A method of screenless solder printing and a preform substrate

Abstract

The application discloses a package steel mesh-free printing and welding method and a prefabricated substrate, and comprises the following steps: step one, providing a carrier plate; step two, prefabricating a circuit and an insulating layer on the surface of the carrier plate; step three, electroplating a solder pad in electrical connection with the prefabricated circuit on the insulating layer, and then performing post-sealing grinding to expose the side of the solder pad away from the carrier plate, and the roughness of the grinding ranges from 200 to 500 meshes so as to facilitate the movement of a printing doctor blade; step four, etching the solder pad to form a pit, forming an anti-oxidation layer at the pit, and then storing the pit for use; and step five, printing solder on the pit by using a printing machine, flip-chip mounting a chip, and then welding and fixing the chip, and finally stripping the carrier plate. The application saves the consumable steel mesh, saves cost, simplifies the printing mechanism of the printing machine, reduces the cost and maintenance cost of the steel mesh-free mechanism, and is suitable for large-size substrate high-precision printing, and does not have the problems of printing deviation and inaccurate position caused by large-size deviation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of package welding, and particularly relates to a package steel mesh-free printing welding method and a prefabricated substrate. BACKGROUND

[0002] In the semiconductor packaging industry in recent years, various packaging methods emerge in an endless stream, realizing advantages such as higher density, stronger function, better performance, smaller size and lower power consumption, etc. In the packaging process, the chip needs to be mounted on the substrate or circuit board (PCB board), and the commonly used mounting method is solder paste welding. When many packaging factories print solder paste on the substrate or circuit board, a solder paste printing machine is generally used.

[0003] A modern solder paste printing machine is generally composed of a board mounting mechanism, a solder paste adding mechanism, a printing mechanism, a circuit board conveying mechanism, etc., and mainly includes a visual positioning system, a wiping system and a solder paste filling and coating system, etc. Its working principle is as follows: first, a corresponding steel mesh is designed according to the chip welding position, the circuit board or substrate to be printed is fixed on the printing positioning table, the steel mesh is placed on the surface of the substrate or circuit board, and then the solder paste is printed on the PCB board or substrate through the steel mesh by the left and right scrapers of the printing machine, and the uniformly printed PCB board or substrate is input to the chip mounter for automatic mounting.

[0004] The printing quality of the solder paste has a great influence on the electrical properties of the circuit, and there are many factors affecting the printing quality, mainly in two aspects. On the one hand, the equipment precision: the solder paste printing machine is the only printing equipment, and its precision is crucial. The visual positioning system of the printing machine positions the pad hole of the board to be printed. When printing high-precision fine-pitch products, the visual positioning system has weak precision, and it is easy to cause missing welding, repeated multiple welding or uneven welding of the solder. Too much solder will cause bridging, and too little solder will cause virtual welding. On the other hand, the quality of the steel mesh: after the design of the steel mesh is completed, a layer of solder resist film is coated on the surface to ensure that the solder falls into the pad. The thickness of the steel mesh needs to be customized according to different production requirements, which has a high cost and cannot be ground. The thickness flexibility is small. The steel mesh needs to be designed according to the actual production of the chip. It is a consumable product, and the cost increases. After the use of the steel mesh is completed, it must be cleaned before use, which is time-consuming and labor-intensive. The opening on the steel mesh itself also has a yield problem. The steel mesh is easy to deviate, which affects the printing quality. More than 75% of the circuit board repair problems are caused by the poor printing quality of the solder paste due to the poor steel mesh. Therefore, how to save the steel mesh, low-cost, high-yield, high-precision soldering of the solder paste and guaranteeing the circuit connection have become technical problems to be solved by packaging factories. SUMMARY

[0005] To solve the problems in the prior art, the present application provides a package steel mesh-free printing welding method and a prefabricated substrate.

[0006] To achieve the above object, the application provides a packaging body steel mesh-free printing and welding method, which comprises the following steps:

[0007] Step 1: providing a carrier plate;

[0008] Step 2: pre-preparing a circuit and an insulating layer on the surface of the carrier plate;

[0009] Step 3: electroplating a solder pad in electrical communication with the pre-prepared circuit on the insulating layer, and encapsulating and then grinding the side of the solder pad away from the carrier plate to expose the side, wherein the roughness of the grinding ranges from 200 to 500 meshes to facilitate the movement of a printing doctor blade;

[0010] Step 4: etching the solder pad to form a pit, and forming an anti-oxidation layer on the pit and then storing for use;

[0011] Step 5: printing solder on the pit using a printing machine, flip-chip mounting a chip, welding and fixing the chip, and finally peeling off the carrier plate.

[0012] Further, the pre-prepared circuit comprises a conductive layer and a rewiring layer, the insulating layer is an epoxy resin plastic encapsulating material, the insulating layer encapsulates the pre-prepared circuit and the pit, and the upper surface of the insulating layer is flush with the upper end of the pit.

[0013] Further, the solder pad is formed by electroplating, and the effective soldering point diameter or width of the solder pad is greater than or equal to 15 μm to ensure flip-chip mounting of the chip.

[0014] Further, the solder pad is etched by a wet method, and the depth of the pit ranges from greater than or equal to 25 μm.

[0015] Further, the anti-oxidation layer is a gold plating layer or an ethylene bis-oleic acid amide glue layer or an organic soldering film layer.

[0016] Further, the carrier plate is peeled off by a physical peeling method.

[0017] A pre-prepared substrate comprises a carrier plate, a pre-prepared circuit and an insulating layer arranged on the surface of the carrier plate, a solder pad formed on the surface of the insulating layer, the side of the solder pad away from the carrier plate exposed by encapsulation and grinding, the roughness of the grinding ranging from 200 to 500 meshes to facilitate the movement of a printing doctor blade, and an anti-oxidation layer arranged on the pit formed by etching the solder pad.

[0018] Further, the anti-oxidation layer is a gold plating layer or an ethylene bis-oleic acid amide glue layer or an organic soldering film layer.

[0019] Beneficial effects: 1. The originally formed shallow pad on the substrate is changed into a pit formed in the insulating layer. After the surface of the insulating layer is ground, the ground surface can be used as the moving surface of the scraper. The grinding height and roughness are controllable, the printing requirements are met, the height of the insulating layer and the depth of the pit are controllable, the additional use of the steel mesh to increase the height of the scraping surface is not needed, the consumable steel mesh is saved, the cost is saved, the printing mechanism of the printing machine is simplified, there is no steel mesh mechanism, the equipment cost and maintenance cost are reduced;

[0020] 2. After the steel mesh is saved, the printing influence caused by the steel mesh offset is avoided. The size of the traditional printing machine steel mesh and the substrate need to be matched with each other. The influencing factors are the substrate, the steel mesh and the matching degree between the two. The size is moderate. The size that is too large or too small directly affects the cost. The precision is improved when the size is too small, but the efficiency is affected. The size is too large, which affects the precision but improves the efficiency. Moreover, the opening rate of the large-size steel mesh cannot be controlled, which has high cost and high risk. The present application directly prints on the package body. The influencing factor is only the substrate. The parameters such as the height and the surface roughness of the substrate are controllable, which meets the printing requirements. The present application uses the most commonly used glass epoxy resin organic plate in the field, which is convenient to obtain in large quantities and has a low price. Therefore, the present application is suitable for high-precision printing of large-size substrates, and there is no problem of printing offset and inaccurate position caused by large-size offset.

[0021] 3. The prefabricated substrate can be used in the steel mesh-free printing equipment during printing, which saves the cost. The prefabricated substrate itself can increase the production efficiency. After a large number of prefabricated substrates are formed, they are put into storage for later use. The subsequent processes such as patching, encapsulation, peeling and cutting can be directly performed. Compared with the traditional process of directly packaging the substrate after patching, encapsulation, wiring, packaging, grinding, plating of pins, peeling and cutting, the process is simple and efficient, and the substrate can be used immediately. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 It is a schematic diagram of the steel mesh structure of the existing tin paste printing machine.

[0023] Figure 2 It is a process flow chart of the packaging body steel mesh-free printing and welding method of the present application.

[0024] Figure 3 It is a structure schematic diagram of the prefabricated circuit of the packaging body steel mesh-free printing and welding method of the present application.

[0025] Figure 4 It is a structure schematic diagram of the pad of the packaging body steel mesh-free printing and welding method of the present application.

[0026] Figure 5 It is a structure schematic diagram of the pad encapsulation of the packaging body steel mesh-free printing and welding method of the present application.

