Heat-resistant resistance welding paper, method of manufacturing and circuit board

Abstract

The application relates to the technical field of printed circuit board manufacturing, in particular to a heat-resistant solder resist paper, a preparation method and a circuit board. The heat-resistant solder resist paper comprises a substrate layer and a solder resist layer, the solder resist layer is arranged on the substrate layer, the substrate layer provides an attaching surface for the solder resist layer, the solder resist layer prevents solder from flowing in an area that should not be welded, the surface of the solder resist layer is provided with solder resist protrusions, the solder resist protrusions form a grid, and the solder resist protrusions and the solder resist layer are made of the same material; in application, the solder resist protrusions are fixed on a substrate. In the application, the solder resist protrusions slow down the pulling force of the solder resist paper on the substrate during thermal expansion; in addition, the solder resist protrusions also slow down the transmission of heat generated by drilling on the solder resist layer. The effects of the two aspects make the solder resist paper more heat-resistant, the substrate provided with the solder resist paper of the application can withstand a higher drilling speed, the drilling efficiency is improved, and the application has a good application prospect in the field of printed circuit board manufacturing.

Description

Technical Field

[0001] This application relates to the field of printed circuit board manufacturing technology, specifically to a heat-resistant solder resist paper, its preparation method, and a circuit board. Background Technology

[0002] Solder mask is a material used in the manufacturing process of printed circuit boards (PCBs). Its main components are the substrate layer and the solder mask layer. Solder mask controls the flow of solder, ensuring that solder is only used in the designed soldering areas, reducing the risk of short circuits. Secondly, solder mask provides mechanical protection to the surface of the circuit board, preventing physical damage, scratches, or impacts. Simultaneously, solder mask has a certain degree of chemical resistance, preventing the circuit board from being corroded by chemicals and improving its durability. Solder mask also protects the circuit board from environmental dust, moisture, and contaminants, improving its stability and reliability.

[0003] Compared to solder resist ink, solder resist paper has a more precise manufacturing process, allowing for precise control of the solder pad layer and ensuring that solder exists only in the designed soldering areas. This reduces the risk of short circuits, and this precision contributes to improved circuit board reliability. Furthermore, the relatively consistent manufacturing process of solder resist paper ensures product consistency in mass production, which is crucial for mass-producing circuit boards. Therefore, solder resist paper is widely used in the mass production of circuit boards.

[0004] After solder mask is applied to the substrate, drilling is typically performed, i.e., through-hole drilling is carried out at predetermined locations on the circuit board using equipment such as CNC drilling machines. Through-holes are used to connect electrical connections between different layers on the circuit board, and are typically used for connections that traverse the entire circuit board. Drilling, especially when using high-speed and high-temperature drill bits, generates a significant amount of heat. Solder mask has a high coefficient of thermal expansion; for example, polyimide, commonly used as a solder mask material, has a coefficient of thermal expansion of 20-60 ppm / ℃. The substrate has a low coefficient of thermal expansion; for example, glass fiber reinforced epoxy resin substrates, commonly used as substrate materials, have a coefficient of thermal expansion of 15-20 ppm / ℃. Because the coefficient of thermal expansion of the solder mask is greater than that of the substrate, the solder mask and the substrate expand or contract at different rates when the temperature changes. This mismatch leads to stress accumulation and deformation, increasing the mechanical stress on the circuit board. Furthermore, the thermal expansion mismatch also causes stress concentration in the pad areas, especially under conditions of large temperature changes. This can lead to cracks and eventual breakage of the pads, affecting the reliability and lifespan of the circuit board.

[0005] Therefore, it is of great significance to develop heat-resistant solder resist paper, reduce the difference between the thermal expansion coefficient of the solder resist paper and the thermal expansion coefficient of the substrate, and reduce the tensile force of the solder resist paper on the substrate during drilling. Summary of the Invention

[0006] To address the above problems, this invention provides a heat-resistant solder resist paper, comprising a substrate layer and a solder resist layer. The solder resist layer is placed on the substrate layer, and the substrate layer provides an adhesion surface for the solder resist layer. The solder resist layer prevents solder from flowing in areas where soldering is not permitted. The surface of the solder resist layer is provided with solder resist protrusions forming a grid. The solder resist protrusions and the solder resist layer are made of the same material. In application, the solder resist protrusions are fixed to a substrate.

