CN203934091U - A kind of flexible circuit board - Google Patents

Abstract

The utility model discloses a flexible circuit board, which comprises a base material, a first circuit pattern layer and a second circuit pattern layer formed on the upper and lower surfaces of the base material, wherein the flexible circuit board further comprises one or A plurality of through holes filled with conductive substances make the first circuit pattern layer and the second circuit pattern layer electrically connected, and the through holes pass through the first circuit pattern layer, the substrate and the second circuit pattern layer. The circuit pattern layer is characterized in that the thicknesses of the first circuit pattern layer and the second circuit pattern layer are respectively 1-10um, and the apertures of the through holes are 20-75um. The flexible circuit board of the utility model can reduce the influence of the wiring of the flexible circuit board and the space position of the layout plate, thereby enabling the function integration of the flexible circuit board to be higher and the circuit to be more precise.

Description

A flexible circuit board

technical field

The utility model relates to a flexible circuit board.

Background technique

Flexible Printed Circuit (FPC) is a printed circuit made of polyimide or polyester film-based copper-clad foil, which has high reliability and excellent flexibility. For example, it can be freely bent, wound, and folded, and can be arranged arbitrarily according to the requirements of the spatial layout, and can be moved and stretched arbitrarily in three-dimensional space, so as to achieve the integration of component assembly and wire connection. At the same time, the flexible circuit board also has the advantages of good heat dissipation and solderability, easy assembly and connection, and low overall cost. The design of the combination of soft and hard also makes up for the slight shortage of flexible materials in the component carrying capacity to a certain extent. As a result, flexible circuit boards have been widely used in aerospace, military, mobile communications, laptop computers, computer peripherals, PDA (Personal Digital Assistant, PDA), digital cameras and other fields or products.

However, with the continuous development of electronic products, higher and higher requirements are put forward for flexible printed circuit boards. The current flexible circuit boards are still difficult to meet the current market requirements for miniaturization and thinning of electronic products.

Utility model content

The purpose of the utility model is to provide a flexible circuit board. The flexible circuit board of the utility model can reduce the influence of the wiring of the flexible circuit board and the space position of the layout, so that the functional integration of the flexible circuit board can be higher and the circuit can be more precise. .

The inventor of the present invention has found through in-depth research that by controlling the thicknesses of the first circuit pattern layer and the second circuit pattern layer in the flexible circuit board within a specific range, and controlling the aperture of the through hole on the flexible circuit board Within a certain range, the above objects can be achieved, and the present invention has been completed.

In order to achieve the above object, the utility model provides a flexible circuit board, which includes a substrate, a first circuit pattern layer and a second circuit pattern layer formed on the upper and lower surfaces of the substrate, wherein the flexible circuit board It also includes one or more through holes filled with conductive substances, so that the first circuit pattern layer and the second circuit pattern layer are electrically connected, and the through holes pass through the first circuit pattern layer, the substrate and The second circuit pattern layer, wherein the thicknesses of the first circuit pattern layer and the second circuit pattern layer are each 1-10um, and the apertures of the through holes are 20-75um.

According to the present invention, by controlling the thicknesses of the first circuit pattern layer and the second circuit pattern layer and the diameter of the through hole within the above range, the following excellent effects can be obtained.

1) The small aperture can reduce the influence of the flexible circuit board wiring and the spatial position of the layout, so that the functional integration of the flexible circuit board is higher and the circuit is more precise;

2) The thickness of copper foil is thin, suitable for making fine lines;

3) The overall thickness of the first circuit pattern layer, the second circuit pattern layer and the substrate is thin, which is suitable for processing micropores.

Other features and advantages of the present utility model will be described in detail in the following specific embodiments.

Description of drawings

Fig. 1 is a schematic diagram of the flexible circuit board of the present invention.

Explanation of reference signs

1: The first circuit pattern layer

2: Second circuit pattern layer

3: Intermediate insulating layer (substrate)

4: Via holes filled with conductive substances

Detailed ways

Specific embodiments of the present invention will be described in detail below. It should be understood that the specific embodiments described here are only used to illustrate and explain the utility model, and are not intended to limit the utility model.

