Glass substrate solder mask additive manufacturing method based on 3D printing

Abstract

The invention relates to the technical field of substrate solder mask processing, in particular to a glass substrate solder mask layer additive manufacturing method based on 3D printing, which comprises the following steps: S1, pretreating the surface of a substrate; s2, preparing printing ink; s3, the 3D printer receives the designed solder mask pattern, and printing forming is carried out based on the 3D printer; s4, carrying out post-treatment on the substrate; and S5, carrying out surface plasma treatment. The solder mask layer is directly printed by adopting the photosensitive ink, and the additive manufacturing is realized through layer-by-layer accumulation forming without exposure and development processes, so that the problems of material waste and manufacturing complexity of a traditional subtractive manufacturing process are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of substrate solder mask processing, and in particular to a 3D printing-based additive manufacturing method for a glass substrate solder mask layer. Background Art

[0002] At present, glass substrates are increasingly used in high-end packaging and advanced IC substrate manufacturing. The solder mask is an essential part of the packaging substrate manufacturing process. Its main functions include: protecting the circuit, preventing short circuits and oxidation; enhancing heat resistance, adapting to reflow soldering process; controlling solder ball flow, and ensuring solder joint quality.

[0003] The traditional solder mask manufacturing method mainly adopts the subtractive manufacturing process, as shown in the attached manual. Figure 2 , the specific steps include rolling on the surface of the substrate to form solder mask ink; pre-baking to remove volatile solvents in the ink and improve adhesion; exposure, selective exposure through laser direct drawing technology to make the ink in the illuminated area undergo photochemical reaction; development, remove the solder mask ink in the unexposed area to form a solder mask pattern; curing, improve heat resistance and chemical stability through heat treatment or UV curing. Although roll coating and screen printing processes have been widely used on organic substrates, they have the following disadvantages on glass substrates: both roll coating and printing rely on positive contact with the substrate to generate pressure to apply the ink to the surface of the substrate. Due to the properties of the stripped substrate material, it cannot withstand excessive pressure, resulting in the inability to achieve the required target thickness; solder mask ink will form side erosion and pins during the development process due to different adhesion with the substrate during the subtractive manufacturing process, which cannot meet the subsequent packaging requirements; the steps are complex and the process is cumbersome, involving exposure, development, baking and other steps, with a long production cycle and low efficiency; large material waste, most of the solder mask ink is removed during the roll coating and development process, resulting in low material utilization; environmental pollution, chemical substances such as developers and ink cleaning agents may cause environmental pollution.

[0004] In the manufacture of solder mask on glass substrates, 3D printing technology (additive manufacturing) brings many advantages over traditional solder mask processes (subtractive manufacturing), such as greater design freedom, less material waste, and shorter production cycles. However, due to the high smoothness of glass substrates, the photosensitive properties of solder mask inks, and the challenges of 3D printing technology in high-precision micron-level manufacturing, there are still many difficulties to overcome. Summary of the invention

[0005] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and provide a method for additive manufacturing of the solder mask layer of a glass substrate based on 3D printing, in which the solder mask layer is directly printed with photosensitive ink, and is formed by layer-by-layer accumulation without the need for exposure and development processes, thereby realizing additive manufacturing and solving the problems of material waste and manufacturing complexity in traditional subtractive manufacturing processes.

[0006] The technical solution adopted by the present application to solve the technical problem is: a method for additive manufacturing of a solder mask layer of a glass substrate based on 3D printing comprises the following steps: S1: pre-treating the substrate surface; S2: prepare printing ink; S3: The 3D printer receives the designed solder mask pattern and prints it based on the 3D printer; S4: perform post-processing of substrate; S5: Perform surface plasma treatment.

[0007] The S1 comprises the following sub-steps: S1-1: Ultrasonic cleaning of substrate: S1-2: Perform O2 plasma treatment.

