Method for making fine characters

Abstract

The invention relates to the technical field of manufacturing of fine characters for component recognition in circuit board production, and discloses a manufacturing method of fine characters, which adopts a mode of integrally forming solder resist characters, when solder resist is produced, required characters are simultaneously designed on a solder resist layer, and a laser printing technology is adopted during solder resist exposure, so that the production efficiency of the fine characters is improved. And the characters are exposed together, so that the production process is reduced, and meanwhile, fine characters are produced.

Description

Technical Field

[0001] The present invention relates to the technical field of fine character production for component identification in a circuit board production process, in particular to a method for producing fine characters. Background Art

[0002] During the SMT process, printed characters are required on the PCB surface to effectively identify component locations. However, current PCB production requires increasingly precise character markings, and the requirements for character production are also becoming increasingly stringent. In existing technology, character widths are typically 100μm and heights range from 10-30μm. These characters are not only large in size, but also present the following challenges during the actual PCB production process:

[0003] First, in designs where the distance between two SMD components is small, the silkscreen characters may cover the pads due to character width issues. This can cause the components to not be firmly attached during SMD placement, and there is a risk of them falling off.

[0004] Second, when silk-screening characters between two pads of smaller components, the components will be lifted up due to the height of the characters, resulting in the risk of cold soldering and falling off.

[0005] Therefore, those skilled in the art need a method for producing precise characters that can meet the high-quality production requirements of PCB boards. Summary of the Invention

[0006] The purpose of the present invention is to solve the problem that large characters easily cover the pads, and also to solve the problem that characters are higher than the ink surface, lifting components and causing cold solder joints and falling off during SMT patching; the present invention designs a method for producing fine characters.

[0007] The technical solution of the present invention to achieve the above object is a method for producing fine characters, which includes the following steps:

[0008] Step 1: Adjust the solder mask parameters. In the solder mask process of the PCB production process, adjust the thickness of the solder mask layer formed by the silk screen solder mask ink.

[0009] Step 2: Character design: select the character layer separately according to the GERBER data and merge the character layer into the outer surface of the solder mask layer;

[0010] Step 3: Exposure treatment. After printing the solder mask ink, a PCB to be exposed is obtained. The PCB is exposed using LDI exposure technology to allow the solder mask ink near the character layer (i.e., the portion of the solder mask layer that does not contact the character layer surface, including the portion of the solder mask layer surface that does not contact the character layer edge and the portion of the solder mask layer that does not contact the character layer surface) to undergo polymerization reaction to obtain a light-cured PCB.

[0011] Step 4: Create precise characters. Rinse the PCB board prepared in step 3 with a developer. The developer retains the light-cured solder mask ink (i.e., the solder mask ink in the polymerization reaction area) and washes away the un-light-cured solder mask ink (i.e., the solder mask ink that has not undergone polymerization reaction), leaving the precise characters on the outer surface of the PCB board.

[0012] Step 5: Curing the precision characters: Use a tunnel furnace to perform high-temperature curing on the outer surface of the PCB board (the outer surface refers to the upper and lower surfaces of the PCB board) with the precision characters produced in step 4, so as to achieve the purpose of producing fine characters on the PCB board.

[0013] The thickness of the solder resist layer in step 1 is not less than 15 μm.

[0014] Merging the character layer into the outer surface of the solder resist layer in step 2 means embedding the character layer into the outer surface of the solder resist layer in a fused manner, ensuring that the character layer is aligned with the outer surface of the solder resist layer and does not protrude from the outer surface of the solder resist layer.

[0015] In step 2, when the character layer intersects or overlaps the solder mask layer, the character pattern in the character layer must avoid or delete the portion that overlaps with the solder mask pads. The intersection or overlap process focuses on the solder mask pads. This produces highly accurate character positions and reduces the need to create a separate character layer after solder masking, saving production time.

[0016] The character width in the character layer in step 2 is 20-30 μm.

