Method for forming a circuit device and circuit device

Abstract

A method for forming a circuit device (200) is provided. The method comprises: arranging an electrically conductive leaf vein structure (204) on or in an electrically insulating substrate (202), wherein the leaf vein structure (204) comprises leaf veins of a biological plant leaf which are coated with a metal such that the leaf veins are encased with the metal, and areas free of the metal are present between the metal-encased leaf veins; and forming an electrical conductor structure (206) on or in a first main surface of the substrate, wherein the electrical conductor structure (206) is electrically insulated from the leaf vein structure (204) by means of the substrate and remains permanently insulated from it even after completion of the circuit device (200).

Description

[0001] The invention relates to a method for forming a circuit device and a circuit device.

[0002] Prior art circuits designed to be populated with circuit components (or simply components) are usually designed to be provided with conductor tracks onto which the circuit components are mounted using solder, which is heated by a soldering iron or - for example, in the case of simultaneous assembly of several components - in an oven.

[0003] These assembly methods are complex due to the individual soldering iron assembly and / or expensive due to the need for an oven.

[0004] CN 113 447 172 A describes a portable pressure sensor that utilizes natural leaf veins and its manufacturing process.

[0005] DE 10 2023 100 149 A1 describes a flexible, biodegradable electrode for organic components and methods for manufacturing such components.

[0006] Exemplary embodiments of the invention are shown in the figures and are explained in more detail below.

[0007] They show Fig. 1 a flowchart of a process for forming a circuit device; Fig. 2A a schematic cross-sectional view of a circuit device according to various embodiments; Fig. 2B a schematic top view of the circuit device according to various embodiments from Fig. 2A; Fig. 3A an illustration of a heat distribution in a leaf vein structure of a circuit device according to various embodiments, while the leaf vein structure is energized or after the current is switched off; Fig. 3B a graphical representation of a temperature change as a function of a current flowing through a leaf vein structure of a circuit device according to various embodiments; Fig. 3C a graphical representation of a change in the layer resistance of a leaf vein structure of a circuit device according to various embodiments as a function of temperature; Fig. 4. An illustration of a method for forming a circuit device according to various embodiments as a sequence of depicted processes; and Fig. Figures 5A to 5E each show a schematic cross-sectional view of a circuit device according to various embodiments.

[0008] The following detailed description refers to the accompanying drawings, which form part thereof and illustrate specific embodiments in which the invention can be implemented. In this context, directional terminology such as "top," "bottom," "front," "back," "anterior," "rear," etc., is used with reference to the orientation of the described figure(s). Since components of embodiments can be positioned in a number of different orientations, the directional terminology serves only for illustration and is in no way limiting. It is understood that other embodiments may be used and structural or logical modifications may be made without deviating from the scope of protection of the present invention.It is understood that the features of the various exemplary embodiments described herein can be combined with one another, unless specifically stated otherwise. The following detailed description is therefore not to be interpreted in a limiting sense, and the scope of protection of the present invention is defined by the appended claims.

[0009] Within the scope of this description, the terms "connected," "attached," and "coupled" are used to describe both direct and indirect connections, direct or indirect links, and direct or indirect couplings. In the figures, identical or similar elements are labeled with identical reference symbols where appropriate.

[0010] In this description, a leaf vein structure refers to a porous lignocellulose structure of a leaf. Such a leaf vein structure can, for example, be created from a leaf of a plant in which flat areas have been or are being removed, leaving only the leaf veins.

[0011] In this context, (quasi-)fractal means that multiscale connections of the leaf veins, which together are also referred to as the (leaf) skeleton, form a fractal-like (quasi-fractal) framework or skeleton.

[0012] Even if the leaf vein structure is not fractal in the mathematical sense, in that the leaf vein structure on smaller scales is formed by (exact) copies of itself, the pattern recognizable on the largest scale (the entire leaf) continues towards smaller scales, namely that smaller leaf veins branch off from large leaf veins, from which even smaller leaf veins branch off, and so on.

