Preparation method of single-sided metal-based circuit board

Abstract

The invention discloses a preparation method of a single-sided metal-based circuit board. The preparation method comprises the following steps: forming a first through hole in a metal substrate; laminating a resin layer on the first surface of the metal substrate, and laminating a heat-conducting bonding sheet and a circuit structure layer at least comprising a surface copper foil layer on the second surface of the metal substrate; wherein the first through hole is filled with a resin layer in the pressing process. The warping problem of the single-sided metal-based circuit board in the production process can be improved, and the manufacturing process of the single-sided metal-based circuit board is simplified.

Description

Technical Field

[0001] The present invention relates to the field of circuit boards; more particularly, to a method for preparing a single-sided metal-based circuit board. Background Art

[0002] The current manufacturing process for single-sided metal-based circuit boards with resin-insulated vias is as follows: drilling the metal substrate → plugging the vias with resin → surface polishing → single-sided lamination → leveling → subsequent processing. After the single-sided lamination step, the metal-based circuit board often warps due to unbalanced stress on both sides. Leveling, which applies pressure to restore the warped board to a flat state, can easily lead to other defects, such as cracks in the via-hole resin in the metal substrate and even the shedding of the via-hole resin in large holes (e.g., through-holes with a diameter or length exceeding 2mm).

[0003] Especially when the metal substrate is an aluminum substrate, since it cannot be pre-brownized like a copper substrate to improve the bonding strength with the resin, the bonding strength between the aluminum substrate and the plugging resin is relatively low, and the plugging resin is more likely to crack or even fall off after leveling. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the main purpose of the present invention is to provide a method for preparing a single-sided metal-based circuit board to improve the warping problem during its production process and simplify its preparation process.

[0005] In order to achieve the above main objectives, the present invention discloses a method for preparing a single-sided metal-based circuit board, comprising the following steps:

[0006] S1, forming a first through hole in a metal substrate; wherein the metal substrate has a first surface and a second surface located on opposite sides thereof;

[0007] S2, laminating a resin layer on the first surface of the metal substrate, and simultaneously laminating a thermally conductive adhesive sheet and a circuit structure layer including at least a surface copper foil layer on the second surface of the metal substrate; wherein the first through hole is filled with the resin layer during the lamination process;

[0008] Wherein, after completing all the thermal processes of the preparation method, the resin layer on the first surface is removed.

[0009] The manufacturing method of the present invention improves the single-sided lamination of existing manufacturing methods to double-sided lamination. Specifically, a resin layer is laminated on the first surface of the metal substrate, while a thermally conductive adhesive sheet and a circuit structure layer, including at least a surface copper foil layer, are laminated on the second surface. This helps balance stress on both sides of the circuit board and improves warping. It eliminates the need for leveling required in existing manufacturing methods, thereby ensuring the quality of the plugging resin and its reliable bonding to the metal substrate. Furthermore, by laminating the resin layer to fill the first through-hole in the metal substrate with resin, the need for separate resin plugging required in existing manufacturing methods is eliminated, simplifying the circuit board production process and reducing production costs.

[0010] Preferably, the resin layer in step S2 includes a first resin layer and a second resin layer, the first resin layer is arranged between the metal substrate and the second resin layer, the first resin layer has a higher fluidity than the second resin layer, and the first through hole is filled with the first resin layer.

[0011] In the above technical solution, the first resin layer has relatively high fluidity, which is conducive to filling the first through-holes during the lamination process. The second resin layer has relatively low fluidity and can provide support for the first resin layer. In addition, when the first through-holes are unevenly distributed (for example, the first through-holes are densely distributed in some areas and sparsely distributed in other areas), the second resin layer can improve the filling effect of the first resin layer on the unevenly distributed first through-holes.

[0012] Preferably, the thickness of the resin layer is a first thickness, the sum of the thicknesses of the thermally conductive adhesive sheet and the circuit structure layer is a second thickness, and the difference between the first thickness and the second thickness is less than 10%, more preferably less than 5%, so as to better balance the stress on both sides of the circuit board and suppress its warping.

[0013] Preferably, in step S1, after the first through hole is machined, the first surface and the second surface of the metal substrate are ground to remove burrs on the hole edges and improve the flatness of the metal substrate.

