Chip mounting structure and mounting method for printed circuit board

Abstract

A chip mounting structure and mounting method for a printed circuit board. The chip mounting method for a printed circuit board comprises: providing a printed circuit board, wherein the printed circuit board comprises a substrate, a conductive layer, and a solder mask layer, the conductive layer is located on the surface of the substrate, and the solder mask layer is located on the surface of the side of the conductive layer away from the substrate (S210); forming multiple first openings in the solder mask layer, wherein the conductive layer exposed by each first opening is a solder mask defined pad (S220); forming a steel mesh on the surface of the side of the solder mask layer away from the conductive layer, wherein the steel mesh comprises multiple second openings, the multiple second openings are arranged in one-to-one correspondence with the multiple first openings, and each first opening is communicated with the respective corresponding second opening (S230); forming a solder paste at each second opening and each first opening (S240); removing the steel mesh (S250); and fixing a chip to the printed circuit board by means of the solder paste located in multiple positions, wherein the pins of the chip are connected to the multiple solder mask defined pads by means of the solder paste located in the multiple positions, and the volume of each first opening is greater than the volume of the respective corresponding second opening (S260).

Description

Chip mounting structure and mounting method of printed circuit board

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 26, 2023, with application number 202311813054.5. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of printed circuit boards, for example, to a chip mounting structure and mounting method of a printed circuit board. Background Art

[0003] A good printed circuit board (PCB) design approach can solve 80% of on-site problems. Currently, PCB product control is basically managed according to the median value of customer-provided specifications. In reality, for example, the solder mask definition pads in the ball grid array (BGA) area are completely controlled according to the median value, which is not the optimal design solution.

[0004] Currently, when chips are mounted on the surface of a printed circuit board, there is a risk of short circuits between two adjacent solder mask defined pads.

[0005] Summary of the Invention

[0006] The present application provides a chip mounting structure and mounting method for a printed circuit board to avoid the risk of short circuit between two adjacent solder mask defined pads.

[0007] According to one aspect of the present application, a chip mounting method for a printed circuit board is provided, comprising:

[0008] A printed circuit board is provided, wherein the printed circuit board comprises a substrate, a conductive layer and a solder resist layer, wherein the conductive layer is located on a surface of the substrate, and the solder resist layer is located on a surface of the conductive layer away from the substrate;

[0009] forming a plurality of first openings in the solder resist layer, wherein the conductive layer exposed by each first opening is a solder resist defining pad;

[0010] forming a steel mesh on a surface of the solder resist layer away from the conductive layer, wherein the steel mesh includes a plurality of second openings, the plurality of second openings are arranged in a one-to-one correspondence with the plurality of first openings, and each first opening is connected to a corresponding second opening;

[0011] forming solder paste at each second opening and each first opening;

[0012] removing the steel mesh;

[0013] Fixing the chip to the printed circuit board through multiple solder pastes, wherein the pins of the chip are connected through the multiple solder pastes and multiple solder mask defined pads;

[0014] Wherein, the volume of each first opening is greater than the volume of the corresponding second opening.

[0015] Optionally, the volume of each first opening is the optimal volume of the solder resist-defined pad, and the optimal volume of the solder resist-defined pad satisfies the following relationship: V1=V2*ρ1 / ρ2

[0016] Among them, V1 is the optimal volume of the solder mask defined pad, V2 is the volume of each second opening of the steel mesh, ρ1 is the corresponding density when the solder paste is solid, and ρ2 is the corresponding density when the solder paste is liquid.

[0017] Optionally, an orthographic projection area of ​​each first opening on the substrate is larger than an orthographic projection area of ​​the corresponding second opening on the substrate.

[0018] Optionally, the method further comprises: providing a blocking structure on a surface of the solder resist layer away from the conductive layer.

[0019] Optionally, providing a blocking structure on a surface of the solder resist layer away from the conductive layer includes: forming a groove on a surface of the solder resist layer away from the conductive layer.

[0020] Optionally, providing a blocking structure on a surface of the solder resist layer away from the conductive layer includes: forming a protrusion on a surface of the solder resist layer away from the conductive layer.

[0021] Optionally, the solder paste is lead-free solder paste.

[0022] Optionally, the mass content of tin in the solder paste is 42%, and the mass content of bismuth is 58%.

[0023] Optionally, the density of the solder paste in a solid state is 8.701 g / cm 3 , or, the density of liquid solder paste is 8.437g / cm 3 .

