Manufacturing method of thick copper circuit board

Abstract

The invention discloses a manufacturing method of a thick copper circuit board. The manufacturing method comprises the following steps of first-time solder mask printing, second-time solder mask printing, third-time solder mask printing and fourth-time solder mask printing, a 36T-gear point screen printing plate is adopted for first-time screen printing, and the ink viscosity is 50-70 dpa.s; after standing for 1 hour, carrying out primary pre-baking; exposing, developing and post-baking; second-time solder mask printing: pre-processing; a 77T gear point screen printing plate is adopted for second-time screen printing, and the ink viscosity ranges from 110 dpa.s to 120 dpa.s; after standing for 30 minutes, pre-baking for the second time; and exposing and developing. According to the manufacturing method of the thick copper circuit board provided by the invention, parameters such as the screen printing plate and the ink viscosity during screen printing manufacturing are optimized, so that the ink thickness of an isolated line of the circuit board and the ink thickness of a copper surface are uniform, and the problem that the ink in a hole is plugged due to the fact that the ink enters the hole during screen printing can be prevented.

Description

Technical Field

[0001] The invention relates to the technical field of circuit board manufacturing, and in particular to a method for manufacturing a thick copper circuit board. Background Art

[0002] Circuit board, also known as printed circuit board, is widely used in various electronic product fields. Because of its characteristics of fast conversion and flexible combination, it plays a vital role in the design of electronic products and is an indispensable and important part of the modern electronic industry. According to the finished copper thickness, it can be divided into ordinary thickness circuit board and thick copper circuit board. The ordinary thickness circuit board generally has a finished copper thickness of ≤43um, while the thick copper circuit board has a copper thickness of ≥70um. Because thick copper product circuit boards have thicker and heavier copper layers, they can withstand higher temperatures for a long time, while handling higher current rates and carrying hundreds or thousands of amperes of current. They are widely used in fields such as communication equipment, automotive electronics, and industrial automation.

[0003] For thick copper circuit boards, the usual production method in the circuit board industry is: pre-treatment → 43T screen printing for the first time → pre-baking → exposure → development → pre-treatment (without grinding and brushing) → 43T screen printing for the second time → pre-baking → exposure → development. Since the thick copper circuit board has a relatively thick copper layer, after the circuit is etched, the distance difference between the line surface copper and the substrate is large. After the solder mask is screen printed, the ink on the circuit will flow down to the substrate due to gravity, especially for isolated lines. The ink dripping is more obvious, resulting in insufficient ink thickness on the line surface and red lines. In the production process, it is screen-printed twice and pre-baked twice. The ink in the small holes is solidified. After development, the ink in the holes cannot be flushed out. There are problems such as blockage of the double-sided window holes, or light-transmitting medicine. This creates quality risks. The thickness of the isolated line ink is inconsistent with that of the copper surface ink. Figure 1 As shown ( Figure 1 a represents the isolated line oil thickness, Figure 1 b indicates the copper surface oil thickness), double-sided window ink entry hole / blocking hole Figure 2 As shown ( Figure 2 a represents the ink entry hole, Figure 2 b indicates ink plugging).

[0004] In view of this, it is necessary to provide a new manufacturing process to solve technical problems such as insufficient and uneven ink thickness of isolated lines on thick copper circuit boards, as well as ink entry / blocking. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for manufacturing thick copper circuit boards, optimize the parameters such as the screen and ink viscosity during silk screen printing, make the ink thickness of the isolated lines of the circuit board and the ink thickness of the copper surface uniform, and prevent the problem of ink plugging in the holes caused by ink entering the holes during silk screen printing.

[0006] The technical solution of the present invention is as follows:

[0007] A method for manufacturing a thick copper circuit board comprises the following steps:

[0008] First solder mask printing:

[0009] Pre-treatment;

[0010] The first screen printing is performed using a 36T dot screen, and the ink viscosity is 50-70 dpa.s; the ink viscosity may be 50 dpa.s, 60 dpa.s or 70 dpa.s, or other values ​​within the range;

[0011] After standing for 1 hour, carry out the first pre-baking;

[0012] Exposure, development;

[0013] Post-baking;

[0014] Second solder mask printing:

[0015] Pre-treatment;

[0016] The second screen printing is performed using a 77T dot screen, and the ink viscosity is 110-120 dpa.s; the ink viscosity can be specifically 110 dpa.s, 115 dpa.s or 120 dpa.s, or other values ​​within the range;

[0017] After standing for 30 minutes, pre-bake for the second time;

[0018] Exposure and development.