[0007] Furthermore, the substrate layer can be made of polyimide film or pulp. Polyimide film exhibits excellent high-temperature stability, maintaining mechanical strength and insulation properties at high temperatures, making it suitable for some high-temperature electronic applications. Additionally, polyimide film possesses good mechanical strength and flexibility, giving the solder mask good adaptability in bending or flexing applications. Pulp is a relatively economical choice for the substrate layer, with lower costs, making it suitable for some cost-sensitive applications. Furthermore, pulp is a natural fiber material with good environmental friendliness, and its preparation process is more environmentally friendly compared to some synthetic materials. Moreover, pulp substrate layers are generally more flexible, making them suitable for applications requiring high flexibility, such as bending circuit boards. In this invention, both polyimide film and pulp can be used as substrate layer materials, and the choice can be made based on the specific application.

[0008] Furthermore, the substrate layer thickness is greater than 50 micrometers and less than 500 micrometers. The specific design of the substrate layer thickness depends on the application requirements, mechanical strength requirements, and manufacturing process considerations of the circuit board. A thicker substrate layer provides better mechanical strength, making the circuit board more robust. A thinner substrate layer offers greater flexibility and is suitable for applications requiring flexible circuit board bending performance, such as flexible electronics or bent circuit boards. To reduce the impact of thermal expansion of the substrate layer on the circuit board, the substrate layer thickness is preferably less than 500 micrometers.

[0009] Furthermore, the solder mask material includes polyimide resin, a hardener, and pigments. Polyimide resin is one of the main components of the solder mask. It possesses properties such as high-temperature stability, electrical insulation, and chemical resistance, forming a robust protective film within the solder mask to cover the pads on the circuit board. The hardener reacts chemically with the polyimide resin, causing it to cure and form a robust structure. The hardener also improves the heat resistance and mechanical strength of the solder mask, enabling it to maintain stability at high temperatures. Pigments are used to adjust the color of the solder mask layer, allowing different areas to be distinguished on the circuit board.

[0010] Furthermore, the solder mask thickness is greater than 40 micrometers and less than 120 micrometers. The solder mask design ensures sufficient coverage of the pads to prevent incorrect soldering. This thickness design also gives the solder mask a degree of transparency, facilitating optical inspection or pad detection using optical methods.

[0011] Furthermore, the width of the solder resist bumps is greater than 5 micrometers and less than 50 micrometers. Even further, the height of the solder resist bumps is greater than 20 micrometers and less than 100 micrometers. Cavities are formed between the solder resist bumps, which improve the solder resist paper's tolerance to thermal expansion and contraction during temperature changes.

[0012] On the other hand, the present invention provides a method for preparing heat-resistant solder resist paper, comprising the following steps:

[0013] Step 1: Prepare the substrate layer;

[0014] Step 2: Apply a solder resist layer onto the substrate layer;

[0015] Step 3: Apply rollers with a grooved array to press and pre-heat-cur the solder resist layer to form solder resist protrusions;

[0016] Step 4: Re-cur the solder mask layer and solder mask bumps.

[0017] Furthermore, in step 3, the initial thermosetting temperature is greater than 80°C.

[0018] In another aspect, the present invention provides a circuit board comprising the aforementioned heat-resistant solder resist paper.

[0019] The beneficial effects of this invention are as follows: This invention provides solder resist protrusions on the solder resist layer in a grid pattern. On one hand, these protrusions reduce the tensile force of the solder resist paper on the substrate during thermal expansion. On the other hand, they slow down the transfer of heat generated during drilling onto the solder resist paper, reducing heat transfer to other parts of the solder resist paper and further reducing the tensile force. Both of these effects make the solder resist paper more heat-resistant, allowing the substrate with the solder resist paper of this invention to withstand higher drilling speeds. While ensuring circuit board quality, this improves drilling efficiency and has promising application prospects in the field of printed circuit board manufacturing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a heat-resistant solder resist paper.