[0024] According to another aspect of the present application, a chip mounting structure for a printed circuit board is provided, which is prepared using any of the chip mounting methods for a printed circuit board described in the first aspect, and the mounting structure includes:

[0025] A printed circuit board, comprising a substrate, a conductive layer and a solder resist layer, wherein the substrate and the solder resist layer are respectively located on two opposite surfaces of the conductive layer;

[0026] The solder resist layer is formed with a plurality of first openings, and the conductive layer exposed by each first opening is a solder resist definition pad;

[0027] Each first opening is filled with solder paste, and the solder paste is filled through a steel mesh having a plurality of second openings formed on a surface of the solder resist layer away from the conductive layer, and the solder paste extends out of each first opening on a surface away from the conductive layer; wherein the plurality of second openings are arranged in a one-to-one correspondence with the plurality of first openings, and each first opening is connected to its corresponding second opening, and the volume of each first opening is greater than the volume of its corresponding second opening, so that a gap exists between the solder paste in each first opening and the first opening where the solder paste is located when in a solid state;

[0028] The chip is fixed to the printed circuit board through multiple solder pastes, and the pins of the chip are connected through the multiple solder pastes and multiple solder mask definition pads. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The following is a brief introduction to the drawings required for describing the embodiments. The drawings described below are only part of the drawings in some embodiments of the present application.

[0030] FIG1 is a schematic flow chart of a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0031] FIG2 is a top view of a printed circuit board provided in an embodiment of the present application;

[0032] FIG3 is a schematic structural diagram of a mounting structure formed in a portion of steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0033] FIG4 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0034] FIG5 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0035] FIG6 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0036] FIG7 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0037] FIG8 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0038] FIG9 is a schematic structural diagram of a mounting structure formed in another part of the steps in a chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0039] FIG10 is a flow chart of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0040] FIG11 is a schematic structural diagram of a mounting structure formed in a portion of steps in another chip mounting method for a printed circuit board according to an embodiment of the present application;

[0041] FIG12 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0042] FIG13 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0043] FIG14 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0044] FIG15 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0045] FIG16 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0046] FIG17 is a schematic structural diagram of a mounting structure formed in another part of the steps of another chip mounting method for a printed circuit board provided in an embodiment of the present application;

[0047] FIG18 is a schematic diagram of a blocking structure provided in an embodiment of the present application that is a protrusion;

[0048] FIG19 is a schematic diagram of a blocking structure provided in an embodiment of the present application that is a groove. DETAILED DESCRIPTION

[0049] The following will describe the technical solutions in the embodiments of this application in conjunction with the drawings in the embodiments of this application. The embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0050] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in a sequence other than those illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, in addition to comprising the process, method, system, product or equipment of a series of steps or units shown in the embodiments of the present application, other processes, methods, systems, products or equipment of this series of steps or units that are not clearly listed may also be included, or other steps or devices inherent to these processes, methods, systems, products or equipment.

[0051] Currently, when mounting chips on the surface of a printed circuit board (PCB), there's a high risk of short circuits between adjacent solder mask-defined pads. Figure 1 is a schematic flow chart of a PCB chip mounting method, Figure 2 is a top view of the PCB, and Figures 3-9 are schematic diagrams of the mounting structure formed during the steps of the PCB chip mounting method. The method includes the following steps.

[0052] S110 , providing a printed circuit board, wherein the printed circuit board includes a substrate 1 , a conductive layer 2 and a solder resist layer 3 , the conductive layer 2 is located on a surface of the substrate 1 , and the solder resist layer 3 is located on a surface of the conductive layer 2 away from the substrate 1 .

[0053] S120 , forming a plurality of first openings 30 in the solder resist layer 3 , wherein the conductive layer 2 exposed by the first openings 30 is the solder resist definition pad 20 , and the first openings 30 are controlled according to the customer's specification.

[0054] S130. A steel mesh 4 is formed on the surface of the solder resist layer 3 away from the conductive layer 2, wherein the steel mesh 4 includes a plurality of second openings 40, the second openings 40 are connected to the first openings 30 and are arranged in one-to-one correspondence, the median of the customer specification is determined based on the second openings 40, and the volume of the first openings 30 is equal to the volume of the second openings 40 (as shown in FIG3 ).

[0055] S140 , forming solder paste 5 at the second opening 40 (as shown in FIG. 4 ).

[0056] S150, removing the steel mesh 4 (as shown in FIG5 ).

[0057] S160 , fixing the chip 6 to the printed circuit board (as shown in FIG6 ) through the solder paste 5 , wherein the pins of the chip 6 are connected to the solder mask definition pads 20 through the solder paste 5 .

