Manufacturing method of back drilling hole solder-resistant plug hole

Abstract

The invention discloses a manufacturing method of a back-drilling solder-resistant plug hole, which comprises the following steps: drilling holes on a production board and metalizing the holes, the drilled holes comprising a first through hole and a second through hole, the first through hole comprising a small hole with the aperture of less than or equal to 0.35 mm and a large hole with the aperture of more than 0.35 mm, and the two surfaces of the production board being a first surface and a second surface respectively; manufacturing an outer layer circuit on the production board; performing depth-controlled back drilling at the second through hole, wherein the back drilling holes in the first surface and the second surface are respectively a first back drilling hole and a second back drilling hole; enabling the first surface of the production board to face upwards, and performing resin hole plugging on the first back drilling hole and the small hole; enabling the second surface of the production board to face upwards, and performing resin hole plugging on the second back drilling hole and the large hole; and carrying out silk-screen printing of solder resist ink on the production board, and carrying out pre-baking, exposure and development in sequence, so that the resin in the plug hole is cured and a surface solder resist layer is prepared. According to the method, the exposure and development times are reduced, the bad problem caused by multiple times of silk-screen hole plugging is solved, and the production efficiency and the production quality are improved.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a method for manufacturing a back-drilled solder resist plugging hole. Background Art

[0002] With the popularization and wide application of electronic products, the production and manufacturing technology of printed circuit boards has been continuously updated and developed. In order to meet product needs, PCB boards have developed from single-layer boards to double-layer boards or multi-layer boards, and via holes are provided between multi-layer boards for performance conduction between layers.

[0003] In addition, PCB back drilling is to remove part of the copper in a through hole after electroplating by controlled depth drilling, leaving only part of the copper in the hole. The key function of back drilling is to reduce the reflection interference of excess copper in the signal during high-speed signal transmission to ensure the integrity of signal transmission. At present, back drilling is a low-cost production method that can meet the performance of high-frequency and high-speed circuit boards.

[0004] As electronic products develop towards "light, thin, short and small", the density of PCB is getting higher and higher. In order to prevent tin from penetrating from the via hole to the component surface during wave soldering, causing short circuit and cold solder joint, and to avoid flux residue in the via hole affecting safety performance, and to ensure that the circuit board forms a vacuum negative pressure state on the test machine after surface mounting and component assembly, and meet the packaging requirements of the electronic packaging end, it is required to perform solder mask plugging on the via hole and / or back drill hole, and design it as a plate inner hole, that is, plug the via hole and / or back drill hole with resin plug hole, use a sand belt to grind and level it after curing, remove the excess resin at the hole mouth, and then deposit copper on the plug hole surface, plate electricity and make circuit graphics. The typical production process of PCB with back drill hole includes: front process → pressing → drilling → deposit copper, plate electricity → back drilling → resin plug hole → sand belt template → deposit copper, plate electricity → outer layer graphics → graphic electroplating → outer layer etching → outer layer AOI → post process.

[0005] For circuit boards with small holes with a diameter of ≤0.35mm, large holes with a diameter of >0.35mm, and back-drilled holes on both sides, the diameter of the back-drilled holes is generally larger, and the plugging method is generally carried out in batches. The current screen printing process is as follows: pre-treatment → plugging → pre-baking → exposure → development → post-segmented curing → pre-treatment → plugging → screen printing → pre-baking → exposure → development → next process, that is, plug the small holes and large holes first, then pre-bake, expose, develop and cure in turn, then plug the back-drilled holes on both surfaces and screen-print the surface solder mask ink, then pre-bake, expose, develop and cure in turn; this method has the following disadvantages: 1. Multiple screen printing and exposure lead to a long production cycle and low efficiency; 2. There are problems such as unstable production procedures, unclean development, and poor plugging, which result in unnecessary rework and scrap. Summary of the invention

[0006] In view of the above-mentioned existing technical defects, the present invention provides a method for making back-drilled hole solder mask plugging holes, which plugs the front and back sides of back-drilled holes with different apertures and different surfaces and then simultaneously performs exposure, development and curing, thereby reducing the number of exposure and development times, improving the defects caused by multiple silk screen plugging holes, and improving production efficiency and production quality.

