A WBCSP substrate and a stepped protection treatment method for copper pads thereof

Abstract

The application provides a stepped protection treatment method for a copper pad of a WBCSP substrate and the WBCSP substrate. The treatment method obtains a substrate provided with a copper pad. A solidified solder resist layer with a preset opening is formed on the substrate, so that a preset area of the copper pad is exposed. The preset area comprises a single copper layer and a copper oxide layer attached to the surface of the single copper layer. The substrate on which the solidified solder resist layer is formed is immersed in a benzotriazole aqueous solution. The benzotriazole reacts with the single copper layer to form a benzotriazole-copper complex film on the surface of the single copper layer. The benzotriazole does not react with the copper oxide layer. The substrate on which the benzotriazole-copper complex film is formed is subjected to pickling to remove the copper oxide layer. An alkaline solution is used to perform stripping treatment on the substrate after pickling to remove the benzotriazole-copper complex film. Surface treatment is performed on the substrate after the stripping treatment is completed to form an organic soldering film on the preset area of the copper pad.

Description

Technical Field

[0001] This invention belongs to the field of printed circuit board and semiconductor packaging substrate manufacturing technology, and particularly relates to a stepped protection treatment method for WBCSP substrate and its copper pads. Background Technology

[0002] WBCSP (Wire Bonding Chip Scale Package) substrate 1, with its advantages of small size, mature technology, and compatibility with various wire bonding processes, is widely used in semiconductor fields such as memory chips, micro sensors, and portable electronic devices. This type of substrate 1 features dense circuitry, tiny copper pads 2, and narrow pad spacing, placing extremely high demands on the precision of surface treatment processes, protective effects, and interface bonding reliability.

[0003] In the conventional manufacturing process of WBCSP substrate 1, after the solder resist coating, pre-curing, exposure, and development processes are completed, a copper oxide layer 6 with a thickness of 30nm~100nm will form on the surface of the exposed copper pads 2 (the elemental copper layer) in the natural environment. To ensure subsequent surface treatment and bonding performance, the industry generally uses a dilute sulfuric acid pickling process to remove this copper oxide layer 6. However, due to the limitations of the substrate 1 structure, such as... Figure 1 As shown, acidic cleaning solutions easily penetrate the gap between the copper pad 2 and the cured solder mask 5, causing excessive corrosion of the copper layer at the interface and leading to problems such as undercutting of the copper pad 2 and localized depressions. Interface corrosion directly damages the adhesion between the cured solder mask 5 and the copper substrate, thereby inducing appearance defects and reliability risks such as whitening, poor adhesion, and solder penetration of the cured solder mask 5, significantly reducing product yield and service life.

[0004] To mitigate corrosion caused by pickling, existing technologies typically employ two conventional improvement methods: one is to reduce the concentration of dilute sulfuric acid, shorten the pickling time, or add multiple water washing processes. This method can only slightly reduce the degree of corrosion and cannot fundamentally block the erosion of the copper-solder resist interface by the acid solution, resulting in frequent defects. The other method is to use benzotriazole (BTA) for overall permanent passivation of copper parts, utilizing the complex film formed by benzotriazole and copper to achieve corrosion protection. However, traditional BTA passivation processes are mostly used as the final protection method for finished products. The passivation film remains on the surface of the copper pads for a long time, which not only causes film residue and reduces the solderability and wire bonding strength of the copper surface, but also cannot meet the requirements of the entire process of pickling and organic solder resist coating (OSP).

[0005] Organic solder resist (OSP) is currently the mainstream final anti-oxidation and solder resist surface treatment technology for bare copper pads on packaging substrates, featuring simple processing, low cost, and no impact on soldering and bonding performance. Existing processes typically perform OSP plating directly after pickling and rinsing, lacking a dedicated pre-treatment structure for the pickling process. In summary, existing process solutions cannot simultaneously meet multiple requirements, including thorough oxidation removal through pickling, zero corrosion at the copper-solder resist interface, complete removal of the passivation film, and satisfactory OSP and wire bonding performance. Summary of the Invention

[0006] In view of the problems existing in the prior art, the main objective of the present invention is to provide a step-by-step protection treatment method for WBCSP substrate and its copper pads. By setting a temporary complexing film for acid pickling protection, the corrosion of copper pads, undercutting and whitening of the cured solder resist layer can be effectively avoided. After acid pickling, the film can be removed to ensure the normal preparation of subsequent organic solder resist film, thereby improving product yield and reliability.

