A through-hole segmented conduction type PCB board and manufacturing method thereof

Abstract

The present invention discloses a through-hole segmented conduction type PCB board and a manufacturing method thereof, the manufacturing method comprising the steps of: arranging a metal foil disc with a coverage area larger than a drilling area at a position where a hole needs to be drilled on the surface of a daughter board to obtain a pre-treated daughter board; stacking and pressing a first outer layer board, at least one pre-treated daughter board and a second outer layer board in sequence to obtain a mother board; drilling a through hole at a position where a hole needs to be drilled on the mother board, and metallizing the through hole, and then removing the remaining part of the metal foil disc after drilling the through hole by acid etching to form a groove that segments the through hole; electroplating the segmented through hole, and then plugging the groove and the through hole after electroplating with resin. The present invention arranges segmented conduction type through holes so that the circuit pattern in each daughter board can be independently conducted through the hole copper, thereby solving the problems of poor alignment accuracy of two back drillings in the back drilling process, difficulty in controlling the back drilling depth, and copper wire in the hole generated by back drilling, as well as the problem of AR limitation of the aspect ratio in the machine drilling blind hole process.

Description

Technical Field

[0001] The invention belongs to the technical field of PCB boards, and in particular relates to a through-hole segmented conduction type PCB board and a manufacturing method thereof. Background Art

[0002] Modern electronic products are getting smaller and smaller, and the size of PCB (printed circuit board) is also developing in the direction of small and dense, so the wiring density in the package is increasing. As the transmission rate of digital signals continues to increase, the rising edge of the signal is getting shorter and shorter, and the influence of vias on the characteristic impedance of transmission lines is becoming more and more obvious.

[0003] like Figure 1 As shown, when current flows through the via 1, the entire via 1 is conductive; however, according to the design of the PCB board, the entire via 1 does not need to be fully conductive, so when a high-frequency current flows through the via 1, the part of the via 1 that does not need to be conductive will form an inductive impedance, affecting the transmission of the high-frequency current signal.

[0004] At present, the industry generally uses back drilling process and machine drilling blind hole process for drilling to overcome the high-frequency loss problem of high-speed signal vias, but both the back drilling process and machine drilling blind hole process have certain defects.

[0005] like Figure 2 As shown, the back drilling process is to first drill a through hole 2, then perform electroplating in the through hole 2 to form a via hole 1, and then drill out the hole copper of the via hole 1 that does not need to be conductive; after drilling out the excess hole copper, the influence of the inductor impedance on the high-frequency current signal transmission can be reduced. However, the back drilling process has problems such as poor alignment accuracy of the two back drillings, difficulty in controlling the back drilling depth, and copper wires generated in the hole by the back drilling.

[0006] like Figure 3 As shown, the machine-drilled blind hole process is to first drill a blind hole 3, and then perform hole metallization and electroplating in the blind hole 3 to form a through hole 1; currently, the aspect ratio AR (AR = hole depth / hole diameter) of the blind hole drilled by the machine-drilled blind hole process in the industry is at most 1.5. This is because when the hole diameter remains unchanged, the deeper the blind hole, the more difficult it is for chemicals to enter, and therefore the more difficult it is to perform hole metallization. Therefore, the machine-drilled blind hole process has a limitation in aspect ratio AR. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies in the prior art, provide a through-hole segmented conduction type PCB board and a manufacturing method thereof, solve the problems of poor alignment accuracy of two back drillings in the back drilling process, difficulty in controlling the back drilling depth and copper wires generated in the hole by back drilling, and the problem of aspect ratio AR limitation in the machine drilling blind hole process.

[0008] The present invention provides the following technical solutions:

[0009] A method for manufacturing a through-hole segmented conductive PCB board comprises the following steps: arranging a metal foil disc with a coverage area larger than a drilling area at a position where a hole needs to be drilled on the surface of a daughter board to obtain a pre-processed daughter board; stacking and pressing a first outer layer board, at least one pre-processed daughter board and a second outer layer board in sequence to obtain a mother board; drilling through holes at positions where holes need to be drilled on the mother board, metallizing the through holes, and then removing the remaining parts of the metal foil disc after drilling the through holes by acid etching to form grooves that segment the through holes; electroplating the segmented through holes, and then plugging the grooves and the electroplated through holes with resin to obtain a through-hole segmented conductive PCB board.

