Processing method capable of reducing tombstone standing of electronic component

Abstract

The invention discloses a processing method capable of reducing tombstone standing of an electronic component, and the method comprises the steps: S1, solder paste printing: arranging a bonding pad of a 0402 component at the central position of a PCB, and coating the surface of a steel mesh with solder paste through a solder paste screen printing machine; s2, solder paste pre-detection: after the steel meshes are filled with the solder paste, a transparent sheet is arranged between the PCB and the first visual camera, a PCB outline identification frame and a bonding pad identification frame which are made of a light-proof material are arranged on the transparent sheet, and the first visual camera collects a pre-detection image of overlapping of the PCB and the transparent sheet; calculating whether the overflow area of the solder paste on the bonding pad in the pre-detection image exceeding the bonding pad identification frame exceeds a set threshold value or not, and if the overflow area does not exceed the set threshold value, judging that the solder paste coating is qualified; s3, element surface mounting is carried out; s4, reflow soldering; and S5, performing AOI optical detection. Compared with the prior art, the problem that electronic components stand up in the SMT process is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of SMT patches, and in particular to a processing method capable of reducing tombstoning of electronic components. Background Art

[0002] Surface mount technology (SMT) is a circuit assembly technology that mounts leadless or short-lead surface mount components on the surface of a printed circuit board (PCB) or other substrate, and assembles them by soldering through methods such as reflow soldering or dip soldering.

[0003] 0402 components are a common electronic component size. The "0402" in their size code represents the length and width of the component. In current PCB SMT patch production, 0402 components are prone to tombstoning due to factors such as PCB expansion and contraction, affecting SMT patch quality. Summary of the Invention

[0004] The object of the present invention is to provide a processing method that can reduce the tombstoning of electronic components, so as to solve the problem of tombstoning of electronic components in the SMT patch process.

[0005] In order to achieve the above-mentioned object, the present invention adopts the following technical solution: a processing method for reducing the tombstoning of electronic components, comprising the following steps:

[0006] S1. Solder paste printing: Lay the stencil flat on the PCB board. The positions of the stencil holes correspond to the pads on the PCB board. The pads of the 0402 components are set in the center of the PCB board. The solder paste screen printer applies solder paste on the surface of the stencil and then fills the stencil holes with the scraper.

[0007] S2. Pre-inspection of solder paste: After solder paste is filled into the stencil holes, the stencil is separated from the PCB board and the PCB board is moved under the first vision camera. A transparent sheet is placed between the PCB board and the first vision camera. The transparent sheet is provided with a PCB outline identification frame and a pad identification frame made of opaque material. Each pad identification frame corresponds to one pad. The first vision camera captures a pre-inspection image of the PCB board and the transparent sheet overlapping. The camera calculates whether the overflow area of ​​the solder paste on the pad exceeding the pad identification frame in the pre-inspection image exceeds a set threshold. If the overflow area does not exceed the set threshold, the solder paste coating is judged to be qualified.

[0008] S3, component placement: Use the placement machine to place the components on the PCB board with qualified solder paste coating;

[0009] S4, reflow soldering: send the PCB board into the reflow soldering furnace to solder and fix the components;

[0010] S5. AOI optical inspection: Perform tombstone defect inspection on the soldered PCB board to obtain optical inspection results.

[0011] As a further description of the above technical solution:

[0012] An identifier frame is provided on the transparent sheet, and the identifier frame is used to distinguish transparent sheets with the same PCB outline identification frame but different pad identification frame positions.

[0013] As a further description of the above technical solution:

[0014] In step S2, a database is established by combining the collected pre-detection images and the optical detection results, and the database is input into the trained image classification algorithm to calculate and judge the estimated welding quality.

[0015] As a further description of the above technical solution:

[0016] In step S1 , the steel mesh hole is a rectangular opening, and the area of ​​the steel mesh hole is 80%-90% of the area of ​​the pad.

[0017] As a further description of the above technical solution:

[0018] In step S1 , the printing speed of the solder paste screen printer is 25-32 mm / s.

[0019] As a further description of the above technical solution:

[0020] In step S1, the scraper pressure of the solder paste screen printer is 30-50N.

