Flexible printed circuit board and manufacturing method thereof

Abstract

The invention provides a flexible printed circuit board and a manufacturing method thereof, the flexible printed circuit board comprises two circuit substrates, and one circuit substrate comprises an insulating layer and two circuit layers. The plurality of conductive blind holes are arranged in the insulating layer and are electrically connected with the two circuit layers. The bonding layer is located on the circuit layer and covers the end face of the conductive blind hole. The plurality of open holes respectively correspond to the conductive blind holes, and the open holes extend from the bonding layer to the other circuit layer through the conductive blind holes. The plurality of welding materials are respectively arranged on the conductive blind holes, are arranged between the two circuit substrates and are electrically connected with the two circuit substrates. In the welding process, the holes contain the overflowing parts of the welding materials, the adjacent welding materials cannot make contact with each other due to overflowing, and then short circuit is avoided.

Description

Technical Field

[0001] The invention relates to a circuit board, and in particular to a flexible printed circuit board and a manufacturing method of the flexible printed circuit board. Background Art

[0002] Hot Bar soldering technology is widely used in the soldering process of flexible printed circuit boards. This technology is to place solder materials (such as solder paste) on the circuit board by default, and then heat them through a thermostat to connect the solder materials to the circuit board and the electronic components to be soldered. Generally speaking, excess solder materials will overflow during the heating and melting process. Therefore, when the distance between the preset solder materials is close, adjacent solder materials are prone to contact each other due to overflow, resulting in a short circuit, making it difficult to improve the yield of the soldering process. Summary of the invention

[0003] Therefore, the present invention provides a flexible printed circuit board and a manufacturing method thereof, so as to improve the short circuit between welding materials.

[0004] A flexible printed circuit board provided in one embodiment of the present invention comprises a first circuit substrate; the first circuit substrate comprises an insulating layer and two circuit layers respectively located on opposite sides of the insulating layer; a plurality of conductive blind holes arranged in the insulating layer and electrically connecting the circuit layers on both sides of the insulating layer; a bonding layer located on one of the circuit layers and covering one end surface of the conductive blind holes; a plurality of openings respectively corresponding to the conductive blind holes, and the openings extend from the bonding layer through the conductive blind holes to another of the circuit layers; a plurality of welding materials, wherein each of the welding materials is respectively located on the conductive blind holes, and a portion of each of the welding materials is located in the opening; and a second circuit substrate arranged on the welding materials, wherein the welding materials are located between the first circuit substrate and the second circuit substrate, and electrically connecting the first circuit substrate and the second circuit substrate.

[0005] In at least one embodiment of the present invention, the flexible printed circuit board further includes a third circuit substrate located on the first circuit substrate, wherein the third circuit substrate is electrically connected to the first circuit substrate through a plurality of conductive through holes, and a bonding layer is located between the first circuit substrate and the third circuit substrate.

[0006] In at least one embodiment of the present invention, the interface between the opening and the bonding layer is located between the insulating layer of the first circuit substrate and the third circuit substrate, and the interface is not flush with the surface of the third circuit substrate.

[0007] In at least one embodiment of the present invention, the flexible printed circuit board further includes a plurality of solder pads respectively located between the conductive blind vias and the soldering material, wherein the solder pads are electrically connected to the soldering material and the first circuit substrate.

[0008] In at least one embodiment of the present invention, the solder material in the opening directly contacts the bonding layer.

[0009] In at least one embodiment of the present invention, the solder material in the opening does not directly contact the bonding layer.

