Reworking method for repairing mark by removing mark ink on circuit board through laser

Abstract

A reworking method for removing marking ink on a printed circuit board by using laser to repair a mark comprises the following steps: irradiating a repairing position on a substrate by using a laser beam with preset power, preset frequency, preset current and preset pulse width to remove marking ink to be removed at the repairing position, and then printing repairing marking ink at the repairing position, and finally, curing the repair mark ink.

Description

Technical Field

[0001] The present invention relates to a reworking method for repairing a mark on a printed circuit board, in particular to a reworking method for repairing the mark by removing the marking ink on the printed circuit board using a laser. Background Art

[0002] Text printing is one of the manufacturing processes of printed circuit boards. Its main working principle is to use a text printer and a screen to squeeze text ink onto the printed circuit board using mechanical pressure, and then bake it at high temperature to form solidified text to mark the names of parts on the printed circuit board. However, during the printing process, there is a certain probability of poor printing, which makes the solidified text substandard and requires rework.

[0003] The existing method of repairing text is for technicians to manually scrape it with a 45-degree bevel surgical blade, and then re-print and solidify it. However, in practice, it takes technicians about 40 to 60 seconds, or even longer, to remove each poorly printed text, making the scraping process inefficient and unsuitable for batch operations. In addition, the scraping operation has very high technical requirements for personnel, and generally requires more than 3 months of manual training. When performing the scraping operation, the personnel must use appropriate cutting force. If the force is too great, the product will be scrapped, and if the force is too small, multiple operations will be required. In addition, due to the influence of the personnel's operating techniques such as the cutting angle and the operating force, a certain proportion of printed circuit boards will be scratched and need to be scrapped. Summary of the invention

[0004] The present invention provides a rework method for removing marking ink on a printed circuit board using laser to repair the marking, thereby solving the problems of low efficiency, high labor cost and high product defect rate in the prior art of manually scraping off poorly printed text.

[0005] An embodiment of the present invention discloses a rework method for removing marking ink on a printed circuit board using a laser to repair a marking, comprising irradiating a repair position on a substrate with a laser beam of preset power, preset frequency, preset current and preset pulse width to remove the marking ink to be removed at the repair position, then printing the repair marking ink at the repair position, and finally curing the repair marking ink.

[0006] According to the rework method disclosed in the above embodiment, which uses laser to remove marking ink on a printed circuit board to repair the marking, poorly printed or misprinted marking ink is removed by machine automation, instead of manual scraping, which can have higher repair efficiency and accuracy, thereby significantly reducing product defective rate. In addition, the rework method has lower technical requirements for the operator, which can save labor costs.

[0007] The above description of the content of the present invention and the following description of the embodiments are used to demonstrate and explain the principles of the present invention, and to provide further explanation of the claims of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 The figure is a schematic top view of a printed circuit board having marking ink to be removed according to an embodiment of the present invention.

[0009] Figure 2 for Figure 1 A schematic cross-sectional view of a printed circuit board having marking ink to be removed.

[0010] Figure 3 for Figure 1 Schematic diagram of a top view of a printed circuit board after the marking ink to be removed is removed by a laser beam.

[0011] Figure 4 for Figure 3 A top view of a printed circuit board having a repair marking ink printed thereon. DETAILED DESCRIPTION

[0012] The detailed features and advantages of the embodiments of the present invention are described in detail in the following embodiments, and the contents are sufficient to enable any person skilled in the art to understand the technical contents of the embodiments of the present invention and implement them accordingly. According to the contents disclosed in this specification, the claims and the drawings, any person skilled in the art can easily understand the relevant purposes and advantages of the present invention. The following embodiments further illustrate the viewpoints of the present invention in detail, but do not limit the scope of the present invention in any viewpoint.

[0013] See also Figures 1 to 4 ,in Figure 1 FIG. 1 is a schematic top view of a printed circuit board having marking ink to be removed according to an embodiment of the present invention. Figure 2 for Figure 1 A schematic cross-sectional view of a printed circuit board having marking ink to be removed, Figure 3 for Figure 1 A schematic top view of a printed circuit board after the marking ink to be removed is removed by a laser beam, and Figure 4 for Figure 3 A top view of a printed circuit board having a repair marking ink printed thereon.

[0014] The exemplary steps of the reworking method of this embodiment for removing marking ink on a printed circuit board using a laser to repair the marking are described as follows.

[0015] First, a plurality of substrates 1 (for example, no more than 150 substrates) printed with marking ink 4 to be removed are stacked and placed on a loading table of a laser engraving machine. Figure 1and Figure 2 As shown, the substrate 1 is provided with a circuit layer 2, for example, by etching, and the substrate 1 and the circuit layer 2 are covered with a solder mask 3, and the marking ink 4 to be removed is, for example, located on the solder mask 3. The solder mask 3 is formed by, for example, screen printing green ink on the substrate 1 and the circuit layer 2 and by thermal curing or photocuring. The marking ink 4 to be removed is, for example, green ink, and the material of the marking ink 4 to be removed can be the same as or different from the material of the solder mask 3. The laser engraving machine is used to emit a laser beam toward the repair position on the substrate 1. The marking ink 4 to be removed is, for example, a cured or semi-cured text or pattern printed on the solder mask 3, and the marking ink 4 to be removed can be used to indicate the product model and / or the name of the parts on the printed circuit board. The thickness of the marking ink 4 to be removed is, for example, 0.5 to 0.6 times the thickness of the solder mask 3.

