Method for adjusting the distribution of flux on a circuit board

Abstract

To provide a method of adjusting a distribution position of flux on a circuit board.SOLUTION: A method of adjusting a distribution position of flux on a circuit board includes steps of: preparing a circuit board provided with flux covering a plurality of solder points distributed on a surface; performing optical position alignment work of sending the circuit board into a work region, imaging the circuit board by using an optical imaging lens, and outputting positional information after calculation; performing laser cleaning work of generating a laser beam by using a laser oscillator, removing excessive flux around the plurality of solder points on the basis of the positional information, and leaving only flux distributed on top surfaces of the solder points; and performing automatic optical inspection work for determining whether the circuit board is nondefective or defective. By the steps, flux having the same distribution region is formed on the top surfaces of the plurality of solder points on the circuit board, and successive soldering quality is improved. If there is remaining flux, the remaining flux can be completely removed via a reflow furnace in the subsequent step, and a step of cleaning excessive flux on the circuit board can be omitted.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to the technical field of forming flux on a circuit board, and particularly to a method for accurately adjusting the distribution position of the flux on the circuit board.

Background Art

[0002] The working principle of the flux used in soldering is that the flux components remove the metal surface oxides on the bonding surface between the soldered object and the conjugate by a chemical method, and wetly extend to closely adhere and fix the solder to the metal interface between the soldered object and the conjugate, so as to obtain a strong conjugate.

[0003] In the semiconductor process, in order to smoothly proceed with the subsequent soldering operation, it is necessary to adopt a technique for forming solder bumps on a certain circuit board. This technique involves applying flux to a plurality of solder points on the circuit board in advance, using spherical solder called solder balls, loading the solder balls on the solder points where the flux is applied, heating through a reflow furnace, and finally forming protruding solder bumps on the solder points of the circuit board.

[0004] And in recent years, as the size of electronic components has been shrinking, the wiring pattern of the circuit board has been miniaturized, the interval between the formed solder bumps has become narrower, and accordingly, smaller-sized and narrower-interval solder bumps are also required. To achieve this purpose, when forming flux on the surface of the circuit board in the previous stage, the distribution area of the flux at the position of each solder point must be more accurate. However, as the interval and size of the solder points are shrinking, when the flux is formed on the surface of the circuit board by an inkjet method or silk screen printing, there is a problem that the diffusion or distribution area is too large. In response to this, the inventor of the present invention has proposed a processing method to effectively remove the extra flux during the operation, distribute the flux only within the area where the solder points of the circuit board are located, and smoothly proceed with the subsequent accurate formation of the solder bumps.

Summary of the Invention

[0005] The main objective of this invention is to provide a method for adjusting the distribution position of flux on a circuit board. After flux is formed on the circuit board, optical alignment and laser cleaning are used to remove excess flux around solder points on the circuit board, and the work area can be precisely controlled using laser cleaning. As a result, the flux is ultimately distributed only to the corresponding solder points, overcoming the problems of conventional flux that tend to diffuse easily and have an excessively large distribution area, thereby meeting the precision required for subsequent packaging work. [Means for solving the problem]

[0006] To achieve the above objective, the present invention employs the following technical solutions.

[0007] The present invention relates to a method for adjusting the distribution position of flux on a circuit board, comprising the steps of: preparing a circuit board on which flux covering a plurality of solder points distributed on its surface is provided; performing an optical alignment operation in which the circuit board is sent into a work area, the circuit board is photographed using an optical photographic lens, and position information is output after calculation; performing a laser cleaning operation in which a laser beam is generated using a laser oscillator, and based on the position information, excess flux around the plurality of solder points is removed, leaving only the flux distributed on the top surface of the solder points; and performing an automated optical inspection operation to determine whether the circuit board is a good product or a defective product.

[0008] In one preferred embodiment, when preparing a circuit board, the region on the circuit board where the flux is located simultaneously covers multiple solder points.

[0009] In one preferred embodiment, when preparing the circuit board, one layer of flux is applied to each solder point on the circuit board, and the area of ​​flux coverage is larger than the area of ​​the solder point.