[0010] The present invention also provides a method for manufacturing a flexible printed circuit board, comprising providing an initial circuit substrate, the initial circuit substrate comprising an insulating layer and two metal layers, wherein the metal layers are respectively located on opposite sides of the insulating layer; forming a plurality of conductive blind holes on the initial circuit substrate, wherein the conductive blind holes are electrically connected to the metal layers on both sides of the insulating layer; after forming the conductive blind holes, patterning at least one layer of the metal layer into at least one circuit layer to form a first circuit substrate comprising the circuit layer; laminating a bonding layer on the first circuit substrate, wherein the bonding layer covers the conductive blind holes; after laminating the bonding layer, forming a plurality of openings on the first circuit substrate, wherein the openings extend from the circuit layer to the bonding layer via the conductive blind holes; and after forming the openings, connecting the first circuit substrate and the second circuit substrate by welding with a plurality of welding materials, wherein the welding materials are respectively located on the conductive blind holes, and a portion of each welding material is located in the opening, while another portion of each welding material covers the opening.

[0011] In at least one embodiment of the present invention, forming a conductive blind hole on the initial circuit substrate further includes removing an insulating layer and a portion of one of the metal layers to form a plurality of grooves, and exposing another of the metal layers to the inner wall of each of the grooves; and depositing a conductive material in each of the grooves, and the conductive material directly contacts another of the metal layers.

[0012] In at least one embodiment of the present invention, the method further comprises disposing a third circuit substrate on the bonding layer before forming the opening, wherein the bonding layer is located between the first circuit substrate and the third circuit substrate.

[0013] In at least one embodiment of the present invention, the method further includes forming a plurality of conductive vias in the first circuit substrate, the bonding layer and the third circuit substrate after bonding the bonding layer on the first circuit substrate, wherein the conductive vias electrically connect the first circuit substrate and the third circuit substrate.

[0014] In at least one embodiment of the present invention, forming an opening on the first circuit substrate further includes removing a portion of the circuit layer and a portion of each conductive blind hole to form a plurality of openings; and after forming the openings, removing a portion of the bonding layer to form a cavity in each of the grooves, and the cavities are respectively connected to the openings.

[0015] In at least one embodiment of the present invention, the method further includes forming a plurality of solder pads on the first circuit substrate before setting the second circuit substrate, wherein the solder pads are located on the conductive blind holes and cover the openings respectively, and a portion of each solder pad is located in the opening.

[0016] Based on the above, when there is excess soldering material on each conductive blind hole and overflows during the soldering process, the excess soldering material can be filled into the openings in the flexible printed circuit board. In this way, adjacent soldering materials can be prevented from contacting each other due to overflow, thereby reducing the occurrence of short circuits during the soldering process and improving the yield rate of the flexible printed circuit board. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be understood from the following detailed description and the accompanying drawings. It should be noted that various features are not drawn to the standard scale in industry practice. In fact, the size of various features may be arbitrarily increased or decreased for clarity of discussion.

[0018] Figures 1A to 1F A cross-sectional view of a method for manufacturing a flexible printed circuit board according to an embodiment of the present invention is shown.

[0019] Figure 2 A cross-sectional view of a method for manufacturing a flexible printed circuit board according to another embodiment of the present invention is shown.

[0020] Figure 3 A cross-sectional view of a flexible printed circuit board according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0021] The present invention will be described in detail with the following examples. It should be noted that the following description of the embodiments of the present invention is only for illustration and is not intended to exhaustively disclose all embodiments or to limit the specific embodiments of the present invention. For example, the description of "a first feature formed on a second feature" includes multiple implementations, including the first feature being in direct contact with the second feature, and also including additional features being formed between the first feature and the second feature so that the two are not in direct contact. In addition, the same element symbols used in the drawings and the specification will represent the same or similar elements as much as possible.

[0022] Spatially relative terms, such as "lower," "below," "beneath," "above," and related terms, are used herein to simply describe the relationship of an element or feature as shown in the figures to another element or feature. These spatially relative terms also cover different orientations when using or operating the device in addition to the orientation depicted in the figures. In addition, when the element is rotatable (rotated 90 degrees or other angles), the spatially relative descriptors used herein can also be interpreted accordingly.

