Moriyasu Izawa Development Dept.
SINTOKOGIO, Ltd.
Key words: abrasive jet machining, micro abrasive, masking, process, semiconductor,
electronic devices, LCD parts, MEMS
　In recent years, when the products such as micro machine parts, integrated sensors and
the like are entering the stage of　practical application in almost all scope of industries,
and when　the wide application of ceramics as the component parts of semiconductor
devices is getting popular, the international　demands for micro processing and fabrication
technology with a high productivity for silicon, glass and ceramics materials are now
tense and urgent.
　 As these process materials generally carry the properties of high hardness, high
brittleness and high melting point, the conventional thermal and chemical processing
technologies like chemical etching, laser machining, electron beam machining, electric-
discharged machining, electrochemical machining, etc. are not capable enough to satisfy
the demands in respects of processing efficiency, accuracy and quality of processing.
Materials processing like ultrasonic machining, grinding and polishing are alsounable to
satisfy the industrial demands fully due to insufficient processing efficiency and accuracy.
　 The abrasive jet machining or abrasive blasting technology represented by dry and wet
blasting has been popularly used for comparatively rough surface finishing such as
deburring, dull surface finishing and cleansing. However, the interest of industries is
growing keener on dry and wet blasting as the appropriate technology for the precision
processing of component parts used for semiconductors, electronic devices and liquid
crystal displays by evaluating environment-friendly characteristics of dry blasting
process and easier control of static electricity problems offered by wet blasting process.
　 Under these circumstances, microblasting technology is now accomplishing a great step
of transfiguration as a fundamental technology for micro processing these hard and brittle
materials like glass, silicon and ceramics by introducing the concept of precision
engineering such as application of fine abrasives, constant feeding devices of blasting
abrasives and photolithographic masking technology added to conventional blasting
process. 1)
　 In this paper, the microblasting equipment commonly used for microblasting process,
outline of masking process by photolithography and the recent application examples of
various materials for semiconductors, electronic devices and liquid crystal displays are
introduced.


<2-1 Micro blasting equipment>
　 SINTOKOGIO has been dealing with manufacturing and marketing of nozzle type air
blasting equipment and systems for over 30 years. On the base of these deep rooted
experience, SINTOKOGIO has developed various elemental technologies of microblast
processing, and introduced microblasting equipment MICRO BLASTING MACHINES.
MICRO BLASTING MACHINES, MB1 has been developed as a standard model for
processing mainly sensor substrates, flat panel display and ceramics components.The
appearance of MB1 is shown in Fig. 1, and its main specifications in Table 1.
【Table 1.Main specifications of
MICRO BLASTING MACHINES,MB1】
Fig1.MICRO BLASTING MACHINES　MB1
Item Specification
Blasting abrasives ♯220～♯800
Maximum work piece size 150×150mm
Blasting mechanism Constant feeding devices of
fine abrasives
Feeding tolerance
plus or minus 3%(30micronm)
plus or minus 5%(10micronm)
Circulation mechanism Foreign substance separator
& Cyclone type for fine
particles
Environment Noise level below 80dB(A)
　 Microblasting process, as shown in Fig. 2, is designed to perform micro processing and
machining of materials having high hardness and brittleness by jetting out the fine
abrasives of several micronm up to several ten mironm in diameter from nozzle,
accelerating the abrasives by carrier gases like compressed air, and making them collide
on the surface of process materials at a high speed and with a high density. For processing
the surface of materials uniformly, the machine is furnished with constant feeding devices
control (Patent Registered) of blasting abrasives, and the micro-processing is performed
by scanning the blasting nozzle over the work to be processed at a predetermined pitch
oreven the work itself scan under the nozzle at a fixed pitch 2).
Fig. 2 A model of microblasting process
　 In case of performing micro-processing of glass, for example, any of conventional
methods can create residual cracks over the processed skin area due to the heat
generated by machining, and it further causes such problems as the generation of
chippings and deterioration of material strength. In microblasting technology, the
processing work progresses in the form of accumulation of minute brittle mode
processes, so the generationof chippings and cracks is kept at a minimum level 3),
appealing clearly that the method is optimum for the processing of hard and brittle
materials.
However, for processing metallic materials with a ductility, particularly soft metals such
as aluminum and copper, there is a possibility of causing the subjects of discussion with
regard to the formation of burrs and fins due to plastic deformation, so the majority of
application of microblasting to the metallic materials goes to such fields as finishing of
metallic dies, fine deburring, dull surface finishing, design markings on stainless steel
plates for construction, and the like where a very high degree of accuracy is not
demanded.
　 In general, the fine abrasive particles of 5- 40 micronm in average diameter are used.
The required volume of abrasives is delivered to the blasting nozzle accurately by
constantfeeding device. As the majority of processing work objects is hard and brittle
like glass, silicon and ceramics, the fine abrasives of alumina and silicon carbide having a
higher hardness than the materials to be processed are commonly used.
　 The fine abrasives is recycled in the system and used repeatedly by separating fine
dust, scraps and coarse wastes generated from the system, work materials and pulverized
abrasives that are no longer contributable to the process when they are passing through
foreign particles separator and fines separating cyclone. These separating mechanisms are
also effective for preventing damages of process materials and for stabilizing the result of
microblasting process.
　 Besides, the machine is provided with the grain fineness control system (Patent
pending) for the purpose of avoiding the process rate variation 4) caused by crushing and
pulverizationof blasting abrasives, and for maintaining the process accuracy.