[0016] A laser engraving machine reads at least three positioning optical point data and repair position data in a drawing exchange format (DXF) file to position the irradiation position of the laser beam at the repair position. Specifically, for example, the laser engraving machine is first adjusted back to the mechanical origin, and then one of the positioning optical points is found with the lens of the laser engraving machine, and then other positioning optical points are found based on the at least three positioning optical point data, and finally the positions of these optical points are saved and memorized. Then, based on the relative position relationship between the repair position data and the at least three positioning optical point data, the irradiation position of the laser beam can be positioned at the repair position. Among them, the number of positioning optical points is at least three, which can be, for example, optical points in the board, so as to facilitate accurate positioning of the laser engraving machine. In one embodiment, the drawing exchange format file is, for example, pre-converted from a Gerber file, wherein the Gerber is a two-dimensional vector image format, which is a universal standard format for defining printed circuit board manufacturing images. In one embodiment, this step may further include a charge-coupled device (CCD) alignment system to compensate for the expansion or contraction of the component size, so as to automatically compensate and correct the positioning optical point data and the repair position data read by the laser engraving machine. For example, when the charge-coupled device alignment system detects that the circuit board to be repaired has expanded or contracted due to the ambient temperature, the charge-coupled device alignment system may automatically compensate and correct the positioning optical point data and the repair position data read by the laser engraving machine in a corresponding proportion according to the expansion or contraction of the circuit board, thereby providing a high-precision repair operation.

[0017] In the reworking method of this embodiment, the parameters of the laser engraving machine can be selectively set before or after the above steps.

[0018] Next, the repair position on the substrate 1 is irradiated with a laser beam having a preset power, a preset frequency, a preset current and a preset pulse width to remove the marking ink 4 to be removed (such as Figure 3 As shown), wherein the preset power is greater than or equal to 8 watts (W) and less than or equal to 12 watts, the preset frequency is greater than or equal to 30 kilohertz (kHz) and less than or equal to 90 kilohertz, the preset current is 1 ampere (A), and the preset pulse width is 9 microseconds (μs) to 12 microseconds. Among them, the laser engraving speed of the laser engraving machine is, for example, 80 millimeters / second (mm / s) to 120 millimeters / second. In one embodiment, the preset power is 8 watts, and the preset frequency is 50 kHz. In one embodiment, the laser beam is an ultraviolet laser beam. In one embodiment, the laser beam is a green laser beam.

[0019] Next, print the repair mark ink 5 (such as Figure 4 As shown). The repair marking ink 5 is, for example, green ink printed on the solder mask 3 by screen printing.

[0020] Finally, the repair marking ink 5 is cured. The curing may be performed by, for example, using a high-temperature tunnel furnace for high-temperature thermal curing, but the present invention is not limited thereto. The step of curing the repair marking ink 5 is, for example, inserting the substrate 1 into a frame and using a high-temperature tunnel furnace for high-temperature curing at, for example, 150°C.

[0021] In the embodiment where the laser beam is an ultraviolet laser beam, the wavelength of the ultraviolet laser beam is 355 nanometers, so that the time for the laser pulse to interact with the ink material can be relatively long, so that the heat generated in the process of removing the marking ink 4 to be removed will diffuse outward, forming a certain thermal effect zone. At the same time, since the laser ablation is achieved by both gasification and thermal ablation, and more laser energy will be converted into heat during the thermal ablation process, the utilization efficiency of the laser is relatively low. However, due to the limited pulse peak power of the nanosecond laser engraving machine, a higher output power (for example, 8 watts) is required. In addition, the true roundness of the output spot of the ultraviolet laser beam is greater than 85%, and it is a typical Gaussian distribution, which can be mainly used for the overflow removal of the flip chip ball grid array (FCBGA) substrate and the removal of polymer ink.

[0022] In this embodiment, the preset pulse width is 9 microseconds to 12 microseconds, thereby ensuring that the laser beam provides sufficient energy to remove the marking ink 4 to be removed, and at the same time ensuring that the laser beam does not damage the solder mask 3 or only slightly damages the solder mask 3.

[0023] It should be noted that the frequency, current and pulse width of the laser beam can be adjusted and set according to the power, beam expansion factor and size of the field lens of the laser engraving machine and the material absorbance of the marking ink 4 to be removed. Different products have different processing environments and different ink compositions and thicknesses, so the above parameters also need to be adjusted according to different products. In the embodiment where the marking ink 4 to be removed is green ink, the preset frequency is preferably 50 kHz, the preset current is preferably 1 ampere, and the preset pulse width is preferably 9 microseconds to 12 microseconds.