[0014] Preferably, during the pressing operation in step S2 , the resin layer is arranged to be located above the metal substrate to facilitate the resin filling of the first through hole.

[0015] Furthermore, the preparation method further comprises the following steps after step S2:

[0016] S3, processing a second through hole smaller than the first through hole at a position corresponding to the first through hole in the metal-based circuit board.

[0017] Furthermore, the preparation method further includes the step of forming copper holes on the hole walls of the second through holes to achieve more reliable connection of components.

[0018] Furthermore, the preparation method further comprises the step of etching an outer layer circuit in the surface copper foil layer, and the device pad of the outer layer circuit is configured to be connected to the second through hole.

[0019] Furthermore, the circuit structure layer also includes an inner copper foil provided with an inner layer circuit.

[0020] Furthermore, the metal substrate is an aluminum substrate.

[0021] In order to more clearly illustrate the purpose, technical solutions and advantages of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of a single-sided metal base circuit board in an embodiment.

[0023] Figure 2 is a schematic structural diagram of the metal substrate after the first through hole is processed in the embodiment;

[0024] Figure 3 2. It is a schematic diagram of the structure in which the resin layer and the circuit structure layer are laminated on both sides of the metal substrate in an embodiment;

[0025] Figure 4 is a schematic diagram showing the structure of the resin layer in the embodiment;

[0026] Figure 5 It is a schematic diagram of the structure after the surface circuit and the resin insulation hole are made in the embodiment. DETAILED DESCRIPTION

[0027] The following description sets forth many specific details to facilitate a thorough understanding of the present invention. However, the present invention may also be implemented in other variations or alternative forms based on these details. Therefore, other possible implementations that may be known to those skilled in the art based on the embodiments described herein are all within the scope of protection of the present invention.

[0028] like Figure 1 As shown, the single-sided metal-based circuit board of the embodiment includes a metal substrate 10, a thermally conductive adhesive sheet 21, a circuit structure including at least an outer layer circuit 221, and a solder resist layer 23, wherein the outer layer circuit 221 has a device pad 222 exposed from the solder resist layer 23; the thermally conductive adhesive sheet 21 is arranged between the metal substrate 10 and the outer layer circuit 221 for heat conduction and electrical insulation between the two.

[0029] The metal substrate 10 is provided with first through-holes 11, which are filled with plugging resin 110. The number, distribution, and shape of the first through-holes 11 can be customized as needed. For example, the shapes can be circular, elliptical, rectangular, or waist-shaped, and the present invention is not limited thereto. The thickness of the metal substrate 10 can range from 0.5 mm to 2 mm, but is not limited thereto.

[0030] The metal-based circuit board has a second through-hole 12 at a position corresponding to the first through-hole 11. The size of the second through-hole 12 is smaller than that of the first through-hole 11. The second through-hole 12 passes through the plugging resin 110, the thermally conductive adhesive sheet 21, and the device pad 222, that is, the second through-hole 12 is connected to the device pad 222. The second through-hole 12 can be used as a socket for a component (not shown in the figure). The pin of the component can be inserted into the second through-hole 12 and connected to the device pad 222 via solder. The plugging resin 110 electrically isolates the component pin from the metal substrate 10.

[0031] like Figures 2 to 5 As shown, the method for preparing the metal-based circuit board in the embodiment includes the following steps:

[0032] S1 , processing a first through hole 11 in the metal substrate 10 .

[0033] S2, laminating the resin layer 100 on the first surface 10a of the metal substrate 10, and laminating the thermal conductive adhesive sheet 21 and the circuit structure layer 22 on the second surface 10b of the metal substrate 10; wherein the first through hole 11 is filled with the resin layer 100 during the laminating process.

[0034] S3 , processing a second through hole 12 smaller than the first through hole 11 at a position corresponding to the first through hole 11 in the metal-based circuit board.

[0035] Specifically, such as Figure 2 As shown, a metal substrate 10 has a first surface 10a and a second surface 10b located on opposite sides thereof. In step S1, a first through-hole 11 extending from the first surface 10a to the second surface 10b is machined in the metal substrate 10. The first through-hole 11 is typically formed by drilling. The metal substrate 10 can be an aluminum substrate, a copper substrate, or a copper-clad aluminum substrate. The preparation method of the present invention is particularly suitable for reducing circuit board warpage and via-hole resin defects when the metal substrate 10 is an aluminum substrate.