[0058] With the steel mesh 4 as support, the scraper 7 forms the solder paste 5 at the second opening 40. A plurality of first openings 30 are formed in the solder resist layer 3, wherein the conductive layer 2 exposed by the first opening 30 is the solder resist definition pad 20. The first opening 30 is controlled according to the median value of the customer specification. The volume of the first opening 30 is equal to the volume of the second opening 40. The orthographic projection area of ​​the first opening 30 on the substrate 1 is equal to the orthographic projection area S0 of the second opening 40 on the substrate 1. Solder paste 5 is formed at the second opening 40, and the solder paste 5 is in a solid state. In the process of fixing the chip 6 to the printed circuit board through the solder paste 5 through the reflow process, the solid solder paste 5 changes from a solid state to a liquid state (as shown in Figures 7 and 8). Without considering the reflow process, the solder paste 5 is formed at the second opening 40. Under the condition of the volume expansion coefficient of the process, the density of the solid state is higher than that of the liquid state, so when the solder paste 5 changes from a solid state to a liquid state, the volume will increase, and the conductive layer 2 exposed by the first opening 30 is the solder mask definition pad 20. The first opening 30 is controlled according to the median value of the customer specification, and the median value of the customer specification is determined according to the second opening 40. The volume of the first opening 30 is equal to the volume of the second opening 40, resulting in the solder mask definition pad 20 defined by the first opening 30 being too small and the amount of tin stored being insufficient. When the chip is mounted on the surface of the printed circuit board, there is a risk of short circuit between two adjacent solder mask definition pads 20 (as shown in Figure 9).

[0059] The embodiments of this application provide the following technical solutions.

[0060] As shown in FIG10 , FIG10 is a flow chart of a chip mounting method for a printed circuit board provided in an embodiment of the present application. The chip mounting method for a printed circuit board includes the following steps.

[0061] S210. Provide a printed circuit board, wherein the printed circuit board includes a substrate, a conductive layer and a solder resist layer, the conductive layer is located on a surface of the substrate, and the solder resist layer is located on a surface of the conductive layer away from the substrate.

[0062] As shown in FIG11 , a printed circuit board is provided, wherein the printed circuit board includes a substrate 100 , a conductive layer 200 and a solder resist layer 300 . The conductive layer 200 is located on a surface of the substrate 100 , and the solder resist layer 300 is located on a surface of the conductive layer 200 away from the substrate 100 .

[0063] S220 , forming a plurality of first openings in the solder resist layer, wherein the conductive layer exposed by each first opening serves as a solder resist definition pad.

[0064] As shown in FIG. 11 , a plurality of first openings 301 are formed in the solder resist layer 300 , wherein the conductive layer 200 exposed by the first openings 301 serve as solder resist defining pads 201 .

[0065] S230. Form a steel mesh on a surface of the solder resist layer away from the conductive layer, wherein the steel mesh includes a plurality of second openings, the plurality of second openings are arranged in one-to-one correspondence with the plurality of first openings, and each first opening is connected to its corresponding second opening.

[0066] As shown in FIG11 , a steel mesh 400 is formed on the surface of the solder resist layer 300 away from the conductive layer 200 , wherein the steel mesh 400 includes a plurality of second openings 401 , which are connected to the first openings 301 and are arranged in one-to-one correspondence.

[0067] The solder resist layer 300 covers the conductive layer 200. The conductive layer 200 exposed by the first opening 301 is the solder resist definition pad 201, which is configured to lead out the electrical signal of the conductive layer 200. The solder resist layer 300 also covers the portion of the substrate 100 surface without the conductive layer 200 to protect the substrate 100.

[0068] S240 , forming solder paste at each second opening and each first opening.

[0069] As shown in FIG12 , the steel mesh 400 serves as a supporting carrier, and the scraper 700 moves the solid solder paste 500 from one side of the steel mesh 400 to the other side, forming the solder paste 500 at the second opening 401 and the first opening 301 .

[0070] S250, remove the steel mesh.

[0071] As shown in FIG. 13 , the steel mesh 400 is removed.

[0072] S260: Fix the chip to the printed circuit board through multiple solder pastes, wherein the pins of the chip are connected through the multiple solder pastes and multiple solder mask defined pads. The volume of each first opening is larger than the volume of the corresponding second opening.

