Thermosetting solder resist, circuit board solder resist film, and method for manufacturing same

Abstract

The present application relates to a kind of hot curing type solder resist, circuit board solder resist film and its manufacturing method, hot curing type solder resist includes: one contains two or more epoxy groups in epoxy resin, polybasic acid anhydride, thermal curing catalyst, filler, adhesion promoter, pigment and solvent;Wherein, the content of epoxy resin is 10-50% of total mass, the molar ratio of polybasic acid anhydride and epoxy group is 0.7-1.1;The thermal curing catalyst is 0.1-5% of the weight of epoxy resin.It can better ensure the precision of the film layer formed by being applied to circuit board, thickness control is better, and insulation reliability is also better.Moreover, the film layer formed by using the hot curing type solder resist, resistivity and resistivity after humidification are high, and dielectric constant is low.Combined with the method of subsequent laser etching, high precision of line width / line spacing=1mil / 1mil can be achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit board manufacturing technology, in particular to a thermosetting solder resist, a circuit board solder resist film and a manufacturing method thereof. BACKGROUND

[0002] In the field of printed circuit board, it is usually required to form a permanent solder resist film layer on the circuit board to play the role of insulation, protection, identification and the like. Generally, there are three kinds of solder resists: thermosetting, energy-curing and photo-developing solder resists. The thermosetting and energy-curing solder resists are formed into a solder resist layer by being respectively heated or irradiated by energy rays after being printed on the circuit board through a screen having a pattern. The photo-developing solder resist is coated on the circuit board in a liquid state through screen printing, roller coating or spraying, and then is pre-cured by low-temperature baking to volatilize the solvent or is laminated on the circuit board in a dry film form to form a pre-cured solder resist film. The pre-cured solder resist film is selectively exposed by a film in a contact / non-contact or laser direct imaging mode, and then is developed by an alkaline developing solution to remove the unexposed part to form a solder resist pattern. Finally, the solder resist layer is formed after high-temperature thermal curing. The thermosetting and energy-curing solder resists are limited by the printing mode through a screen having a pattern to form a solder resist pattern, and cannot meet the requirement of high precision. Meanwhile, the thickness of the solder resist layer is difficult to adjust to ensure the precision of the pattern.

[0003] The photo-developing solder resist can be flexibly formed on the circuit board in various ways, and can form a solder resist pattern with high precision due to the selective exposure mode. Benefited from these advantages, the photo-developing solder resist has become the current mainstream solder resist. From the aspect of the physical and chemical properties of the solder resist, the photo-developing solder resist after curing contains a large number of polar groups such as hydroxyl and ester groups, and has poor electrical properties such as insulation, insulation after humidification and dielectric constant. The thermosetting and energy-curing solder resists, especially the thermosetting solder resist, can obtain excellent electrical properties. The carrier circuit board requires a solder resist capable of providing high insulation, insulation reliability, low dielectric constant and other electrical properties while meeting the requirement of high-precision pattern.

[0004] Therefore, the current general solder resist film layer preparation technology is difficult to achieve both high production precision and good insulation reliability. It is urgent to solve the above problems by selecting the solder resist and improving the manufacturing process. SUMMARY

[0005] Therefore, it is necessary to provide a thermosetting solder resist, a circuit board solder resist film and a manufacturing method thereof, which are applied to circuit board soldering, have relatively high production precision, good thickness control, good insulation reliability and low dielectric constant.

[0006] In a first aspect, the present application provides a thermosetting solder resist, comprising: an epoxy resin containing two or more epoxy groups, a polybasic anhydride, a thermosetting catalyst, a filler, an adhesion promoter, a pigment and a solvent;

[0007] The content of the epoxy resin is 10-50% of the total mass, the molar ratio of the polybasic anhydride to the epoxy group is 0.7-1.1, and the thermosetting catalyst is 0.1-5% of the weight of the epoxy resin.

