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Precision Engineering 34 (2010) 376–386

Contents lists available at ScienceDirect

Precision Engineering

journa l homepage: www.e lsev ier .com/ locate /prec is ion

evelopment of micro-diamond tools through electroless composite platingnd investigation into micro-machining characteristics

eung-Kil Parka, Hiromichi Onikurab,∗, Osamu Ohnishib, Ahmad Sharifuddinc

Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, JapanFaculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, JapanTokyo Electron Kyushu Limited, Fukuhara 1-1, Koshi-shi, Kumamoto 861-1116, Japan

r t i c l e i n f o

rticle history:eceived 2 July 2008eceived in revised form 4 June 2009ccepted 5 September 2009vailable online 20 September 2009

eywords:

a b s t r a c t

This research deals with the development of micro-diamond tools through electroless Ni–P compositeplating and micro-machining in single-crystalline silicon. The purpose of this paper is to testify the appli-cation of electroless plating to micro-tool fabrication. In this study, we investigated the effects of variousplating parameters and diamond grit size on the tool fabrication process. The plating parameters arecomposite plating time, embedding time, solution stirring speed, and rotation speed of substrate. Thesubstrate material of micro-tools is cemented carbide and its tip has basically a cylindrical shape with adiameter of 100 �m and a length of 500 �m. We fabricated micro-tools using three kinds of diamond grits

icro-machiningicro-diamond tool

lectroless platingicro-grooving

iliconicro-channel device

with sizes of 0.5–2 �m, 2–4 �m, and 5–10 �m. The tool diameter was about 115–120 �m after fabricationfor each diamond size. Tool life was investigated in micro-grooving in silicon. According to the results,the bigger the diamond grit was, the longer the life of the tool was. When the 5–10 �m-grit tool was used,micro-grooving with a groove depth of 100 �m could be performed up to more than 550 mm in lengthunder a grinding speed of 11.3 m/min and a feed rate of 2.4 mm/min. We also applied the 2–4 �m-grit

a few

tool for the fabrication of

. Introduction

In recent years various micro-machining technologies haveecome more important due to the increasing demand for the man-facture of precision parts and micro-structured surfaces. The LIGArocess and laser machining are well known as precision machin-

ng methods. Although the LIGA process is suitable for the massroduction of 2D micro-structures, the cost of the synchrotronnd other devices is great. Laser machining does not match up tohe other processes from the standpoint of quality. On the otherand, the mechanical process plays a significant role in the gen-ration of micro-structured surfaces and precision parts. Since theechanical process is considered as the most economical method,

he demand for the development of micro-tools and componentsy this process is continuously increasing. Among the mechanicalrocesses, micro-grinding has a prominent advantage with respecto the applicability to hard and brittle materials, e.g. silicon, glass,

eramics, and cemented carbide, etc. And micro-diamond tools areenerally used for micro-machining of hard and brittle materials1–3]. The tools can be simply fabricated by either electroplatingr electroless plating at low cost, but electroplating has been in

∗ Corresponding author. Tel.: +81 92 802 3213; fax: +81 92 802 3213.E-mail address: onikura@mech.kyushu-u.ac.jp (H. Onikura).

141-6359/$ – see front matter © 2009 Elsevier Inc. All rights reserved.oi:10.1016/j.precisioneng.2009.09.001

micro-channel devices.© 2009 Elsevier Inc. All rights reserved.

the mainstream in the fabrication of micro-diamond tools. In fact,electroless plating does not require any electrical energy and theplating film thickness is very uniform and hard compared with elec-troplating. So we think that electroless plating is suitable for thefabrication process of micro-tools.

Electroless plating just uses chemical reduction plating thatdepends on the catalytic reduction process of nickel ions in a platingsolution that contains a chemical reducing agent and depends onthe subsequent plating of nickel metal without electrical energy.So it results in a uniform film thickness on the whole substratesurface and a high plating speed. In addition, electroless nickel plat-ing film can have a high hardness due to its amorphous structureand a greater wear resistance compared with electrolytic nickelplating [4] and the process of tool fabrication is simplified becauseelectricity is not needed.

