Metal-based multi-layer PCB and manufacturing method thereof

Abstract

The invention relates to the technical field of printed circuit boards, and discloses a metal-based multi-layer PCB and a manufacturing method thereof, and the manufacturing method of the metal-based multi-layer PCB comprises the steps: providing a metal substrate which is provided with a first side and a second side, and comprises a molding region; manufacturing a first blind groove in the forming area from the first side; sequentially stacking a first filling assembly and a daughter board on the first side; pressing the metal substrate, the first filling assembly and the daughter board together; manufacturing a second blind groove in the forming area from the second side; stacking a second filling assembly on the second side; and pressing the metal substrate and the second filling assembly together. The metal-based multi-layer PCB and the manufacturing method thereof provided by the invention are used for solving the problems that the metal substrate is seriously warped due to stress release of the metal substrate after the two sides of the metal substrate are etched and then filled with resin, and the resin is easy to break due to the fact that the resin needs to be filled and cured for multiple times in the related technology. And the resin cured for multiple times also has the problem of chromatic aberration.

Description

Technical Field

[0001] The present application relates to the technical field of printed circuit boards, and in particular to a metal-based multilayer PCB and a manufacturing method thereof. Background Art

[0002] The rapid development of new energy vehicles (NEVs) and the trend toward higher charging power are driving demands for high current and voltage capabilities in metal-based multilayer PCBs (Printed Circuit Boards) for the vehicle's three-electric system. The copper thickness of a metal-based multilayer PCB is directly proportional to the current it carries: the greater the current, the thicker the PCB. Furthermore, the demands placed on metal-based multilayer PCBs for electric and intelligent vehicles are significantly increased, making their design and processing more challenging.

[0003] To enable new fast-charging technologies for electric vehicles, a multi-network process for metal-based multi-layer PCBs was designed to support the high-current, high-power battery requirements. The high-current conductive circuit layers of metal-based multi-layer PCBs typically utilize ultra-thick metal substrates (such as copper substrates) as conductors. These products, based on thick metal substrates, typically require the metal substrate to be segmented into multiple networks to support the high-power, high-current battery and heat dissipation requirements. Specifically, the metal substrate is first etched into multi-network copper blocks, and then insulating material is inserted between the etched grooves.

[0004] In related techniques, one side of a metal substrate is first etched, then the etched area on that side is filled with resin plugs. The other side is then etched, and the etched area on that side is then filled with resin plugs. Due to the large aspect ratio of the metal substrate, this process, after etching both sides and then plugging the resin, can cause severe warping of the metal substrate due to stress release. Furthermore, because the resin needs to be cured through multiple plugging processes, it can easily break and can also exhibit color variations. Summary of the Invention

[0005] The present application provides a metal-based multi-layer PCB and a method for manufacturing the same, which is used to solve the problem in the related art that etching is performed on both sides of a metal substrate and then filling it with resin, which causes severe warping of the metal substrate due to stress release. At the same time, since the resin needs to be cured through multiple fillings, it not only causes the resin to be easily broken, but also the resin cured multiple times has color differences.

[0006] In a first aspect, an embodiment of the present application provides a method for manufacturing a metal-based multi-layer PCB, comprising:

[0007] providing a metal substrate having a first side and a second side opposed to each other, the metal substrate including a forming area;

[0008] A first blind groove is formed in the forming area by the first side;

[0009] stacking a first filling component and a sub-plate in sequence on the first side;

[0010] Pressing the metal substrate, the first filling component, and the daughter board together, with a portion of the first filling component filling the first blind groove;

[0011] A second blind groove is formed in the forming area by the second side, the first filling component filling the first blind groove defines a bottom surface of the second blind groove, and the first blind groove and the second blind groove divide the forming area into a plurality of network parts;

[0012] stacking a second filling component on the second side;

[0013] The metal substrate and the second filling component are pressed together, and at least a portion of the second filling component fills the second blind groove.

[0014] In some embodiments, the first filling assembly includes a first prepreg, a first optical core board, and a connecting layer arranged in sequence, the first prepreg includes a first connecting portion, the first optical core board includes a first limiting portion, and the first connecting portion is located between the bottom surface of the first blind groove and the first limiting portion;

[0015] When the metal substrate, the first filling component, and the sub-board are pressed together, the first connecting portion and the first limiting portion jointly fill the first blind groove, and the connecting layer covers the notch of the first blind groove;

[0016] When the second side forms the second blind groove in the molding area, the first connecting portion defines the bottom surface of the second blind groove;

[0017] The second filling assembly includes a second prepreg and a second optical core board arranged in sequence, the second prepreg includes a second connecting portion, the second optical core board includes a second limiting portion, and the second connecting portion is located between the bottom surface of the second blind groove and the second limiting portion;

[0018] When the metal substrate and the second filling assembly are pressed together, the second connecting portion and the second limiting portion jointly fill the second blind groove.

[0019] In some embodiments, the metal substrate includes a process edge, the molding area is arranged inside the process edge, and the arrangement direction of the process edge and the molding area is perpendicular to the arrangement direction of the first side and the second side; when the first side makes a first blind groove in the molding area, the first side makes a first glue flow groove in the process edge; when the metal substrate, the first filling component and the sub-board are pressed together, part of the first filling component fills the first glue flow groove; when the second side makes a second blind groove in the molding area, the second side makes a second glue flow groove in the process edge, the filling component located in the first blind groove defines at least part of the bottom surface of the second glue flow groove, and the first glue flow groove and the second glue flow groove divide the process edge into at least two parts; when the metal substrate and the second filling component are pressed together, at least part of the second filling component fills the second glue flow groove.

[0020] In some embodiments, when the first filling component and the sub-plate are stacked in sequence on the first side, the metal base plate, the first filling component and the sub-plate are riveted together using a first rivet, and the first rivet passes through the bottom wall of the first glue flow groove.

[0021] In some embodiments, the second glue flow trough and the first glue flow trough are arranged alternately, and the first filling component located in the first blind groove defines a portion of the bottom surface of the second blind groove; when the second filling component is stacked on the second side, a second rivet is used to rivet the metal substrate and the second filling component together, and the second rivet passes through the bottom wall of the second glue flow trough and the bottom wall of the first glue flow trough.