[0013] In various embodiments, a self-soldering printed circuit board based on (quasi-)fractals made from natural leaf lignocellulose is provided.

[0014] According to various embodiments, the leaf vein structure can be electrically conductive.

[0015] For this purpose, the sheet lignocellulose (quasi-)fractal can be coated with metal microparticles or metal nanoparticles, forming a highly electrically conductive, freestanding, essentially transparent electrode. These conductive fractals exhibit high, tunable electrical conductivity and can be used in a manner described below. Fig. 3B and Fig. The example shown in 3C can be exposed indefinitely to currents up to 6 A DC and temperatures around 200 °C without sustaining damage.

[0016] The exemplary quasi-fractal leaf framework has dimensions of 2.5 cm x 2.5 cm, where this defines the length and one axis of the conductor cross-section. The second length of the conductor cross-section is defined by the thickness of the fractal (100 µm to 300 µm). The scaling of the current (possibly also to currents with intensities greater than 6 A) with respect to the geometry of the leaf framework follows Ohm's law, assuming homogeneous electrical conductivity.

[0017] This is in Fig. 3B and Fig. 3C illustrates.

[0018] Fig. Figure 3B shows a graphical representation 301 of a temperature change as a function of a current flowing through a leaf vein structure of a circuit device according to various aspects of this disclosure, and Fig. 3C shows a graphical representation 302 of a change in the layer resistance of a leaf vein structure of a circuit device according to various aspects of this disclosure as a function of temperature.

[0019] As in Fig. As shown in Figure 3B, with a current of approximately 4 A through the exemplary leaf vein structure, the temperature of the leaf structure is around 110 °C. Increasing the current to approximately 6 A suggests that the temperature will remain significantly below 200 °C.

[0020] For this temperature range, in Fig. 3C showed that the layer resistance of the leaf vein structure corresponds to that at room temperature, i.e., no temperature-related degradation occurs. Such degradation can occur, for example, if the leaf vein structure is exposed to temperatures of 400 °C (possibly over a longer period) (see Fig. 3C).

[0021] In various aspects of this revelation, a substrate is provided which consists of conductive (quasi-)fractals and, when an external voltage (for example, a DC voltage, an AC voltage, or voltage pulses) is applied, acts like a heating element that can be used for soldering circuit components, for example, electronic components or passive components such as resistors or capacitors, without the need for an oven (or, for example, a soldering iron).

[0022] Furthermore, in various embodiments, printing electrically conductive connections and bonding components can be carried out in a single process without the need for intermediate curing steps.

[0023] Fig. Figure 3A shows an illustration 300 of a temperature distribution in a leaf vein structure of a circuit device according to various aspects of this disclosure, while the leaf vein structure is energized or after the current is switched off.

[0024] The temperature distributions were determined using thermographic measurements of the surface temperature. The actual surface temperature may differ. The current intensity and duration for which the current flows through the leaf vein structure can be selected to achieve a surface temperature suitable for melting the solder.

[0025] The individual illustrations of the Fig. 3A represents - from left to right and from top to bottom - the temperature increase at 500 mA current flow, at an increase to 1.5 A current flow after 2 seconds, at an increase to 3 A current flow after another 2 seconds, and after a 5-second cooling period after the current supply is removed.

[0026] The grayscale representation of the images of the Fig. Scale 3A is based on color distributions in which different colors have been converted into the same or similar shades of gray. Therefore, arrows are provided to correlate shades of gray between the scale and the distribution. The correspondences for the remaining shades of gray are clear from the sequence. The range of values ​​for each scale extends from 30°C (lower end) to 100°C (upper end).

[0027] Fig. 2A shows a schematic cross-sectional view of a circuit device 200 according to various aspects of this disclosure, and Fig. Figure 2B shows a schematic top view of the circuit device 200 according to various aspects of this disclosure. Fig. 2A and two enlarged partial representations.

[0028] The circuit device 200 has an electrically insulating substrate 202, an electrically conductive leaf vein structure 204 and an electrical conductor structure 206.

