Multi-order HDI circuit board and manufacturing method thereof

Abstract

The invention discloses a multi-stage HDI circuit board and a manufacturing method thereof. The circuit board comprises a first core board, a second core board and a porous filling layer. The first core plate is composed of a porous material base layer and first conductive pattern layers on the upper and lower sides; the second core plate is arranged on the outer layer of the first core plate and comprises an inner side PP layer and a second conductive pattern layer covering the inner side PP layer, the PP layer is provided with conducting holes and heat dissipation holes, the conducting holes are filled with conductive metal materials to achieve conduction, the heat dissipation holes are blind holes, the bottoms of the heat dissipation holes directly penetrate through the base layer, and the heat dissipation holes are filled with porous materials to enhance heat dissipation. The manufacturing method comprises the steps of cutting, pressing, etching, drilling, conductive material filling, polishing, secondary etching, secondary drilling, porous material hole filling, plate cutting and the like. Through the cooperation of the porous material base layer and the porous filling layers in the heat dissipation holes, the heat dissipation performance of the HDI circuit board is significantly improved, the conduction structure is optimized, the structural strength is enhanced, the manufacturing flexibility is improved, the cost is reduced, and the HDI circuit board is suitable for various application scenes of high-density interconnection circuit boards.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit board production, and in particular to a multi-level HDI circuit board and a manufacturing method thereof. Background Art

[0002] HDI circuit boards have become an indispensable component of modern electronic devices due to their high integration, high signal transmission speed and high reliability. However, as the integration of electronic components continues to increase, the problem of heat generation and accumulation on circuit boards has become increasingly prominent, placing higher requirements on the heat dissipation performance of circuit boards.

[0003] Traditional HDI circuit boards usually use solid materials as the base layer. Although these materials have excellent electrical performance and mechanical strength, their thermal conductivity is often low and it is difficult to meet the heat dissipation requirements of high-density electronic components. In a high temperature environment, the heat on the circuit board is difficult to dissipate effectively, resulting in the performance of electronic components being degraded, and may even cause serious consequences such as short circuits and burns. Summary of the invention

[0004] One object of the present invention is to provide a multi-level HDI circuit board to solve the technical problem of poor heat dissipation performance of traditional HDI circuit boards.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a multi-level HDI circuit board, comprising A first core board, the first core board comprising a base layer and a first conductive layer disposed on upper and lower sides of the base layer, the base layer being made of a porous material; A second core board, the second core board is arranged on the outer layer of the first core board, the second core board includes an inner PP layer and a second conductive layer covering the PP layer, the PP layer is provided with a via hole and a heat dissipation hole, the via hole connects the first conductive layer and the second conductive layer, the via hole is filled with a conductive metal material; the heat dissipation hole is a blind hole, the heat dissipation hole is located at a blank position of the first conductive layer, and the bottom of the heat dissipation hole directly passes through the base layer; A porous filling layer is arranged in the heat dissipation hole.

[0006] Another object of the present invention is to provide a method for manufacturing a multi-level HDI circuit board, which is used to manufacture the multi-level HDI circuit board in the above embodiment, and the multi-level HDI circuit board manufacturing method comprises the following steps: S1, cutting the base sheet and the first conductive metal layer sheet according to the required size; S2, first lamination, laminating the base layer and the first conductive metal layer into a sandwich structure including the base layer, and performing lamination; S3, first layer etching, etching the first conductive metal layer to form a first conductive layer, and completing the production of the first core board; S4, laminating for the second time, stacking the PP layer and the second conductive metal layer on the upper and lower sides of the first core board in sequence, and then laminating; S5, drilling for the first time, using laser drilling to open a via hole between the second conductive metal layer and the first conductive layer, the via hole is a blind hole, and the depth of the via hole reaches the surface of the first conductive layer; S6, filling with conductive material, filling the conductive material into the via hole, so that the second conductive metal layer is conductively connected to the first conductive layer; S7, grinding, grinding the second conductive metal layer to remove the conductive material protruding from the via hole; S8, second layer etching, etching the second conductive metal layer to form a second conductive layer; S9, drilling for the second time, using laser drilling to drill heat dissipation holes on the PP layer, the drilling position avoids the first conductive layer and the second conductive layer, and the depth of the heat dissipation holes reaches the surface of the base layer; S10, porous material filling, using porous material to fill the heat dissipation holes; S11, cutting the board, cutting the board into the target size according to the usage requirements.

[0007] In one embodiment, the porous material is selected from ceramics, metal oxides, porous polymers or combinations thereof, and the porous material has high thermal conductivity and good electrical insulation properties to optimize heat dissipation effects and ensure circuit safety.