[0022] In some embodiments, a plurality of the first glue flow grooves and a plurality of the second glue flow grooves are provided, and the first glue flow grooves and the second glue flow grooves are provided in a one-to-one correspondence.

[0023] In some embodiments, before stacking the first filling component and the daughter board in sequence on the first side, the method for manufacturing the metal-based multi-layer PCB further includes:

[0024] Providing the daughterboard, the daughterboard is provided with a solder pad and a PTH hole, the daughterboard has an immersion gold surface, the solder pad is provided on the immersion gold surface, and the PTH hole has an orifice formed on the immersion gold surface;

[0025] Covering the immersion gold surface with a protective film, wherein the protective film is provided with a first window and a second window, wherein the first window exposes the solder pad, and the second window exposes the opening of the PTH hole formed on the immersion gold surface;

[0026] The daughter board is subjected to an immersion gold electroplating process so that the pad is covered with an immersion gold layer.

[0027] In some embodiments, the daughter board is provided with a conductive portion, and the conductive portion is located at the edge of the immersion gold surface; the protective film is provided with a third window, and the third window exposes the conductive portion.

[0028] In some embodiments, the daughter board is provided with solder pads and PTH holes that are connected and electrically conductive, the solder pads are located on the side of the daughter board facing the metal substrate, the PTH holes are located in the cover area of ​​the daughter board, and the PTH holes at least conduct the two layers of circuits of the daughter board; after the metal substrate and the second filling component are pressed together, the metal substrate and the first filling component corresponding to the cover area are removed.

[0029] In a second aspect, an embodiment of the present application provides a metal-based multi-layer PCB, which is processed by the metal-based multi-layer PCB manufacturing method as described in the first aspect.

[0030] The manufacturing method of the metal-based multi-layer PCB provided in the embodiment of the present application has the beneficial effect that: since the first blind groove is first made in the molding area by the first side, and then the first filling component and the sub-board are stacked in sequence on the first side, and then the metal substrate, the first filling component and the sub-board are pressed together, part of the first filling component fills the first blind groove, and then the second blind groove is made in the molding area by the second side, the first filling component filling the first blind groove defines the bottom surface of the second blind groove, the first blind groove and the second blind groove divide the molding area into multiple network parts, and after the second filling component is stacked on the second side, the metal substrate and the second filling component are pressed together, so the molding area of ​​the metal substrate can be divided into multiple network parts by the first blind groove and the second blind groove, and part of the first filling component fills the first blind groove, and at least part of the second filling component fills the second blind groove, thereby solving the problem in the related art of etching both sides of the metal substrate and then filling the resin, which will cause the metal substrate to be severely bent due to the stress release. At the same time, since the resin needs to be cured through multiple fillings, it will not only cause the resin to break easily, but also the resin cured multiple times will have color difference.

[0031] The beneficial effects of the metal-based multi-layer PCB provided in this application compared with the existing technology can be referred to the description of the beneficial effects of the metal-based multi-layer PCB manufacturing method provided in this application compared with the existing technology, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0033] Figure 1 It is a structural schematic diagram of a metal substrate in the prior art;

[0034] Figure 2 Is a Figure 1 Schematic diagram of uncovering the metal-based multi-layer PCB with a metal substrate shown;

[0035] Figure 3 yes Figure 2 The schematic diagram of the metal-based multi-layer PCB after the cover is removed is shown;

[0036] Figure 4 yes Figure 2 Schematic diagram of the immersion gold treatment of the multilayer board in the metal-based multilayer PCB shown;

[0037] Figure 5 This is a flow chart of a method for manufacturing a metal-based multilayer PCB in one embodiment of the present application;

[0038] Figure 6 is a top view of a metal substrate in one embodiment of the present application;

[0039] Figure 7 yes Figure 6 A cross-sectional view of the metal substrate shown;

[0040] Figure 8 It will Figure 6 Schematic diagram of the metal substrate, the first filling component and the daughter board pressed together;

[0041] Figure 9 yes Figure 7 A top view of the metal base plate and the first rivet is shown;

[0042] Figure 10 yes Figure 7 A top view of the metal substrate and the first filler assembly is shown;

[0043] Figure 11 is Figure 8 A schematic diagram showing a second blind groove formed in a forming area on the second side of the metal substrate is shown;

[0044] Figure 12 It will Figure 11 A schematic diagram showing the metal substrate and the second filling component being pressed together;

[0045] Figure 13 yes Figure 12 A top view of the metal substrate is shown;

[0046] Figure 14 It will Figure 11 A schematic diagram of the metal substrate and the second filling component being pressed together;

[0047] Figure 15 A top view of a daughterboard in one embodiment of the present application;

[0048] Figure 16 This is a schematic diagram of the metal substrate and the first filling component corresponding to the uncovering area of ​​the sub-board removed in one embodiment of the present application.

[0049] The meanings of the marks in the figure are:

[0050] 1. Metal substrate; 2. Resin; 3. Network; 4. Multilayer board; 5. Solder pad; 6. Dry film;

[0051] 100. Metal-based multilayer PCB;

[0052] 10. Metal substrate; 101. First side; 102. Second side; 11. Forming area; 110. Network section; 111. First blind groove; 112. Second blind groove; 12. Process edge; 121. First glue flow groove; 122. First rivet hole 122; 123. Second glue flow groove;

[0053] 20. First connecting portion;

[0054] 30. Connection layer;

[0055] 40. daughter board; 401. cover area; 41. solder pad; 42. PTH hole; 43. conductive part;

[0056] 50. First rivet;

[0057] 60, second rivet;

[0058] 70. Second connecting portion;

[0059] 80. Protective film;

[0060] 200, steel plate;

[0061] 300, release film;

[0062] 400. Silicone pad. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0064] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0065] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more such features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0066] References to "one embodiment," "some embodiments," or "an embodiment" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present invention. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. Furthermore, in one or more embodiments, particular features, structures, or characteristics may be combined in any suitable manner.

[0067] In order to illustrate the technical solution of the present application, the following description is given with reference to specific drawings and embodiments.

[0068] The rapid development of new energy vehicles (NEVs) and the trend toward higher charging power are driving demands for metal-based multilayer PCBs (PCBs) to handle high currents and voltages for the vehicle's three-electric system. The copper thickness of a metal-based multilayer PCB is directly proportional to the current it carries; the greater the current, the thicker the PCB. Furthermore, the demands placed on metal-based multilayer PCBs for electrified and intelligent electric vehicles (EVs) are significantly higher, making their design and processing more challenging.