[0021] As a further description of the above technical solution:

[0022] In step S3, after the collected pre-detection images, optical detection results, and placement pressure of the placement machine are established in a database, the placement pressure of the placement machine is adjusted according to the pre-detection images collected in real time.

[0023] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0024] 1. In the present invention, on the one hand, the PCB board is optimized so that the 0402 components on it are concentrated in the center of the board, reducing the impact of PCB expansion and contraction on the component mounting position and effectively reducing the tombstone phenomenon; on the other hand, after the solder paste is printed on the pad, the solder paste coating quality inspection is realized by using a transparent sheet combined with a First Vision camera instead of an SPI solder paste tester, thus realizing low-cost solder paste printing quality control, effectively reducing the tombstone phenomenon and lowering equipment costs.

[0025] 2. In this invention, a database is created by combining the collected pre-test images and optical inspection results, which are then fed into a trained image classification algorithm to calculate and determine the estimated solder quality. This image classification algorithm, trained using a convolutional neural network, calculates and determines the estimated solder quality based on the pre-test images. Using the estimated solder quality and overflow area as criteria, the solder paste coating quality is comprehensively judged, improving the accuracy of determining whether the solder paste coating is acceptable. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 A flow chart of a processing method that can reduce tombstoning of electronic components.

[0028] Figure 2 A schematic diagram of the structure of a transparent sheet in a processing method that can reduce tombstoning of electronic components.

[0029] Legend:

[0030] 1. Transparent sheet; 11. PCB outline identification frame; 12. Pad identification frame; 13. Identifier frame. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0033] Example 1

[0034] See also Figure 1-2 The present invention provides a technical solution: a processing method for reducing the tombstoning of electronic components, comprising the following steps:

[0035] S1. Solder paste printing: Lay the stencil flat on the PCB board, with the stencil holes corresponding to the pads on the PCB board. The pads of the 0402 components are set in the center of the PCB board. After the solder paste is applied to the stencil surface by the solder paste screen printer, the solder paste is filled into the stencil holes by a scraper. The printing speed of the solder paste screen printer is 25-32mm / s. The speed of printing solder paste is controlled to prevent the solder paste from collapsing. The scraper pressure of the solder paste screen printer is 30-50N. When applying solder paste, control the scraper pressure to ensure good contact with the stencil.

[0036] S2. Pre-inspection of solder paste: After solder paste is filled into the stencil holes, the stencil is separated from the PCB board and the PCB board is moved under the first visual camera. A transparent sheet 1 is provided between the PCB board and the first visual camera. The transparent sheet 1 is provided with a PCB outline identification frame 11 and a pad identification frame 12 made of opaque material. Each pad identification frame 12 corresponds to one pad. The first visual camera captures a pre-inspection image of the PCB board and the transparent sheet 1 overlapping each other. The camera calculates whether the overflow area of ​​the solder paste on the pad exceeding the pad identification frame 12 in the pre-inspection image exceeds a set threshold. If the overflow area does not exceed the set threshold, the solder paste coating is judged to be qualified.

[0037] S3, component placement: Use the placement machine to place the components on the PCB board with qualified solder paste coating;

[0038] S4, reflow soldering: send the PCB board into the reflow soldering furnace to solder and fix the components;

[0039] S5. AOI optical inspection: Perform tombstone defect inspection on the soldered PCB board to obtain optical inspection results.

[0040] In addition, an identifier frame 13 is provided on the transparent sheet 1 , and the identifier frame 13 is used to distinguish transparent sheets 1 having the same PCB outline identification frame 11 but different pad identification frames 12 .

[0041] The transparent sheet 1 is specifically made of acrylic sheet. By engraving grooves and filling pigments on the transparent sheet 1, a PCB outline identification frame 11, a pad identification frame 12, and an identifier frame 13 are formed. Identifier frames 13 of different shapes can distinguish transparent sheets 1 with the same PCB outline identification frame 11 and different positions of the pad identification frames 12, ensuring accurate calculation of the overflow area during image processing.

