Exposure method for solder resist ink

Abstract

A method for exposing solder mask ink involves projecting a pattern from a spatial light modulator on an exposure lens through an imaging lens onto a substrate. The exposure lens and substrate move relative to each other in a scanning direction, creating a stripe-like pattern. Adjacent imaging areas in a direction perpendicular to the scanning direction overlap or have gaps between them. This method effectively addresses the issue of noticeable splicing marks.

Description

Technical Field

[0001] The present invention relates to an exposure method for solder resist ink, in particular to an exposure method for improving splicing marks of solder resist ink. Background Art

[0002] Exposure technology is widely used in the fields of semiconductor and PCB production. It is one of the process steps in manufacturing products such as semiconductor devices, chips and PCB boards. It is used to print characteristic patterns on the surface of the substrate, and finally obtain the pattern structure required by the circuit design. Traditional exposure technology requires the production of a master mask or film negative for exposure operation. The production cycle is long, and each plate corresponds to a single pattern, which cannot be widely used. In order to solve the problems of traditional exposure technology, direct writing exposure mechanism came into being. It uses digital light processing technology and a programmable digital mirror device to edit different required graphic structures. It can quickly switch graphics, which can not only reduce costs, but also reduce process time. It is being widely used in the field of exposure technology.

[0003] The principle of direct-write exposure is to transfer the design image to the surface of a substrate coated with a photosensitive material by exposure, and then finally obtain the desired graphic structure through processes such as development and etching. Photosensitive material is one of the key materials in the exposure process. Commonly used photosensitive materials include photoresist, solder mask ink, wet film, dry film and other materials. After being exposed to light, it forms soluble or insoluble substances relative to certain solvents. The photoresist is removed or retained by etching to form the desired graphic structure. Solder mask ink is coated on the printed circuit board to cover the electronic circuit and copper surface to prevent short circuits during welding and to protect the circuit board. The direct-write exposure mechanism used to process solder mask ink on the circuit board usually includes multiple exposure lenses, which complete the exposure of the entire area of ​​the circuit board by splicing strips between lenses or splicing adjacent strips of adjacent lenses. During production, it was found that the solder mask ink would whiten at the splicing of adjacent strips, and the splicing marks were obvious, affecting the overall exposure effect. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an exposure method for improving the splicing marks of solder mask ink.

[0005] In order to solve the above problems, the present invention provides an exposure method for solder mask ink, in which the projection pattern area of ​​the spatial light modulation element of the exposure lens forms an imaging area on the substrate through the imaging lens, and the exposure lens and the substrate move relative to each other in the scanning direction. The imaging area forms a strip in the scanning direction, and the adjacent imaging areas in the direction perpendicular to the scanning direction overlap or have a gap.

[0006] Furthermore, the overlapping or spacing of the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by adjusting the length of the projection graphic area of ​​the spatial light modulation element in the direction perpendicular to the scanning direction.

[0007] Furthermore, the overlapping or gapped imaging areas adjacent to each other in the direction perpendicular to the scanning direction are achieved by increasing the length in the direction perpendicular to the scanning direction based on the projection graphic area corresponding to the fully joined adjacent imaging areas.

[0008] Furthermore, the overlapping or gapped imaging areas adjacent to each other in the vertical direction to the scanning direction is achieved by reducing the length in the vertical direction to the scanning direction based on the projection graphic area corresponding to the fully joined adjacent imaging areas.

[0009] Furthermore, the overlapping of the imaging areas adjacent to each other in the perpendicular scanning direction is achieved by adding at least one column of pixels on both sides perpendicular to the scanning direction based on the projection graphic area corresponding to when the imaging areas adjacent to each other in the perpendicular scanning direction are fully joined.

[0010] Furthermore, the spacing between the adjacent imaging areas perpendicular to the scanning direction is achieved by reducing at least one column of pixels on both sides perpendicular to the scanning direction based on the projection graphic area corresponding to when the adjacent imaging areas perpendicular to the scanning direction are fully joined.

[0011] Furthermore, the overlapping of the imaging areas adjacent to each other in the vertical direction to the scanning direction is achieved by reducing the distance between the exposure lenses in the vertical direction to the scanning direction.

[0012] Furthermore, the spacing between the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by increasing the distance between the exposure lenses in the direction perpendicular to the scanning direction.

[0013] Furthermore, the distance of overlap or spacing of the imaging areas corresponding to the adjacent strips in the perpendicular scanning direction is adjusted by adjusting the length of the projection graphic area in the perpendicular scanning direction, detecting the exposure scale energy grid of a single exposure and the exposure scale energy grid of two separate exposures, wherein the light source energy of the single exposure is twice the light source energy of the two exposures, and obtaining the length of the projection graphic area when the exposure scale energy grids are the same.

