Flexible circuit board with fast heat dissipation and preparation method thereof

Abstract

The invention discloses a flexible circuit board with fast heat dissipation and a preparation method thereof, and the method comprises the following steps: carrying out the thermocompression bonding and glue curing of a first insulating layer and a copper foil, carrying out the local gradual etching of the copper foil to form a needed circuit layer, and obtaining an FPC prefabricated product, carrying out the thermocompression bonding and hardening of a second insulating layer and the FPC prefabricated product, and carrying out the heat dissipation of the FPC prefabricated product. And the flexible circuit board with the heat dissipation flow channel is manufactured. According to the manufactured flexible circuit board, the circuit layer is provided with the through heat dissipation flow channel, the first insulating layer and the second insulating layer wrap the circuit layer, meanwhile, the heat dissipation flow channel allowing the heat dissipation medium to flow is formed, and the flexible circuit board has the advantages of being fast in heat dissipation and high in interlayer binding force.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible circuit boards, and in particular to a flexible circuit board with fast heat dissipation and a preparation method thereof. Background Art

[0002] With the continuous development of electronic devices, high-power and high-integration electronic devices have increasingly stringent requirements on the heat dissipation performance of flexible printed circuit boards (FPCs).

[0003] There are already some invention patents to solve the problem of improving the heat dissipation performance of electronic equipment and improving the performance and reliability of the equipment. For example: Patent CN109922599A discloses a circuit board and its manufacturing method, as well as an electronic component and electronic equipment including a circuit board. This patent adds a heat-conducting layer in the circuit board, and through the changes in the liquid phase and gas phase of the cooling medium in the heat-conducting layer, it can efficiently transfer heat from the high-temperature area to the low-temperature area, thereby enhancing the heat transfer effect of the circuit board. CN207283913U discloses a microchannel heat dissipation circuit board, the front of the circuit substrate is printed with a metal circuit layer, the back side is arranged corresponding to the front side of the heat dissipation substrate, the board surface of the heat dissipation substrate is provided with a penetrating microchannel, the back side of the heat dissipation substrate is arranged with a packaging substrate, and the board surface of the packaging substrate is provided with water inlet and outlet holes at both ends of the microchannel. The existing solutions all require an additional heat-conducting layer or heat dissipation layer to achieve the heat dissipation effect, with many processing steps and high costs.

[0004] In addition, the traditional FPC heat dissipation method has the following problems: the service life of the traditional FPC is short, which can easily cause the insulation layer and the copper layer of the circuit to delaminate and disintegrate, thus causing serious quality accidents caused by the spraying of coolant; secondly, the heat transfer efficiency and uniformity are poor, which makes it difficult to meet the heat dissipation requirements of high-power and highly integrated electronic devices. The heat dissipation effect is unstable, and continuous and uniform heat dissipation cannot be achieved. The existing FPC heat dissipation structure is complex, and an additional heat dissipation layer or heat conductive layer is required, which is costly.

[0005] The above problems restrict the heat dissipation performance of FPC, which in turn affects the overall performance and reliability of electronic equipment. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to design a flexible circuit board with a heat dissipation channel, increase the flow rate and improve the cooling efficiency by designing a reasonable channel structure; optimize the channel corner structure to reduce resistance and increase the flow rate; use high temperature resistant and chemical corrosion resistant materials to extend the service life and avoid coolant spray accidents. Through the above-mentioned technical means, the heat dissipation performance of electronic equipment can be effectively improved, thereby improving the overall performance and reliability of the equipment.

[0007] In order to achieve the above-mentioned purpose, the technical solution provided by the present invention is: a method for preparing a flexible circuit board with fast heat dissipation, comprising the following steps: hot pressing and adhesive curing treatment of a first insulating layer and a copper foil; performing local progressive etching on the copper foil to form a circuit layer with a hollow flow channel to obtain an FPC preform; the local progressive etching is to etch the copper foil in multiple times, and apply a layer of anti-etching ink each time etching to prevent etching of the side of the copper foil;

[0008] The second insulating layer is covered on the surface of the FPC preform away from the first insulating layer, and subjected to heat pressing and hardening treatment to obtain a flexible circuit board with a heat dissipation channel.

