A method for preparing a flip chip

Abstract

The invention discloses a method for preparing a flip chip, comprising: 1) providing a wafer, the wafer comprising a plurality of flip chips and preset cutting paths between the flip chips, the flip chip having a first and a second surface side arranged relatively, the preset cutting paths comprising a first preset cutting path formed on a wafer surface corresponding to the first surface side, and a second preset cutting path formed on a wafer surface corresponding to the second surface side; 2) sequentially performing: grooving on the second preset cutting path to form a pre-grooving; arranging a back gold layer on the wafer surface corresponding to the second surface side and on the surface of the pre-grooving; performing laser grooving along the thickness direction of the wafer from the back gold layer in the pre-grooving to form a secondary groove with a depth greater than the thickness of the back gold layer; 3) grooving on the first preset cutting path until it is connected with the secondary groove to obtain a plurality of discrete flip chips; the method can reduce or even avoid the problems of metal debris short circuit and back gold shedding after packaging the flip chip with the back gold layer.

Description

Technical Field

[0001] The invention relates to the technical field of chip preparation, and in particular to a method for preparing a flip chip. Background Art

[0002] High-power CPUs generate a lot of heat when working, so they are usually equipped with heat dissipation components such as heat dissipation covers. The CPU and the heat dissipation cover need to be connected with solder. The most commonly used solder is indium metal solder, which has a better heat dissipation effect. However, due to the large difference between the thermal expansion coefficient of indium and the expansion coefficient of silicon / silicon dioxide on the back of the chip, if they are directly connected, a large internal stress will be generated when heated, causing cracks at the connection between the chip and the solder layer. Therefore, the back of the chip will be formed with a back metal layer by evaporation or sputtering, referred to as the back gold layer. The back gold layer plays the role of connecting the solder and the chip and is indispensable. However, according to statistics, the proportion of metal debris short circuit (flame short) after the flip chip package with back gold is generally about 300ppm, and some products with poor back gold bonding even reach 1000ppm. In addition, the back gold shedding caused by the chip cutting process is also very high, and can even reach several thousand ppm, resulting in yield loss. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an improved method for preparing a flip chip, which can simultaneously avoid short circuits and back gold shedding caused by metal debris after packaging a flip chip with a back gold layer.

[0004] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a flip chip, the preparation method comprising:

[0005] (1) Providing a wafer, the wafer comprising a plurality of flip chips and preset cutting paths between the flip chips, the flip chips having a first surface side and a second surface side arranged opposite to each other, the preset cutting paths comprising a first preset cutting path formed on a wafer surface corresponding to the first surface side, and a second preset cutting path formed on a wafer surface corresponding to the second surface side and arranged opposite to the first preset cutting path;

[0006] (2) performing the following steps in sequence: performing grooving on the second preset cutting path to form a pre-grooving;

[0007] Disposing a back gold layer on the wafer surface corresponding to the second surface side and the pre-grooved surface;

[0008] In the pre-grooving, laser grooving is performed starting from the back gold layer along the thickness direction of the wafer to form a secondary groove with a depth greater than the thickness of the back gold layer;

[0009] (3) Grooving is performed on the first preset cutting path until it is connected with the secondary groove to obtain a plurality of discrete flip chips.

[0010] According to some preferred aspects of the present invention, in step (2), the depth of the pre-grooving is controlled so that the upper end surface of any point in the pre-grooving after laser grooving is not higher than the upper surface of the back gold layer at the opening of the pre-grooving.

[0011] According to the present invention, in step (2), after laser grooving, a protrusion that is raised after laser ablation will be formed on the bottom plane of the pre-grooved surface. Furthermore, the upper end surface of the protrusion is controlled not to be higher than the upper surface of the back gold layer at the opening of the pre-grooved surface, and the width of the pre-grooved surface is controlled to be greater than the sum of the width of the secondary groove opening, twice the length of the protrusion, and twice the thickness of the back gold layer.

