Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

With the rapid development of industrial technology, high-accuracy micro-holes are used in various industries. The development trend is small diameter, large depth, high accuracy, and a wide range of applications (such as high strength, high hardness, high toughness, Metals, ceramics, glass, polymer materials, crystals, etc.). Traditional micro-hole processing technologies mainly include machining, electric spark, chemical corrosion, ultrasonic drilling and other technologies. These technologies have their own characteristics, but they can no longer meet the higher needs of micro-hole processing.

introduction

With the rapid development of industrial technology, high-accuracy micro-holes are used in various industries. The development trend is small diameter, large depth, high accuracy, and a wide range of applications (such as high strength, high hardness, high toughness, Metals, ceramics, glass, polymer materials, crystals, etc.). Traditional micro-hole processing technologies mainly include machining, electric spark, chemical corrosion, ultrasonic drilling and other technologies. These technologies have their own characteristics, but they can no longer meet the higher needs of micro-hole processing. For example, machining is very inefficient for materials with high hardness and high brittleness, and it is difficult to machine holes smaller than 0.2mm; EDM can only process metal materials. Laser drilling has the advantages of high efficiency, small limit aperture, high accuracy, low cost, and almost no material selectivity. It has become one of the mainstream technologies for micro-hole processing.

Laser Rotary Cutting Drilling Technology

At present, the most commonly used processing method for laser drilling is galvanometer scanning, which can be layer-by-layer circular scanning or spiral scanning. However, the disadvantage of galvanometer scanning is that the taper cannot be avoided. As shown in Figure 1, during the hole making process, Due to the divergence and multiple reflections of the focused laser beam, the material ablation rate will drop sharply as the depth of the hole increases. Therefore, it is more difficult to prepare micropores with a larger aspect ratio on thicker materials.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 1: Multiple reflections during shallow and deep hole processing

Therefore, it is challenging to obtain micro-holes with high depth-to-diameter ratio (R10:1), high processing quality, zero taper or even inverted taper. For such needs, the most suitable processing method is to use a rotary cutting head module. The cutting head can not only make the beam rotate at a high speed around the optical axis, but also change the inclination angle β of the beam relative to the material surface. By changing the value of β, the change from a positive cone to a zero cone or even an inverted cone can be realized.

At present, the commonly used rotary cutting head modules are concentrated in four optical wedge scanning heads, Dove prism scanning heads and parallel flat-panel scanning heads. Their optical principles are similar, and the light beam entering the focusing lens is appropriately translated and tilted through optical devices. Rely on the rotation of the high-speed motor to make the beam rotate around the optical axis, as shown in Figure 2.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 2: The forming principle of holes with different tapers

Figure 3 is the optical path diagram of the four optical wedge scanning device. The two large-angle optical wedges on the left side of the figure can realize the translation of the incident beam, and the taper of the processing hole can be adjusted by changing the distance between the two optical wedges; The angular deflection of the beam makes the focused spot deviate from the optical axis of the focusing lens. When working, the four optical wedges rely on the servo motor to rotate synchronously to realize the focal spot rotating and scanning around the optical axis of the focusing lens to remove the material on the circumference, and at the same time, the micro-feed along the optical axis direction, and finally realize the circular holes with different apertures, tapers and depths. Processing. In order to realize the synchronous rotation of the four optical wedges and the adjustment of the distance between the two optical wedges on the left, the device generally adopts a complicated squirrel cage structure.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 3: Four optical wedge scanning device system

Figure 4 is the optical path diagram of the Dove prism scanning system. The Dove prism is mounted on a high-speed rotating hollow torque motor. One rotation of the prism can make the laser rotate and scan twice. The collimated laser|After the front-end angular deflection and lateral translation, it enters the Dove prism and adjusts the optical wedge, and finally focuses on the working plane through the focusing lens to realize the circular cutting scanning drilling. The three optical wedges compensate the processing and assembly errors of the Dove prism through deflection and rotation. This device can realize the rotation of the light spot twice the speed, avoiding the influence of the light spot quality on the hole quality, but the processing of the Dove prism is accurate The requirements for precision and assembly accuracy are very high, and the subsequent three-light wedge compensation adjustment structure is also relatively complicated, which has certain limitations for mass production engineering applications.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 4: Dove prism rotating scanning system

Figure 5 is the optical path diagram of the parallel flatbed scanning system. The parallel flatbed replaces the translational wedge in the four optical wedge module, and the parallel flatbed is placed at a fixed angle to generate the translation of the beam. The biggest advantage is lower cost and use. Longer life, the disadvantage is that when processing taper holes with different tapers, the inclination of the parallel plate needs to be adjusted, and the parallel plate must be reinstalled, and due to the existence of vibration during processing, the accuracy of the lateral displacement is not easy to guarantee.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 5: Parallel flatbed scanning system

Application of Rotary Cutting Drilling Technology in the semiconductor Industry

1. Probe card

The probe card is the interface between the tested chip and the tester in the wafer test. It is mainly used for preliminary measurement of the electrical performance of the chip before chip slicing and packaging, and after screening out bad chips, the subsequent packaging process can be carried out. It is very important for the development of the preliminary test and the yield guarantee of the later mass production test. It is an important process that has a considerable impact on the manufacturing cost in the wafer manufacturing process.

