Manufacturing method and inspection method of PCB (Printed Circuit Board) via hole

Abstract

The invention discloses a manufacturing and inspection method of a PCB via hole, and the method comprises the following steps: drilling holes in a production board, and drilling at least one inspection hole in the edge of the board; depositing a layer of conductive carbon powder on the hole wall after drilling; cutting the plate edge of the production plate so as to cut at least one slice for detection, and the slice is provided with at least one detection hole; the slice is embedded into a conductive mold, a hollowed-out groove for embedding the slice is formed in the mold in a penetrating mode, and a conductive cloth adhesive tape for connecting the slice and the hollowed-out groove is attached to the junction position between the slice and the hollowed-out groove; placing the mold in a Harlin groove for flash plating so as to plate a thin copper layer on the hole wall of the detection hole; and the slice in the mold is detached and then placed under a microscope to be subjected to a backlight test so as to observe the deposition effect in the hole wall. According to the method, the deposition effect in the hole wall can be directly observed, the method is simple, the single detection time is greatly shortened, and the labor cost is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of printed circuit board manufacturing, and in particular to a manufacturing method and an inspection method of a PCB via hole. Background Art

[0002] At present, the traditional method of PCB via-hole conduction process is the metallized via-hole conduction process, that is, a thin layer of copper is deposited on the hole wall, and the inside of the hole wall is dark red. At this time, the deposition quality of the metallized copper layer in the hole can be determined by backlight testing. For the conductive via made by the deposition of nano-carbon powder, that is, a layer of nano-carbon powder is deposited on the hole wall, and the hole wall is black, the hole wall quality cannot be monitored by the backlight test method. For the hole wall quality test of this type of hole, a special test piece provided by the potion manufacturer is usually used, and the copper climbing method is used for indirect monitoring. Only the copper climbing effect on the surface can be monitored, and the deposition effect inside the hole wall cannot be directly monitored by the backlight test method. Not only is the method complicated, but the operation is time-consuming. A single test takes about 70 minutes, and the labor cost is high. Summary of the invention

[0003] In view of the above-mentioned existing technical defects, the present invention provides a method for making and inspecting a PCB via hole. By slicing and flash plating and then performing a backlight test, the deposition effect inside the hole wall can be directly observed. The method is simple, greatly reduces the single inspection time, and effectively reduces labor costs.

[0004] In a first aspect, in order to solve the above technical problems, the present invention provides a method for making and inspecting a PCB via hole, comprising the following steps:

[0005] S1. Drill holes on the production board and drill at least one detection hole on the edge of the board;

[0006] S2, depositing a layer of conductive carbon powder on the hole wall after drilling;

[0007] S3, cutting the edge of the production board to cut out at least one slice for detection, wherein the slice has at least one detection hole;

[0008] S4, embedding the cut slices into a conductive mold, wherein the mold is provided with a hollow groove for embedding the slices, and a conductive cloth tape is attached at the junction between the slices and the hollow groove to connect the two;

[0009] S5, placing the mold in a Haring cell for flash plating to plate a thin copper layer with a thickness of 0.2-0.5 μm on the hole wall of the detection hole;

[0010] S6. Remove the slices from the mold and then place them under a microscope for backlight testing to observe the deposition effect inside the hole wall.

[0011] Furthermore, in step S2, a layer of conductive carbon powder with a thickness of 0.3-0.5 um is deposited on all hole walls after drilling through a black hole process.

[0012] Furthermore, the size of the hollow groove is 0.5 mm larger on one side than the size of the slice.

[0013] Furthermore, the slice is square, and the length of the slice is 10 mm and the width is 15 mm.

[0014] Furthermore, the hollow groove is a square that is adapted to the slice, and the length of the hollow groove is 10.5 mm and the width is 15.5 mm.

[0015] Furthermore, the mold has a length of 100 mm, a width of 50 mm, and a thickness of 2 mm.

[0016] Furthermore, the mold is made of stainless steel.

[0017] Furthermore, the width of the conductive cloth tape is 2 mm.

[0018] Furthermore, in step S5, the flash plating time is 1-2 minutes and the current is 2A.

[0019] Furthermore, in step S6, after the slices are removed, they are first dried with a hair dryer, and then the slices are observed under a 50x microscope, with the backlight of the microscope turned on and the positive light turned off, to observe the deposition effect inside the hole wall.

[0020] 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.