[0017] Before exposure in step 3, the energy uniformity must be tested to ensure that the exposure energy uniformity is not less than 90%. At the same time, the accuracy of the exposure machine must not exceed 15μm. The exposure energy is designed to be 700-900MJ based on the solder mask ink and 9-10 grids on the exposure ruler.

[0018] The light (ultraviolet light) emitted by the LDI machine in step 3 causes the solder resist ink (photosensitive material) to undergo a polymerization reaction (i.e., a photocuring reaction). Since the solder resist pads are large, the light will penetrate from the side of the characters to the bottom of the solder resist layer during exposure, resulting in a PCB board (such as a PCB board) with the solder resist ink near the character layer being photocured. Figure 2 ).

[0019] In step 4, the concentration of the developer is controlled to be between 0.8% and 1.2%.

[0020] The resistance ink that is not photocured in the step four includes the resistance ink that is not exposed to light on the surface of the solder mask layer and the resistance ink that is blocked by the character layer inside the solder mask layer. The resistance ink that is photocured includes the resistance ink that is exposed to light on the surface of the solder mask layer and the resistance ink that is not blocked by the character layer inside the solder mask layer.

[0021] The temperature of the high temperature curing in the step 5 is 155° C.±5° C., and the time of the high temperature curing is 75±3 minutes.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention reduces the character silk screen printing process by combining the character and solder mask design method, and solves the problem of producing fine characters (characters with a width of 25-50μm) by avoiding the problem of solder pads on small character spacing.

[0024] 2. The present invention solves the problem of components being lifted up due to characters protruding from the outer surface of the ink, ensuring that the character height is no higher than the ink thickness, so that the problem of components being lifted up due to high characters and causing cold soldering or falling off will not occur during SMT patching. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of a method for producing fine characters according to the present invention;

[0026] Figure 2 Schematic diagram of the structure of the light-cured PCB board of the present invention;

[0027] Figure 3 It is a schematic structural diagram of the PCB board after being cleaned by the developer according to the present invention. DETAILED DESCRIPTION

[0028] The present invention will be described in detail below with reference to the accompanying drawings. Figure 1-3 As shown;

[0029] A method for producing fine characters, the method comprising the following steps:

[0030] Step 1: Adjust the solder mask parameters. In the solder mask process of the PCB production process, adjust the thickness of the solder mask layer formed by the silk screen solder mask ink.

[0031] Step 2: Character design: select the character layer separately according to the GERBER data and merge the character layer into the outer surface of the solder mask layer;

[0032] Step 3: Exposure treatment: After printing the solder mask ink, a PCB to be exposed is obtained. The PCB is exposed using LDI exposure technology to allow the solder mask ink near the character layer (i.e., the portion not in contact with the character layer surface, including the portion not in contact with the edge of the solder mask layer and the portion within the solder mask layer not in contact with the character layer surface) to polymerize, thereby obtaining a light-cured PCB.

[0033] Step 4: Create precise characters. Use a developer to rinse the PCB board from step 3. The developer will retain the light-cured solder mask ink (i.e., the solder mask ink in the polymerization reaction area) and rinse away the un-light-cured solder mask ink (i.e., the solder mask ink that has not undergone polymerization reaction), leaving the precise characters on the solder mask layer on the outer surface of the PCB board.

[0034] Step 5: Curing the precision characters: Use a tunnel furnace to perform high-temperature curing on the outer surface of the PCB board (the outer surface refers to the upper and lower surfaces of the PCB board) with the precision characters produced in step 4, so as to achieve the purpose of producing fine characters on the PCB board.

[0035] The thickness of the solder resist layer in step 1 is not less than 15 μm.

[0036] Merging the character layer into the outer surface of the solder resist layer in step 2 means embedding the character layer into the outer surface of the solder resist layer in a fused manner, ensuring that the character layer is aligned with the outer surface of the solder resist layer and does not protrude from the outer surface of the solder resist layer.