[0073] During the process of attaching chip 600 to the printed circuit board using solder paste 500, as shown in Figure 14, during the reflow process, solder paste 500 is in a solid state before being heated. As shown in Figure 15, after being heated, solder paste 500 transforms from a solid state to a liquid state. Because the density of the solid state is greater than that of the liquid state, the volume of solder paste 500 increases after the solid state transforms into a liquid state. In related art, the volume of first opening 301 is equal to the volume of second opening 401. The conductive layer 200 exposed by first opening 301 is the solder mask defining pad 201. First opening 301 is controlled according to the median value of the customer specification. In the embodiment of the present application, the volume of the first opening 301 is greater than the volume of the second opening 401. When the size of the second opening 401 of the steel mesh 400 remains unchanged, the amount of solder paste 500 entering the second opening 401 does not increase, and the volume of each first opening 301 in the solder mask layer 300 is increased, that is, the capacity of the solder paste 500 is increased. As shown in Figures 16 and 17, when the chip 600 is mounted on the surface of the printed circuit board, there is no risk of short circuit between two adjacent solder mask definition pads 201.

[0074] After the chip 600 is fixed to the printed circuit board through the solder paste 500 , the pins of the chip 600 are connected to the solder paste 500 and the solder mask defined pads 201 .

[0075] In the technical solution provided by the embodiment of the present application, during the process of fixing the chip 600 to the printed circuit board via the solder paste 500, the solder paste 500 is in a solid state before being heated during the reflow soldering process. After being heated, the solder paste 500 changes from a solid state to a liquid state. Since the density of the solid state is greater than that of the liquid state, the volume of the solder paste 500 increases after the solid state changes to a liquid state. In the related art, the volume of the first opening 301 is equal to the volume of the second opening 401. The conductive layer 200 exposed by the first opening 301 is the solder mask defining pad 201. The first opening 301 is controlled according to the median value of the customer specification, and the median value of the customer specification is determined based on the second opening 40. In the embodiment of the present application, the volume of the first opening 301 is greater than the volume of the second opening 401. When the size of the second opening 401 of the steel mesh 400 remains unchanged, the amount of solder paste 500 entering the second opening 401 does not increase, and the volume of each first opening 301 in the solder mask layer 300 is increased, that is, the capacity of the solder paste 500 is increased. When the chip 600 is mounted on the surface of the printed circuit board, the risk of short circuit between two adjacent solder mask definition pads 201 is avoided, thereby reducing material and labor costs.

[0076] Optionally, the volume of the first opening 301 is the optimal volume of the solder resist defined pad, and the optimal volume of the solder resist defined pad satisfies the following relationship: V1=V2*ρ1 / ρ2

[0077] Among them, V1 is the optimal volume of the solder mask defining the pad, V2 is the volume of the second opening 401 of the steel mesh 400, ρ1 is the density corresponding to the solder paste 500 when it is solid, and ρ2 is the density corresponding to the solder paste 500 when it is liquid.

[0078] The solder paste 500 changes from a solid state to a liquid state, and the density of the solid state is greater than that of the liquid state. Therefore, the volume of the first opening 301, that is, the optimal volume of the solder mask definition pad, is greater than the volume of the second opening 401. When the size of the second opening 401 of the steel mesh 400 remains unchanged, the amount of solder paste 500 entering the second opening 401 does not increase, and the volume of each first opening 301 in the solder mask layer 300 is increased, that is, the holding volume of the solder paste 500 is increased. When the chip 600 is mounted on the surface of the printed circuit board, the risk of short circuit between two adjacent solder mask definition pads 201 is avoided.

[0079] Optionally, an orthographic projection area of ​​the first opening 301 on the substrate 100 is larger than an orthographic projection area of ​​the second opening 401 on the substrate 100 .

[0080] As shown in Figure 11 or Figure 12, the orthographic projection area of ​​the first opening 301 on the substrate 100 is area S1, and the orthographic projection area of ​​the second opening 401 on the substrate 100 is area S0. The orthographic projection area of ​​the first opening 301 on the substrate 100 is larger than the orthographic projection area of ​​the second opening 401 on the substrate 100, which increases the accommodating volume of the solder paste 500. When the chip 600 is mounted on the surface of the printed circuit board, the risk of short circuit between two adjacent solder mask definition pads 201 is avoided.

[0081] Optionally, a blocking structure is provided on the surface of the solder resist layer 300 away from the conductive layer 200 .

[0082] After the solder paste 500 is heated, it changes from a solid state to a liquid state. The blocking structure can block the flow of the liquid solder paste 500, thereby avoiding the risk of short circuit between two adjacent solder mask definition pads 201 when the chip 600 is mounted on the surface of the printed circuit board.

