Process method for mounting chip on back surface of sprayed wafer

Abstract

The invention relates to a process method for mounting a chip on the back surface of a sprayed wafer. The process method comprises the following steps: step 1, drawing a program graph; step 2, wafer cleaning; 3, spraying the back surface of the wafer; step 4, pre-curing; step 5, pasting the wafer; step 6, cutting the wafer; 7, cleaning the chip; step 8, chip installation and lamination; and ninthly, post-curing is conducted. According to the method, pattern spraying is carried out on the position of the back face of the wafer through the program pattern, the UV lamp is synchronously adopted for irradiation in the spraying process, UV conductive (non-conductive) electric glue is promoted to be pre-cured, and it is facilitated that the chip mounting and attaching position cannot be easily moved or a chip cannot fall off due to movement or slight vibration in the subsequent chip mounting and attaching process.

Description

TECHNICAL FIELD

[0001] The present application relates to a process method for spraying the back of a wafer chip, belonging to the technical field of semiconductor packaging. BACKGROUND

[0002] In the chip mounting process of the traditional chip packaging process, the existing traditional dispensing technology or painting technology is used to stick or draw the chip bonding material in the form of conductive or non-conductive gel, which is coated on the upper layer of the lead frame or substrate island, and then the chip type after cutting is mounted on the upper layer of the bonding material on the lead frame or substrate island, and finally high temperature baking is carried out to promote the evaporation of water and organic matter in the conductive or non-conductive gel, so as to achieve permanent solidification.

[0003] Another method is to use the technology of sticking conductive or non-conductive adhesive film to the back of the wafer, and then cutting the wafer with the conductive or non-conductive adhesive film to form a single chip type, and then mounting the chip with the conductive or non-conductive adhesive film on the island of the lead frame or substrate to complete the chip mounting work.

[0004] The process flow is as follows: 1.1 Traditional dispensing / painting technology Empty island Dispensing or painting glue on the lead frame or substrate island Chip mounting on the island High temperature baking Complete chip mounting.

[0005] 1.2 Traditional film sticking technology Empty wafer Wafer back film sticking Wafer cutting Empty metal lead frame Chip mounting on the lead frame or substrate island Complete chip mounting.

[0006] The defects of the traditional technology are as follows: 2.1 Traditional dispensing / painting technology 2.1.1 Bonding glue diffusion pollutes wire bonding area When the traditional or dispensing or painting bonding glue is coated on the upper layer of the lead frame or substrate island, due to the relationship between surface tension, wettability, temperature or time length, the bonding glue will spread outward after coating, which will pollute the ground wire area of the lead frame or substrate island that needs to be bonded, and the chip or internal pin cannot continue to be bonded with the island, or the bonding combination will become unstable and unsafe due to slight pollution; 2.1.2 Only large island small chip specifications can be pasted (such as Figure 1 As shown) The die mounting technology of the conventional dispensing process is a gel or liquid due to the material properties. After the dispensing or drawing is completed, the die mounting is performed. Due to the pressure and height position relationship in the chip mounting process, the gel or liquid conductive (non-conductive) adhesive material is extruded, which causes the gel or liquid adhesive material to expand, resulting in the contamination of the adhesive material on the island position outside the chip size. In addition to affecting the bonding of the ground wire, it can also cause short circuit of the inner pins or gold fingers outside the island (as shown). Figure 2 2.1.3 Contamination of organic substances causes delamination Due to the material properties of the conductive (non-conductive) adhesive material, it is a gel or liquid. When high-temperature baking is performed after the chip mounting is completed, the gel or liquid adhesive material will release water and organic substances (the greater the volume of the gel or liquid adhesive material, the more water and organic substances will be released) during the high-temperature baking solidification process. The released water and organic substances will adhere to the surface of the chip and the surface of the lead frame or substrate, and even contaminate the oven, thereby forming an organic thin film medium on the surface of the chip and the surface of the lead frame or substrate. This layer of organic thin film medium will block the bonding between the epoxy resin plastic encapsulant and the surface layer of the chip and the surface layer of the lead frame or substrate, resulting in delamination between the epoxy resin plastic encapsulant and the chip or the lead frame or substrate (as shown). Figure 3

