Exposure method of photopolymer
By combining low-power UV light sources and high-power mercury lamps for exposure, the yield problem of patterning photopolymer layers with photomasks and the difficulty of UV light sources curing thick photopolymer layers were solved, thus achieving efficient patterning of photopolymer layers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- 李蕙如
- Filing Date
- 2022-09-07
- Publication Date
- 2026-06-16
AI Technical Summary
In existing technologies, the use of photomasks leads to a decrease in the yield of patterning the photopolymer layer, and DMD combined with a UV light source is difficult to completely cure the thick photopolymer layer, resulting in an inward rotation problem during development.
After the first exposure using a low-power UV light source, a photomask is covered, followed by a second exposure using a high-power mercury lamp. The exposure range is controlled by a digital micromirror device to avoid direct contact between the photomask and the photopolymer layer and to prevent particle contamination, thus ensuring complete curing of the photopolymer layer.
It improves the patterning yield of photopolymerization layers, especially the curing effect of thicker photopolymerization layers, reduces the inward rotation problem during the development process, and provides a cost-effective photolithography solution.
Smart Images
Figure CN117111410B_ABST
Abstract
Description
Technical Field
[0001] This application relates to a patterned process for a photopolymerization layer in a printed circuit board, and more particularly to a process for improving the yield of the photopolymerization process by providing different light sources. Background Technology
[0002] Printed circuit boards typically have multiple layers of insulating materials and multiple layers of circuitry. Some of the insulating materials and photoresist layers used to pattern copper foil into circuits may be made of photopolymer materials (existing in the form of photopolymer layers). These photopolymer layers can be patterned by exposure and development.
[0003] Traditionally, photopolymer layers are patterned by covering them with a photomask and then exposing them. However, because the photopolymer layer is in an uncured or semi-cured state before exposure, after repeated use of the photomask, environmental particles may adhere to the areas that should be exposed. This can cause these areas to be blocked by particles and not receive light, resulting in many unnecessary small holes in the photopolymer layer during subsequent development. Furthermore, the photomask itself may also damage the photopolymer layer during the process of covering it. In other words, a long-standing problem with existing technology is that, for the reasons mentioned above, the use of the photomask negatively impacts the yield of the patterning process.
[0004] On the other hand, maskless lithography is gradually becoming the current trend for improvement. This involves using a digital micromirror device (DMD) with a UV light source for direct imaging (DI), allowing the exposure range to be controlled via the DMD without a photomask, thus patterning the photopolymerization layer. However, this DMD-UV light source combination has significant drawbacks. Because the DMD cannot withstand excessively high energy (otherwise it might exceed the load on its heat sink), the UV light source power cannot be too high. To provide the energy required for photopolymerization, the UV light source must supply energy to the photopolymerization layer at low power and high frequency. However, if the photopolymerization layer is thick (e.g., a solder resist layer), or even if the photopolymerization layer is colored (with low transmittance), the low-power UV light will struggle to reach the bottom of the photopolymerization layer, resulting in insufficient curing at the bottom. This leads to severe overcutting at the development and windowing edges during subsequent development and windowing processes.
[0005] Therefore, how to solve or at least mitigate all of the above problems is a question that deserves consideration by those in the field. Summary of the Invention
[0006] The technical problem to be solved by this application is to provide a process that can solve the problem that the aforementioned photomask can adversely affect the yield of patterning processing, while also being able to be used to process large-thickness photopolymerization layers.
[0007] To achieve the above objectives, this application provides a method for exposing a photopolymer, comprising:
[0008] A printed circuit board with a photopolymer layer on its top surface is provided;
[0009] The photopolymer layer is first exposed using a UV light source through a digital micromirror device. The energy provided by the UV light source during the first exposure is less than the exposure energy required for the complete curing of the photopolymer layer, and the power of the UV light source is less than 0.2kW.
[0010] Stop the first exposure;
[0011] A photomask is placed on the photopolymerization layer, with one bottom surface of the photomask contacting the photopolymerization layer;
[0012] The photopolymer layer is exposed a second time through the photomask using a mercury lamp. The energy provided by the mercury lamp during the second exposure is not less than the exposure energy required for the complete curing of the photopolymer layer minus the energy supplied during the first exposure, and the power of the mercury lamp is greater than 5kW.