[0069] To enable new fast-charging technologies for electric vehicles, a multi-network process for metal-based multi-layer PCBs was designed to support the high-current, high-power battery requirements. The high-current conductive circuit layers of metal-based multi-layer PCBs typically utilize ultra-thick metal substrates (such as copper substrates) as conductors. These products, based on thick metal substrates, typically require the metal substrate to be segmented into multiple networks to support the high-power, high-current battery and heat dissipation requirements. Specifically, the metal substrate is first etched into multi-network copper blocks, and then insulating material is inserted between the etched grooves.

[0070] Please refer to Figures 1 to 4 In the related art, a 2.0mm metal base 1 needs to be etched into a multi-network copper block. First, a 1.0mm thickness is etched on one side of the copper substrate serving as the metal substrate 1. Then, the etched area on the current side is filled with resin 2 plugging. Then, a 1.0mm thickness is etched on the other side of the metal substrate 1. Then, resin 2 is plugged into the etched area on the current side using a resin plugging slot / hole process to form multiple snake-shaped long networks 3. Due to the large aspect ratio of the metal substrate 1, this process requires etching on both sides and then plugging resin 2. There is no copper base support between networks 3 and networks 3, and between design units and process edges (only resin filling). The stress release of the metal substrate 1 will cause it to bend severely. At the same time, since the resin 2 needs to be plugged and cured multiple times, it will not only cause the resin 2 to break easily, but also the molecular chains of the epoxy resin may break, rearrange, and other reactions during multiple high-temperature curing, resulting in changes in the molecular structure. These changes will not only affect the mechanical properties of the resin, but may also cause the color to turn yellow, resulting in color difference problems after curing.

[0071] In addition, after the etched area on the front side is filled with 1.0mm thick resin 2 using a resin plug method, since the grooves in the etched area are only filled with 1.0mm thick resin, the board will bend, warp, or even break during product handling. On the other hand, after etching, the resin is plugged, and before plugging the grooves / holes, the board surface needs to be cleaned by a browning horizontal line. For example, metal substrates have high bending and warping. Since the resin is composed of epoxy resin, curing agent, and filler, silica is usually added to the filler to enhance its performance. After curing, silica is brittle and cannot withstand force. When it passes the horizontal line, it is subjected to the pressure of the roller and non-woven grinding plate, which will crack the resin in the grooves of the etched area, thereby causing the product to be scrapped.

[0072] In addition, in the existing metal-based multi-layer PCB manufacturing method, after the multi-layer board 4 and the metal substrate 1 are pressed together to form the metal-based multi-layer PCB, in order to expose the pads 5 of the internal metal substrate 1, the metal substrate 1 and the semi-cured cover corresponding to the pads 5 need to be removed. When removing the cover, it is necessary to use a depth-controlled gong plate to complete this. If the gong plate depth exceeds the tolerance when removing the gong plate, the circuit layer of the metal substrate 1 will be gonged off, thereby causing the corresponding circuit layer to be interrupted. The circuit layer is designed to be connected to other layers in the area outside the pads 5 (that is, there is no inter-layer conduction within the pads 5). If the gong plate depth exceeds the tolerance when removing the cover, the circuit layer will be damaged, thereby causing the circuit layer and other layers to fail to conduct.

[0073] At the same time, when the pads 5 of the multilayer board 4 are subjected to immersion gold treatment, the dry film 6 only exposes the pads 5 that need immersion gold. Since the immersion gold area of ​​the pads 5 is small and only one side needs immersion gold, the conditions for chemical reactions such as current and chemicals are insufficient during immersion gold treatment. The PTH (Plating Through Hole) hole is sealed by the dry film 6, resulting in poor exchange of chemicals, which depends on the current distribution. Due to the potential difference, abnormal problems such as poor immersion gold treatment occur.

[0074] In view of this, the present application provides a method for manufacturing a metal-based multi-layer PCB and a metal-based multi-layer PCB, wherein a first blind groove is first made in the molding area by the first side, and then a first filling component and a sub-board are stacked in sequence on the first side, and then the metal substrate, the first filling component and the sub-board are pressed together, part of the first filling component fills the first blind groove, and then a second blind groove is made in the molding area by the second side, and the first filling component filling the first blind groove defines the bottom surface of the second blind groove, the first blind groove and the second blind groove divide the molding area into multiple network parts, and after the second filling component is stacked on the second side, the metal substrate and the second filling component are pressed together, so the molding area of ​​the metal substrate can be divided into multiple network parts by the first blind groove and the second blind groove, and part of the first filling component fills the first blind groove, and at least part of the second filling component fills the second blind groove, thereby solving the problem in the related art of etching both sides of the metal substrate and then filling with resin, which will cause the metal substrate to be severely bent due to the stress release of the metal substrate. At the same time, since the resin needs to be cured through multiple fillings, it will not only cause the resin to break easily, but also the resin cured multiple times will also have color difference problems.

[0075] Please refer to Figures 1 to 13 In a first aspect, an embodiment of the present application provides a method for manufacturing a metal-based multilayer PCB 100, comprising:

[0076] S100 : providing a metal substrate 10 , wherein the metal substrate 10 has a first side 101 and a second side 102 opposite to each other, and the metal substrate 10 includes a molding area 11 .

[0077] Specifically, the metal substrate 10 may be a copper substrate or an aluminum substrate.

[0078] S200 : forming a first blind groove 111 in the molding area 11 from the first side 101 .

[0079] Specifically, the first blind groove 111 can be made in the molding area 11 from the first side 101 by etching, laser cutting or mechanical milling. The depth of the first blind groove 111 can be 1 / 3, 1 / 2 or 2 / 3 of the thickness of the metal substrate 10.

[0080] For example, dry films can be attached to both the first side 101 and the second side 102. When the inner layer circuit is exposed, the dry film on the second side 102 is first exposed to death, and then the dry film on the first side 101 corresponding to the area other than the first blind groove 111 is exposed. After development, the area to be etched is exposed. When etching, the first side 101 is placed downward, the short side is fed into the board, and the distance between the front and back boards is 3 rollers. The etching depth is 1.0±0.1mm, and the upper spray pressure during etching is 1.5kg / cm 2 , the lower spray pressure is 3.0kg kg / cm 2 The etching conveying parameters are 0.6m / min-0.7m / min. The depth of the first groove of the first piece etched is ensured to be 1.0±0.1mm. After etching, it is pre-stacked according to the process to the subsequent process.