[0007] In order to solve the above technical problems, the present invention provides a method for manufacturing a back-drilled solder mask plug hole, comprising the following steps:

[0008] S1. Drilling holes on a production board, the drilled holes include first through holes to be plugged and second through holes to be back-drilled, the first through holes include small holes with a hole diameter ≤ 0.35 mm and large holes with a hole diameter > 0.35 mm, and the two surfaces of the production board are respectively a first surface and a second surface;

[0009] S2, the production board is subjected to copper deposition and full-board electroplating processes in sequence to metalize the drilled holes; then the outer layer circuit is made on the production board;

[0010] S3, performing controlled depth back drilling at the second through hole to be back drilled in the production board according to the design requirements, wherein the hole back drilled at the first surface is the first back drilled hole, and the hole back drilled at the second surface is the second back drilled hole;

[0011] S4, facing the first surface of the production board upward, and plugging the first back-drilled holes and small holes in the surface with resin;

[0012] S5, turning over the production board so that the second surface of the production board faces upward, and plugging the second back-drilled holes and the large holes in this surface with resin;

[0013] S6. Screen print solder mask ink on both surfaces of the production board;

[0014] S7. Pre-bake, expose and develop the production board in sequence to solidify the resin in the plug hole and obtain a surface solder mask.

[0015] Furthermore, in step S4, a first plugging screen is used to perform resin plugging.

[0016] Furthermore, the production process of the first plug-hole screen is as follows: first, photosensitive paste is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and the first plug-hole screen is obtained after development; wherein, the plug-hole film is provided with a first non-light-transmitting hole and a second non-light-transmitting hole at the positions corresponding to the small hole and the first back-drilled hole, respectively, so that the photosensitive paste at the first non-light-transmitting hole and the second non-light-transmitting hole can be removed after exposure and development.

[0017] Furthermore, the aperture of the first non-light-transmitting hole is 0.1 mm larger than the aperture of the small hole.

[0018] Furthermore, the aperture of the second non-light-transmitting hole is the same as the aperture of the first back-drilled hole.

[0019] Furthermore, in step S5, a second via plugging screen is used to perform resin via plugging.

[0020] Furthermore, the production process of the first plug-hole screen is as follows: first, photosensitive slurry is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and a second plug-hole screen is obtained after development; wherein, a third non-light-transmitting hole and a fourth non-light-transmitting hole are respectively provided in the plug-hole film corresponding to the large hole and the second back-drilled hole, so that the photosensitive slurry at the third non-light-transmitting hole and the fourth non-light-transmitting hole can be removed after exposure and development.

[0021] Furthermore, the aperture of the third non-light-transmitting hole is the same as the aperture of the large hole.

[0022] Furthermore, the aperture of the fourth non-light-transmitting hole is the same as the aperture of the second back-drilled hole.

[0023] Furthermore, the production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a prepreg, and the inner core board has undergone an inner circuit production process before pressing.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] In the present invention, the first surface of the production board is firstly faced upward, and the first back-drilled holes and small holes in this surface are plugged with resin, the production board is turned over, the second surface of the production board is faced upward, and the second back-drilled holes and large holes in this surface are plugged with resin, the resin ink itself has a certain viscosity, after the production board is turned over, the resin ink of the first plugging hole will not have the problem of dripping, and then the solder mask ink is screen-printed on both surfaces, and then the production board is pre-baked, exposed and developed to solidify the resin in the plugging hole and obtain a surface solder mask layer, and the plugging of conductive holes and back-drilled holes of different apertures and the production of solder mask layers can be completed by one pre-baking, exposure and development. Compared with the method of multiple plugging, exposure and development in the prior art, the number of exposure and development is reduced, the undesirable problems caused by multiple screen printing plugging are improved, and the production efficiency and production quality are improved.

[0026] Secondly, the aperture of the first non-light-transmitting hole on the first plugging screen is controlled to be 0.1mm larger than the aperture of the small hole, which facilitates the plugging operation of the small hole and ensures that the fullness of the small hole plugging meets the requirements; the aperture of the third non-light-transmitting hole on the second plugging screen is the same as the aperture of the large hole, and the second non-light-transmitting hole on the first plugging screen and the fourth non-light-transmitting hole on the second plugging screen are the same size as their corresponding back-drilled hole apertures, reducing the problem of ink on the solder pad. DETAILED DESCRIPTION

[0027] In order to more fully understand the technical content of the present invention, the technical solution of the present invention will be further introduced and illustrated in conjunction with specific embodiments below.

[0028] Example

[0029] A method for manufacturing a circuit board shown in this embodiment includes the following processing steps in sequence:

[0030] (1) Cutting: Cut the core board according to the panel size of 520mm×620mm. The thickness of the core board is 0.5mm, and the thickness of the copper layer on both surfaces of the core board is 0.5oz.

