Stretchable rigid-flexible interconnection structure having gradient rigidity

Abstract

Disclosed in the present invention is a stretchable rigid-flexible interconnection structure having gradient rigidity, comprising: a support body; a stretchable substrate provided on a side of the support body; a stretchable circuit layer and a non-stretchable circuit layer both provided on the side of the stretchable substrate facing away from the support body, the non-stretchable circuit layer and the support body being arranged opposite to each other, the non-stretchable circuit layer and the stretchable circuit layer being electrically connected to each other and having an overlapping area at a junction, and the projection of the support body on the stretchable substrate covering the projection of the non-stretchable circuit layer on the stretchable substrate; and a sealing layer provided on the side of the stretchable circuit layer facing away from the stretchable substrate and covering the stretchable circuit layer, the stretchable circuit layer having a stretching direction and a normal direction, and the support body having gradient rigidity in the stretching direction or in the normal direction. On the basis of the support body having gradient rigidity, the stretchable rigid-flexible interconnection structure of the present invention can reduce the risk of an interconnection interface being prone to detachment and breakage, and exhibits high stability and reliability.

Description

Stretchable rigid-flexible interconnects with gradient stiffness Technical Field

[0001] The present invention relates to the technical field of rigid-flexible interconnection, and in particular to a rigid-flexible interconnection structure with gradient stiffness. Background Art

[0002] With the development of science and technology, rigid-flexible interconnects have been widely used in fields such as medicine, military, and robotics, especially in the field of wearable electronics. Rigid-flexible interconnects refer to electronic systems that have both rigid circuit systems (hard and non-stretchable) and flexible circuit systems (soft and stretchable), with electrical interconnection between the two circuit systems.

[0003] Currently, most rigid-flex interconnects employ methods such as designing serpentine circuits within flexible circuit systems or directly using stretchable silver paste to create circuits to reduce tensile stress within the interconnect, thereby making the rigid-flex interconnects stretchable. However, these rigid-flex interconnects rarely focus on the design of the interface between the rigid and flexible circuit systems. The cumulative strain damage inflicted by repeated stretching of wearable electronic devices with rigid-flex interconnects typically occurs at the interface between the rigid and flexible circuit systems. This means that repeated stretching (e.g., 250 times) can easily lead to detachment and fracture at the interface, resulting in poor stability and reliability of rigid-flex electronic products such as wearable electronic devices. Technical issues

[0004] The present invention provides a stretchable rigid-flexible interconnect structure with gradient stiffness to solve the problem that the existing rigid-flexible interconnect structure is prone to detachment and breakage at the interconnection interface after repeated stretching, which leads to poor stability and reliability of the product. Technical Solutions

[0005] The present invention provides a stretchable rigid-flexible interconnect structure with gradient stiffness, comprising:

[0006] Support body;

[0007] a stretchable substrate, disposed on one side of the support;

[0008] A stretchable circuit layer and a non-stretchable circuit layer are both arranged on a side of the stretchable substrate facing away from the support, and the non-stretchable circuit layer is arranged opposite to the support; the non-stretchable circuit layer is electrically connected to the stretchable circuit layer; the non-stretchable circuit layer and the stretchable circuit layer have an overlapping area at the junction, and the projection of the support on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate; and

[0009] a sealing layer, disposed on a side of the stretchable circuit layer facing away from the stretchable substrate, and covering the stretchable circuit layer;

[0010] The stretchable circuit layer has a stretching direction and a normal direction, and the support body has a gradient stiffness along the stretching direction of the stretchable circuit layer, or the support body has a gradient stiffness along the normal direction of the stretchable circuit layer.

[0011] Optionally, when the support body has a gradient stiffness in a normal direction along the stretchable circuit layer, the support body includes:

[0012] A first material layer and at least two second material layers; wherein the elastic modulus of the first material layer is greater than or equal to the elastic modulus of the second material layer, and the projection of the first material layer on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate;

[0013] All the second material layers are stacked in sequence on a side of the stretchable substrate away from the non-stretchable circuit layer according to a first preset order, and the first material layer is stacked on the outer side of the second material layer farthest from the non-stretchable circuit layer.

[0014] Optionally, in the support body, according to the first preset order, the second spacing between all the second material layers and the stretchable circuit layer along the stretching direction increases successively, and the first spacing between the first material layer and the stretchable circuit layer along the stretching direction is greater than the second spacing between the second material layer farthest from the non-stretchable circuit layer and the stretchable circuit layer, so that all the second material layers close to the outer edge of the stretchable circuit layer and the outer edge of the first material layer close to the stretchable circuit layer form a stepped stack structure together.

[0015] Optionally, the elastic moduli of all the second material layers are the same, or the elastic moduli of all the second material layers increase sequentially according to the first preset order.

[0016] Optionally, when the support body has a gradient stiffness along the stretching direction of the stretchable circuit layer, the support body includes:

[0017] a first material layer and a second material layer; wherein the elastic modulus of the first material layer is greater than or equal to the elastic modulus of the second material layer, and the projection of the first material layer on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate;

[0018] The second material layer is disposed on a side of the stretchable substrate facing away from the non-stretchable circuit layer, and the first material layer is embedded in the interior of the second material layer.

[0019] Optionally, the thickness of the first material layer and the thickness of the second material layer are both greater than 0.1 mm.

[0020] Optionally, the elastic modulus of the first material layer and the elastic modulus of the second material layer are both greater than or equal to the elastic modulus of the stretchable substrate.

[0021] Optionally, the elastic modulus of the second material layer is less than 0.1 GPa.

[0022] Optionally, the second material layer includes any one of a silicone layer, an acrylic polymer layer and a polyurethane layer.

[0023] Optionally, when the elastic modulus of the first material layer is greater than the elastic modulus of the second material layer, the first material layer includes any one of a steel layer, a reinforcement layer, an FR-4 substrate layer, a polycarbonate layer, a polyethylene terephthalate layer and a polyimide layer.