[0081] S300 : stacking the first filling component and the sub-plate 40 in sequence on the first side 101 .

[0082] Specifically, the first filling component may be a prepreg (PP) or the like, and the sub-board 40 may be a multi-layer board.

[0083] S400 : Pressing the metal substrate 10 , the first filling component and the sub-plate 40 together, and partially filling the first blind groove 111 with the first filling component.

[0084] Specifically, the metal substrate 10, the first filling component and the sub-plate 40 can be pressed together by mechanical pressing, the first blind groove 111 is partially filled with the first filling component, the first filling component and the sub-plate 40 enhance the strength of the metal substrate 10, and the sub-plate 40 and the metal substrate 10 are connected through part of the first filling component.

[0085] S500: A second blind groove 112 is made in the forming area 11 by the second side 102 , and the first filling component filling the first blind groove 111 defines the bottom surface of the second blind groove 112 . The first blind groove 111 and the second blind groove 112 separate the forming area 11 into a plurality of network parts 110 .

[0086] Specifically, the second blind groove 112 can be formed in the molding area 11 from the second side 102 by etching, laser cutting, or mechanical milling, and the second blind groove 112 is connected to the first blind groove 111. A plurality of the second blind grooves 112 and the first blind grooves 111 can be provided, and the plurality of second blind grooves 112 and the plurality of first blind grooves 111 are provided in a one-to-one correspondence, and all the second blind grooves 112 are connected, and all the first blind grooves 111 are connected.

[0087] For example, the metal substrate 10 is a copper substrate with a thickness of 2.0 mm. The first blind groove 111 and the second blind groove 112 separate the forming area 11 into multiple small copper blocks or copper bars, namely the network part 110, to achieve multi-network high current conduction.

[0088] S600 : stacking a second filling component on the second side 102 .

[0089] Specifically, the second filling component may be a prepreg or the like.

[0090] S700 : Pressing the metal substrate 10 and the second filling component together, so that at least a portion of the second filling component fills the second blind groove 112 .

[0091] Specifically, the metal substrate 10 and the second filling component can be pressed together by mechanical pressing, and the second blind groove 112 is at least partially filled with the second filling component, thereby enhancing the strength of the metal substrate 10. After the metal substrate 10 and the second filling component are pressed together, the metal-based multilayer PCB 100 is obtained.

[0092] From the above, it can be seen that the manufacturing method of the metal-based multi-layer PCB100 provided in the embodiment of the present application is as follows: first, the first blind groove 111 is made in the molding area 11 by the first side 101, and then the first filling component and the sub-board 40 are stacked in sequence on the first side 101, and then the metal substrate 10, the first filling component and the sub-board 40 are pressed together, and part of the first filling component fills the first blind groove 111, and then the second blind groove 112 is made in the molding area 11 by the second side 102, and the first filling component filling the first blind groove 111 defines the bottom surface of the second blind groove 112, and the first blind groove 111 and the second blind groove 112 separate the molding area 11 into a plurality of network parts 110, and After the second filling component is stacked on the second side 102, the metal substrate 10 and the second filling component are pressed together, so the molding area 11 of the metal substrate 10 can be divided into multiple network parts 110 by the first blind groove 111 and the second blind groove 112, and part of the first filling component fills the first blind groove 111, and at least part of the second filling component fills the second blind groove 112, thereby solving the problem in the related art that the metal substrate 10 is etched on both sides and then filled with resin, which will cause the metal substrate 10 to be severely bent due to the stress release. At the same time, since the resin needs to be cured through multiple fillings, it will not only cause the resin to break easily, but also the resin cured multiple times will have color difference.

[0093] Please refer to Figure 14 Optionally, when the metal substrate 10, the first filling component and the sub-board 40 are pressed together, and when the metal substrate 10 and the second filling component are pressed together, the stacking structure can be from bottom to top: steel plate 200, release film 300, silicone pad 400, release film 300, metal-based multi-layer PCB 100, release film 300, silicone pad 400, release film 300 and steel plate 200.

[0094] Please refer to Figures 1 to 13 In this embodiment, the first filling component includes a first semi-cured sheet, a first optical core board and a connecting layer 30 arranged in sequence, the first semi-cured sheet includes a first connecting portion 20, the first optical core board includes a first limiting portion (not shown in the figure), and the first connecting portion 20 is located between the bottom surface of the first blind groove 111 and the first limiting portion.

[0095] Specifically, the first prepreg can be windowed, leaving only the first connection portion 20 corresponding to the area requiring glue filling corresponding to the first groove, and removing the entire first prepreg corresponding to the network portion 110. The first connection portion 20 and the first stopper match the depth of the first blind groove 111.

[0096] The copper foil on both sides of the double-sided copper clad laminate can be etched away to form an optical board, and then the optical core board is windowed to obtain a first optical core board. When opening the window, only the first limiting portion corresponding to the area requiring glue filling corresponding to the first groove is retained, and the first optical core board corresponding to the network part 110 is completely removed. The material of the first optical core board can be the same as that of the first semi-cured sheet.

[0097] The connecting layer 30 may be a prepreg.

[0098] When the metal substrate 10 , the first filling component and the sub-plate 40 are pressed together, the first connecting portion 20 and the first limiting portion jointly fill the first blind groove 111 , and the connecting layer 30 covers the notch of the first blind groove 111 .

[0099] Specifically, the connection layer 30 covers the notch of the first blind groove 111 , and the metal substrate 10 and the sub-board 40 are connected via the connection layer 30 .

[0100] Since the first connecting portion 20 is located between the bottom surface of the first blind groove 111 and the first limiting portion, when the metal substrate 10, the first filling component and the sub-plate 40 are pressed together, the glue formed by the first connecting portion 20 can be prevented from overflowing the first blind groove 111.

[0101] When the second blind groove 112 is formed in the molding area 11 by the second side 102 , the first connecting portion 20 defines the bottom surface of the second blind groove 112 .

