Manufacturing process for improving surface flatness of thick copper micro-pitch carrier board

Abstract

The application relates to a manufacturing process for improving the surface flatness of a thick copper micro-spacing carrier plate, which comprises the following steps: cutting, drilling, copper sinking, first-time electroplating, second-time electroplating, circuit, sectional selective solder mask and surface treatment; wherein the sectional selective solder mask process comprises the following steps: solder mask pretreatment, selective solder mask printing, first-time pre-baking, initial ink leveling, whole-plate solder mask printing, second-time pre-baking, whole-plate ink leveling, solder mask exposure, solder mask development and solder mask post-baking. In the manufacturing process, the sectional selective solder mask is adopted, the manufacturing process is shortened, the production efficiency is improved, and the whole-plate flatness is less than or equal to 2 mu m.

Description

Technical Field

[0001] This application relates to substrate fabrication, specifically to a fabrication process for improving the surface flatness of a thick copper micro-pitch substrate. Background Technology

[0002] With the advent of the big data era, the market demand for application processors (APs) is becoming increasingly widespread. The heat generated by high-speed computing is receiving increasing attention, and the need for smaller space constraints exacerbates the heat dissipation problem. To address heat dissipation in small spaces, substrate design is increasingly trending towards thicker copper to ensure heat dissipation, while using finer pitch to meet miniaturization requirements. Currently, the production process of thick copper substrates uses a double-layer solder mask method, which has the following drawbacks: longer process, lower production efficiency; poor surface flatness of the entire board (flatness ≥8μm); and ink bubbles at the fine-pitch areas, resulting in poor airtightness. Summary of the Invention

[0003] To overcome the above-mentioned defects, this application provides a manufacturing process for improving the surface flatness of thick copper micro-pitch substrates. This manufacturing process employs segmented selective solder masking, which shortens the manufacturing process, improves production efficiency, and achieves a flatness of ≤2μm for the entire board.

[0004] The technical solution adopted by this application to solve its technical problem is:

[0005] A manufacturing process for improving the surface flatness of a thick copper micro-pitch substrate includes the following steps: material preparation, drilling, copper plating, first electroplating, second electroplating, circuitry, segmented selective solder masking, and surface treatment.

[0006] The segmented selective solder resist process includes the following steps: solder resist pretreatment, selective solder resist printing, first pre-baking, initial ink leveling, whole-board solder resist printing, second pre-baking, whole-board ink leveling, solder resist exposure, solder resist development, and post-solder resist baking.

[0007] Optionally, in the selective solder resist printing process: ink is applied to the substrate surface by screen printing, and the ink printing amount of the board surface is differentiated, that is, the ink thickness of the micro-pitch area is greater than the ink thickness of the circuit area. The ink used is AUS308 ink No. 1, and the viscosity η1 of AUS308 ink No. 1 is 80-120 dPa.s.

[0008] Optionally, in the selective solder resist printing process, single-blade printing is used, and the printing pressure F1 is 5±2 kg / cm. 2 The printing speed V1 is 100-150 mm / sec.

[0009] Optionally, the entire board is printed with ink using the whole-board solder resist printing process, thereby increasing the thickness of the ink layer. The conditions for the whole-board solder resist printing process are: double-blade printing is used, and the printing pressure F2 is 3±1Kg / cm. 2 The printing speed V2 is 150-250 mm / sec, and the ink used is AUS308 ink No. 2. The viscosity η2 of AUS308 ink No. 2 is 120-180 dPa.s.

[0010] Optionally, η1 is 0.60-0.85 times η2, F1 is 1.3-1.8 times F2, and V1 is 0.5-0.7 times V2.

[0011] Optionally, the ink in the circuit area is squeezed into the micro-pitch area through the initial ink leveling process, thereby reducing the height difference H1 of ink thickness between the circuit area and the micro-pitch area, where H1 ≤ 15 μm.

[0012] Optionally, the uniformity of the flatness of the entire board can be achieved through the whole board ink leveling process, further reducing the height difference H2 between the line area and the micro-pitch area, where H2≤2μm.

[0013] Optionally, in the pretreatment process for solder resist, the surface of the substrate is roughened by micro-etching with a roughening micro-etching agent, and then dried after pickling.

[0014] Optionally, the selective solder resist printing ink is initially cured by a first pre-bake; the entire board of solder resist printing ink is initially cured by a second pre-bake.

[0015] Optionally, in solder resist exposure, selective regional ink exposure and curing are achieved through image transfer technology; in solder resist development, ink in uncured areas is dissolved by a chemical solution, while ink in photocured areas is retained; and the ink layer is completely cured through a post-solder resist baking process.