[0036] Preferably, after forming the first through hole 11 in step S1, the first surface 10a and the second surface 10b of the metal substrate 10 may be ground to remove burrs around the holes and maintain a good flatness of the metal substrate 10. Furthermore, the second surface 10b of the metal substrate 10 may be brushed and / or mechanically roughened to enhance its bonding strength with the thermally conductive adhesive sheet 21.

[0037] like Figure 3 As shown, step S2 involves laminating a resin layer 100 onto the first surface 10a of the metal substrate 10, while simultaneously laminating a thermally conductive adhesive sheet 21 and a surface copper foil layer, exemplified as a circuit structure layer 22, onto the second surface 10b of the metal substrate 10. This double-sided lamination balances stress on both sides of the circuit board, improving circuit board warpage and ensuring the quality of the plugging resin 110 and its reliable bonding to the metal substrate 10. The first through-hole 11 is filled with the resin layer 100 during the lamination process, eliminating the need for resin plugging, thereby simplifying the circuit board manufacturing process.

[0038] In other embodiments of the present invention, the circuit structure layer 22 may further include an inner copper foil having an inner layer circuit, for example: (1) the circuit structure layer 22 is a single double-sided copper clad core board (for example, a FR-4 double-sided copper clad core board), the outer surface of which is provided with a surface copper foil layer for forming an outer layer circuit 221, and the inner surface is provided with an inner copper foil having an inner layer circuit etched therein before lamination; (2) the circuit structure layer 22 includes multiple copper clad core boards and semi-cured sheets located between the copper clad core boards, the outer surface of the outermost copper clad core board is provided with a surface copper foil layer for forming an outer layer circuit 221, and the inner surface and the inner copper clad core board are provided with an inner layer copper foil having an inner layer circuit etched therein; (3) the circuit structure layer 22 includes a copper clad core board + semi-cured sheet + surface copper foil layer stacked in sequence from the inside to the outside, and the surface of the copper clad core board is provided with an inner layer copper foil having an inner layer circuit etched therein.

[0039] Preferably, during the pressing operation in step S2 , the resin layer 100 is disposed above the metal substrate 10 to facilitate filling of the first through hole 11 by the resin layer 100 .

[0040] Preferably, Figure 3 As shown, the thickness of the resin layer 100 is a first thickness H1, and the sum of the thicknesses of the thermally conductive adhesive sheet 21 and the circuit structure layer 22 is a second thickness H2. The difference between the first thickness H1 and the second thickness H2 is less than 10%, and more preferably less than 5%, to achieve better stress balance and warpage suppression. Both the first thickness H1 and the second thickness H2 are the thicknesses after the lamination step S2.

[0041] In the present invention, the number of layers of the resin layer 100 can be one or more layers, and the multiple resin layers 100 can be the same or different. Figure 4As shown, the resin layer 100 includes at least one first resin layer 101 and at least one second resin layer 102. The first resin layer 101 is disposed between the metal substrate 10 and the second resin layer 102. The first through-hole 11 is filled with the first resin layer 101. That is, during the lamination process, a portion of the resin in the first resin layer 101 flows into the first through-hole 11, forming a plugging resin 110 that fills the first through-hole 11. The first resin layer 101 has a higher fluidity than the second resin layer 102 to ensure that the first through-hole 11 can be effectively filled during the lamination process.

[0042] For example, the fluidity of the first resin layer 101 can be 30% to 40%, and the fluidity of the second resin layer 102 is relatively low (for example, less than 20%). On the one hand, the second resin layer 102 with relatively low fluidity can play the role of providing appropriate support for the first resin layer 101 to facilitate processing. On the other hand, when the first through holes 11 have an uneven distribution (for example, the first through holes 11 in some areas are relatively dense, while the first through holes 11 in other areas are relatively sparse), the second resin layer 102 can improve the filling effect of the first resin layer 101 on the unevenly distributed first through holes.