[0102] The second filling assembly includes a second prepreg and a second optical core board arranged in sequence. The second prepreg includes a second connecting portion 70. The second optical core board includes a second limiting portion. The second connecting portion 70 is located between the bottom surface of the second blind groove 112 and the second limiting portion.

[0103] Specifically, the second prepreg can be windowed, leaving only the second connection portion 70 corresponding to the area requiring glue filling corresponding to the second groove, and the second prepreg corresponding to the network portion 110 is completely removed. The second connection portion 70 and the second stopper match the depth of the second blind groove 112.

[0104] The copper foil on both sides of the double-sided copper clad laminate can be etched away to form an optical board, and then the optical core board can be windowed to obtain a second optical core board. When opening the window, only the second limiting portion corresponding to the area requiring glue filling corresponding to the second groove is retained, and the second optical core board corresponding to the network part 110 is completely removed. The material of the second optical core board can be the same as that of the second semi-cured sheet.

[0105] When the metal substrate 10 and the second filling assembly are pressed together, the second connecting portion 70 and the second limiting portion jointly fill the second blind groove 112 .

[0106] Since the second connecting portion 70 is located between the bottom surface of the second blind groove 112 and the second limiting portion, when the metal substrate 10 and the second filling component are pressed together, the glue formed by the second connecting portion 70 can be prevented from overflowing the second blind groove 112.

[0107] By adopting the above scheme, the first optical core board in the first filling component is a cured core board, and its glue will no longer melt and flow. The first optical core board is combined with the first semi-cured sheet to fill the first blind groove 111, which can reduce the amount of glue flow in the first connection part 20 and avoid the glue flow formed by the first connection part 20 overflowing the first blind groove 111. The second optical core board in the second filling component is a cured core board, and its glue will no longer melt and flow. The second optical core board is combined with the second semi-cured sheet to fill the second blind groove 112, which can reduce the amount of glue flow in the second connection part 70 and avoid the glue flow formed by the second connection part 70 overflowing the second blind groove 112 and causing the problem of glue overflow.

[0108] It is understandable that the cost of the first core plate plus the first prepreg is less than the cost of not using the first core plate and using only the first prepreg. Using prepreg instead of resin to fill the slots / holes provides stable interlayer insulation, adjusts the thermal expansion coefficient of the metal substrate 10, and provides mechanical support between the layers by bonding multiple layers of glass cloth. High rigidity (including glass fiber reinforcement) is achieved by filling the first blind groove 111 and the second blind groove 112. This provides increased support strength, a stable structure, and can also solve the problem of warping of the metal substrate 10.

[0109] For example, the thickness of the metal substrate 10 is 2.0 mm, the depth of the first blind groove 111 and the depth of the second blind groove 112 are both 1.0 mm, and the thickness of the first optical core board and the thickness of the second optical core board are both 0.4 mm.

[0110] It should be noted that the thickness of the first prepreg and the thickness of the first core board can be matched based on the depth of the first blind groove 111, and the thickness of the second prepreg and the thickness of the second core board can be matched based on the depth of the second blind groove 112. For example, the thickness of the first prepreg is 60%-80% of the depth of the first blind groove 111, and the thickness of the first optical core board is 20%-40% of the depth of the first blind groove 111. In other words, the thickness of the first prepreg can be 80% of the depth of the first blind groove 111, and the thickness of the first optical core board can be 20% of the depth of the first blind groove 111. Alternatively, the thickness of the first prepreg can be 70% of the depth of the first blind groove 111, and the thickness of the first optical core board can be 30% of the depth of the first blind groove 111. Alternatively, the thickness of the first prepreg can be 60% of the depth of the first blind groove 111, and the thickness of the first optical core board can be 40% of the depth of the first blind groove 111. In this embodiment, the thickness of the first prepreg is 60% of the depth of the first blind groove 111 , and the thickness of the first optical core is 40% of the depth of the first blind groove 111 .

[0111] Among them, if the thickness of the first optical core board exceeds 40% of the depth of the first blind groove 111, the first blind groove 111 will be insufficiently filled with glue, and if the thickness of the first optical core board is less than 20% of the depth of the first blind groove 111, the control effect of glue overflow during pressing will be worse. On the other hand, the thickness of the first optical core board is 40% of the depth of the first blind groove 111, which can also reduce the investment in the first semi-cured sheet to reduce costs. For example, based on the case where the thickness of the metal substrate 10 is 2.0mm and the depth of the first blind groove 111 is 1.0mm, a first optical core board with a thickness of 0.4mm is selected to be pressed together with 6 first semi-cured sheets. The thickness of the first semi-cured sheet is 0.13mm and the glue content is 58%. The thickness of the second semi-cured sheet and the thickness of the second core board can be matched based on the depth of the second blind groove 112, which can be similar to the thickness of the first semi-cured sheet and the thickness of the first core board being matched based on the depth of the first blind groove 111.

[0112] Optionally, when making the first semi-cured sheet, a cold punching pad of the same size as the semi-cured sheet can be cut out at the same time, and the edges in the middle of the four diagonal extended sides of the cut first semi-cured sheet and the cold punching pad are wrapped with wrinkle glue. When cutting, the first semi-cured sheet needs to be windowed, and only the first connecting part 20 corresponding to the first blind groove 111 is retained, and the first semi-cured sheet corresponding to the network part 110 is completely removed.

[0113] Among them, the first semi-cured sheet is afraid of dirt and foreign objects sticking back, so it is necessary to use a cold punching pad to protect the first semi-cured sheet. The size of the cold punching pad is the same as the first semi-cured sheet. Wrap the first semi-cured sheet in the middle and then wrap it with wrinkle glue. Rivet them in sequence during pre-stacked.

[0114] In the related art, since the process edge 12 of the metal substrate 10 and the molding area 11 have no support, if the second blind groove 112 is made in the molding area 11 by the second side 102, the process edge 12 becomes the entire large frame strip, and the large frame strip exerts a large stress pull on the metal substrate 10, which can easily cause the metal substrate 10 to bend after pressing the metal substrate 10 and the second filling component together.

[0115] In which, the metal substrate 10 includes a process edge 12, the molding area 11 is arranged inside the process edge 12, and the arrangement direction of the process edge 12 and the molding area 11 is perpendicular to the arrangement direction of the first side 101 and the second side 102; when the first blind groove 111 is made in the molding area 11 by the first side 101, the first glue flow groove 121 is made in the process edge 12 by the first side 101; when the metal substrate 10, the first filling component and the sub-board 40 are pressed together, part of the first filling component fills the first glue flow groove 121.