[0009] Furthermore, it also includes a flow channel stamping molding process. Specifically, a convex structure with an arc or semi-elliptical shape is punched out at the position corresponding to the hollow flow channel of the first insulating layer in the FPC preform, and hardened; a matching arc or semi-elliptical convex structure is punched out on the second insulating layer, and hardened; the convex structure on the insulating layer and the hollow flow channel form a heat dissipation flow channel of the flexible circuit board.

[0010] After the channel stamping process, the second insulating layer is covered on the side of the FPC preform away from the first insulating layer, and hot pressing and adhesive curing are performed.

[0011] Furthermore, it also includes a surface roughening treatment of the copper foil, wherein the roughening treatment is a combination of combined wire drawing and sandblasting to roughen the surface of the copper foil; the combined wire drawing refers to horizontal wire drawing once and vertical wire drawing once to form a tic-tac-toe-shaped mark on the surface of the copper foil.

[0012] Furthermore, the etching rate is set at 800nm / min-1200nm / min.

[0013] Furthermore, the hardening treatment temperature is 180°C-185°C and the baking time is 20-24 hours.

[0014] Furthermore, the heat pressing temperature is between 180° C. and 185° C., the pressure is between 100 PSI and 105 PSI, and the heat pressing time is between 120 seconds and 180 seconds.

[0015] Preferably, the glue curing treatment is carried out by baking at a temperature of 160° C.-165° C. for 2 h-3 h.

[0016] Another object of the present invention is to provide a flexible circuit board with fast heat dissipation, comprising a circuit layer and an insulating layer stacked in layers; the insulating layer comprises a first insulating layer and a second insulating layer, the first insulating layer and the second insulating layer are arranged on two surfaces of the circuit layer opposite to each other; the circuit layer is provided with a penetrating heat dissipation channel, the first insulating layer and the second insulating layer wrap the circuit layer therein, forming a heat dissipation channel for the flow of heat dissipation medium. A liquid inlet and a liquid outlet are respectively arranged at both ends of the heat dissipation channel.

[0017] Preferably, the first insulating layer and the second insulating layer are provided with protruding structures matching the heat dissipation channels, and the protruding structures on the upper and lower layers facing each other form a receiving groove for accommodating the heat dissipation medium.

[0018] Preferably, the corners of the heat dissipation channel are chamfered.

[0019] The characteristics of the structure of the present invention are mainly:

[0020] 1. The process of the present invention forms a new type of FPC with optimized structure design, improves the heat dissipation performance of the FPC, reduces the operating temperature, and improves the reliability and stability of the equipment. The heat dissipation flow channel is directly designed in the circuit layer, and the shape, size and layout of the flow channel are reasonably designed to improve the heat dissipation efficiency and reduce the production cost.

[0021] 2. The process of the present invention maintains the flexibility and bendability of the FPC and does not affect its installation and use in electronic equipment.

[0022] 3. The process of the present invention increases the adhesion between the FPC layers, and the joints are completely cured to prevent disintegration and delamination. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the process flow of Example 1 of the present invention.

[0024] Figure 2 It is a schematic diagram of the process flow of Example 2 of the present invention.

[0025] FIG3(a) is a schematic diagram of the structure of Example 1 of the present invention, and FIG3(b) is a partial enlarged diagram of (a).

[0026] FIG4(a) is a schematic diagram of the structure of Example 2 of the present invention, and (b) is a partial enlarged view of (a).

[0027] Figure 5 This is a schematic diagram of the circuit layer formed after copper foil etching.

[0028] Figure 6 It is a schematic diagram of the decomposition of Figure 4(a).