As the design of the chip becomes smaller and smaller, the density becomes larger and larger, which requires more and more needles of the probe card. The distance between adjacent needle tips has grown from millimeters to tens of microns, and the aperture and hole spacing of the guide plate It must be correspondingly smaller and smaller, and rectangular and irregularly shaped holes are also a trend. At present, the most widely used probe card in China is the cantilever beam type epoxy probe card. The chip test for high-end devices still uses imported vertical probe card.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 6: Upper cover (UD) and lower cover (LD) of the probe guide plate

Figure 6 shows the upper cover (UD) and lower cover (LD) of the vertical probe card guide plate. The micro-hole parameters of the probe guide plate are determined by the test point setting of the chip design and the diameter of the probe used. Generally speaking, the processing aperture is 20-200μm, the hole spacing is 40-200μm, the thickness is 0.1-1mm, and the hole wall requirements are required. Vertical, high position accuracy. The material of the guide plate is mostly ceramic and silicon nitride (Si3N4). Silicon nitride is increasingly used in the new generation of probe cards, but the extremely high hardness of silicon nitride makes it impossible to use machinery like traditional machinable ceramics. Processing, and conventional laser drilling methods can not meet the requirements.

The laser rotary cutting drilling technology solves the above-mentioned problems very well. It is not limited by the material, but also can process non-tapered holes with high depth-to-diameter ratio. Inno Laser uses its self-developed laser rotary cutting drilling technology to do a lot of research and experiments on the micro-hole processing of the probe card. At present, it can realize the processing capacity of the smallest hole diameter of 25μm, the depth-to-diameter ratio of R10:1, and the largest thickness of 1mm. 7 and 8 are photomicrographs of the micro-holes drilled by Inno Laser in Si3N4 material. In addition to round holes, it can also process square holes required by some probe cards, the smallest size can reach 35×35μm, the R angle is Q6μm, and there is no taper. Figure 9 shows a 50×50μm square hole with an R angle of about 6μm.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 7: Micrograph of 45μm pore size

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 8: SEM photo of the side wall

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 9: Probe card 50×50μm square hole

2. Bonding wedges

In the semiconductor packaging industry, there is a process called wire bonding, which uses metal wires with a wire diameter of 15-50μm to connect the chip and the lead frame, so that the tiny chip can be connected to the outside. The circuit does communication without adding too much area.

The joining method is divided into wedge joining and spherical joining. The vertical needle is mainly used for wedge joining, which allows the wire to pass through, similar to the needle in the sewing machine. After the wire of the needle tip is pressed down on the chip side to complete the first solder joint, the wire will be connected to the substrate on the chip, and the robot arm will rise to draw the wire out of the needle tip, and then move the wire to the second solder joint while pressing it down. Cut the wire to complete a cycle, and then continue to the next cycle of wire bonding, as shown in Figure 10.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 10: Wedge joining process

The materials of vertical needles generally include tungsten steel, titanium alloy, ceramics, etc. Figure 11 shows the typical morphology of the tip of the vertical needle. The position marked in red in the figure is a micro-hole with a diameter of about 50μm. The current processing method is mostly EDM, but EDM There are disadvantages such as low efficiency and easy to produce recast layers on the sidewalls. However, the use of laser rotary cutting drilling technology with ultra-fast lasers can avoid the above problems. hole.

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 11: Typical morphology of the tip of a vertical needle

Application of Laser Rotary Cutting Drilling Technology in Semiconductor Industry

Figure 12: The micro-holes of the vertical needle tip made by laser rotary cutting and drilling technology

Summarize

Laser rotary cutting drilling technology has the advantages of small processing aperture, large depth-to-diameter ratio, adjustable taper, and good sidewall quality. Although the principle of the technology is simple, the structure of the rotary cutting head is often more complicated and requires higher motion control. Therefore, there is a certain technical threshold, and the high cost also limits its wide application.

In recent years, with the development of chip manufacturing processes from 7nm to 5nm and the advent of the 5G era, the semiconductor industry’s demand for smaller and smaller devices is foreseeable. Laser rotary cutting drilling technology is an advanced method of making holes. The advantages of machining and EDM are obvious, which will help the development of the semiconductor industry.

The Links:   LB043WQ2-TD04 M150XN05-V5

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *