The primary action of the LED chip grinding process is “above waxingâ€, which has the same meaning as the CMP chemical grinding of silicon chips. The chip is mounted on an iron (Lapping process) or ceramic (Grounding process) disk. Firstly apply the solid wax evenly on the disc heated to about 90~110 °C, then place the front side of the chip on the disc. After pressing and cooling, the chip is fixed on the disc surface to complete the waxing action. .
First, grinding the first song - waxing
The process of waxing must control the thickness of the wax to 2~3um, which has a direct influence on the choice of the wax, the pressing method and the conditions, and directly relates to the uniformity of the finished thickness after grinding. The parts of the pressurizing and cooling mechanism of the waxing machine can be roughly divided into two types, one is to directly pressurize the two discs, and the other is to add a vacuum chamber in addition to the pressurized disc. When the pressure is applied, the cabin is evacuated to increase the effect of evenly flattening the wax.
In both ways, strictly speaking, the difference is not large. However, some chips are not suitable for waxing in a vacuum-pressing manner. For example, if the chip is marked on the flat side of the front side of the chip before the epitaxial process, when the vacuum is applied, the grade of the flat side is used. The bulge will cause the wax under the chip to be sucked out by vacuum, resulting in insufficient wax thickness. When grinding, the flat edge area is easily worn away. In addition to causing the grinding of the corners, it is also easy to crack the chip due to the occurrence of cracks.
However, the design of pressurization and cooling is also different. Generally, the lower disc will have a cooling water pipe coiled in the disc. However, some of them start to add cooling water for cooling after tens of seconds or two minutes of pressurization, while others are pressurized while cooling.
When working on waxing, there is a problem, that is, bubbles on the chip when waxing. Air bubbles can make the chip not completely attached to the iron plate or ceramic plate, which will cause small cracks after grinding. (If the chip produces a small cross or herringbone crack after grinding, it is caused by the dust not being removed when the wax is applied.) However, there have been automatic waxing machines such as WEC and TECDIA. When the robot takes the film, the bubble size can be controlled to be less than 0.5 mm, and after the pressure cooling, the wax on the chip is in a good condition. However, if you use the SpeedFAM manual waxing machine to remove wax, remove the 1mm bubble in the wax, you must rely on the operator's experience and methods to get the best waxing effect.
Second, LED chip grinding two songs - grinding
After the completion of the waxing process, the next process is the "debris process" with the highest destructive power.
The most mature grinding process in the past was Lapping, which was to use the alumina grinding powder for the first grinding. The method of operation is to measure and set the diamond dots on the periphery of the iron plate using a dial gauge, and then place it on the grinding disc and use the grinding powder for grinding. The purpose of using diamond dots is to make the chip to a set thickness. Since the hardness of the diamond is the highest, the chip will not be worn again.
However, since the blue LED substrate is sapphire and has high hardness, when the Lapping method is used for polishing, the process time is too long. Therefore, in recent years, the chip polishing of blue LEDs has been carried out in the manner of Grinding to reduce the process time.
Grinding process equipment can be divided into horizontal and vertical. The horizontal grinder refers to the grinding motor parallel to the horizontal plane, which can be applied to the grinding design below eight pieces. However, in the case of 12-piece grinding, this design method cannot be used because the ceramic disk is too large. Vertical grinders refer to the grinding motor being perpendicular to the horizontal plane, while the eight-piece grinder is based on this design.
In Grinding's process, use a diamond wheel with coolant (cooling oil + RO water or DI water) or diamond cutting fluid to grind the chip. Although the cooling method will vary according to the original designer's process philosophy and experience, it does not affect the process results. The main thing in this process is that the adjustment of the working axis and the grinding wheel axis must be parallel. Again, it is the grinding stone structure of the grinding wheel.
Due to the high speed efficiency of the Grinding polishing process, if the thickness of the chip can be reduced as much as possible during polishing, the man-hour and cost of polishing can be reduced. However, grinding is a highly destructive process, so there is a limit on chip thinning. In addition, the scratch caused by diamonds in the grinding process is about 15um, so the thickness of the finished layer also affects the thickness setting of the grinding and thinning. .
However, in the Grinding grinder used, the maximum limit is 95~105um, whether it is T, W or SF. Because of the hardness and warpage of the sapphire substrate, the result below 100 um after completion is quite unstable.
Therefore, the LED grinding process is mainly in the combination of equipment design and user experience. But the nature of the chip is still the main cause of the impact.
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