[0012] The depth of the pre-groove is controlled so that the upper end surface of any point in the pre-groove after laser grooving is not higher than the upper surface of the back gold layer at the opening of the pre-groove. In this way, some molten materials formed after laser grooving, such as protrusions formed after cooling, can be hidden in the pre-groove so that they do not protrude outside the pre-groove, that is, do not protrude from the wafer surface, which is convenient for subsequent processes.

[0013] According to some preferred aspects of the present invention, in step (2), the laser grooving position is located in the middle of the bottom of the pre-grooving, and the width of the secondary groove opening is smaller than the width of the bottom of the pre-grooving.

[0014] According to some preferred aspects of the present invention, in step (2), the operation of setting the back gold layer includes the following processes performed in sequence: thinning and grinding the wafer surface corresponding to the second surface side and the selective pre-grooved surface, etching the silicon surface, and applying the back gold layer, and coating the back gold layer surface on the wafer surface and the selective pre-grooved surface with a protective liquid.

[0015] In some embodiments of the present invention, in step (2), the pre-grooving is performed by mechanical sawing or laser grooving.

[0016] According to some preferred aspects of the present invention, in step (2), before performing grooving to form the pre-grooving, a first protective film is firstly provided on the wafer surface corresponding to the first surface side;

[0017] After the secondary grooves are formed by grooving, the first protective film is removed;

[0018] The first protective film is selectively removed before the back gold layer is applied, and the first protective film is selectively provided on the wafer surface corresponding to the first surface side before the protective liquid is coated.

[0019] According to some preferred aspects of the present invention, in step (2), the depth of the pre-grooving is controlled to be greater than the sum of twice the thickness of the back gold layer and the thickness of the wafer after thinning and grinding. Further, the depth of the pre-grooving is controlled to be greater than the sum of twice the thickness of the back gold layer, the height of the protrusion and the thickness of the wafer after thinning and grinding.

[0020] According to some preferred aspects of the present invention, in step (3), the width of the slot directly connected to the secondary slot is controlled to be smaller than the width of the secondary slot opening.

[0021] According to some preferred aspects of the present invention, in step (3), before grooving, a second protective film is provided on the surface of the back gold layer; or, in step (3), before grooving, a second protective film is provided on the surface of the back gold layer except in the pre-grooved portion.

[0022] In some embodiments of the present invention, there are a plurality of the first preset cutting lanes and a plurality of the second preset cutting lanes, and each of the first preset cutting lanes has a corresponding second preset cutting lane.

[0023] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0024] The present invention sets preset cutting paths on opposite sides of the wafer, and then cuts from both sides to penetrate and obtain discrete flip chips. At the same time, it innovatively opens a pre-groove before applying the back gold layer, and performs laser grooving of the secondary groove after applying the back gold layer. No long metal debris will be generated in the whole process. Even if mechanical cutting is performed later, the saw teeth cannot contact the back gold area, and no long metal debris will be generated. Not only the short circuit caused by the back gold metal debris is avoided, but also because there is no contact stress in the grooving process, there is no tearing and stretching effect, which solves the problem of back gold falling off in the prior art. At the same time, the present invention also solves the problem that bubbles may be generated between the existing back gold layer and the protective film that protects the back gold layer during the processing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the preparation process of a flip chip in the prior art;

[0026] Figure 2 It is a schematic diagram of the structure of the flip chip after cutting in the prior art process; wherein, 1, UV film; 2, back gold layer; 3, silicon layer; 4, circuit layer; 5, solder ball (bump); 6, metal debris of the back gold layer;

[0027] Figure 3 The schematic diagram of the preparation process of the flip chip according to the embodiment of the present invention;

[0028] Figure 4It is a structural schematic diagram of a flip chip and a preset cutting path between the flip chips according to an embodiment of the present invention; wherein 10 is a first preset cutting path;