[0008] In S1-1, the substrate is placed in an ultrasonic cleaning tank and cleaned with DI water at 40 kHz for 10 minutes; After cleaning, continue to rinse the residue on the surface of the glass substrate with DI water; Finally, N2 is used to dry the substrate surface; In the S1-2, O2 plasma is used with a power of 50-80 W and a time of 60 s.

[0009] The printing ink in S2 is photosensitive ink, and the viscosity of the photosensitive ink is in the range of 10-50 mPa·s; The photosensitive ink is stirred evenly and then subjected to vacuum degassing treatment.

[0010] In S3, the 3D printer receives the solder mask pattern to be printed. Before executing the printing program, the camera of the printer captures the positioning point information on the surface of the substrate, performs information matching, and then starts to execute the printing program.

[0011] In the S3, the parallelism between the nozzle of the 3D printer and the substrate is maintained in the range of 0-5um.

[0012] The S3 printing process uses a mixed wavelength light source of 365nm, 385nm, and 405nm, with an exposure time of 5s; Adopt adaptive light source energy distribution algorithm to dynamically adjust ink thickness.

[0013] In S3, for the pad opening area: the ink thickness ranges from 5 to 10 um, and a 365 nm and 385 nm light source is used; For the ink area: the ink thickness ranges from 20 to 30 um, and a mixed wavelength light source of 365 nm, 385 nm and 405 nm is used.

[0014] The S4 comprises the following sub-steps: S4-1: Clean the surface of the printed substrate; place the finished substrate in an ultrasonic cleaning tank and use DI water to clean it at 40kHZ for 3 to 5 minutes; S4-2: UV-heat composite curing, including the following sub-steps: S4-2-1: UV pre-curing: UV light exposure at 600-800mj for 5-10 minutes to enhance the cross-linking structure between resins; S4-2-2: Perform thermal curing: maintain at 150°C for 60 minutes to enhance the mechanical strength of the photosensitive resin ink.

[0015] In the S5, Ar plasma is used for treatment, with a power of 120 W and a time of 60-90 s.

[0016] Compared with the prior art, this application has the following beneficial effects: The present invention uses photosensitive resin-based ink to directly print the solder mask layer, and forms it through layer-by-layer accumulation without the need for exposure, development and curing processes, thereby realizing additive manufacturing, solving the problems of side erosion and pins that occur in the traditional solder mask layer during the development process, and reducing material waste and manufacturing complexity.

[0017] Traditional organic substrates are suitable for low-frequency circuits, while the glass substrate used in this application has low dielectric loss and low thermal expansion coefficient, and is suitable for high-speed and high-frequency signal transmission, high-density packaging, IC substrates, and optical waveguide circuits. This application uses 3D printing solder mask technology to meet the application of glass substrates in advanced packaging fields such as high-end packaging (FC-BGA) and optical waveguide circuits.

[0018] This application simplifies the process and improves production efficiency; the traditional photolithography process requires multiple steps such as roll coating, exposure, development, and curing, while 3D printing only requires printing + post-processing, reducing process complexity. Through DLP technology, the solder mask layer can be directly constructed on the glass substrate without multiple processing, thereby improving production efficiency.

[0019] This application has a high material utilization rate and reduces manufacturing costs. The traditional process removes a large amount of unexposed ink during the development process, and the material utilization rate is low (<50%); 3D printing is additive manufacturing, and ink is only printed where it is needed. The ink utilization rate can reach more than 90%, reducing material costs.

[0020] This application avoids chemical waste liquid pollution such as developer. Traditional photolithography uses developer and cleaning liquid, which will produce a large amount of harmful waste liquid and require additional environmental treatment costs. 3D printing is pure additive manufacturing, avoiding these chemical pollution and reducing corporate environmental protection expenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1It is a flow chart of the present invention; Figure 2 It is a schematic diagram of the manufacturing method of the prior art. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0024] In the present invention, unless otherwise clearly specified and limited, the terms "connection", "fixation", etc. should be understood in a broad sense. For example, "fixation" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Reference Figure 2 The traditional solder mask manufacturing method mainly adopts the subtractive manufacturing process. The specific steps include rolling on the surface of the substrate to form solder mask ink; pre-baking to remove the volatile solvent in the ink and improve the adhesion; exposure, selective exposure through laser direct writing technology, so that the ink in the illuminated area undergoes a photochemical reaction; development, removes the solder mask ink in the unexposed area to form a solder mask pattern; curing, improves heat resistance and chemical stability through heat treatment or UV curing.