[0031] (2) Inner layer circuit production (negative film process): Inner layer pattern transfer, use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled to 8μm, and a fully automatic exposure machine is used to complete the exposure of the inner layer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the inner layer circuit pattern is formed; inner layer etching, the exposed and developed core board is etched to etch the inner layer circuit, and the inner layer line width is measured to be 3mil; inner layer AOI, and then check the inner layer circuit for defects such as open short circuits, circuit gaps, and circuit pinholes. Defective products are scrapped, and non-defective products are sent to the next process.

[0032] (3) Lamination: The browning speed is based on the bottom copper thickness. The core board, prepreg, and outer copper foil are laminated in sequence as required. Then, appropriate lamination conditions are selected according to the Tg of the sheet material to laminate the laminated board to form a production board. The two surfaces of the production board are the first surface and the second surface, respectively.

[0033] (4) Drilling: Based on the existing drilling technology, drilling processing is performed on the production board according to the design requirements; the holes drilled include the first through holes to be plugged and the second through holes to be back-drilled, and the first through holes include small holes with a hole diameter ≤ 0.35 mm and large holes with a hole diameter > 0.35 mm.

[0034] (5) Copper plating: A thin layer of copper is deposited on the board surface and hole wall by chemical copper plating. The backlight test is level 10, and the thickness of the copper plating in the hole is 0.5μm.

[0035] (6) Full-board electroplating: The production board is subjected to full-board electroplating to thicken the copper layer in the holes and on the board surface.

[0036] (7) Production of outer circuit (negative film process): Use a vertical coating machine to coat the photosensitive film, the film thickness of the photosensitive film is controlled to 8μm, and a fully automatic exposure machine is used to complete the exposure of the outer circuit with a 5-6 grid exposure ruler (21 grid exposure ruler). After development, the outer circuit pattern is formed; outer layer etching, the production board after exposure and development is etched to etch out the outer layer circuit, and the outer layer line width is measured to be 3mil; outer layer AOI, using an automatic optical inspection system, by comparing with the CAM data, detect whether the outer layer circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0037] (8) Back drilling: Controlled depth back drilling is performed at the second through hole to be back drilled in the production board according to the design requirements, wherein the hole back drilled at the first surface is the first back drilled hole, and the hole back drilled at the second surface is the second back drilled hole.

[0038] (9) Primary plugging: Place the first surface of the production board facing upward, and plug the first back-drilled holes and small holes with a diameter of ≤ 0.35 mm on this surface with resin.

[0039] In the above, the first plugging screen is used to perform resin plugging.

[0040] Preferably, the production process of the first plug-hole screen is as follows: first, photosensitive paste is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and the first plug-hole screen is obtained after development; wherein, the plug-hole film is provided with a first non-light-transmitting hole and a second non-light-transmitting hole corresponding to the small hole and the first back-drilled hole, respectively, so that the photosensitive paste at the first non-light-transmitting hole and the second non-light-transmitting hole can be removed after exposure and development, and then the small hole and the first back-drilled hole are plugged with resin using the silk screen on which the photosensitive paste is not coated at the first non-light-transmitting hole and the second non-light-transmitting hole.

[0041] The aperture of the first non-light-transmitting hole is 0.1 mm larger than that of the small hole, so that the ink can fully enter the small hole; the aperture of the second non-light-transmitting hole is the same as that of the first back-drilled hole, that is, they are designed to be equal in size.

[0042] (10) Secondary plugging: Flip the production board so that the second surface of the production board faces upward, and perform resin plugging on the second back-drilled holes and large holes on this surface.

[0043] In the above, the second plugging screen is used to perform resin plugging.

[0044] Preferably, the production process of the second plug-hole screen is as follows: first, photosensitive paste is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and the second plug-hole screen is obtained after development; wherein, a third non-light-transmitting hole and a fourth non-light-transmitting hole are respectively provided in the plug-hole film corresponding to the large hole and the second back-drilled hole, so that the photosensitive paste at the third non-light-transmitting hole and the fourth non-light-transmitting hole can be removed after exposure and development, and then the large hole and the second back-drilled hole can be plugged with resin using the silk screen on which the photosensitive paste is not coated at the third non-light-transmitting hole and the fourth non-light-transmitting hole.

[0045] The aperture of the third non-light-transmitting hole is the same as the aperture of the large hole, and the aperture of the fourth non-light-transmitting hole is the same as the aperture of the second back-drilled hole.

[0046] (11) Solder mask and silk screen characters: After silk screen printing solder mask ink on both surfaces of the production board, it is subjected to pre-curing, exposure, development and heat curing treatments in sequence, so that the resin in the plug hole is cured and the solder mask ink on both surfaces is cured into a solder mask layer; specifically, the solder mask ink on the TOP side and the characters on the TOP side are added with a "UL mark", so that a layer is coated on the circuits and substrates that do not require soldering to prevent bridging between circuits during soldering, provide a permanent electrical environment and a protective layer against chemical corrosion, and at the same time beautify the appearance.