[0007] The objective of this invention is achieved through the following technical solution: This invention provides a stepped protection method for copper pads on a WBCSP substrate, comprising the following steps: Obtain a substrate with copper pads; Liquid solder resist is coated onto the obtained substrate and pre-cured to form a pre-cured solder resist film on the substrate. A photomask is used to expose and develop the pre-cured solder resist film to form a cured solder resist layer; a predetermined area of ​​the copper pad is exposed outside the cured solder resist layer; the predetermined area includes a pure copper layer and a copper oxide layer attached to the surface of the pure copper layer; The substrate on which the cured solder resist layer is formed is immersed in an aqueous solution of benzotriazole, where benzotriazole undergoes a coordination reaction with the elemental copper layer to form a benzotriazole-copper complex film on the surface of the elemental copper layer; wherein, the benzotriazole does not react with the copper oxide layer. The substrate on which the benzotriazole-copper complex film is formed is acid-washed to remove the copper oxide layer; The benzotriazole-copper complex film was removed by peeling the acid-washed substrate with an alkaline solution. The substrate that has undergone the stripping process is surface treated to form an organic solder resist film on a predetermined area of ​​the copper pads.

[0008] As a further description of the above technical solution, in the step of "immersing the substrate with the cured solder resist layer into an aqueous solution of benzotriazole, where benzotriazole undergoes a coordination reaction with the elemental copper layer to form a benzotriazole-copper complex film on the surface of the elemental copper layer", the temperature is controlled at 40℃~45℃, the processing time is 2min~4min, and the concentration of the aqueous solution of benzotriazole is 0.8g / L~1.5g / L.

[0009] As a further description of the above technical solution, in the step of "acid washing the substrate on which the benzotriazole-copper complex film is formed to remove the copper oxide layer", a sulfuric acid solution with a volume fraction of 5 vol %~10 vol % is used to acid wash the substrate on which the benzotriazole-copper complex film is formed, and the acid washing temperature is 35°C.

[0010] As a further description of the above technical solution, in the step of "acid washing the substrate on which the benzotriazole-copper complex film is formed to remove the copper oxide layer", when the thickness of the copper oxide layer is 30nm~50nm, the volume fraction of the sulfuric acid solution used is 5vol%~6vol%, and the acid washing time is 0.5min~1.0min. When the thickness of the copper oxide layer is 50 nm to 80 nm, the volume fraction of the sulfuric acid solution used is 7 vol % to 8 vol, and the pickling time is 1.0 min to 1.5 min. When the thickness of the copper oxide layer is 80nm~100nm, the volume fraction of the sulfuric acid solution used is 9vol%~10vol%, and the pickling time is 1.5min~2.0min.

[0011] As a further description of the above technical solution, in the step of "using an alkaline solution to peel off the acid-washed substrate to remove the benzotriazole-copper complex film", the alkaline solution used is a sodium hydroxide solution with a mass fraction of 3%~5%, the processing temperature is 50℃~60℃, and the processing time is 2min~5min.

[0012] As a further description of the above technical solution, before the step of "performing surface treatment on the substrate after the stripping process to form an organic solder resist film on the preset area of ​​the copper pad", the substrate after the stripping process is also washed with water.

[0013] The present invention also provides a WBCSP substrate, which is prepared by the stepped protection treatment method for copper pads of WBCSP substrate as described above.