[0024] It is also noted that the use of a carbon dioxide laser can easily over-ablate the solder mask while ablating the marking ink to be removed, causing the circuit layer under the solder mask to be exposed. If the energy of the carbon dioxide laser is reduced to avoid damaging the solder mask, the carbon dioxide laser will become unable to completely remove the marking ink to be removed. Compared to the carbon dioxide laser, the reworking method in some embodiments of the present invention uses an ultraviolet laser beam or a green laser beam, which can ensure that the ultraviolet laser beam or the green laser beam will not damage the solder mask 3 while removing the marking ink 4 to be removed, or only slightly damage the solder mask 3 without exposing the circuit layer 2 under the solder mask 3.

[0025] In one embodiment, before the step of printing the repair marking ink 5 at the repair position, the rework method may further include the step of first piece inspection to confirm whether the first piece of the marking ink 4 to be removed is effectively removed and whether the degree of damage to the solder mask 3 is within the allowable range. The inspection method can use a magnifying glass with a magnification of 50 times or more, for example, to inspect the appearance of the repair position, and for example, use 3D scanning to inspect the depth of laser ablation of the solder mask 3. When the first piece inspection meets the standards, the laser engraving machine is automatically operated to repair the remaining substrates 1 on the loading platform. Among them, the number of first pieces can be, for example, but not limited to, two. In one embodiment, different drawing exchange format files need to be prepared for the marks of different repair positions, and the laser engraving machine needs to operate separately.

[0026] In one embodiment, after the step of curing the repair marking ink 5, the reworking method may further include a step of finished product inspection to inspect the quality of the mark after the repair marking ink 5 is cured. The inspection method may be to inspect the appearance of the mark using a magnifying glass with a magnification of 50 times or more.

[0027] In one embodiment, the substrate 1 can be placed on and removed from the loading platform of the laser engraving machine by automatic loading and unloading auxiliary equipment, thereby realizing automated operation.

[0028] According to the rework method of the above-mentioned embodiment, a laser is used to remove the marking ink on the printed circuit board to repair the marking. The marking ink with poor printing or printing error is removed by machine automation, instead of manual scraping. This can have a higher repair efficiency and accuracy, thereby greatly reducing the product defect rate. In addition, the rework method has lower technical ability requirements for the operator, which can save labor costs.

[0029] In addition, when the preset pulse width is 9 microseconds to 12 microseconds, it can ensure that the laser beam provides sufficient energy to remove the marking ink to be removed, and at the same time ensure that the laser beam does not damage the solder mask or only slightly damages the solder mask.

[0030]

Explanation of symbols

[0031] 1:Substrate

[0032] 2: Circuit layer

[0033] 3: Solder mask

[0034] 4: Marking ink to be removed

[0035] 5: Repair marking ink.

Claims

1. A reworking method for removing marking ink on a printed circuit board using a laser to repair the marking, characterized in that: The reworking method comprises: Irradiating the repair position on the substrate with a laser beam having a preset power, a preset frequency, a preset current and a preset pulse width to remove the marking ink to be removed located at the repair position; Printing repair marking ink at the repair position; as well as The repair marking ink is cured. 2 . The reworking method according to claim 1 , wherein the laser beam is an ultraviolet laser beam or a green laser beam, and the marking ink to be removed is green ink.

3. The reworking method according to claim 2, wherein the wavelength of the ultraviolet laser beam is 355 nanometers. 4 . The reworking method according to claim 1 , wherein the substrate is covered with a solder resist layer, and the repair marking ink is located on the solder resist layer. 5 . The reworking method according to claim 4 , wherein the repair marking ink is screen printed on the solder resist layer.

6. The reworking method according to claim 1, wherein the preset power is greater than or equal to 8 watts and less than or equal to 12 watts, the preset frequency is greater than or equal to 30 kHz and less than or equal to 90 kHz, the preset current is 1 ampere, and the preset pulse width is 9 microseconds to 12 microseconds. The reworking method according to claim 6 , wherein the preset power is 8 watts. The reworking method according to claim 6 , wherein the preset frequency is 50 kHz.

9. The reworking method according to claim 1, wherein before the step of removing the marking ink to be removed located at the repairing position with the laser beam, the reworking method further comprises: Set the parameters of the laser engraving machine; in, The laser engraving machine is used to emit the laser beam toward the repairing position on the substrate. 10 . The reworking method according to claim 9 , wherein the laser engraving speed of the laser engraving machine is 80 mm / s to 120 mm / s.

11. The reworking method according to claim 1, wherein before the step of removing the marking ink to be removed located at the repairing position with the laser beam, the reworking method further comprises: The laser engraving machine is used to read at least three positioning optical point data and repair position data in the drawing exchange format file, so as to position the irradiation position of the laser beam at the repair position.

12. The rework method according to claim 11, wherein the step of using the laser engraving machine to read the at least three positioning optical point data and the repair position data in the drawing exchange format file includes performing a compensation operation for component size expansion or contraction through a charge-coupled device alignment system to automatically compensate and correct the at least three positioning optical point data and the repair position data read by the laser engraving machine.

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