[0024] Optionally, when the support body has a gradient stiffness along the stretching direction of the stretchable circuit layer, the support body includes:

[0025] at least two third material layers laid in sequence according to a second preset order on a side of the stretchable substrate facing away from the stretchable circuit layer, wherein all the third material layers are coplanar and edge lines of two adjacent third material layers at their junctions overlap;

[0026] According to the second preset order, the elastic moduli of all the third material layers increase successively, and the projection of the third material layer with the largest elastic modulus on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate.

[0027] Optionally, the thickness of all the third material layers is greater than 0.1 mm.

[0028] Optionally, the elastic modulus of all the third material layers is greater than or equal to the elastic modulus of the stretchable substrate.

[0029] Optionally, the elastic modulus of the third material layer having the highest elastic modulus among all the third material layers is greater than 0.1 GPa, and the elastic moduli of the remaining third material layers are all less than 0.1 GPa.

[0030] Optionally, the third material layer having the highest elastic modulus among all the third material layers includes any one of a steel layer, a reinforcement layer, a FR-4 substrate layer, a polycarbonate layer, a polyethylene terephthalate layer and a polyimide layer, and the remaining third material layers include any one of a silicone layer, an acrylic polymer layer and a polyurethane layer.

[0031] Optionally, the stretchable substrate comprises:

[0032] A polymer film layer and a hot melt adhesive layer are stacked in sequence, the stretchable circuit layer and the non-stretchable circuit layer are both bonded to the outer sides of the polymer film layer, and the support body is bonded to the outer side of the hot melt adhesive layer;

[0033] Wherein, the thickness of the polymer film layer is 75 μm, and / or the thickness of the hot melt adhesive layer is 25 μm.

[0034] Optionally, the polymer film layer includes any one of an organic silicon film layer, an acrylic polymer film layer and a polyurethane film layer.

[0035] Optionally, the stretchable circuit layer is made of a liquid metal composite material;

[0036] The liquid metal composite material is specifically a mixture of silver powder, liquid metal and styrene-ethylene-butylene-styrene block copolymer, and the weight percentages of the silver powder, the liquid metal and the styrene-ethylene-butylene-styrene block copolymer in the liquid metal composite material are 28.2%, 68.3% and 3.4%, respectively.

[0037] Optionally, a length of the overlapping area between the non-stretchable circuit layer and the stretchable circuit layer along the stretching direction of the stretchable circuit layer is greater than or equal to 0.1 mm.

[0038] Optionally, the non-stretchable circuit layer is made of silver paste. Beneficial effects

[0039] The beneficial effects of the present invention are as follows: a stretchable substrate is arranged on one side of the support body, and a stretchable circuit layer and a non-stretchable circuit layer are respectively arranged on the side of the stretchable substrate away from the support body, the two circuit layers respectively form a flexible circuit system and a rigid circuit system, the two are electrically connected and there is an overlapping area at the junction, forming a stretchable rigid-flexible interconnection structure; wherein, the non-stretchable circuit layer is arranged opposite to the support body, and the projection of the support body on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate, which can better utilize the support body to provide good support for the non-stretchable circuit layer, and effectively avoid the rigid circuit system from being damaged when the rigid-flexible interconnection structure is stretched; gradient stiffness means that the stiffness of the material is not unique and constant, but changes in a gradient, because Furthermore, the support body has a gradient stiffness along the stretching direction or a gradient stiffness along the normal direction of the stretchable circuit layer. This can disperse the stress concentration intensity at the interconnection interface when the rigid-flexible interconnect structure is stretched, and can also buffer the stress transferred from the stretchable substrate to the non-stretchable circuit layer, reducing the stress received by the rigid circuit system. This reduces the risk of separation and fracture between the rigid circuit system and the flexible circuit system at the interconnection interface after repeated stretching, effectively ensuring the stability and reliability of electronic products using the rigid-flexible interconnect structure. Among them, the sealing layer provided on the side of the stretchable circuit layer away from the stretchable substrate can seal and protect the stretchable circuit layer, further improving the stability and reliability of the product.

[0040] The stretchable rigid-flexible interconnect structure with gradient stiffness of the present invention is based on a support body with gradient stiffness. After repeated stretching, it can reduce the risk of detachment and breakage at the interconnection interface in the rigid-flexible interconnect structure, and has high stability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0042] FIG1 shows a top view of a stretchable rigid-flexible interconnect structure with gradient stiffness according to an embodiment of the present invention;

[0043] FIG2 shows a partial cross-sectional structural diagram of a stretchable rigid-flexible interconnect structure with gradient stiffness according to an embodiment of the present invention;

[0044] FIG3 shows a cross-sectional structural diagram of a support body according to a first optional embodiment of the present invention;

[0045] FIG4 shows a cross-sectional structural diagram of a support body according to a second alternative embodiment of the present invention;

[0046] FIG5 shows a cross-sectional structural diagram of a support body according to a third alternative embodiment of the present invention;

[0047] FIG6 shows a cross-sectional structural diagram of a stretchable substrate according to an embodiment of the present invention;

[0048] FIG7 shows a top view of another stretchable rigid-flexible interconnect structure with gradient stiffness according to an embodiment of the present invention;

[0049] FIG8 shows a tensile test curve of the example samples in the first group of comparative experiments according to the present invention;

[0050] FIG9A shows a physical picture of the sample in the first set of comparative experiments according to the present invention;

[0051] FIG9B shows an enlarged view of the interconnection interface corresponding to the example sample in the first set of comparative experiments according to the present invention;

[0052] FIG10 shows a physical picture of comparative sample 1 in the first set of comparative experiments according to an embodiment of the present invention;

[0053] 11A and 11B respectively show enlarged views of two interconnection interfaces of comparative sample 1 in the first set of comparative experiments according to an embodiment of the present invention;

[0054] FIG12 shows a statistical graph of tensile properties of Example samples and Comparative Sample 2 in the second set of comparative experiments according to the present invention;

[0055] FIG13A shows a stress distribution diagram of comparative sample 2 on the upper surface of a stretchable substrate in the second set of comparative experiments according to an embodiment of the present invention;

[0056] FIG13B shows a stress distribution diagram of an example sample on the upper surface of a stretchable substrate in a second set of comparative experiments according to an embodiment of the present invention;

[0057] FIG14A shows a stress distribution diagram of comparative sample 2 on the lower surface of a stretchable substrate in the second set of comparative experiments according to an embodiment of the present invention;

[0058] FIG14B shows a stress distribution diagram of the example sample on the lower surface of the stretchable substrate in the second set of comparative experiments according to an embodiment of the present invention. Modes for Carrying Out the Invention

[0059] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0060] In the description of the present invention, it should be noted that the terms "upper" and "lower" etc. indicate orientations or positional relationships 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 cannot be understood as a limitation on the present invention.