[0029] The leaf vein structure 204 features leaf veins of a biological plant leaf which are coated with a metal in such a way that the leaf veins are encased with the metal and there are areas between the metal-encased leaf veins that are free of the metal.

[0030] The leaf vein structure 204 can be described vividly as being formed by first removing the flat chlorophyll from a plant leaf, leaving only the leaf veins (the leaf vein framework or leaf vein skeleton).

[0031] This leaf vein skeleton can be coated with metal – possibly after suitable pretreatment, for example with tridodecylmethylammonium chloride (TDMAC) or chitosan – for example with microparticles, nanoparticles or (possibly cost-effective after pretreatment) using a metal ion solution.

[0032] The metal coating process can be set up so that the surface of the leaf vein skeleton is coated with a metal layer that replicates the structure, i.e., conforms to the surface contours. This is also known as conformal coating.

[0033] This can, for example, lead to the situation that in the metal-coated leaf vein skeleton, each leaf vein section has a diameter that is twice the thickness of the metal layer larger than before the coating, but that otherwise the leaf vein structure 204 is essentially unchanged, i.e., areas free of leaf veins are also predominantly free of metal after metal coating.

[0034] The left of the enlarged partial views of the Fig. Figure 2B shows part of the leaf vein structure (i.e., a lignocellulose structure), in particular the metal-coated (Ag-coated) veins and the free areas between them, which together form the quasi-fractal structure. The scale for comparison is 100 µm.

[0035] The right-hand of the enlarged partial images shows Ag particles that completely cover the leaf vein (lignocellulose) structures up to the edges (scale 2 µm).

[0036] By means of metal coating, the leaf vein structure was transformed into an electrically conductive leaf vein structure 204.

[0037] The leaf vein structure 204 may be arranged on or in the substrate 202 in various aspects of this revelation. Fig. 2A, Fig. 4 and Fig. Figure 5A shows exemplary aspects of this disclosure in which the leaf vein structure 204 is arranged on the substrate 202 (specifically on the lower surface of the substrate 202). Instead of resting on the substrate, the leaf vein structure 204 can be partially or completely recessed into the surface (e.g., flush with the substrate surface).

[0038] Fig. 5B to Fig. Figure 5E shows aspects of this revelation in which the leaf vein structure 204 is arranged in the substrate 202. There, the leaf vein structure 204 is sandwiched between two layers of the substrate 202.

[0039] In various aspects of this disclosure, the leaf vein structure 204 can be arranged such that it is protected by at least two spaced-apart electrodes 444A, 444B (see Fig. 4) can be contacted to apply a (direct) voltage to the leaf vein structure 204.

[0040] The electrical conductor structure 206 can be arranged on or in a surface of the substrate 202. In the exemplary aspects of this disclosure, which are set forth in Fig. 2A, Fig. 2B and Fig. 4 to Fig. As shown in Figure 5E, the electrical conductor structure 206 is arranged on the surface of the substrate 202. Such a configuration can result, for example, from printing or coating followed by etching.

[0041] The electrical conductor structures 206 can be produced, for example, by screen printing, e.g., with flexible silver or copper inks, which reduces the carbon footprint of the invention without impairing the current flow. Circuit components with a grid spacing of more than 100 µm can thus be easily applied to the conductor structure and mounted (soldered).

[0042] According to various embodiments, the conductor track structure 206 can, for example, be completely (i.e. flush with the substrate surface) or partially embedded in the substrate 202.

[0043] In various embodiments, a surface of the conductor track structure 206 (e.g., facing away from the substrate 202 or flush with the substrate surface) can be exposed for contact with a circuit component.

[0044] Substrate 202 is formed from at least one electrically insulating material. Substrate 202 can, for example, comprise or consist of a polymer, such as a thermoplastic or a cellulose-based polymer, e.g., ethylcellulose.

[0045] In various embodiments, the leaf vein structure 204 is electrically insulated by means of the substrate 204. In particular, the leaf vein structure 204 is electrically insulated from the conductor track structure 206, for example by means of the electrically insulating substrate 202.