[0014] By employing the above technical solutions, the outstanding effects of this invention are as follows: 1. In the stepped protection treatment method for copper pads on WBCSP substrates of the present invention, a curing solder resist layer is first applied to the substrate with formed copper pads, exposing the predetermined area of ​​the copper pads outside the curing solder resist layer. The difference is that before acid washing the substrate, the substrate is first immersed in a benzotriazole aqueous solution. Utilizing the characteristic that benzotriazole only forms a coordination complex with elemental copper and does not react with copper oxide, a dense, acid-resistant benzotriazole-copper complex film is generated only on the surface of the exposed elemental copper layer, effectively protecting the copper pad substrate and its interface with the curing solder resist layer, while the copper oxide layer is completely exposed without a film layer covering it. The subsequent acid pickling process allows for the smooth and unobstructed removal of the copper oxide layer. Simultaneously, the benzotriazole-copper complex film effectively isolates the acidic solution, preventing defects such as undercutting, solder mask whitening, and interface loosening caused by acid erosion of the copper pads and penetration into the solder resist interface, common in traditional acid pickling processes. After acid pickling, the substrate is then peeled off using an alkaline solution to precisely remove all the benzotriazole-copper complex film without damaging the copper pad substrate structure, completely eliminating the potential for organic film residue. Finally, the cleaned copper pad surface is surface-treated to prepare a uniform and stable organic solder resist film, forming a permanent protective structure for the finished product. Therefore, this invention adopts a step-by-step protection approach of "temporary complex film pickling protection + alkaline film removal + finished organic solder resist film", which realizes copper pad protection in stages and layers. This ensures that the pickling process can completely remove the oxide layer and eliminates copper pad corrosion, interface undercut, and poor solder resist whitening from the root. At the same time, there are no residual impurities that interfere with subsequent film formation. This effectively improves the appearance quality of copper pads on WBCSP substrates, wire bonding stability and welding reliability, and significantly reduces the substrate defect rate. 2. The stepped protection treatment method for copper pads on WBCSP substrates of the present invention quantifies and links the thickness of copper oxide layer with pickling solution concentration and time, which can more accurately control the pickling endpoint, avoid over-etching or under-etching, and is more suitable for mass production processes. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of a WBCSP substrate after acid washing in the prior art. Figure 2 This is a schematic diagram of the structure used in this embodiment of the invention to expose the pre-cured solder resist film on the WBCSP substrate using a photomask; Figure 3 This is a schematic diagram of the structure of the WBCSP substrate after development processing in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of the benzotriazole-copper complex film formed on the surface of the elemental copper layer in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the WBCSP substrate after acid washing in an embodiment of the present invention; Figure 6This is a schematic diagram of the structure of the WBCSP substrate after the removal of the benzotriazole-copper complex film (and water washing) in an embodiment of the present invention; Figure 7 This is a schematic diagram of the structure in which an organic solder mask is formed on a preset area of ​​a copper pad in an embodiment of the present invention.

[0016] Icon labels: 1. Substrate; 2. Copper pads; 3. Pre-cured solder resist film; 4. Photomask; 5. Cured solder resist layer; 6. Copper oxide layer; 7. Benzotriazole-copper complex film; 8. Organic solder resist film. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] In the description of this invention, it should be noted that the terms "upper," "middle," "lower," "inner," "outer," "front," "rear," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0019] Please see Figures 2 to 7 This invention discloses a stepped protection treatment method for a WBCSP substrate 1 and its copper pads 2, wherein the disclosed stepped protection treatment method for the copper pads 2 of the WBCSP substrate 1 includes the following steps: Obtain a substrate 1 with copper pads 2; Liquid solder resist is coated onto the obtained substrate 1 and pre-cured to form a pre-cured solder resist film 3 on the substrate 1. The pre-cured solder resist film 3 is exposed and developed using a photomask 4 to form a cured solder resist layer 5; the preset area of ​​the copper pad 2 is exposed outside the cured solder resist layer 5; the preset area includes a pure copper layer and a copper oxide layer 6 attached to the surface of the pure copper layer. The substrate 1, to which the cured solder resist layer 5 is formed, is immersed in an aqueous solution of benzotriazole. Benzotriazole undergoes a coordination reaction with the elemental copper layer to form a benzotriazole-copper complex film 7 on the surface of the elemental copper layer. The benzotriazole does not react with the copper oxide layer 6. The substrate 1 on which the benzotriazole-copper complex film 7 is formed is acid-washed to remove the copper oxide layer 6; The substrate 1 after acid washing was peeled off using an alkaline solution to remove the benzotriazole-copper complex film 7; The substrate 1, after the stripping process is completed, is subjected to surface treatment to form an organic solder resist film 8 on the predetermined area of ​​the copper pad 2.