[0021] Figure 2 This is a schematic diagram of a solder resist layer and solder resist protrusions.

[0022] In the diagram: 1. Substrate layer; 2. Solder resist layer; 21. Solder resist protrusion. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments.

[0024] Example 1

[0025] This invention provides a heat-resistant solder resist paper, such as Figure 1 As shown, the heat-resistant solder resist paper includes a substrate layer 1 and a solder resist layer 2, with the solder resist layer 2 placed on the substrate layer 1. The substrate layer 1 provides an adhesion surface for the solder resist layer 2, and the solder resist layer 2 prevents solder from flowing into areas where soldering is not permitted. The substrate layer 1 is made of polyimide film, with a thickness greater than 50 micrometers and less than 500 micrometers. The solder resist layer 2 is made of polyimide resin, a hardener, and pigments, with a thickness greater than 40 micrometers and less than 120 micrometers. The hardener in the solder resist layer 2 reacts chemically with the polyimide resin, causing the polyimide resin to cure and form a compound with a robust structure. The hardener can be an aromatic amine hardener, such as p-phenylenediamine, which can effectively condense with the polyimide resin to form a high-strength network structure with good heat resistance and mechanical properties. The hardener can also be an epoxy resin hardener, such as some epoxy compounds, which have good adhesion and chemical stability, and can improve the chemical corrosion resistance of the solder resist layer 2. The pigment in the solder mask layer 2 is iron oxide pigment, forming a red, brown, or black solder mask layer 2 to identify different functional areas and provide visual identification; that is, by adding color to the solder mask layer 2, pads of different functions or areas are identified. The color on the solder mask layer 2 makes it easier for people to identify the pads on the circuit board, thus facilitating the manufacturing, repair, and testing stages. The surface of the solder mask layer 2 is provided with solder mask protrusions 21, such as... Figure 2 As shown, the solder resist bumps 21 form a grid, and the solder resist bumps 21 and the solder resist layer 2 are made of the same material. The width of the solder resist bumps 21 is greater than 5 micrometers and less than 50 micrometers, and the height of the solder resist bumps 21 is greater than 20 micrometers and less than 100 micrometers. In this invention, a grid and cavities are formed between the solder resist bumps 21. The cavities reduce the thermal stress caused by temperature changes due to drilling; in addition, the presence of cavities makes the solder resist paper more flexible and easier to adapt to unevenness on the substrate surface, which is very beneficial for some flexible electronics applications or scenarios requiring bending. In application, the solder resist bumps 21 are fixed to the substrate. The cavities between the solder resist bumps 21 are in contact with the surface of the substrate. Due to the thermal expansion and contraction effect of the gas in the cavities (the solder resist paper is adhered to the substrate by hot pressing), the solder resist paper can be firmly fixed to the substrate.

[0026] Because the solder resist protrusions 21 in this invention reduce the pulling force of the solder resist paper on the substrate during thermal expansion caused by drilling, and also slow down the transfer of heat generated during drilling on the solder resist paper, both of these effects result in less expansion of the solder resist paper, making it more heat-resistant. This allows the substrate with the solder resist paper of this invention to withstand higher drilling speeds, improving drilling efficiency while ensuring circuit board quality. Therefore, this invention has promising application prospects in the field of printed circuit board manufacturing.

[0027] like Figure 2 As shown, the solder resist protrusions 21 can form either a square mesh or a triangular mesh. The triangular structure has a better effect on reducing tensile stress during thermal expansion compared to other shapes. In high-temperature environments, the thermal expansion of materials causes stress, and each side of the triangle can transmit force. When stress is applied to the triangular mesh, the force can be distributed to each side, reducing stress concentrated in specific areas; that is, the triangular structure helps to alleviate this stress. Furthermore, the triangular structure has a certain ability to absorb deformation and strain. When subjected to stress, the triangular shape allows it to deform to a certain extent without becoming unstable, thereby reducing stress.