[0013] The inventors discovered that when using a low-power UV light source for the first exposure, the photopolymer layer exhibits a characteristic of curing from the top down. Simultaneously, the digital micromirror device does not need to contact the photopolymer layer, thus avoiding particle contamination and damage to the uncured / semi-cured photopolymer layer. Subsequently, during the second exposure with a mercury lamp, its high power is sufficient to completely cure even the bottom of a thicker photopolymer layer. Furthermore, since the top of the photopolymer layer is already cured from the first exposure before the second exposure, even if particles adhere to the area that should have been exposed for the second exposure, they will not form pinholes during subsequent development (the hardened top of the photopolymer layer provides protection), nor will they damage the already cured top of the photopolymer layer. This solves a long-standing problem associated with patterning using photomasks. Therefore, this application represents a superior photopolymer patterning process, particularly for processing generally thick solder resist layers, and offers a cost-effective alternative against the trend of photomask-less lithography.
[0014] The other effects and embodiments of this application are described in detail below with reference to the accompanying drawings. Attached Figure Description
[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is a schematic diagram of a first embodiment of an exposure device to which this application can be applied;
[0017] Figure 2 This is a side view schematic diagram of a first embodiment of an exposure device to which this application can be applied, wherein some components are omitted and not shown;
[0018] Figures 3 to 5 This is a schematic diagram of the workflow of a first embodiment of the exposure equipment to which this application is applicable;
[0019] Figure 6 This is a side view of a second embodiment of an exposure device to which this application is applicable, wherein some components are omitted and not shown.
[0020] Symbol Explanation
[0021] 1: Photopolymerization layer; 2: Printed circuit board; 10: Transfer platform
[0022] 20: Digital micromirror device; 30: UV light source; 40: Photomask
[0023] 50: Mercury lamp; S1: First working area; S2: Second working area
[0024] S3: Third Working Area Detailed Implementation
[0025] In the embodiments described below, the positional relationships include: up, down, left, and right. Unless otherwise specified, they are all based on the direction shown by the components in the diagram.
[0026] Please refer to Figure 1 , Figure 2This is a first embodiment of an exposure device applicable to this application, which can be used for the exposure polymerization of photopolymer layers on printed circuit boards for patterning. The printed circuit board can be a single-layer board structure or a multi-layer composite board structure, and can be a carrier board for flexible printed circuits (FPCs) or rigid printed circuit boards (PCBs). The material used can be, but is not limited to, polyethylene terephthalate (PET) or other polyester films, polyimide films, polyamide-imide films, polypropylene films, and polystyrene films. The photopolymer layer refers to a layered material formed by photopolymers, which polymerize and then solidify upon irradiation with light. Possible photopolymer layers include, for example, photoresist layers used for patterning copper foil or dielectric layers of printed circuit boards, such as opaque solder resist ink. The exposure device of this embodiment includes a first working area S1, a second working area S2, a third working area S3, a transfer platform 10, a digital micromirror device 20, a UV light source 30, a photomask 40, and a mercury lamp 50.
[0027] A transfer platform 10 is used to carry printed circuit boards 2 with a photopolymerization layer 1 on their top surface. The transfer platform 10 is preset in a first working area S1. When the transfer platform 10 is in the first working area S1, the printed circuit board 2 can be moved onto the transfer platform 10 manually or automatically. When the transfer platform 10 is working, the carried printed circuit board 2 can be moved from the second working area S2 to the third working area S3 using a screw mechanism or other displacement mechanism. In a possible implementation, after the photopolymerization layer 1 has completed exposure and polymerization, the transfer platform 10 will return to the first working area S1, and the printed circuit board 2 can then be removed from the transfer platform 10 manually or automatically.
[0028] The digital micromirror device 20 is located in the second working area S2. The digital micromirror device 20 has a number of micromirrors and uses control signals to control the flipping of each micromirror to become a fast digital light switch. It can control whether light can pass through the digital micromirror device 20, thereby having the function of performing patterned exposure and polymerization processing on the photopolymerization layer 1.
[0029] The UV light source 30 is also located in the second working area S2. It has multiple UV lamps that can excite the photopolymer to polymerize. When the power of the UV light source is high, it may damage the digital micromirror device 20. Therefore, the power of the UV light source is less than 0.2kW, or even less than 0.1kW. The UV light source 30 can expose the photopolymerization layer 1 for the first time through the digital micromirror device 20 during the process of the transfer platform 10 passing through the second working area S2.
[0030] The photomask 40 is used to cover and contact the photopolymerization layer 1 with its bottom surface when the transfer platform 10 moves to the third working area S3. The photomask 40 can be placed within a photomask frame and moved by automated equipment. In possible implementations, different photomasks 40 may be selected based on the expansion and contraction values of different printed circuit boards or for other considerations, and photomask replacement can be performed manually or by automated equipment.