[0037] In step 2, when the character layer intersects or overlaps the solder mask layer, the character pattern in the character layer must avoid or delete the portion that overlaps with the solder mask pads. The intersection or overlap process focuses on the solder mask pads. This produces highly accurate character positions and reduces the need to create a separate character layer after solder masking, saving production time.

[0038] The character width in the character layer in step 2 is 20-30 μm.

[0039] Before exposure in step 3, the energy uniformity must be tested to ensure that the exposure energy uniformity is not less than 90%. At the same time, the accuracy of the exposure machine must not exceed 15μm. The exposure energy is designed to be 700-900MJ based on the solder mask ink and 9-10 grids on the exposure ruler.

[0040] In the step 3, the ultraviolet light emitted by the LDI machine causes the solder resist ink (photosensitive material) to undergo a polymerization reaction (i.e., a curing reaction). Since the pads of the solder resist layer are large, the light will directly penetrate into the bottom layer of the solder resist ink during exposure. The character width is designed to be only 20-30 μm, which cannot completely block the light on the exposure line. During exposure, the light will penetrate from the side of the character to the bottom, and photocuring the solder resist ink below it, obtaining a photocured PCB board (such as Figure 3 ).

[0041] In step 4, the concentration of the developer is controlled to be between 0.8% and 1.2%.

[0042] The resistance ink that is not photocured in the step four includes the resistance ink that is not exposed to light on the surface of the solder mask layer and the resistance ink that is blocked by the character layer inside the solder mask layer. The resistance ink that is photocured includes the resistance ink that is exposed to light on the surface of the solder mask layer and the resistance ink that is not blocked by the character layer inside the solder mask layer.

[0043] Because the character layer is embedded in the surface of the solder mask layer, and the width of the characters in the character layer is only 20-30μm, the solder mask ink near the characters on the outer surface of the solder mask layer and the solder mask ink below the characters in the solder mask layer (not in contact with the surface of the character layer) are all exposed to light and penetrated and produce a polymerization reaction - that is, they are photocured. Since the character layer is embedded in the outer surface of the solder mask layer by means of fusion, the character layer can only block the solder mask ink in contact with its surface. In other words, the part of the solder mask layer in contact with the surface of the character layer will not be photocured, and the character layer and the solder mask ink in contact with its surface are both in an un-photocured state. When the developer rinses the surface of the PCB board, the character layer and the solder mask ink in contact with the surface of the character layer are washed away, while the solder mask ink below the character layer that is not in contact with its surface (due to being photocured) remains on the PCB board (such as Figure 3 ), thereby achieving the technical effect of retaining precise characters on the outer surface of the PCB board.

[0044] The temperature of the high temperature curing in the step 5 is 155° C.±5° C., and the time of the high temperature curing is 75±3 minutes.

[0045] Example 1

[0046] A smartphone motherboard PCB needs to be within 1mm 2 Ten 0402 package components are mounted in the area, and the characters need to be printed within the gaps between the pads (50 μm spacing). The traditional character width of 100 μm will cause the pads to be covered. The technical solution of the present invention can achieve fine character production. The specific process is as follows:

[0047] 1. Screen printing of solder mask ink;

[0048] Use a screen printer to apply solder resist ink on the PCB surface, controlling the thickness to 18μm (≥15μm).

[0049] 2. Merge the characters with the solder mask layer;

[0050] In the GERBER file, merge the character layer with the solder mask layer, adjust the character width to 25μm, and avoid the pad area (spacing 50μm).

[0051] 3. LDI exposure

[0052] Laser direct imaging (LDI) equipment was used, with an exposure energy of 850 MJ, an exposure scale of 9.5 grids, a tested energy uniformity of 92%, and an exposure machine accuracy of 12 μm.