[0008] In one embodiment, the epoxy resin is o-cresol formaldehyde epoxy resin; and / or, the polybasic anhydride is at least one of tetrahydrophthalic anhydride and styrene-maleic anhydride resin; and / or, the thermosetting catalyst is 2-ethyl-4-methylimidazole; and / or, the filler is silicon dioxide; and / or, the adhesion promoter is epoxy silane; and / or, the solvent is divalent acid ester.

[0009] In one embodiment, the thermosetting solder resist comprises the following components: 30% of epoxy resin, 19%-20% of polybasic anhydride, 3% of thermosetting catalyst, 28%-29% of filler, 3% of adhesion promoter, 1% of pigment and 15% of solvent.

[0010] In a second aspect, the present application provides a method for manufacturing a circuit board solder resist film, comprising the following steps:

[0011] The thermosetting solder resist described in any one of the above embodiments is printed on the circuit board by screen printing to form a film layer;

[0012] The film layer is cured at high temperature;

[0013] The circuit board after curing of the film layer is subjected to selective ablation by a picosecond UV laser machine to obtain a circuit board with a patterned solder resist film layer.

[0014] In one embodiment, the dry film thickness of the film layer is controlled to be 20-25 microns during screen printing.

[0015] In one embodiment, the picosecond UV laser machine uses a wavelength of 355 nm and a beam diameter of 10 μm.

[0016] In one embodiment, the film layer is cured at a temperature of 150°C for 90 minutes.

[0017] In one embodiment, the film layer is cured at a temperature of 150°C for 90 minutes in an oven.

[0018] In one embodiment, the cross section of the solder resist film layer is rectangular or right trapezoidal.

[0019] In a third aspect, the present application provides a circuit board with a solder resist film layer, which is prepared by the method as described in any of the above embodiments.

[0020] The heat-curable solder resist described above uses an epoxy resin containing two or more epoxy groups, with a content of 10-50%, which can provide the basic structure and mechanical strength of the solder resist, and after curing, a three-dimensional cross-linked structure is formed, which enhances the stability and durability of the material, and also has excellent chemical resistance, high temperature resistance, impact resistance and insulation performance, which can effectively protect the circuit from moisture and chemical corrosion. By using a polybasic anhydride, and the molar ratio of the polybasic anhydride to the epoxy group is 0.7-1.1, the polybasic anhydride reacts with the epoxy resin to form a 3D network structure, so that the solder resist has good mechanical properties, high temperature resistance and chemical corrosion resistance after curing. The use of epoxy resin, polybasic anhydride, heat-curing catalyst, filler, adhesion promoter, pigment and solvent can better ensure the precision of the film layer formed on the circuit board, the thickness control is good, and the insulation reliability is also good. Moreover, the film layer formed by using the heat-curable solder resist has high resistivity and high resistivity after humidification, and low dielectric constant. Combined with the subsequent laser etching method, high precision of line width / line spacing=1mil / 1mil can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The schematic diagram for showing the cross-sectional results in the embodiments of the present application. DETAILED DESCRIPTION

[0022] For the purpose of facilitating the understanding of the present application, in order to make the above-mentioned objects, features and advantages of the present application more apparent, the specific embodiments of the present application will be described in detail below with reference to the drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application is best understood with reference to the accompanying drawings. However, the present application can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. The present application can be embodied in other ways than those specifically disclosed herein without departing from the spirit and essential characteristics of the present application, and the scope of the present application should not be limited by the specific embodiments disclosed below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. As used in the description of the application, the terms "and / or" includes a combination of one or more associated listed items. In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0023] In a first aspect, the present application provides a thermosetting solder resist, comprising: an epoxy resin containing two or more epoxy groups, a polybasic acid anhydride, a thermosetting catalyst, a filler, an adhesion promoter, a pigment and a solvent;

[0024] The content of the epoxy resin is 10-50% of the total mass, the molar ratio of the polybasic acid anhydride to the epoxy group is 0.7-1.1, and the thermosetting catalyst is 0.1-5% of the weight of the epoxy resin.

