CN116583009A - A bending-resistant copper-based self-healing double-layer circuit and its high-precision manufacturing process - Google Patents

Abstract

A bending-resistant copper-based self-healing double-layer circuit and its high-precision manufacturing process, including a base layer, a conductive layer, and a conductive repair layer arranged in sequence; the conductive layer covered above the base layer is a copper film, using different line widths Copper path; the conductive repair layer is gallium indium tin alloy; the manufacturing process is to perform photolithography and other treatments on the conductive layer covered on the base layer, so that the conductive layer becomes a copper path with a set line width; then the base layer processed by the copper path And the conductive layer is placed in the solution environment, the liquid metal is dropped into the solution, and the surface of the conductive layer is naturally wetted; then the base layer and the conductive layer that have been wetted with the liquid metal are cured at low temperature to obtain a conductive repair layer, and the conductive repair layer The polyimide precursor solution is spin-coated as the encapsulation layer, and finally the polyimide precursor solution is cured at high temperature; the anti-bending copper-based self-healing double-layer circuit of the present invention will automatically crack the copper conductor under the condition of multiple bending healing, improving the electrical performance of flexible circuits and enabling high-precision fabrication.

Description

A bending-resistant copper-based self-healing double-layer circuit and its high-precision manufacturing process

technical field

The invention relates to the technical field of micro-nano manufacturing and flexible circuit processing, in particular to a bending-resistant copper-based self-healing double-layer circuit and its high-precision manufacturing process.

Background technique

Flexible circuit (FPC) is a printed circuit with high reliability and excellent flexibility made of polyester film or polyimide as the base material. By embedding the circuit design on a bendable thin plastic sheet, Stack a large number of precision components in a small and limited space to form a bendable flexible circuit.

The existing flexible circuit (FPC) structure is a base layer of polyester film or polyimide, a conductive layer of copper, which is prepared above the base layer by gluing or hot pressing, and then wraps the conductive layer through the packaging layer to form a flexible circuit ([ 1]Y.Tang,H.Li,J.Sheng,B.Sun,J.Wang,C.Zhang,D.Zhang,Y.Huang.Study on wet chemicaletching of flexible printed circuit board with 16-μm line pitch. Journal of Electronic Materials. 52(6), 4030-4036(2023).

https://doi.org/10.1007/s11664-023-10368-z; [2] A. Salahouelhadj, M. Martiny, S. Mercier, L. Bodin, D. Manteigas, B. Stephan. Reliability of thermally stressed rigid– flex printed circuit boards for high density interconnect applications.Microelectronics Reliability.54(1),204-213(2014).https://doi.org/https://doi.org/10.1016/j.microrel.2013.08.005) . However, the current flexible circuit (FPC) has the disadvantage of poor bending durability. The bending durability of the flexible circuit will directly affect the service life of the flexible circuit. The durability of flexible electronic devices under strain largely depends on the formation of cracks/ Expansion, flexible circuits often need to be bent during work. Under a certain number of bending times, the copper conductor of the conductive layer will cause cracks in the copper circuit under the action of bending fatigue stress, which will lead to a decrease in the electrical performance of the flexible circuit and even lead to a flexible circuit. Circuit failure ([3]H.D.Merchant, M.G.Minor, S.J.Clouser, D.T.Leonard.18m electrodeposited copper foil for flexfatigue applications.Circuit World.25(1),38-46(1999).

https://doi.org/10.1108/03056129910244842; [4] B.-J.Kim, H.-A.S.Shin, J.-H.Lee, Y.-C.Joo. Effect of cyclic outer and inner bending on the fatigue behavior of a multi-layer metal film on a polymer substrate. Japanese Journal of Applied Physics. 55(6S3), 06JF01(2016).

https://doi.org/10.7567/JJAP.55.06JF01; [5]K.-H.Huang, J.-G.Duh.Fatiguecharacterization for flexible circuit with polyimide on adhesivelesscopper.Journal of Electronic Materials.44(10) , 3934-3941 (2015). https://doi.org/10.1007/s11664-015-3865-7).