[0027] Figure 6A structure diagram of pad etching of a packaging body screen printing welding method is provided in the application;

[0028] Figure 7 A structure diagram of a prefabricated substrate for packaging body screen printing welding is provided in the application;

[0029] Figure 8 A schematic diagram of printing tin paste of a packaging body screen printing welding method is provided in the application;

[0030] Figure 9 A structure diagram of flip chip of a packaging body screen printing welding method is provided in the application;

[0031] Figure 10 A structure diagram of BGA chip mounting of a packaging body screen printing welding method is provided in the application.

[0032] Marked in the figure: carrier plate 1, insulating layer 2, prefabricated circuit 3, pad 4, pit 5, oxidation prevention layer 6. DETAILED DESCRIPTION

[0033] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, the same numbers are used to indicate the same or similar elements, unless otherwise indicated. The following exemplary embodiments described in the following description are not meant to be limiting of all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with aspects of the present application as detailed in the appended claims.

[0034] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0035] For better understanding of the purpose, structure and function of the application, the following will be combined with the attached drawings to further describe the application. Figures 1-10 A packaging body screen printing welding method and a prefabricated substrate are provided in the application, which will be described in further detail.

[0036] The application relates to a packaging body screen printing welding method, Figure 2 A process flow chart of a packaging body screen printing welding method is provided in the application, please refer to Figure 1The present application comprises the following steps: step one, providing a carrier plate 1; step two, pre-preparing a circuit 3 and an insulating layer 2 on the surface of the carrier plate 1; step three, electroplating a solder pad 4 on the insulating layer 2 in electrical communication with the pre-prepared circuit 3, and encapsulating the solder pad 4 and then grinding to expose the side of the solder pad 4 away from the carrier plate 1, the roughness of the grinding being in the range of 200-500 mesh to facilitate the movement of the printing doctor blade; step four, etching the solder pad 4 to form a pit 5, forming an anti-oxidation layer 6 at the pit 5, and then storing for use; step five, printing solder on the pit 5 using a printing machine, and then soldering and fixing after flip-chip mounting, and finally peeling off the carrier plate 1.

[0037] Please refer to the accompanying drawings Figure 2 , the accompanying drawings Figure 3 , step one and step two, providing a carrier plate 1, pre-preparing a circuit 3 and an insulating layer 2 on the surface of the carrier plate 1, the carrier plate 1 being a common glass epoxy resin organic PCB raw material plate in the art, such as an FR-4 substrate, the pre-prepared circuit 3 being an encapsulation layer, specifically a common epoxy resin encapsulation layer in the art, the pre-prepared circuit 3 including a conductive layer and a rewiring layer, the conductive layer being formed on the carrier plate 1 by electroplating process, and the rewiring layer being formed by electroplating process according to production conditions, and then using plastic encapsulation material to encapsulate the pre-prepared circuit 3 and exposing the top of the pre-prepared circuit 3 by grinding, at which time the top of the pre-prepared circuit 3 is flush with the insulating layer 2.

[0038] Please refer to the accompanying drawings Figure 2 , the accompanying drawings Figure 4 , the accompanying drawings Figure 5 and step three, forming a solder pad 4 on the upper surface of the insulating layer 2 by electroplating, the effective soldering point of the solder pad 4 being ≥15μm to ensure normal flip-chip mounting of the subsequent chip, using the same material as in step two to encapsulate the solder pad 4, and grinding to expose the side of the solder pad 4 away from the carrier plate 1, at which time the top of the solder pad 4 is flush with the insulating layer 2, the roughness of the grinding being in the range of 200-500 mesh to facilitate the movement of the printing doctor blade, and the present application taking 300 mesh as an example, the roughness being too small to have a higher smoothness of the movement of the doctor blade, the speed control of the doctor blade needing to be more precise, otherwise a situation of less soldering may occur, and the roughness being too large to have a lower smoothness of the movement of the doctor blade, the rough surface being prone to residual solder paste, causing waste.

[0039] Please refer to the accompanying drawings Figure 2 , the accompanying drawings Figure 6 , the accompanying drawings Figure 7And step four, all the pads 4 are etched by wet etching method commonly used in the art, by controlling the concentration of etching line, etching time and other parameters to ensure that the pads 4 are etched and the pre-made line 3 is not etched, because the lower end of the pad 4 is in electrical communication with the upper end of the pre-made line 3, after the pad 4 is etched to form the pit 5, the pre-made line 3 is partially exposed, the exposed pre-made line 3 is provided with an anti-oxidation layer 6, which is a gold plating layer or an ethylene bis-oleic acid amide glue layer or an organic solder mask layer, which is a common treatment method in the art. At this time, the upper surface of the insulating layer 2 is flush with the upper end of the pit 5, and the insulating layer 2 includes two encapsulation layers of the entire substrate manufacturing process of the application. The pre-made substrate is prepared and can be put into storage for use.