[0025] The heat-curable solder resist agent contains 10-50% of an epoxy resin containing two or more epoxy groups, which can provide the basic structure and mechanical strength of the solder resist agent, and after curing, a three-dimensional cross-linked structure is formed, which enhances the stability and durability of the material, and also has excellent chemical resistance, high temperature resistance, impact resistance and insulation performance, which can effectively protect the circuit from moisture and chemical corrosion. By using a polybasic anhydride, and the molar ratio of the polybasic anhydride to the epoxy group is 0.7-1.1, the polybasic anhydride reacts with the epoxy resin to form a 3D network structure, so that the solder resist agent has good mechanical properties, high temperature resistance and chemical corrosion resistance after curing. The use of epoxy resin, polybasic anhydride, heat-curing catalyst, filler, adhesion promoter, pigment and solvent can better ensure the precision of the formed film layer applied to the circuit board, the thickness control is good, and the insulation reliability is also good. Moreover, the film layer formed by using the heat-curable solder resist agent has high resistivity and high resistivity after humidification, and low dielectric constant. Combined with the subsequent laser etching method, a high precision of line width / line spacing=1mil / 1mil can be achieved.

[0026] In the present application, by adding an adhesion promoter, the adhesion between the solder resist agent and the PCB substrate can be improved, and the solder resist layer can be prevented from peeling off during long-term use; the wettability of the solder resist agent on the substrate surface can also be improved, so that it can spread and penetrate better. At the same time, the corrosion resistance and wear resistance of the solder resist layer can also be enhanced.

[0027] By adding pigments, the solder resist agent can be given a specific color, which is convenient for identification and inspection.

[0028] The solvent used in the present application can dissolve and dilute other components in the solder resist agent, so that a uniform mixture is formed, and it can also help the solder resist agent to wet and spread better on the PCB surface during the coating process. During the curing process, it is volatilized completely and does not remain on the PCB surface, so as not to affect the performance of the circuit.

[0029] In one embodiment, the epoxy resin is o-cresol formaldehyde epoxy resin; and / or, the polybasic anhydride is at least one of tetrahydrophthalic anhydride and styrene-maleic anhydride resin; and / or, the heat-curing catalyst is 2-ethyl-4-methylimidazole; and / or, the filler is silicon dioxide; and / or, the adhesion promoter is epoxy silane; and / or, the solvent is divalent acid ester (DBE). Of course, it should be understood that the above components are not limited to this.

[0030] In one embodiment, the thermosetting solder resist comprises the following components: 30% of epoxy resin, 19%-20% of polybasic anhydride, 3% of thermosetting catalyst, 28%-29% of filler, 3% of adhesion promoter, 1% of pigment, and 15% of solvent. Thus, the applicant has found that the volume resistivity, resolution, and solder resist line cross-sectional shape are all significantly improved.

[0031] In a second aspect, the application provides a method for manufacturing a solder resist film for a circuit board, comprising the following steps:

[0032] The thermosetting solder resist described in any of the above embodiments is screen printed on the circuit board to form a film layer.

[0033] The film layer is cured at high temperature.

[0034] The circuit board with the cured film layer is subjected to selective ablation by a picosecond UV laser machine to obtain a circuit board with a patterned solder resist film layer.

[0035] In one embodiment, the film layer has a dry film thickness of 20-25 microns when screen printed. For example, the picosecond UV laser machine has a wavelength of 355 nm and a beam diameter of 10 microns. For example, the film layer is cured at a temperature of 150°C for 90 minutes. For example, the film layer is cured in an oven at a temperature of 150°C for 90 minutes. For example, the solder resist film layer has a rectangular or right trapezoidal cross-section.

[0036] In a third aspect, the application also provides a circuit board with a solder resist film layer, which is prepared by the method described in any of the above embodiments.