[0026] Reference Figure 1 The present application proposes a 3D printing-based additive manufacturing method for a glass substrate solder mask layer, comprising the following steps: S1: Pre-treat the substrate surface; the surface of the glass substrate is smooth and hydrophobic, and the wettability of the solder mask ink on it is poor, which leads to uneven coating and affects the quality of the final solder mask layer. During the 3D printing process, the ink is difficult to spread stably, which may lead to insufficient interlayer bonding, resulting in peeling or cracking. Therefore, this application pre-treats the substrate surface before 3D printing.

[0027] Furthermore, the S1 includes the following sub-steps: S1-1: Perform ultrasonic cleaning on the substrate: Place the glass substrate in an ultrasonic cleaning tank and use DI water to clean it at 40 kHz for 10 minutes; After cleaning, continue to rinse the residue on the surface of the glass substrate with DI water, and finally use N2 to dry the surface of the substrate.

[0028] S1-2: O2 plasma treatment: O2 plasma is used with a power of 50-80W for 60s to improve the hydrophilicity of the glass surface, enhance the wettability of the ink, and enhance the chemical bonding between the resin and the glass. Based on the mechanical interlocking effect between the ink and the glass substrate, the bonding between the solder mask layer and the glass substrate is enhanced. In addition, the present application also uses nano-silicon dioxide (10-20%) to improve the rheological properties of the ink so that it can adapt to the surface of the glass substrate.

[0029] This application uses ultrasonic cleaning + O2 plasma treatment before 3D printing the solder mask layer, which enhances the bonding strength between the glass substrate and the photosensitive resin. This avoids the uneven film thickness caused by substrate warping in the traditional solder mask process when printing layer by layer, thereby improving overall reliability.

[0030] S2: Modulating printing ink; in this embodiment, the printing ink uses photosensitive ink, and the viscosity of the photosensitive ink is modulated by 10-50 mPa·s to reduce the viscosity of the ink (to prevent the filler in the ink from blocking the nozzle), so that it can pass through the printing nozzle better and form a finer pattern; After the photosensitive ink is stirred, it is subjected to vacuum degassing treatment to avoid bubbles during the 3D printing process and prevent stratification during subsequent use.

[0031] S3: The 3D printer receives the designed solder mask pattern and prints it based on the 3D printer. The 3D printer can use a DLP light-curing printer.

[0032] In S3, the 3D printer receives the solder mask pattern to be printed. Before executing the printing program, the camera of the printer captures the positioning point information on the surface of the substrate, performs information matching, and then starts to execute the printing program.

[0033] During the printing process, the parallelism between the 3D printer nozzle and the substrate is maintained within the range of 0-5um. Based on the horizontal correction function, the SR thickness of the substrate surface after printing is ensured; The printer nozzle and the focus height of the light beam are automatically adjusted. This embodiment uses an ultrasonic displacement sensor to detect small height changes on the surface of the glass substrate and automatically adjust the nozzle height to ensure a consistent printing layer thickness.

[0034] During the photosensitive ink printing process, a mixed wavelength light source of 365nm, 385nm, and 405nm is used for irradiation, and the exposure time is about 5s, so that printing and curing can be achieved. Through the energy and thickness adaptive control technology, high precision in detail areas and high efficiency in filling areas are ensured. In the fine circuit area, a 5um layer thickness is used, while in the large area, a 10~20um layer thickness is used to increase the overall printing speed.