[0040] Please refer to the attached Figure 2 , attached Figure 6 , attached Figure 7 , attached Figure 8 And step five, take stock, place the pre-made substrate as a whole into the printing machine, the insulating layer 2 has a controllable height, the pit 5 has a controllable depth, the insulating layer 2 replaces the steel mesh, and the doctor blade directly scrapes the solder mass or the flux on the surface of the insulating layer 2. The flux is used to pretreat the soldering parts to enhance the soldering effect, which volatilizes during soldering. The structure of the printing machine is simplified, and the consumable steel mesh is removed to reduce the cost of the equipment.

[0041] Please refer to the attached Figure 9 and attached Figure 10 , the pre-made substrate is suitable for chip package with protruding pins, such as BGA package and flip-chip package. BGA package refers to ball grid array package, and flip-chip package refers to chip pin facing the substrate package. The chip can be a power supply type, an antenna type, an oscilloscope, etc. The ball mounting package refers to mounting a matrix array of tin balls on the inner pins of the package as external pins. The flip-chip package refers to electroplating conductive copper columns on the inner pins of the package as external pins, and plating tin on one end of the conductive copper column. During soldering, the ball and the tin paste in the pit 5 are combined into a large tin ball, and the conductive copper column is welded together through the tin and the tin paste. The soldering of the present application adopts the common reflow soldering in the art. Reflow soldering refers to heating air or nitrogen to a high enough temperature and blowing it onto the substrate with the components attached. The solder melts and the components are bonded to the substrate.

[0042] The attached Figure 1 is a structural diagram of the existing traditional steel mesh of the tin paste printing machine. Please refer to the attached Figure 1The working principle of the existing printing machine is mainly that the circuit board or substrate to be printed is first fixed on a printing positioning table, the surface of the circuit board or substrate has been pre-fabricated with a solder pad, the shape of the solder pad is indefinite, which can be circular or square, and is determined according to actual production, the steel mesh is placed on the surface of the substrate or circuit board, and then the tin paste is printed on the PCB or substrate through the steel mesh by the left and right scrapers of the printing machine to the corresponding solder pad, the PCB or substrate with uniform printing is input to the chip mounter for automatic chip mounting, the chip is mounted on the substrate to use the substrate as an intermediate carrier plate, the chip is routed or connected electrically on the substrate, and then encapsulated, and finally the intermediate carrier plate is peeled off by a physical method. In order to ensure the peeling of the intermediate carrier plate, the solder pad on the substrate has a shallow depth, and a large-depth solder pad cannot complete the peeling action, which easily causes the chip and the solder pad to be broken at the welding position, affects subsequent packaging and circuit connection, and therefore there is no case of etching a large-depth solder pad on the substrate to save the steel mesh. The chip is mounted on the PCB to mount the chip and components on the circuit board to realize the electrical connection between the components, the surface of the circuit board is etched with a circuit diagram, the circuit board has one or more layers of circuit connection, and even the double-sided PCB has components mounted, in order to not affect the internal circuit connection and double-sided mounting, the etching depth of the circuit diagram on the surface is shallow, which can ensure the welding and mounting fixation, and therefore there is no case of etching a large-depth solder pad on the PCB to save the steel mesh.

[0043] In summary, the present application has the following advantages compared with the existing printing technology:

[0044] 1. The shallow-port solder pad originally formed on the substrate is changed to the pit 5 formed in the insulating layer 2, the surface of the insulating layer 2 can be used as the moving surface of the scraper after being ground, the grinding height and roughness are controllable, meet the printing requirements, and the height of the insulating layer 2 and the depth of the pit 5 are controllable, without the need for additional use of a steel mesh to increase the scraping surface height, saving the consumable steel mesh and saving costs, simplifying the printing mechanism of the printing machine, without the steel mesh mechanism, reducing the equipment cost and maintenance cost;