In this paper, we deal with the development of chemicallyplated micro-diamond tools and micro-machining of hard andbrittle materials using those tools. After the micro-tools were fab-ricated by electroless composite plating, which means the platingis performed with particles including diamond grit in its solu-

tion, the tool life was investigated in micro-grooving of a 100 �mgroove depth. Micro-tools can be used to manufacture microflu-idic devices, microreactors and the separators of microfuel cells,etc. and the cost may be competitive. Of course, micro-machiningtechnology is needed to make those devices. Finally we used the

H.-K. Park et al. / Precision Engineering 34 (2010) 376–386 377

Table 1Material characteristics of tool substrate.

Material Cemented carbide

Vickers hardness [HV] 2500Grain size [nm] 90Young modulus [GPa] 600Fracture toughness [MPa m1/2] 6Transverse rupture strength [GPa] 4.2

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the solution of the next step [8]. Table 3 shows the composition ofNi strike plating solution which was heated to 30 ◦C in a water bath(SB-350, EYELA).

Fig. 1. Tool substrate; cemented carbide.

ools in fabricating micro-channel devices in single-crystalline sili-on applying micro-grooving technology. Single-crystalline siliconas a good thermal conductivity compared with other hard andrittle materials, for example, quartz glass and ceramics. We expecthat the grinding heat generated in the machining process could beisposed well through the coolant. Single-crystalline silicon can besed to manufacture various microfluidic devices and the separa-ors of microfuel cells, etc. We therefore selected single-crystallineilicon as the workpiece in this research.

. Tool fabrication and tool life for micro-grooving

.1. Experimental setup

In this research, cemented carbide was used as the tool substrateHF-K30, Sumitomo Electric Industries, Ltd.). As shown in Table 1,he substrate material is WC–Co with WC particle size of 90 nmnd it is suitable for the precision machining process. As shown inig. 1(a), the substrate has a cylindrical tip of 100 �m diameter and00 �m length which is to be plated. Masking tape is used to maskhe shank part not to be plated as in Fig. 1(b).

We have developed and used a plating solution composed ofickel sulfate, sodium hypophosphite, sodium acetate and a smallmount of thiourea[5–7]. In this research, electroless Ni-P plat-ng was selected as it is known to be the most general plating

ethod in the electroless plating industry. And the plating filmardness deposited on the cemented carbide (WC–Co) substrateas about 700 HV as determined by a plating test using a micro-

ardness tester (MVK-E, AKASHI Corporation). This plating filmontains more than 7 wt. % P which means that the plating films amorphous [6,7]. Table 2 shows the solution composition andhe solution containing diamond grits was heated to 80–90 ◦C in a

able 2omposition of electroless plating solution.

Composition Concentration

Nickel sulfate (NiSO4[6H2O]) [g/L] 30Sodium hypophosphite (Na[H2PO2]) [g/L] 20Sodium acetate (CH3COONa) [g/L] 20Thiourea (H2NCSNH2) [ppm] 0.04

Fig. 2. Schematic diagram of tool fabrication process.

water bath (EYELA PS-1000, TOKYO RIKAKIKAI Co., Ltd.) [5–7]. Inthe tool fabrication process, diamond grits were added to the solu-tion and the solution was stirred to distribute the grits uniformly.Fig. 2 shows the experimental procedure involving micro-tool fab-rication. The tool substrate is rotated to 3 min−1 by the substraterotation device in Fig. 3. As shown in Fig. 3, several tools can be fab-ricated at the same time using a substrate holder which decreasesthe fabrication time and cost. The tool fabrication process consistsof pretreatment to clean and activate the substrate surface, elec-troless composite plating with diamond grits and the embeddingof them in the plated film as shown in Fig. 4. First, the cleaningof the substrate surface was conducted by acetone with ultrasonicvibration, and then degreasing, acid pickling, Ni strike plating, elec-troless composite plating and embedding were carried out in order.Electroless composite plating was carried out with stirring of thesolution in order to keep the diamond grits in suspension. This wasfollowed by embedding, which was carried out in the same solu-tion but without stirring in order to let the diamond grits settle tothe bottom of the container. Cleaning with distilled water betweenvarious steps was carried out not to bring the former solution to

Fig. 3. Substrate rotation device.

Table 3Composition of Ni strike plating solution.