[0037] The thermosetting solder resist described above contains 10-50% of an epoxy resin containing two or more epoxy groups, which provides the basic structure and mechanical strength of the solder resist, forms a three-dimensional cross-linked structure after curing, enhances the stability and durability of the material, and also has excellent chemical resistance, high temperature resistance, impact resistance, and insulation performance, effectively protecting the circuit from moisture and chemical corrosion. By using a polybasic anhydride, and the molar ratio of the polybasic anhydride to the epoxy group is 0.7-1.1, the polybasic anhydride reacts with the epoxy resin to form a 3D network structure, so that the solder resist has good mechanical properties, high temperature resistance, and chemical corrosion resistance after curing. The use of epoxy resin, polybasic anhydride, thermosetting catalyst, filler, adhesion promoter, pigment, and solvent can better ensure the precision of the film layer formed on the circuit board, the thickness control is good, and the insulation reliability is also good. Moreover, the film layer formed by the thermosetting solder resist has high resistivity and high resistivity after humidification, and low dielectric constant. Combined with the subsequent laser etching method, a high precision of line width / line spacing = 1 mil / 1 mil can be achieved.

[0038] The present application will be further described below in connection with specific examples and comparative examples.

[0039] Example 1

[0040] The heat-curable solder resist includes each component in Table 1 below:

[0041] Table 1 Mass percentage (100%) of each component of the heat-curable solder resist in Example 1

[0042]

[0043] Example 2

[0044] The heat-curable solder resist includes each component in Table 2 below:

[0045] Table 2 Mass percentage (100%) of each component of the heat-curable solder resist in Example 2

[0046]

[0047]

[0048] Comparative Example 1

[0049] The existing general green photosensitive imaging solder resist ink CH-800B G30 (HuaChuang Science and Technology Co., Ltd.) was used.

[0050] The solder resist inks of Examples 1, 2 and the comparative example were applied to the circuit board or tested for performance in the following manner:

[0051] 1. Each component in Example 1, Example 2 was mixed and milled with a three-roll mill to obtain a solder resist. The solder resist was printed on a treated circuit substrate by silk screen printing (the dry film thickness was controlled to be 20-25 microns). The printed circuit substrate was cured in an oven at a temperature of 150°C for 90 minutes.

[0052] The general green photosensitive imaging solder resist ink CH-800B G30 (HuaChuang Science and Technology Co., Ltd.) of Comparative Example 1 was printed on the circuit substrate in the same manner. The printed substrate was baked in an oven at 75°C for 40 minutes to remove the solvent, cured the coating with a UV machine, and finally cured in an oven at a temperature of 150°C for 90 minutes.

[0053] 2. The cured circuit board was subjected to selective ablation with a picosecond UV laser machine (wavelength 355 nm, beam diameter 10 um) to obtain a solder resist layer with a pattern.

[0054] 3. Evaluation of physical and chemical properties of the solder resist film

[0055] 1) Tg and CTE (coefficient of thermal expansion) evaluation

[0056] Sample preparation: The solder resist obtained from Example 1, 2 was coated on a PET film using a wire bar coater and cured in an oven at a temperature of 150°C for 90 minutes. The PET film was peeled to obtain a free solder resist film.

[0057] A general-purpose green photosensitive development-type solder resist ink CH-800B G30 was coated on a PET film in the same manner, baked in an oven at 75°C for 40 minutes to remove the solvent, cured the coating using a UV machine, and finally cured in an oven at a temperature of 150°C for 90 minutes. The PET film was peeled to obtain a free solder resist film.

[0058] The Tg point and CTE of the free solder resist film were measured using a TMA measuring instrument.

[0059] 2) Volume resistivity and resistivity after humidification measurement

[0060] Sample preparation:

[0061] The solder resist ink formed in Example 1 and 2 was coated on a 20 cm x 20 cm single-sided copper circuit board substrate using a 00 mesh screen printer, with a dry film thickness of 20-25 μm, with a 2 cm margin around the periphery. The printed circuit board was cured in an oven at a temperature of 150°C for 90 minutes.