[0043] Usually, the higher the resin content of the resin layer, the better its fluidity. Therefore, the first resin layer 101 can be selected from prepregs with higher resin content (for example, the resin content of the first resin layer 101 can be more than 70wt%, preferably more than 80wt%), and the second resin layer 102 can be selected from prepregs with lower resin content. Exemplary, the first resin layer 101 can be selected from prepregs containing non-woven fabrics, and the second resin layer 102 can be selected from prepregs containing glass fiber cloth. Compared with the prepregs using glass fiber cloth as reinforcement, the prepregs using non-woven fabrics as reinforcement have higher resin content, and the non-woven fabric prepreg has loose short fiber structure and better glue flow characteristics, which can make the first through hole 11 reliably filled. It is easy to understand that the second resin layer 102 also can be selected from non-glue glue-flowing prepregs.

[0044] like Figure 5 As shown, the preparation method of the embodiment also includes the step of etching the surface copper foil layer of the circuit structure layer 22 to form the outer layer circuit 221 and the step of forming the second through hole 12 after the pressing operation in step S2. The implementation of these steps and other steps not described here (such as the preparation of the solder resist layer 23) can refer to the existing technology and will not be described in detail.

[0045] Furthermore, the manufacturing method of the embodiment may further include the step of forming a copper hole in the hole wall of the second through hole 12. When the component is installed, the pin inserted into the second through hole 12 can be connected to the copper hole by solder, thereby improving the connection reliability between the component and the circuit board.

[0046] In the present invention, after all thermal processes of the metal-based circuit board are completed, the resin layer 100 on the first surface 10a of the metal substrate 10 is removed (for example, by grinding the resin layer 100), so that the first surface 10a of the metal substrate 10 forms an exposed heat dissipation surface. Here, "thermal process" refers to a process that requires heating during implementation (such as pressing, solder mask, characterization, tin spraying, etc.). The resin layer 100 is retained during other thermal processes after pressing, and the retained double-sided pressing structure can be used to balance thermal stress, thereby suppressing the warping problem that may occur in the circuit board during these processes, so that the circuit board always has better flatness.

[0047] Preferably, after completing the normal production process of the metal-based circuit board, the resin layer 100 on the first surface 10a of the metal substrate 10 is removed, so that the resin layer 100 can be used to protect or isolate the metal substrate 10 during the preparation process (for example, the resin layer is used to isolate the metal substrate 10 when etching to produce the outer layer circuit 221).

[0048] Although the present invention has been disclosed above with reference to specific embodiments, these embodiments are not intended to limit the scope of the present invention. Any person skilled in the art may make modifications or substitutions without departing from the scope of the present invention. In other words, any equivalent modifications made in accordance with the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a single-sided metal-based circuit board, comprising the following steps: S1, forming a first through hole in a metal substrate; wherein, The metal substrate has a first surface and a second surface located on opposite sides thereof; S2, laminating a resin layer on the first surface of the metal substrate, and simultaneously laminating a thermally conductive adhesive sheet and a circuit structure layer including at least a surface copper foil layer on the second surface of the metal substrate; wherein the first through hole is filled with the resin layer during the lamination process; Wherein, after completing all the thermal processes of the preparation method, the resin layer on the first surface is removed.

2. The preparation method according to claim 1; wherein The resin layer in step S2 includes a first resin layer and a second resin layer. The first resin layer is disposed between the metal substrate and the second resin layer. The first resin layer has a higher fluidity than the second resin layer. The first through hole is filled with the first resin layer.

3. The preparation method according to claim 1; wherein The thickness of the resin layer is a first thickness, the sum of the thicknesses of the thermally conductive adhesive sheet and the circuit structure layer is a second thickness, and the difference between the first thickness and the second thickness is less than 10%.

4. The preparation method according to claim 1; wherein Step S1: After machining the first through hole, grinding the first surface and the second surface of the metal substrate.

5. The preparation method according to claim 1; wherein During the pressing operation in step S2 , the resin layer is arranged to be located above the metal substrate.

6. The preparation method according to claim 1, further comprising performing, after step S2: S3, processing a second through hole smaller than the first through hole at a position corresponding to the first through hole in the metal-based circuit board. 7 . The preparation method according to claim 6 , further comprising the step of forming copper on the hole wall of the second through hole.

8. The preparation method according to claim 6, further comprising the step of etching an outer layer circuit in the surface copper foil layer, wherein the device pad of the outer layer circuit is configured to be connected to the second through hole.

9. The preparation method according to claim 1; wherein The circuit structure layer further includes an inner copper foil provided with an inner circuit.

10. The preparation method according to claim 1; wherein The metal substrate is an aluminum substrate.

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