[0029] Reference numerals: 100, flexible circuit board; 1, circuit layer; 2, insulation layer; 3, bonding layer; 4, heat dissipation channel; 5, liquid inlet; 6, liquid outlet; 7, corner; 8, first insulation layer; 9, second insulation layer; 10, protrusion structure; 11, etched copper foil DETAILED DESCRIPTION

[0030] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below in conjunction with specific embodiments. It should be clear that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] The "first\second" mentioned in the embodiments is only to distinguish similar objects, and does not represent a specific order for the objects. It is understandable that the "first\second" can be interchanged with the specific order or sequence where permitted. It should be understood that the objects distinguished by "first\second" can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than those illustrated or described herein.

[0032] A flexible circuit board 100 with fast heat dissipation includes a circuit layer 1 and an insulating layer 2 which are stacked; the insulating layer 2 is a polyimide film, including a first insulating layer 8 and a second insulating layer 9; the first insulating layer 8 and the second insulating layer 9 are arranged on two surfaces of the circuit layer 1 opposite to each other; the circuit layer 1 is a metal layer. The circuit layer 1 and the insulating layer 2 are connected by an adhesive layer 3. The circuit layer 1 is provided with a penetrating heat dissipation channel 4, and the first insulating layer 8 and the second insulating layer 9 wrap the circuit layer 1 therein, and at the same time form a heat dissipation channel 4 for the flow of heat dissipation medium. A liquid inlet 5 and a liquid outlet 6 are respectively provided at both ends of the heat dissipation channel 4. Preferably, the cross section of the heat dissipation channel 4 is rectangular, elliptical or arc-shaped. Preferably, the corner 7 of the heat dissipation channel 4 is chamfered.

[0033] When in use, a heat dissipation medium is injected into the heat dissipation channel 4. The heat dissipation medium may be water, ethylene glycol or ethylene glycol aqueous solution, etc. When the heat dissipation medium flows in the heat dissipation channel 4, due to the optimized design of the heat dissipation channel 4 structure, the flow rate is large and the flow rate is fast, so that the heat of the heating area can be replaced in time.

[0034] Embodiment 1, rectangular heat dissipation channel 4

[0035] (1) Preliminary preparation

[0036] Material selection: Choose the right copper foil and polyimide film. The copper foil should have good conductivity and etching properties, and generally use electrolytic copper foil or rolled copper foil with a thickness of 210μm-350μm; the polyimide film needs to have excellent insulation properties, high temperature resistance and mechanical strength, and the commonly used thickness is 50μm-75μm.

[0037] Copper foil pretreatment: Clean and surface treat the copper foil to remove impurities such as oil and oxides on the surface, enhance the contact effect between the copper foil and the etching solution, and improve the etching quality. Common pretreatment methods include chemical cleaning, mechanical polishing, etc.

[0038] (2) Prepare the first insulating layer 8, and combine the polyimide film with the roughened copper foil after backing. The industry generally adopts chemical micro-etching, polishing, and sandblasting to roughen the copper foil. The roughening effect is limited, mainly because the depth of the copper surface roughening is shallow. The present invention uses a combination of combined wire drawing and sandblasting to roughen the copper foil surface. The combined wire drawing refers to drawing horizontally once and vertically once, so as to form a well-shaped trace. Sandblasting is performed on the basis of wire drawing to deepen and evenly increase the roughness of the copper surface, increase the adhesion of polyimide and copper surface, and meet the use requirements of FPC after testing. The specific test data are shown in Table 1 below.

[0039] Table 1 Example 1 Insulation layer and copper layer adhesion tensile test

[0040]

[0041] (3) Thermal pressing and adhesive curing of the first insulating layer and copper foil

[0042] The polyimide film coated with adhesive is laminated with the copper foil to ensure that the copper foil and the polyimide film are tightly bonded without bubbles or wrinkles. After bonding, hot pressing is performed, followed by adhesive curing. The selection of adhesives should consider factors such as compatibility with copper foil and polyimide film, bonding strength, and high temperature resistance. Commonly used adhesives include acrylics and epoxy resins. The coating method can be screen printing, coating machine coating, etc. to ensure that the adhesive is evenly distributed on the surface.