[0116] Specifically, multiple first connection parts 20 and first limiting parts can be provided, part of the first connection parts 20 and part of the first limiting parts fill the first blind groove 111 , and part of the first connection parts 20 and part of the first limiting parts fill the first glue flow groove 121 .

[0117] When the second blind groove 112 is made in the molding area 11 by the second side 102, the second glue flow groove 123 is made in the process edge 12 by the second side 102. The filling component located in the first blind groove 111 defines at least part of the bottom surface of the second glue flow groove 123. The first glue flow groove 121 and the second glue flow groove 123 divide the process edge 12 into at least two parts.

[0118] Specifically, the second glue flow groove 123 can be manufactured on the process edge 12 from the second side 102 by etching, laser cutting, or mechanical milling.

[0119] When the metal substrate 10 and the second filling component are pressed together, at least a portion of the second filling component fills the second glue flow groove 123 .

[0120] Specifically, multiple second connecting parts 70 and second limiting parts can be provided, part of the second connecting parts 70 and part of the second limiting parts fill the second blind groove 112 , and part of the second connecting parts 70 and part of the second limiting parts fill the second glue flow groove 123 .

[0121] Since the first glue flow groove 121 and the second glue flow groove 123 divide the process edge 12 into at least two parts, stress can be released, thereby preventing the metal substrate 10 from being bent when the metal substrate 10 and the second filling component are pressed together.

[0122] By adopting the above solution, the problem of warping of the metal substrate 10 when the metal substrate 10 and the second filling component are pressed together can be avoided.

[0123] Optionally, when the first filling assembly and the sub-plate 40 are stacked in sequence on the first side 101 , the metal substrate 10 , the first filling assembly and the sub-plate 40 are riveted together using a first rivet 50 , and the first rivet 50 passes through the bottom wall of the first glue flow groove 121 .

[0124] Such an arrangement can improve the drilling efficiency when drilling the first rivet hole 122 corresponding to the first rivet 50, and can also reduce the problem of tool breakage during drilling.

[0125] It should be noted that before using the first rivet 50 to rivet the metal substrate 10, the first filling component and the sub-plate 40 together, it is necessary to drill a first rivet hole 122 on the metal substrate 10. Since the first glue flow groove 121 has been produced, the thickness of the metal substrate 10 corresponding to the bottom wall of the first glue flow groove 121 is relatively low at this time. Therefore, the first rivet hole 122 can be passed through the bottom wall of the first glue flow groove 121, thereby improving drilling efficiency and reducing the problem of broken drilling tools.

[0126] It can be understood that the first rivet 50 can be used to rivet the metal substrate 10, the first filling component and the sub-board 40 together. The first rivet 50 can be used to rivet the metal substrate 10, the edge of the first semi-cured sheet, the edge of the first optical core board, the edge of the bonding layer and the edge of the sub-board 40 together, and the edge of the first semi-cured sheet, the edge of the first optical core board, the edge of the bonding layer and the edge of the sub-board 40 are all provided with rivet holes.

[0127] Optionally, the second glue flow groove 123 is arranged alternately with the first glue flow groove 121, and the first filling component located in the first blind groove 111 defines a portion of the bottom surface of the second blind groove 112; when the second filling component is stacked on the second side 102, the metal substrate 10 and the second filling component are riveted together using a second rivet 60, and the second rivet 60 passes through the bottom wall of the second glue flow groove 123 and the bottom wall of the first glue flow groove 121.

[0128] Such a setting can not only divide the process edge 12 into at least two parts through the first glue flow groove 121 and the second glue flow groove 123, avoiding the problem of bending of the metal substrate 10 when the metal substrate 10 and the second filling component are pressed together, but also improve the drilling efficiency when drilling the second rivet hole corresponding to the second rivet 60, and at the same time reduce the problem of broken drilling tools.

[0129] For example, the width of the first glue flow groove 121 and the width of the second glue flow groove 123 are both 10 mm. The first glue flow groove 121 and the second glue flow groove 123 are connected but do not completely overlap. The two are staggered by 5 mm to provide two riveting positioning.

[0130] It should be noted that before using the second rivet 60 to rivet the metal substrate 10 and the second filling component together, a second rivet hole needs to be drilled on the metal substrate 10. Since the second glue flow groove 123 has been produced, the thickness of the metal substrate 10 corresponding to the bottom wall of the second glue flow groove 123 is relatively low at this time. Therefore, the second rivet hole can be passed through the bottom wall of the second glue flow groove 123 to improve drilling efficiency and reduce the problem of broken drilling tools. In addition, the staggered arrangement of the second glue flow groove 123 and the first glue flow groove 121 can increase the width of the second glue flow groove 123.

[0131] It can be understood that the second rivet 60 can be used to rivet the metal substrate 10 and the second filling component together, and the second rivet 60 can be used to rivet the metal substrate 10, the edge of the second semi-cured sheet and the edge of the second optical core board together, and the edge of the second semi-cured sheet and the edge of the second optical core board are both provided with rivet holes.

[0132] It should also be noted that in conventional technology, when the metal substrate 10 and the sub-plate 40 are overlapped and riveted together, the rivets will not explode on the surface of the metal substrate 10. The main reason is that the metal substrate 10 is a high-hardness plate, and the rivet hole is the same size as the rivet, leaving no space for pulling and exploding. If the rivets do not explode, the metal substrate 10 and the sub-plate 40 cannot be riveted together, which will lead to positioning problems. In the embodiment of the present application, the diameter of the developed rivet hole is enlarged to 3.25mm, and the diameter of the first rivet 50 and the diameter of the second rivet 60 are both 3.15mm. The rivet hole is larger than the diameter of the first rivet 50 and the second rivet 60, which can provide the first rivet 50 and the second rivet 60 to explode on the surface of the metal substrate 10 during riveting, and more stably fix the metal substrate 10 and the sub-plate 40.

[0133] Optionally, a plurality of the first glue flow grooves 121 and the second glue flow grooves 123 are provided, and the first glue flow grooves 121 and the second glue flow grooves 123 are provided in a one-to-one correspondence.