[0029] Figures 5 to 18 The schematic diagram of the preparation process of the flip chip of the embodiment of the present invention; wherein, 101, first protective film; 102, solder ball (bump) of the flip chip; 103, silicon layer of the flip chip; 104, circuit layer of the flip chip; 105, mechanical saw; 106, water washing mechanism; 107, pre-grooving; 108, back gold layer; 109, laser cutting protective liquid; 110, laser groover; 111, gasification dust collection device; 112, secondary groove; 113, protrusion; 114, second protective film; 115, wider cutting saw blade; 116, narrower cutting saw blade;

[0030] Fig.19 The figure is a detailed schematic diagram of the process of manufacturing a flip chip according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] At present, according to statistics, in the cutting process of the prior art gold-backed chips, especially the gold-backed flip chips, the short circuit (flame short) ratio caused by metal debris after the gold-backed flip chips are packaged is generally about 300ppm, and some products with poor gold-backed bonding can even reach 1000ppm. In addition, the gold-backed chips produced during the chip cutting process also have a high ratio of falling off, which can even reach several thousand ppm, resulting in yield loss. Figure 1-2 As shown, in the prior art, a back gold layer is first formed on the back of the wafer, and then multiple cuts and grooves are made at corresponding positions on the circuit layer side of the chip (opposite to the back gold layer), and finally a chip as shown in FIG. Figure 2 The schematic diagram of the discrete flip chip after cutting is shown. After repeated practice and analysis by the inventor, it is believed that: in the wafer cutting process, a circular cutting saw with a diamond edge is used for cutting. When the workpiece is a hard and brittle material such as silicon or silicon dioxide, the diamond particles will smash the workpiece by impact, and then the powder will be removed by the blade. However, the bottom layer of the back gold product is a metal layer or a composite metal layer. The metal layer has good toughness and is not easy to break into powder when it is impacted by a saw surface such as a diamond material. Moreover, because of its ductility, when the last cut is performed immediately after the back gold layer, it is easy to be drawn when it is brought out by the saw teeth, and it will stick to the nearby bump (tin ball of the flip chip) surface, which cannot be washed away by water flow, and will short-circuit the connected bumps in the subsequent process. In addition, the second cut will produce longitudinal stretching and lateral tearing stress on the cutting edge of the back gold layer, resulting in the problem of edge back gold falling off. Specifically, if Figure 2As shown, when the cutting continues downward and penetrates the back gold layer 2, the metal debris generated needs to be taken out of the cutting groove by the cutting saw, and then the metal debris may fall on the surface of the bump (the solder ball of the flip chip) or between them. When it cannot be washed away or the washing is missed, it is very easy to cause a short circuit in the bump. At the same time, based on the metal characteristics of the back gold layer itself and the existing cutting method, it will be difficult to avoid wire drawing or back gold falling off.

[0032] Therefore, the present invention provides a method for preparing a flip chip, which uses cutting channels preset on two opposite surfaces of a wafer. In this process, before forming a back gold layer on one side, a groove is first made to obtain a pre-groove, and then a back gold layer is formed, and then a secondary groove is formed by laser grooving, and then the wafer is penetrated from the opposite side of the back gold layer to achieve the separation of a plurality of flip chips. This process method not only makes good use of the advantage that the target area material is vaporized during laser cutting and can be absorbed and removed by the vaporized dust collection device, so that no long metal debris is generated when the back gold layer is cut and separated, but also removes the back gold layer from the back gold layer. When penetrating the wafer on the opposite side, even if mechanical cutting is used, the saw teeth cannot contact the back gold layer area, further avoiding the generation of long metal debris and eliminating the problem of metal debris remaining on the solder ball (bump) surface of the flip chip to cause a short circuit; moreover, laser ablation in this way has no contact stress at all, and there is no tearing and stretching effect, which can solve the problem of back gold falling off due to the mechanical cutting process; at the same time, the method of the present invention also avoids the problem of conventional laser cutting that causes the metal to be melted at high temperature and form unexpected protrusions after cooling, which affects the generation of bubbles between the back gold layer protective film and the back gold layer.