[0043] The heat pressing temperature, pressure and time are the key parameters that affect the heat pressing effect. Generally, the heat pressing temperature is between 180℃-185℃, the pressure is between 100PSI-105PSI, and the heat pressing time is between 120 seconds-180 seconds. The selection of specific parameters should be adjusted according to the characteristics of the material and the requirements of the product.

[0044] The adhesive curing treatment is carried out by baking at 160°C-165°C for 2 hours-3 hours to cure the adhesive.

[0045] (4) The copper foil is locally and gradually etched into the required circuit layer 1, such as Figure 5 shown.

[0046] Coating photoresist: A layer of photoresist is evenly coated on the surface of the copper foil. The thickness of the photoresist is generally between a few microns and more than ten microns. The coating method can be spin coating, spray coating or roller coating to ensure that the photoresist forms a complete and uniform protective film on the surface of the copper foil.

[0047] Exposure and development: The copper foil coated with photoresist is exposed through an exposure device, so that the photoresist undergoes a photochemical reaction in a specific area, changing its solubility. The exposed copper foil is then developed to remove the photoresist in the unexposed area, exposing the copper foil surface that needs to be etched.

[0048] Etching: The copper foil that has been exposed and developed is placed in an etching solution for etching. The etching solution usually uses an acidic or alkaline solution, such as ferric chloride solution, ammonium persulfate solution, etc., which corrodes the exposed copper foil through a chemical reaction to form the desired circuit pattern, such as Figure 5 The schematic diagram of the circuit layer 1 after etching is shown, and a continuous hollow flow channel is formed in the etched area. During the etching process, it is necessary to control the concentration, temperature, etching time and other parameters of the etching solution to ensure the accuracy and quality of the etching. Generally, the etching temperature is controlled between 40°C and 60°C, and the etching rate is determined according to the thickness of the copper foil and the complexity of the circuit pattern. The etching rate of the present invention is set at 800nm / min-1200nm / min.

[0049] After demoulding, the FPC preform is obtained.

[0050] It is worth noting that the existing process for etching thick copper ( ≧ 3OZ) is prone to side corrosion, causing the line spacing to deform into a "trapezoidal" shape. In order to solve this problem and prevent the heat dissipation channel 4 from deforming, the present invention adopts a new local progressive etching process. This process etches the copper foil multiple times, that is, each time it is etched, it is coated with an anti-etching ink, and this process is repeated. This can prevent the side corrosion of the line and achieve the purpose of preventing the heat dissipation channel 4 from deforming. Finally, it is formed Figure 5 In the circuit layer 1 shown, the etched portion and the etched copper foil 11 form a hollow flow channel.

[0051] (5) Thermal compression and hardening of the second insulating layer 9 and the circuit layer 1

[0052] Applying adhesive: Apply a layer of adhesive on one side of the circuit layer 1 of the FPC preform.

[0053] Lamination: Take another polyimide film as the second insulating layer 9 and cover it on the adhesive on the surface of the FPC preform to make the etched surface of the copper foil fit closely with the second insulating layer 9. During the lamination process, care should be taken to avoid bubbles and wrinkles. Vacuum assisted lamination or pressurized lamination can be used to improve the quality of lamination.

[0054] The laminated materials are placed in a heat press machine for heat pressing and then hardening treatment. The heat pressing parameters are the same as those for processing the first insulating layer 9.

[0055] The curing treatment is carried out at a temperature of 180°C-185°C and a time of 20-24 hours. Compared with the commonly used parameters of 160°C in the industry, the present invention can not only fully crosslink and cure the adhesive, improve the bonding strength between the copper foil and the polyimide film, but also harden the polyimide film at the same time to ensure that the shape of the subsequent heat dissipation channel 4 is not deformed. The hardness test data of the polyimide film after hardening is shown in Table 2.