[0083] Optionally, as shown in FIG19 , the blocking structure includes a groove.

[0084] The blocking structure includes a groove. After the solder paste 500 is heated, the solder paste 500 changes from a solid state to a liquid state. The groove can store the liquid solder paste 500, thereby blocking the flow of the liquid solder paste 500. When the chip 600 is mounted on the surface of the printed circuit board, the risk of short circuit between two adjacent solder mask definition pads 201 is avoided.

[0085] Optionally, as shown in FIG18 , the blocking structure includes a protrusion.

[0086] The blocking structure includes protrusions. FIG18 shows the thickness of a normal solder mask layer 300 and the thickness of a solder mask layer 300 with protrusions. When the solder paste 500 is heated, the solder paste 500 changes from a solid state to a liquid state. The protrusions can block the flow of the liquid solder paste 500, thereby preventing the risk of a short circuit between two adjacent solder mask-defining pads 201 when mounting a chip 600 on the printed circuit board surface.

[0087] Optionally, the solder paste 500 is lead-free solder paste.

[0088] Optionally, the mass content of tin in the solder paste 500 is 42%, and the mass content of bismuth is 58%. The density of solid tin is 7.184 g / cm 3 When tin is liquid, the corresponding density is 6.988g / cm 3 The density of solid bismuth is 9.8 g / cm 3 When bismuth is liquid, the corresponding density is 9.487 g / cm 3 .

[0089] Optionally, the density of the solder paste 500 when it is solid is 8.701 g / cm 3 When solder paste 500 is liquid, the corresponding density is 8.437g / cm 3 .

[0090] The density of solder paste 500 when solid is 8.701g / cm 3 When solder paste 500 is liquid, the corresponding density is 8.437g / cm 3 , that is, the solder paste 500 changes from a solid state to a liquid state, and the density of the solid state is greater than that of the liquid state. Therefore, the volume of the first opening 301, that is, the optimal volume of the solder mask definition pad, is greater than the volume of the second opening 401. When the size of the second opening 401 of the steel mesh 400 remains unchanged, the amount of solder paste 500 entering the second opening 401 does not increase, and the volume of each first opening 301 in the solder mask layer 300 is increased, that is, the holding volume of the solder paste 500 is increased. When the chip 600 is mounted on the surface of the printed circuit board, the risk of short circuit between two adjacent solder mask definition pads 201 is avoided.

[0091] The present application also provides a chip mounting structure for a printed circuit board. The chip mounting structure for a printed circuit board is prepared using any of the chip mounting methods for printed circuit boards described in any of the present application embodiments, and the mounting structure includes:

[0092] A printed circuit board, comprising a substrate, a conductive layer and a solder resist layer, wherein the substrate and the solder resist layer are respectively located on two opposite surfaces of the conductive layer;

[0093] The solder resist layer is formed with a plurality of first openings, and the conductive layer exposed by each first opening is a solder resist definition pad;

[0094] Each first opening is filled with solder paste, and the solder paste is filled through a steel mesh having a plurality of second openings formed on a surface of the solder resist layer away from the conductive layer, and the solder paste extends out of each first opening on a surface away from the conductive layer; wherein the plurality of second openings are arranged in a one-to-one correspondence with the plurality of first openings, and each first opening is connected to its corresponding second opening, and the volume of each first opening is greater than the volume of its corresponding second opening, so that a gap exists between the solder paste in each first opening and the first opening where the solder paste is located when in a solid state;

[0095] The chip is fixed to the printed circuit board through multiple solder pastes, and the pins of the chip are connected through the multiple solder pastes and multiple solder mask definition pads.

[0096] The chip mounting structure of the printed circuit board can achieve the effect of the chip mounting method of the printed circuit board described above, and will not be described in detail here.

[0097] It should be understood that the various forms of processes described above can be used to reorder, add, or delete steps. For example, the multiple steps described in this application can be performed in parallel, sequentially, or in a different order, as long as the desired results of the technical solution of this application can be achieved. This is not limited herein.