[0020] Using the above method, firstly, a WBCSP substrate 1 with the formed copper pads 2 is obtained as the processing substrate; then, liquid solder resist is coated onto the entire surface of the substrate 1 and pre-cured to form a structurally stable pre-cured solder resist film 3, meeting the requirements of subsequent photolithography processes; then, exposure and development are completed through the photomask 4, exposing a predetermined area of ​​the copper pads 2 outside the cured solder resist layer 5. The exposed copper pads 2 surface simultaneously contains a stable elemental copper layer and a copper oxide layer 6 generated by the process and air oxidation; subsequently, the substrate 1 is immersed in a benzotriazole aqueous solution. Utilizing the characteristic that benzotriazole only coordinates with elemental copper and does not react with copper oxide, a dense, acid-resistant benzotriazole-copper complex film 7 is formed only on the surface of the exposed elemental copper layer. The copper pad 2 substrate and its interface with the cured solder resist layer 5 form effective protection, while the copper oxide layer 6 is completely exposed without any film layer covering. Subsequently, during the pickling process of the substrate 1, the copper oxide layer 6 can be removed smoothly and without obstruction. At the same time, the benzotriazole copper complex film effectively isolates the acid solution, avoiding the defects such as undercut, solder resist whitening, and interface loosening caused by acid corrosion of the copper pad 2 body and penetration into the solder resist interface in the traditional pickling process. After pickling, the substrate 1 is then peeled off with an alkaline solution to accurately remove all the benzotriazole-copper complex film 7 without damaging the copper pad 2 substrate structure, thus completely eliminating the hidden danger of organic film residue. Finally, the clean surface of the peeled copper pad 2 is surface treated to prepare a uniform and stable organic solder resist film 8, forming a permanent protective structure for the finished product. Therefore, this invention adopts a step-by-step protection approach of "temporary complexing film pickling protection + alkaline film removal + finished organic solder resist film 8", which realizes the protection of copper pad 2 in stages and layers. This ensures that the pickling process can completely remove the oxide layer, and eliminates the corrosion of copper pad 2, interface undercut, and poor solder resist whitening from the root. At the same time, there are no residual impurities that interfere with subsequent film formation. This effectively improves the appearance quality, wire bonding stability and welding reliability of copper pad 2 of WBCSP substrate 1, and significantly reduces the defect rate of substrate 1.

[0021] Please see Figures 2 to 7Specifically, in this embodiment, the stepped protection treatment method for the copper pads 2 of the WBCSP substrate 1 includes the following steps: First, a WBCSP substrate 1 with pre-formed copper pads 2 is obtained. The substrate 1 has completed circuit etching and pad forming, providing a basic structure for subsequent solder mask fabrication and surface treatment.

[0022] Next, liquid (photosensitive) solder resist ink is uniformly coated onto the surface of the obtained substrate 1 and pre-cured to form a uniform, dry, and photosensitive pre-cured solder resist film 3 on the entire surface of the substrate 1. This pre-curing process can fully evaporate the organic solvents inside the ink, preventing adhesion to the photomask 4 in subsequent exposure processes, while ensuring the resolution of the solder resist film pattern. It is a necessary pre-process for achieving fine pad opening.

[0023] Subsequently, the photomask 4 is used to align, expose, and develop the pre-cured solder resist film 3, selectively retaining the solder resist film in the circuit and substrate areas to form a structurally stable cured solder resist layer 5, and completely exposing the preset (functional) area of ​​the copper pad 2 outside the cured solder resist layer 5. The exposed preset area includes a dense elemental copper layer, and due to the process environment and air oxidation, an uneven copper oxide layer 6 will naturally form on the surface of the elemental copper layer. This copper oxide layer 6 directly affects the subsequent soldering and wire bonding performance and needs to be removed through a further acid pickling process.