[0033] The above scheme is further described below in conjunction with specific embodiments; it should be understood that these embodiments are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following embodiments; the implementation conditions adopted in the embodiments can be further adjusted according to specific requirements.

[0034] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0035] The present invention provides a method for preparing a flip chip. Figure 3 , is a schematic diagram of the preparation process of the flip chip of this embodiment, which specifically includes:

[0036] Step (1): providing a wafer, the wafer comprising a plurality of flip chips and preset cutting paths between the flip chips, the flip chips having a first surface side and a second surface side arranged opposite to each other, the preset cutting paths comprising a first preset cutting path formed on a surface of the wafer corresponding to the first surface side, and a second preset cutting path formed on a surface of the wafer corresponding to the second surface side and arranged opposite to the first preset cutting path;

[0037] Step (2): performing the following steps in sequence: performing grooving on the second preset cutting path to form a pre-grooving;

[0038] Disposing a back gold layer on the wafer surface corresponding to the second surface side and the pre-grooved surface;

[0039] In the pre-grooving, laser grooving is performed along the thickness direction of the wafer starting from the back gold layer to form a secondary groove with a depth greater than the thickness of the back gold layer;

[0040] Step (3): Grooving is performed on the first preset cutting path until it is connected to the secondary groove to obtain a plurality of discrete flip chips.

[0041] Please refer to Figure 4 As shown, it is a schematic diagram of the structure of the flip chip on the wafer of this embodiment and the preset cutting path between the flip chips. The figure only exemplarily shows a schematic diagram of one side of the first preset cutting path 10, and the other side is located on the back side of the side (i.e., the side where the back gold layer is set). At the same time, there are multiple first preset cutting paths 10 and second preset cutting paths, respectively, and each first preset cutting path 10 has a second preset cutting path set corresponding to it.

[0042] Please refer to Figure 5-Figure 12 As shown, a processing schematic diagram of one side of the second preset cutting path is given as an example.

[0043] like Figure 5 As shown, this example exemplarily shows a schematic diagram of the side of the wafer, including a silicon layer 103 of a flip chip, a circuit layer 104 of a flip chip disposed on one side of the silicon layer, and a solder bump 102 of the flip chip formed on the circuit layer. In the following other figures, the same structure is not described in detail, and is only marked with reference numbers for easy understanding. Further, Figure 5 The diagram is a diagram of a wafer surface corresponding to the first surface side of the flip chip after a first protective film 101 (also referred to as the first protective film 101 attached to the front side) is provided before processing. In fact, the first protective film 101 is partially attached to and covered on the surface of structures such as solder balls (bumps) 102 of the flip chip, thereby protecting the solder balls and other structures of the flip chip during processing to prevent impurities such as debris generated during processing from adhering to the solder balls or entering between structures such as solder balls. At the same time, the solder balls or circuit layers are also protected accordingly to prevent unnecessary damage or other unexpected problems.

[0044] After the first protective film 101 is attached, Figure 6-7As shown, a mechanical saw 105 (in other embodiments, laser ablation may also be used) is used to cut and groove the second preset cutting path on the wafer surface corresponding to the second surface side of the flip chip to form a pre-groove 107. During the process of forming the pre-groove 107, a water washing mechanism 106 is also provided to wash away particles generated after cutting. The schematic diagram of the structure after pre-groove is shown in FIG. Figure 7 shown.

[0045] Furthermore, before performing the pre-groove 107 processing operation, the wafer provided with the first protective film 101 can be placed on a transparent carrier, with one side of the first protective film 101 facing downward, and the first protective film 101 is preferably made of a transparent material to obtain a transparent first protective film. A CCD positioning camera is installed under the transparent carrier, and the CCD positioning camera is used to scan and position the second preset cutting path through the transparent carrier and the first protective film 101, so that the operation can be performed more accurately and facilitates subsequent processes.