[0021] In a first aspect, in order to solve the above technical problems, the present invention provides a method for making and inspecting a PCB via hole, comprising the following steps:

[0022] S1. Drill holes on the production board and drill at least one detection hole on the edge of the board;

[0023] S2, depositing a layer of conductive carbon powder on the hole wall after drilling;

[0024] S3, cutting the edge of the production board to cut out at least one slice for detection, wherein the slice has at least one detection hole;

[0025] S4, embedding the cut slices into a conductive mold, wherein the mold is provided with hollow grooves for embedding the slices, and conductive glue is filled between the slices and the hollow grooves;

[0026] S5, placing the mold in a Haring cell for flash plating to plate a thin copper layer with a thickness of 0.2-0.5 μm on the hole wall of the detection hole;

[0027] S6. Remove the slices from the mold and then place them under a microscope for backlight testing to observe the deposition effect inside the hole wall.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] In the present invention, a detection hole is firstly set on the edge of the board and conductive carbon powder is deposited on the hole wall, and then the part with the detection hole in the edge of the board is cut off as a slice for detection. The size of the slice is small, and it is not convenient to perform electroplating and transfer operations on it. Therefore, a mold is added to embed the slice into the mold and then put it into the Haring slot for flash plating, so as to plate a thin copper layer with a thickness of 0.2-0.5μm on the hole wall, so that the inside of the hole wall is dark red, which is convenient for the slice to use a conventional backlight test method to detect whether the deposition effect inside the hole wall meets the requirements and whether the quality is qualified. In order to ensure the conductive layer between the slice and the mold, a thin copper layer with a thickness of 0.2-0.5μm is plated on the hole wall. The electrical effect is achieved by pasting conductive cloth tape or filling conductive glue between the two to make the two fully connected, thereby improving the connection reliability; and the Haring trough flash plating method does not require an additional large copper trough to be specially set up as a flash plating cylinder, and the flash plating operation can be completed directly in the laboratory, and the Haring trough and the mold can be used repeatedly, thereby solving the problem that the via hole uses deposited nano-carbon powder (i.e., conductive carbon powder) as the conductive layer and cannot be backlit for testing. The deposition effect inside the hole wall can be directly observed using a microscope, and the method is simple, which greatly reduces the single detection time, improves production efficiency, and reduces labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the slice after being embedded in the mold in Example 1;

[0031] Figure 2 This is a schematic diagram of a conductive cloth tape attached to the boundary between the slice and the hollow groove in Example 1;

[0032] Figure 3 This is a schematic diagram of Example 2 after the conductive glue is filled between the slice and the hollow groove. DETAILED DESCRIPTION

[0033] 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.

[0034] Example 1

[0035] A method for manufacturing a circuit board shown in this embodiment includes the following processing steps in sequence:

[0036] (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.

[0037] (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.

[0038] (3) Lamination: The browning speed is based on the browning thickness of the bottom copper. 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.

[0039] (4) Drilling: Based on the existing drilling technology, drilling is performed on the production board according to the design requirements, and at least one detection hole is drilled on the edge of the board. The diameter of the detection hole is preferably 0.2-0.5 mm.

[0040] (5) Black hole: Through the black hole process, a layer of conductive carbon powder with a thickness of 0.3-0.5um is deposited on the wall of all holes after drilling. This conductive carbon powder is nano carbon powder.

[0041] (6) Cutting: Cutting is performed on the edge of the production board to cut out at least one slice for testing, and the slice has at least one testing hole.

[0042] In the above, the slice is square, and the length of the slice is 10 mm and the width is 15 mm.

[0043] Of course, the slice shape can also be circular, polygonal, etc.

[0044] (7) Assembly: Figure 1 As shown, the cut slice 1 is embedded in a conductive mold 2, and a hollow groove 21 is provided on the mold for the slice 1 to be embedded, and a conductive cloth tape 3 (such as Figure 2 As shown), a circle of conductive cloth tape is pasted on both surfaces of the junction of the two, and the conductive cloth tape is used to improve the conductive reliability and conductive effect between the two, so as to avoid the gap between the two causing poor conductive effect and affecting the subsequent electroplating effect.

[0045] In the above, the length of the mold is 100mm, the width is 50mm, and the thickness is 2mm. The length and width dimensions are compatible with the Haring trough used in the later flash plating. The thickness of 2mm can be compatible with the back end of most production boards. The thickness of the production board can be thinner or thicker than the mold.

[0046] In the above, the hollow groove is a square that is adapted to the slice, and the length of the hollow groove is 10.5 mm and the width is 15.5 mm.

[0047] It is understandable that when the size of the slice is other sizes, it is only necessary to make the size of the hollow groove larger than the size of the slice by 0.5 mm on one side, so as to facilitate the embedding of the slice into the hollow groove.

[0048] In one embodiment, the width of the conductive tape is 2 mm, which is sufficient to cover the gap between the slice and the hollow groove.

[0049] In one embodiment, the mold is made of stainless steel.

[0050] (8) Flash plating: The mold with the embedded slice is placed in a Haring cell for flash plating to plate a thin copper layer with a thickness of 0.2-0.5 μm on the hole wall of the test hole.

[0051] In the above, the flash plating time is 1-2 minutes and the current is 2A.

[0052] (9) Backlight test: First remove the conductive cloth tape, and then remove the slices from the mold; after the slices are removed, first use a hair dryer to dry them, and then place the slices under a 50x microscope for observation, turn on the backlight of the microscope, turn off the positive light, and you can directly observe the deposition effect inside the hole wall.