[0019] Furthermore, in the first solder mask printing process, volcanic ash line pre-treatment was used with a line speed of 2.5 m / min.

[0020] Furthermore, for the first pre-baking, the process parameters are baking the plate at 75±2°C for 15-20 minutes, and the baking time can be 15 minutes, 18 minutes or 20 minutes, or other values ​​within the range.

[0021] Furthermore, for the first solder resist printing, the developing speed is 3.5-4 m / min, such as 3.5 m / min or 4 m / min, or other values ​​within the range.

[0022] Furthermore, in the first solder mask printing process, the post-baking process parameters are: first bake the board at 70-75°C for 55-65 minutes, then bake the board at 85-95°C for 30-35 minutes, and then bake the board at 115-125°C for 25-35 minutes. Specifically, it can be: first bake the board at 75°C for 60 minutes, then bake the board at 90°C for 30 minutes, and then bake the board at 120°C for 30 minutes.

[0023] Furthermore, in the second solder mask printing process, volcanic ash line or micro-etching line pre-treatment is used, the line speed is 2.5m / min, and the grinding brush is turned off.

[0024] Furthermore, for the second pre-baking, the process parameters are baking the plate at 75±2°C for 40-45 minutes, and the baking time can be 40 minutes, 42 minutes or 45 minutes, or other values ​​within the range.

[0025] Furthermore, for the second solder resist printing, the developing speed is 3.5-4 m / min, such as 3.5 m / min or 4 m / min, or other values ​​within the range.

[0026] Furthermore, it also includes the production of the stop point screen. The stop point designed by the engineering Gerbe data of the stop point is 4 mil larger than the single side of the via hole and 4 mil smaller than the single side of the solder mask window.

[0027] Compared with the prior art, the method for manufacturing a thick copper circuit board provided by the present invention has the following beneficial effects:

[0028] 1. The manufacturing method of the thick copper circuit board provided by the present invention adopts screens with different mesh sizes to be produced by silk screen printing twice, and the ink is more uniform after silk screen printing; the use of the stop point screen can prevent the ink from entering during silk screen printing, thereby effectively solving the problem of ink plugging in the hole due to the failure of the developer to flush out; at the same time, screens with different silk screen mesh sizes are matched with different ink viscosities, which is conducive to the oiling of the ink and can ensure the uniformity of the ink thickness.

[0029] Second, in the prior art, screen printing with a dot screen is usually not used. During screen printing, the ink will enter the holes at the same time, and a set of solder mask exposure film is required. After exposure, the ink in the holes is developed and washed away, and then screen printing is performed again. Then a second set of solder mask exposure film is produced, and then developed to wash away the ink in the holes. Therefore, the prior art needs to use two sets of films. The method for making thick copper circuit boards provided by the present invention saves a set of solder mask exposure films, thereby saving costs.

[0030] 3. The manufacturing method of thick copper circuit boards provided by the present invention has a short secondary solder mask manufacturing time, which can reduce the sensible / insensible scratches caused by excessive human contact and improve the quality of the circuit boards; since the solder mask production time is shortened, the production efficiency of the thick copper plate solder mask is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1It is a schematic diagram of the thickness of isolated line ink and copper surface ink in the prior art;

[0033] Figure 2 It is a schematic diagram of a double-sided window ink inlet / blocking hole in the prior art;

[0034] Figure 3 It is a schematic diagram of manufacturing a mid-range dot screen plate of the present invention;

[0035] Figure 4 It is a schematic diagram of ink thickness of isolated lines and large copper surface of thick copper circuit board made by the present invention;

[0036] Figure 5 It is a partial schematic diagram of a thick copper circuit board made by the present invention;

[0037] Figure 6 It is a schematic diagram of a thick copper circuit board made by the present invention. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation modes of the present invention are further described below.

[0039] It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as there is no conflict between them.

[0040] A method for manufacturing a thick copper circuit board, using a two-step solder mask manufacturing process, includes the following steps:

[0041] First solder mask printing:

[0042] The volcanic ash line pretreatment is adopted, and the line speed is 2.5m / min;

[0043] The first screen printing was done with a 36T dot screen, and the ink viscosity was 60dpa.s;

[0044] After lying flat for 1 hour, the first pre-baking is carried out, and the process parameters are: baking the plate at 75±2℃ for 20 minutes;

[0045] Exposure and development; the exposure adopts GBS1+GTS1 data exposure, and the development rate is 4m / min; it should be noted that the circuit board is divided into side A and side B, and the solder mask exposure data is named GBS and GTS in the Genesis software, representing the two sides of the circuit board that need to be exposed. Usually, the naming method of the secondary exposure data is: the first exposure data of the two sides is GBS1 and GTS1, and the second exposure is GBS and GTS, which is convenient for data identification.

