A heat radiation resistant circuit board

Abstract

The utility model discloses a kind of heat radiation resistance circuit boards. The circuit board includes circuit board base body (2), upper protective film (1) and lower protective film (3). Circuit board base body (2) is the integrated structure formed by etching copper foil. Lower protective film (3) is layered composite structure, and from inside to outside, it includes TPI adhesive film layer (31), PI film layer (32) and aluminum foil layer (33) in sequence, and aluminum foil layer (33) is outwardly arranged to reflect heat radiation. In the windowed area of lower protective film (3), the opening size of aluminum foil layer (33) is greater than the opening size of TPI adhesive film layer (31), to form safety spacing (d), to avoid voltage breakdown resistance. The circuit board can effectively resist external heat radiation, with excellent electrical safety and reliability, especially suitable for flexible circuit board and high-temperature outdoor environment.

Description

Technical Field

[0001] This utility model relates to the field of circuit board manufacturing technology, specifically to a flexible circuit board and its structure with excellent heat radiation resistance and suitable for high temperature or outdoor environments. Background Technology

[0002] Flexible printed circuit boards (FPCs) are increasingly used in automotive electronics, aerospace, and outdoor displays. In these applications, the circuit boards are often exposed to strong sunlight or other heat radiation sources. Continuous heat radiation can cause the circuit board temperature to rise sharply, which not only accelerates the aging of circuits and components and affects the stability of electrical performance, but can also lead to component burnout and circuit failure in severe cases.

[0003] In existing technologies, heat dissipation for circuit boards typically employs active cooling methods such as adding heat sinks or fans, but this increases system size, weight, and energy consumption. Some technologies also cover the circuit board surface with a protective film, but ordinary protective films (such as pure PI film) have a high absorption rate of heat radiation, resulting in limited heat insulation and ineffective reflection of radiant heat. Furthermore, if a metal layer (such as aluminum foil) is introduced into the protective film to reflect heat, how to address the risk of short circuits introduced by the metal layer, particularly the voltage breakdown problem caused by the metal layer being too close to the solder pads, while ensuring reliable bonding processes, remains a challenge for existing technologies. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a heat-resistant circuit board. This circuit board can effectively reflect external heat radiation, prevent excessive internal temperature rise, and also has good electrical insulation and reliability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A heat radiation resistant circuit board, comprising: The circuit board substrate is an integrated copper layer structure containing circuits and pads, formed by etching copper foil; A protective film is applied to cover the upper surface of the circuit board substrate; A lower protective film covers the lower surface of the circuit board substrate; A gold layer is formed on the surface of the exposed pads on the front side and on the surface of the circuitry on the back side; Both the upper protective film and the lower protective film are provided with openings corresponding to the positions of the solder pads; The lower protective film has a layered composite structure, which includes a TPI film layer, a PI film layer and an aluminum foil layer from the inside to the outside, with the aluminum foil layer facing outwards.

[0006] Preferably, the upper protective film is a polyimide film.

[0007] Preferably, the upper protective film is a composite structure of TPI film and polyimide film.

[0008] Preferably, the thickness of the aluminum foil layer is 0.1~5 µm.

[0009] Preferably, in the window area of ​​the lower protective film, the opening size of the aluminum foil layer is larger than the opening size of the TPI adhesive film layer, so that a gap is formed between the edge of the solder pad and the edge of the aluminum foil layer.

[0010] More preferably, the spacing is 0.5 to 3 mm.

[0011] Preferably, the window edge of the upper protective film coincides with or is located within the edge of the pad.

[0012] Preferably, the thickness of the circuit board substrate is 12µm to 70µm.

[0013] Preferably, the thickness of the gold layer is 0.05µm to 0.2µm.

[0014] Preferably, the circuit board is a flexible circuit board.

[0015] The beneficial effects of this utility model are as follows: 1. Excellent heat radiation resistance: This invention introduces a unique PI film-aluminum foil composite structure as a lower protective film on the outside of the circuit board. The aluminum foil layer facing outward can efficiently reflect most of the radiant heat from sunlight back, fundamentally preventing the FPC and its components from temperature runaway due to external heat radiation, and improving the reliability and lifespan of the product in high-temperature environments.