[0010] In one preferred embodiment, the flux is formed on the circuit board using an inkjet method.

[0011] In one preferred embodiment, the thickness of the flux at the solder point is 1 to 100 μm.

[0012] In one preferred embodiment, the thickness of the flux at the solder point is 2 to 50 μm.

[0013] In one preferred embodiment, the shape of the solder point is circular, and the diameter of the circle is 1 to 1000 μm.

[0014] In one preferred embodiment, the shape of the solder point is rectangular, and the length of any side of the rectangular shape is 1 to 1000 μm.

[0015] In one preferred embodiment, the spacing between adjacent solder points is 20 to 100 μm.

[0016] In one preferred embodiment, the flux is formed on the circuit board by a printing method. [Effects of the Invention]

[0017] Compared to conventional techniques, the method used in the present invention allows for precise adjustment of the flux distribution position on the circuit board and satisfies the objective of distributing flux only on the top surface of the corresponding solder points when the spacing and size of solder points are small, ultimately facilitating the process of forming solder bumps on the circuit board. Furthermore, after laser cleaning using the method of the present invention, only a very small amount of flux remains on the circuit board. Subsequently, the remaining flux is completely removed via a reflow oven in a later process, eliminating the need for a step to clean excess flux from the surface of the circuit board, simplifying the production flow and reducing cleaning costs. [Brief explanation of the drawing]

[0018] [Figure 1] This is the flowchart of the present invention. [Figure 2] This is a schematic diagram showing the formation of flux in the circuit of the present invention. [Figure 3] This is a schematic diagram showing the optical alignment operation on the circuit board of the present invention. [Figure 4] This is a schematic diagram showing the laser cleaning operation on the circuit board of the present invention. [Figure 5] This is a schematic diagram showing the automatic optical inspection operation on the circuit board of the present invention. [Figure 6] This is a partially enlarged view showing the formation of flux by an inkjet method on the circuit board of the present invention.

Embodiments for Carrying out the Invention

[0019] Hereinafter, the technical solution of the present invention will be clearly and fully described in combination with specific embodiments and drawings. It should be noted that when a component is referred to as "attached or fixed to" another component, it may be understood that it is directly located on the other component, or it may be understood that there are further intervening components. When a component is considered to be "connected" to another component, it may be understood that it is directly connected to the other component, or it may be understood that there are intervening components therebetween.

[0020] In the illustrated embodiments, expressions such as up, down, left, right, front, and back, which represent directions, are relative, and are used to explain that the structures and movements of different components in the present application are relative. When the components are in the positions shown in the figures, these expressions are appropriate. However, when the position description of the components changes, it is considered that these expressions will also change accordingly.

[0021] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the technical field of the present invention. The technical terms used in this specification are not intended to limit the present invention, but are for the purpose of explaining specific embodiments. The technical term "and / or" used herein includes any and all combinations of one or more of the recited related items.

[0022] The present invention is a method for adjusting the distribution position of flux on a circuit board. The ultimate goal is to accurately form a single layer of flux on the top surface of each solder point on the circuit board, and then perform a processing operation to form solder bumps. The technique for forming these solder bumps is to load solder balls onto the solder points where flux exists, heat them through a reflow furnace, and finally form solder bumps on the solder points of the circuit board. This part is not the focus of the present invention, so it will not be described further.

[0023] As shown in FIG. 1, it is a flowchart of a method for adjusting the distribution position of flux on a circuit board according to the present invention, and includes the following steps.

[0024] Step 101: Prepare a circuit board, on the surface of which a plurality of solder points are distributed, and flux covering the solder points is provided on the circuit board.

[0025] Step 102: Perform an optical alignment operation, send the circuit board into the working area, photograph the circuit board using an optical imaging lens, and output position information after calculation.

[0026] Step 103: Perform a laser cleaning operation, generate a laser beam using a laser oscillator, remove the excess flux around a plurality of solder points based on the position information, and leave only the flux distributed on the top surface of the solder points.

[0027] Step 104: Perform an automatic optical inspection operation to determine whether the circuit board is a good product or a defective product.