(Microblasting technology - Part 2)
<2.2 Machining characteristic of microblasting process>
　 Fig. 3 6) illustrates the processing characteristic and machinability of microblasting on
various materials having a high hardness and high brittleness. Fig. 3 clearly indicates that
the machinability of microblasting is higher on the materials having a lower strength and
higher brittleness, while the machinability is lower on the materials having a higher
strength. It is possible to improve the machinability by the application of harder blasting
abrasives, but the study on cost increase should also be necessary.
Fig. 4 shows the roughness distribution of processed surface of glass obtained by
differentparticle size of blasting abrasives. The glass used here as work materials for
roughness measurement is common soda-lime glass. From this figure it is possible to
recognize the interrelation of a certain extent between the particle size of blasting
abrasives and the roughness of processed surface, and this phenomenon further suggests
the possibility of obtaining desired surface roughness by using the blasting abrasives of
a certain average fineness distribution.
　 The characteristic values of microblasting process is shown in Table 2.
Fig. 3 Machinability of microblasting on
various hard &brittle materials
 Fig.4 Surface roughness of glass in relation to
average particle diameter of blasting abrasives
【Table 2 Characteristic values of microblasting process】
Items Characteristic values
Processing accuracy
Drilling

Grooving
Depth of cut		 (Minimum machining dimensions)
30 micronm (plus or minus 5 micronm)
(Aspect ratio 1:1, tapered shape)
20 micronm (plus or minus 5 micronm)
Tolerance plus or minus 5%
Processing grade
Chippings
Surface roughness		 (Superior grade)
More or less 5micronm
0.02micronmRa
<2.3 Masking process>
　 In microblasting process, there are two typical processing methods. One is to perform
blasting on all surface of rather broad area of work with or without specified pattern
masking efficiently and uniformly by the blasting nozzle of 4 - 10mm diam. or by flat nozzle,
and another is to perform concentrated spot blasting 5) on minute parts set at the blasting
position by using the nozzle having a small blasting hole of more or less 0.15mm diam.. As
the result of research and development of nozzle and blasting mechanism for spot blasting
by micro-nozzle, MICROBLASTER MB2 has been introduced for a higher efficiency and
higher aspect processing (Patent Registered) of localized spot blasting, and has been sold
successfully in the market by demonstrating a clear functional distinction with MB1.
　 This chapter explains about masking process as one of the important component factors
other than mechanical equipment. For performing efficient blasting with a specified
pattern, it is essential to apply masking on the work surface. As the masking restricts the
size of pattern, the methods of masking should be selected carefully. By paying
considerations to these factors as the required accuracy, cost and controllability, the type
of masking is selectable out of photo resist, metallic and printing mask.
　 The photo resist mask is suitable for the processes demanding the highest level of
accuracy. Resist mask is commonly sold in the form of dry film, and the resolving power of
resist varies in accordance with the thickness of film. As an example ofhighly accurate and
minute masking, photo resist method is capable to resolve the line width of 20 microm at
L/S = 1/3, and the groove machining shown in Fig. 5 is possible by microblasting
(Patent pending). For dry film, photosensitive urethane resin is commonly used because
the material is capable to absorb the impact energy of blasting abrasives effectively.
　 A flow chart of microblasting process using photo litho-masking is shown in Fig. 6.
Laminate the work surface by dry film as masking material, and apply ultraviolet rays
through photo-mask on the masked surface, develop by alkalescent solution, dry and bake