[0134] Such a configuration can better release the stress of the metal substrate 10 and avoid the problem of warping of the metal substrate 10 when the metal substrate 10 and the second filling component are pressed together.

[0135] For example, 2-3 first glue flow grooves 121 are designed on one side of the long side of the process side 12 , and 1-2 first glue flow grooves 121 are designed on one side of the short side.

[0136] Please refer to Figure 15 In this embodiment, before stacking the first filling component and the daughter board 40 in sequence on the first side 101, the method for manufacturing the metal-based multi-layer PCB 100 further includes:

[0137] First, a daughter board 40 is provided. The daughter board 40 is provided with a solder pad 41 and a PTH hole 42. The daughter board 40 has an immersion gold surface. The solder pad 41 is provided on the immersion gold surface. The PTH hole 42 has an opening formed on the immersion gold surface.

[0138] Specifically, a plurality of pads 41 and PTH holes 42 may be provided.

[0139] Then, the immersion gold surface is covered with a protective film 80 . The protective film 80 is provided with a first window and a second window. The first window exposes the pad 41 , and the second window exposes the opening of the PTH hole 42 formed on the immersion gold surface.

[0140] Specifically, the protective film 80 may be a dry film or the like.

[0141] Next, the daughter board 40 is subjected to an immersion gold electroplating process, so that the pads 41 are covered with an immersion gold layer.

[0142] By adopting the above solution, immersion gold solution can pass through the PTH hole 42 , thereby increasing the current and improving the gold deposition effect of the pad 41 .

[0143] The daughter board 40 is provided with a conductive portion 43 , which is located at the edge of the immersion gold surface; the protective film 80 is provided with a third window, which exposes the conductive portion 43 .

[0144] With such a configuration, the conductive portion 43 can be used to increase the gold deposition area, reduce the potential difference, and facilitate gold deposition on the pad 41 .

[0145] It should be noted that the conductive portion 43 may be made of copper, and a plurality of the third window and the conductive portion 43 may be provided, and the two are provided in a one-to-one correspondence.

[0146] Please refer to Figure 16 In this embodiment, the daughter board 40 is provided with a solder pad 41 and a PTH hole 42 that are connected and electrically conductive. The solder pad 41 is located on the side of the daughter board 40 facing the metal substrate 10, and the PTH hole 42 is located in the cover area 401 of the daughter board 40. The PTH hole 42 conducts at least two layers of circuits of the daughter board 40; after the metal substrate 10 and the second filling component are pressed together, the metal substrate 10 and the first filling component corresponding to the cover area 401 are removed.

[0147] By adopting the above-mentioned solution, when the metal substrate 10 and the first filling component corresponding to the uncovering area 401 are removed, even if the inner layer circuit of the daughter board 40 is lost due to excessive depth control, the pad 41 can be connected to other circuits of the daughter board 40 through the PTH hole 42, thereby not affecting the connection between the pad 41 and other circuits of the daughter board 40.

[0148] It is understandable that a high-temperature brown protective film 80 can be provided between the metal substrate 10 and the first filling component corresponding to the uncovering area 401 and the sub-board 40 to facilitate the removal of the metal substrate 10 and the first filling component corresponding to the uncovering area 401. The metal substrate 10 and the first filling component corresponding to the uncovering area 401 can be removed by a secondary countersinking method, and the depth is controlled to the pad 41 on the sub-board 40, and the residual thickness is controlled to be 0.2mm. Then the finished countersink is processed and then the film is applied. The total thickness of the metal-based multi-layer PCB 100 is 3.7mm, and the total thickness of the metal substrate 10 and the first filling component corresponding to the uncovering area 401 is 2.3mm. The total board thickness of 3.7mm must be controlled to the pad 41, and the depth control accuracy is 1.97±0.1mm. The pad 41 must not be damaged. After completion, the finished countersink is processed and then laser engraved.

[0149] The laser engraving parameters are: cutting speed 350mm / s, pulse frequency 45KHZ, cutting times 10 times, and the first piece confirmation depth is 0.2mm-0.3mm.

[0150] It should be noted that the sub-board 40 can be produced through the processes of cutting, baking, drilling before pressing, inner layer circuit, inner layer etching, inner layer AOI (Automated Optical Inspection), browning, one-time pressing, laminating CCD (Charge-coupled Device) shooting, one-time milling, two-time drilling before pressing, copper plating, electroplating, resin plugging of slots / holes, ceramic grinding, one-time copper plating, one-time electroplating, one-time inner layer circuit, one-time inner layer etching, one-time inner layer AOI, two-time inner layer circuit, gold plating, film tearing, film pasting, laser engraving, film tearing, browning, and pre-stacking.

[0151] Among them, the second drilling before pressing: the PTH hole 42 designed on the pad 41 has a hole diameter of 0.6mm, is electroplated after drilling, and the hole copper thickness is ≥28um, and then the hole is plugged with resin and covered with electroplating.

[0152] Secondary inner layer circuit: protective film 80 is applied on both sides of the daughter board 40, and a third is designed on the long side of the process side 12. There are 6 third windows in total, with a size of 10mm*20mm.

[0153] After the immersion gold plating, high-temperature brown films are pasted on both sides of the daughter board 40 . After laser engraving, the films are torn off, leaving only the high-temperature brown films on the pads 41 .

[0154] In the embodiment of the present application, after the metal substrate 10 and the second filling component are pressed together, CCD targeting, three times of milling, sanding, overflow glue detection, one-time drilling, non-woven grinding, copper plate electroplating, outer dry film circuit, graphic electroplating, outer film stripping, outer layer etching, outer layer tin stripping, solder mask, pre-baking, one-time silk screen text, film pasting, laser engraving, gold plating, film tearing, secondary drilling, film pasting, one-time gong sinking, laser insulation layer, film tearing, film pasting, two-time gong sinking, finished gong board, film pasting, one-time laser engraving, uncovering, film tearing, flying probe test, gold plate washing line, FQC (Final Quality Control), FQA (Final Quality Assurance) and packaging processes can be continued.

[0155] In a second aspect, an embodiment of the present application provides a metal-based multi-layer PCB 100 , which is manufactured by the manufacturing method of the metal-based multi-layer PCB 100 according to the first aspect.