[0045] 2. After the steel mesh is saved, there is no printing influence caused by the offset of the steel mesh, the size of the steel mesh and the substrate of the traditional printing machine needs to be matched with each other, the influencing factors are the substrate, the steel mesh and the matching degree between the two, and the size is moderate, and the size that is too large or too small directly affects the cost, the precision is improved when the size is too small, but the efficiency is affected, the size is too large, the precision is affected, but the efficiency is improved, and the opening rate of the large-size steel mesh cannot be controlled, which has high cost and high risk. The present application directly prints on the packaging body, the influencing factor is only the substrate, but the parameters such as the height and surface roughness of the substrate are controllable, which meet the printing requirements, the present application adopts the most commonly used glass epoxy resin organic plate in the field, which is convenient to obtain in large quantities and has a low price, and therefore the present application is suitable for large-size substrate high-precision printing, and there is no problem of printing offset and inaccurate position caused by large-size offset.

[0046] 3、Preform substrate can be used in printing without steel printing equipment, saving costs, preform substrate itself can increase production efficiency, large quantities of preform substrate into the warehouse after forming, subsequent directly patch package, stripping, cutting can, compared with the traditional packaging directly on the substrate after packaging, wiring, package, grinding, plated pin, stripping, cutting process, simple and efficient, take and use.

[0047] It can be understood that the present application is described by some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to the features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, the features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of the present application.

Claims

1. A method for printing and soldering a package without a stencil, comprising the following steps: Step 1: Provide a carrier board (1); characterized in that, Step 2: Prefabricate the circuit (3) on the surface of the carrier board (1) and encapsulate the prefabricated circuit (3) with an encapsulation layer for the first time; Step 3: Electroplating pads (4) electrically connected to the pre-fabricated circuit (3) on the first encapsulation layer. The effective solder joint diameter or width of the pads (4) is ≥15μm to ensure the flip chip mounting. The pads (4) are encapsulated a second time to form the second encapsulation layer. Then, the side of the pads (4) away from the carrier board (1) is exposed by grinding. The roughness range of grinding is 200 to 500 mesh to facilitate the movement of the printing squeegee. Step 4: The pad (4) is fully etched to form a pit (5). The depth of the pit (5) is ≥25μm. An insulating layer (2) is formed by encapsulation layer 1 and encapsulation layer 2. The upper surface of the insulating layer (2) is flush with the upper end of the pit (5). After an anti-oxidation layer (6) is formed at the pit (5), it is put into storage for later use. Step 5: Use a printer to print solder on the recess (5), then solder the flip-chip to fix it, and finally peel off the carrier board (1).

2. The method for printing and soldering a package without a stencil according to claim 1, characterized in that, The prefabricated circuit (3) includes a conductive layer and a rewiring layer, and the insulating layer (2) is an epoxy resin molding compound.

3. The method for printing and soldering a package without a stencil according to claim 2, characterized in that, The pad (4) is formed by electroplating.

4. The method for printing and soldering a package without a stencil according to claim 3, characterized in that, The pads (4) are etched using a wet etching process.

5. The method for printing and soldering a package without a stencil according to claim 4, characterized in that, The anti-oxidation layer (6) is a gold plating layer, an ethylene bisoleic acid amide adhesive layer, or an organic solder resist film layer.

6. The method for printing and soldering a package without a stencil according to claim 5, characterized in that, The carrier plate (1) is peeled off by physical peeling.

7. A prefabricated substrate formed by the stencil-free printing and soldering method for an encapsulation body according to claim 1, comprising a carrier plate (1), characterized in that, The carrier board (1) is provided with a pre-fabricated circuit (3) and a first encapsulation layer for the pre-fabricated circuit (3). A pad (4) is formed on the surface of the first encapsulation layer. The effective solder joint diameter or width of the pad (4) is ≥15μm to ensure the flip chip mounting. The pad (4) is encapsulated for the second time to form the second encapsulation layer. After grinding, the side of the pad (4) away from the carrier board (1) is exposed. The roughness range of the grinding is 200 to 500 mesh to facilitate the movement of the printing squeegee. The pad (4) is etched to form a pit (5). The depth range of the pit (5) is ≥25μm. An insulating layer (2) is formed by the first encapsulation layer and the second encapsulation layer. The upper surface of the insulating layer (2) is flush with the upper end of the pit (5). An anti-oxidation layer (6) is provided at the pit (5).

8. The prefabricated substrate according to claim 7, characterized in that, The anti-oxidation layer (6) is a gold plating layer, an ethylene bisoleic acid amide adhesive layer, or an organic solder resist film layer.

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