[0016] The beneficial effects of this application are:

[0017] 1) This application adopts a segmented selective solder mask process, which ultimately achieves a flatness of ≤2μm for the entire board, greatly improving the flatness of the entire board and thus meeting the flatness requirements of thick copper and micro-pitch board packaging; Compared with the traditional thick copper micro-pitch substrate manufacturing process, this application reduces one exposure, one development and one post-baking process, thereby shortening the substrate manufacturing time, reducing the substrate manufacturing cost and improving production efficiency;

[0018] 2) In the segmented selective solder mask process, AUS308 ink with a special viscosity is first used. The viscosity of AUS308 ink is about 0.7 times that of ordinary ink. Single-blade special parameters are used for printing, that is, the printing pressure is about 1.7 times that of normal printing pressure and the printing speed is about 0.6 times that of normal printing speed. The ink printing amount that achieves the difference on the board surface is achieved, that is, the ink thickness in the micro-pitch area is greater than the ink thickness in the circuit area. Then, ink leveling is used to achieve a height difference of ≤15μm between the micro-pitch area and the circuit area. Then, the ink of the whole board is thickened through normal printing. Therefore, the photocuring and thermal curing process between the two ink printing is reduced, and the ink is completely photocured and thermally cured through a single post-baking, thereby increasing the bonding force between the two inks. In the reliability test, there is no peeling in the ink pull-out test, and there is no ink bubbling or peeling after three times at 288℃ and 10s.

[0019] 3) By performing two ink leveling processes, ink bubbles between micro-spacing areas are eliminated; after ink printing and pre-baking, an ink leveling machine is used to squeeze the ink at the micro-spacing positions, and ink bubbles at the micro-spacing positions are completely eliminated before the ink is cured; therefore, the ink bubbles between micro-spacing areas are resolved visually, and the airtightness of the ink at the micro-spacing positions of thick copper is increased. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the carrier plate in this application;

[0021] Figure 2 This is a schematic diagram of the substrate structure after cutting in this application;

[0022] Figure 3 This is a schematic diagram of the structure of the substrate after drilling in this application;

[0023] Figure 4 This is a schematic diagram of the substrate structure after the first electroplating in this application;

[0024] Figure 5 This is a schematic diagram of the substrate structure after the second electroplating in this application;

[0025] Figure 6 This is a schematic diagram of the structure of the substrate behind the circuit board in this application;

[0026] Figure 7 This is a schematic diagram of the structure of the substrate after selective solder mask printing in this application;

[0027] Figure 8 This is a schematic diagram of the substrate structure after initial ink leveling in this application;

[0028] Figure 9 This is a schematic diagram of the structure of the substrate after the entire board of solder mask is printed in this application;

[0029] Figure 10This is a schematic diagram of the substrate structure after the ink leveling is completed in this application;

[0030] In the diagram: 10-substrate, 11-insulating layer, 12-copper foil layer, 13-ink layer, 20-carrier plate. Detailed Implementation

[0031] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such uses of the terms can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0034] A manufacturing process for improving the surface flatness of a thick copper micro-pitch substrate includes the following steps: material preparation, drilling, copper plating, first electroplating, second electroplating, circuitry, segmented selective solder masking, and surface treatment.

[0035] The segmented selective solder resist process includes the following steps: pre-treatment for solder resist, selective solder resist printing, first pre-baking, initial ink leveling, full-board solder resist printing, second pre-baking, full-board ink leveling, solder resist exposure, solder resist development, and post-baking. This manufacturing process is suitable for the production of carrier boards with thick copper (≥50μm) and micro-pitch (minimum micro-pitch 20μm). The carrier board obtained by this process from the initial substrate achieves a flatness of ≤2μm, meeting the flatness requirements for thick copper and micro-pitch full-board packaging. Compared to traditional thick copper micro-pitch carrier board manufacturing processes, this application reduces one exposure, one development, and one post-baking step, thereby shortening the carrier board manufacturing time, reducing manufacturing costs, and improving production efficiency. Furthermore, it visually eliminates ink bubbles between micro-pitch areas, increasing the airtightness of the ink at the micro-pitch locations on thick copper.

[0036] In the selective solder resist printing process: ink is applied to the substrate surface via screen printing, achieving a differential ink printing amount across the board surface. Specifically, the ink thickness in the micro-pitch area is greater than that in the circuit area. The ink used is AUS308 Ink No. 1, with a viscosity η1 of 80-120 dPa.s. Specifically, Ink No. 1 is a solar PSR-4000 AUS308 green glossy ink.

[0037] In the selective solder resist printing process, single-blade printing is used, and the printing pressure F1 is 5±2Kg / cm. 2 The printing speed V1 is 100-150 mm / sec. By using AUS308 ink of a specific viscosity and controlling the printing pressure and speed, it is possible to achieve different ink printing amounts on the board surface, that is, the ink thickness in the micro-pitch area is greater than the ink thickness in the line area.