[0024] Before the pickling process, the substrate 1 with the cured solder resist layer 5 is immersed in a benzotriazole aqueous solution. Utilizing the coordination properties of benzotriazole, it reacts only with the exposed elemental copper layer, forming a dense, acid-resistant benzotriazole-copper complex film 7 on the surface of the elemental copper layer. The copper oxide layer 6 does not participate in the coordination reaction and remains uncovered. This temporary complex film completely covers the copper pad 2 substrate and the delicate interface between the copper pad 2 and the solder resist layer, providing a reliable protective barrier for the subsequent pickling process. Specifically, in this embodiment, the concentration of the benzotriazole aqueous solution is controlled at 0.8 g / L to 1.5 g / L, the processing temperature is controlled at 40°C to 45°C, and the processing time is 2 min to 4 min. This parameter range ensures that benzotriazole and elemental copper fully complex into a film, resulting in a dense, uniform film free of pinholes and thin areas, which can stably withstand subsequent acid pickling corrosion. If the concentration is too low, the temperature is insufficient, or the time is too short, the complexed film will be thin and the protection will be discontinuous, posing a risk of acid pickling corrosion leakage. If the parameter is too high, the film may be too thick and contain too many residual impurities, increasing the difficulty of subsequent stripping.

[0025] Next, the substrate 1 with the benzotriazole-copper complex film 7 can be acid-washed to remove the copper oxide layer 6. More specifically, in this embodiment, a sulfuric acid solution with a volume fraction of 5 vol% to 10 vol% is used to acid-wash the substrate 1 with the benzotriazole-copper complex film 7 at a constant temperature of 35°C to remove the exposed copper oxide layer 6. During this process, the elemental copper layer and its interface with the cured solder resist layer 5 are completely protected by the benzotriazole-copper complex film 7 and will not be corroded by the acid solution, thereby fundamentally avoiding defects such as undercutting, solder resist whitening, and interface loosening. Specifically, in this embodiment, differentiated acid-washing parameters are matched for copper pads 2 with different oxidation levels to achieve precise deoxygenation and zero corrosion protection. When the thickness of the copper oxide layer 6 is 30nm~50nm, the volume fraction of the sulfuric acid solution used is 5vol%~6vol%, and the pickling time is 0.5min~1.0min to avoid over-pickling when quickly removing the thin oxide layer; when the thickness of the copper oxide layer 6 is 50nm~80nm, the volume fraction of the sulfuric acid solution used is 7vol%~8vol%, and the pickling time is 1.0min~1.5min to meet the removal requirements of medium oxide thickness; when the thickness of the copper oxide layer 6 is 80nm~100nm, the volume fraction of the sulfuric acid solution used is 9vol%~10vol%, and the pickling time is 1.5min~2.0min to thoroughly remove the thick oxide layer and ensure the copper surface is clean. This grading parameter setting balances the thoroughness of oxide layer removal with the protective safety of the copper pads 2 and the interface between the copper pads 2 and the solder mask.

[0026] After pickling, the pickled substrate 1 is then subjected to a peeling treatment using an alkaline solution to remove the benzotriazole-copper complex film 7. Specifically, in this embodiment, a 3%~5% sodium hydroxide solution is used as the peeling solution, the treatment temperature is controlled at 50℃~60℃, and the treatment time is 2min~5min. This alkaline washing condition can precisely destroy the coordination bond structure of the complex film, achieving complete peeling of the temporary film layer without corroding or damaging the copper pad 2 substrate structure, leaving the copper surface clean and residue-free after peeling. The coordinated matching of temperature, concentration, and time range can ensure a balance between peeling efficiency and the structural safety of the substrate 1.

[0027] Specifically, in this embodiment, before completing the peeling process and preparing the organic solder resist film 8, the substrate 1 is also subjected to a water washing process, for example, using pure water. The purpose of the water washing process is to thoroughly remove residual sodium hydroxide solution, film peeling residue, and trace impurities from the board surface, avoid alkaline residue contamination of the subsequent film-forming bath solution, ensure the high cleanliness of the copper pad 2 surface, and provide a good foundation for the uniform and dense formation of the organic solder resist film 8.

[0028] Finally, the cleaned copper pads 2 are subjected to surface treatment to form a uniform and stable organic solder resist film 8, resulting in a finished WBCSP substrate 1 with excellent protective performance. The organic solder resist film 8 can continuously protect the copper pads 2 from oxidation during product storage, soldering, and wire bonding, ensuring the long-term reliability of the substrate 1.