[0010] Furthermore, the method for making the pre-treated sub-board includes: stacking and pressing the sub-board, the semi-cured sheet and the metal foil in sequence; pressing a dry film on the surface of the metal foil, and then exposing and developing the dry film to obtain a circuit pattern that has been developed; etching the circuit pattern that has been developed by acid etching to corrode the metal foil outside the area covered by the dry film, retaining the metal foil at the position of the drilled hole, and obtaining a metal foil disc; removing the dry film on the metal foil by a sodium carbonate solution to obtain a pre-treated sub-board.

[0011] Furthermore, the thickness of the metal foil is recorded as c, the thickness of the prepreg between the metal foil and the sub-board is recorded as d, and the thickness of the electroplated layer in the through hole after electroplating is recorded as e, then 3e <c<0.5d。

[0012] Furthermore, the acid etching solution used in the acid etching is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 5% to 20%.

[0013] Furthermore, the specific production method of the motherboard includes: stacking a semi-cured sheet between the first outer layer board, each layer of pre-treated sub-board and the second outer layer board, and pressing them together to obtain the motherboard; the first outer layer board and the second outer layer board are copper-clad substrates or copper foils.

[0014] Furthermore, the diameter of the through hole is recorded as a mil, and the diameter of the metal foil disc is recorded as b mil, where b≥a+10.

[0015] Furthermore, the metal foil includes one of aluminum foil, zinc foil and iron foil.

[0016] Furthermore, the resin used for the resin plugging hole is epoxy resin adhesive or phenolic resin adhesive.

[0017] Furthermore, the metallization treatment method includes: after performing electroless metallization treatment on the through hole, immersing the motherboard in a copper electroplating solution to perform pre-electroplating of copper.

[0018] Furthermore, the electroless metallization treatment method includes one of a chemical copper method, a black hole method, and a polymer conductive film method.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. When drilling a hole in the PCB board of the present invention, only one through hole penetrating the upper and lower surfaces of the motherboard needs to be drilled, so there are no problems such as poor positioning accuracy, difficulty in controlling the back drilling depth, and copper wires generated in the hole by back drilling, thereby overcoming the disadvantages of the back drilling process.

[0021] 2. The through hole is segmented by setting the grooves. After electroplating, the electroplated layers in different sections of the through hole cannot be conductive due to the presence of the grooves. Therefore, the circuit can be designed in sections according to the conductive parts in the hole, so no invalid circuit will be generated. At the same time, when drilling a hole in the PCB board of the present invention, only one through hole that passes through the upper and lower surfaces needs to be drilled. Compared with a blind hole, it is easier for chemical solutions to enter the through hole. Therefore, the PCB board of the present invention has no aspect ratio limitation when drilling a hole, and can overcome the disadvantages of the machine-drilled blind hole process.

[0022] 3. By filling the grooves and through-holes with resin, the through-holes can be solidified and the reliability of the through-holes can be enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the structure of drilling a through hole on a PCB board in the background technology.

[0024] Figure 2 It is a structural schematic diagram of drilling holes on a PCB board by a back drilling process in the background technology.

[0025] Figure 3 It is a structural schematic diagram of drilling holes on a PCB board by a machine-drilled blind hole process in the background technology.

[0026] Figure 4 The figure is a flow chart of a method for manufacturing a PCB board in the first embodiment of the present invention.

[0027] Figure 5 This is a flow chart of preprocessing a sub-board in the first embodiment of the present invention.

[0028] Figure 6 The figure is a schematic diagram of the structure of manufacturing a pre-processing sub-board in the first embodiment of the present invention.

[0029] Figure 7 It is a schematic diagram of the structure of the pressed dry film in the first embodiment of the present invention.

[0030] Figure 8 It is a schematic diagram of the structure of the metal foil retaining the drilling position by etching in the first embodiment of the present invention.

[0031] Fig. 9 It is a structural schematic diagram of manufacturing a motherboard in the first embodiment of the present invention.

[0032] Fig.10The figure is a schematic diagram of the structure of the PCB board after the through holes are drilled in the first embodiment of the present invention.

[0033] Fig.11 The figure is a schematic diagram of the structure of the PCB board after metallization treatment in the first embodiment of the present invention.

[0034] Fig.12 The figure is a schematic diagram of the structure of the PCB board after acid etching in the first embodiment of the present invention.

[0035] Fig.13 The figure is a schematic diagram of the structure of the PCB board after copper electroplating in the first embodiment of the present invention.

[0036] Numbers in the figure: conductive hole 1, through hole 2, blind hole 3, daughter board 4, first outer layer board 5, metal foil 6, prepreg 7, dry film 8, second outer layer board 9, groove 10, metallized thin copper layer 11, hole copper 12. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0038] It should be noted that, in the description of the present invention, the directions or positional relationships indicated by terms such as "front", "rear", "left", "right", "up", "down", "inside" and "outside" are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and do not require that the present invention must be constructed and operated in a specific direction. Therefore, they should not be understood as limitations on the present invention.