[0008] In one embodiment, thermally conductive particles are embedded in the porous filling layer. The thermally conductive particles are any one of graphite, diamond, silicon carbide or aluminum oxide materials with high thermal conductivity, so as to further enhance the heat dissipation capacity of the heat dissipation holes.

[0009] In one embodiment, the laser drilling technology used in step S5 "first drilling" and step S9 "second drilling" is any one of CO2 laser, UV laser or femtosecond laser to ensure the accuracy and efficiency of drilling while reducing the thermal impact on surrounding materials.

[0010] In one embodiment, the porous material of the base layer has a gradient pore structure, wherein the porosity gradually changes from one side of the base layer to the other side, so as to optimize the heat dissipation performance and meet different requirements of thermal conductivity in different regions.

[0011] In one embodiment, thermally conductive fibers are further arranged in the porous filling layer, and the thermally conductive fibers extend along the depth direction of the heat dissipation hole to enhance the heat conduction capacity of the heat dissipation hole in the vertical direction.

[0012] In one embodiment, at least one reinforcement layer is disposed between the first core board and the second core board, and the reinforcement layer is made of a high-strength, high-toughness material to improve the overall mechanical strength and impact resistance of the circuit board.

[0013] In one embodiment, after step S3 "first layer etching" and step S8 "second layer etching", steps S3A and S8A are added respectively: electroplating thickening is performed on the etched first conductive layer and the second conductive layer to increase the thickness and current carrying capacity of the conductive layer, while enhancing the reliability of the circuit.

[0014] One or more of the above technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The multi-stage HDI circuit board and its manufacturing method provided by the embodiment of the present invention effectively increase the heat dissipation area and heat dissipation channel of the circuit board by setting heat dissipation holes in the base layer made of porous material and filling the porous material as a porous filling layer. The porous material has good air permeability and thermal conductivity, and can quickly conduct the heat generated inside the circuit board to the external environment, thereby greatly reducing the operating temperature of the circuit board and improving its stability and reliability. In addition, the via hole in the present application is cleverly designed. The via hole is accurately opened between the second conductive layer and the first conductive layer by laser drilling technology, and the conductive metal material is filled to achieve reliable conduction between the two conductive layers. This structure not only improves the efficiency of signal transmission, but also ensures the stability and accuracy of circuit connection. The design of the multi-layer structure, especially the addition of the PP layer (prepreg material layer), not only provides good insulation performance for the circuit board, but also significantly enhances its structural strength. This enables the circuit board to maintain a stable shape in a complex use environment and improves its bending and impact resistance. Finally, the use of porous materials as the base and filling layers not only reduces the cost of raw materials, but also reduces the need for additional heat dissipation devices or measures by optimizing the heat dissipation structure, thereby further reducing the overall manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the structure of a multi-level HDI circuit board provided by an embodiment of the present invention; Figure 2 A schematic diagram of a process flow of a method for manufacturing a multi-stage HDI circuit board provided in an embodiment of the present invention.

[0017] The respective reference numerals are as follows: 1. First core board; 2. Second core board; 3. Porous filling layer; 11. Base layer; 12. First conductive layer; 21. PP layer; 22. Second conductive layer; 23. Through hole; 24. Heat dissipation hole. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0020] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0021] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] See also Figure 1 to Figure 2, the embodiment of the present application provides a multi-stage HDI circuit board, including a first core board 1, a second core board 2 and a porous filling layer 3. The first core board 1 is composed of a porous material base layer 11 (such as foam metal, porous ceramic, etc.) and a first conductive layer 12 on the upper and lower sides. The second core board 2 is arranged on the outer layer of the first core board 1, including an inner PP layer 21 (prepreg material layer) and a second conductive layer 22 covering it. A via 23 and a heat dissipation hole 24 are opened on the PP layer 21 by laser drilling technology. The via 23 is filled with conductive metal material (such as copper, silver, etc.) to achieve conduction between the first conductive layer 12 and the second conductive layer 22. The heat dissipation hole 24 is a blind hole, located in the blank position of the first conductive layer 12, and the bottom is directly connected to the porous material base layer 11 to enhance the heat dissipation effect. The porous filling layer 3 is filled with a porous material with high thermal conductivity in the heat dissipation hole 24.