[0056] Table 2 Example 1 Insulation layer hardness test

[0057]

[0058] (6) Finally, the flexible circuit board 100 with a rectangular heat dissipation channel 4 as shown in FIG. 3(a) is obtained. FIG. 3(b) is a partial enlarged view of A in FIG. 3(a), which is a first insulating layer 8, an adhesive layer 3, a circuit layer 1, an adhesive layer 3, and a second insulating layer 9 from top to bottom. A heat dissipation channel 4 is formed at the hollow channel. The flow rate test of the flexible circuit board 100 is performed, and the data is shown in Table 3:

[0059] Table 3 Flow rate test of rectangular heat dissipation channel 4

[0060]

[0061] In addition, the final product is tested, including appearance inspection, dimension measurement, electrical performance test, etc., to ensure that the product quality meets the requirements. The appearance inspection mainly checks whether there are defects such as bubbles, wrinkles, delamination, etc.; the dimension measurement checks whether the dimensional accuracy of the circuit pattern meets the design requirements; the electrical performance test includes the measurement of parameters such as resistance, capacitance, inductance, etc. to evaluate the electrical performance of the product.

[0062] Embodiment 2 is a method for manufacturing an FPC having an arc-shaped heat dissipation channel 4. The specific steps are the same as those of embodiment 1, except that a channel stamping molding step is added.

[0063] More specifically, according to step (1) to step (4) of embodiment 1, after step (4) is completed, that is, after etching is completed, the FPC preform removed from the mold is punched out with a protruding structure 10 having an arc or semi-elliptical shape at the position corresponding to the hollow channel of the first insulating layer 8, and then hardened immediately to keep the shape of the protruding structure 10 stable. At the same time, a matching protruding structure 10 having an arc or semi-elliptical shape is punched out of the second insulating layer 9 in the same mold, and hardened in the same manner. In this way, the protruding structures 10 of the first insulating layer 8 and the second insulating layer 9 and the hollow channel form the heat dissipation channel 4 of the flexible circuit board 100.

[0064] After the hardening treatment, take out the FPC preform and the second insulating layer 9 respectively, apply adhesive on the surface of the circuit layer 1 of the FPC preform, fit it tightly with the second insulating layer 9, put it into the corresponding jig (the jig has a yielding position that matches the heat dissipation channel 4), and put the jig into a vacuum hot press for hot pressing and glue curing treatment. The hot pressing temperature is 180℃-185℃, the pressure is 10PSI-15PSI, and the time is 120 seconds-180 seconds. The glue curing treatment uses 160℃-165℃ for 2 hours-3 hours to cure the adhesive.

[0065] Finally, a flexible circuit board 100 with an arc-shaped heat dissipation channel 4 or an elliptical heat dissipation channel 4 as shown in FIG. 4(a) is obtained. FIG. 4(b) is a partial enlarged view of B in FIG. 4(a), which is a first insulating layer 8, an adhesive layer 3, a circuit layer 1, an adhesive layer 3, and a second insulating layer 9 from top to bottom. The protruding structure 10 of the first insulating layer 8 and the second insulating layer 9 together with the hollow channel form a heat dissipation channel 4. The flow rate test of the flexible circuit board 100 is shown in Table 6. Figure 6 4(a) is an exploded schematic diagram, the heat dissipation channel 4 is arranged on the circuit layer 1, and no additional heat conduction structure is required. The heat dissipation channel 4 with the protruding structure 10 designed in the second embodiment has a flow rate greater than the rectangular heat dissipation channel 4 in the first embodiment, and has better heat dissipation performance.