[0028] Example 2

[0029] This invention provides a method for preparing heat-resistant solder resist paper, comprising: Step 1, preparing a substrate layer 1; Step 2, coating a solder resist layer 2 onto the substrate layer 1; Step 3, using a roller with a groove array to extrude and initially heat-cur the solder resist layer 2, forming solder resist protrusions 21; Step 4, further heat-curing the solder resist layer 2 and the solder resist protrusions 21 in an oven. For a detailed description of the preparation method of this invention, each step is detailed below:

[0030] Step 1: Prepare substrate layer 1.

[0031] In this step, the material of substrate layer 1 is a polyimide film. This step includes: (1) selecting a polyimide film of appropriate specifications and performance to ensure that the polyimide film meets the requirements of the product, including selecting a specific polyimide type, thickness and size; (2) cleaning and surface treating the polyimide film to ensure that the surface of the polyimide film is clean and to perform surface treatment to improve the adhesion of the coating.

[0032] Step 2: Apply solder resist layer 2 onto substrate layer 1.

[0033] In this step, the solder resist layer 2 comprises polyimide resin, a hardener, and pigments. The prepared solder resist layer 2 material is applied to the substrate layer 1. Specifically, the solder resist layer 2 can be applied to the substrate layer 1 using methods such as roller coating, spraying, scraping, and brushing. When using roller coating, the solder resist layer 2 material is evenly applied to the surface of the substrate layer 1 using a roller: first, the polyimide film is placed on a flat surface, and then the solder resist layer 2 material is applied to its surface using a roller. The movement of the roller ensures uniform coating distribution. When using spraying, the solder resist layer 2 material is sprayed onto the substrate layer 1 in the form of gas using a nozzle. The nozzle parameters are designed according to specific circumstances to ensure coating uniformity. When using scraping, the solder resist layer 2 material is scraped onto the substrate layer 1 using a scraper through a mold. When using the roller coating method, a roller carries the solder resist layer 2 material and transfers it onto the substrate layer 1. Specifically, the polyimide film passes through a rotating roller, on which the solder resist layer 2 material is attached, and then the solder resist layer 2 material is transferred onto the substrate layer 1. When using the brush coating method, a brush is used to apply the solder resist layer 2 material onto the substrate layer 1. Preferably, the present invention uses the roller coating method, which facilitates application in high-speed production lines.

[0034] Step 3: Apply a roller with a groove array to press and pre-heat cure the solder resist layer 2 to form solder resist protrusions 21.

[0035] In this step, during the initial drying stage of the solder resist layer 2, a roller with a groove array is used to press the solder resist layer 2. Simultaneously, the roller has a heating function, achieving preliminary curing of the solder resist layer 2. During the initial heating stage, the solder resist layer 2 is pressed, maintaining a certain degree of fluidity to adapt to the groove shape of the roller during the pressing process. By controlling the pressing pressure and temperature, the roller press forces the solder resist layer 2 into the groove, forming a raised portion within the groove, i.e., forming the solder resist protrusion 21. The preliminary curing temperature is greater than 80°C to facilitate the formation of a stable solder resist protrusion 21. Preferably, during preliminary curing, the roller temperature gradually increases, which facilitates the full entry of the solder resist layer 2 material into the groove, and after preliminary curing, forms a stable solder resist protrusion 21 structure. After the solder resist protrusion 21 is formed, the roller and the solder resist protrusion 21 are separated. During separation, the cooling roller, made of stainless steel, separates from the groove on the roller surface due to the difference in the coefficients of thermal expansion between the weld resist protrusion 21 and the roller (the coefficient of thermal expansion of the weld resist protrusion 21 is greater than that of stainless steel). Specifically, most of the roller is in a heated state, while a small portion is in a cooled state. As the weld resist layer 2 rotates on the roller, the processes of forming and separating the weld resist protrusion 21 are realized.

[0036] Step 4: Re-cur the solder mask layer 2 and the solder mask protrusion 21.