the surface, and the desired pattern is formed on the work surface. Then, perform
microblasting to etch the exposed area without masking selectively. After the processing,
peel off the mask and clean to complete the process. For the patterning of high accuracy,
it is important to select the optimum equipment and devices for each stage of process and
setting of condition (Patent Registered), involving a substantial volume of know-how. In
SINTOKOGIO, besides the microblasting equipment, various other auxiliary equipment
including exposing equipment, film developing equipment, etc. are ready for immediate
application
Fig.5 Example of machining
20 micronm grooves
Fig. 6 Flow chart of microblasting process
　 Printing mask is cheaper in respect of materials and equipment, but is not suitable for the
work demanding a high level of accuracy. The printing method is generally used for
processing glass and patterning of stainless steel panels for interior decoration and
construction materials of houses and buildings.
　 Surface etched thin stainless steel plates and electroformed nickel plates are used as the
material for metal masking. Due to its superior durability against abrasion by microblasting,
the metallic material is considered ideal for masking, but it also carries the problem of
deformation by processing strain. Accordingly, the application of metallic masking is limited
only to special purposes.
　 As microblasting is a physical impact erosion process with a high abrasive property, the
durability of masking material is strongly required. The masking plays such animportant
role in microblasting as a regulator of machining dimensions, so it is necessary to set up
the most appropriate values of design parameters paying considerations to their abrasive
durability 7).
　 The accuracy achievable by microblasting, as explainedabove, is on the level of 10
micronm with a high productivity, and microblasting process is placed at the position of
supporting either the processing scopes such as grinding, electron beam and etching
requiring the accuracy level of 1 micronm, or the scopes such as machining and electric-
discharge processing requiring the accuracy of more or less 100micronm.


　 Needless to repeat, such work materials as semiconductor, electronic parts and Flat
Panel Display-related parts particularly require a high level of accuracy,and one of
important expectations of the manufacturers of these parts in microblasting process is
the high quality finish. This finish is so-called ‘damage-free’ in which the problems
such as cracks and chippings caused by processing should be minimized. The case of
drilling holes on glass board for sensor by utilizing the above mentioned photo-resist
mask is shown in Fig. 7. In this application, the through holes of 0.4mm diameter are
bored on the glass substrate of 0.5mm thick using about 30micronm size blasting
abrasives. As the figure shows, the chippings are kept within the level of several micronm,
and the processing with aspect ratio of more than 1 is materialized. Fig. 8 shows that the
processing with accuracy of 20.8 micronm at 3 sigma for the hole with diameter of
0.433mm diam. is possible by microblasting. The accuracy level achieved by
these processingmethods with masks is more or less plus or minus 10 - 50 micronm,
and the accuracyis restricted by the thickness of mask, kind of work material and
blasting condition.
　 An example of processing via holes on silicon wafer is shown in Fig. 9. The checkered
pattern (4 x 2mm) for the depth of 0.17mm is machining on the surface of silicon wafer.
【Table 3. Application examples of microblast processing】
Field Purpose of application
Electronic parts Drilling on sensor board, grooving,electrode forming
(Solar cell, filter, multi-layer substrate)
De-Smearing treatment for printed circuit board
Patterning of HDD parts
Semiconductor Deburring of IC resin mold package
Drilling and grooving on device wafer
Etching of ceramics wafer susceptor
FPD related Conductive membrane removing
Barrier forming
Etching of cover glass