[0035] Furthermore, in the printing of the solder mask layer on the glass substrate, different wavelengths of UV light have different effects on the curing depth, curing rate, resolution and penetration of the photosensitive resin. The use of a mixed light source of 365nm, 385nm, and 405nm can simultaneously optimize the curing effect and improve the printing accuracy and mechanical strength. The different curing characteristics are shown in Table 1: Table 1 Curing characteristics of different wavelength ratios

[0036] In order to optimize the curing effect of different wavelengths on photosensitive resin, an adaptive light source energy allocation algorithm is used to adjust the power ratio of different wavelengths through spectral distribution control to optimize the light curing process.

[0037] Specifically, the main variables that affect the photocuring capacity K are: the printing thickness of each layer h, the exposure time t, the absorption coefficient of the photosensitive resin to light m, and the wavelength power of the light source P. The relationship of influence on the finished photocuring capacity K is as follows: (1-1) Since different wavelengths correspond to different depths of cured ink, this application adopts a strategy of dynamically adjusting the ink thickness, corresponding different light-curing thicknesses to different wavelength light sources, as shown in the following table.

[0038] Table 2 Strategy table for dynamically adjusting ink thickness

[0039] Referring to the table above, in the process of 3D printing solder mask, this application adopts the strategy of adaptive light source energy distribution and dynamic adjustment of ink thickness. The adaptive light source energy distribution avoids the optical diffusion effect of exposure and development, as well as the limitations of photosensitive film thickness and exposure machine accuracy, to achieve a smaller pad opening; dynamic layer thickness adjustment technology, especially for large areas, improves printing efficiency while ensuring local accuracy. Optimize the molding uniformity of large areas and avoid splicing errors.

[0040] Furthermore, for the pad opening area (high precision), the present application has the following characteristics: the layer thickness is small, and the ink thickness is controlled within the range of 5~10um. In order to prevent the overflow of the photosensitive resin ink during the curing process, 365nm and 385nm high-absorption light sources are mainly used to improve the surface resolution.

[0041] For large ink areas (high efficiency): When the ink area here is between 1 mm²~50 mm² and the layer thickness is large, in order to improve printing efficiency, the ink thickness is generally controlled in the range of 10~20um, and a mixed wavelength light source of 365nm, 385nm and 405nm is used to improve deep curing and enhance interlayer bonding.

[0042] Large ink area mainly refers to the continuous coverage of the solder mask area, which is large in area and has no opening structure. For example, the large ink area of ​​IC packaging glass substrate ranges from 1 mm² to 50 mm².

[0043] In addition, layer-by-layer curing based on 3D printing technology can reduce stress accumulation and improve the overall stability of the solder mask layer.

[0044] S4: Perform post-processing of the substrate; S4 includes the following sub-steps: S4-1: Clean the surface of the printed substrate; place the finished substrate in an ultrasonic cleaning tank and use DI water to clean it at 40kHZ for 3 to 5 minutes; S4-2: Perform UV-heat composite curing. Due to the different curing rates in different areas, stress concentration may occur, affecting the mechanical strength of the solder mask layer. Therefore, this application adopts a step-by-step light-heat composite curing process during the curing process. First, use low-energy UV pre-curing to form a preliminary solder mask structure and reduce internal stress. Then use mild heat curing to promote the complete curing of residual unpolymerized monomers and improve toughness.

[0045] Furthermore, S4-2 includes the following sub-steps: S4-2-1: UV pre-curing: UV light exposure at 600-800mj for 5-10 minutes to enhance the cross-linking structure between resins; S4-2-2: Perform thermal curing: maintain at 150°C for 60 minutes to enhance the mechanical strength of the photosensitive resin ink.

[0046] S5: Perform surface plasma treatment. During the layer-by-layer printing process, resin may accumulate at the opening, resulting in burrs after printing. In order to remove the burrs on the surface of the glass substrate, Ar plasma treatment is used with a power of 120W and a time of 60-90s, while optimizing the opening of the pad.

[0047] After 3D printing is completed, there may be burrs or accumulation inside the solder mask opening (pad area), which requires additional cleaning. This application uses ultrasonic cleaning to remove tiny burrs and improve the flatness of the pad area. Ar plasma is used to treat the pad opening to improve the reliability of subsequent ball implant packaging.

