Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
1Development of Advanced Machining Technology UsingABLASER® Laser Micromachining System- Targeting Laser Solutions in the Fields of Mobilityand Electronics -KIYOTAKA NAKAGAWA*1 SATORU AKAMA*2

In recent years, laser machining has been applied to products in various fields including thesemiconductor industry. However, it is difficult for conventional laser machining techniques tomeet the need for high-precision, high-quality micromachining that accompanies theminiaturization and performance improvement of parts because of the thermal effects on theworkpiece material. Therefore Mitsubishi Heavy Industries Machine Tool Co., Ltd. has adopted ashort pulse laser, combined it with our proprietary technologies including the laser head and thecontrol mechanism to develop the ABLASER® laser micromachining system and realized
high-precision and high-quality micromachining stably during long periods of time. We have also
clarified that not only metallic materials, but also brittle materials such as ceramics and glass canbe micromachined by laser.

|1. Introduction
Since its introduction in the 1960s, laser machining has made remarkable progress to this day
and has spread widely to the industrial world. Laser machining is applicable not only to metallicmaterials, but also to non-metallic materials such as brittle materials and has been utilized invarious fields. On the other hand, in all industries including the automobile and semiconductor
industries, as products become smaller and more sophisticated and the need for high-precision andhigh-quality micromachining increases, conventional laser machining has become unable to satisfy
the quality required for such products in terms of hole diameter accuracies, machined surface
properties, etc., because of the thermal effects on the workpiece material. In addition, it isextremely difficult for conventional laser machining techniques to secure positional accuracy on
the 1/1000 mm level during operation over long periods of time for mass production machining.
Therefore, we adopted a short pulse laser based on the laser technologies we have cultivatedin the heavy industry field and combined it with our machine tool expertise, enabling application toaccuracy improvement to develop the ABLASER® laser micromachining system, which realizes
high-precision and high-quality machining stably during long periods of time.. This report presents
micromachining technologies for various materials using the developed ABLASER®.

|2. Features of ABLASER® laser micromachining system
2.1

Features of ABLASER® laser micromachining system

Figure 1 presents the three features of ABLASER®. The first feature, ablation machining,uses a short pulse laser to sublimate (ablate) the material and suppress the thermal effect to aminimum on the surroundings. Figure 2 illustrates the features of the short pulse laser. The shorterpulse width can reduce the heat damages such as thermal-affected layer and micro crack to theworkpiece material and the deposits on the periphery such as residue (dross) generated during*1

Engineering Headquarters, Mitsubishi Heavy Industries Machine Tool Co., Ltd.

*2

Engineering Manager, Engineering Headquarters, Mitsubishi Heavy Industries Machine Tool Co., Ltd.

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machining. The second feature, high precision and high stability, is achieved by using granite,which has little thermal displacement and a high vibration damping effect, for the main structure,and adopting a precision scale for the positioning mechanism. As a result, not only is highpositioning accuracy achieved, but also the positional accuracy change during operation over long
periods of time is also suppressed, and a machining accuracy higher than that of conventional laser
machine tools is achieved. The third feature, helical machining, enables high-precision andhigh-quality hole machining. We applied the laser optical systems and a control mechanism thatprovides precise synchronous control to develop our proprietary optical laser head that enables
helical machining.
With the technologies for the three features above, high-precision and high-quality laser
machining was achieved and the stability during continuous operation over long periods of time
was secured. As a result, we realized a laser micromachining system that can even be applied tomass-production machining, which was difficult to put into practical use until now.

Figure 1 Features of ABLASER® laser micromachining system

Figure 22.2

Features of short pulse laser machining

Features of helical drilling

Generally, laser hole machining techniques include (a) percussion machining and (b) helicaldrilling as shown in Figure 3.