Contents of the invention

In order to overcome the shortcomings of the above-mentioned prior art, the object of the present invention is to provide a bending-resistant copper-based self-healing double-layer circuit and its high-precision manufacturing process. Cracks in the copper conductor will self-heal when bent, improving the electrical performance of the flexible circuit and enabling high-precision manufacturing.

In order to achieve the above object, the technical scheme that the present invention takes is:

A bending-resistant copper-based self-healing double-layer circuit, including a base layer 1, a conductive layer 2, and a conductive repair layer 3 arranged in sequence;

The base layer 1 is polyimide; the conductive layer 2 covered above the base layer 1 is a copper film, and copper paths with different line widths are used;

The conductive repair layer 3 is a gallium indium tin alloy, which is a liquid metal alloy, and the conductive repair layer 3 has a repair effect on the conductive layer 2 .

The height H of the conductive repair layer 3 has the following relationship with the line width 1 of the conductive layer 2:

Where θ is the contact angle of the conductive repair layer 3 on the conductive layer 2 .

An encapsulation layer 4 is arranged above the conductive repair layer 3, and the encapsulation layer 4 is a polyimide precursor solution.

The high-precision manufacturing process of a bending-resistant copper-based self-healing double-layer circuit includes the following steps:

S1: Perform photolithography, development, and etching on the conductive layer 2 covered on the base layer 1, so that the conductive layer 2 forms a copper path with a set line width;

S2: Place the base layer 1 and the conductive layer 2 processed with copper vias in step S1 in a solution environment, drop the liquid metal into the solution, and naturally wet the surface of the conductive layer 2;

S3: The base layer 1 and the conductive layer 2 that have been wetted with liquid metal in step S2 are cured at low temperature to obtain a conductive repair layer 3, and a polyimide precursor solution is used to spin coat the conductive repair layer 3 as the encapsulation layer 4, and finally the polyimide The imide precursor solution is cured at high temperature.

In the step S1, the base layer 1 is a polyimide film with a thickness of 20-30 μm; the conductive layer 2 is a rolled copper film with a thickness of 10-15 μm; the copper etching solution is FeCl ₃ solution.

The solution environment in the step S2 is NaOH solution with a mass fraction of 20-40%.

In the low-temperature curing process in step S3, the temperature is below 8°C.

In the anti-bending copper-based self-healing double-layer circuit prepared through steps S1-S3, when the copper circuit cracks under a certain number of times of bending, the liquid metal in the conductive repair layer 3 flows into the cracks in the conductive layer 2, thereby To improve the bending resistance of the electrical performance of the circuit.

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

The manufacturing process of the present invention, through photolithography and etching technology, can make the copper path width of the flexible circuit conductive layer 2 below the micron scale, realize the high precision and high density of the flexible circuit, and provide the possibility for the development of high integration of flexible electronic technology .

The principle of the anti-bending copper-based self-healing double-layer circuit of the present invention is to fill copper cracks with liquid metal. When the flexible circuit is bent for a certain number of times, the conductive layer 2 generates cracks, and the liquid metal in the conductive repair layer 3 will be filled to In order to improve the electrical performance of the circuit, in the bending performance test of the flexible circuit, the flexible circuit can still maintain good electrical performance under the condition of 60,000 folds; 230,000 times of 0.5mm bending Radius, the flexible circuit can still maintain good electrical performance.

Description of drawings:

FIG. 1 is a cross-sectional view of a bending-resistant copper-based self-healing double-layer circuit structure according to an embodiment of the present invention.

Fig. 2 is a schematic diagram of the contact angle of the liquid metal on the copper surface according to the embodiment of the present invention.

Fig. 3 is a working principle diagram of a flexible circuit without a conductive repair layer and an anti-bending copper-based self-healing double-layer circuit according to an embodiment of the present invention.

Fig. 4 is an electron microscope top view of a bending-resistant copper-based self-healing double-layer circuit according to an embodiment of the invention.

FIG. 5 is a physical diagram of a bending-resistant copper-based self-healing double-layer circuit according to an embodiment of the present invention.