[0038] The entire board is printed with solder resist through the aforementioned whole-board printing process, achieving a thicker ink layer. The conditions for this whole-board solder resist printing process are: double-blade printing, and a printing pressure F2 of 3±1 kg / cm². 2 The printing speed V2 is 150-250 mm / sec, and the ink used is AUS308 Ink No. 2, with a viscosity η2 of 120-180 dPa.s. This printing process uses conventional printing, i.e., ordinary ink viscosity, printing pressure, printing speed, and double-blade printing. Ink No. 2 is a Sun PSR-4000 AUS308 green gloss ink. Ink No. 1 and Ink No. 2 have the same brand but different viscosity; Ink No. 2 is a common ink.

[0039] Wherein, η1 is 0.60-0.85 times η2, F1 is 1.3-1.8 times F2, and V1 is 0.5-0.7 times V2. Preferably, η1 is 0.7 times η2, F1 is 1.7 times F2, and V1 is 0.6 times V2; that is, by reasonably controlling the parameters of the two ink printing stages, the ink thickness in the micro-pitch area is made greater than that in the circuit area. Moreover, only pre-baking and leveling processes are performed between the two printing stages, thus reducing the generation of ink bubbles and improving the adhesion between the two ink stages.

[0040] The initial ink leveling process compresses the ink from the circuit area into the micro-pitch area, thereby reducing the height difference H1 of the ink thickness between the circuit area and the micro-pitch area, where H1 ≤ 15 μm. In other words, the initial ink leveling process can achieve a height difference of ≤ 15 μm between the micro-pitch area and the circuit area.

[0041] The overall board flatness is consistent through the aforementioned whole-board ink leveling process, further reducing the height difference H2 between the circuit area and the micro-pitch area, where H2 ≤ 2μm. Through a segmented selective solder mask process, the overall board flatness is ultimately achieved to ≤ 2μm. Two ink leveling processes eliminate ink bubbles in the micro-pitch areas. After ink printing pre-baking, an ink leveling machine is used to squeeze the ink in the micro-pitch areas, thoroughly removing ink bubbles before ink photocuring, thus increasing the airtightness of the ink in the thick copper micro-pitch areas.

[0042] In the pretreatment process for solder resist, the surface of the substrate is roughened by micro-etching with a roughening micro-etching agent, followed by pickling and drying. This pretreatment creates a certain roughness on the board surface, increasing the adhesion between the board and the ink and preventing the applied ink from detaching. The roughening micro-etching agent can be a mixture of sulfuric acid and hydrogen peroxide.

[0043] The selective solder resist printing ink is initially cured through a first pre-baking process; the entire board of solder resist printing ink is initially cured through a second pre-baking process. During solder resist exposure, selective area ink exposure and curing are achieved using image transfer technology; during solder resist development, the ink in uncured areas is dissolved by chemicals, while the ink in the photocured areas remains; a post-bake process ensures complete curing of the ink layer. In the post-bake process, a combination of heat baking and UV curing equipment accelerates the thermal polymerization reaction, allowing the green paint to fully react, further bonding and strengthening to form a stable network structure, thus completely curing the solder resist ink layer and achieving certain physical and chemical resistance.

[0044] Example:

[0045] The fabrication process of the thick copper micro-pitch substrate for the application processor in this application is as follows:

[0046] S1: Material cutting, such as Figure 2As shown, the base plate is cut using a cutting device to obtain a substrate 10. The substrate 10 includes an insulating layer 11 and a copper foil layer 12 attached to both sides of the insulating layer.

[0047] S2: Drilling, such as Figure 3 As shown, the substrate 10 is drilled using a drilling tool;

[0048] S3: Plating copper, first electroplating, such as Figure 4 As shown, the substrate 10 after drilling is subjected to chemical electroplating.

[0049] S4: Second electroplating, such as Figure 5 As shown, the substrate 10 undergoes a second chemical electroplating process;

[0050] S5: Line, such as Figure 6 As shown, the image on the film is transferred onto the substrate 10 to form a circuit by utilizing the photosensitivity of the dry film;

[0051] S6: Segmented selective solder mask

[0052] S6.1: Pre-treatment before solder resist application involves using a roughening micro-etching agent to roughen the surface of the substrate, followed by pickling and drying. This process creates a certain degree of roughness on the board surface, increasing the adhesion between the board surface and the ink.

[0053] S6.2: Selective solder resist printing, such as Figure 7 As shown, AUS308 ink No. 1 is coated onto the substrate surface by screen printing to form ink layer 13. Single-blade printing is used, with printing pressure F1 of 5 kg / cm2, printing speed V1 of 120 mm / sec, and viscosity η1 of AUS308 ink No. 1 of 100 dPa.s. This achieves different ink printing amounts on the board surface, that is, the ink thickness in the micro-pitch area is greater than the ink thickness in the circuit and copper foil areas.