[0023] In the following text, in order to clearly present the technical features of the present invention, the dimensions (such as length, width, thickness and depth) of the elements (such as layers, films, substrates and regions, etc.) in the drawings will be enlarged in unequal proportions. Therefore, the description and explanation of the embodiments below are not limited to the dimensions and shapes presented by the elements in the drawings, but should cover the dimensions, shapes and deviations thereof caused by actual processes and / or tolerances. For example, the flat surface shown in the drawings may have rough and / or nonlinear features, and the acute angles shown in the drawings may be replaced with obtuse angles. Therefore, the elements presented in the drawings of the present invention are mainly for illustration, and are not intended to accurately depict the actual shape of the elements, nor are they intended to limit the claims of the present invention.

[0024] Furthermore, the words "about", "approximately" or "substantially" appearing in the present case not only cover the numerical values ​​and numerical ranges clearly recorded, but also cover the permissible deviation range that can be understood by those skilled in the art, wherein the deviation range can be determined by the error generated during measurement, and the error is caused by, for example, the limitation of the measurement system or process conditions. In addition, "about" can mean within one or more standard deviations of the above numerical values, such as ±30%, ±20%, ±10% or ±5%. The words "about", "approximately" or "substantially" appearing in the present case can select the acceptable deviation range or standard deviation according to the optical properties, etching properties, mechanical properties or other properties, and not just one standard deviation can be applied to all the above optical properties, etching properties, mechanical properties and other properties.

[0025] The present invention discloses a method for manufacturing a flexible printed circuit board. The method may include: Figures 1A to 1F Please refer to Figure 1A In this embodiment, an initial circuit substrate 110' is first provided, and the initial circuit substrate 110' includes an insulating layer 112, a metal layer 114a and a metal layer 114b. In various embodiments of the present invention, the initial circuit substrate 110' can be a general copper clad laminate (CCL), wherein the metal layer 114a and the metal layer 114b are respectively located on opposite sides of the insulating layer 112.

[0026] Please refer to Figure 1A and Figure 1B , a plurality of conductive blind vias 120 are formed on the initial circuit substrate 110', wherein the conductive blind vias 120 are electrically connected to the metal layer 114a and the metal layer 114b on both sides of the insulating layer 112. The method for forming the conductive blind vias 120 also includes the following steps: First, a portion of the insulating layer 112 and one of the metal layers (metal layer 1104a or metal layer 114b) is removed to form a plurality of grooves 122. For example, the plurality of grooves 122 can be formed on the initial circuit substrate 110' by drilling or routing.

[0027] It is particularly noted that the grooves 122 extend from the metal layer 114a through the insulating layer 112 and stop before the metal layer 114b. In other words, the grooves 122 do not extend to the metal layer 114b, and the metal layer 114b is exposed to the inner wall 122w of each groove 122. Subsequently, a conductive material 124 is deposited in each groove 122, and the conductive material 124 directly contacts the metal layer 114b. In the present embodiment, the conductive material 124 may include copper.

[0028] After forming the conductive blind via 120, at least one metal layer is patterned into at least one circuit layer. Figure 1B As shown, in this embodiment, the metal layer 114a can be patterned into the circuit layer 116a by methods such as lithography and etching to form the circuit substrate 110 including the circuit layer 116a. However, the present invention is not limited thereto, and in other embodiments, this step can also pattern the metal layer 114a and the metal layer 114b to form the circuit substrate 110 including the circuit layer 116a and the circuit layer 116b.

[0029] Please refer to Figure 1C After forming the circuit substrate 110, a bonding layer 140 is attached to the circuit substrate 110, and the bonding layer 140 covers the conductive material 124 of the conductive blind via 120. The material of the bonding layer 140 can be a composite material including glass fiber and resin, such as prepreg, or other similar insulating materials.

[0030] In addition, the circuit substrate 130 is disposed on the bonding layer 140, wherein the bonding layer 140 is located between the circuit substrate 110 and the circuit substrate 130. Figure 1C In the embodiment, the circuit substrate 130 includes an insulating layer 132 and a single circuit layer 136, but the present invention is not limited thereto. In other embodiments, the circuit substrate 130 may also include another circuit layer (not shown), and the circuit layer and the circuit layer 136 are respectively located on both sides of the insulating layer 132.