[0046] After the pre-groove 107 is successfully opened, the following steps are performed in sequence: the wafer surface corresponding to the second surface side and the surface of the pre-groove are thinned and polished to obtain a relatively flat plane, and then the silicon surface is etched (for example, acid etching can be used, and the acid includes but is not limited to nitric acid solution or hydrofluoric acid, etc.), which can not only weaken or even eliminate the internal stress that may be generated by the aforementioned thinning and polishing, but also make the surface rougher, so that metal is easier to deposit on it to obtain an excellent back gold layer 108, and then the back gold layer 108 operation is performed. The process of the back gold layer 108 can adopt evaporation or sputtering methods, and a variety of metals can be used to form a composite metal layer as the back gold layer 108. Preferably, before the back gold layer 108 is applied, the surface is cleaned after the silicon surface is etched to obtain good surface cleanliness, thereby improving the bonding strength between the back gold layer 108 and the wafer surface.

[0047] After the above-mentioned operations such as applying the back gold layer 108 are completed, a laser slotter 110 is used to perform laser slotting along the thickness direction of the wafer from the back gold layer 108 in the pre-slotting 107 to form a secondary slot 112 with a depth greater than the thickness of the back gold layer 108. At the same time, in this embodiment, when the laser slotter 110 is used to perform laser slotting on the back side of the chip, a vaporized dust suction device 111 may be added, or a laser cutting protection liquid 109 such as monopropylene glycol methyl ether may be used to protect the back gold surface to prevent laser cutting debris from contaminating the back gold surface. After the cutting is completed, the protection liquid is washed away, that is, the laser cutting protection liquid 109 may be coated on the surface of the back gold layer 108 located on the surface of the wafer.

[0048] For example Figure 8The exemplary structure shown is a schematic diagram of thinning and grinding, silicon surface etching, cleaning, back-gold coating, and coating of laser cutting protection liquid. In addition, in this embodiment, before applying the back-gold layer 108, the first protective film 101 that is bonded can be removed to prevent the first protective film 101 from being damaged by the high temperature of the back-gold coating. After applying the back-gold layer 108, the first protective film 101 (which can be the original or a new first protective film 101 of the same material) is bonded, and then the laser cutting protection liquid is coated.

[0049] like Fig. 9 As shown, it is a schematic diagram of using a laser slotter 110 to perform laser slotting in the pre-slotting 107 starting from the back gold layer 108 along the thickness direction of the wafer. Some vapors will be generated during the laser slotting process, and a vapor dust suction device 111 can absorb and remove them.

[0050] Furthermore, if Fig.10 As shown, due to the high temperature at the cutting point of the laser slotting, the back gold metal at the junction of the slotting area will be melted into liquid by the high temperature, and shrink after cooling to form bumps. These irregular protrusions 113 will affect the back gold layer 108 on the surface of the wafer during subsequent cutting. The tiny protrusions 113 will cause the back gold layer 108 in this area to separate from the film surface, forming bubbles. In the subsequent mechanical cutting process, the rinse water enters these bubbles, causing the protective film (such as UV film) to adhere poorly, resulting in die cutting and throwing. Therefore, in this example, it is preferred to pre-groove the back to form a step, and the wafer silicon substrate-back gold boundary is located between the upper and lower steps, and the depth of the pre-groove 107 is controlled to allow the laser to After the optical grooving, the upper end surface of any point in the pre-grooved 107 is not higher than the upper surface of the back gold layer 108 at the opening of the pre-grooved 107. For example, the upper end surface of the unexpected irregular protrusions 113, such as concave and convex, is not higher than the upper surface of the back gold layer 108 at the opening of the pre-grooved 107. Then, these protrusions 113 can be hidden in the pre-grooved 107 to avoid protruding from the wafer surface and causing bulging when the back gold layer 108 protective film is subsequently attached, and to avoid the back gold layer 108 from separating from the film surface. It can be seen that in this embodiment, the problem of UV film bubbles at the boundary of laser grooving is solved, and the formation of side back gold is also conducive to preventing the back gold from falling off.