[0061] It should be noted that, in the present invention, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element. Example

[0062] This embodiment provides a stretchable rigid-flexible interconnect structure with gradient stiffness, as shown in FIG1 and FIG2 . FIG1 is a top view of the interconnect structure, and FIG2 is a cross-sectional view of the interconnect interface. The interconnect structure includes:

[0063] Support 1;

[0064] A stretchable substrate 2 is provided on one side of the support body 1;

[0065] A stretchable circuit layer 3 and a non-stretchable circuit layer 4 are both arranged on a side of the stretchable substrate 2 facing away from the support body 1, and the non-stretchable circuit layer 4 is arranged opposite to the support body 1; the non-stretchable circuit layer 4 is electrically connected to the stretchable circuit layer 3; an overlapping area 5 exists between the non-stretchable circuit layer 4 and the stretchable circuit layer 3 at the junction, and the projection of the support body 1 on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2; and

[0066] a sealing layer 6, disposed on a side of the stretchable circuit layer 3 facing away from the stretchable substrate 2, and covering the stretchable circuit layer 3;

[0067] The stretchable circuit layer 3 has a stretching direction and a normal direction, the support body 1 has a gradient stiffness along the stretching direction of the stretchable circuit layer 3, or the support body 1 has a gradient stiffness along the normal direction of the stretchable circuit layer 3.

[0068] In this embodiment, a stretchable substrate is provided on one side of the support body, and a stretchable circuit layer and a non-stretchable circuit layer are respectively provided on the side of the stretchable substrate away from the support body, wherein the two circuit layers respectively form a flexible circuit system and a rigid circuit system, which are electrically connected and have an overlapping area at the junction, forming a stretchable rigid-flexible interconnect structure; wherein the non-stretchable circuit layer is arranged opposite to the support body, and the projection of the support body on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate, which can better utilize the support body to provide good support for the non-stretchable circuit layer, and effectively avoid the rigid circuit system from being damaged when the rigid-flexible interconnect structure is stretched; gradient stiffness means that the stiffness of the material is not unique and constant, but changes in a gradient, therefore Furthermore, the support body has a gradient stiffness along the stretching direction or a gradient stiffness along the normal direction of the stretchable circuit layer, which can disperse the stress concentration intensity at the interconnection interface when the rigid-flexible interconnection structure is stretched, and can also buffer the stress transferred from the stretchable substrate to the non-stretchable circuit layer, thereby reducing the stress received by the rigid circuit system, thereby reducing the risk of separation and breakage between the rigid circuit system and the flexible circuit system at the interconnection interface after repeated stretching, effectively ensuring the stability and reliability of electronic products using the rigid-flexible interconnection structure; wherein, the sealing layer arranged on the side of the stretchable circuit layer away from the stretchable substrate can seal and protect the stretchable circuit layer, further improving the stability and reliability of the product.

[0069] The stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment is based on a support body with gradient stiffness. After repeated stretching, it can reduce the risk of detachment and breakage at the interconnection interface in the rigid-flexible interconnect structure, and has high stability and reliability.

[0070] In this embodiment, the stiffness of a material refers to its ability to resist elastic deformation when subjected to stress. It is a mechanical property of a material that indicates how easily its shape and size change when subjected to stress. The greater the stiffness, the less the material deforms when subjected to the same force. Stiffness can be measured using the elastic modulus, which describes the proportional relationship between stress and strain in a material under unidirectional stress. Therefore, stiffness is determined by both the elastic modulus and the structural dimensions. Given a fixed structural dimension, a higher elastic modulus indicates greater stiffness.

[0071] Each component of the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment is described in detail below.

[0072] In Figure 2, the stretching direction of the stretchable circuit layer 3 is specifically the x direction in Figure 2, and its normal direction includes the upward direction and the downward direction. This embodiment refers to the downward direction, that is, the y direction in Figure 2.

[0073] For the support body 1, having a gradient stiffness in the x-direction or a gradient stiffness in the y-direction can disperse the stress concentration intensity at the interconnection interface, and can also buffer the stress transferred from the stretchable substrate to the non-stretchable circuit layer, reducing the stress received by the rigid circuit system, thereby reducing the risk of separation and fracture at the interconnection interface. Of course, in more sophisticated designs, the support body 1 can also have a gradient stiffness in both the x-direction and the y-direction.

[0074] Preferably, when the support body has a gradient stiffness in the normal direction (i.e., the y direction) along the stretchable circuit layer, the support body 1 comprises:

[0075] A first material layer 11 and at least two second material layers 12; wherein the elastic modulus of the first material layer 11 is greater than or equal to the elastic modulus of the second material layer 12, and the projection of the first material layer 11 on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2;

[0076] All the second material layers 122 are stacked in sequence on the side of the stretchable substrate away from the non-stretchable circuit layer 4 according to a first preset order, and the first material layer 11 is stacked on the outside of the second material layer 12 farthest from the non-stretchable circuit layer 4.

[0077] The number of second material layers is two or more, which can obtain a fine support structure, thereby dispersing the stress concentration intensity more evenly, gradually buffering the stress transferred from the stretchable substrate to the non-stretchable circuit layer, and effectively reducing the risk of detachment and fracture at the interconnect interface while ensuring that the rigid-flexible interconnect structure has excellent stretchability. The elastic modulus of the first material layer is greater than or equal to the elastic modulus of the second material layer, and the projection of the first material layer on the stretchable substrate overlaps the projection of the non-stretchable circuit layer on the stretchable substrate, ensuring that the material layer with the largest elastic modulus in the support body supports the non-stretchable circuit layer, thereby ensuring that the support body effectively supports the non-stretchable circuit layer, effectively preventing the rigid circuit system from being damaged when the rigid-flexible interconnect structure is stretched.