[0031] After the bonding layer 140 is bonded to the circuit substrate 110 , a plurality of conductive vias 160 may be formed in the circuit substrate 110 , the bonding layer 140 , and the circuit substrate 130 , and the conductive vias 160 electrically connect the circuit substrate 110 and the circuit substrate 130 .

[0032] It is worth mentioning that in this embodiment, the conductive vias 160 are formed first and then the circuit substrate 130 is formed. Specifically, the circuit substrate 130 (not shown) that has not yet been patterned is first attached to the bonding layer 140. Then, a plurality of openings (not shown) are formed in the circuit substrate 110, the bonding layer 140 and the circuit substrate 130 that has not yet been patterned by drilling or routing, and a conductive metal material such as copper is deposited in these openings to form a plurality of conductive vias 160. After the conductive vias 160 are formed, the circuit substrate 130 that has not yet been patterned is patterned to form the circuit layer 136.

[0033] After forming the circuit layer 136, a conductive layer may be formed on the circuit substrate 130 by electroplating. For example, in this embodiment, a conductive layer 138 is formed on the circuit layer 136 of the circuit substrate 130 by electroplating, and the material of the conductive layer 138 may include copper. Although not shown in this embodiment, in other embodiments of the present invention, a conductive layer (not shown) may also be formed on the circuit layer 116b of the circuit substrate 110 by electroplating.

[0034] After forming the conductive via 160, the metal layer 114b of the circuit substrate 110 is patterned to form a circuit layer 116b (eg, Figure 1C However, the present invention is not limited thereto. In other embodiments, the circuit layer 116b may be formed before forming the conductive via 160. For example, in the aforementioned step of forming the circuit substrate 110, the metal layer 114a and the metal layer 114b are patterned to form the circuit layer 116a and the circuit layer 116b.

[0035] Please refer to Figure 1D as well as Figure 1E After the bonding layer 140 (and the circuit substrate 130) are attached, a plurality of openings 180 are formed on the circuit substrate 110. The openings 180 extend from the circuit layer 116b to the bonding layer 140 via the conductive blind vias 120.

[0036] Furthermore, the steps of forming the opening 180 include: Figure 1DAs shown in FIG. 1 , a portion of the circuit layer 116b and a portion of each of the conductive blind vias 120 are removed to form a plurality of openings 180p. Each opening 180p connects two opposite sides of the circuit substrate 110. After the openings 180p are formed, Figure 1E As shown, a portion of the bonding layer 140 is removed to form a cavity 180c in each groove 122. These cavities 180c are respectively connected to the openings 180p, thereby forming a plurality of openings 180. In various embodiments of the present invention, the openings 180p can be formed by, for example, laser ablation or the like. In addition, the bonding layer 140 can be removed by, for example, plasma debonding to form the cavity 180c.

[0037] After the opening 180 is formed, the circuit substrate 110 and the circuit substrate 150 are connected by welding with a plurality of welding materials 190. Figure 1F , the welding materials 190 are respectively located on the conductive blind vias 120. In this embodiment, the welding method may include: pre-setting (e.g., pre-welding) a plurality of welding materials 190 on the circuit substrate 150, and welding the welding materials 190 to the circuit substrate 110 by, for example, hot pressing tin melting welding. The welding materials 190 may include, for example, solder paste, copper paste, or silver paste.

[0038] When the soldering material 190 is heated and melted during the soldering process, a portion of the soldering material 190 flows into the cavity 180c through the opening 180p, so that a portion of the soldering material 190 is located in the opening 180. On the other hand, the other portion of the soldering material 190 covers the opening 180 and is located between the opening 180 and the circuit substrate 150 (see Figure 3 shown).