[0051] Furthermore, the position of the laser grooving is located in the middle of the bottom of the pre-groove 107, the width of the opening of the secondary groove 112 is smaller than the width of the bottom of the pre-groove 107, and the width of the opening of the pre-groove 107 is controlled to be greater than the sum of the width of the opening of the secondary groove 112, twice the length of the protrusion 113 and twice the thickness of the back gold layer 108, and preferably the depth of the pre-groove 107 is greater than twice the thickness of the back gold layer 108, the height of the laser ablation protrusion (protrusion 113) and the thickness of the thinned and ground surface, so as to facilitate better process operation, further ensure the excellent effect of laser grooving and reduce negative effects.

[0052] In a specific aspect, the thickness of the back gold layer 108 is about 1-3μm, the back surface grinding thickness is assumed to be 7-20μm (depending on actual needs), and the width of the secondary groove 112 formed by the back laser grooving is preset to 40-120μm. The width of the pre-groove 107 is set to: 90-200μm, and the depth of the pre-groove 107 is 10-30μm, which can basically meet the needs.

[0053] In this embodiment, during the processing of the pre-grooving 107 and the secondary groove 112, a slight offset can be eliminated by appropriately expanding the laser scanning width and sacrificing a very small amount of back-gold coverage. Therefore, it is allowed to use laser processing equipment and pre-grooving equipment with lower positioning accuracy. In a specific aspect, assuming that the chip size is 15*15mm, in order to overcome the problem of insufficient positioning accuracy of the processing equipment, a laser cutting path with a width of 120μm is used, and the width of the pre-grooving 107 is set to 200μm (0.2mm) to meet the cutting requirements, then the back-gold coverage rate lost at the top is only about 2.6%, and because of the solder overflow, the slightly lower edge position can still be filled with solder, which basically does not affect the chip's heat dissipation capacity.

[0054] like Fig.11 As shown in the figure, the structural schematic diagram after laser cutting and removal of the first protective film 101 is exemplarily shown. At the same time, in this example, after the laser grooving forms the secondary groove 112, the surface and the surrounding area after the laser grooving can be cleaned through cleaning and drying steps to remove impurities generated by the grooving, and then dried.

[0055] After the above-mentioned back gold layer 108 and the corresponding cutting and grooving are completed, the other side is cut to penetrate the wafer, and further grooves are made on the first preset cutting road 10 until it is connected to the secondary groove 112 to obtain a number of discrete flip chips. For details, please refer to Figure 12-18 shown.

[0056] like Fig.12 As shown, a second protective film 114, such as a UV film, is provided on the side where the above-mentioned back gold layer 108 and the corresponding cutting grooves are completed. Specifically, the second protective film 114 can be provided on the surface of the back gold layer 108, or the second protective film 114 can be provided on the surface of the back gold layer 108 except in the pre-grooved 107. In this example, Fig.12 In the example, the second protective film 114 is disposed on the surface of the back gold layer 108 except in the pre-grooved groove 107. At the same time, due to the aforementioned specially designed processing operation, the second protective film 114 can obtain an excellent bonding effect with the back gold layer 108, and the bonding is tight without hollowing or bulging, which is convenient for subsequent processing and ensures that no bubble phenomenon such as bubble will be generated during the subsequent processing.