[0078] The above structure is a first optional embodiment of the support body. As shown in Figure 3, when the number of second material layers 12 is 2, the two second material layers 12 are stacked in sequence on the side of the stretchable substrate 2 away from the non-stretchable circuit layer 4 in a first preset order, and the first material layer 11 is stacked on the outside of a second material layer 12 farthest from the non-stretchable circuit layer 4, that is, it is stacked on the outermost second material layer 12. The outermost second material layer 12 is specifically the bottommost second material layer 12 in Figure 3.

[0079] In the above-mentioned first optional embodiment, multiple second material layers are stacked in sequence on the side of the stretchable substrate facing away from the stretchable circuit layer, and the second material layer is stacked on a second material layer of the outermost layer; the first material and the second material layers are stacked in a multi-level manner, and based on the thickness superposition of the first material layer and the multiple second material layers, a gradient stiffness in the normal direction can be achieved, thereby making the entire support body have a gradient stiffness in the normal direction, thereby effectively reducing the risk of detachment and fracture at the interconnection interface.

[0080] It should be understood that FIG3 only shows two second material layers, and the situations with other numbers of second material layers are similar and are not listed here.

[0081] Preferably, in the support body 1 of the above-mentioned first optional embodiment, according to the first preset order, the second spacing between all the second material layers 12 and the stretchable circuit layer 3 along the stretching direction increases successively, and the first spacing between the first material layer 11 and the stretchable circuit layer 3 along the stretching direction is greater than the second spacing between the second material layer 12 farthest from the non-stretchable circuit layer 4 and the stretchable circuit layer 3, so that all the second material layers 12 close to the outer edge of the stretchable circuit layer 3 and the outer edge of the first material layer 11 close to the stretchable circuit layer 3 form a stepped stacking structure.

[0082] The first spacing between the first material layer and the stretchable circuit layer along the stretching direction refers to the center-to-center spacing between the first material layer and the stretchable circuit layer along the x-direction; similarly, the second spacing between the second material layer and the stretchable circuit layer along the stretching direction refers to the center-to-center spacing between the second material layer and the stretchable circuit layer along the x-direction. In the first optional embodiment described above, the second spacing increases sequentially, and the first spacing is greater than the second spacing, which is equivalent to the second material layer being closer to the stretchable circuit layer in the x-direction relative to all the first material layers; the stepped stacking structure formed by the two material layers near the outer edge of the stretchable circuit layer can make the stiffness gradually decrease along the stretching direction and gradually increase toward the non-stretchable circuit layer, that is, forming a gradient stiffness along the stretching direction, which can then act as a strain buffer at the interconnection interface, achieving graded buffering of the stress transferred from the stretchable substrate to the non-stretchable circuit layer.

[0083] Preferably, in the first optional embodiment above, the elastic moduli of all the second material layers 12 are the same, or the elastic moduli of all the second material layers 12 increase sequentially according to the first preset order.

[0084] For the second material layers stacked in sequence, the elastic moduli of each layer can be the same or can increase in sequence along the first preset order (i.e., the stacking order, specifically the y direction in Figure 3), both of which can ensure that a support body with gradient stiffness along the y direction is obtained.

[0085] Preferably, when the support body 1 has a gradient stiffness along the stretching direction of the stretchable circuit layer 3, as shown in FIG4 , the support body 1 includes:

[0086] a first material layer 11 and a second material layer 12; wherein the elastic modulus of the first material layer 11 is greater than or equal to the elastic modulus of the second material layer 12, and the projection of the first material layer 11 on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2;

[0087] The second material layer 12 is disposed on a side of the stretchable substrate 2 facing away from the non-stretchable circuit layer 4 , and the first material layer 11 is embedded in the interior of the second material layer 12 .

[0088] In the above-mentioned second optional embodiment, the first material layer is embedded in the interior of the second material layer, that is, the first material layer and the second material layer are embedded. Based on the superposition of the elastic moduli of the two material layers, a gradient stiffness in the tensile direction can be achieved, thereby making the entire support body have a gradient stiffness in the tensile direction. It can also act as a strain buffer at the interconnection interface, thereby effectively reducing the risk of detachment and fracture at the interconnection interface.

[0089] For the support bodies of the above two optional embodiments, as shown in Figures 3 and 4, the projection of the first material layer 11 on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2, which means that the edge line B1 of the first material layer 11 close to the stretchable circuit layer 3 in Figures 3 and 4 is flush with the boundary line A between the non-stretchable circuit layer 4 and the stretchable circuit layer 3, or line B1 exceeds line A.

[0090] In the above two optional embodiments, the thickness of the first material layer 11 and the thickness of the second material layer 12 are both greater than 0.1 mm.

[0091] The first material layer and the second material layer within the above-mentioned thickness range can not only support the non-stretchable circuit layer, but also conveniently form a support body with gradient stiffness in the normal direction, thereby ensuring a stress buffering effect.

[0092] In a specific embodiment, the thickness of the first material layer 11 is 0.125 mm, and a 0.125 mm hard PET film is selected.

[0093] In the above two optional embodiments, the elastic modulus of the first material layer 11 and the elastic modulus of the second material layer 12 are both greater than or equal to the elastic modulus of the stretchable substrate 3 .

[0094] That is, the elastic modulus of the first material layer and the second material layer in the support body needs to be greater than the elastic modulus of the stretchable substrate, which can ensure that the support body has greater rigidity relative to the stretchable substrate, thereby ensuring that it plays a supporting role for the non-stretchable circuit layer on the stretchable substrate.

[0095] In the above two optional embodiments, the elastic modulus of the second material layer 12 is less than 0.1 GPa.