Figure 3

Laser hole machining techniquesMitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
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Percussion machining is a technique that irradiates a laser at a single point without moving or
rotating the laser. This technique can perform micromachining of the smallest diameter but cannot
form a precise hole shape. In addition, since the spread generated by the light condensing occurringat the lens is transferred, the cross section of a machined hole is unintentionally taper-shaped.
On the other hand, helical drilling irradiates a laser while adjusting the hole diameter androtating the laser at a high speed. The beam rotating mechanism of our proprietary laser opticalsystem adopts a spindle structure using precision machine tool bearings and can precisely control
the rotating diameter of the laser. Furthermore, as shown in Figure 4, the incident angle of the laser
can also be adjusted. As a result, this system can perform machining of any hole diameter andsectional shape.

Figure 4

Hole cross-sectional shape examples provided by laser incident angle control|3. Comparison with machining holes by fine-hole electric dischargemachining machine and ABLASER® machining system
Micro-hole machining techniques other than laser machining include mechanical machining,
electric discharge machining, etc. With either of them, generally the machining time tends to belonger as the hole diameter is smaller. However, with laser machining, which concentrates energy
in a minute area for machining, as the hole diameter is smaller, the removal volume decreases andthe machining time becomes shorter.
In addition, when performing high-precision micromachining, mechanical machining andelectric discharge machining need to use appropriate small diameter tools and electrodes, so
continuous machining over long periods of time is difficult because of necessity of small diametertools and electrodes consumed by processing. However, since ABLASER® dose not require tochange tools or electrodes, making continuous high-precision micromachining over long periods oftime possible by using laser.
Figure 5 compares case examples of machining hole between ABLASER® and an electric
discharge fine-hole machining machine used for the micro-hole machining of molds. With theelectric discharge fine-hole machining machine, it took 290 hours to drill 10,000 holes with a holediameter of φ0.12 mm in a cemented carbide plate with a thickness of 1.1 mm, and it wasnecessary to replace the electrodes frequently during the process. Minute burrs were generated on
the edge and a modified layer appeared due to electric discharge on the inner surface of the hole.
On the other hand, with ABLASER®, the machining time was 44 hours, that is, the machining
efficiency was 6 times or more than that of electric discharge machining and non-stop machining
was possible from start to finish. In addition, there were no burrs generated on the edge and theinner surface could be machined so smoothly that cobalt and tungsten, which are components of
cemented carbide, could be seen.

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Figure 5 Comparison with machining holes between by electric discharge machining andABLASER®

|4. Machining examples of ABLASER®
4.1(1)

High-precision and high-stability hole machining
High-precision hole machining (workpiece material: stainless steel SUS304)
Figure 6 gives an example of high-precision hole machining of a hole with a diameter of
φ0.04 mm in a stainless steel (SUS304) plate with a thickness of 0.05 mm. Helical drillingwith the proprietary laser head realized a hole shape with a roundness of 0.2 µm.

Figure 6 High-precision hole machining(2)

High-stability hole machining (workpiece material: tungsten)
Figure 7-(a) is a photograph of the appearance of 9 holes with a diameter of φ0.025
mm machined continuously in a tungsten plate with a thickness of 0.1 mm. Figure 7-(b) depicts
the transition of the measured hole diameter. Even the continuous machining of 9 holes resulted
in high-precision hole shapes equivalent to the one shown in Figure 6, and the hole diametervariation was within 0.3 µm. High precision and excellent stability are achieved, soABLASER® can be expected to be applied for a semiconductor manufacturing device formachining parts.

Figure 7

High-stability hole machining

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54.2

High-aspect ratio machining (workpiece material: hardened steel SKD11)

Figure 8 presents an example of high-aspect ratio machining of a hole with a diameter of φ
0.05 mm in an hardened steel SKD11 plate with a thickness of 0.8 mm. By optimizing theconditions, machining with an aspect ratio of 16 was achieved. The smooth inner surface of themachined hole indicates that the thermal effect during machining was minor. This technique isapplied to the machining of press dies holes in green sheets used in ceramic substrates
manufacturing for semiconductor products.