Composition Concentration

Nickel chloride [g/L] 250Hydrochloric acid [mL/L] 90

378 H.-K. Park et al. / Precision Engineering 34 (2010) 376–386

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length of 100 �m and 5 mm respectively was conducted repeatedlyat the determined feed rate until tool breakage occurred. In thisstudy, we define the tool life as the total grooving length that toolsachieve before breakage occurs. We had to determine the condi-

Fig. 4. Experimental flow

.2. Mechanism of electroless composite plating

In the electroless nickel plating process, the driving force forhe reduction of nickel metal ions and their deposition is suppliedy a chemical reducing agent in solution. This driving potential isssentially constant at all points on the surface of a substrate, if stir-ing of the solution is sufficient to ensure a uniform concentrationf metal ions and reducing agents. Electroless plating is thereforeery uniform in thickness for any shape and size of the part.

The electroless composite plating film is deposited by collisionnd settling of particles on the substrate surface and these particlesre fixed by the subsequent envelopment of the matrix materials it is deposited. Fig. 5 shows a schematic diagram of electrolessomposite plating and the mechanism can be easily explained asollows;

(a) Dispersed particles are moved to the interface of substrate andsolution.

b) Particles adhere to the surface of the plated film on substrate.(c) Particles are fixed by the metal that is plated subsequently on

substrate.d) Fixed particles are embedded.

.3. Fabrication of the 2–4 �m-grit tool and tool life for eachactor

When the tool was fabricated, the experimental factors adoptedn this research were composite plating time, embedding time,olution stirring speed and substrate rotation as shown in Table 4.

able 4lating conditions.

Parameter Condition

Plating time [min] 10 15 20Embedding time [s] 60 75 90Solution stirring speed [min−1] 60 180 240Substrate rotation [min−1] 0 1 3

tool fabrication process.

2–4 �m diamond grits were used to investigate the effect of eachfactor and 5 g/L grits were added. Micro-grooving was performed toinvestigate the influence on tool life of each factor right after micro-tools were fabricated. A grooving process with a groove depth and

Fig. 5. Mechanism of electroless composite plating. (a) Dispersed diamond parti-cles; (b) Particles adhered to the surface of the plated film; (c) Particles fixed by thesubsequently plated film; (d) Embedded particles.

H.-K. Park et al. / Precision Engin

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Tool diameters fabricated with composite plating times of 10, 15

FD

Fig. 6. Grooving on electroless composite plating time.

ions under which the tool life for micro-grooving was maximized.

specially, in this research, we performed the grooving processecause micro-grooving is a very important machining processor some applications, for example, microreactors or microfluidicevices, etc. This section will deal with the experimental factors for

ig. 7. Tools fabricated under different embedding times. (a) Tool tip embedded for 60 s;etailed view of the tool embedded for 75 s; (e) Tool tip embedded for 90 s; (f) Detailed v

eering 34 (2010) 376–386 379

tool fabrication and the tool life for micro-grooving. Micro-groovingwas conducted with a grinding speed of 11.3 m/min. Before thegrooving test, the workpiece surface was ground with a #1500 dia-mond wheel (Cup type metal bond diamond wheel, NORITAKE Co.,Ltd.) and then micro-machining was carried out on a vertical CNCmachining center (M80, MAKINO Milling Machine Co., Ltd.) whichhas 0.1 �m scale feedback resolution. The micro-tool was thenrotated with a high-speed spindle (ASTRO E500Z, NAKANISHI Inc.).After tool fabrication and machining, SEM (VE-8800, KEYENCE) wasused to observe and measure the appearance, size and geometry ofthe micro-tool and the workpiece surface.

2.3.1. Effect of composite plating timeFirst, tool fabrication started with the selection of the most

appropriate plating time because it is very important to fabricatetools that can transcribe the shape of the tool substrate as fast aspossible and composite plating time affects the tool diameter. Com-posite plating time was set at 10, 15 and 20 min. Solution stirringspeed and embedding time were 60 min−1 and 60 s, respectively.

and 20 min were 110–115, 115–120 and 120–125 �m, respectively.To investigate tool life on machining, micro-grooving was per-

formed three times under the same fabrication conditions insingle-crystalline silicon with a feed rate of 1.8 mm/min as shown

(b) Detailed view of the tool embedded for 60 s; (c) Tool tip embedded for 75 s; (d)iew of the tool embedded for 90 s.

380 H.-K. Park et al. / Precision Engineering 34 (2010) 376–386

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Fig. 8. Grooving for different embedding times.

n Fig. 6. From the result, the tools fabricated with a composite plat-ng time of 15 min showed the longest tool life. There exists a greatispersion for the tool life in the case of 15 and 20 min, but we thinkhe fluctuation in tool life could be stabilized by other experimentalactors. The radius of tip corner for 15 min plating was about 8 �mnd it was one half of the tool fabricated with 20 min plating. So,e selected 15 min as the composite plating time in the aspect of

he tool shape and life.