[0096] Through this range of elastic modulus, it can be ensured that the stiffness of the support body closer to the stretchable circuit layer is smaller, and the stiffness of the support body farther away from the stretchable circuit layer is larger, thereby meeting the required stretchability at the rigid-flexible interconnection interface and ensuring that the stress transmitted to the rigid circuit system is effectively buffered when the flexible circuit system is stretched.

[0097] In the above two optional embodiments, the second material layer includes any one of an organic silicon layer, an acrylic polymer layer and a polyurethane layer.

[0098] The elastic modulus of the above materials is relatively small, and they can form a support body that meets the requirements.

[0099] Among them, silicone (such as Dragon Skin silicone produced by Smooth-On in the United States) is mainly made of polydimethylsiloxane (PDMS) polymer cross-linked and solidified. It has a low Young's modulus and good flexibility and stretchability; it has strong corrosion resistance, high dielectric strength, and good transparency and stability in a wide range of operating temperatures. It can be used as a substrate material for large-area transparent flexible electronic devices or thermally stable devices; in addition, it is easy to combine with electronic materials to fix the electronic materials on its surface.

[0100] Acrylic polymers (such as 3M VHB glue produced by 3M) have excellent film-forming properties, outstanding chemical stability, good mechanical properties and good processing performance; polyurethane (PU for short, such as thermoplastic polyurethanes, TPU) has a unique block molecular structure, with excellent wear resistance, flexibility, tear resistance and good elasticity, and can adapt to various complex deformations and stretching.

[0101] In the above two optional embodiments, when the elastic modulus of the first material layer is greater than the elastic modulus of the second material layer, the first material layer includes any one of a steel layer, a reinforcement layer, a FR-4 substrate layer, a polycarbonate layer, a polyethylene terephthalate layer and a polyimide layer.

[0102] When the elastic modulus of the first material layer is greater than that of the second material layer, the first material layer is made of the above material, which can ensure that the support body exhibits greater stiffness in the area where the second material layer is located, thereby obtaining a support body with gradient stiffness that meets the requirements.

[0103] Among them, the steel layer is made of steel; the reinforcement layer is made of organic glass fiber reinforcement material, which is composed of glass fiber and epoxy resin; the FR-4 base material layer is made of glass fiber reinforced epoxy resin; the polycarbonate layer is made of PC, which is Polycarbonate, a thermoplastic plastic; the polyethylene terephthalate layer is made of PET, which is Polyethylene Terephthalate, a thermoplastic polyester; the polyimide layer is made of PI, which is Polyimide.

[0104] Preferably, as shown in FIG5 , when the support body 1 has a gradient stiffness along the stretching direction of the stretchable circuit layer, the support body 1 comprises:

[0105] at least two third material layers 13 laid in sequence on the side of the stretchable substrate 2 facing away from the stretchable circuit layer 3 according to a second preset order, wherein all the third material layers 13 are coplanar and the edge lines of two adjacent third material layers at the junction overlap;

[0106] According to the second preset order, the elastic moduli of all the third material layers 13 increase successively, and the projection of the third material layer 13 with the largest elastic modulus on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2.

[0107] The above structure is a third optional embodiment of the support body, in which all third material layers are coplanar and the edge lines of two adjacent third material layers at the junction coincide, that is, a continuous and flat support body can be obtained; the elastic moduli of these third material layers increase successively along the second preset order (specifically in the direction toward the non-stretchable circuit layer, that is, the opposite direction of the x direction in the figure), so that the stiffness of the entire support body decreases successively in the stretching direction and increases successively in the direction toward the non-stretchable circuit layer; based on the elastic moduli of these materials, a gradient stiffness in the stretching direction is achieved, thereby effectively reducing the risk of detachment and fracture at the interconnection interface.

[0108] For the support body of the third optional embodiment mentioned above, as shown in Figure 5, the projection of the third material layer 13 with the largest elastic modulus on the stretchable substrate 2 covers the projection of the non-stretchable circuit layer 4 on the stretchable substrate 2, which means that the edge line B2 of the third material layer 13 on the rightmost side of Figure 5 close to the stretchable circuit layer 3 is flush with the boundary line A between the non-stretchable circuit layer 4 and the stretchable circuit layer 3, or the B2 line exceeds the A line.

[0109] It should be understood that FIG5 only shows the case of two third material layers, and the cases of other numbers of third material layers are similar and are not shown here.

[0110] In the third optional embodiment, the thickness of all the third material layers 13 is greater than 0.1 mm.

[0111] Similar to the two aforementioned optional embodiments, the third material layer within the above-mentioned thickness range can not only support the non-stretchable circuit layer, but also facilitate the formation of a support body with gradient stiffness in the normal direction, thereby ensuring a stress buffering effect.

[0112] In a specific embodiment, the thickness of the third material layer 13 having the highest elastic modulus among all the third material layers 13 is 0.125 mm, and a 0.125 mm hard PET film is selected.

[0113] In the third optional embodiment described above, the elastic modulus of all the third material layers 13 is greater than or equal to the elastic modulus of the stretchable substrate 2 .

[0114] The elastic modulus of all third material layers in the support body needs to be greater than the elastic modulus of the stretchable substrate, which can ensure that the entire support body is more rigid relative to the stretchable substrate, thereby ensuring that it plays a supporting role for the non-stretchable circuit layer on the stretchable substrate.

[0115] In the third optional embodiment, the elastic modulus of the third material layer 13 with the highest elastic modulus among all the third material layers 13 is greater than 0.1 GPa, and the elastic moduli of the remaining third material layers 13 are all less than 0.1 GPa.

[0116] Through the third material layer with the above-mentioned elastic modulus, it can be ensured that the stiffness of the support body closer to the stretchable circuit layer is smaller, and the stiffness of the support body farther away from the stretchable circuit layer is larger, thereby meeting the required stretchability at the rigid-flexible interconnection interface and ensuring that the stress transmitted to the rigid circuit system is effectively buffered when the flexible circuit system is stretched.