[0039] In particular, please refer to Figure 2 In another embodiment, before connecting the circuit substrate 110 and the circuit substrate 150, a plurality of pads 117 may be formed on the circuit substrate 110. The pads 117 disposed on the circuit substrate 110 correspond to the conductive blind vias 120, respectively, and cover the openings 180, respectively. In addition, a portion of the pads 117 is located in the openings 180.

[0040] The method of this embodiment further includes, before connecting the circuit substrate 110 and the circuit substrate 150 with a plurality of welding materials 190, respectively disposing a covering layer 170b and a covering layer 170a on the circuit substrate 110 and the circuit substrate 130. The covering layer 170b and the covering layer 170a are respectively attached to the circuit layer 116b of the circuit substrate 110 and the circuit layer 136 of the circuit substrate 130 with a bonding layer (not shown), and the material of these bonding layers can be the same as that of the bonding layer 140.

[0041] Although not shown in the figure, in this embodiment, a protective layer (not shown) can be formed on the circuit layer 116b of the circuit substrate 110 by a surface treatment method such as electroless nickel immersion gold (ENIG). In this embodiment, the protective layer covers a portion of the circuit layer 116b, and this portion of the circuit layer 116b is not covered by the covering layer 170b.

[0042] Through the steps of the above embodiments, a Figure 3 The flexible printed circuit board 30 shown in FIG. Figure 3 3 is a cross-sectional view of a flexible printed circuit board 30. The flexible printed circuit board 30 includes a circuit substrate 110, and the circuit substrate 110 includes an insulating layer 112, a circuit layer 116a and a circuit layer 116b. The circuit layer 116a and the circuit layer 116b are respectively located on opposite sides of the insulating layer 112. The material of the insulating layer 112 may include an insulating material such as an organic resin (such as epoxy resin) or the like.

[0043] The flexible printed circuit board 30 includes a plurality of conductive blind vias 120. Figure 3 , the conductive blind via 120 is disposed in the insulating layer 112 of the circuit substrate 110, and electrically connects the circuit layer 116a and the circuit layer 116b located on both sides of the insulating layer 112. The bonding layer 140 of the flexible printed circuit board 30 is located on one of the circuit layers and covers one end surface of the conductive blind via 120. For example, in this embodiment, the bonding layer 140 is located on the circuit layer 116a and covers the end surface 120e of the conductive blind via 120.

[0044] The flexible printed circuit board 30 includes a plurality of openings 180, each of which corresponds to a conductive blind via 120. The openings 180 extend from the bonding layer 140 to the circuit layer 116b through the conductive blind via 120. In other words, each opening 180 connects two opposite sides of the circuit substrate 110. The flexible printed circuit board 30 includes a plurality of soldering materials 190, such as Figure 3 As shown, the welding materials 190 are respectively located on the conductive blind vias 120 , and a portion of each welding material 190 is located in the opening 180 .

[0045] The flexible printed circuit board 30 further includes a circuit substrate 130, which is located on the circuit substrate 110. The circuit substrate 130 is electrically connected to the circuit substrate 110 through a plurality of conductive vias 160, and the bonding layer 140 is located between the circuit substrate 110 and the circuit substrate 130. In some embodiments of the present invention, an interface 140i between the opening 180 and the bonding layer 140 is located between the insulating layer 112 of the circuit substrate 110 and the insulating layer 132 of the circuit substrate 130, and the interface 140i does not cut into the surface 130s of the circuit substrate 130. For example, in this embodiment, the interface 140i is located between the surface 112s of the insulating layer 112 and the surface of the insulating layer 132 (substantially the same as the surface 130s of the circuit substrate 130).

[0046] It is worth mentioning that in this embodiment, the welding material 190 in the opening 180 is in direct contact with the bonding layer 140, but the present invention is not limited thereto. In other embodiments, the welding material 190 in the opening 180 may not be in direct contact with the bonding layer 140. In other words, the welding material 190 may not fill the opening 180, so that air or other gas exists in the opening 180.