[0057] After the second protective film 114 is attached, Fig.13 As shown, firstly, a laser slotter 110 is used to perform laser slotting on the first preset cutting path 10. During the laser slotting process, a gasification dust collecting device 111 is used to assist in preventing the high-temperature gasified material from cooling into large particles. The gasification dust collecting device 111 can remove all the materials generated by high-temperature gasification during the laser slotting process. The schematic diagram of the structure after laser slotting is shown in FIG. Fig.14 As shown;

[0058] After laser grooving, Fig.15 As shown, a machine with a wider cutting saw blade 115 (which may be a saw blade made of diamond material or covered with diamond particles on the surface, etc.) is first used to further cut and groove in the groove formed after laser grooving (roughly in the middle of the bottom of the groove), forming a groove as shown in FIG. Fig.16 The structure after cutting is shown. During this process, the particles broken by cutting are taken out by the saw blade teeth and then taken away by a fluid such as the water flow of the water washing mechanism 106 to be washed clean, so as to avoid being left between structures such as the solder balls (bumps) 102 of the flip chip, which may affect subsequent processing and chip performance.

[0059] Finally Fig.17 As shown, a machine with a narrower cutting saw blade 116 (which may be a saw blade made of diamond material or covered with diamond particles, etc.) is used to further cut and groove the middle part of the bottom of the groove formed in the previous step until it penetrates and connects with the secondary groove 112. In this process, it is preferred to control the width of the groove opened this time to be smaller than the width of the opening of the secondary groove 112 (which can be achieved by controlling the width of the narrower cutting saw blade 116), thereby avoiding tearing of the back gold layer 108 on the other side, completely avoiding the back gold layer 108, avoiding the back gold layer 108 from falling off or bringing metal debris to the solder ball (bump) 102 of the flip chip to cause short circuits and other problems. Similarly, in this process, the cut and broken particles are brought out by the saw teeth of the saw blade, and then carried away by a fluid such as the water flow of the water washing mechanism 106 to be rinsed clean. In one specific aspect, if the width of the narrower cutting saw blade 116 for chip cutting is 35μm (normal saw width), the width of the back laser grooving (secondary groove 112) must be larger than the narrower cutting saw blade 116, preferably at least 40μm, allowing a wider cutting path to be set, such as a width of 40-120μm.

[0060] In this embodiment, the water washing mechanisms in various places are represented by the same reference numerals without specific distinction. As long as they are water washing mechanisms and realize the preset functions, they can be different branches of the same one, or they can be independently equipped water washing mechanisms.

[0061] like Fig.18 As shown, after the above operations are completed, a discrete flip chip is obtained, and the second protective film 114 (eg, UV film) can be removed later.

[0062] In summary, the schematic diagram of the flip chip processing process in this example can be further shown as follows: Fig.19 The detailed process shown includes the following processes performed in sequence: setting a first protective film 101 on the wafer surface corresponding to the first surface side of the flip chip (also referred to as attaching the first protective film 101 on the front side) → cutting and grooving the second preset cutting path on the wafer surface corresponding to the second surface side of the flip chip to obtain a pre-groove 107 (also referred to as providing the pre-groove 107 on the back side) → thinning and grinding → etching the silicon surface → cleaning → removing the attached first protective film 101 → applying a back gold layer 108 → attaching the first protective film 101 on the front side again → applying a laser cutting protective liquid → Laser grooving to obtain secondary grooves 112 → cleaning / drying → removing the first protective film 101 → setting a second protective film 114 (which can be referred to as the second protective film 114 on the back) on the side where the above-mentioned back gold layer 108 and the corresponding cutting and grooving are completed → using a laser grooving device 110 to perform laser grooving on the first preset cutting path 10 → using a machine with a wider cutting saw blade 115 to perform cutting and grooving → using a machine with a narrower cutting saw blade 116 to perform cutting and grooving until it penetrates and connects with the secondary grooves 112, thereby obtaining discrete flip chips.