[0117] In the above-mentioned third optional embodiment, the third material layer 13 having the highest elastic modulus among all the third material layers 13 includes any one of a steel layer, a reinforcement layer, a FR-4 substrate layer, a polycarbonate layer, a polyethylene terephthalate layer and a polyimide layer, and the remaining third material layers 13 include any one of a silicone layer, an acrylic polymer layer and a polyurethane layer.

[0118] Through the third material layer of the above-mentioned material, it can also be ensured that the stiffness of the support body closer to the stretchable circuit layer is smaller, and the stiffness of the support body farther away from the stretchable circuit layer is greater, thereby meeting the required stretchability at the rigid-flexible interconnection interface and ensuring that the stress transmitted to the rigid circuit system is effectively buffered when the flexible circuit system is stretched.

[0119] Preferably, as shown in FIG6 , the stretchable substrate 2 comprises:

[0120] The polymer film layer 21 and the hot melt adhesive layer 22 are stacked in sequence, the stretchable circuit layer 3 and the non-stretchable circuit layer 4 are both adhered to the outer side of the polymer film layer 21 , and the support body 1 is adhered to the outer side of the hot melt adhesive layer 22 .

[0121] The polymer film layer has better elongation. Utilizing this polymer film layer can make the entire stretchable substrate have good stretchability, making it easy to combine with the stretchable circuit layer to form a flexible circuit system with excellent stretchable performance; the hot melt adhesive layer can provide good adhesion, which can facilitate the subsequent easy bonding of the support layer, ensuring that it provides good support for the non-stretchable circuit layer, forming a high-quality rigid circuit system.

[0122] It should be understood that when the polymer film layer 21 and the hot melt adhesive layer 22 are stacked in sequence, the outer side of the polymer film layer 21 and the outer side of the hot melt adhesive layer 22 are the two outer surfaces of the entire stretchable substrate 2 (i.e., the upper and lower surfaces of the stretchable substrate 2 in Figure 6).

[0123] Preferably, the polymer film layer 21 includes any one of an organic silicon film layer, an acrylic polymer film layer and a polyurethane film layer.

[0124] The above-mentioned polymer film layers can all ensure that the stretchable substrate has good stretchability.

[0125] In a specific embodiment, the stretchable substrate 2 is made of TPU5855 film, that is, the polymer film layer 21 thereof is a TPU film with a thickness of 75 μm, better elongation, a typical elongation at break exceeding 500%, and a good recovery ability of less than 5% after 100% strain; the hot melt adhesive layer 22 thereof is a hot melt adhesive of model FDS5855X1 with a thickness of 25 μm.

[0126] Preferably, the stretchable circuit layer 3 is made of liquid metal composite material;

[0127] The liquid metal composite material is specifically a mixture of silver powder, liquid metal and styrene-ethylene-butylene-styrene block copolymer.

[0128] Liquid metal is an excellent electrical conductor for soft and stretchable media. However, it is difficult to use directly as a conductive ink because it quickly forms an oxide layer that hinders wetting of the substrate. This embodiment uses a liquid metal polymer composite (LMPC), which not only maintains the material properties of liquid metal, namely softness and stretchability, but also overcomes the disadvantages of liquid metal, avoiding the rapid formation of an oxide layer that hinders wetting of the substrate. This embodiment adds flaky silver powder together with a compatible stretchable polymer (i.e., styrene-ethylene-butylene-styrene block copolymer) binder, and uses liquid metal as a dual phase in the Ag / binder matrix to improve the processability of the liquid metal.

[0129] Specifically, the weight percentages of the silver powder, the liquid metal, and the styrene-ethylene-butylene-styrene block copolymer in the liquid metal composite material are 28.2%, 68.3%, and 3.4%, respectively.

[0130] The stretchable circuit layer formed by the liquid metal composite material (LMPC) with the above weight percentage has excellent stretchability and can be used in areas of rigid-flexible interconnects that require high tensile strain; it can be used as a conductive line in a flexible circuit system and as a strain buffer for rigid-flexible interconnects; in addition, the liquid metal in the LMPC acts as a "healing" medium to bridge the separated flaky Ag powder when it is stretched apart, thereby maintaining electrical continuity.

[0131] Specifically, the liquid metal is a gallium-indium alloy, and the weight ratio of gallium to indium in the gallium-indium alloy is 3:1.

[0132] When the weight ratio of gallium and indium in the gallium-indium alloy is 3:1, it has the advantages of low melting point, good thermal stability, high electrical conductivity, good plasticity and ductility, etc., which can facilitate the production of liquid metal composite materials while ensuring the functionality of the formed stretchable circuit layer.

[0133] In a specific embodiment, the thickness of the stretchable circuit layer 3 is in the range of 1 to 300 μm.

[0134] Preferably, as shown in FIG2 , the length of the overlapping region 5 between the non-stretchable circuit layer 4 and the stretchable circuit layer 3 along the stretching direction of the stretchable circuit layer 3 is greater than or equal to 0.1 mm.

[0135] By limiting the length of the above-mentioned overlapping area, the electronic interconnection at the interconnection interface between the flexible circuit system and the rigid circuit system can be better guaranteed, thereby effectively ensuring the functionality of the rigid-flexible interconnection component; at the same time, it also facilitates the sealing layer to better fill the edge of the stretchable circuit layer, better encapsulate or seal the stretchable circuit layer, and play a better sealing role.

[0136] In FIG2 , the stretching direction of the stretchable circuit layer 3 is the x direction in the figure, and the length L of the overlapping area 5 at the junction of the non-stretchable circuit layer 4 and the stretchable circuit layer 3 along the x direction is ≥0.1 mm.

[0137] Preferably, the non-stretchable circuit layer 4 is made of silver paste.

[0138] Silver paste is conductive and can be made flexible but not stretchable. It also has good chemical stability and is not easily oxidized. Even if its surface is partially oxidized, the resulting oxide can still be conductive. It has good adhesion to the substrate and is not easy to fall off on a stretchable substrate, so it can form a rigid circuit system with excellent quality and no stretchability.

[0139] In a specific embodiment, the silver paste in the non-stretchable circuit layer 4 can be ASH LS-411 or ASH LS-453 silver paste, which can maintain good conductivity when the strain is kept within 10%.