[0048] This application replaces the subtractive manufacturing process of the traditional solder mask, improves manufacturing freedom, reduces material waste, and is suitable for high-end packaging (such as FC-BGA) and high-frequency and high-speed substrates (such as IC substrates, optical waveguide circuits).

[0049] Glass substrates have the characteristics of low dielectric loss (low Dk / Df) in high-frequency applications and are suitable for 5G millimeter wave antenna packaging. Traditional solder mask processes are difficult to accurately manufacture high-precision solder mask layers, which affects signal transmission performance. The high-precision 3D printing technology of this application can form a solder mask layer with high-density pad openings, greatly increasing the number of I / O points per unit area.

[0050] Ultra-fine glass substrate solder mask for optical waveguide packaging on glass substrates to improve the packaging accuracy of photonic chips: Photonic integrated circuits require a high-precision solder mask (5~10 µm) on the glass substrate for optical fiber coupling and electro-optical signal connection. This application uses DLP 3D printing to directly print ultra-fine optical solder mask on the glass substrate, which is suitable for photonic packaging.

[0051] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention specification under the concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for additive manufacturing of a solder mask layer of a glass substrate based on 3D printing, characterized in that: The steps include: S1: pre-treating the substrate surface; S2: prepare printing ink; S3: The 3D printer receives the designed solder mask pattern and prints it based on the 3D printer; S4: perform post-processing of substrate; S5: Perform surface plasma treatment.

2. The method for additive manufacturing of a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: The S1 comprises the following sub-steps: S1-1: Ultrasonic cleaning of the substrate: S1-2: Perform O2 plasma treatment.

3. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 2, characterized in that: In S1-1, the substrate is placed in an ultrasonic cleaning tank and cleaned with DI water at 40 kHz for 10 minutes; After cleaning, use DI to continue to rinse the residue on the surface of the glass substrate; Finally, N2 is used to dry the substrate surface; In the S1-2, O2 plasma is used with a power of 50-80 W and a time of 60 s.

4. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: The printing ink in S2 is photosensitive ink, and the viscosity of the photosensitive ink is in the range of 10-50 mPa·s; The photosensitive ink is stirred evenly and then subjected to vacuum degassing treatment.

5. The method for additive manufacturing of a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: In S3, the 3D printer receives the solder mask pattern to be printed. Before executing the printing program, the camera of the printer captures the positioning point information on the surface of the substrate, performs information matching, and then starts to execute the printing program.

6. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: In the S3, the parallelism between the nozzle of the 3D printer and the substrate is maintained in the range of 0-5um.

7. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: The S3 printing process uses a mixed wavelength light source of 365nm, 385nm, and 405nm, with an exposure time of 5s; Adopt adaptive light source energy distribution algorithm to dynamically adjust ink thickness.

8. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 7, characterized in that: The S3 For the pad opening area: the ink thickness range is 5~10um, using 365nm and 385nm light sources; For the ink area: the ink thickness ranges from 20 to 30 um, and a mixed wavelength light source of 365 nm, 385 nm and 405 nm is used.

9. The method for additive manufacturing of a glass substrate solder mask layer based on 3D printing according to claim 1, characterized in that: The S4 comprises the following sub-steps: S4-1: Clean the surface of the printed substrate; place the finished substrate in an ultrasonic cleaning tank and use DI water to clean it at 40kHZ for 3 to 5 minutes; S4-2: UV-heat composite curing, including the following sub-steps: S4-2-1: UV pre-curing: UV light exposure at 600-800mj for 5-10 minutes to enhance the cross-linking structure between resins; S4-2-2: Perform thermal curing: Maintain at 150°C for 60 minutes to enhance the mechanical strength of the photosensitive resin ink.

10. The method for additively manufacturing a solder mask layer of a glass substrate based on 3D printing according to claim 1, characterized in that: In the S5, Ar plasma is used for treatment, with a power of 120 W and a time of 60-90 s.

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