Figure 84.3

High-aspect ratio machining (aspect ratio: 16)

Multi-hole machining of ceramic material

Figure 9 is an example of the machining of 25,600 holes with a diameter of φ0.02 mm anda hole pitch of 0.06 mm in a plate made of alumina, which is a ceramic material, with a thickness of
0.4 mm. For not only metallic materials, but also alumina, brittle material, small-diametermachining with an aspect ratio of 20 could be performed. For mechanical machining with tools, itis very difficult to perform narrow-pitch machining because it generates cracking by chipping on
the hole edges. In addition, mechanical machining with tools causes a large amount of tool wear,resulting in a significant burden in terms of cost. ABLASER® realizes machining that results inedges without cracking between holes by the combination of ablation machining with less thermalaffect and high precision helical drilling machining, which is free from the problems describedabove. Furthermore, high-aspect ratio micromachining of 25,600 holes could be completed without
stopping the machine for the replacement of consumables such as tools, despite continuousmachining for about 60 hours. ABLASER® is capable of machining ceramic materials as describedabove and can be expected to be applied to the machining of parts that require insulation and thosethat require wear resistance, such as inspection tools and precision parts for semiconductor
products.

Figure 94.4

Multi-hole machining of alumina

Hole machining of glass material

Figure 10 gives an example of machining holes with a diameter of φ0.185 mm in a quartz
glass plate with a thickness of 0.2 mm by directly irradiating a laser. Holes with a good shape could
be machined stably without generating large cracks or gouging. It is very difficult for conventionallaser machining of the machining of glass material to control the hole diameter and the taper angle
to any value , but ABLASER® can control them

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
6Figure 10

4.5

Hole machining of quartz glass

Hole machining of multi-layer material (lithium tantalate and silicon)

Figure 11 is a cross-sectional photograph of forward taper holes with a diameter of φ0.015mm machined in a multi-layer material (with a thickness of 0.2 mm) made of lithium tantalate
and silicon used for electronic devices. Conventionally, etching with different processes dependingon the material was used. However, ABLASER® can perform machining of different materials
simultaneously through the selection of the optimum machining conditions. This is greatly
advantageous for the reduction of cost and cycle time.

Figure 11 Cross-sectional photograph ofholes machined in multi-layer material

4.6

Figure 12 Cross-sectional photograph ofgroove and hole machined in micro pins

Machining of micro pins

Figure 12 shows an example of machining grooves with a width of 0.02 mm and a hole witha diameter of φ0.02 mm in a steel pin with a diameter of φ0.06 mm. It is difficult for contact
machining such as mechanical machining to perform machining of a micro pin, etc., because of thereaction force. However, laser machining does not generate a reaction force, so it can perform themachining of micro pins and can be applied to the manufacture of stents and syringes used in themedical field.
In this way, ABLASER® is capable of not only hole machining, but also micromachining ofparts with various shapes.

|5. Conclusion
The ABLASER® laser micromachining system, which was developed based on ourproprietary technologies, realizes higher-precision and higher-quality machining in comparison
with conventional laser machining and also ensures stability during operation over long periods oftime. This report demonstrated that ABLASER® is a laser machining system featuring highaccuracy and excellent stability while also presenting machining examples. This paper also gave
examples of micromachining of not only metallic materials, but also brittle materials such as
ceramics and glass. It is expected that products will become smaller and more sophisticated in awide range of fields, centering on the fields of mobility—where electrification technology such as

Mitsubishi Heavy Industries Technical Review Vol. 57 No. 3 (September 2020)
7autonomous driving will continue to advance—and electronics, including IoT and 5G. In thiscontext, we will continue to offer laser micromachining solutions that satisfy the needs of ourcustomers.
“ABLASER” is registered trademarks of Mitsubishi Heavy Industries Machine Tool Co., Ltd.

References(1)(2)

Kiyotaka Nakagawa, et al., Microdrilling Technology using Short Pulsed-laser, Mitsubishi Heavy
Industries Technical Review Vol. 52 No. 3 (2015)
Yuji Imamiya et al., Development of Microfabrication Technology using DUV Laser, Mitsubishi Heavy
Industries Technical Review Vol. 53 No. 4 (2016)