[0007] 2.2 Die mounting technology of traditional film pasting process 2.2.1 The die mounting process technology of the traditional wafer back pasting conductive (non-conductive) adhesive film (DAF) is not suitable for chip sizes below 3*3 mm due to the material properties. Because the material properties of the conductive (non-conductive) adhesive film cannot be used for high-temperature re-solidification, the conductive (non-conductive) adhesive film is soft and cannot really adhere to the chip and the island when used with chip sizes below 3*3 mm, which seriously affects the wire bonding capability of chips below 3*3 mm in the subsequent process; 2.2.2 The use cost of the conductive (non-conductive) adhesive film (DAF) is at least 2 times more expensive than the conventional or point or draw process conductive (non-conductive) adhesive. SUMMARY

[0008] ​​The technical problem solved by the present application is to provide a process method for spraying wafers back chip mounting, which sprays the wafer back through a program, and synchronously uses a UV lamp to irradiate during the spraying process, so as to promote the UV conductive (non-conductive) glue to achieve pre-curing and promote the original glue liquid state to form a solid state. After the conductive (non-conductive) glue is irradiated by the UV rays, the water and organic substances in the conductive (non-conductive) glue are evaporated, and the conductive (non-conductive) glue changes from a liquid state to a solid state, but the adhesive substance does not change, which is beneficial to the subsequent chip mounting and bonding process, and the chip mounting and bonding position can be kept from moving or falling off the chip due to movement or slight vibration.

[0009] The technical solution adopted by the present application to solve the above problems is a process method for spraying wafers back chip mounting, which comprises the following steps: Step one, program graphic drawing; Step two, wafer cleaning; Step three, wafer back spraying; Step four, pre-curing; Step five, wafer pasting; Step six, wafer cutting; Step seven, chip cleaning; Step eight, chip mounting and bonding; Step nine, post-curing.

[0010] Optionally, step one performs AutoCAD graphic drawing on the relevant position of the wafer to be sprayed, and converts the AutoCAD file format of the required coating pattern into JPG, PDF or a file format that can adapt to the spraying equipment.

[0011] Optionally, the wafer cleaning process in step two includes grease removal, rust removal, pure water cleaning and drying.

[0012] Optionally, in step three, the graphic data drawn according to the design is used to position the device workbench and the wafer back position.

[0013] Optionally, in step three, the spraying equipment adopts fixed L-shaped positioning block positioning, circular groove positioning block positioning or visual non-discriminatory positioning.

[0014] Optionally, in step three, the graphic spraying adds UV conductive / non-conductive glue through the UV spraying equipment, and sprays the wafer back according to the designed pattern.

[0015] Optionally, in step three, the graphic spraying material uses chemical materials added with UV conductive / non-conductive glue.

[0016] Optionally, the pre-curing in step four is performed by irradiation of UV light to decompose the UV chemical composition of the conductive / non-conductive adhesive, and the conductive / non-conductive adhesive film is in a solid state and does not flow.

[0017] Optionally, the post-curing in step nine is performed by high-temperature and long-time infrared baking to achieve permanent curing of the UV conductive / non-conductive adhesive.