Fig. 7 Drilling on glass substrate for sensor
Fig. 8 Hole diameter histogram

Fig. 9 Via hole machining on silicon wafer
Fig. 10 Depth of cut histogram
Fig.11 PZT Microstructure
　 As shown in Fig. 10, the machining accuracy achievedhere by microblasting is
6micronm in 3sigma for the depth of 0.17mm. Microblasting technology is also applied
to the micro-processing of parts for MEMS, the research and development of which is
quite hot in recent years, and the application example is shown in Fig. 11. In this
application, the micro-structure is etched and formed on PZT board, the popular
piezoelectric materials. Furthermore, the creation of multi-staged shape with
complicated three-dimensional configuration is materialized by repeating masking and
microblast processing alternately.
　 Other various examples of microblast application are given in Table 3. The application
fields of microblasting technology are expanding widely over electronic parts,
semiconductor and FPD industries
　 Outline of microblasting process and micro-processing technology in the industrial
fields of semiconductor, electronic parts, FPD related, etc. has thus been introduced.
SINTOKOGIO is, not only manufacturing and marketing micro-processing equipment and
systems including microblasting system and relative products, but also operating the
test processing for users and sub-contracting the production by microblasting in
commercial basis. It is the eager wish of the group that the experience, know-how
and micro-processing technology particularly for various hard and brittle materials
established through these in-house operations would be utilized for the immediate
advantage of users.
Finally, the writer of this paper will appreciate it very much if further assistance,
advices and guidance by users and parties concerned are rendered to help upgrading
the microblasting technology.
SINTOKOGIO, LTD.
Shinmei 51, Ubukuji, Nishiharu-cho, Kitanagoya, Aichi, 481-8678 Japan
E-mail : izawam@brator.sinto.co.jp
List of reference
1) “Micro-processing of hard and brittle materials by abrasive jet machining” by M. Izawa, M. Watanabe,
H. Yashiro, N. Hagiwara, H. Horikawa, M. Ozawa.
Collected papers, 1998 Lecture meeting of Society of Grinding Engineers.
(1998) 217
2) “Characteristics of masking materials in microblast processing” by M. Izawa, M. Sugimoto.
Collected papers, 1999 Lecture meeting of Society of Grinding Engineers. (1999)
3) “Basic study on dry blasting process” (Report No. 3) by M. Izawa, K. Kitajima, M. Nonaka, T. Yamamoto.
Collected papers, 2001 Lecture meeting of Society of Grinding Engineers.
(2001) B39, P195
4) “Basic study on dry blasting process” (Report No. 2) by K. Kitajima, M. Nonaka, M. Izawa
Collected lecture papers, 2000 Spring lecture meeting of Japan Society for Precision
Engineering (2000) 238
5) “Study on micro-processing of hard and brittle materials by micro abrasive jet machining”
by T. Kuriyagawa Report on result of study under Grant-in-Aid for Scientific Research 1995, 47
6) “Machining characteristics of hard & brittle materials by microblasting process” by M. Izawa,
M. Sugimoto,K. Kitajima, Collected lecture papers, Industrial Processing-machine tool category of
JapanSociety of Mechanical Engineers. (2000) 221
7) “Wearing characteristics of masking materials in dry blast processing” by M. Izawa, M. Sugimoto,
K. Kitajima, Society of Grinding Engineers. Journal 45, 12 (2001) 580


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