Ultrasonic Dicing Technology

Dicing Application with Ultrasonic Technology

2015-04-22

Dicing with ultrasonic technology has been developed as a new application to support the processing of electronic components (ceramic parts) and optical devices (optical disc parts, optical transmission parts). Using ultrasonic technology will enable the processing of materials such as glass and ceramics, which until now have been difficult to cut with a blade.

Issues when processing difficult to cut materials

When blade dicing difficult to cut materials such as glass, ceramics, metal and resin, the following issues can occur.

Process current will increase due to the occurrence of blade glazing^*1 and blade loading^*2. If process current increases^*3, various problems occur such as increased chipping and burring, blade breakage, abnormal blade wear and workpiece burning.

The grit on the blade tip wears down and new grit does not become exposed. In this situation, the blade can not process normally.

Workpiece cutting scraps and tape adhesive coat the blade tip and prevent the exposure of the grit. Similar to blade glazing, the blade can not process normally in this situation.

The process current increases even if finer grit is used or the feed speed is increased. An increase in process current can be confirmed by an increase in the spindle current value.

The usable blade variety is limited. Since it is necessary to select a bond that will appropriately wear to prevent blade glazing and loading, it is difficult to use a bond other than a resin. In addition, when selecting a grit size, it is necessary to use a comparatively large grit size from #320 to #600.

Dicing with ultrasonic waves has been developed as one countermeasure for blade dicing issues with difficult to cut materials described above.

The principle of dicing with ultrasonic technology

When dicing with ultrasonic technology, the forward and backward vibration from the ultrasonic wave oscillator, which is installed at the rear of the spindle, converts into a motion that travels through the spindle shaft and blade base, and expands in the blade radial-direction. Due to the vibration conversion principle, it is possible to achieve an ideal vibration direction for processing with ultrasonic waves (Refer to figure 1).

Figure 1: Vibration mechanism of the generated ultrasonic wave

Due to the ultrasonic wave vibration, the dicing blade momentary expands and contracts in the radial-direction and for very small intervals of time the grit repeatedly collides with the workpiece at high speed (Refer to figure 2). As a result, a microscopic fractural layer is generated on the processing surface and this significantly lowers the processing current (Refer to figure 3). Also, due to this ultrasonic wave vibration, the blade's cooling capability is greatly improved by the space produced between the blade and workpiece, and this leads to an improvement in process quality and blade life by preventing blade dulling and clogging (Refer to figure 4).

Figure 2: Ultrasonic wave dicing processing mechanism

[process conditions]
Workpiece:
Soda glass 1 mm thick
Spindle rotation: 12000rpm
Cutting depth: 0.5mm

Figure 3: Spindle current comparison for soda glass processing

Ultrasonic OFF

The blade tip becomes polished, new grit is not exposed and glazing occurs.

Ultrasonic ON

New grit is continually being exposed.

Ultrasonic wave on/off photograph comparison for quartz processing

Figure 4: Effective in preventing blade glazing

Merits of Dicing with ultrasonic technology

Various merits are achieved by lowering the spindle current and improving the cooling of the grit.

Fine grit blades like the electroformed bond #2000, which could not be used due to blade breakage, can now be used to process difficult to cut materials such as glass, quartz and ceramics. Consequently, this can greatly improve process quality. Also, a significant improvement in feed speed is possible, due to the lower spindle current (Refer to figure 5 and 6), even if the same grit size is used.

[process conditions]
Workpiece:
Quartz glass 300 µm thick
Blade: #2000 electroformed bond
Spindle rotation: 12000rpm

Figure 5: Feed speed comparison for quartz class processing

Ultrasonic OFF

Feed speed: Ultrasonic wave off 1 mm/sec^*4
*4 Blade breakages occurred

Ultrasonic ON

Ultrasonic wave on 6 mm/sec

[process conditions]
Workpiece:
Quartz glass 300 µm thick
Blade:#2000 electroformed bond
Spindle rotation: 12000rpm

Figure 6: Surface chipping when quartz processing

As a result of the strong vibration from the ultrasonic wave and the cooling effect on the grit, it is difficult for cutting scrap to adhere to the blade tip, even for ductile materials such as resin and metal. Also, it prevents processing issues (enlargement of burring) due to blade glazing (Refer to figure 7).

Ultrasonic OFF

Ultrasonic wave off 20 mm/sec

Ultrasonic ON

Ultrasonic wave on 20 mm/sec

[process conditions]
Workpiece: QFN (full metal)
Blade: #360 electroformed bond
Spindle rotation: 12000rpm

Figure 7: Electrode burring from QFN

Electroformed bond, which has high strength but under normal processing conditions is prone to glazing and loading, can be combined with fine grit sizes to produce thin blades. As a result, there is potential for improvements in product yield.

Purpose-built blades for ultrasonic dicing

DISCO has developed purpose-built blades for ultrasonic dicing based on its own extensive blade manufacturing know-how. DISCO is able to select either resin bond, metal bond or electroformed bonds to meet the various requirements from customers.

A dicer equipped with an ultrasonic spindle

A spindle mounted with an ultrasonic wave oscillator can be provided as an option for the DAD3350. In the future, DISCO plans to expand the lineup of machines that can apply this spindle.