[0047] (12) Surface treatment (nickel-gold immersion): The copper surface of the pad at the solder mask opening is treated with chemical principles to uniformly deposit nickel and gold layers of a certain required thickness. The thickness of the nickel layer is 3-5 μm; the thickness of the gold layer is 0.05-0.1 μm. After immersion, the chemical-resistant gold ink is removed.

[0048] (13) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0049] (14) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0050] (15) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and the applicant's inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0051] (16) FQA: Re-test the circuit board’s appearance, hole copper thickness, dielectric layer thickness, green oil thickness, inner layer copper thickness, etc. to see if they meet customer requirements.

[0052] (17) Packaging: According to the packaging method and packaging quantity required by the customer, the circuit boards are sealed and packed with desiccant and humidity card before shipment.

[0053] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for making a back-drilled solder mask plug hole, characterized in that: The following steps are involved: S1. Drilling holes on a production board, the drilled holes include first through holes to be plugged and second through holes to be back-drilled, the first through holes include small holes with a hole diameter ≤ 0.35 mm and large holes with a hole diameter > 0.35 mm, and the two surfaces of the production board are respectively a first surface and a second surface; S2, the production board is subjected to copper deposition and full-board electroplating processes in sequence to metalize the drilled holes; then the outer layer circuit is made on the production board; S3, performing controlled depth back drilling at the second through hole to be back drilled in the production board according to the design requirements, wherein the hole back drilled at the first surface is the first back drilled hole, and the hole back drilled at the second surface is the second back drilled hole; S4, facing the first surface of the production board upward, and plugging the first back-drilled holes and small holes in the surface with resin; S5, turning over the production board so that the second surface of the production board faces upward, and plugging the second back-drilled holes and the large holes in this surface with resin; S6. Screen print solder mask ink on both surfaces of the production board; S7. Pre-bake, expose and develop the production board in sequence to solidify the resin in the plug hole and obtain a surface solder mask.

2. The method for manufacturing back-drilled solder-resist plugged vias according to claim 1, characterized in that: In step S4, the first via plugging screen is used to perform resin via plugging.

3. The method for manufacturing back-drilled solder-resist plugged vias according to claim 2, characterized in that: The production process of the first plug-hole screen is as follows: first, photosensitive paste is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and the first plug-hole screen is obtained after development; wherein, the plug-hole film is provided with a first non-light-transmitting hole and a second non-light-transmitting hole at positions corresponding to the small hole and the first back-drilled hole, respectively, so that the photosensitive paste at the first non-light-transmitting hole and the second non-light-transmitting hole can be removed after exposure and development.

4. The method for manufacturing back-drilled solder-resist plugged vias according to claim 3, characterized in that: The aperture of the first non-light-transmitting hole is 0.1 mm larger than the aperture of the small hole.

5. The method for manufacturing back-drilled solder-resist plugged vias according to claim 3, characterized in that: The aperture of the second non-light-transmitting hole is the same as the aperture of the first back-drilled hole.

6. The method for manufacturing back-drilled solder-resist plugged vias according to claim 1, characterized in that: In step S5, a second via plugging screen is used to perform resin via plugging.

7. The method for manufacturing back-drilled solder-resist plugged vias according to claim 6, characterized in that: The production process of the first plug-hole screen is as follows: first, photosensitive paste is coated on the silk screen, and then the silk screen is exposed using a plug-hole film, and a second plug-hole screen is obtained after development; wherein, the plug-hole film is provided with a third non-light-transmitting hole and a fourth non-light-transmitting hole at positions corresponding to the large hole and the second back-drilled hole, respectively, so that the photosensitive paste at the third non-light-transmitting hole and the fourth non-light-transmitting hole can be removed after exposure and development.

8. The method for manufacturing back-drilled solder-resist plugged vias according to claim 7, characterized in that: The aperture of the third non-light-transmitting hole is the same as the aperture of the large hole.

9. The method for manufacturing back-drilled solder-resist plugged vias according to claim 7, characterized in that: The aperture of the fourth non-light-transmitting hole is the same as the aperture of the second back-drilled hole.

10. The method for manufacturing back-drilled solder-resist plugged vias according to claim 1, characterized in that: The production board is a multi-layer board in which an inner core board and an outer copper foil are pressed together by a semi-cured sheet, and the inner core board has undergone an inner layer circuit production process before pressing.