[0046] The leaf vein structure 204 is not intended to form part of or be connected to the conductor track structure 206, but is intended to heat the substrate 202 and the conductor track structure 206 in order to electrically connect one or more circuit components 442 to the conductor track structure 206.

[0047] To heat the leaf-vein structure 204, a (DC) voltage can be applied, for example, using electrodes 444A and 444B. The voltage level and duration can be adapted to the materials and dimensions of the circuit device 200. For example, the voltage can be selected such that a temperature of approximately 120°C to approximately 160°C is reached at the conductor track structure 206, which may require a current of up to approximately 6 amperes or possibly more.

[0048] Fig. Figure 4 illustrates a method for forming a circuit device 200 according to various embodiments as a sequence of processes shown.

[0049] View a) illustrates both the arrangement of an electrically conductive leaf vein structure 204 (e.g. as described above) on or in an electrically insulating substrate 202 (e.g. as described above) and the formation of an electrical conductor structure 206 on or in a first main surface of the substrate 202.

[0050] The electrical conductor structure 206 is electrically isolated from the leaf vein structure 204 by means of the substrate 202 after formation and remains permanently isolated from it even after completion of the circuit device 200.

[0051] In view b) an arrangement of a circuit component 442 is shown, which is attached to the conductor track structure 206 by means of a solder medium 440 and thus electrically connected.

[0052] The soldering medium 440 can, for example, be arranged before the circuit component 442 is placed on the conductor track structure 206. The circuit device 200 can, for example, be delivered to customers with the soldering medium 440 arranged on the conductor track structure 206.

[0053] In various aspects of this disclosure, the soldering compound 440 can be applied together with the circuit component 442. For example, the circuit component 442 can be coated with the soldering compound 440 on the side to which it is to be electrically connected, and thus be mounted together.

[0054] In various aspects of this disclosure, the solder medium 440 can be separate from the substrate 202 and the circuit component 442, for example as solder medium discs or solder paste, and can be applied to the conductor track structure 206 prior to the arrangement of the circuit component.

[0055] After the solder medium 440 and the circuit component 442 are positioned at the intended mounting position on the conductor track structure 206, a voltage can be applied to the leaf-vein structure 204 (see view c)), causing it to be at least partially energized and thus heated (symbolically represented by the wave symbols 450). At least some of the generated heat can cause the substrate 202 and the conductor track structure 206 to heat up. The voltage can be applied until the solder medium 440 reaches its melting temperature, at which point the solder medium 440 liquefies and, at the latest upon resolidification during subsequent cooling, electrically bonds the circuit component 442 to the conductor track structure 206 to form a functional element of the circuit device.

[0056] In Fig. Figure 4 shows an exemplary embodiment in which one side of the substrate 202 is insulating and the other side is provided with a conductive layer (the leaf vein structure 204) without the need for additional deposition steps.

[0057] Current passed through the conductive leaf vein structure 204 heats the conductive and thus also the insulating side of the substrate 202, which can then be used for soldering the circuit components 442 (e.g. electronic components) placed there.

[0058] As briefly mentioned above, substrate 202 can be made from a cellulose-based polymer in various embodiments. Its softening point (e.g., glass transition temperature) can be lower (for example, approximately 145 °C) than the temperature required to melt commercially available solder (approximately 180–190 °C).

[0059] This can lead to the substrate 202 partially melting when electrically heated via the leaf vein structure 204, and the circuit component(s) 442 being partially submerged in it by gravity or by means of contact pressure. This is shown in outline in Fig. 5A is indicated, even though only the conductor track structure 206 is partially embedded in the substrate 202, and the circuit component 442 is still located above the substrate 202. Depending on the actual thickness ratios and the desired result, however, this illustrates how a partial embedding of the circuit component(s) 442 in the substrate 202 can be achieved.

[0060] After cooling, the circuit components 442 adhere so well to the substrate 202 that bending and kinking of the circuit device 200 does not cause any damage.

[0061] According to various embodiments, the substrate 202 can be provided on both sides with conductor track structures 206, 506 (see e.g. Fig. 5B to 5E).