FIG. 6 is a comparison diagram of the bending performance of an anti-bending copper-based self-healing double-layer circuit and a copper circuit according to an embodiment of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the embodiments and the accompanying drawings. The following examples help those skilled in the art to better understand the contents of the invention, but do not limit the invention in any form. It should be noted that, on the premise of no creative work, those skilled in the art may also make some deformations or improvements in materials, structures or array types on the basis of the basic concept of the present invention, which all belong to the protection of the present invention. scope.

As shown in FIG. 1 , a self-healing double-layer circuit of anti-bending copper base includes a base layer 1, a conductive layer 2, a conductive repair layer 3 and an encapsulation layer 4 arranged in sequence;

The base layer 1 is a polyimide film, the conductive layer 2 is a rolled copper film, adopts copper paths with different line widths, and the conductive layer 2 will be used as the base of the conductive repair layer 3;

The conductive repair layer 3 is gallium indium tin alloy, which is a liquid metal alloy. The conductive repair layer 3 is located above the conductive layer 2. The conductive repair layer 3 has a repair effect on the conductive layer 2 and will not remain in the base layer 1. ; The height H of the conductive repair layer 3 has the following relationship with the line width 1 of the conductive layer 2 simultaneously:

Wherein θ is the contact angle of the conductive repair layer 3 on the conductive layer 2. In this embodiment, θ is 26°. As shown in FIG. 2, the liquid metal of the conductive repair layer 3 can easily wet on the copper of the conductive layer 2.

An encapsulation layer 4 is provided above the conductive repair layer 3, and the encapsulation layer 4 is a polyimide precursor to protect and isolate the circuit. The entire flexible circuit is a four-layer stacked flexible circuit structure.

As shown in Figure 3, the working principle of the anti-bending copper-based self-healing double-layer circuit is: the copper circuit on the conductive layer 2 produces cracks due to bending fatigue stress during the bending process, and the conductive layer 2 above The conductive repair layer 3 liquid metal has high fluidity, high conductivity and good wettability on the copper surface. When the conductive layer 2 copper produces bending fatigue cracks, the conductive repair layer 3 liquid metal fills the conductive layer 2 copper cracks, so as to improve the bending resistance of the flexible circuit; the existing flexible circuit that does not contain the liquid metal of the conductive repair layer 3, after the cracks appear in the copper of the conductive layer 2, the electrical performance declines, and the anti-bending copper base of the present invention The self-healing double-layer circuit has the advantages of high-precision design and resistance to bending.

As shown in Figure 4, Figure 4 is a top view of the anti-bending copper-based self-healing double-layer circuit electron microscope, it can be seen that there is no liquid metal on the base layer 1 polyimide film, and the conductive repair layer 3 liquid metal It only exists directly above the copper of the conductive layer 2, so as to ensure that there will be no short circuit between the wires in the flexible circuit.

The thickness of the base layer 1 polyimide film is 25 μm; the thickness of the conductive layer 2 is 13 μm.

The high-precision manufacturing process of a bending-resistant copper-based self-healing double-layer circuit includes the following steps:

S1: First make the pattern of the copper circuit on the conductive layer 2, and the copper patterning process chooses the traditional photolithography-etching process; spin-coat a layer of photoresist on the surface of the base layer 1, that is, the PI copper-clad film, the model is EPG535, the parameters of the homogenizer are set at a low speed of 50rpm, the duration is 15s, and the high speed is 1500rpm, and the duration is 40s; after the homogenization is completed, place the PI copper clad film on the drying table at 90°C for 7min to ensure the PI copper clad The photoresist on the surface of the film is completely dried; then a specific mask is placed on the PI copper-clad film and exposed for 8s with a photolithography machine, then placed in a 5‰ NaOH solution for 12s, and then blown dry after taking it out, so that The conductive layer 2 forms a copper path with a set line width;

S2: Place the base layer 1 and the conductive layer 2 with the copper vias processed in step S1 in a 30% NAOH solution environment, drop the liquid metal into the solution, and naturally wet the surface of the conductive layer 2 to move the base layer. The bottom layer 1 and the conductive layer 2 make the liquid metal evenly wet the surface of the copper circuit;