[0014] Compared with the existing technology, the problem of obvious splicing marks is effectively solved by adjusting the splicing width between adjacent strips. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of a spatial light modulation element.

[0016] Figure 2This is a schematic diagram of exposure using a single-row exposure lens.

[0017] Figure 3 This is a schematic diagram of exposure using a double-row exposure lens.

[0018] Figure 4 It is a schematic diagram of the graphic area projected by the spatial light modulation element.

[0019] Figure 5 It is a schematic diagram of the projection graphic area and the corresponding imaging area.

[0020] Figure 6 It is a schematic diagram of the structure of the exposure lens.

[0021] Figure 7 FIG. 1 is a schematic diagram of a projection pattern area of ​​a spatial light modulation element according to an embodiment.

[0022] Figure 8 This is a schematic diagram of splicing adjacent strips in one embodiment.

[0023] Figure 9 Schematic diagram of an imaging area according to an embodiment.

[0024] Figure 10 FIG. 1 is a schematic diagram of a projection pattern area of ​​a spatial light modulation element according to another embodiment.

[0025] Figure 11 This is a schematic diagram of splicing adjacent strips in another embodiment. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described below with reference to specific embodiments shown in the accompanying drawings.

[0027] Figure 1 The figure shows a spatial light modulator 10 in an exposure lens used for solder mask ink exposure. The spatial light modulator 1 can be a device capable of spatially adjusting the light projection position, such as a digital micromirror device (DMD), a liquid crystal display, or a grating light valve (GLV). The spatial light modulator 1 includes a plurality of pixels 100 arranged in an array, each independently controlled. By controlling the pixels 100 of the spatial light modulator 10, light from a light source is projected onto the substrate according to the projected image. To achieve smooth exposure lines, higher resolution, and increased exposure area, an oblique scanning method is often used to project the exposure pattern. This means that the spatial light modulator 10 has a certain tilt angle relative to the scanning direction of the substrate.

[0028] like Figure 2As shown, in practical applications, an exposure system typically employs multiple exposure lenses 1 to simultaneously expose a substrate 2. The exposure lenses 1 are arranged perpendicular to the scanning direction. Each movement of the exposure lenses 1 along the scanning direction forms a stripe 20. After exposing a stripe, the exposure lenses 1 and substrate 2 are required to move relative to each other by a distance of one stripe, allowing the exposure lens 1 to splice the next stripe 20 in the unexposed area of ​​the substrate 2. In this example, the substrate 2 is moved leftward perpendicular to the scanning direction by a distance of one stripe, and the exposure lens 1 completes the exposure of the next stripe. Two adjacent strips 20 are then spliced ​​together, completing the exposure of the area to be exposed. The splicing of two adjacent strips 20 requires not only splicing strips 20 between different exposure lenses 1, but also splicing strips 20 formed by the same lens 1. Of course, the relative movement of the exposure lenses 1 and substrate 2 can also be achieved by moving the exposure lens 1 while the substrate 2 remains stationary.

[0029] like Figure 3 As shown, to enable complete exposure of the entire area with a single scan direction movement, the exposure lenses 1 may be arranged in at least two rows in the scan direction, so that the projection area of ​​the exposure lenses 1 can simultaneously cover an area perpendicular to the scan direction. The exposure strips 20 of the first row of exposure lenses 3 and the second row of exposure lenses 4, which are adjacent in the perpendicular scan direction, are spliced ​​together to complete exposure of the substrate 2.

[0030] like Figure 4-5 As shown, a certain area of ​​pixels 100 in the spatial light modulator 10 is selected as the projected pattern area 110. The projected pattern area 110 is typically rectangular. Because the spatial light modulator 10 is tilted relative to the scanning direction, the projected pattern area 110 is divided along the scanning direction to form triangular areas 120 at both ends. The images of the triangular areas 120 of adjacent projected pattern areas 110 on the substrate form a spliced ​​area 220 of adjacent strips. The imaged areas 210 formed by the projected pattern area 110 on the substrate are transformed into strips 20 along the scanning direction by the relative motion of the exposure lens 1 and the substrate 2. The projected pattern areas 110 corresponding to adjacent strips 20 are completely aligned on the substrate's imaged area 210, achieving a smooth transition between adjacent strips. When exposing solder mask ink, it was found that the exposure effect of the spliced ​​area 220 of adjacent strips was significantly different from that of other areas, with obvious splicing marks.

[0031] Analysis of the substrate exposure process reveals that the spatial light modulation element 10 stitches adjacent triangular stitching regions to form adjacent stripe stitching regions. The number of pixels contained in these adjacent stripe stitching regions is the same as the number of pixels contained in other regions of the same width, excluding the triangular stitching regions. The width is perpendicular to the scanning direction. Using the same light source with the same light intensity, all regions receive the same total light energy.