As shown in Figure 1, the flexible circuit board of the present invention includes a substrate 3, a first circuit pattern layer 1 and a second circuit pattern layer 2 formed on the upper and lower surfaces of the substrate 3, wherein the flexible circuit board also includes One or more through holes 4 filled with conductive substances, so that the first circuit pattern layer 1 and the second circuit pattern layer 2 are electrically connected, and the through holes 4 pass through the first circuit pattern layer 1, the The substrate 3 and the second circuit pattern layer 2, wherein the thicknesses of the first circuit pattern layer 1 and the second circuit pattern layer 2 are respectively 1-10um, and the apertures of the through holes 4 are 20-75um.

According to the present invention, preferably, the thicknesses of the first circuit pattern layer 1 and the second circuit pattern layer 2 are respectively 6-8um, and the apertures of the through holes 4 are 20-50um. In addition, considering the balance of electrical properties of the product, it is preferable that the first circuit pattern layer 1 and the second circuit pattern layer 2 have the same thickness.

In the present invention, "through hole 4 filled with conductive substance" means that the through hole 4 in the circuit board is filled with conductive substance, so that the first circuit pattern layer 1 and the second circuit pattern layer 2 can conduct electricity. Pass. For example, the through hole 4 in the circuit board can be filled with various metals (such as copper) often used in this field, so that the first circuit pattern layer 1 and the second circuit pattern layer 2 can be electrically connected.

According to the present invention, preferably, the flexible circuit board further includes a protective layer (not shown) formed on the first circuit pattern layer 1 and the second circuit pattern layer 2 . Such protective layers are well known to those skilled in the art. For example, it may be a layer formed by polyimide (PI) cover film, liquid photosensitive ink (PSR).

The thickness of the protective layer is not particularly limited, and may be a conventional thickness in the field, but preferably, the thickness of the protective layer is 10-25um, preferably 15-20um.

According to the utility model, the base material 3 is usually an insulating material, such as polyimide (PI), acrylic acid, polyether nitrile, polyether sulfonate, polyethylene naphthalate, polyethylene terephthalate Ethylene glycol ester (PET), polyethylene terephthalate, aramid cellulose ester or polyvinyl chloride. Among these, one type may be used alone, or two or more types may be used in mixture.

According to the present invention, the first circuit pattern layer 1 and the second circuit pattern layer 2 may be formed of edge copper (RA) and/or electrolytic copper (ED).

According to the utility model, the preparation method of the above-mentioned flexible circuit board may include the following steps:

1) Forming a first copper foil layer and a second copper foil layer on the upper and lower surfaces of the substrate, and making the thickness of the first copper foil layer and the second copper foil layer 1-10um;

2) Perforating the first copper foil layer, the substrate and the second copper foil layer by laser to form one or more through the first copper foil layer, the substrate and the A through hole in the second copper foil layer, and the process of making the aperture of the through hole 20-75um;

3) A process of filling the through holes formed in process 2) by hole filling plating;

4) A step of forming a first circuit pattern layer and a second circuit pattern layer on the upper and lower surfaces of the substrate.

According to the present utility model, preferably, the process 1) includes the following steps:

(1) Hot pressing is performed in the order of the first copper foil layer, the base material and the second copper foil layer to obtain a substrate with the first copper foil layer formed on the upper surface of the base material and the second copper foil layer formed on the lower surface, Wherein the thickness of the first copper foil layer and the second copper foil layer is greater than 12um;

(2) Contacting the substrate obtained in step (1) with a microetching solution, so that the thickness of the first copper foil layer and the second copper foil layer is 1-10 um.

In addition, from the aspect of easily obtaining the substrate in step (1), the thickness of the first copper foil layer and the second copper foil layer in step (1) is preferably 12-70 um.