[0140] In one embodiment, the thickness of the non-stretchable circuit layer 4 is in the range of 1 to 100 μm.

[0141] Preferably, the sealing layer 6 includes a thin film layer formed by any one of an organic silicon layer, an acrylic polymer layer and a polyurethane layer, or a combination of any of the above.

[0142] The above-mentioned sealing layer can not only encapsulate or seal the stretchable circuit layer, but also ensure that the sealing layer also has a certain degree of stretchability, so that it can be stretched together with the stretchable circuit layer, thereby realizing a rigid-flexible interconnect structure with excellent stretchable performance.

[0143] In a specific embodiment, the sealing layer 6 is an ecoflex-010 silicone layer with a thickness of 0.25 mm.

[0144] Preferably, as shown in FIG7 , it further includes:

[0145] A plurality of electronic components 7 are mounted on a side of the non-stretchable circuit layer 4 facing away from the stretchable substrate 2 , and each of the electronic components 7 is electrically connected to the non-stretchable circuit layer 4 .

[0146] By mounting electronic components and the electrical connection between the electronic components and the non-stretchable circuit layer, a final rigid circuit system can be formed according to the actual product design requirements, thereby obtaining a rigid-flexible interconnection structure with high stability and reliability.

[0147] The electronic components in this embodiment refer to electronic components such as resistors, capacitors, and diodes, and their specific types depend on the specific product design.

[0148] In order to demonstrate the advantages of the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment, the following two sets of comparative experiments were conducted in this embodiment:

[0149] Group 1: Comparative Sample 1 was compared with the sample of the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment (referred to as the embodiment sample for ease of description). Comparative Sample 1 only included a circuit layer and a stretchable substrate, meaning that a stretchable silver paste (such as commercial stretchable ink LS-453) was used as the circuit layer, and the circuit layer was directly applied to the stretchable substrate described in this embodiment.

[0150] The second group: Comparative sample 2 was compared with the sample of the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment (for the sake of convenience, referred to as the embodiment sample). The comparative sample 2 and the sample of the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment were different only in the support body part, and the structures and materials of other parts were the same. The support body of comparative sample 2 was a hard PET film, which did not have gradient stiffness.

[0151] For the first group of comparative experiments, two samples in the first group of samples (i.e., comparative sample 1 and example sample) were subjected to tensile tests, wherein the tensile test of the example sample was carried out at 100% strain and a tensile rate of 3 mm / sec, while the tensile test of comparative sample 1 was carried out at 50% strain and tensile rates of 0.6 mm / sec and 6 mm / sec, respectively.

[0152] The stretchability test curve of the example sample is shown in Figure 8. In Figure 8, the resistance ratio of the example sample after about 10,000 repeated stretches (i.e., R / R0, which refers to the ratio of the resistance of the stretchable conductive trace after repeated stretching to the initial resistance before stretching) is stable, and is about 2.20 at the 9823rd repeated stretch (wherein, R0 is in the range of 1-2Ω, which is suitable for most electronic applications), and there is no sign of cracking at the interconnection interface between the rigid circuit system and the flexible circuit system when stretched 2000 times, as shown in Figures 9A and 9B. Figure 9A is a physical picture of the example sample when stretched 2000 times, and Figure 9B is an enlarged picture of the corresponding interconnection interface of the example sample when stretched 2000 times. In Figures 9A and 9B, the dotted box indicates the interconnection interface 8.

[0153] The tensile test results of Comparative Sample 1 are shown in Table 1. As can be seen from Table 1, Comparative Sample 1 exhibits a very large R / R0 and cracking occurs at the interconnection interface, as shown in Figure 10. Figure 10 is a physical image of Comparative Sample 1, and the dotted box also refers to the interconnection interface 8. Figures 11A and 11B are enlarged views of two interconnection interfaces 8 of Comparative Sample 1. This shows that the stretchable rigid-flexible interconnect structure with gradient stiffness of this embodiment has enhanced stretchability and bonding performance and can be widely used in stretchable electronic devices.

[0154] Table 1 Tensile test results of comparative sample 1

[0155]

[0156] For the second set of comparative experiments, two samples from the second set (i.e., Comparative Sample 2 and the Example sample) were subjected to tensile testing. The tensile testing for both samples was conducted at 100% strain and a stretching rate of 3 mm / sec. A statistical graph of the tensile testing is shown in Figure 12. As can be seen from Figure 12, Comparative Sample 2 experienced detachment after 500 repeated stretches, while the Example sample remained intact after 10,000 repeated stretches. A comparative data table of the tensile testing is shown in Table 2. Table 2 shows that Comparative Sample 2 experienced circuit disconnection and infinite resistance after less than 1,000 stretch cycles, while the Example sample maintained its electronic circuit even after more than 10,000 stretch cycles.

[0157] Table 2 Comparative data of tensile test of comparative sample 2 and example sample

[0158]

[0159] For the second set of comparative experiments, stress distribution simulations were also performed on two samples in the second set of samples. The stress distribution simulations included simulations of the stress distribution on the upper surface of the stretchable substrate (i.e., the interface between the stretchable substrate and the stretchable circuit layer and the non-stretchable circuit layer) and simulations of the stress distribution on the lower surface of the stretchable substrate (i.e., the interface between the stretchable substrate and the support). The stress distribution diagram of comparative sample 2 on the upper surface of the stretchable substrate is shown in Figure 13A, and its maximum average stress is 41 MPa; the stress distribution diagram of the embodiment sample on the upper surface of the stretchable substrate is shown in Figure 13B, and its maximum average stress is 34 MPa. The stress distribution diagram of comparative sample 2 on the lower surface of the stretchable substrate is shown in Figure 14A, and its maximum average stress is 58 MPa; the stress distribution diagram of the embodiment sample on the upper surface of the stretchable substrate is shown in Figure 14B, and its maximum average stress is 36 MPa.

[0160] Therefore, the stretchable rigid-flexible interconnect structure with gradient stiffness in this embodiment not only has better stretchability, but also can effectively reduce the maximum average stress, has a lower risk of detachment and fracture, and has higher stability and reliability.