[0023] The porous material base layer 11 has a large number of pore structures, which can increase the heat dissipation area of ​​the circuit board and improve the heat conduction efficiency. The design of the heat dissipation hole 24 further increases the heat dissipation channel, so that the heat generated inside the circuit board can be quickly conducted to the external environment through the porous filling layer 3. At the same time, the realization of the through hole 23 ensures the efficient and stable connection of the circuit. This structural design significantly improves the heat dissipation performance and electrical performance of the HDI circuit board, and is suitable for high-density, high-power electronic devices.

[0024] Another object of the present invention is to provide a method for manufacturing a multi-level HDI circuit board, which is used to manufacture the multi-level HDI circuit board in the above embodiment. The method for manufacturing a multi-level HDI circuit board comprises the following steps: S1, cutting, cutting the base layer 11 sheet material and the first conductive metal layer sheet material according to the required size; specifically, using a high-precision CNC cutting machine to cut the base layer 11 sheet material and the first conductive metal layer sheet material, after cutting, the cutting edge is required to be smooth and burr-free, and the cut sheet material is cleaned to remove oil and impurities on the surface.

[0025] S2, the first lamination, the base layer 11 and the first conductive metal layer are stacked into a sandwich structure including the base layer 11, and a lamination process is performed; the base layer 11 sheet material and the first conductive metal layer sheet material are pressed together by a laminating machine, the pressing temperature is between 150-200°C, the pressing pressure is between 5-10MPa, and the pressing time is between 1-2 hours (the specific parameters are set according to the material properties), to ensure that the layers are tightly bonded.

[0026] S3, first layer etching, etching the first conductive metal layer to form the first conductive layer 12, and completing the production of the first core board 1. Select a suitable etching solution according to the material of the conductive metal layer, and during etching, the etching speed needs to be controlled at 0.1-0.2 mm / min to ensure uniform etching.

[0027] S4, second lamination, stacking the PP layer 21 and the second conductive metal layer on the upper and lower sides of the first core board 1, and then laminating; S5. Drill for the first time by laser drilling to open a via hole 23 between the second conductive metal layer and the first conductive layer 12. The via hole 23 is a blind hole, and the depth of the via hole 23 reaches the surface of the first conductive layer 12. The drilling method can be CO2 laser or ultraviolet laser (can be selected according to the material properties). The specific position of the via hole 23 is designed according to the conductive layer of the HDI board (the overlapping position of the first conductive layer 12 and the second conductive layer 22). The diameter of the via hole 23 is 0.3-0.5mm. When drilling, it is necessary to ensure that the depth reaches the surface of the first conductive layer 12.

[0028] S6, filling with conductive material, filling the conductive material (copper paste, silver paste or conductive polymer, etc.) into the via hole 23, so that the second conductive metal layer is connected to the first conductive layer 12; before filling the conductive material, a layer of electroplating can be electroplated on the inner wall of the via hole 23 by electroplating, and then the molten conductive material is filled into the conductive hole. The electroplating layer can fill the tiny unevenness of the inner wall of the via hole 23 to form a smoother surface, thereby reducing the resistance during current transmission and improving the conductive performance. In addition, the electroplating layer itself also has good conductivity, which can further reduce the contact resistance and make the conduction between the second conductive metal layer and the first conductive layer 12 smoother. And the electroplating layer can enhance the adhesion between the molten conductive material and the inner wall of the via hole 23, ensuring that the conductive material can fit tightly to the hole wall during the filling process and is not easy to fall off. It helps to improve the overall stability and reliability of the circuit board.

[0029] S7, grinding, grinding the second conductive metal layer to remove the conductive material protruding from the via hole 23; S8, second layer etching, etching the second conductive metal layer to form a second conductive layer 22; S9, drilling for the second time, using laser drilling to drill heat dissipation holes 24 on the PP layer 21, the drilling position avoids the first conductive layer 12 and the second conductive layer 22, and the heat dissipation holes 24 reach the surface of the base layer 11; S10, filling the holes with porous materials: filling the heat dissipation holes 24 with porous materials.

[0030] Specifically, the porous material is a polyolefin foam porous structure, which is filled by chemical foaming. First, a chemical foaming agent suitable for polyolefin materials is selected, such as azobisisobutyronitrile, trinitrosotrimethylenetriamine, etc.; an appropriate polyolefin material, such as polyethylene, polypropylene, etc., is selected as a matrix material; in addition, additives such as a compatibilizer, an antioxidant, and a lubricant can be added as needed. Then, the polyolefin, the chemical foaming agent and other additives are mixed evenly in a certain proportion. The mixed raw materials are added to an extruder or an injection molding machine for heating and plasticization. The plasticizing temperature should be controlled within the melting temperature range of the polyolefin material to ensure that the raw materials are fully melted and mixed evenly. During the plasticizing process, the chemical foaming agent will decompose and produce gas. These gases form bubble nuclei in the polyolefin melt. The polyolefin melt is squeezed into the heat dissipation hole 24 by an extruder or an injection molding machine. As the gas is continuously generated, the bubble nuclei gradually grow and form a cellular structure. After cooling, a polyolefin foam porous structure is formed in the heat dissipation hole 24.