In addition, the substrate obtained in step (1) can also be obtained commercially, for example, it can be purchased from Doosan Electronics Co., Ltd.

As long as the microetching solution in the above step (2) can corrode the copper foil, it can be various microetching solutions commonly used in the field. Preferably, the microetching solution can be a mixed solution of microetching solution (model: ES171) commercially available from Shenzhen Chuangfeng Electronic Equipment Co., Ltd., sulfuric acid, hydrogen peroxide and water. Wherein, the content of the microetching liquid of Shenzhen Chuangfeng Electronic Equipment Co., Ltd. is 10-17% by weight, preferably 13-15% by weight, more preferably 15% by weight; the content of the sulfuric acid is 1-6% by weight, preferably It is 2-5% by weight; the content of the hydrogen peroxide is 2-7% by weight, preferably 3-6%. In addition, it is further preferred that the total content of the sulfuric acid and the hydrogen peroxide is 4-6% by weight, and it is even more preferred that the total content of the sulfuric acid and the hydrogen peroxide is 5% by weight.

The conditions for contacting the substrate obtained in step (1) with the microetching solution include: the contact temperature is 28-30° C., and the contact time is 1-2 minutes.

Preferably, the substrate obtained in step (1) is contacted with a microetching solution, so that the thickness of the first copper foil layer and the second copper foil layer is 1-5 um; more preferably 1-3 um.

In the present invention, the first copper foil layer, the base material and the second copper foil layer are perforated by laser. The conditions of the perforation as long as the obtained aperture can be within the above range, for example, the conditions for perforation include: laser energy 1-4 millijoules, laser operating speed 100-150 holes/minute, laser continuous action times 1- 3 times, laser beam size 20-75um (preferably 20-50um).

In the utility model, the first copper foil layer, the base material and the second copper foil layer are perforated by laser under the above-mentioned conditions. Advantage of small holes. In addition, by perforating the first copper foil layer, the base material and the second copper foil layer, compared with the conventional blind holes (blind holes only process the first copper foil layer, the intermediate insulating layer (base) material), retaining the second copper foil layer, which is difficult to process and high in cost), can reduce costs.

In the present utility model, the process of filling the through holes formed in process 2) by hole-filling electroplating includes:

(1) Deposit a layer of conductive substance on the wall of the through hole formed in step 2);

(2) The conductive substance deposited on the hole wall of the through hole is used to conduct electricity, and the conductive layer is electroplated, and the conductive layer fills the through hole.

In the above (1), the conductive substance deposited on the hole wall of the through-hole formed in the step 2) may be various conductive substances commonly used in the field, preferably copper. The method of depositing a conductive substance (preferably copper) on the hole wall of the through-hole formed in step 2) can adopt various methods commonly used in this field, for example, it can be performed by electroplating.

In the above (2), the electroplating method is preferably VCP electroplating known in the art. The conditions of the VCP electroplating include: the current density is 10-200A, and the electroplating time is 10-60 minutes.

The electroplating solution used in the VCP electroplating can be obtained commercially, for example, the electroplating solution with the commercial model VP-100 can be purchased from MacDermid.

In the present invention, the through hole is filled by the above method, so that the whole welding pad becomes a flat surface, and the soldering reliability is obviously better compared with the case of no filling.

According to the utility model, the process of forming the first circuit pattern layer and the second circuit pattern layer on the upper and lower surfaces of the substrate can be carried out by various methods known in the art, for example, it can be formed on the upper and lower surfaces of the substrate after hole filling and electroplating. The surface uses H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine lines to obtain the first circuit pattern layer and the second circuit pattern layer. The conditions for processing fine circuits by using H-Y920 (Hitachi Chemical Co., Ltd.) dry film are well known in the art, and will not be repeated here.

The utility model will be described in detail below through examples.