[0039] Embodiment 1:

[0040] like Figure 4 As shown, this embodiment provides a method for manufacturing a through-hole segmented conduction type PCB board, and the steps are as follows:

[0041] Step 1: Make a daughterboard.

[0042] Copper foil, prepreg, inner layer board with circuit pattern, outer steel plate and other materials are stacked according to process requirements. The stacking order is from bottom to top: steel plate, copper foil, prepreg, inner layer board, prepreg, copper foil and steel plate. There can be multiple inner layer boards. When there are multiple inner layer boards, prepreg is arranged between adjacent inner layer boards. Then the copper foil, prepreg and inner layer board are pressed into an integrated structure to make a sub-board.

[0043] Step 2: Make a pre-processing sub-board. Figure 5 As shown, the specific steps are as follows:

[0044] (1) Figure 6 As shown, the sub-board 4, the prepreg 7 and the metal foil 6 are stacked and pressed in sequence.

[0045] (2) Figure 7 As shown, a dry film 8 is laminated on the surface of the metal foil 6, and then the dry film 8 is exposed and developed to obtain a circuit pattern that has been developed. The developed circuit pattern is circular and is set at the position where drilling is required, and the coverage area needs to be larger than the drilling area.

[0046] (3) Figure 8 As shown, the developed circuit pattern is etched by acid etching to corrode the metal foil outside the area covered by the dry film 8, and the metal foil 6 at the position of the drilled hole is retained, that is, a metal foil disc with a coverage area larger than the drilling area is obtained (the metal foil disc has the same shape as the developed circuit pattern); the dry film 8 on the metal foil is removed by sodium carbonate solution to obtain a pre-treated sub-board.

[0047] The metal foil is made of a metal that is more active than copper in an acid solution; the metal foil may be one of aluminum foil, zinc foil and iron foil. In this embodiment, the metal foil is zinc foil.

[0048] Step 3: Make the motherboard.

[0049] like Fig. 9 As shown, the first outer layer board 5, the prepreg 7, at least one pretreated sub-board (a prepreg is arranged between each pretreated sub-board), the prepreg 7 and the second outer layer board 9 are stacked and pressed in sequence to obtain a motherboard.

[0050] In this embodiment, the number of the pre-processing sub-board is 1. In other embodiments, the number of the pre-processing sub-board can be increased according to the design of the PCB board.

[0051] In this embodiment, the first outer layer board 5 is a copper clad board, and the second outer layer board 9 is a copper foil. In other embodiments, the design of the PCB board can be changed.

[0052] Step 4: Drilling and metallization.

[0053] like Fig.10 As shown, a through hole is drilled at the position where the motherboard needs to be drilled. In this embodiment, the diameter of the through hole is recorded as a mil, the value range of a is 0.15mm-10mm, and the diameter of the metal foil is recorded as b mil, b=a+0.25mm, b≥a+10.

[0054] like Fig.11 As shown, the through hole is metallized. Specifically, the through hole is firstly electrolessly metallized, and then the motherboard is immersed in a copper electroplating solution for pre-electroplating copper to obtain a metallized thin copper layer 11.

[0055] Among them, there are three methods for electroless metallization treatment: (1) chemical copper method; (2) black hole method; (3) polymer conductive film method. Any one of the methods can be selected according to production needs. In this embodiment, the chemical copper method is selected for electroless metallization treatment; during the treatment process, activated palladium is chemically deposited on the inner wall of the through hole, and the activated palladium can catalyze the deposition of chemical copper to form a conductive seed layer for subsequent electroplating process.

[0056] Step 5: Etching.

[0057] like Fig.12 As shown, the remaining portion of the metal foil disc after drilling the through hole is removed by acid etching to form grooves 10 that segment the through hole 2.

[0058] The acid etching solution used in step 2 and step 5 is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 5% to 20%. In this embodiment, dilute sulfuric acid with a concentration of 10% is selected as the acid etching solution.

[0059] Step 6: Electroplating copper.

[0060] like Fig.13 As shown, copper is electroplated on the segmented through-holes to form hole copper 12 .

[0061] Step 7: Plug the holes with resin.

[0062] The groove 10 and the through hole 2 after copper electroplating are plugged with resin to enhance the reliability of the through hole, that is, a through hole segmented conduction type PCB board is obtained. The resin used for the resin plugging is an epoxy resin adhesive or a phenolic resin adhesive. In this embodiment, the epoxy resin adhesive is selected.