[0062] For this purpose, the leaf vein structure 202 can be embedded in the substrate 202 in a sandwich-like manner, and the first conductor structure 206 can be arranged on a first main surface of the substrate 202, and the second conductor structure 506 on an opposite second main surface of the substrate 202.

[0063] The properties and application possibilities of the second conductor structure 506 are similar or identical to those of the first conductor structure 206, so repetition is omitted.

[0064] Soldering of circuit components 442 onto the second conductor track structure 506 can be carried out separately from soldering of the circuit components 442 onto the first conductor track structure 206, or in a common process.

[0065] The conductor track structure 206 and the second conductor track structure 506 can be electrically connected (an exemplary embodiment is shown in Fig. 5E is shown; the conductor track structures 206, 506 are connected by means of a through-hole through the substrate 202).

[0066] It must be ensured that contact is made without contacting the leaf vein structure 204.

[0067] To apply voltage to the leaf vein structure 204, it can have at least two contact areas for attaching the electrodes 444A, 444B. The contact areas can, for example, be exposed. In the case of the leaf vein structure 204, which is only connected to the substrate 202 on one side, the back side is exposed and can therefore be contacted by means of the electrodes 444A, 444B.

[0068] In the sandwich-like design, in which the back of the leaf vein structure 204 is also covered with substrate 202, contact areas can be provided, for example, by not completely covering the leaf vein structure 204 with the substrate 202 on both sides, and / or by designing the edge areas so that they extend laterally beyond the substrate 202, and / or by attaching contact elements to the leaf vein structure 204, for example, before encapsulating the leaf vein structure with the substrate 202.

[0069] Alternatively, contact areas can be provided by providing free areas from conductor track structures 206 that are large enough to bring electrodes 444A, 444B into contact with the leaf vein structure 204 through the substrate 202.

[0070] Contact areas can be located, for example, at opposite edges of the leaf vein structure 204, which can lead to essentially the entire leaf vein structure 204 being heated simultaneously. This essentially corresponds to the phenomenon described in Fig. Design shown in 3A.

[0071] Alternatively or additionally, the contact areas can be arranged to be located at opposite ends of a mounting position for one or more circuit component(s) 442.

[0072] Fig. Figure 1 shows a flowchart 100 of a method for forming a circuit device.

[0073] The method comprises: arranging an electrically conductive leaf vein structure on or in an electrically insulating substrate, wherein the leaf vein structure comprises leaf veins of a biological plant leaf which are coated with a metal such that the leaf veins are encased with the metal, and areas free of the metal are present between the metal-encased leaf veins, in 110, and forming an electrical conductor structure on or in a first main surface of the substrate, wherein the electrical conductor structure is electrically insulated from the leaf vein structure by means of the substrate and remains permanently insulated from it even after completion of the circuit device (in 120).

[0074] The following are some examples that relate to what is described herein and depicted in the figures.

[0075] Example 1 is a method for forming a circuit device, comprising: arranging an electrically conductive leaf vein structure on or in an electrically insulating substrate, wherein the leaf vein structure comprises leaf veins of a biological plant leaf which are coated with a metal such that the leaf veins are encased with the metal, and areas free of the metal are present between the metal-encased leaf veins; forming an electrical conductor structure on or in a first main surface of the substrate, wherein the electrical conductor structure is electrically insulated from the leaf vein structure by means of the substrate and remains permanently insulated from it even after completion of the circuit device; and applying a circuit component to the conductor structure, wherein a solder medium is arranged between the conductor structure and the circuit component.and soldering the circuit component to the conductor track structure by applying an electrical voltage to the leaf vein structure in such a way that at least a part of the leaf vein structure heats up and causes the solder to heat up to its melting point.

[0076] In Example 2, the method according to Example 1 can further include forming a second electrical conductor structure on or in a second main surface of the substrate opposite the first main surface, wherein the second electrical conductor structure is electrically isolated from the leaf vein structure by means of the substrate and remains permanently isolated from it even after completion of the circuit device, applying a second circuit component to the second conductor structure with a second solder medium between the second conductor structure and the second circuit component, and soldering the second circuit component to the second conductor structure by applying an electrical voltage to the leaf vein structure such that the sub-area and / or a second sub-area of ​​the leaf vein structure heats up and causes the second solder medium to heat up to its melting point.