[0063] Since the present embodiment sets preset cutting paths on opposite sides of the wafer respectively, and then cuts from both sides to penetrate and obtain discrete flip chips, and innovatively opens a pre-groove 107 before applying the back gold layer 108, and performs laser grooving of the secondary groove 112 after applying the back gold layer 108, no long metal debris will be generated during the whole process. Even if mechanical cutting is performed later, the saw teeth cannot contact the back gold area, and no long metal debris will be generated. This not only greatly reduces or even avoids the short circuit caused by the back gold metal debris, but also solves the problem of back gold falling off in the prior art because there is no contact stress at all during the grooving process, and there is no tearing and stretching effect. At the same time, the present embodiment also solves the problem that bubbles may be generated between the existing back gold layer 108 and the protective film protecting the back gold layer 108 during the processing process.

[0064] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a flip chip, characterized in that: The preparation method comprises: (1) Providing a wafer, the wafer comprising a plurality of flip chips and preset cutting paths between the flip chips, the flip chips having a first surface side and a second surface side arranged opposite to each other, the preset cutting paths comprising a first preset cutting path formed on a wafer surface corresponding to the first surface side, and a second preset cutting path formed on a wafer surface corresponding to the second surface side and arranged opposite to the first preset cutting path; (2) performing the following steps in sequence: performing grooving on the second preset cutting path to form a pre-grooving; Disposing a back gold layer on the wafer surface corresponding to the second surface side and the pre-grooved surface; In the pre-grooving, laser grooving is performed starting from the back gold layer along the thickness direction of the wafer to form a secondary groove with a depth greater than the thickness of the back gold layer; Controlling the depth of the pre-grooving so that the upper end surface of any point in the pre-grooving after laser grooving is not higher than the upper surface of the back gold layer at the opening of the pre-grooving; After laser grooving, a protrusion is formed on the bottom plane of the pre-grooving, and the upper end surface of the protrusion is controlled not to be higher than the upper surface of the back gold layer at the opening of the pre-grooving, and the width of the opening of the pre-grooving is controlled to be greater than the sum of the width of the secondary groove opening, twice the length of the protrusion, and twice the thickness of the back gold layer; The width of the secondary groove at the opening is smaller than the width of the bottom of the pre-groove; Controlling the width of the slot directly connected to the secondary slot to be smaller than the width of the secondary slot opening; (3) Grooving is performed on the first preset cutting path until it is connected with the secondary groove to obtain a plurality of discrete flip chips.

2. The method for preparing a flip chip according to claim 1, characterized in that: In step (2), the laser grooving position is located in the middle of the bottom of the pre-grooving; and / or, in step (2), the pre-grooving is performed by mechanical sawing or laser grooving.

3. The method for preparing a flip chip according to claim 1, characterized in that: In step (2), the operation of setting the back gold layer includes the following processes performed in sequence: thinning and grinding the wafer surface corresponding to the second surface side and the selectively pre-grooved surface, etching the silicon surface, and applying the back gold layer, and coating the back gold layer surface on the wafer surface and the selectively pre-grooved surface with a protective liquid.

4. The method for preparing a flip chip according to claim 3, characterized in that: In step (2), before performing grooving to form the pre-grooving, a first protective film is firstly provided on the wafer surface corresponding to the first surface side, and after performing grooving to form the secondary groove, the first protective film is removed; The first protective film is selectively removed before the back gold layer is applied, and the first protective film is selectively provided on the wafer surface corresponding to the first surface side before the protective liquid is coated.

5. The method for preparing a flip chip according to claim 3, characterized in that: In step (2), the depth of the pre-grooving is controlled to be greater than the sum of twice the thickness of the back gold layer and the thickness of the wafer after thinning and grinding.

6. The method for preparing a flip chip according to claim 1, characterized in that: In step (3), before grooving, a second protective film is provided on the surface of the back gold layer; or, in step (3), before grooving, a second protective film is provided on the surface of the back gold layer except in the pre-grooved area.

7. The method for preparing a flip chip according to claim 1, characterized in that: There are a plurality of the first preset cutting lanes and a plurality of the second preset cutting lanes, respectively, and each of the first preset cutting lanes has a corresponding second preset cutting lane.

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