[0066] Table 4 Example 2 Insulation layer and copper layer adhesion tensile test

[0067]

[0068] Table 5 Insulation layer hardness test of Example 2

[0069]

[0070] Table 6 Flow rate test of heat dissipation channel 4 in Example 2

[0071]

[0072] Embodiment 2, through reasonable design and optimization, develops a flexible circuit board 100 with fast heat dissipation and simple structure. Compared with embodiment 1, the flow rate is faster, which can solve the problems of slow flow rate, inability to replace and cool the coolant in time, short service life and easy stratification and disintegration of coolant injection, and the heat dissipation performance, electrical performance and mechanical performance are reliable, which can realize efficient heat dissipation of FPC and improve the performance and stability of electronic equipment.

[0073] In some embodiments, the corner 7 of the heat dissipation channel can be designed as a chamfer to further reduce resistance. For example, the corner 7 is optimized by using a chamfer design of R0.5MM to reduce resistance and achieve the best channel flow parameters.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a flexible circuit board with fast heat dissipation, characterized in that: The following steps are involved: Thermal pressing and adhesive curing of the first insulating layer and the copper foil; Performing local progressive etching on the copper foil to form a circuit layer with a hollow flow channel to obtain an FPC preform; The local progressive etching is to etch the copper foil piece several times, and apply a layer of anti-etching ink each time etching to prevent the copper foil from being etched on the side; The second insulating layer is covered on the surface of the FPC preform away from the first insulating layer, and subjected to heat pressing and hardening treatment to obtain a flexible circuit board with a heat dissipation channel.

2. The method for preparing a flexible circuit board with fast heat dissipation according to claim 1, characterized in that: It also includes a channel stamping molding process: specifically, a convex structure with an arc or semi-elliptical shape is punched out at the position of the first insulating layer in the FPC preform corresponding to the hollow channel, and the convex structure is hardened; a matching arc or semi-elliptical convex structure is punched out from the second insulating layer, and the convex structure is hardened; the convex structure and the hollow channel form a heat dissipation channel for the flexible circuit board.

3. The method for preparing a flexible circuit board with fast heat dissipation according to claim 2, characterized in that: After the channel stamping process, the second insulating layer is covered on the side of the FPC preform away from the first insulating layer, and hot pressing and adhesive curing are performed.

4. The method for preparing a flexible circuit board with fast heat dissipation according to claim 1, characterized in that: It also includes a surface roughening treatment of the copper foil, wherein the roughening treatment is a combination of a combined wire drawing and a sandblasting process; the combined wire drawing refers to a horizontal wire drawing once and a vertical wire drawing once, forming a tic-tac-toe-shaped mark on the surface of the copper foil.

5. The method for preparing a flexible circuit board with fast heat dissipation according to claim 1, characterized in that: The etching rate of the local progressive etching is set at 800nm / min-1200nm / min.

6. The method for preparing a flexible circuit board with fast heat dissipation according to claim 1, characterized in that: The hardening treatment is carried out by baking at a temperature of 180° C.-185° C. for 20-24 hours.

7. The method for preparing a flexible circuit board with fast heat dissipation according to claim 1, characterized in that: The hot pressing temperature is between 180°C and 185°C, the pressure is between 100PSI and 105PSI, and the hot pressing time is between 120 seconds and 180 seconds; the adhesive curing process adopts baking at a temperature of 160°C to 165°C for 2h to 3h.

8. A flexible circuit board, made according to the preparation method according to any one of claims 1 to 7, characterized in that: It comprises a circuit layer and an insulating layer which are stacked; the insulating layer comprises a first insulating layer and a second insulating layer, the first insulating layer and the second insulating layer are arranged oppositely on two surfaces of the circuit layer; the circuit layer is provided with a penetrating heat dissipation channel, the first insulating layer and the second insulating layer wrap the circuit layer therein, forming a heat dissipation channel for the flow of heat dissipation medium.

9. The flexible circuit board according to claim 8, characterized in that: The first insulating layer and the second insulating layer are provided with protruding structures matching the heat dissipation flow channel, and the protruding structures on the upper and lower layers facing each other form a receiving groove for accommodating the heat dissipation medium.

10. The flexible circuit board according to claim 8, characterized in that: The corners of the heat dissipation channel are chamfered.

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