[0047] like Figure 3 As shown, the flexible printed circuit board 30 includes a circuit substrate 150. The circuit substrate 150 is disposed on a soldering material 190, wherein the soldering material 190 is located between the circuit substrate 110 and the circuit substrate 150, and electrically connects the circuit substrate 110 and the circuit substrate 150. In particular, in other embodiments, the flexible printed circuit board 30 may further include a plurality of solder pads 117 (see Figure 2 ), respectively located between the conductive blind via 120 and the welding material 190.

[0048] The soldering pads 117 are electrically connected to the soldering material 190 and the circuit substrate 110. Specifically, the soldering material 190 is electrically connected to the circuit layer 116b of the circuit substrate 110 through the soldering pads 117. It should be noted that in some embodiments, the temperature of the soldering process causes the soldering material 190 and the soldering pads 117 to melt into each other. Therefore, there is no obvious boundary between the soldering pads 117 and the soldering material 190 visible to the naked eye, so the soldering pads 117 can be regarded as a part of the soldering material 190.

[0049] In this embodiment, the flexible printed circuit board 30 further includes a covering layer 170a and a covering layer 170b. The covering layer 170b and the covering layer 170a are respectively located on the circuit layer 116b of the circuit substrate 110 and the circuit layer 136 of the circuit substrate 130. Figure 3As shown, a bonding layer (not shown) is located between the cover layer 170a and the circuit substrate 130, and another bonding layer (not shown) is located between the cover layer 170b and the circuit substrate 110. Figure 3 In the embodiment, the flexible printed circuit board 30 of this embodiment may further include a protective layer covering a portion of the circuit layer 116b, and this portion of the circuit layer 116b is not covered by the covering layer 170b.

[0050] In this embodiment, the covering layer 170a and the covering layer 170b may be a solder mask. Therefore, the material of the covering layer 170a and the covering layer 170b may include an insulating material such as resin. Figure 3 However, the circuit substrate 150 of this embodiment may also include two covering layers. These covering layers may cover both sides of the insulating layer 152 of the circuit substrate 150 and respectively cover the circuit layer 156a and the circuit layer 156b.

[0051] In summary, during the welding process, when there is excess welding material on each conductive blind hole, the excess welding material can be filled into the opening in the flexible printed circuit board. In this way, it is possible to prevent the welding material on each conductive blind hole from overflowing and contacting each other, thereby reducing the occurrence of short circuits during the welding process and improving the yield rate of the flexible printed circuit board.

[0052] Although the embodiments of the present invention have been disclosed above, they are not intended to limit the embodiments of the present invention. Any person skilled in the art may make some changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention shall be determined by the definition of the attached claims.

[0053]

Explanation of symbols

[0054] 110,130,150: Circuit board

[0055] 110': Initial circuit substrate

[0056] 112,132,152: Insulation layer

[0057] 112s,130s:Surface

[0058] 114a, 114b: metal layer

[0059] 116a,116b,136,156a,156b: circuit layer

[0060] 117: Solder pad

[0061] 120: Conductive blind via

[0062] 120e: End face

[0063] 124: Conductive material

[0064] 122: Groove

[0065] 122w: Inner wall

[0066] 138: Conductive layer

[0067] 140: Bonding layer

[0068] 140i: Interface

[0069] 160: Conductive via

[0070] 170a, 170b: Covering layer

[0071] 180: Opening

[0072] 180c: Cavity

[0073] 180p: Open

[0074] 190: Welding materials

[0075] 30: Flexible printed circuit board.