[0032] In terms of timing, during the substrate exposure process, all areas except the triangular stitching area are exposed at once. The triangular stitching area is first exposed by one exposure lens and then by the other exposure lens, or is exposed twice in succession by the same exposure lens. The triangular stitching area is exposed twice at different times to complete the exposure of the adjacent strip stitching area.

[0033] The experiment was conducted by using different doses of light to expose the substrate and using the exposure scale energy grid to display the effect. When using a specific solder mask ink for the experiment, the substrate was exposed using the Mmj light source, and the exposure scale energy grid result was 9 grids, respectively. When the substrate is exposed to the light source of Mmj, the energy grid of the exposure scale is only 8 grids, which shows that the curing effect of the ink is reduced. When another solder resist ink is used for experiment, the substrate is exposed to the light source of Nmj, and the energy grid of the exposure scale is 9 grids. The Nmj light source exposed the substrate, achieving a higher exposure energy scale. Different solder mask inks have different photosensitive properties, resulting in completely opposite results in the two experiments. However, both experimental results demonstrate that achieving sufficient light energy through superposition cannot achieve the same exposure effect as direct exposure.

[0034] In order to achieve the same exposure effect at the strip joints as other areas and improve and eliminate the splicing marks, the splicing method of adjacent strips is changed. By increasing the splicing area between adjacent strips, the total light energy received by the splicing area is adjusted.

[0035] like Figure 6 As shown, the exposure lens 5 includes a spatial light modulator 50 and an imaging lens 51. The light beam of the spatial light modulator 50 projects a pattern and forms an image on the substrate through the imaging lens 51. The spatial light modulator 50 selects some pixels to form a projection pattern area 510. The pattern of the projection pattern area 510 forms an imaging area 520 on the substrate through the imaging lens 51.

[0036] For the case where the energy of light sources is superimposed and the energy grid of the exposure scale is reduced, the total light energy received in the splicing area is increased. Figure 7-9As shown, with the lens position unchanged, the length of the projected pattern area of ​​the spatial light modulator is increased in the direction perpendicular to the scanning direction. Preferably, the length of the projected pattern area of ​​the spatial light modulator is increased at both ends of the direction perpendicular to the scanning direction. The projected pattern areas 610 of the spatial light modulators corresponding to adjacent strips partially overlap in the horizontal direction of the imaging area 620 formed on the substrate; the projected pattern areas of the spatial light modulators corresponding to adjacent strips form a trapezoidal splicing area 630 in the scanning direction.

[0037] Specifically, the spatial light modulation element selects W rows of pixels in the scanning direction and selects L columns of pixels in the horizontal direction perpendicular to the scanning direction. When the pixel area is the projection pattern area of ​​the spatial light modulation element, the projection pattern area of ​​the spatial light modulation element can be joined with the imaging area formed on the substrate through the imaging lens. Figure 7 As shown, for solder mask ink whose exposure performance is weakened after the light source energy is superimposed, the projection imaging area of ​​the spatial light modulation element selects L+S columns of pixels in the lateral direction perpendicular to the scanning direction, where S is greater than or equal to 1. Preferably, the S columns of pixels are arranged on both sides of the L column of pixels, that is, The pixels in column S are located to the left of the pixels in column L. The pixels in the S column are located to the right of the pixels in the L column.

[0038] For the case where the energy of light sources is superimposed and the energy grid of the exposure scale is increased, the total light energy received in the splicing area is reduced. Figure 10-11 As shown, with the lens position unchanged, the length of the projection pattern area of ​​the spatial light modulator is reduced in the direction perpendicular to the scanning direction. Preferably, the length of the projection pattern area of ​​the spatial light modulator is reduced at both ends perpendicular to the scanning direction. The projection pattern areas 710 of the spatial light modulators corresponding to adjacent strips are spaced apart in the lateral direction from the imaging area 720 on the substrate. The projection pattern areas of the spatial light modulators corresponding to adjacent strips form a splicing area 730 in the scanning direction.

[0039] Specifically, the spatial light modulation element selects W rows of pixels in the scanning direction and selects L columns of pixels in the horizontal direction perpendicular to the scanning direction. The pixel area is the projection pattern area of ​​the spatial light modulation element. In this case, the projection pattern area of ​​the spatial light modulation element can be joined with the imaging area formed on the substrate by the imaging lens. For solder mask ink with enhanced exposure performance after light energy superposition, the projection imaging area of ​​the spatial light modulation element is selected in LT columns in the horizontal direction perpendicular to the scanning direction, and T is greater than or equal to 1. Preferably, as Figure 10 As shown, the reduced T-column pixels are arranged on both sides of the L-column pixels, that is, The pixels in column T are located to the left of the pixels in column L. The pixels in the T column are located to the right of the pixels in the L column.