[0028] Next, each step of the present invention will be described in detail with reference to Figures 2 to 5.

[0029] As shown in Figure 2, the circuit board 10 used in the present invention has multiple solder points 11 distributed therein. In this embodiment, the circuit board 10 is applied to surface mount technology (SMT), which uses pinless or short-lead electronic components to directly mount electronic components to the circuit board 10. Therefore, the circuit board 10 has a large number of solder points 11 distributed therein, corresponding to the electronic components. In this embodiment, the spacing between each solder point 11 is only 20 to 100 μm, so there are many solder points and they are quite densely packed. The shape of the solder points is circular or square. If circular, its diameter is 1 to 1000 μm; if square, the length of one of its sides is 1 to 1000 μm. In step 101, as shown in Figure 2, in this embodiment, one layer of flux 20 is formed on the surface of the circuit board 10 using an inkjet method with an inkjet device 30. In Figure 2, solder points 11 covered by flux 20 are shown with dashed lines, and uncovered solder points 11 are shown with solid lines. However, once the inkjet process is complete, the flux 20 covers all solder points 11.

[0030] As shown in Figure 3, in step 102, the present invention uses an optical imaging lens 40 to photograph the circuit board 10, adjusts the proportion of the captured image based on alignment lines or alignment symbols (not shown in the figure) on the circuit board 10, and obtains coordinate information within the work area of ​​the circuit board 10. Simultaneously with obtaining the coordinate information, it connects to a database to obtain the distribution positions of multiple solder points 11 on the circuit board 10, and finally obtains position information after calculating and correcting the above information together. This position information is used as the basis for operating the subsequent laser oscillator 50. Of course, the optical imaging lens 40 can also obtain an identification code (e.g., a QR code) while photographing the circuit board 10, obtain each data of the circuit board 10 from the identification code via the database, and simultaneously verify it during the calculation process to confirm whether it is the product that was processed this time, thereby reducing the occurrence of processing errors.

[0031] As shown in Figure 4, in step 103, the laser oscillator 50 used in the present invention generates a laser beam 51 with a wavelength of 355 nm, a power of 5 w, a pulse energy of 100 μJ, a frequency of 20 to 200 kHz, and a speed of 1 to 5000 mm / sec. Based on the acquired position information, the laser oscillator 50 removes excess flux 20 around the solder point 11 with the laser beam 51, leaving the flux 20 only at the solder point 11. In the figure, the solder point 11 on the right already has flux 20, so it is shown with a thick line. In this embodiment, the thickness of the flux 20 is 1 to 100 μm, and the optimal thickness is preferably 2 to 50 μm.

[0032] As shown in Figure 5, in step 104, the present invention performs quality control using automated optical inspection (AOI), and the manufacturer can select an appropriate automated optical inspection device 60 (simply shown as blocks in the figure) as needed to inspect the circuit board 10. The automated optical inspection device 60 is equipped with a high-speed, high-precision optical image detection system and uses machine vision as the detection standard technology to measure the thickness of the flux 20, its distribution location, and whether the flux 20 is distributed at the solder points 11. If flux 20 is present on the top surface of all solder points 11, the circuit board 10 is judged to be a good product. If flux 20 is absent at some solder points or the distribution area is too small, it is judged to be a defective product. Defective products can be collected, cleaned, and reprocessed, while good products are collected and proceed to the next processing step.

[0033] As described above, the method for adjusting the distribution position of flux on a circuit board according to the present invention utilizes optical alignment and laser cleaning to remove excess flux 20 around solder points 11 on the circuit board 10 with a laser beam 51. Furthermore, since a single layer of flux 20 is formed on the circuit board 10 using an inkjet method, a relatively thin flux 20 can be formed, allowing for effective and reliable removal of excess flux 20 when using the laser beam 51, and enabling precise control of the removal area. Ultimately, the flux 20 is distributed only on the top surface of the solder points 11, solving the problem of not being able to accurately control the distribution position of flux 20 when the current size and spacing of solder points 11 are reduced. This allows for smoother subsequent processing work to form solder bumps on the solder points 11.