[0031] A mercury lamp 50 is located in the third working area S3 to expose the photopolymerization layer 1 a second time through the photomask 40 after it has covered the photopolymerization layer 1. In this application, the power of the mercury lamp 50 is greater than 5kW to ensure that the bottom of the photopolymerization layer 1 is fully exposed.
[0032] The following describes the exposure method of the photopolymer of this application:
[0033] First, a printed circuit board 2 with a photopolymer layer 1 on its top surface is provided. The photopolymer layer 1 can be formed by directly coating the printed circuit board 2 with a photopolymer paste, or the photopolymer can be first made into a dry film and then laminated onto the top surface of the printed circuit board 2 to form the photopolymer layer 1. After the photopolymer layer 1 is formed, the printed circuit board 2 can be moved manually or by automated equipment to a transfer platform 10 located in the first working area S1, i.e. Figure 3 As shown;
[0034] Next, as Figure 4 As shown, the transfer platform 10 moves from the first working area S1 to the second working area S2, and then uses the UV light source 30 to expose the photopolymer layer 1 for the first time through the digital micromirror device 20. The energy provided by the UV light source 30 during the first exposure is less than the exposure energy required for the complete curing of the photopolymer layer 1. Preferably, the energy provided by the UV light source 30 during the first exposure is less than half of the exposure energy required for the complete curing of the photopolymer layer 1, so as to reduce the process time of the first exposure. After the first exposure, at least the top of the photopolymer layer can be cured.
[0035] Afterwards, the first exposure was stopped, and the transfer platform 10 continued to move towards the third working area S3;
[0036] Next, as Figure 5 As shown, a photomask 40 is covered on the photopolymerization layer 1, and the bottom surface of the photomask 40 contacts the photopolymerization layer 1. Since the top surface of the photopolymerization layer 1 has been cured after the first exposure, it will not be damaged by the photomask 40, and no particles of the photopolymerization layer 1 will stick to the photomask 40.
[0037] Finally, the photopolymer layer 1 is exposed a second time using a mercury lamp 50 through a photomask 40. The energy provided by the mercury lamp 50 during the second exposure is no less than the exposure energy required for complete curing of the photopolymer layer 1 minus the energy supplied during the first exposure. Furthermore, since the power of the mercury lamp 50 exceeds 5kW, even the photopolymer at the bottom of the photopolymer layer 1 can be completely cured (even the bottom of the photopolymer layer 1 with a maximum thickness of no less than 20μm), thus avoiding severe inward rotation problems during subsequent development and windowing of the photopolymer layer 1. In a possible implementation, after the second exposure, the printed circuit board 2 may also be removed from the third working area S3.
[0038] Additionally, please refer to Figure 6 This is a second embodiment of the exposure equipment. The difference between this embodiment and the first embodiment is that it has two transfer platforms 10. When one of the transfer platforms 10 moves in the second to third working areas, the other transfer platform can continue to move another printed circuit board in and out. The two platforms can alternately transport the printed circuit board in the first to third working areas.
[0039] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the technology of this application, and are not intended to limit the implementation methods of the technology of this application in any way. Any person skilled in the art may make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in this application, but these should still be regarded as the technology or embodiments that are substantially the same as those of this application.
Claims
1. A method for exposing a photopolymer, characterized in that, include: A printed circuit board with a photopolymer layer on its top surface is provided; The photopolymer layer is first exposed using a UV light source through a digital micromirror device. The energy provided by the UV light source during the first exposure is less than the exposure energy required for the complete curing of the photopolymer layer, and the power of the UV light source is less than 0.2kW. Stop the first exposure; A photomask is placed on the photopolymerization layer, with one bottom surface of the photomask contacting the photopolymerization layer; The photopolymer layer is exposed a second time through the photomask using a mercury lamp. The energy provided by the mercury lamp during the second exposure is not less than the exposure energy required for the complete curing of the photopolymer layer minus the energy supplied during the first exposure, and the power of the mercury lamp is greater than 5kW.
2. The exposure method for the photopolymer according to claim 1, characterized in that, The UV light source provides less than half the exposure energy required for the complete curing of the photopolymer layer during the first exposure.
3. The exposure method for the photopolymer according to claim 1, characterized in that, The power of this UV light source is less than 0.1kW.
4. The exposure method for the photopolymer according to claim 1, characterized in that, The maximum thickness of the photopolymerization layer is not less than 20 μm.
5. The exposure method for the photopolymer according to any one of claims 1 to 4, characterized in that, The photopolymer layer is an opaque solder resist ink.