[0156] The metal-based multilayer PCB 100 provided in the embodiment of the application, during processing, firstly makes a first blind groove 111 in the molding area 11 by the first side 101, then stacks the first filling component and the daughter board 40 in sequence on the first side 101, and then presses the metal substrate 10, the first filling component and the daughter board 40 together, and part of the first filling component fills the first blind groove 111, and then makes a second blind groove 112 in the molding area 11 by the second side 102, and the first filling component filling the first blind groove 111 defines the bottom surface of the second blind groove 112, and the first blind groove 111 and the second blind groove 112 separate the molding area 11 into a plurality of network parts 110, and on the second side 1 02 After stacking the second filling component, the metal substrate 10 and the second filling component are pressed together, so the molding area 11 of the metal substrate 10 can be divided into multiple network parts 110 by the first blind groove 111 and the second blind groove 112, and part of the first filling component fills the first blind groove 111, and at least part of the second filling component fills the second blind groove 112, thereby solving the problem in the related art that the metal substrate 10 is etched on both sides and then filled with resin, which will cause the metal substrate 10 to be severely bent due to the stress release. At the same time, since the resin needs to be cured through multiple fillings, it will not only cause the resin to break easily, but also the resin cured multiple times will have color difference.

[0157] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for manufacturing a metal-based multilayer PCB, characterized in that: include: providing a metal substrate having a first side and a second side opposed to each other, the metal substrate including a forming area; A first blind groove is formed in the forming area by the first side; stacking a first filling component and a sub-plate in sequence on the first side; Pressing the metal substrate, the first filling component, and the daughter board together, with a portion of the first filling component filling the first blind groove; A second blind groove is formed in the forming area by the second side, the first filling component filling the first blind groove defines a bottom surface of the second blind groove, and the first blind groove and the second blind groove divide the forming area into a plurality of network parts; stacking a second filling component on the second side; The metal substrate and the second filling component are pressed together, and at least a portion of the second filling component fills the second blind groove.

2. The method for manufacturing a metal-based multi-layer PCB according to claim 1, wherein: The first filling assembly includes a first prepreg, a first optical core board, and a connecting layer arranged in sequence, the first prepreg includes a first connecting portion, the first optical core board includes a first limiting portion, and the first connecting portion is located between the bottom surface of the first blind groove and the first limiting portion; When the metal substrate, the first filling component, and the sub-board are pressed together, the first connecting portion and the first limiting portion jointly fill the first blind groove, and the connecting layer covers the notch of the first blind groove; When the second side forms the second blind groove in the molding area, the first connecting portion defines the bottom surface of the second blind groove; The second filling assembly includes a second prepreg and a second optical core board arranged in sequence, the second prepreg includes a second connecting portion, the second optical core board includes a second limiting portion, and the second connecting portion is located between the bottom surface of the second blind groove and the second limiting portion; When the metal substrate and the second filling assembly are pressed together, the second connecting portion and the second limiting portion jointly fill the second blind groove.

3. The method for manufacturing a metal-based multi-layer PCB according to claim 1, wherein: The metal substrate includes a process edge, the molding area is arranged inside the process edge, and the arrangement direction of the process edge and the molding area is perpendicular to the arrangement direction of the first side and the second side; when the first side makes a first blind groove in the molding area, the first side makes a first glue flow groove in the process edge; when the metal substrate, the first filling component and the sub-board are pressed together, part of the first filling component fills the first glue flow groove; when the second side makes a second blind groove in the molding area, the second side makes a second glue flow groove in the process edge, the filling component located in the first blind groove defines at least part of the bottom surface of the second glue flow groove, and the first glue flow groove and the second glue flow groove divide the process edge into at least two parts; when the metal substrate and the second filling component are pressed together, at least part of the second filling component fills the second glue flow groove.

4. The method for manufacturing a metal-based multi-layer PCB according to claim 3, wherein: When the first filling component and the sub-plate are stacked in sequence on the first side, the metal base plate, the first filling component and the sub-plate are riveted together using a first rivet, and the first rivet passes through the bottom wall of the first glue flow groove.

5. The method for manufacturing a metal-based multi-layer PCB according to claim 4, wherein: The second glue flow trough is staggered with the first glue flow trough, and the first filling component located in the first blind groove defines a portion of the bottom surface of the second blind groove; when the second filling component is stacked on the second side, a second rivet is used to rivet the metal substrate and the second filling component together, and the second rivet passes through the bottom wall of the second glue flow trough and the bottom wall of the first glue flow trough.

6. The method for manufacturing a metal-based multi-layer PCB according to claim 3, wherein: A plurality of the first glue flow grooves and a plurality of the second glue flow grooves are provided, and the first glue flow grooves and the second glue flow grooves are provided in a one-to-one correspondence.

7. The method for manufacturing a metal-based multi-layer PCB according to any one of claims 1 to 6, characterized in that: Before stacking the first filling component and the daughter board in sequence on the first side, the method for manufacturing the metal-based multi-layer PCB further includes: Providing the daughterboard, the daughterboard is provided with a solder pad and a PTH hole, the daughterboard has an immersion gold surface, the solder pad is provided on the immersion gold surface, and the PTH hole has an orifice formed on the immersion gold surface; Covering the immersion gold surface with a protective film, wherein the protective film is provided with a first window and a second window, wherein the first window exposes the solder pad, and the second window exposes the opening of the PTH hole formed on the immersion gold surface; The daughter board is subjected to an immersion gold electroplating process so that the pad is covered with an immersion gold layer.

8. The method for manufacturing a metal-based multi-layer PCB according to claim 7, wherein: The daughter board is provided with a conductive portion, and the conductive portion is located at the edge of the immersion gold surface; the protective film is provided with a third window, and the third window exposes the conductive portion.

9. The method for manufacturing a metal-based multi-layer PCB according to any one of claims 1 to 6, wherein: The daughter board is provided with solder pads and PTH holes that are connected and electrically conductive. The solder pads are located on the side of the daughter board facing the metal substrate. The PTH holes are located in the uncovering area of ​​the daughter board. The PTH holes at least conduct the two layers of circuits of the daughter board. After the metal substrate and the second filling component are pressed together, the metal substrate and the first filling component corresponding to the uncovering area are removed.

10. A metal-based multi-layer PCB, characterized in that: The metal-based multi-layer PCB is manufactured by the method for manufacturing a metal-based multi-layer PCB according to any one of claims 1 to 9.

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