Claims

1. A flexible printed circuit board, characterized in that: Include: The first circuit substrate comprises: Insulation layer; and Two circuit layers are respectively located on two opposite sides of the insulating layer; A plurality of conductive blind holes are disposed in the insulating layer and electrically connect the circuit layers on both sides of the insulating layer; A bonding layer, located on one of the circuit layers and covering one end surface of the conductive blind hole; A plurality of openings, each corresponding to the conductive blind holes, and the openings extend from the bonding layer through the conductive blind holes to another one of the circuit layers; a plurality of welding materials, wherein each of the welding materials is respectively located on the conductive blind vias, and a portion of each of the welding materials is located in the opening; as well as The second circuit substrate is disposed on the welding material, wherein the welding material is located between the first circuit substrate and the second circuit substrate and electrically connects the first circuit substrate and the second circuit substrate.

2. The flexible printed circuit board according to claim 1, wherein: Also includes: A third circuit substrate is located on the first circuit substrate, wherein the third circuit substrate is electrically connected to the first circuit substrate through a plurality of conductive through holes; The bonding layer is located between the first circuit substrate and the third circuit substrate.

3. The flexible printed circuit board according to claim 2, wherein: The interface between the opening and the bonding layer is located between the insulating layer of the first circuit substrate and the third circuit substrate, and the interface is not flush with the surface of the third circuit substrate.

4. The flexible printed circuit board according to claim 1, wherein: Also includes: A plurality of welding pads are respectively located between the conductive blind holes and the welding material, wherein the welding pads are electrically connected to the welding material and the first circuit substrate.

5. The flexible printed circuit board according to claim 1, wherein: The welding material located in the opening directly contacts the bonding layer.

6. The flexible printed circuit board according to claim 1, wherein: The welding material in the opening does not directly contact the bonding layer.

7. A method for manufacturing a flexible printed circuit board, characterized in that: Include: Providing an initial circuit substrate, the initial circuit substrate comprising an insulating layer and two metal layers, wherein the metal layers are respectively located on opposite sides of the insulating layer; On the initial circuit substrate, a plurality of conductive blind holes are formed, wherein the conductive blind holes are electrically connected to the metal layers on both sides of the insulating layer; After forming the conductive blind vias, patterning at least one layer of the metal layer into at least one circuit layer to form a first circuit substrate including the circuit layer; Laminating a bonding layer on the first circuit substrate, wherein the bonding layer covers the conductive blind hole; After attaching the bonding layer, forming a plurality of openings on the first circuit substrate, wherein the openings extend from the circuit layer through the conductive blind holes to the bonding layer; as well as After forming the opening, the first circuit substrate and the second circuit substrate are connected by welding with a plurality of welding materials, wherein the welding materials are respectively located on the conductive blind holes, and a portion of each of the welding materials is located in the opening, while another portion of each of the welding materials covers the opening.

8. The method according to claim 7, characterized in that The method of forming the conductive blind via on the initial circuit substrate further comprises: removing a portion of the insulating layer and one of the metal layers to form a plurality of grooves, and exposing another one of the metal layers to an inner wall of each of the grooves; and In each of the grooves, a conductive material is deposited, and the conductive material directly contacts another one of the metal layers.

9. The method according to claim 7, characterized in that: Also includes: Before forming the opening, a third circuit substrate is disposed on the bonding layer, wherein the bonding layer is located between the first circuit substrate and the third circuit substrate.

10. The method according to claim 9, characterized in that Also includes: After the bonding layer is attached to the first circuit substrate, a plurality of conductive through holes are formed in the first circuit substrate, the bonding layer and the third circuit substrate, wherein the conductive through holes electrically connect the first circuit substrate and the third circuit substrate.

11. The method according to claim 8, characterized in that The step of forming the opening on the first circuit substrate further comprises: removing a portion of the circuit layer and a portion of each of the conductive blind vias to form a plurality of openings; as well as After forming the openings, a portion of the bonding layer is removed to form cavities in each of the grooves, and the cavities are respectively communicated with the openings.

12. The method according to claim 7, characterized in that Also includes: Before setting the second circuit substrate, a plurality of welding pads are formed on the first circuit substrate, wherein the welding pads are respectively located on the conductive blind holes and respectively cover the openings, and a portion of each of the welding pads is located in the openings.

Images