[0062] As Comparative Example 1, the existing general-purpose green photosensitive development-type solder resist ink CH-800B G30 (Heraeus Holding GmbH) was printed on a copper circuit board in the same manner. The printed board was baked in an oven at 75°C for 40 minutes to remove the solvent, the coating was cured using a UV machine, and finally cured in an oven at a temperature of 150°C for 90 minutes.

[0063] Volume resistivity test:

[0064] Volume resistivity test before humidification: The volume resistivity sample was heated in an oven at 150°C for 30 minutes before testing, and the volume resistivity was tested according to the method of IPC-TM-6402.5.17E; resistivity test after humidification: the sample that had completed the volume resistivity test before humidification was placed in a constant temperature and humidity chamber at 60°C, 85% for 24 hours, and after being taken out and placed in a drying box to room temperature, the volume resistivity was tested.

[0065] 3) Resolution evaluation

[0066] The solder resist ink formed in Examples 1 and 2 was printed on the treated circuit substrate (the dry film thickness was controlled to be 20-25 micrometers). The printed circuit substrate was cured in an oven at a temperature of 150°C for 90 minutes. The cured circuit substrate was then subjected to selective ablation using a picosecond UV laser machine (wavelength 355 nm, beam diameter 10 um) to obtain a solder resist layer having a pattern with line width:line space of 25 um:25 um, 50 um:50 um, 75 um:75 um, and 100 um:100 um, respectively.

[0067] As Comparative Example 1, the existing general-purpose green photosensitive development-type solder resist ink CH-800B G30 (Hongsung Technology Co., Ltd.) was printed on a copper circuit substrate in the same manner. The printed substrate was baked in an oven at 75°C for 40 minutes to remove the solvent, and a film having a pattern with line width:line space of 25 um:25 um, 50 um:50 um, 75 um:75 um, and 100 um:100 um, respectively, was coated on the solder resist layer, and then exposed using a 7KW exposure machine, developed using a developer, and cleaned with tap water. The developer concentration was 1.0% sodium carbonate, the temperature was 30°C, the pressure was 2.0 kgf / cm 2 , and the time was 60 seconds. The developed sample was then cured in an oven at a temperature of 150°C for 90 minutes.

[0068] The presence or absence of residual ink between the lines was observed using a 50x optical microscope. The results were as follows:

[0069] The A line group formed in Example 1 had no residual ink between the lines and was not completely developed or ablated:.

[0070] The B line group formed in Example 2 had a small amount of residual ink between the lines and was partially developed or ablated, and the underlying copper could be seen: o.

[0071] The C line group formed in Comparative Example 1 had residual ink between the lines and was not completely developed or ablated: X.

[0072] 4. Evaluation of the cross-section of the line group pattern

[0073] The samples evaluated for resolution were cut into sections at the line groups with line width:line space of 25 um:25 um, 50 um:50 um, 75 um:75 um, and 100 um:100 um, respectively, and the cross-sections of the patterns were observed using a microscope after polishing.

[0074] A schematic diagram of the cross-section results is shown in Figure 1 .

[0075] indicates that the cross-section was as shown in a of Figure 1 (no side etching, rectangular shape):

[0076] indicates that the cross-section was as shown in b of Figure 1 (negative side etching, trapezoidal shape):

[0077] X section as shown in c of Figure 1

[0078] The evaluation results are shown in Table 3.

[0079] Table 3 Evaluation results

[0080]

[0081]

[0082] From the above, the embodiment 1 and embodiment 2 of the present application have advantages in Tg, CTE, volume resistivity, solubility, and solder resist line section shape compared to the comparative examples.

[0083] The heat-curable solder resist of the present application has high resistivity and high resistivity after humidification, and low dielectric constant. The method of laser etching proposed in the present application can achieve high precision of line width / line distance = 1 mil / 1 mil.