[0077] In Example 3, the procedure according to Example 2 can also be optionally set up so that the soldering of the second circuit component takes place simultaneously with the soldering of the circuit component or at a time interval.

[0078] In Example 4, the method according to Example 3 can optionally be configured such that the formation of the conductor track structure comprises at least one of a group of methods, wherein the group consists of printing at least one electrically conductive material, laminating, for example copper laminating, structured metal coating, and coating with metal followed by structuring, for example by etching.

[0079] In Example 5, the method according to one of Examples 1 to 3 can optionally be configured such that the formation of the conductor track structure is carried out using a screen printing process or an inkjet printing process of at least one electrically conductive material.

[0080] In Example 6, the method according to one of Examples 1 to 5 can optionally be configured such that the circuit component is a surface-mounted electronic component.

[0081] In Example 7, the method according to one of Examples 1 to 5 can optionally be further configured such that the circuit component is an organic electronic component.

[0082] In Example 8, the method according to one of Examples 1 to 7 can optionally be configured such that the electrically insulating substrate has or consists of a thermoplastic polymer, for example a cellulose-based polymer.

[0083] In Example 9, the process according to Example 8 can optionally be configured such that the cellulose-based polymer contains ethyl cellulose.

[0084] In Example 10, the method according to Example 8 or 9 can optionally be further configured such that the part of the thermoplastic polymer on which the circuit component is applied is heated above its softening point (e.g. its glass transition temperature) during soldering, so that the circuit component sinks into the heated thermoplastic polymer.

[0085] In Example 11, the process according to Example 10 can optionally be configured such that the softening point of the thermoplastic polymer is at most 160 °C.

[0086] In Example 12, the method according to one of Examples 1 to 11 may also optionally be configured such that the metal of the leaf vein structure and / or a metal of the conductor track structure comprises at least one of the group consisting of gold, silver, copper, and an alloy of the aforementioned metals.

[0087] In Example 13, the method according to one of Examples 2 to 12 may optionally include an electrically conductive connection of the conductor track structure with the second conductor track structure through the substrate and / or along an outside of the substrate away from the leaf vein structure.

[0088] In Example 14, the process according to one of Examples 1 to 13 may optionally include cooling of the substrate.

[0089] Example 15 is a circuit device. The circuit device comprises an electrically insulating substrate, an electrically conductive leaf vein structure arranged on or in the substrate, wherein the leaf vein structure comprises leaf veins of a biological plant leaf coated with a metal such that the leaf veins are encased with the metal, and areas free of metal are present between the metal-encased leaf veins, and an electrical conductor structure on or in a first main surface of the substrate, wherein the electrical conductor structure is electrically insulated from the leaf vein structure by means of the substrate, and a circuit component attached to the conductor structure by means of a solder medium and thus electrically connected to it.

[0090] In Example 16, the circuit device according to Example 15 can further include a second electrical conductor structure on or in a second main surface of the substrate opposite the first main surface, wherein the second electrical conductor structure is electrically isolated from the leaf vein structure by means of the substrate.

[0091] In Example 17, the circuit device according to Example 16 can further include a second circuit component which is attached to the second conductor structure by means of a second solder medium and is thus electrically connected.

[0092] In Example 18, the circuit device according to one of Examples 15 to 17 can optionally be configured such that the electrically conductive leaf vein structure has at least two exposed, spaced-apart contact areas for applying a voltage to at least a sub-area of ​​the leaf vein structure.

[0093] In Example 19, the circuit device according to one of Examples 16 to 18 may further optionally be configured such that the first main surface and / or the second main surface together have at least two laterally spaced areas that are free from the first and second circuit components and whose smallest dimension is larger than a smallest structural spacing of the leaf vein structure. wherein the two spaced-apart areas are suitable to form contact areas for temporarily contacting the leaf vein structure through the substrate to apply a voltage to at least a part of the leaf vein structure.