.3.2. Effect of embedding timeEmbedding time is an important factor next to composite plat-

ng time because it may control the size of chip pockets on the toolurface and eventually affect both tool wear and tool life. Whenmbedding time is too long, diamond grits on tool surface are cov-red and buried by the plating film. On the contrary, a shortagef embedding time results in shedding of diamond grits from thelating layer. We fabricated the micro-tools with embedding timesf 60, 75 and 90 s and the other fabrication conditions were 15 minnd 60 min−1 in composite plating time and solution stirring speed,espectively. Fig. 7 shows the fabricated tools and Fig. 8 indicateshe result of grooving in silicon with those tools. The tool life withn embedding time of 60 s has a big dispersion although it is theongest compared with other conditions. As a result, we selected5 s for the embedding time because the dispersion for the tool lifeas smaller and the tool life can be secured to a certain degree.

.3.3. Effect of solution stirring speedIt is necessary to find out an appropriate stirring speed for plat-

ng solution in order to distribute diamond grits uniformly in theolution. We think that will make the distance between cuttingdges uniform and affect the tool life. Stirring speed was adjustedo 60, 180, and 240 min−1 in this experiment. A magnetic stirreras rotated by water bath in the solution container to stir plating

olution. SEM photographs of fabricated tools are shown in Fig. 9.omposite plating time and embedding time were 15 min and 75 s,espectively. Only a small number of diamond grits adhered to theool surface at a solution stirring speed of 240 min−1 and so the toolas not used for grooving in silicon. It seems there is no remarkableifference between Fig. 9(a) and (b), but the tool fabricated with atirring speed of 180 min−1 had a higher tool life by 100–200 mmompared with that which was fabricated with a stirring speed of0 min−1. The tool fabricated with a stirring speed of 60 min−1 hadtool life of 56–120 mm. From this result, we selected 180 min−1

or the solution stirring speed.

.3.4. Effect of substrate rotationTo distribute diamond grits more uniformly on tool surface, tool

ubstrate was rotated with the device of Fig. 3 at the step of com-

Fig. 9. Tools fabricated under different solution stirring speeds. (a) 60 min−1 stir-ring; (b) 180 min−1 stirring; (c) 240 min−1 stirring.

posite plating. As mentioned earlier, the tool life after stirring thesolution was 100–200 mm but that is still a great dispersion. Wethink just stirring the solution is not yet sufficient to distributediamond grits uniformly enough. Unless the substrate is rotated,diamond grits may be distributed according to the direction of solu-tion flow and become attached in great amounts to the substratenon-uniformly. If the substrate is rotated too fast, diamond grits arenot able to adhere to the tool surface. Therefore we fabricated tools

−1

without substrate rotation and with 3 min rotation [9]. Fig. 10shows SEM photographs of the tools fabricated with and withoutsubstrate rotation. Diamond grits are distributed uniformly on thetool surface by substrate rotation. It means that the chip pocketson the tool surface are placed uniformly so that chips can be dis-

H.-K. Park et al. / Precision Engineering 34 (2010) 376–386 381

Fig. 10. Effect of tool substrate rotation on the uniform grits distribution. (a) Tool fabricated without substrate rotation; (b) Detailed view of the tool fabricated withoutrotation; (c) Tool fabricated under 3 min−1 rotation; (d) Detailed view of the tool fabricated with 3 min−1 rotation.

grit to

pcstam

Fig. 11. 0.5–2 �m-grit tool. (a) Tip of the 0.5–2 �m-

osed more smoothly all over the tool surface. Actually, when weonducted micro-grooving with the tools, the tool life increased

lightly to the range of 150–210 mm and also the dispersion for theool life decreased. It can be considered that stirring the solutionnd substrate rotation affect the uniformity of chip pockets and theean distance between cutting edges.

Fig. 12. 5–10 �m-grit tool. (a) Tip of the 5–10 �m-grit to

ol; (b) Detailed view of the 0.5–2 �m -grit tool tip.

2.4. Fabrication of the 0.5–2 �m and 5–10 �m-grit tools

Micro-diamond tools using 0.5–2 �m and 5–10 �m diamondgrits were fabricated with the method based on Section 2.3. First,the 0.5–2 �m-grit tool was fabricated with a composite platingtime of 15 min and an embedding time of 40 s. In this case, the

ol; (b) Detailed view of the 5–10 �m-grit tool tip.