[0018] Compared with the prior art, the present application has the following advantages: 1. The UV spraying equipment used in the wafer back chip mounting technology process is a general type, and a commercial spray head or an industrial spray head can be used. The general spraying can be full-area spraying, partial-area spraying, or different shapes and sizes. Except for the need for design and drawing, no other expenses are required, and the chip mounting process of point / paint adhesive is eliminated, thereby increasing the chip mounting speed by at least 30%. 2. Ultra-small outer expansion clean base island: due to the characteristics of the UV conductive / non-conductive adhesive, the UV light is used to decompose the chemical composition of the UV adhesive. The UV rays are irradiated at the same time as spraying, so that the UV conductive / non-conductive adhesive reaches the first stage of pre-curing. Because the pre-curing stage is achieved instantaneously, the conductive / non-conductive adhesive that would flow is stopped from flowing due to surface tension and expansion. Because of this, the base island on the wafer back is very clean and pollution-free except for the bonded material in the sprayed area. Because of the instantaneous light-curing characteristics of the UV conductive / non-conductive adhesive, the difficulty of large chip and small base island is fully solved. Figure 4 3. Risk of organic material pollution of the chip and lead frame or substrate: because the UV light is used to decompose the UV chemical in a short time, the water and organic material in the conductive / non-conductive adhesive are also evaporated. Because the water and organic material are evaporated before the chip mounting, there is almost no organic material volatilization in the subsequent chip mounting and post-curing process, thereby fully ensuring that the chip surface and the lead frame or substrate are not polluted by organic material. 4. Difficulty of stable thickness of the conductive / non-conductive adhesive: the sprayed UV conductive / non-conductive adhesive on the lead frame or substrate base island can be adjusted in thickness according to the speed, viscosity, temperature, and layer number, so as to obtain the required thickness, thereby fully solving the crisis of chip and base island delamination caused by unstable thickness of the conductive / non-conductive adhesive. ​5. More stable super level chip mounting key bonding eutectic: Because of the adoption of the spray island chip mounting technology, the UV conductive (non-conductive) glue is sprayed and instantaneously pre-solidified into a solid state, so when the chip is mounted on the flat solid conductive (non-conductive) adhesive material, the chip can be stably pasted on the solid conductive (non-conductive) adhesive material, thus fully solving the risk of chip tilt after chip installation because the chip is installed on soft and unstable glue, thereby indirectly helping the wire bonding pressure parameter and ultrasonic parameter to be more stable, and the bonding eutectic stability is higher. 6. Increase the bonding ability and safety reliability: Because of the adoption of the spray island chip mounting technology, the gel-like conductive (non-conductive) glue is instantaneously evaporated under UV irradiation to form a solid state, so in the subsequent chip installation and high-temperature baking process, because there is no excess water and organic matter in the conductive (non-conductive) glue layer, there is no evaporation of excess water and organic matter during the chip installation and high-temperature baking process, so that the chip surface and the lead frame or substrate surface are not polluted by water and organic matter, which fully helps the chip surface and the lead frame or substrate surface to bond with the epoxy resin. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a schematic diagram of a large island small chip mounting defect.

[0020] Figure 2 It is a schematic diagram of a pollution defect outside the island.

[0021] Figure 3 It is a schematic diagram of an island and chip delamination defect.

[0022] Figure 4 It is a schematic diagram of a large chip small island chip mounting structure.

[0023] Figure 5 It is a schematic diagram of a chip stack mounting structure.

[0024] Figure 6 It is a schematic diagram of any heat sink bearing device mounting structure on the surface of the package. DETAILED DESCRIPTION

[0025] The application will be further described in detail below in conjunction with the embodiments of the drawings.

[0026] The application relates to a spray wafer back chip mounting process, which comprises the following steps: Step 1, program graph drawing; Draw the AutoCAD graphics at the relevant locations on the wafer to be sprayed, complete the AutoCAD file format of the graphics to be coated, and then convert it into JPG, PDF or a file format that can be adapted to the spraying equipment; Step 2: Wafer cleaning; During the production or transportation process, wafers are inevitably contaminated by organic matter due to hand-held wafers. Therefore, they need to be cleaned before spraying UV conductive (non-conductive) adhesive to avoid organic contamination affecting the bonding ability of UV conductive (non-conductive) adhesive and wafers. The cleaning process depends on the characteristics of the material, and includes grease removal, oxide removal, pure water cleaning, and drying and baking to ensure that the wafer surface is clean and to increase the bonding ability between the UV conductive (non-conductive) adhesive and the back of the wafer. Step 3: Spray coating on the back of the wafer; 3.1 Positioning: Position the equipment workbench and the back of the wafer according to the designed graphic data. The spray equipment can be positioned using fixed L-shaped positioning blocks or circular groove positioning blocks, or visual indiscriminate positioning (indiscriminate positioning means that there is no need to specify the position. Simply place the wafer within the effective scanning area with the back facing up, and then use visual scanning to remember the position). 3.2 Graphic spraying: Use UV spraying equipment and add UV conductive (non-conductive) glue to spray the back of the wafer according to the designed pattern; 3.3 Spraying material: It is a chemical material with UV conductive (non-conductive) glue added, the purpose of which is to quickly and quickly achieve a non-flowing solid state with preliminary shaping; 3.4 Spraying thickness: It is determined by the viscosity, temperature, spraying pressure, spraying amount and spraying moving speed of the UV conductive (non-conductive) adhesive matched with the nozzle in the spraying equipment; 3.5 Number of spray layers: The number of spray layers is determined by the thickness of each layer and the total thickness required for spraying; Step 4: pre-curing; After the UV conductive (non-conductive) glue chemical material is sprayed on the back of the wafer by the UV spraying equipment, the UV lamp is immediately turned on to irradiate to decompose the UV chemical components of the UV conductive (non-conductive) glue. At this time, the conductive (non-conductive) glue film has become solid and non-flowing; Step 5: Wafer pasting; Before wafer dicing, the front side of the wafer faces upwards, and the back side of the wafer is pasted on the adhesive film (blue film or UV film) using wafer laminating equipment. Because the back side of the wafer is firmly pasted on the adhesive film, in the subsequent wafer dicing process, the wafer will not be blown away due to lateral force during the dicing process because the wafer is firmly pasted on the adhesive film. Step 6: Wafer cutting; After the back of the wafer is firmly attached to the mucosa, the wafer cutting equipment can be used to align the chip cutting lanes to cut the wafer. After the wafer cutting is completed, each chip will be separated independently, but each independent chip is still firmly attached to the mucosa. Step 7: Chip cleaning; After the wafer is cut, a lot of silicon chips will be attached to the surface of the chip, so the chip cleaning equipment needs to be used to clean the chip after the chip is cut; Step 8: Chip installation and bonding; After the chip is cleaned, the chip can be mounted on the lead frame or substrate island using chip mounting equipment. Due to the material properties of UV conductive (non-conductive) adhesive, heating may be required during mounting to increase the chip mounting and pasting on the lead frame or substrate island. The temperature used for pasting will vary depending on the type of conductive (non-conductive) adhesive. Step nine, post-curing; Once the chip is mounted and attached to the leadframe or substrate island, it enters a high-temperature, long-term infrared bake to achieve a truly permanent cure of the UV conductive (or non-conductive) adhesive. The bake temperature and time are adjusted based on the material type and characteristics.