[0094] In Example 20, the circuit device according to one of Examples 15 to 19 can further optionally be configured such that the conductor track structure has at least one of a group of structures, wherein the group consists of: a printed conductive trace structure, a laminated conductor track structure, for example a copper-laminated conductor track structure, a structured conductor track structure, and a conductor track structure formed from a subsequently structured metal layer, for example from an etched metal layer.

[0095] In Example 21, the circuit device according to one of Examples 15 to 20 may also optionally be configured such that the conductor track structure has screen-printed and / or inkjet-printed electrically conductive material.

[0096] In Example 22, the circuit device according to one of Examples 15 to 21 may also optionally be configured such that the circuit component is a surface-mounted electronic component.

[0097] In Example 23, the circuit device according to one of Examples 15 to 22 may also optionally be configured such that the circuit component is an organic electronic component.

[0098] In Example 24, the circuit device according to one of Examples 15 to 23 may also optionally be configured such that the electrically insulating substrate has or consists of a thermoplastic polymer, for example a cellulose-based polymer.

[0099] In Example 25, the circuit device according to Example 24 can also optionally be configured such that the cellulose-based polymer contains ethyl cellulose.

[0100] In Example 26, the circuit device according to Example 24 or 25 can optionally be further configured such that the part of the thermoplastic polymer on which the circuit component is applied is heated above its softening point (e.g. its glass transition temperature) during soldering, so that the circuit component sinks into the heated thermoplastic polymer.

[0101] In Example 27, the circuit device according to Example 26 can optionally be configured such that the softening point of the thermoplastic polymer is at most 160 °C.

[0102] In Example 28, the circuit device according to one of Examples 15 to 27 may also optionally be configured such that the metal of the leaf vein structure and / or a metal of the conductor track structure comprises at least one of the group consisting of: gold, silver, copper and an alloy of the aforementioned metals.

[0103] In Example 29, the circuit device according to one of Examples 16 to 28 may further include an electrically conductive connection between the conductor track structure and the second conductor track structure through the substrate and / or along an outside of the substrate away from the leaf vein structure.

[0104] In Example 30, the circuit device according to one of Examples 15 to 29 may further include solder material arranged on the conductor track structure.