[0053] In the above, it took about 20 minutes from cutting the film to completing the test.

[0054] (10) Full-board electroplating: The production boards that have passed the backlight test are subjected to full-board electroplating to thicken the copper layer on the holes and the board surface, and also to thicken the surface copper layer on the countersunk holes or platforms.

[0055] (11) Production of outer circuits (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 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 circuit has defects such as open circuit, gap, incomplete etching, short circuit, etc.

[0056] (12) Solder mask and silk screen characters: After the solder mask ink is silk screen printed on the surface of the production board, it is sequentially subjected to pre-curing, exposure, development and thermal curing treatments to solidify the solder mask ink into a solder mask layer; specifically, a "UL mark" is added to the solder mask ink on the TOP surface and the characters on the TOP surface, thereby coating a layer on the circuits and substrates that do not require soldering to prevent bridging between circuits during soldering, provide a permanent electrical environment and resist chemical corrosion, and at the same time beautify the appearance.

[0057] (13) 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 gold, the chemical-resistant gold ink is removed.

[0058] (14) Electrical test: Test the electrical conductivity of the finished board. The test method used for this board is: flying probe test.

[0059] (15) Molding: According to the existing technology and the design requirements, the circuit board is manufactured with a shape tolerance of + / -0.05mm.

[0060] (16) FQC: Inspect the appearance of the circuit board according to the customer's acceptance standards and our inspection standards. If there are any defects, repair them in time to ensure that we provide customers with excellent quality control.

[0061] (17) 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.

[0062] (18) 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.

[0063] Example 2

[0064] The manufacturing method of a circuit board shown in this embodiment has a processing procedure that is basically the same as the method shown in the embodiment, except that step (7) is specifically:

[0065] (7) Assembly: Figure 3 As shown, the cut slice 1 is embedded in a conductive mold 2, and a hollow groove for the slice to be embedded is provided on the mold, and a conductive glue 4 is filled between the slice 1 and the hollow groove, that is, the conductive glue is used to fill the gap between the two, thereby improving the conductive reliability and conductive effect between the two, and avoiding the poor conductive effect caused by the gap between the two and affecting the subsequent electroplating effect.

[0066] 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 and inspecting a PCB via hole, characterized in that: The following steps are involved: S1. Drill holes on the production board and drill at least one detection hole on the edge of the board; S2, depositing a layer of conductive carbon powder on the hole wall after drilling; S3, cutting the edge of the production board to cut out at least one slice for detection, wherein the slice has at least one detection hole; S4, embedding the cut slices into a conductive mold, wherein the mold is provided with a hollow groove for embedding the slices, and a conductive cloth tape is attached at the junction between the slices and the hollow groove to connect the two; S5, placing the mold in a Haring cell for flash plating to plate a thin copper layer with a thickness of 0.2-0.5 μm on the hole wall of the detection hole; S6. Remove the slices from the mold and then place them under a microscope for backlight testing to observe the deposition effect inside the hole wall.

2. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: In step S2, a layer of conductive carbon powder with a thickness of 0.3-0.5 um is deposited on all hole walls after drilling by a black hole process.

3. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: The size of the hollow groove is 0.5 mm larger than the size of the slice on one side.

4. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: The slice is square, with a length of 10 mm and a width of 15 mm; the hollow groove is square to match the slice, with a length of 10.5 mm and a width of 15.5 mm.

5. The method for making and inspecting a PCB via according to any one of claims 1 to 4, characterized in that: The mold has a length of 100 mm, a width of 50 mm and a thickness of 2 mm.

6. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: The material of the mold is stainless steel.

7. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: The width of the conductive cloth tape is 2 mm.

8. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: In step S5, the flash plating time is 1-2 minutes and the current is 2A.

9. The method for making and inspecting a PCB via hole according to claim 1, characterized in that: In step S6, after the slices are removed, they are first dried with a hair dryer, and then placed under a 50x microscope for observation, with the backlight of the microscope turned on and the positive light turned off to observe the deposition effect inside the hole wall.

10. A method for making and inspecting a PCB via hole, characterized in that: The following steps are involved: S1. Drill holes on the production board and drill at least one detection hole on the edge of the board; S2, depositing a layer of conductive carbon powder on the hole wall after drilling; S3, cutting the edge of the production board to cut out at least one slice for detection, wherein the slice has at least one detection hole; S4, embedding the cut slices into a conductive mold, wherein the mold is provided with hollow grooves for embedding the slices, and conductive glue is filled between the slices and the hollow grooves; S5, placing the mold in a Haring cell for flash plating to plate a thin copper layer with a thickness of 0.2-0.5 μm on the hole wall of the detection hole; S6. Remove the slices from the mold and then place them under a microscope for backlight testing to observe the deposition effect inside the hole wall.

Images