In the following examples, the microetching solution used is a mixed solution of microetching solution (model ES171) from Shenzhen Chuangfeng Electronic Equipment Co., Ltd., sulfuric acid, hydrogen peroxide and water. Among them, Shenzhen Chuangfeng Electronic Equipment Co., Ltd. The content of the etching solution is 15% by weight, the content of sulfuric acid is 2% by weight, the content of hydrogen peroxide is 3% by weight, and the balance is water.

In the following examples, the electroplating solution for hole filling electroplating was purchased from MacDermid, and the product model is VP-100.

In the following examples, the thickness of the copper foil layer is measured by a CMI700 coating thickness gauge in Oxford, UK.

Example 1

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 2 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 3um, and the total thickness of the substrate after copper reduction is 18um.

3) Use laser processing equipment (Germany Le Puke Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 20um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 20um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 8um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer to obtain a flexible circuit board A1.

Example 2

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 30°C, contact the substrate with the microetching solution for 2.2 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 2um, and the total thickness of the substrate after copper reduction is 16um.

3) Use laser processing equipment (Germany Lepco Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (3) with a diameter of 35um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 35um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 7um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer to obtain a flexible circuit board A2.

Example 3

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 30°C, contact the substrate with the microetching solution for 2.5 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 1um, and the total thickness of the substrate after copper reduction is 14um.

3) Use laser processing equipment (Germany Le Puke Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (3) with a diameter of 50um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 50um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 6um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer to obtain a flexible circuit board A3.

Example 4

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 1.8 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 4um, and the total thickness of the substrate after copper reduction is 20um.

3) Use laser processing equipment (Germany Le Puke Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 20um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 20um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 9um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer to obtain a flexible circuit board A4.

Example 5

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 2 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 3um, and the total thickness of the substrate after copper reduction is 18um.

3) Use laser processing equipment (Germany Le Puke Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 60um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 60um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 8um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer to obtain a flexible circuit board A5.

Comparative example 1

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 1.5 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 6um, and the total thickness of the substrate after copper reduction is 24um.

3) Use laser processing equipment (Germany Le Puke Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 20um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 20um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 11 um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer 1 to obtain a flexible circuit board D1.

Comparative example 2

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 2 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 3um, and the total thickness of the substrate after copper reduction is 18um.

3) Use laser processing equipment (Germany Lepco Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 80um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 80um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 8um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer 1 to obtain a flexible circuit board D2.

Comparative example 3

1) The upper surface layer is the first copper foil layer, the middle insulating layer (PI) and the lower surface layer are the substrate of the second copper foil layer (the thickness of the first copper foil layer is 12um, the thickness of the second copper foil layer is 12um, the middle The thickness of the insulating layer is 12um), and the material is cut to obtain a substrate with a size of 250mm×300mm.

2) Copper reduction: at 28°C, contact the substrate with the microetching solution for 1.3 minutes to obtain a substrate with both the first copper foil layer and the second copper foil layer of 8um, and the total thickness of the substrate after copper reduction is 28um.

3) Use laser processing equipment (Germany Lepco Optoelectronics Co., Ltd.) to drill holes on the substrate to obtain through holes (1) with a diameter of 80um. The drilling conditions include: laser energy 1 millijoule, laser operating speed 100 holes / minute, the number of continuous laser processing operations is 1 time, and the laser beam is 80um.

4) Deposit a layer of copper on the wall of the above-mentioned through hole by electroplating; the electroplating solution used for electroplating is: copper sulfate 2.3g/L (based on copper content), HCHO3.5g/L, NaOH10g/L; electroplating The temperature is 30° C., and the plating time is 20 minutes.

5) Hole filling electroplating is performed by VCP electroplating. The electroplating current is 70A and the electroplating time is 40 minutes. After electroplating, the copper in the hole is filled, and the thickness of the copper layer on the upper and lower surfaces is increased by 5um. After electroplating, the thicknesses of the first copper foil layer and the second copper foil layer are each 13um.

6) Circuit processing: use H-Y920 (Hitachi Chemical Co., Ltd.) dry film to process fine circuits on the surface of the first copper foil layer and the second copper foil layer 1 to obtain a flexible circuit board D3.