[0054] S6.3: First pre-baking, initial curing of selective solder resist printing ink;

[0055] S6.4: Initial ink leveling, such as Figure 8 As shown, the leveling process extrudes ink from the circuit area to the micro-pitch area, reducing the height difference between the circuit area and the micro-pitch area.

[0056] S6.5: Full-board solder resist printing, such as Figure 9As shown, the entire board was printed with ink using normal printing technology, which achieved an overall thickening of ink layer 13. The conditions for the entire board solder resist printing were: double-blade printing was used, ordinary AUS308 ink No. 2 was used, the viscosity η2 of ordinary ink No. 2 was 140 dPa.s, the printing pressure F2 was 3Kg / cm2, and the printing speed V2 was 200mm / sec.

[0057] S6.6: Second pre-baking, initial curing of the solder resist printing ink on the entire board;

[0058] S6.7: Leveling of ink on the entire board, such as... Figure 10 As shown, the flatness of the entire board is consistent through the leveling process, which further reduces the height difference between the circuit area and the micro-pitch area.

[0059] S6.8: Solder resist exposure, which achieves selective regional ink exposure and curing through image transfer technology;

[0060] S6.9: Solder resist developer, which dissolves the ink in the uncured areas with chemicals, while the ink in the cured areas is retained;

[0061] S6.10: Anti-soldering after baking, such as... Figure 1 As shown, the ink layer 13 is completely cured through the solder resist baking process;

[0062] S7: Surface treatment, after surface treatment of the substrate, a packaging substrate 20 with thick copper, micro pitch and high flatness is obtained.

[0063] In this embodiment, the copper thickness of the carrier board 20 is 55μm, the micro-pitch is 20μm, and the overall flatness is 2μm. In terms of appearance, there are no ink bubbles between the micro-pitches, which increases the airtightness of the ink at the micro-pitch positions of the thick copper. In the reliability test, there is no peeling in the ink pull-out test, and there is no ink bubbling or peeling after three tests at 288℃ for 10 seconds.

[0064] It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. Therefore, the scope of protection of this patent application shall be determined by the appended claims.

Claims

1. A manufacturing process for improving the surface flatness of thick copper micro-pitch substrates, characterized in that: The process includes the following steps: material preparation, drilling, copper plating, first electroplating, second electroplating, circuit design, segmented selective solder masking, and surface treatment. The segmented selective solder resist includes the following steps: solder resist pretreatment, selective solder resist printing, first pre-baking, initial ink leveling, whole-board solder resist printing, second pre-baking, whole-board ink leveling, solder resist exposure, solder resist development, and post-solder resist baking. In selective solder resist printing: ink is applied to the substrate surface by screen printing, and the ink printing amount varies across the board surface, that is, the ink thickness in the micro-pitch area is greater than the ink thickness in the circuit area. The ink used is AUS308 ink No. 1, and the viscosity η1 of AUS308 ink No. 1 is 80-120 dPa.s. In the selective solder resist printing, single-blade printing is used, the printing pressure F1 is 5±2Kg / cm2, and the printing speed V1 is 100-150mm / sec; The entire board is printed with ink through the aforementioned whole-board solder resist printing, thereby achieving a thicker ink layer on the entire board. The conditions for the whole-board solder resist printing are as follows: double-blade printing is used, the printing pressure F2 is 3±1Kg / cm2, the printing speed V2 is 150-250mm / sec, and the ink used is AUS308 ink No. 2, with a viscosity η2 of 120-180dPa.s. The η1 is 0.60-0.85 times η2, the F1 is 1.3-1.8 times F2, and the V1 is 0.5-0.7 times V2; The initial ink leveling process squeezes the ink in the circuit area into the micro-pitch area, thereby reducing the height difference H1 of the ink thickness between the circuit area and the micro-pitch area, where H1 ≤ 15 μm. The uniformity of the flatness of the entire board is achieved by the whole board ink leveling, which further reduces the height difference H2 between the line area and the micro-pitch area, H2≤2μm.

2. The manufacturing process for improving the surface flatness of thick copper micro-pitch substrates according to claim 1, characterized in that: In the pretreatment of solder resist, the surface of the substrate is roughened by micro-etching with a roughening micro-etching agent, and then dried after pickling.

3. The manufacturing process for improving the surface flatness of thick copper micro-pitch substrates according to claim 1, characterized in that: The selective solder resist printing ink is initially cured by the first pre-baking process; The solder resist printing ink on the entire board is initially cured by a second pre-baking process.

4. The manufacturing process for improving the surface flatness of thick copper micro-pitch substrates according to claim 1, characterized in that: In solder resist exposure, selective regional ink exposure and curing are achieved through image transfer technology; in solder resist development, the ink in the uncured areas is dissolved by a chemical solution, while the ink in the curable areas is retained; and the ink layer is completely cured by post-solder resist baking.

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