S3: The base layer 1 and the conductive layer 2 that have been wetted with the liquid metal in step S2 are subjected to low-temperature cooling with liquid nitrogen, so that the liquid metal appears in a solid state to obtain a conductive repair layer 3, and polyimide is used on the conductive repair layer 3 The precursor solution is spin-coated as the encapsulation layer 4. The spin-coating parameters of the homogenizer are: the high-speed rotation speed is 500rpm, and the duration is 20s, so that the polyimide precursor solution is uniformly coated on the surface of the wet liquid metal, and finally the entire flexible The circuit is put into a constant temperature oven for curing. The curing parameters are: constant temperature 200°C, keep for 1h, and obtain a bending-resistant copper-based self-healing double-layer circuit.

As shown in Figure 5, Figure 5 is a physical diagram of the anti-bending copper-based self-healing double-layer circuit, it can be seen that the bending-resistant copper-based self-healing double-layer circuit 5 passes through the flexible circuit interface 6 It is directly connected with the standard flexible cable 7.

As shown in Figure 6, Figure 6 is a comparison of the bending performance of the anti-bending copper-based self-healing double-layer circuit and the copper circuit. The test results in the figure show that the two circuits are at a bending radius of 0.5mm From the performance comparison below, it can be seen that the resistance change rate of the copper-based self-healing double-layer circuit reaches 200% after 230,000 times of bending, and the resistance change rate of the circuit of the pure copper circuit reaches 200% after 90,000 times of bending. It can be shown that the bending performance of the copper-based self-healing double-layer circuit is improved by more than 100% compared with the pure copper circuit under the bending radius of 0.5mm.

Claims (8)

1. A bending-resistant copper-based self-healing double-layer circuit is characterized in that: it includes a base layer (1), a conductive layer (2), and a conductive repair layer (3) arranged in sequence; the base layer (1) is covered with The conductive layer (2) is a copper film, using copper paths with different line widths; the conductive repair layer (3) is a gallium indium tin alloy. 2. A kind of anti-bending copper-based self-healing double-layer circuit according to claim 1, characterized in that: the height H of the conductive repair layer (3) and the line width l of the conductive layer (2) have The following relationship: Wherein θ is the contact angle of the conductive repair layer (3) on the conductive layer (2). 3. The anti-bending copper-based self-healing double-layer circuit according to claim 1, characterized in that: an encapsulation layer (4) is provided above the conductive repair layer (3), and the encapsulation layer (4) It is the precursor of polyimide. 4. The high-precision manufacturing process of a bending-resistant copper-based self-healing double-layer circuit according to any one of claims 1-3, characterized in that it comprises the following steps: S1: Perform photolithography, development, and etching on the conductive layer (2) covered on the base layer (1), so that the conductive layer (2) becomes a copper path with a set line width; S2: Place the base layer (1) and the conductive layer (2) processed by the copper path in step S1 in a solution environment, drop the liquid metal into the solution, and naturally wet the surface of the conductive layer (2); S3: The base layer (1) and the conductive layer (2) that have been wetted with liquid metal in step S2 are cured at low temperature to obtain a conductive repair layer (3), and the polyimide precursor solution is used to spin coat the conductive repair layer (3) As the encapsulation layer (4), the polyimide precursor solution is finally cured at high temperature. 5. The process according to claim 4, characterized in that: in the step S1, the base layer (1) is a polyimide film with a thickness of 20-30 μm; the conductive layer (2) is a rolled copper film with a thickness of 10-15μm; copper etching solution is FeCl ₃ solution. 6. The process according to claim 4, characterized in that: the solution environment in the step S2 is NaOH solution with a mass fraction of 20-30%. 7. The process according to claim 4, characterized in that in the low-temperature curing process in the step S3, the temperature is below 8°C. 8. The process according to claim 4, characterized in that: the anti-bending copper-based self-healing double-layer circuit prepared by steps S1-S3, when the copper circuit is bent to produce cracks, the conductive repair layer (3) The liquid metal flows into the cracks of the conductive layer (2), so as to improve the bending resistance of the electrical performance of the circuit.