[0053] 4. Development and graphic transfer

[0054] Use 1.0% sodium carbonate developer for 60 seconds to remove uncured ink and retain the character area.

[0055] 5. High temperature curing

[0056] The tunnel oven was set at 155°C for 75 minutes to allow the ink to fully cure.

[0057] In the application of this embodiment:

[0058] The method proposed in the present invention can maintain the measured character width at 28μm (in line with the 20-30μm requirement) and the height at 15μm (≤ ink thickness), reducing the defective rate (cold solder joints / fall-off) of traditional process patches from 5% to 0.8%. In the tape peeling test according to the IPC-TM-650 standard, no characters fell off. At the same time, the individual character silk-screen printing process is reduced, shortening the production cycle by 20%.

[0059] This embodiment successfully achieved fine character production through the integration of solder mask characters and LDI exposure technology, solving the problems of covering pads and lifting components in traditional processes. Verification data shows that the technical effect is significant and meets the "significant progress" requirement of invention patents.

[0060] The above technical solutions only reflect the preferred technical solutions of the technical solutions of the present invention. Any changes that may be made to certain parts thereof by those skilled in the art all reflect the principles of the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for producing fine characters, characterized in that: The method comprises the following steps: Step 1: Adjust the solder mask parameters, print solder mask ink on the outer surface of the PCB board to form a solder mask layer, and adjust the thickness of the solder mask layer; Step 2: character design, merge the selected character layer into the outer surface of the solder mask layer; Step 3: Exposure treatment: Use LDI exposure technology to expose the PCB board and cause the solder mask ink near the character layer to undergo polymerization reaction to obtain a light-cured PCB board; Step 4: Make precise characters. Use developer to rinse the photocured PCB board, retain the photocured solder resist ink, rinse away the un-photocured solder resist ink, and retain the precise characters on the outer surface of the PCB board. Step 5: Curing the precision characters: Use a tunnel furnace to perform high-temperature curing on the outer surface of the PCB board that retains the precision characters, completing the process of making fine characters on the PCB board.

2. The method for producing fine characters according to claim 1, wherein: The thickness of the solder resist layer in step 1 is not less than 15 μm.

3. The method for producing fine characters according to claim 1, wherein: Merging the character layer into the outer surface of the solder resist layer in step 2 means embedding the character layer into the outer surface of the solder resist layer in a fused manner, ensuring that the character layer is aligned with the outer surface of the solder resist layer and does not protrude from the outer surface of the solder resist layer.

4. The method for producing fine characters according to claim 3, wherein: When the character layer intersects or covers the solder mask layer in the step 2, the character graphics in the character layer need to avoid / delete the part overlapping with the solder mask layer pad.

5. The method for producing fine characters according to claim 4, characterized in that: The character width in the character layer in step 2 is 20-30 μm.

6. The method for producing fine characters according to claim 1, characterized in that: The uniformity of the exposure energy in step 3 is not less than 90%, and the accuracy of the exposure machine cannot exceed 15 μm.

7. The method for producing fine characters according to claim 6, characterized in that: The PCB board that is photocured in step 3 refers to a PCB board structure formed after all the solder resist ink near the character layer and not in contact with the character layer is photocured.

8. The method for producing fine characters according to claim 1, wherein: In step 4, the concentration of the developer is controlled to be between 0.8% and 1.2%.

9. The method for producing fine characters according to claim 8, characterized in that: The resistance ink that is not photocured in the step 4 includes the resistance ink that is not exposed to light on the surface of the solder mask layer and the resistance ink that is blocked by the character layer inside the solder mask layer. The resistance ink that is photocured includes the resistance ink that is exposed to light on the surface of the solder mask layer and the resistance ink that is not blocked by the characters inside the solder mask layer.

10. The method for producing fine characters according to claim 1, characterized in that: The temperature of the high temperature curing in the step 5 is 155° C.±5° C., and the time of the high temperature curing is 75±3 minutes.

Images