[0031] S11, cutting the board, cutting the board into the target size according to the usage requirements.

[0032] In one embodiment, the porous material is selected from ceramics, metal oxides, porous polymers or combinations thereof, and the porous material has high thermal conductivity and good electrical insulation properties to optimize the heat dissipation effect and ensure the safety of the circuit. The selection of porous materials is crucial to the heat dissipation performance of the circuit board. The porous material with high thermal conductivity can quickly conduct heat from the inside of the circuit board to the external environment, reducing the operating temperature of the circuit board. At the same time, good electrical insulation properties ensure the safety and stability of the circuit. This material selection optimizes the heat dissipation effect and improves the reliability and service life of the circuit board.

[0033] In one embodiment, thermally conductive particles are also embedded in the porous filling layer 3, and the thermally conductive particles are any one of graphite, diamond, silicon carbide or aluminum oxide with high thermal conductivity, so as to further enhance the heat dissipation capacity of the heat dissipation hole 24. The embedding of thermally conductive particles further enhances the heat dissipation capacity of the heat dissipation hole 24. These particles have high thermal conductivity and can more effectively conduct heat from the inside of the circuit board to the external environment. At the same time, the dispersed distribution of the particles also increases the heat dissipation area and improves the heat dissipation efficiency. This design enables the circuit board to maintain stable performance in a high-power, high-density working environment.

[0034] In one embodiment, the laser drilling technology used in step S5 "first drilling" and step S9 "second drilling" is any one of CO2 laser, UV laser or femtosecond laser to ensure the accuracy and efficiency of drilling while reducing the thermal impact on surrounding materials. Laser drilling technology has the advantages of high precision and high efficiency. By selecting the appropriate laser type (such as CO2 laser, UV laser or femtosecond laser), precise aperture control and depth control can be achieved. At the same time, laser drilling has less thermal impact on the surrounding materials, avoiding material damage or performance degradation caused by thermal effects. This technology ensures the accuracy and efficiency of drilling and improves the manufacturing quality of circuit boards.

[0035] In one embodiment, the porous material of the base layer 11 has a gradient pore structure, wherein the porosity gradually changes from one side of the base layer 11 to the other side, so as to optimize the heat dissipation performance and meet different requirements of thermal conductivity in different regions.

[0036] The design of the gradient pore structure optimizes the heat dissipation performance and meets the different requirements of thermal conductivity in different areas. By adjusting the change of porosity, precise control of heat conduction can be achieved. In areas where higher heat dissipation efficiency is required, the porosity can be increased to improve thermal conductivity; in areas where higher mechanical strength is required, the porosity can be reduced to enhance material performance. This design improves the adaptability and flexibility of the circuit board.

[0037] Specifically, the porosity of the base layer 11 gradually increases from the side away from the electronic component mounting surface to the side close to the electronic component mounting surface, so that the heat generated by the electronic components on the HDI board and the HDI board itself can be quickly dissipated from the pores of the base layer 11.

[0038] In one embodiment, the porous filling layer 3 is further provided with heat-conducting fibers, which extend in the depth direction of the heat dissipation hole 24 to enhance the heat conduction capacity of the heat dissipation hole 24 in the vertical direction. The provision of the heat-conducting fibers enhances the heat conduction capacity of the heat dissipation hole 24 in the vertical direction. These fibers have high thermal conductivity and can more effectively conduct heat from the inside of the circuit board to the external environment. At the same time, the extension direction of the fibers also optimizes the heat conduction path and improves the heat dissipation efficiency. This design significantly improves the heat dissipation performance of the circuit board in the vertical direction.

[0039] In one embodiment, at least one reinforcement layer is provided between the first core board 1 and the second core board 2 , and the reinforcement layer is made of a high-strength, high-toughness material to improve the overall mechanical strength and impact resistance of the circuit board.

[0040] The setting of the reinforcement layer improves the overall mechanical strength and impact resistance of the circuit board. By selecting high-strength and high-toughness materials (such as glass fiber cloth, carbon fiber cloth, etc.), the circuit board's resistance to external impact and vibration can be enhanced. This design ensures the stability and reliability of the circuit board in harsh environments.