Claims

1. A method for chip mounting on a printed circuit board, comprising: Providing a printed circuit board, wherein the printed circuit board includes a substrate, a conductive layer, and a solder mask layer, the conductive layer is located on the surface of the substrate, and the solder mask layer is located on the surface of the conductive layer away from the substrate; Forming a plurality of first openings in the solder mask layer, wherein the conductive layer exposed by each first opening is a solder mask defined pad; Forming a stencil on the surface of the solder mask layer away from the conductive layer, wherein the stencil includes a plurality of second openings, the plurality of second openings are arranged in one-to-one correspondence with the plurality of first openings, and each first opening communicates with its corresponding second opening; Forming solder paste at each second opening and each first opening; Removing the stencil; Fixing the chip to the printed circuit board through multiple solder pastes, wherein the pins of the chip are connected to a plurality of solder mask defined pads through the multiple solder pastes; Wherein, the volume of each first opening is greater than the volume of its corresponding second opening.

2. The method for chip mounting on a printed circuit board according to claim 1, wherein, The volume of each first opening is the optimal volume of the solder mask defined pad, and the optimal volume of the solder mask defined pad satisfies the following relationship: V1 = V2 * ρ1 / ρ2 Wherein, V1 is the optimal volume of the solder mask defined pad, V2 is the volume of each second opening of the stencil, ρ1 is the density corresponding to the solder paste when it is solid, and ρ2 is the density corresponding to the solder paste when it is liquid.

3. The method for chip mounting on a printed circuit board according to claim 1, wherein, The orthographic projection area of each first opening on the substrate is greater than the orthographic projection area of its corresponding second opening on the substrate.

4. The chip mounting method for a printed circuit board according to claim 1 further includes: A blocking structure is provided on the surface of the solder mask layer away from the conductive layer.

5. The chip mounting method for a printed circuit board according to claim 4, wherein, The providing a blocking structure on the surface of the solder mask layer away from the conductive layer includes: Forming a groove on the surface of the solder mask layer away from the conductive layer.

6. The chip mounting method for a printed circuit board according to claim 4, wherein, The providing a blocking structure on the surface of the solder mask layer away from the conductive layer includes: Forming a protrusion on the surface of the solder mask layer away from the conductive layer.

7. The chip mounting method of the printed circuit board according to claim 1, wherein, The solder paste is lead-free solder paste.

8. The chip mounting method for a printed circuit board according to claim 7, wherein, The mass content of tin in the solder paste is 42%, and the mass content of bismuth is 58%.

9. The chip mounting method for a printed circuit board according to claim 8, wherein, The density of the solder paste in solid state is 8.701 g / cm 3 , or the density of the solder paste in liquid state is 8.437 g / cm 3 .

10. A chip mounting structure for a printed circuit board, prepared by using the method for chip mounting on a printed circuit board according to any one of claims 1-9, the mounting structure includes: A printed circuit board, the printed circuit board includes a substrate, a conductive layer, and a solder mask layer, the substrate and the solder mask layer are respectively located on two opposite surfaces of the conductive layer; The solder mask layer is formed with a plurality of first openings, and the conductive layer exposed by each first opening is a solder mask defined pad; Each first opening is filled with solder paste, and the solder paste is filled through a stencil with a plurality of second openings formed on the surface of the solder mask layer away from the conductive layer side, and the surface of the solder paste away from the conductive layer side extends out of each first opening; wherein, the plurality of second openings and the plurality of first openings are arranged in one-to-one correspondence, and each first opening communicates with its corresponding second opening, and the volume of each first opening is greater than the volume of its corresponding second opening, so that there is a gap between the solder paste located in each first opening and the first opening where the solder paste is located when in a solid state; A chip, the chip is fixed to the printed circuit board through multiple solder pastes, and the pins of the chip are connected through the multiple solder pastes and a plurality of solder mask defined pads.

11. The chip mounting structure of a printed circuit board according to claim 10, wherein, The volume of each first opening is the optimal volume of the solder mask defined pad, and the optimal volume of the solder mask defined pad satisfies the following relationship: V1 = V2 * ρ1 / ρ2 Wherein, V1 is the optimal volume of the solder mask defined pad, V2 is the volume of each second opening of the stencil, ρ1 is the density corresponding to the solder paste when it is solid, and ρ2 is the density corresponding to the solder paste when it is liquid.

12. The chip mounting structure of the printed circuit board according to claim 10, wherein, The orthographic projection area of each first opening on the substrate is greater than the orthographic projection area of its corresponding second opening on the substrate.

13. The chip mounting structure of the printed circuit board according to claim 10 further includes: A blocking structure; the blocking structure is arranged on the surface of the solder mask layer away from the conductive layer.

14. The chip mounting structure of the printed circuit board according to claim 13, wherein, The blocking structure includes a groove.

15. The chip mounting structure of the printed circuit board according to claim 13, wherein, The blocking structure includes a protrusion.

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