Voltage (V)
Capacitance (pF)
polarity
Sensitivity (%)
Range
1-24
33-10000
Both, normal and reverse
65-85
Figure 2: Schematic diagram of mask made on
design software (Solid-work)
3.2 Performance evaluation of fabricated
circuit
Experimental set-up which is explained in the previous
section is used for fabrication of complex circuit on
PCB using ECMM process.
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
(c)
Figure 3: Depth and width measurement at four
different region
3.2.1
Channel depth
Effect of voltage
Fig. 4 shows the effect of voltage on depth of channel at
different capacitance values for individual region. In
Fig. 4, 41 µm is the minimum value in region 2 and 4 at
6 V and 33 pF capacitance, and maximum value 54 µm
in region 1 for 11 V and 10000 pF capacitance. It is
clear from the graph that depth increases approximately
linearly from 6 V to 11 V. A dial gauge having 1 µm
least count is used to measure the depth at different
sections (or regions). Channel depth is measured at
twenty seven points on the structure in which regions 1,
2 and 4 have six points each and region 3 has nine
points. The whole structures has many sharp corners
and curves. The average depth readings of different
points in different regions plotted in the graphs.
(a)
(d)
Figure 4: Effect of voltage on channel depth at
different regions with variation in capacitances
Effect of capacitance
Fig. 5 shows the effect of capacitance on channel depth
for different voltages. As the capacitance level
increases, channel depth is changing marginally in all
regions. As capacitance increases energy per sparks
increases hence MRR also increases. As a results, depth
of micro channel also increases.
(a)
(b)
(b)
Figure 5: Effect of capacitance on channel depth at
different regions with variation in voltages.
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Fabrication of Complex Circuit Using Electrochemical Micromachining on Printed Circuit Board (PCB)
3.2.2
Channel width
Channel width can be measured by the optical
microscope BX51. Whole structure is divided into four
regions, in Fig. 3. Regions 1 and 2 have fourteen points
each, region 3 has twenty, and region 4 has eight points.
There are total fifty eight points. Image is taken on
every point with 5X magnification, and channel widths
are measured at 3-4 points on every image. The average
readings in different regions are taken.
(a)
Four images of a channel cut on a PCB are taken by the
optical microscope as shown in the Fig 6 with their
machining conditions used.
V = 6 V,
Width of channel= 436 µm
V = 7 V,
Width of channel= 436 µm
(b)
(a)
(b)
Figure 7: Effect of voltage on channel width at
different regions with variation in capacitances
Effect of capacitance
V = 10 V,
Width of channel= 436 µm
(c)
Fig. 8 shows the effect of capacitance on channel width
at different voltages. It is clear from that as the
) increases, the
capacitance level (i.e. energy (=
V = 11 V,
Width of channel= 436 µm
(d)
Figure 6: Variation in channel width at different
voltages at 100 pF capacitance and 25 g/l electrolyte
concentration
channel width increases up to 1000 pF beyond which it
starts decreasing. In the present case, voltage varies
from 6V-11 V.
Effect of voltage
Effect of voltage on channel width for different
capacitance values is shown in Fig. 7. It is clear from
the graphs that channel width increases with increase in
voltage. According to Faraday’s laws, with increase in
voltage, current (I) increases and material removal (m)
is proportional to the current flowing through IEG as
given below,
(a)
(1)
Where, E is chemical equivalent of anode material, F is
Faraday’s constant.
Therefore, the size of the channel is increased as the
voltage increases. Other region (3, 4) have similar trend.
(b)
Figure 8: Effect of capacitance on channel width at
different regions with variation in voltage
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
4
Inspection of circuit
After fabricating the complex circuit, it was checked
using a microscope for continuity, and some defects
were found as explained below. For testing the circuit,
fifty eight points are selected on every circuit. In some
points, the channel was not cut properly up to the
required depth, and at some points of PCB, substrate
reacted with electrolyte and depth increased. At other
points, the overcut was greater than the channel width
on the mask because of improper adhesion of mask on
the work piece. Because of this, the gap between two
channels at some points is decreasing. This is clearly
seen in Fig. 9 (a), (b). Fig. 10 shows a discontinuity in
the circuit, which is present due to mask design. These
discontinuities can be removed by taking an additional
selected cutting. There is no contact between tool and
work piece so no mechanical defects are present in the
circuit.