[0161] Although the embodiments of the present invention have been described with reference to the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention. Such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A stretchable rigid-flexible interconnect structure with gradient stiffness, characterized in that: include: Support body; a stretchable substrate, disposed on one side of the support; A stretchable circuit layer and a non-stretchable circuit layer are both arranged on a side of the stretchable substrate facing away from the support, and the non-stretchable circuit layer is arranged opposite to the support; the non-stretchable circuit layer is electrically connected to the stretchable circuit layer; the non-stretchable circuit layer and the stretchable circuit layer have an overlapping area at their junction, and the projection of the support on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate; as well as a sealing layer, disposed on a side of the stretchable circuit layer facing away from the stretchable substrate, and covering the stretchable circuit layer; The stretchable circuit layer has a stretching direction and a normal direction, and the support body has a gradient stiffness along the stretching direction of the stretchable circuit layer, or the support body has a gradient stiffness along the normal direction of the stretchable circuit layer.

2. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, characterized in that: When the support body has a gradient stiffness in a normal direction along the stretchable circuit layer, the support body comprises: A first material layer and at least two second material layers; wherein the elastic modulus of the first material layer is greater than or equal to the elastic modulus of the second material layer, and the projection of the first material layer on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate; All the second material layers are stacked in sequence on a side of the stretchable substrate away from the non-stretchable circuit layer according to a first preset order, and the first material layer is stacked on the outer side of the second material layer farthest from the non-stretchable circuit layer.

3. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2, characterized in that: In the support body, according to the first preset order, the second spacing between all the second material layers and the stretchable circuit layer along the stretching direction increases successively, and the first spacing between the first material layer and the stretchable circuit layer along the stretching direction is greater than the second spacing between the second material layer farthest from the non-stretchable circuit layer and the stretchable circuit layer, so that all the second material layers close to the outer edge of the stretchable circuit layer and the outer edge of the first material layer close to the stretchable circuit layer form a stepped stack structure together.

4. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2, wherein: The elastic moduli of all the second material layers are the same, or the elastic moduli of all the second material layers increase sequentially according to the first preset order.

5. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, wherein: When the support has a gradient stiffness along the stretching direction of the stretchable circuit layer, the support comprises: a first material layer and a second material layer; wherein the elastic modulus of the first material layer is greater than or equal to the elastic modulus of the second material layer, and the projection of the first material layer on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate; The second material layer is disposed on a side of the stretchable substrate facing away from the non-stretchable circuit layer, and the first material layer is embedded in the interior of the second material layer.

6. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2 or 5, characterized in that: The thickness of the first material layer and the thickness of the second material layer are both greater than 0.1 mm.

7. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2 or 5, characterized in that: The elastic modulus of the first material layer and the elastic modulus of the second material layer are both greater than or equal to the elastic modulus of the stretchable substrate.

8. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 7, characterized in that: The elastic modulus of the second material layer is less than 0.1 GPa.

9. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2 or 5, characterized in that: The second material layer includes any one of an organic silicon layer, an acrylic polymer layer, and a polyurethane layer.

10. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 2 or 5, characterized in that: When the elastic modulus of the first material layer is greater than the elastic modulus of the second material layer, the first material layer includes any one of a steel layer, a reinforcement layer, an FR-4 base material layer, a polycarbonate layer, a polyethylene terephthalate layer, and a polyimide layer.

11. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, characterized in that: When the support has a gradient stiffness along the stretching direction of the stretchable circuit layer, the support comprises: at least two third material layers laid in sequence according to a second preset order on a side of the stretchable substrate facing away from the non-stretchable circuit layer, wherein all the third material layers are coplanar and edge lines of two adjacent third material layers at their junctions overlap; According to the second preset order, the elastic moduli of all the third material layers increase successively, and the projection of the third material layer with the largest elastic modulus on the stretchable substrate covers the projection of the non-stretchable circuit layer on the stretchable substrate.

12. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 11, characterized in that: The thickness of all the third material layers is greater than 0.1 mm.

13. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 11, characterized in that: The elastic modulus of all the third material layers is greater than or equal to the elastic modulus of the stretchable substrate.

14. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 11, characterized in that: The elastic modulus of the third material layer having the highest elastic modulus among all the third material layers is greater than 0.1 GPa, and the elastic moduli of the remaining third material layers are all less than 0.1 GPa.

15. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 11, characterized in that: The third material layer having the highest elastic modulus among all the third material layers includes any one of a steel layer, a reinforcement layer, a FR-4 substrate layer, a polycarbonate layer, a polyethylene terephthalate layer and a polyimide layer, and the remaining third material layers include any one of a silicone layer, an acrylic polymer layer and a polyurethane layer.

16. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, wherein: The stretchable substrate comprises: A polymer film layer and a hot melt adhesive layer are stacked in sequence, the stretchable circuit layer and the non-stretchable circuit layer are both bonded to the outer sides of the polymer film layer, and the support body is bonded to the outer side of the hot melt adhesive layer; Wherein, the thickness of the polymer film layer is 75 μm, and / or the thickness of the hot melt adhesive layer is 25 μm.

17. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 16, characterized in that: The polymer film layer includes any one of an organic silicon film layer, an acrylic polymer film layer and a polyurethane film layer.

18. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, wherein: The stretchable circuit layer is made of liquid metal composite material; The liquid metal composite material is specifically a mixture of silver powder, liquid metal and styrene-ethylene-butylene-styrene block copolymer, and the weight percentages of the silver powder, the liquid metal and the styrene-ethylene-butylene-styrene block copolymer in the liquid metal composite material are 28.2%, 68.3% and 3.4%, respectively.

19. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, wherein: A length of the overlapping region between the non-stretchable circuit layer and the stretchable circuit layer along the stretching direction of the stretchable circuit layer is greater than or equal to 0.1 mm.

20. The stretchable rigid-flexible interconnect structure with gradient stiffness according to claim 1, wherein: The non-stretchable circuit layer is made of silver paste.

Images