Comparative example 4

According to the method of Example 1, the difference is that a through hole (one) with a diameter of 100 um is obtained by mechanical drilling, and a flexible circuit board D4 is obtained accordingly.

Comparative example 5

According to the method of Example 1, the difference is that step 2) (that is, the step of copper reduction) is not carried out, and the flexible circuit board D5 is obtained correspondingly.

By taking a cross-section of the circuit, using a metal microscope to photograph and measure the upper line width, lower line width and copper thickness of the circuit, the processing capabilities (CPK values) of the above-mentioned flexible circuit boards A1-A5 and D1-D3 are tested, where CPK =2*copper thickness/(lower line width-upper line width), wherein, the relationship between the index CPK and PPM is shown in Table 1, and the measurement results of processing capability are shown in Table 2.

Table 1

CPK PPM (one side) 0.33 158655 0.67 22751 1.00 1350 1.33 32 1.67 0.13 2.00 0.001

In Table 1, the CPK value less than 0.67 indicates that the processing ability is very poor, which is an unacceptable level; the CPK value between 0.67-0.1 indicates that the processing ability is poor; the CPK value between 1-1.33 indicates that the processing ability is average; the CPK value is 1.33 Between -1.67 means good processing ability; CPK value greater than 1.67 means excellent processing ability. In addition, PPM means parts per million, which means probability, and 1PPM means that 1 product out of 1 million products does not meet the standard.

Table 2

serial number CPK value A1 1.55 A2 1.47 A3 1.53 A4 1.23 A5 1.19 D1 0.78 D2 0.72 D3 0.69 D4 0.75 D5 0.68

It can be seen from Table 2 that the processing capabilities of the flexible circuit boards meeting the requirements of the utility model are all good. In addition, when the thicknesses of the first circuit pattern layer and the second circuit pattern layer are not within the scope of the present invention, the processability is poor; when the diameter of the through hole is not within the scope of the present invention, the processability is poor.

The preferred embodiment of the utility model has been described in detail above, but the utility model is not limited to the specific details in the above embodiment, and within the scope of the technical concept of the utility model, various simple modifications can be made to the technical solution of the utility model , these simple modifications all belong to the protection scope of the present utility model. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner if there is no conflict. Any combination is also possible, as long as it does not violate the idea of the utility model, it should also be regarded as the disclosed content of the utility model.

Claims (8)

1. A flexible circuit board, which comprises a substrate, a first circuit pattern layer and a second circuit pattern layer formed on the upper and lower surfaces of the substrate, wherein the flexible circuit board also includes one or more substrates A through hole filled with a conductive substance, so that the first circuit pattern layer and the second circuit pattern layer are electrically connected, and the through hole runs through the first circuit pattern layer, the substrate and the second circuit pattern layer , characterized in that the thicknesses of the first circuit pattern layer and the second circuit pattern layer are each 1-10um, and the apertures of the through holes are 20-75um. 2 . The flexible circuit board according to claim 1 , wherein the thicknesses of the first circuit pattern layer and the second circuit pattern layer are each 6-8 um, and the diameter of the through hole is 20-50 um. 3. The flexible circuit board according to claim 1 or 2, wherein the first circuit pattern layer and the second circuit pattern layer have the same thickness. 4. The flexible circuit board according to claim 1 or 2, wherein the conductive substance is copper. 5 . The flexible circuit board according to claim 1 , further comprising a protective layer formed on the surface of the first circuit pattern layer and the second circuit pattern layer. 6. The flexible circuit board according to claim 5, wherein the protective layer has a thickness of 10-25um. 7. The flexible circuit board according to claim 1 or 2, wherein the base material is formed of an insulating material. 8. The flexible circuit board according to claim 7, wherein the insulating material is polyimide, acrylic acid, polyether nitrile, polyether sulfonate, polyethylene naphthalate, polyethylene terephthalate One of glycol formate, polyethylene terephthalate, aramid cellulose ester and polyvinyl chloride.