382 H.-K. Park et al. / Precision Engineering 34 (2010) 376–386

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Table 5Grinding conditions.

Grinding speed [m/min] 1.88–18.8

Feed rate [mm/min] 0.2–3.6Tool diameter [�m] 115–120

might be not able to endure the increase in depth of cut at the feedrate and the tool was finally worn and then fractured. Then we car-ried out micro-grooving with a grinding speed of 11.3 m/min andfeed rates of 1.2–3.6 mm/min using the 2–4 �m and 5–10 �m-grit

Fig. 13. Frame for counting diamond grits on the tool surface.

mbedding time was set to one half of that of the 2–4 �m-girt toolecause 0.5 and 2 �m diamond grits have roughly one half the sizef that of 2–4 �m diamond grits and the other conditions are theame as for the 2–4 �m-grit tool. Fig. 11 shows the fabricated tool.ext the 5–10 �m-grit tool was fabricated with a composite plat-

ng time of 15 min, an embedding time of 150 s, a solution stirringpeed of 60 min−1 and a substrate rotation of 1 min−1. Of course,he embedding time was set to twice of that of the 2–4 �m-gritool. A low stirring speed of 60 min−1 had to be adopted becausehe grits were not able to adhere to the tool surface with a stirringpeed of 180 min−1. 5–10 �m grits are bigger than 0.5–2 �m and–4 �m grits and so the deposition speed of metal ions in solutionannot keep up with a high-speed solution stirring and substrateotation to fix the big grits with its plating film. Fig. 12 shows theabricated 5–10 �m-grit tool.

.5. Cutting edge density and mean distance of cutting edges

After fabricating three kinds of micro-tools, we investigated theutting edge density for each tool. The cutting edge density will beiscussed by the grit number for the surface area of each micro-iamond tool. When the grit size was 0.5–2 �m or 2–4 �m, weounted the grits in three frames with all sides of 20 �m accordingo the substrate center as shown in Fig. 13. Then the mean numberf grits was calculated. Three frames with all sides of 40 �m weresed to calculate the diamond grits when 5–10 �m grits were used.ext, the cutting edge density on the tool surface was calculated

or each millimeter square. At this time, the actual calculated arean the tool surface was used to find out the cutting edge densityxactly. As shown in Fig. 14, the actual area S was calculated withhe circular arc L′ which means the actual frame length and S wasalculated by the following formula:

= L × L′ = L × D × q = L × D × sin−1(L/D) (1)

here L = frame length, 20 or 40 �m; L′ = real frame length on cir-ular arc, �m; D = tool tip diameter, 120 �m.

The cutting edge densities for each tool using 0.5–2 �m,–4 �m, and 5–10 �m grits are about 230,000 pieces/mm2,

Fig. 14. Projected and real frame lengths.

Workpiece Single-crystalline siliconCoolant Water-solubleGroove depth [�m] 100

93,000 pieces/mm2, and 19,000 pieces/mm2, respectively. Andthen we also investigated the mean distance between cutting edgesby the following formula:

1/�1/2 (2)

where � is the cutting edge density, pieces/mm2.The mean distances between cutting edges of the 0.5–2 �m,

2–4 �m and 5–10 �m-grit tools are roughly 2, 3 and 7 �m, respec-tively. Of course, it increased gradually as diamond grit sizeincreased, resulting in a chip pocket increase. So we can guess thatthe 5–10 �m-grit tool will have the longest tool life compared withthe other tools under the same machining condition since smallchip pockets indicate severe loading on tool surface.

3. Machining conditions for the improvement of tool life

3.1. Effect of feed rate

Using the 2–4 �m-grit tools, micro-grooving was carried out insilicon to select the best feed rate between 0.2 and 0.5 mm/minwith a grinding speed of 1.88 m/min. We performed this exper-iment to find out which feed rate results in the longest tool lifefor the low grinding speed. And then we increased the feed ratein proportion as the grinding speed increased. Table 5 shows thegrinding conditions. As shown in Fig. 15, the tool life increased grad-ually until a feed rate of 0.4 mm/min, but it decreased sharply at afeed rate of 0.5 mm/min. From the result of Fig. 15, it can be seenthat as the contacting time between diamond particles on tool sur-face and workpiece becomes shorter, the tool life increases, but ata feed rate of 0.5 mm/min the feed rate seems to be a little fastcompared with the grinding speed. Therefore, diamond particles

Fig. 15. Grooving result with a grinding speed of 1.88 m/min using the 2–4 �m-grittools.