(a)
Figure 10: Discontinuity present in circuits due to
mask design in ECMM process
5
Comparisons between Circuit fabricated
by ECMM process and Milling process
Fig. 11 shows a complex circuit fabricated by ECMM
process, and milling process. Width and depth of the
channels are compared to each other and % error is
found, (Table 2).
(b)
Figure 9: Uncut channel with at (a) volt=5, C= 33pF,
concentration = 20g/l (b) volt = 11V, Cap. = 1000pF,
concentration = 25g/l
Figure 11: Circuits fabricated on (a) on ECMM
(Voltage =7 V, capacitance = 1000 pF, NaCl
concentration =25 g/l of water, IEG= 1000 µm and,
(b) on LPKF Protomat 955/II (milling)
Fig. 12 and Fig. 13 show a comparison of width and
depth of the machined channels by ECMM and micromilling. In some regions, there is substantial difference
(33%) between ECMM’d work piece and micro milled
work piece.
Table 2: Comparisons between circuits fabricated by ECMM process and micromilling process
Average width (µm)
Average Depth (µm)
Region
By ECMM
By Milling
% error
By ECMM
By Milling
% error
1
479.48
309.5
54.92
51
38.5
32.46
2
476.92
271.0
54.34
49
38
28.54
3
493.87
283.33
43.01
49
40
22.5
4
482.97
348
38.78
48
45.5
5.5
AV.
483.3
302.96
59.52
49.25
40.5
21.60
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Fabrication of Complex Circuit Using Electrochemical Micromachining on Printed Circuit Board (PCB)
4) B. Bhattacharyya, S. Mitra, and A. K. Boro,
“Electrochemical machining: new possibilities for
micromachining,” Robotics and Computer Integrated
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5) B. Bhattacharyya, S. Mitra, and A. K. Boro,
“Electrochemical machining: new possibilities for
micromachining,” Robotics and Computer Integrated
Manufacturing, vol. 18, pp. 283–289, 2002.
6) A. S. Chauhan, “Micro tool fabrication using electro
chemical micromachining,” Master’s thesis, Indian
Institute of Technology Kanpur, UP, India, 2009.
7) B. Bhattacharyya, J. Munda, “Experimental
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Figure 12: Caparisons of channel width at different
(EMM) process”, Journal of Materials Processing
regions
Technology, vol. 140, pp. 287–291, 2003.
8) L. Yong, D. Zhu , Y. Zeng, Huang Shaofu, Yu
Hongbing, “Experimental Investigation on Complex
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Aeronautics, vol. 23, pp. 578-584, 2010.
9) M. Datta, L.T. Romankiw, “Application of chemical
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Figure 13: Caparisons of channel depth at different
regions
6
Conclusions
From the present work, following conclusions are made:
1.
2.
7
A circuit of complex structure is made by
electrochemical micromachining. It is capable to
successfully cut micro feature such as circle,
rectangle and zigzag.
Minimum average channel width on complex
circuit is 345 µm at 7 V, 25 g/l concentration, and
10000 pF capacitance.
References
1) B. Bhattacharyya and J. Munda, “Experimental study
on electrochemical micromachining,” Journal of
Materials Processing Technology, vol. 169, pp. 485–
492, 2005.
2) V. K. Jain, “Advanced machining processes”,
Electrochemical Machining (ECM), pp. 232–279.
New Delhi: Allied publishers, 2002.
3) K. P. Rajurkar, D. Zhu, and B. Wei, “Minimization
of machining allowance in electrochemical
Machining,” Annals of the CIRP, vol. 47, pp. 165–
168, 1998.
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