[0027] The above process method can be used on the metal lead frame base island of traditional packaging, the organic substrate base island of traditional packaging, the panel-level package (PLP) base island of advanced packaging, the panel-level (PLP) glass substrate base island of advanced packaging, or any chip carrier device that can be mounted with chip bonding, and the use of spray coating falls within the scope of this technology; The above process method can be used not only on the metal lead frame base island of traditional packaging, the organic base island of traditional packaging, the board level packaging (PLP) base island of advanced packaging, and the board level (PLP) glass substrate base island of advanced packaging, but also on the installation of chip stacking bonding surface (such as Figure 5 as shown), or any heat sink supporting device that fits on the surface of the package (such as Figure 6 As shown in the figure), and the use of spraying method all fall into this technical category.

[0028] In addition to the above embodiments, the present invention also includes other implementation methods. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of protection of the claims of the present invention.

Claims

1. A process for spray coating the backside of a wafer-chip, characterized by The method comprises the following steps: Step one, program graph drawing; Step two, wafer cleaning; Step three, wafer back spraying; Step four, pre-curing; Step five, wafer sticking; Step six, wafer cutting; Step seven, chip cleaning; Step eight, chip mounting and sticking; Step nine, post-curing.

2. The process for backside die attach by spray coating of claim 1, wherein: Step one, AutoCAD graph drawing is performed on the wafer position to be sprayed, and the AutoCAD file format of the required coating graph is converted into JPG, PDF or a file format that can be adapted to the spraying equipment.

3. The process for backside die attach by spray coating of claim 1, wherein: The wafer cleaning process in step two includes grease removal, rust removal, pure water cleaning and drying and baking.

4. The process for backside die attach by spray coating of claim 1, wherein: In step three, the device workbench and wafer back position are positioned according to the designed graph data.

5. The process for backside die attach of a wafer by spray coating according to claim 4, wherein: In step three, the spraying equipment adopts fixed L-shaped positioning block positioning, circular groove positioning block positioning or visual non-discriminatory positioning.

6. The process for backside die attach by spray coating of claim 1, wherein: In step three, the graph spraying is performed on the wafer back by adding UV conductive / non-conductive glue to the UV spraying equipment according to the designed graph.

7. The process for backside die attach by spray coating of claim 1, wherein: In step three, the graph spraying material adopts chemical material added with UV conductive / non-conductive glue.

8. The process for backside die attach by spray coating of claim 1, wherein: In step four, pre-curing is performed by irradiation of a UV lamp to achieve decomposition of the UV chemical composition of the UV conductive / non-conductive glue, at this time, the conductive / non-conductive glue film has already presented a solid state without flowing.

9. The process for backside die attach by spray coating of claim 1, wherein: In step nine, post-curing is performed by high-temperature long-time infrared baking, the purpose is to achieve true permanent curing of the UV conductive / non-conductive glue.

Images