H.-K. Park et al. / Precision Engineering 34 (2010) 376–386 383

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Fig. 16. Effect of feed rate; grinding speed 11.3 m/min.

ools. As mentioned earlier, first, we increased the feed rate to 6imes from 0.4 to 2.4 mm/min as the grinding speed increased to

times from 1.88 to 11.3 m/min. And then we changed only theeed rate to investigate the effect of that. Fig. 16 shows the resultf micro-grooving for the different feed rates. As mentioned ear-ier, the grooving length of the 2–4 �m-grit tool is a maximum of50–210 mm under a feed rate of 1.8 mm/min, but under a feed ratef 2.4 mm/min the tool life increased by 30%. For the 5–10 �m-gritool the best tool life exists in the same feed rate and it is almostwice as long as that of the 2–4 �m-grit tool. Eventually, regardless

f grit size, tool life maximized at a feed rate of 2.4 mm/min for the–4 �m and 5–10 �m-grit tools.

Next, we investigated the width change between the first andast grooves made by each of two tools due to tool wear. When the

ig. 18. Grooves machined in silicon using the 2–4 �m-grit tool; feed rate 2.4 mm/min, g

Fig. 17. Effect of grinding speed; feed rate 2.4 mm/min.

2–4 �m-grit tool was used, the first groove became 1–2 �m widerthan the tool diameter. The width of the last groove decreased to3–4 �m compared with that of the first groove. In other words, thegroove width decreased to 3–4 �m between the first and last ones.On the other hand, in the case of the 5–10 �m-grit tool, the firstgroove became about 6–8 �m wider than the tool diameter andthe width of the last groove decreased to 3–5 �m compared withthat of the first groove. The first groove of the 5–10 �m-grit toolbecame 5–6 �m wider than that on the 2–4 �m-grit tool for theirtool diameter. We think that it results from the bigger grit holding

a wider surface on the workpiece when the tool contacts the work-piece compared with the smaller grit. Eventually, the width changebetween the first and last grooves was about 3–5 �m and almostthe same for the two tools.

rinding speed 15.1 m/min. (a) 25 mm; (b) 105 mm; (c) 175 mm; (d) 265 mm.

3 Engineering 34 (2010) 376–386

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84 H.-K. Park et al. / Precision

.2. Effects of grinding speed and grit size

As shown in Fig. 17, the tool life changed with grinding speed.he tool life of the 2–4 �m-grit tool increased gradually to a grind-ng speed of 15.1 m/min and then decreased sharply. We think thathe tool wear would be severe with a grinding speed of 15.1 m/minr more and it could result in the dramatic decrease of tool life. Theool life of the 5–10 �m-grit tool tended to decrease at a grindingpeed of 11.3 m/min or more, but it did not decreased as much ashe 2–4 �m-grit tool whose tool life decreased by about 50% whenhe grinding speed increased from 15.1 to 18.8 m/min. The 2–4 �m-rit tools could not be used with a grinding speed of more than8.8 mm/min. From the result of Fig. 17, it is seen that the 2–4 �m-rit tool is more sensitive to the increase of grinding speed thanhe 5–10 �m-grit tool since the small chip pocket of the 2–4 �m-rit tool can cause severe loading on its surface. Fig. 18 shows therooves machined in silicon with a grinding speed of 15.1 m/min.

Next, we compared the life of tools with different grit sizes, i.e..5–2, 2–4 and 5–10 �m when grooving in silicon under the sameachining conditions to figure out how the size of chip pockets

ffects the tool life as mentioned in Section 2.5. Fig. 19 indicateshe machining result and the tool life for micro-grooving increasess the grit size increases. The grit size is related to the size of chipocket directly and as the chip pocket doubled in size, the tool lifef the 5–10 �m-grit tool nearly doubled that of the tool life of the–4 �m-grit tool. Micro-grooving with the 0.5–2 �m-grit tool waserformed with grinding speeds of 1.88–11.3 m/min, but the tool

ife reached a maximum of 23 mm. It is considered that as the dia-ond grits become smaller, the chip pockets become smaller, too.f course, it results in the decrease of tool life by severe chip loading,nd the grit’s resistance for grinding force decreases due to its size.