[0016] 2. High Reliability and Voltage Withstand Safety: Through a unique structural design, the opening size of the lower protective aluminum foil layer is larger than that of the adhesive film layer, forming a safe gap of 0.5~3mm between the pads and the edge of the aluminum foil. This gap effectively avoids electric field concentration and voltage breakdown problems that may be caused by the aluminum foil being too close to the pads, ensuring the electrical safety of the circuit.

[0017] 3. Excellent conductivity and durability: The chemical gold layer formed on the surface of the circuit and pads significantly improves the conductivity, solderability and anti-aging ability of the circuit.

[0018] 4. Structural Optimization and Reliability: The protective films on both sides of the circuit board can adopt a composite structure of PI substrate and TPI adhesive film, which helps to reduce internal stress caused by material differences and improves the structural stability and flatness of the circuit board. The overall product structure is compact, suitable for applications with strict requirements on size and weight, and is particularly suitable for constructing highly reliable flexible circuit boards. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the heat-resistant circuit board provided in this embodiment of the utility model.

[0020] In the diagram: 1-Upper protective film; 2-Circuit board substrate; 3-Lower protective film; 11-PI film layer; 12-TPI adhesive film layer; 31-TPI adhesive film layer; 32-PI film layer; 33-Aluminum foil layer; 4-Solder pad; 5-Gold layer; d-Spacing. Detailed Implementation

[0021] To further illustrate the various embodiments, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention and are mainly used to illustrate the embodiments, and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementations and the advantages of the present invention. Components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] like Figure 1 As shown, this embodiment provides a heat-resistant flexible circuit board. The core structure of the circuit board includes: A circuit board substrate 2 is an integrated conductive structure formed by patterning copper foil, containing designed circuit patterns and pads 4 for soldering components. In this structure, the circuits and pads themselves constitute the conductive body, and the surrounding area is a blank area without copper foil. Electrical isolation between the circuits is achieved by air or a protective film filled later. The copper foil thickness of the circuit board substrate 2 is preferably between 12µm and 70µm. Within this range, the circuit board maintains sufficient mechanical strength and current carrying capacity while possessing excellent flexibility, making it suitable for flexible circuit board applications. When the thickness is less than 12µm, the mechanical strength decreases significantly, making it prone to breakage during production; when the thickness is greater than 70µm, the flexibility of the circuit deteriorates. In this embodiment, the substrate thickness is 18µm.

[0024] An upper protective film 1 covers the upper surface of the circuit board substrate 2. In this embodiment, the upper protective film 1 is a composite film of TPI adhesive film and polyimide film (i.e., a PI-TPI composite film, including a PI film layer 11 and a TPI adhesive film layer 12), which is firmly bonded to the substrate by a hot-pressing process. Windows are opened in the upper protective film 1 to precisely expose the solder pads 4, with the edges of the windows essentially coinciding with the edges of the solder pads 4.

[0025] A lower protective film 3 is applied to the lower surface of the circuit board substrate 2, which is the key innovation of this invention. The lower protective film 3 is a three-layer composite structure, consisting of a TPI adhesive film layer 31, a PI film layer 32, and an aluminum foil layer 33 from the inside out. The TPI adhesive film layer 31 is bonded to the lower surface of the circuit board substrate 2 by hot pressing; the aluminum foil layer 33 faces outwards to reflect external heat radiation. The thickness of the aluminum foil layer 33 is preferably 0.1~5 µm. This thickness range can effectively reflect most of the solar radiation heat while ensuring good flexibility of the composite film. If the thickness is less than 0.1 µm, the heat reflection effect is poor; if the thickness is greater than 5 µm, the flexibility of the aluminum foil layer decreases, making it prone to cracking when bent, and increasing costs. In this embodiment, the aluminum foil layer thickness is 1 µm.