[0034] In step 101 described above, the present invention forms a layer of flux 20 on the surface of the circuit board 10 using an inkjet method, but is not limited to this, and a layer of flux 20 can also be formed on the circuit board 10 using a printing method. In this embodiment, a silk screen printing (silk printing) method for steel plates is used to form the flux 20 on the circuit board 10.

[0035] Furthermore, when using an inkjet method to form the flux 20, the inkjet method allows for precise control of the inkjet area. As shown in Figure 6, each distribution area 21 of the flux 20 corresponds to the area where each solder point 11 is located. This embodiment is applied to surface mount technology (SMT) with minute sizes, where multiple solder points 11 are small in size and spaced only 20-100 μm apart. This means that the coverage area of ​​some flux 20 distribution areas 21 may be larger than the area of ​​the solder points 11. Even in this case, the size of the flux 20 distribution areas 21 can be adjusted and modified using the method of the present invention, so that the distribution position and shape of the flux 20 match those of the solder points. The advantage of spray-coating a small amount of flux 20 onto the corresponding solder points 11 in this embodiment is that the amount of flux 20 used can be further reduced, thereby lowering production costs.

[0036] As described above, the present invention allows for the precise formation of flux 20 on the circuit board 10 in a shape corresponding to the top surface of each solder point 11. Subsequently, solder balls can be placed on the solder points 11 where flux 20 is present, and by heating in a reflow oven, solder bumps are ultimately formed on the solder points 11. Furthermore, since the present invention employs a laser beam 61 to remove the flux 20, the amount of flux 20 remaining on the circuit board 10 is extremely small. When the circuit board 10 proceeds to the reflow soldering process, the extremely small amount of flux 20 remaining on the circuit board 10 is completely removed by the high temperature. In this way, the process of cleaning excess flux 20 from the surface of the circuit board 10 is eliminated, thereby simplifying the production flow and reducing cleaning costs.

[0037] The above are preferred embodiments of the present invention and do not limit the scope of the embodiments of the present invention. That is, all equivalent variations and modifications according to the claims of the present invention are included within the scope of the claims of the present invention. [Explanation of Symbols]

[0038] Steps 101-104 10 Circuit boards 11 Handa points 20 Flux 21 Distribution area 30 Inkjet equipment 40 Optical shooting lenses 50 Laser Oscillators 51 Laser beam 60. Automated Optical Inspection Equipment

Claims

1. A method for adjusting the distribution position of flux on a circuit board, The steps include: preparing the circuit board having flux provided to cover multiple solder points distributed on its surface; The steps include: sending the circuit board into the work area, photographing the circuit board using an optical lens, and performing an optical alignment operation to output position information after calculation; A laser cleaning operation is performed using a laser oscillator to generate a laser beam, remove excess flux around multiple solder points based on the position information, and leave only the flux distributed on the top surface of the solder points. The process includes the step of performing an automated optical inspection to determine whether the circuit board is a good product or a defective product. A method for adjusting the distribution of flux on a circuit board.

2. When preparing the circuit board, the region on the circuit board where the flux is located simultaneously covers multiple solder points. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

3. When preparing the circuit board, one layer of flux is applied to each solder point on the circuit board, and the area of ​​flux coverage is larger than the area of ​​the solder point. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

4. The flux is formed on the circuit board using an inkjet method. A method for adjusting the distribution position of flux on a circuit board according to claim 2 or 3.

5. The thickness of the flux at the solder point is 1 to 100 μm. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

6. The thickness of the flux at the solder point is 2 to 50 μm. A method for adjusting the distribution position of flux on a circuit board according to claim 5.

7. The shape of the solder point is circular, and the diameter of the circle is 1 to 1000 μm. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

8. The shape of the solder point is rectangular, and the length of any side of the rectangular shape is between 1 and 1000 μm. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

9. The spacing between adjacent solder points is 20 to 100 μm. A method for adjusting the distribution position of flux on a circuit board according to claim 1.

10. The flux is formed on the circuit board by a printing method. A method for adjusting the distribution position of flux on a circuit board according to claim 2.

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