[0029] Please see Figure 7 Specifically, the WBCSP substrate 1 disclosed in this embodiment is prepared by the stepped protective treatment method of copper pads 2 of WBCSP substrate 1 as described above. The interface between the copper pads 2 and the cured solder resist layer 5 is free from corrosion and undercut defects. The solder resist layer is firmly attached. The organic solder resist film 8 on the surface of the copper pads 2 is uniformly completed, which can meet the requirements for wire bonding and soldering.

[0030] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any changes, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A stepped protection treatment method for copper pads on a WBCSP substrate, characterized in that, Includes the following steps: Obtain a substrate with copper pads; Liquid solder resist is coated onto the obtained substrate and pre-cured to form a pre-cured solder resist film on the substrate. A photomask is used to expose and develop the pre-cured solder resist film to form a cured solder resist layer; a predetermined area of ​​the copper pad is exposed outside the cured solder resist layer; the predetermined area includes a pure copper layer and a copper oxide layer attached to the surface of the pure copper layer; The substrate on which the cured solder resist layer is formed is immersed in an aqueous solution of benzotriazole, where benzotriazole undergoes a coordination reaction with the elemental copper layer to form a benzotriazole-copper complex film on the surface of the elemental copper layer; wherein, the benzotriazole does not react with the copper oxide layer. The substrate on which the benzotriazole-copper complex film is formed is acid-washed to remove the copper oxide layer; The benzotriazole-copper complex film was removed by peeling the acid-washed substrate with an alkaline solution. The substrate that has undergone the stripping process is surface treated to form an organic solder resist film on a predetermined area of ​​the copper pads.

2. The stepped protection treatment method for copper pads of WBCSP substrate according to claim 1, characterized in that, In the step of "immersing the substrate with the cured solder resist layer into an aqueous solution of benzotriazole, where benzotriazole undergoes a coordination reaction with the elemental copper layer to form a benzotriazole-copper complex film on the surface of the elemental copper layer", the temperature is controlled at 40°C to 45°C, the processing time is 2 min to 4 min, and the concentration of the aqueous solution of benzotriazole is 0.8 g / L to 1.5 g / L.

3. The stepped protection treatment method for copper pads of WBCSP substrate according to claim 1, characterized in that, In the step of "acid washing the substrate on which the benzotriazole-copper complex film is formed to remove the copper oxide layer", the substrate on which the benzotriazole-copper complex film is formed is acid washed with a sulfuric acid solution with a volume fraction of 5 vol % to 10 vol % at a temperature of 35°C.

4. The stepped protection treatment method for copper pads of WBCSP substrate according to claim 3, characterized in that, In the step of "acid washing the substrate on which the benzotriazole-copper complex film is formed to remove the copper oxide layer", when the thickness of the copper oxide layer is 30nm~50nm, the volume fraction of the sulfuric acid solution used is 5vol%~6vol%, and the acid washing time is 0.5min~1.0min. When the thickness of the copper oxide layer is 50 nm to 80 nm, the volume fraction of the sulfuric acid solution used is 7 vol % to 8 vol %, and the pickling time is 1.0 min to 1.5 min; When the thickness of the copper oxide layer is 80nm~100nm, the volume fraction of the sulfuric acid solution used is 9vol%~10vol%, and the pickling time is 1.5min~2.0min.

5. The stepped protection treatment method for copper pads of WBCSP substrate according to claim 1, characterized in that, In the step "using an alkaline solution to peel off the acid-washed substrate to remove the benzotriazole-copper complex film", the alkaline solution used is sodium hydroxide solution with a mass fraction of 3%~5%, the treatment temperature is 50℃~60℃, and the treatment time is 2min~5min.

6. The stepped protection treatment method for copper pads of WBCSP substrate according to claim 1, characterized in that, Before the step of "surface treatment of the substrate after the stripping process to form an organic solder resist film on the preset area of ​​the copper pad", the substrate after the stripping process is also washed with water.

7. A WBCSP substrate, characterized in that, It is prepared using the stepped protection treatment method for copper pads of WBCSP substrate as described in any one of claims 1 to 6.

Images