[0026] In the area of ​​pad 4, the lower protective film 3 also has openings. Crucially, through processes such as laser ablation, the opening size of the outer aluminum foil layer 33 is made larger than the opening size of the inner TPI adhesive film layer 31, thus forming a safety gap d between the edge of pad 4 and the edge of aluminum foil layer 33. This gap d is preferably 0.5~3 mm. This gap is determined through withstand voltage testing based on the circuit's operating voltage, effectively preventing air breakdown by the electric field and avoiding short-circuit failure. A gap smaller than 0.5 mm poses a risk of breakdown under normal operating voltage; while a gap larger than 3 mm is too conservative, unnecessarily occupying valuable wiring space. In this embodiment, the gap d is approximately 1 mm.

[0027] A gold layer 5 is formed on the conductive parts of the circuit board, namely the exposed pads 4 on the front side of the circuit board substrate 2 and the circuit surface on the back side, using a chemical immersion gold process. The thickness of this gold layer 5 is preferably between 0.05µm and 0.2µm. This thickness range effectively controls production costs while ensuring excellent conductivity, solderability, and anti-aging properties. A thickness below 0.05µm results in an inability to form a continuous and dense plating layer, leading to poor protection and conductivity; a thickness exceeding 0.2µm significantly increases costs, and the increased internal stress of the gold layer can easily cause cracks. In this embodiment, the gold layer thickness is approximately 0.08µm.

[0028] This invention successfully manufactures a high-performance flexible circuit board that can effectively resist external heat radiation and is electrically safe and reliable by introducing a composite protective film with a specific reflective structure and safe spacing. It is particularly suitable for harsh environments such as automobile engine compartments and outdoor displays.

[0029] Although the present invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the present invention without departing from the spirit and scope of the present invention as defined in the appended claims, and all such changes shall be within the scope of protection of the present invention.

Claims

1. A heat-resistant circuit board, characterized in that, include: The circuit board substrate (2) is an integrated copper layer structure containing circuits and pads (4) formed by etching copper foil; A protective film (1) is applied to the upper surface of the circuit board substrate (2); A lower protective film (3) is applied to the lower surface of the circuit board substrate (2); A gold layer (5) is formed on the surface of the exposed pads (4) on the front side and on the surface of the circuit on the back side; Both the upper protective film (1) and the lower protective film (3) are provided with openings corresponding to the positions of the pads (4); The lower protective film (3) is a layered composite structure, which includes a TPI film layer (31), a PI film layer (32) and an aluminum foil layer (33) from the inside to the outside, with the aluminum foil layer (33) facing outward.

2. The heat-resistant circuit board according to claim 1, characterized in that, The upper protective film (1) is a polyimide film.

3. The heat-resistant circuit board according to claim 2, characterized in that, The upper protective film (1) is a composite structure of TPI film and polyimide film.

4. A heat-resistant circuit board according to claim 1, characterized in that, The thickness of the aluminum foil layer (33) is 0.1~5 µm.

5. A heat-resistant circuit board according to claim 1, characterized in that, In the windowed area of ​​the lower protective film (3), the opening size of the aluminum foil layer (33) is larger than the opening size of the TPI adhesive film layer (31), so that a gap (d) is formed between the edge of the pad (4) and the edge of the aluminum foil layer (33).

6. A heat-resistant circuit board according to claim 5, characterized in that, The spacing (d) is 0.5~3mm.

7. A heat-resistant circuit board according to claim 1, characterized in that, The window edge of the upper protective film (1) coincides with the edge of the pad (4) or is located within the edge of the pad (4).

8. A heat-resistant circuit board according to claim 1, characterized in that, The thickness of the circuit board substrate (2) is 12µm to 70µm.

9. A heat-resistant circuit board according to claim 1, characterized in that, The thickness of the gold layer (5) is 0.05µm to 0.2µm.

10. A heat-resistant circuit board according to any one of claims 1 to 9, characterized in that, The circuit board is a flexible circuit board.

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