[0041] In one embodiment, after step S3 "first layer etching" and step S8 "second layer etching", steps S3A and S8A are added respectively: electroplating thickening is performed on the etched first conductive layer 12 and the second conductive layer 22 to increase the thickness and current carrying capacity of the conductive layer, while enhancing the reliability of the circuit.

[0042] The addition of the electroplating thickening step increases the thickness and current carrying capacity of the conductive layer. Depositing metal (such as copper) on the conductive layer through the electroplating process can increase its thickness and conductivity. This design improves the current density and reliability of the circuit board and is suitable for high-power, high-density electronic devices. At the same time, electroplating thickening also enhances the resistance of the conductive layer to the external environment and extends the service life of the circuit board.

[0043] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-level HDI circuit board, characterized in that: The multi-stage HDI circuit board: A first core board, the first core board comprising a base layer and a first conductive layer disposed on upper and lower sides of the base layer, the base layer being made of a porous material; A second core board, the second core board is arranged on the outer layer of the first core board, the second core board includes an inner PP layer and a second conductive layer covering the PP layer, the PP layer is provided with a via hole and a heat dissipation hole, the via hole connects the first conductive layer and the second conductive layer, the via hole is filled with a conductive metal material; the heat dissipation hole is a blind hole, the heat dissipation hole is located at a blank position of the first conductive layer, and the bottom of the heat dissipation hole directly passes through the base layer; A porous filling layer is arranged in the heat dissipation hole.

2. A method for manufacturing a multi-level HDI circuit board, used for manufacturing the multi-level HDI circuit board according to claim 1, characterized in that: The multi-stage HDI circuit board manufacturing method comprises the following steps: S1, cutting the base sheet and the first conductive metal layer sheet according to the required size; S2, first lamination, laminating the base layer and the first conductive metal layer into a sandwich structure including the base layer, and performing lamination; S3, first layer etching, etching the first conductive metal layer to form a first conductive layer, and completing the production of the first core board; S4, laminating for the second time, stacking the PP layer and the second conductive metal layer on the upper and lower sides of the first core board in sequence, and then laminating; S5, drilling for the first time, using laser drilling to open a via hole between the second conductive metal layer and the first conductive layer, the via hole is a blind hole, and the depth of the via hole reaches the surface of the first conductive layer; S6, filling with conductive material, filling the conductive material into the via hole, so that the second conductive metal layer is conductively connected to the first conductive layer; S7, grinding, grinding the second conductive metal layer to remove the conductive material protruding from the via hole; S8, second layer etching, etching the second conductive metal layer to form a second conductive layer; S9, drilling for the second time, using laser drilling to drill heat dissipation holes on the PP layer, the drilling position avoids the first conductive layer and the second conductive layer, and the depth of the heat dissipation holes reaches the surface of the base layer; S10, porous material filling, using porous material to fill the heat dissipation holes; S11, cutting the board, cutting the board into the target size according to the usage requirements.

3. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: The porous material is selected from ceramics, metal oxides, porous polymers or a combination thereof. The porous material has high thermal conductivity and good electrical insulation properties to optimize heat dissipation effects and ensure circuit safety.

4. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: The porous filling layer is also embedded with heat-conducting particles, which are any one of graphite, diamond, silicon carbide or aluminum oxide materials with high thermal conductivity, so as to further enhance the heat dissipation capacity of the heat dissipation holes.

5. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: The laser drilling technology used in step S5 "first drilling" and step S9 "second drilling" is any one of CO2 laser, UV laser or femtosecond laser to ensure the accuracy and efficiency of drilling while reducing the thermal impact on surrounding materials.

6. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: The porous material of the base layer has a gradient pore structure, in which the porosity gradually changes from one side of the base layer to the other side, so as to optimize the heat dissipation performance and meet the different requirements of thermal conductivity in different areas.

7. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: The porous filling layer is also provided with heat-conducting fibers, which extend along the depth direction of the heat dissipation holes to enhance the heat conduction capacity of the heat dissipation holes in the vertical direction.

8. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: At least one reinforcement layer is further arranged between the first core board and the second core board. The reinforcement layer is made of a high-strength, high-toughness material to improve the overall mechanical strength and impact resistance of the circuit board.

9. The method for manufacturing a multi-level HDI circuit board according to claim 2, characterized in that: After step S3 "first layer etching" and step S8 "second layer etching", steps S3A and S8A are added respectively: electroplating thickening, the first conductive layer and the second conductive layer after etching are electroplated to increase the thickness and current carrying capacity of the conductive layer, while enhancing the reliability of the circuit.

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