[0040] The widths of the stitching regions 730 and 630 in a direction perpendicular to the scanning direction are both greater than the stitching region 220 .

[0041] In the above embodiment, the splicing width of adjacent strips is adjusted by adjusting the projection pattern area of ​​the spatial light modulation element. While the projection pattern area remains unchanged, the splicing width of adjacent strips can be achieved by adjusting the lateral distance between the lenses. Alternatively, both the width of the projection pattern area and the lateral distance between the exposure lenses can be adjusted simultaneously. If the energy of the light sources overlaps and the energy scale of the exposure scale decreases, the lateral distance between the lenses is reduced. If the energy of the light sources overlaps and the energy scale of the exposure scale increases, the lateral distance between the lenses is increased.

[0042] Adjusting the horizontal overlap or spacing of the projected pattern areas of the spatial light modulators corresponding to adjacent strips can be accomplished by experimentally determining the values ​​of S or T. The energy grids of the exposure scale for a single exposure and the energy grids of the exposure scale for two exposures are measured, and the corresponding values ​​of S or T are determined when the energy grids are the same. The horizontal overlap or spacing of the projected pattern areas of the spatial light modulators corresponding to adjacent strips can be determined. The light source energy for the single exposure is twice that of the light source for the two exposures.

[0043] By adjusting the splicing width between adjacent strips, the problem of obvious splicing marks can be effectively solved.

Claims

1. A method for exposing solder mask ink, characterized in that: The projection pattern area of ​​the spatial light modulation element of the exposure lens forms an imaging area on the substrate through the imaging lens. The spatial light modulation element is arranged obliquely relative to the scanning direction. When the projection pattern area is divided along the scanning direction, triangular splicing areas are formed at both ends. The exposure lens and the substrate move relative to each other in the scanning direction, and the imaging area forms a strip in the scanning direction. For solder mask ink whose exposure performance is weakened after the light source energy is superimposed, the adjacent imaging areas perpendicular to the scanning direction overlap; for solder mask ink whose exposure performance is enhanced after the light source energy is superimposed, the adjacent imaging areas perpendicular to the scanning direction are separated.

2. The exposure method of solder mask ink according to claim 1, wherein: The overlapping or spacing of the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by adjusting the length of the projection graphic area of ​​the spatial light modulation element in the direction perpendicular to the scanning direction.

3. The exposure method of solder mask ink according to claim 1, wherein: The overlapping or spacing of the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by increasing the length in the direction perpendicular to the scanning direction based on the corresponding projection graphic area when the adjacent imaging areas are fully joined.

4. The exposure method of solder mask ink according to claim 1, wherein: The overlapping or spacing of the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by reducing the length in the direction perpendicular to the scanning direction based on the corresponding projection graphic area when the adjacent imaging areas are fully joined.

5. The exposure method of solder resist ink according to claim 1, wherein: The overlapping of the imaging areas adjacent to each other in the perpendicular scanning direction is achieved by adding at least one column of pixels on both sides perpendicular to the scanning direction based on the projection graphic area corresponding to when the imaging areas adjacent to each other in the perpendicular scanning direction are fully joined.

6. The exposure method of solder resist ink according to claim 1, wherein: The spacing between the adjacent imaging areas perpendicular to the scanning direction is achieved by reducing at least one column of pixels on both sides perpendicular to the scanning direction based on the projection graphic area corresponding to when the adjacent imaging areas perpendicular to the scanning direction are fully joined.

7. The exposure method of solder resist ink according to claim 1, wherein: The overlapping of the imaging areas adjacent to each other in the vertical direction to the scanning direction is achieved by reducing the distance between the exposure lenses in the vertical direction to the scanning direction.

8. The exposure method of solder resist ink according to claim 1, wherein: The spacing between the adjacent imaging areas in the direction perpendicular to the scanning direction is achieved by increasing the distance between the exposure lenses in the direction perpendicular to the scanning direction.

9. The exposure method of solder resist ink according to claim 1, wherein: The overlapping or spaced distances of the imaging areas corresponding to adjacent strips in the perpendicular scanning direction are determined by adjusting the length of the projection graphic area in the perpendicular scanning direction, detecting the exposure scale energy grid of a single exposure and the exposure scale energy grid of two separate exposures, wherein the light source energy of the single exposure is twice the light source energy of the two separate exposures, and obtaining the length of the projection graphic area when the exposure scale energy grids are the same.

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