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Dicing process of wafer

2023.06.01More SuperHard Products Co., Ltd42

1. Dicing process after the wafer is prepared through the previous process, the chip is prepared, and it needs to be cut to separate the chips on the wafer, and finally packaged. The wafer cutting process for different thickness wafer selection is also different:

* Wafers with a thickness of more than 100um are generally cut with a blade.

* Wafers with a thickness of less than 100um are generally cut by laser. Laser cutting can reduce the problems of peeling and cracks, but when the thickness is above 100um, the production efficiency will be greatly reduced.

* Wafers with a thickness of less than 30um are cut by plasma. The plasma cutting speed is fast and will not cause damage to the wafer surface, thereby improving the yield rate, but the process is more complicated.

Blade dicing or blade sawing

During the blade cutting (sawing) process, the attachment and removal of the protective film, in order to protect the wafer from external damage during the cutting process, an adhesive film will be applied to the wafer in advance to ensure a safer "singling". In the "Back Grinding" process, the adhesive film will be attached to the front side of the wafer. But in contrast, in the "blade" dicing, the adhesive film will be attached to the back side of the wafer. In eutectic bonding (Die Bonding, the separation During the process of fixing the chip on the PCB or the fixed frame), the adhesive film on the back will automatically fall off. Due to the high friction during cutting, DI water (deionized water) should be continuously sprayed from all directions. Moreover, the impeller Diamond particles must be attached so that it can be sliced better. At this time, the incision (blade thickness: width of the groove) must be uniform and must not exceed the width of the scribing groove. For a long time, sawing has been the most widely used The biggest advantage of the traditional dicing method used is that a large number of wafers can be cut in a short time.However, if the feeding speed of the dicing is greatly increased, the possibility of peeling off the edge of the small chip will increase. Therefore, the number of rotations of the impeller should be controlled at about 30,000 times per minute.

2. Wafer dicing machine wafer cutting often encounters a narrow street width, which requires the ability to place each cut within a few microns of the center of the street. This requires the use of equipment with high indexing axis accuracy, high optical magnification and advanced alignment algorithms. When dicing wafers with narrow lanes, the thinnest blade possible should be chosen. However, very thin inserts (20µm) are very fragile and more prone to premature fracture and wear. As a result, its life expectancy and process stability are poorer than thicker inserts. The blade push thickness for 50~76µm traces should be 20~30µm.

Key points of scribing process

1. Chipping Top-side chipping (TSC, top-side chipping), which occurs on the top surface of the wafer, becomes a pass rate problem. When the slice is close to the active area of the chip, it mainly depends on the blade grinding granularity, cooling agent flow and feed rate. Back-side chipping (BSC, back-side chipping) occurs on the underside of a wafer when large, irregular micro-cracks propagate away from the diced underside and merge together (Fig. 1b). When these microcracks are long enough to cause unacceptably large particles to be removed from the cut, BSC becomes a yield issue. If the size of the backside debris is below 10 µm, ignore it. On the other hand, when the size is larger than 25 µm, it can be considered as potential damage. However, an average size of 50µm is acceptable, depending on the thickness of the wafer.

2. Blade optimization is to meet new slicing challenges, and collaboration between slicing systems and blades is necessary. This is especially true for high-end applications. Inserts play a major role in process optimization. In addition to size, three key parameters determine insert characteristics: diamond grit size, diamond content and type of bond. The bond is a matrix of various metals and/or diamond abrasives distributed therein. Other factors, such as feed rate and spindle speed, may also affect insert selection. The relative importance of the three key blade elements (diamond size, concentration and bond hardness) depends on the blade abrasive size and process parameters. An understanding of these relationships is necessary in order to select the most suitable insert for a particular application.

3. Coolant Flow Stabilization A system operating at a stable torque requires stabilization of feed rate, spindle speed and coolant flow. The coolant exerts drag on the blade, it creates torque. The latest generation of slicing systems maintains a constant flow rate and resistance by controlling the coolant flow, thus keeping the coolant torque impact stable. Maintain a steady torque while the microtome has steady coolant flow and all other parameters are under control. If documented, any deviation from stable torque is due to uncontrolled factors. These include changes in coolant flow due to clogged nozzles, changes in nozzle adjustment, blade-to-blade variations, blade condition, and operator error. Slicing processes are becoming more and more demanding. The dicing lane becomes narrower, may be filled with test pads, and the blade may need to cut various coatings made of different materials. Achieving maximum slicing process yield and productivity under these conditions requires careful blade selection and advanced process control capabilities.

4. The difference between UV film and blue film Before the wafer is diced, a layer of film will be glued on the back of the wafer. Integrity, reducing the problems of chipping, displacement and falling during cutting. In actual production, the film used to fix the wafer and chip generally uses UV film or blue film. UV film: mainly used for wafer thinning process.

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Blue film: mainly used for wafer dicing process

UV film is usually called ultraviolet radiation tape, the price is relatively high, and the validity period is short when it is not used. It is divided into three types: high viscosity, medium viscosity and low viscosity. The viscosity of the high-viscosity UV film is 5000mN/20mm ~ 12000mN/20mm when it is not irradiated by ultraviolet rays. After ultraviolet irradiation, the peeling viscosity is below 1000mN/20mm; the peeling viscosity of the low-viscosity UV film is 1000mN/20mm without ultraviolet radiation. After ultraviolet irradiation, the peel viscosity drops to about 100mN/20mm. After the low-viscosity UV film is irradiated with ultraviolet rays, there will be no glue residue on the surface of the wafer, and the crystal grains are easy to remove. The UV film has proper expansibility, and water will not penetrate between the grain and the tape during the thinning and scribing process.

Blue film is usually called electronic grade adhesive tape, which is relatively cheap. It is a blue film with constant viscosity. Its adhesive peeling degree is generally 100~3000mN/20mm, and it will produce residual glue due to the influence of temperature. In contrast, UV film is more stable than blue film. the

Application analysis of UV film and blue film in production:

Generally speaking, UV film is used for thinning and scribing of small chips, and blue film is used for thinning and scribing of large chips, because the viscosity of UV film can use ultraviolet rays Control the irradiation time and intensity to prevent the chip from being missed or broken during the grabbing process. If the chip is directly placed on the flip packaging label production line after thinning and scribing, it is best to use UV film, because the chips in the flip packaging production line are generally relatively small, and the thimble of the equipment is at the bottom of the blue film to lift the chip up. If a blue film with a large adhesive peeling degree is used, the ejector pin may break the chip during the process of jacking up the chip.

The viscosity of the blue film will change due to the influence of its temperature, and its own viscosity is relatively high. Therefore, generally, the chip or wafer with a large area is thinned and cut, and then the post-package process is directly performed instead of the flip-package process. When inlaying, you can consider using blue film. Compared with the blue film, the UV film has a great advantage due to its variable adhesiveness and peeling degree. Its main function is: it is used to fix the wafer during the wafer thinning process; it is used to protect the chip during the wafer cutting process to prevent It falls off or collapses; it is used for flipping and transporting the wafer to prevent the chips that have been scribed from falling off. Standardize the use of various parameters of UV film and blue film, and select the appropriate UV film or blue film according to the processing technology required by the chip, which can save costs and contribute to the development of chip industrialization.

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