[0084] The heat-curable solder resist proposed in the present application can meet the requirements of high precision and good electrical performance at the same time: a heat-curable solder resist is provided, which is coated on a circuit board, and after the solder resist is cured, the solder resist layer is selectively etched by laser to obtain a solder resist pattern. The present application relates to the technology of preparing a solder resist film with high insulation reliability and low dielectric constant by laser etching method, which can be applied to circuit boards with high requirements for high insulation reliability and low dielectric constant, especially circuit boards for carrier boards.

[0085] The heat-curable solder resist described above uses an epoxy resin containing two or more epoxy groups in an amount of 10-50%, which can provide the basic structure and mechanical strength of the solder resist, and after curing, a three-dimensional cross-linked structure is formed, which enhances the stability and durability of the material, and also has excellent chemical resistance, high temperature resistance, impact resistance and insulation performance, which can effectively protect the circuit from moisture and chemical corrosion. By using a polybasic anhydride, and the molar ratio of the polybasic anhydride to the epoxy group is 0.7-1.1, the polybasic anhydride reacts with the epoxy resin to form a 3D network structure, so that the solder resist has good mechanical properties, high temperature resistance and chemical corrosion resistance after curing. The use of epoxy resin, polybasic anhydride, heat-curable catalyst, filler, adhesion promoter, pigment and solvent can better ensure the precision of the formed film layer applied to the circuit board, the thickness control is good, and the insulation reliability is also good. Moreover, the film layer formed by using the heat-curable solder resist has high resistivity and high resistivity after humidification, and low dielectric constant. Combined with the subsequent laser etching method, high precision of line width / line distance = 1 mil / 1 mil can be achieved.

[0086] ​Any technical features in the above-described embodiments can be combined in any manner, and for the sake of brevity, not all possible combinations are described, however, as long as there is no conflict, any combination of the above technical features is deemed to be within the scope of the present disclosure. It should be noted that "in an embodiment", "for example", "for instance", and the like in the present application are intended to serve as examples of the present application, and are not intended to limit the present application. The above-described embodiments only express several embodiments of the present application, and the description is relatively specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims.

Claims

1. A heat-curable solder resist, characterized by, consists of the following components in the following mass percentages consists of: o-cresol novolac epoxy resin 30%, polybasic anhydride 19%-20%, thermal curing catalyst 3%, filler 28%-29%, adhesion promoter 3%, pigment 1%, and solvent 15%; The molar ratio of the polybasic anhydride to the epoxy group of the o-cresol novolac epoxy resin is 0.7-1.1, the polybasic anhydride is at least one of tetrahydrophthalic anhydride and styrene-maleic anhydride resin, the thermal curing catalyst is 2-ethyl-4-methylimidazole, the filler is silicon dioxide, the adhesion promoter is epoxy silane, and the solvent is divalent acid ester.

2. A method of manufacturing a solder resist film for a circuit board, characterized by, The method comprises the following steps: The thermally cured solder resist as claimed in claim 1 is printed on a circuit board by screen printing to form a film layer; The film layer is cured at high temperature; The circuit board after curing of the film layer is subjected to selective ablation by a picosecond UV laser machine to obtain a circuit board with a patterned solder resist film layer.

3. The method of manufacturing according to claim 2, wherein, The film layer is controlled to have a dry film thickness of 20-25 microns during screen printing.

4. The method of manufacturing according to claim 2, wherein, The picosecond UV laser machine uses a wavelength of 355 nm and a beam diameter of 10 microns.

5. The method of manufacturing according to claim 2, wherein, The film layer is cured at a temperature of 150°C for 90 minutes.

6. The method of manufacturing according to claim 5, wherein, The film layer is cured at a temperature of 150°C for 90 minutes in an oven.

7. The method of making of claim 2, wherein, The cross section of the solder resist film layer is rectangular or right trapezoidal.

8. A circuit board having a solder resist film layer, characterized by, The method is prepared by using the method as claimed in any one of claims 2 to 7. The method is prepared by using the method as claimed in any one of claims 2 to 7.

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