. Application

Silicon is widely used in the electronics industry and recentlyany micro-products have been proposed for practical indus-

ig. 20. Micro-channel machining on silicon. (a) Overall view; (b) Enlarged character; (channel.

Fig. 19. Effect of diamond grit size.

trial applications ranging from sensors, chemical and biologicaldevices to computational and control devices through using thissilicon-based micro-electronics technology combined with micro-machining technology [10–12]. And so we applied our micro-toolto manufacturing a few micro-devices using silicon. Fig. 20 showsChinese writing characters machined in silicon. Fig. 20(a) meansthe characters “KYU” and “SHU” in Japanese and the right charac-ter “SHU” is enlarged in Fig. 20(b). Fig. 20(c) and (d) indicate thecross-type and T-type channels enlarged from Fig. 20(b) respec-tively and the roughness of the channel bottom surfaces were Ra0.012 and 0.013 �m, respectively using a Zygo. Fig. 21 shows pin-type micro-channel machined on silicon with a pitch of 300 �m and

a pin height of 100 �m. There is no large chipping and sharp edgesare well maintained at each pin. Fig. 22 shows a channel havingtwo different depths. Its entrance is composed of a deep reservoirchannel with a channel depth of 400 �m and a width of 300 �m. Itsend shows a normal channel with a depth of 100 �m and a width

) Detailed view of A part; cross-type channel; (d) Detailed view of B part; T-type

H.-K. Park et al. / Precision Engineering 34 (2010) 376–386 385

Fig. 21. Pin-type micro-channel on silicon; 300 �m channel pitch. (a) Pin-type micro-channel; (b) Detailed view of micro-channel.

l; (b) D

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Fig. 22. Deep reservoir channel on silicon. (a) Design of deep reservoir channe

f 115 �m. As shown in this section, application for many micro-evices is possible with our micro-tool fabricated by electrolesslating and our micro-machining technology.

. Conclusions

We have fabricated micro-diamond tools by electroless Ni–Plating and three kinds of diamond grits of 0.5–2, 2–4 and 5–10 �mere used in the tool fabrication process. Effects of composite plat-

ng time, embedding time, solution stirring speed and substrateotation were investigated and finally the 0.5–2 �m and 2–4 �m-rit tools could be fabricated with a composite plating time of5 min, a solution stirring speed of 180 min−1, and a substrate rota-ion of 3 min−1, respectively. But the 5–10 �m-grit tool could note fabricated in the same solution stirring speed and substrate rota-ion. It is considered that because the grits are larger than 0.5–2 �mnd 2–4 �m grits, the deposition speed of metal ions in solutionould not keep up with a high-speed solution stirring and sub-

trate rotation to fix the big grits with its plating film. Finally, the–10 �m-grit tool could be fabricated with a solution stirring speednd substrate rotation of 60 and 1 min−1 respectively.

To choose the best condition among the experimental fac-ors of tool fabrication, micro-grooving was conducted in

etailed view of part A; (c) Detailed view of part B; (d) Detailed view of part C.

single-crystalline silicon using the fabricated micro-tools. The0.5–2 �m-grit tool became fractured soon and the great tool lifewas just 23 mm long. The 2–4 �m-grit tool had a maximum toollife of 250–300 mm with a grinding speed of 15.1 m/min and a feedrate of 2.4 mm/min. The 5–10 �m-grit tool had the longest tool lifeat a feed rate of 2.4 mm/min with a grinding speed of 11.3 m/minand the longest tool life of the 5–10 �m-girt tool, 550–650 mm, wastwice as long as that of the 2–4 �m-grit tool. We applied our tools tomanufacturing micro-devices and fabricated a few kinds of micro-channels which can be used as parts of micro-devices. There wasno great chipping, and sharp edges were well-maintained at eachchannel. Of course, we handled micro-grooving technology mainlyin this paper to investigate the tool performance. But micro-drillingseems to be able to be conducted with our tools and we expect thatthe application of our tools for micro-devices will widen.

Acknowledgements

The measurement of the phosphorus content in the plating filmwas made using Genesis 2000 at the Center of Advanced Instru-mental Analysis, Kyushu University. We are indebted to the Centerof Advanced Instrumental Analysis, Kyushu University for the mea-surement.

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[et al. Improvement of the gas sensor response via silicon �-preconcentrator.

86 H.-K. Park et al. / Precision

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