[0042] Working principle: On the one hand, the PCB board is optimized so that the 0402 components on it are concentrated in the center of the board, reducing the impact of PCB expansion and contraction on the component mounting position and effectively reducing the tombstone phenomenon; on the other hand, after the solder paste is printed on the pad, the transparent sheet 1 is combined with the First Vision camera instead of the SPI solder paste tester to realize the solder paste coating quality inspection, realizing the low-cost quality control of solder paste printing, effectively reducing the tombstone phenomenon and reducing the equipment cost.

[0043] Example 2

[0044] This embodiment further improves upon the above-described embodiment by providing the following technical solutions: In step S2, a database is created using the collected pre-test images and optical inspection results. This database is then fed into a trained image classification algorithm to calculate and determine the estimated solder quality. A convolutional neural network is used to train the image classification algorithm, which calculates and determines the estimated solder quality based on the pre-test images. The solder paste coating quality is comprehensively judged using the estimated solder quality and overflow area as criteria, improving the accuracy of determining whether the solder paste coating is acceptable.

[0045] The specific comprehensive judgment method can assign points to the judgment results of the estimated welding quality and overflow area, calculate the total score, and judge the welding quality.

[0046] Example 3

[0047] Based on the above embodiments, this embodiment further makes the following improved technical solutions: in step S1, the steel mesh hole is a rectangular opening, and the area of ​​the steel mesh hole is 80%-90% of the pad area, reducing the resistance released into the steel mesh hole during solder paste filling, avoiding solder paste overflow after the steel mesh is demolded, and effectively ensuring the quality of solder paste coating on the pad.

[0048] Example 4

[0049] Based on the above embodiment, this embodiment further makes the following improved technical solutions: in step S3, after establishing a database of the collected pre-detection images, optical detection results, and placement pressure of the placement machine, the placement pressure of the placement machine is adjusted according to the pre-detection images collected in real time.

[0050] Specifically: for the pre-detection images collected in real time, the five past welding cases with the highest similarity and qualified optical inspection results in the database are selected according to the image algorithm, the average placement pressure of the five past welding cases is calculated, the optimal placement pressure is obtained, and the placement machine is controlled to make adjustments.

[0051] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A processing method for reducing tombstoning of electronic components, characterized in that: The following steps are involved: S1. Solder paste printing: Lay the stencil flat on the PCB board. The positions of the stencil holes correspond to the pads on the PCB board. The pads of the 0402 components are set in the center of the PCB board. The solder paste screen printer applies solder paste on the surface of the stencil and then fills the stencil holes with the scraper. S2. Pre-inspection of solder paste: After solder paste is filled into the stencil holes, the stencil is separated from the PCB board and the PCB board is moved under the first vision camera. A transparent sheet is placed between the PCB board and the first vision camera. The transparent sheet is provided with a PCB outline identification frame and a pad identification frame made of opaque material. Each pad identification frame corresponds to one pad. The first vision camera captures a pre-inspection image of the PCB board and the transparent sheet overlapping. The camera calculates whether the overflow area of ​​the solder paste on the pad exceeding the pad identification frame in the pre-inspection image exceeds a set threshold. If the overflow area does not exceed the set threshold, the solder paste coating is judged to be qualified. S3, component placement: Use the placement machine to place the components on the PCB board with qualified solder paste coating; S4, reflow soldering: send the PCB board into the reflow soldering furnace to solder and fix the components; S5. AOI optical inspection: Perform tombstone defect inspection on the soldered PCB board to obtain optical inspection results.

2. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: An identifier frame is provided on the transparent sheet, and the identifier frame is used to distinguish transparent sheets having the same PCB outline identification frame but different pad identification frame positions.

3. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: In step S2, a database is established by combining the collected pre-detection images and the optical detection results, and the database is input into a trained image classification algorithm to calculate and judge the estimated welding quality.

4. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: In step S1, the steel mesh hole is a rectangular opening, and the area of ​​the steel mesh hole is 80%-90% of the area of ​​the pad.

5. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: In step S1, the printing speed of the solder paste screen printer is 25-32 mm / s.

6. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: In step S1, the scraper pressure of the solder paste screen printer is 30-50N.

7. A processing method for reducing tombstoning of electronic components according to claim 1, characterized in that: In step S3, after the collected pre-detection image, optical detection result, and placement pressure of the placement machine are established in a database, the placement pressure of the placement machine is adjusted according to the pre-detection image collected in real time.

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