[0063] Working principle:

[0064] The present invention arranges a metal foil disc with a coverage area larger than a drilling area in a pre-processing sub-board. After the drilling is completed, the middle part of the metal foil disc is drilled away, and the metal foil remaining in the PCB board is in a ring shape. Then, a metallized copper layer is formed on the inner wall of the entire through hole through metallization treatment. Since the thickness of the metallized copper layer is small, it will not hinder the etching of the ring-shaped metal foil by the acid etching liquid, so the acid etching liquid will corrode the ring-shaped metal foil. At the same time, part of the metallized copper layer originally attached to the metal foil disappears due to the loss of the attachment point. Therefore, after acid etching, an annular groove can be etched in the circumference of the inner wall of the through hole, and the metallized copper layer that can be fully conductive originally is divided into a plurality of sections that cannot be conductive to each other by the groove. Before acid etching, the metal foil disc is located between two prepregs; after acid etching, the corresponding groove is also located between the two prepregs. At this time, electroplating is performed to form copper holes. The copper holes in different sections cannot be conductive due to the presence of the grooves, while the same section can be conductive independently due to the presence of the copper holes. Therefore, all circuit patterns in each sub-board can be conductive through the copper holes in the corresponding sections, while the circuit patterns between different sub-boards cannot be conductive due to the presence of the grooves.

[0065] Embodiment 2:

[0066] The present embodiment provides a through-hole segmented conduction type PCB board, and the PCB board of the present embodiment is obtained by the manufacturing method of the first embodiment.

[0067] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for manufacturing a through-hole segmented conduction type PCB board, characterized in that: The following steps are involved: A metal foil disc with a coverage area larger than the drilling area is arranged at a position where a hole is to be drilled on the surface of the sub-board to obtain a pre-treated sub-board; The first outer layer board, at least one pre-processed sub-board and the second outer layer board are sequentially stacked and pressed together to obtain a mother board; Drilling through holes at the positions where holes are needed on the motherboard, metallizing the through holes, and then removing the metal foil discs remaining after drilling the through holes by acid etching to form grooves that segment the through holes; The segmented through holes are electroplated, and then the grooves and the electroplated through holes are plugged with resin to obtain a through-hole segmented conductive PCB board; The method for making the pre-treated daughter board comprises: stacking and pressing the daughter board, the prepreg and the metal foil in sequence; pressing a dry film on the surface of the metal foil, then exposing and developing the dry film to obtain a circuit pattern that has been developed; etching the circuit pattern that has been developed by acid etching to corrode the metal foil outside the area covered by the dry film and retain the metal foil at the position of the through hole to obtain a metal foil disc; removing the dry film on the metal foil by sodium carbonate solution to obtain the pre-treated daughter board; The metallization treatment method includes: after performing electroless metallization treatment on the through hole, immersing the motherboard in a copper electroplating solution for pre-electroplating copper to obtain a metallized thin copper layer; the electroless metallization treatment method includes one of a chemical copper method, a black hole method, and a polymer conductive film method.

2. The method for manufacturing a through-hole segmented conduction PCB board according to claim 1, characterized in that: The thickness of the metal foil is recorded as c, the thickness of the prepreg between the metal foil and the sub-board is recorded as d, and the thickness of the electroplated layer in the through hole after electroplating is recorded as e. .

3. The method for manufacturing a through-hole segmented conduction type PCB board according to claim 1, characterized in that: The acid etching solution used in the acid etching is dilute sulfuric acid or dilute hydrochloric acid with a concentration of 5% to 20%.

4. The method for manufacturing a through-hole segmented conduction type PCB board according to claim 1, characterized in that: The specific manufacturing method of the motherboard includes: stacking a prepreg between a first outer layer board, each layer of pre-treated sub-boards and a second outer layer board, and pressing together to obtain the motherboard; the first outer layer board and the second outer layer board are copper-clad substrates or copper foils.

5. The method for manufacturing a through-hole segmented conduction type PCB board according to claim 1, characterized in that: The diameter of the through hole is recorded as a mil, and the diameter of the metal foil disc is recorded as b mil, where b≥a+10.

6. The method for manufacturing a through-hole segmented conduction PCB board according to claim 1, characterized in that: The metal foil includes one of aluminum foil, zinc foil and iron foil.

7. A through-hole segmented conduction PCB board, characterized in that: The invention is prepared by the method according to any one of claims 1 to 6.

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