[0037] In this step, the solder resist layer 2 and the solder resist protrusions 21 are further cured, forming a robust structure. Methods for further curing the solder resist layer 2 and the solder resist protrusions 21 include hot air baking or microwave curing. Hot air baking works by heating the solder resist layer 2 and the solder resist protrusions 21 to the curing temperature using hot air equipment. Specifically, the solder resist layer 2 and the solder resist protrusions 21 are exposed to heated hot air to promote a chemical reaction between the resin and the hardener, forming a fixed solder resist layer 2 and solder resist protrusions 21. The temperature of the hot air is greater than 100℃ and less than 150℃, and the drying time is greater than 30 minutes and less than several hours. Microwave curing works by using microwave energy to heat the solder resist layer 2 and the solder resist protrusions 21, promoting their curing. Specifically, the solder resist layer 2 and the solder resist protrusions 21 are placed in a microwave field, absorbing microwave energy and heating up, causing the polymer resin and hardener to undergo a curing reaction. Preferably, hot air baking and microwave curing are carried out in an inert atmosphere to prevent oxidation or other adverse reactions. After drying, the heat-resistant solder resist paper of the present invention is obtained.

[0038] Example 3

[0039] This invention provides a circuit board comprising the heat-resistant solder resist paper of this invention. The heat-resistant solder resist paper of this invention is fixed to a substrate by lamination, hot pressing, or adhesive bonding. Specifically, the solder resist paper is pre-cut into segments matching the substrate size, ensuring the shape and size of the solder resist paper are suitable for a specific circuit board design, and holes are punched in the solder resist paper to set pad areas. Then, the solder resist paper is placed on the substrate, ensuring correct alignment; preferably, a hot-pressing film is added between the solder resist paper and the substrate to prevent adhesion, wherein the hot-pressing film can remain flat under high temperature and pressure. Then, the solder resist paper, substrate, and hot-pressing film are assembled in the correct stacking order, ensuring all layers are aligned and tightly stacked. Then, the stacked components are placed in a hot press, which has the function of controlling temperature and pressure: by raising the temperature of the hot press, the entire stacked layers reach the required curing temperature; while heating, the hot press applies pressure to ensure that the solder resist paper adheres tightly to the substrate surface, ensuring that the solder resist layer 2 and the solder resist protrusions 21 are uniformly fixed across the entire substrate surface. After the curing process is complete, the entire component is cooled to ensure that the solder mask is fully cured before removing the component from the hot press.

[0040] In summary, the present invention provides solder resist protrusions 21 on the solder resist layer 2, which reduces the pulling force of the solder resist paper on the substrate during thermal expansion, making the solder resist paper more heat-resistant and the substrate able to withstand higher drilling speeds. While ensuring the quality of the circuit board, it improves drilling efficiency and has good application prospects in the field of printed circuit board manufacturing.

[0041] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A solder resist paper, comprising a base layer and a solder resist layer, said solder resist layer being disposed on said base layer, said base layer providing an adhering surface for said solder resist layer, said solder resist layer preventing solder flow in areas where soldering should not occur, characterized in that: The surface of the solder resist layer is provided with solder resist protrusions, the solder resist protrusions form a grid, and the solder resist protrusions and the material of the solder resist layer are the same; the material of the substrate layer is polyimide film or paper pulp; the material of the solder resist layer comprises polyimide resin, hardener, and pigment; the width of the solder resist protrusions is greater than 5 microns and less than 50 microns, and the height is greater than 20 microns and less than 100 microns; in use, the solder resist protrusions are fixed on the substrate.

2. The heat-resistant solder resist paper according to claim 1, wherein: The thickness of the substrate layer is greater than 50 microns and less than 500 microns.

3. The solder resist paper of claim 2, wherein: The thickness of the solder resist layer is greater than 40 microns and less than 120 microns.

4. A method for producing the heat-resistant resistance welding paper according to any one of claims 1 to 3, characterized by, The method comprises the following steps: Step 1, preparing the substrate layer; Step 2, coating the solder resist layer on the substrate layer; Step 3, extruding and preliminarily heat-curing the solder resist layer by using a roller with a groove array to form the solder resist protrusions; Step 4, re-curing the solder resist layer and the solder resist protrusions.

5. The method of producing heat-resistant resistance welding paper according to claim 4, characterized by: In step 3, the temperature of the preliminary heat-curing is greater than 80℃.

6. A circuit board, characterized by The circuit board comprises the heat-resistant solder resist paper according to any one of claims 1-3.

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