Claims

[1] Method for forming a circuit device (200), comprising: • Arranging an electrically conductive leaf vein structure (204) on or in an electrically insulating substrate (202), wherein the leaf vein structure (204) comprises leaf veins of a biological plant leaf which are coated with a metal such that the leaf veins are encased with the metal, and between the metal-encased leaf veins there are areas which are free of the metal (110); • Forming an electrical conductor structure (206) on or in a first main surface of the substrate (202) wherein the electrical conductor structure (206) is electrically isolated from the leaf vein structure (204) by means of the substrate (202) and remains permanently isolated from it even after completion of the circuit device (200) (120); • Applying a circuit component to the conductor track structure (206), wherein a solder medium is arranged between the conductor track structure (206) and the circuit component; and • Soldering the circuit component to the conductor structure (206) by applying an electrical voltage to the leaf vein structure (204) such that at least a part of the leaf vein structure (204) heats up and causes the solder to heat up to its melting point. [2] Method according to claim 1, further comprising: • Forming a second electrical conductor structure (506) on or in a second main surface of the substrate (202) opposite the first main surface, wherein the second electrical conductor structure (506) is electrically isolated from the leaf vein structure (204) by means of the substrate (202) and remains permanently isolated from it even after completion of the circuit device (200); • Applying a second circuit component to the second conductor structure (506) with a second solder medium between the second conductor structure (506) and the second circuit component; and • Soldering the second circuit component to the second conductor structure by applying an electrical voltage to the leaf vein structure (204) such that the sub-area and / or a second sub-area of ​​the leaf vein structure (204) heats up and causes the second solder medium to heat up to the melting point. [3] Method according to claim 2, wherein the soldering of the second circuit component is carried out simultaneously with the soldering of the circuit component or at a time interval therefrom. [4] Method according to claim 3, wherein the forming of the conductor track structure (206) comprises at least one of a group of methods, the group consisting of: a printing process involving at least one electrically conductive material; a lamination process, for example copper lamination; a structured metal coating; and a coating with metal followed by structuring, for example by means of etching. [5] Method according to any one of claims 1 to 3, wherein the formation of the conductor track structure (206) is carried out by means of a screen printing process or by means of an inkjet printing process of at least one electrically conductive material. [6] Method according to any one of claims 1 to 5, wherein the circuit component is a surface-mounted electronic component. [7] Method according to any one of claims 1 to 6, wherein the circuit component is an organic electronic component. [8] Method according to any one of claims 1 to 7, wherein the electrically insulating substrate (202) comprises or consists of a thermoplastic polymer, for example a cellulose-based polymer. [9] Method according to claim 8, wherein the part of the thermoplastic polymer on which the circuit component is applied is heated above its softening point during soldering, so that the circuit component sinks into the heated thermoplastic polymer. [10] Method according to claim 9, wherein the softening point of the thermoplastic polymer is at most 160 °C. [11] Method according to any one of claims 1 to 10, wherein the metal of the leaf vein structure (204) and / or a metal of the conductor track structure (206) comprises at least one of the group consisting of: • Gold; • Silver; • Copper; and • an alloy of the aforementioned metals. [12] Method according to any one of claims 2 to 11 further comprising: electrically conductive connection of the conductor structure (206) with the second conductor structure (506) through the substrate (202) and / or along an outside of the substrate (202) away from the leaf vein structure (204). [13] Circuit device (200), comprising: • an electrically insulating substrate (202); • an electrically conductive leaf vein structure (204) arranged on or in the substrate (202), wherein the leaf vein structure (204) comprises leaf veins of a biological plant leaf which are coated with a metal such that the leaf veins are encased with the metal, and between the metal-encased leaf veins there are areas which are free of the metal; • an electrical conductor structure (206) on or in a first main surface of the substrate (202) wherein the electrical conductor structure (206) is electrically insulated from the leaf vein structure (204) by means of the substrate (202); • a circuit component which is attached to the conductor track structure (206) by means of a solder medium and is thus electrically connected. [14] Circuit device (200) according to claim 13, further comprising: a second electrical conductor structure (506) on or in a second main surface of the substrate (202) opposite the first main surface, wherein the second electrical conductor structure (506) is electrically insulated from the leaf vein structure (204) by means of the substrate (202). [15] Circuit device (200) according to claim 14, further comprising: a second circuit component which is attached to the second conductor structure (506) by means of a second solder medium and is thus electrically connected. [16] Circuit device (200) according to one of claims 14 to 15, wherein the first main surface and / or the second main surface together have at least two laterally spaced areas which are free of the first and second circuit components and whose smallest dimension is larger than a smallest structural spacing of the leaf vein structure (204); wherein the two spaced-apart areas are suitable to form contact areas for temporarily contacting the leaf vein structure (204) through the substrate (202) to apply a voltage to at least a part of the leaf vein structure (204). [17] Circuit device (200) according to any one of claims 13 to 16, wherein the conductor track structure (206) comprises at least one of a group of structures, the group consisting of: a printed conductor track structure (206); a laminated conductor structure (206), for example a copper-laminated conductor structure (206); a structured conductor track structure (206); and a conductor track structure (206) formed from a subsequently structured metal layer, for example from an etched metal layer. [18] Circuit device (200) according to one of claims 13 to 17, wherein the conductor track structure (206) comprises screen-printed and / or inkjet-printed electrically conductive material. [19] Circuit device (200) according to any one of claims 13 to 18, wherein the circuit component is a surface-mounted electronic component. [20] Circuit device (200) according to any one of claims 13 to 19, wherein the circuit component is an organic electronic component. [21] Circuit device (200) according to any one of claims 13 to 20, wherein the electrically insulating substrate (202) comprises or consists of a thermoplastic polymer, for example a cellulose-based polymer.

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