[0046] Post-baking, the process parameters are: first bake the plate at 75°C for 60 minutes, then bake the plate at 90°C for 30 minutes, and then bake the plate at 120°C for 30 minutes;

[0047] Second solder mask printing:

[0048] Use volcanic ash line or micro-etching line for pre-treatment, with a line speed of 2.5m / min and no grinding or brushing;

[0049] The second screen printing was carried out using a 77T dot screen with an ink viscosity of 120dpa.s;

[0050] After laying flat and standing for 30 minutes, the second pre-baking is carried out, and the process parameters are: baking the plate at 75±2℃ for 40 minutes;

[0051] Exposure and development; the exposure adopts GBS+GTS data exposure, and the development rate is 4m / min.

[0052] The present invention also includes a method for making a stop point network. The T number of the stop point network is generally 43T or 36T. The present invention uses 36T and 77T. First, a layer of photoresist is coated on the screen, and the thickness is generally 8-12um. Then, the Gerber stop point data is used by laser imaging to directly draw the required graphics on the screen coated with photoresist. After development, the required stop point screen is obtained. The stop point designed by the engineering Gerbe data of the stop point is 4mil larger than the single side of the via hole and 4mil smaller than the single side of the solder mask window. Figure 3 As shown, Figure 3 The green box in the middle represents the screen frame, the yellow area represents the screen plate, the red area represents the oil application area, and the pink dots represent the points that need to be blocked from oil application. The holes on the circuit board below this point do not allow or accept ink to enter the holes.

[0053] Taking a thick copper circuit board with a surface copper thickness of 70 μm as an example, by adopting the thick copper circuit board manufacturing method of the present invention, there is no ink entering the double-sided window via hole with a minimum aperture of 0.25 mm in the circuit board, so there is no problem of ink plugging in the hole after development; after development, micro-section measurement shows that the oil thickness of the isolated line corner is 16.78 um, the ink thickness of the line surface is 22.64 um, the oil thickness of the large copper surface line corner is 16.03 um, and the ink thickness of the copper surface is 23.35 um. Figure 4 As shown in the figure, it shows that the ink thickness of isolated lines is equivalent to the ink thickness of copper surface. This process ensures the uniformity of ink thickness. The thick copper circuit board produced has no oil accumulation on the edge of the hole and no ink protrusion. Figure 5 As shown; at the same time, the circuit board has no unclean development, no film printing, no isolated red lines, etc. Figure 6 As shown, the product quality is improved.

[0054] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the protection scope of the present invention.

Claims

1. A method for manufacturing a thick copper circuit board, characterized in that: The steps include: First solder mask printing: Pre-treatment; Use 36T dot screen for the first screen printing, the ink viscosity is 50-70dpa.s; After standing for 1 hour, carry out the first pre-baking; Exposure, development; Post-baking; Second solder mask printing: Pre-treatment; Use 77T dot screen for the second screen printing, the ink viscosity is 110-120dpa.s; After standing for 30 minutes, pre-bake for the second time; Exposure and development.

2. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: In the first solder mask printing process, volcanic ash line pre-treatment was used with a line speed of 2.5m / min.

3. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: The first pre-baking process parameters are 75±2℃ baking plate for 15-20min.

4. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: For the first solder mask printing, the developing speed is 3.5-4m / min.

5. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: In the first solder mask printing process, the post-baking process parameters are: first bake the board at 70-75℃ for 55-65min, then bake the board at 85-95℃ for 30-35min, and then bake the board at 115-125℃ for 25-35min.

6. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: In the second solder mask printing process, volcanic ash line or micro-etching line pre-treatment is used, the line speed is 2.5m / min, and the grinding brush is turned off.

7. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: The second pre-baking process parameters are 75±2℃ baking plate for 40-45min.

8. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: The second solder mask printing, the development speed is 3.5-4m / min.

9. The method for manufacturing a thick copper circuit board according to claim 1, characterized in that: It also includes the production of the point screen. The point designed by the engineering Gerbe data of the point is 4 mil larger than the single side of the via and 4 mil smaller than the single side of the solder mask window.

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