FLEXIBLE SUBSTRATE AND METHOD FOR FABRICATING THE SAME

Abstract

A flexible substrate is provided, including a coreless substrate body having a flexible section, and an additional element formed on the substrate body and having a through hole exposing the flexible section, thereby reducing the overall thickness of the flexible substrate and meeting the thinning requirement

Claims

1. A flexible substrate, comprising: a coreless substrate body having at least a dielectric layer as a soft portion, wherein a flexible section is defined by the dielectric layer, and the dielectric layer is made of a molding compound or a primer; and an additional element as a rigid portion formed on the coreless substrate body with a through hole exposing the flexible section, wherein the through hole and the flexible section form a cavity.

2. The flexible substrate of claim 1, wherein the coreless substrate body further has a circuit structure bonded to the dielectric layer.

3. The flexible substrate of claim 1, wherein the additional element further has a conductive post embedded in an insulating layer.

4. The flexible substrate of claim 3, wherein the insulating layer is made of a dielectric material.

5. The flexible substrate of claim 4, wherein the dielectric material is a molding compound or a primer.

6. The flexible substrate of claim 1, wherein the additional element is a metal sheet.

7. A method for fabricating a flexible substrate, comprising: providing a coreless substrate body having a flexible section and at least a dielectric layer; forming an additional element on the coreless substrate body, wherein the additional element has an insulating layer, a conductive post embedded in the insulating layer, and a block penetrating the additional element; and removing the block to form in the additional element a through hole exposing the flexible section, wherein the through hole and the flexible section form a cavity.

8. The method of claim 7, wherein the dielectric layer is made of a molding compound or a primer.

9. The method of claim 7, wherein the coreless substrate body further has a circuit structure bonded to the dielectric layer.

10. The method of claim 7, wherein the insulating layer is made of a dielectric material.

11. The method of claim 10, wherein the dielectric material is a molding compound or a primer.

12. A method for fabricating a flexible substrate, comprising: forming a coreless substrate body on a carrier, wherein the coreless substrate body has a flexible section and at least a dielectric layer made of a molding compound or a primer; and removing a portion of the carrier to form a through hole penetrating the carrier and exposing the flexible section for the carrier having the through hole to serve as an additional element, wherein the through hole and the flexible section form a cavity.

13. The method of claim 12, wherein the coreless substrate body further has a circuit structure bonded to the dielectric layer.

14. The method of claim 12, wherein the carrier is a metal sheet.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0052] FIGS. 1A to 1D are schematic cross-sectional views showing a method for fabricating a rigid-flexible packaging substrate according to the prior art;

[0053] FIGS. 2A to 2D are schematic cross-sectional views showing another method for fabricating a rigid-flexible packaging substrate according to the prior art;

[0054] FIGS. 3A to 3E are schematic cross-sectional views showing a further method for fabricating a rigid-flexible packaging substrate according to the prior art;

[0055] FIG. 4 is a schematic cross-sectional view showing another method for fabricating a rigid-flexible packaging substrate according to the prior art;

[0056] FIGS. 5A to 5F are schematic cross-sectional views showing a method for fabricating a flexible substrate according to a first embodiment of the present disclosure;

[0057] FIG. 5G is a schematic top view of FIG. 5F;

[0058] FIGS. 6A to 6C are schematic cross-sectional views showing a method for fabricating a flexible substrate according to a second embodiment of the present disclosure; and

[0059] FIGS. 7A to 7B are schematic cross-sectional views showing a method for fabricating a flexible substrate according to a third embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0060] The following illustrative embodiments are provided to illustrate the disclosure of the present disclosure, these and other advantages and effects can be apparent to those in the art after reading this specification. It should be noted that all the drawings are not intended to limit the present disclosure.

[0061] Various modifications and variations can be made without departing from the spirit of the present disclosure. Further, terms such as first, second, on, a etc. are merely for illustrative purposes and should not be construed to limit the scope of the present disclosure.

[0062] FIGS. 5A to 5F are schematic cross-sectional views showing a method for fabricating a flexible substrate 5 according to a first embodiment of the present disclosure.

[0063] Referring to FIG. 5A, a plurality of first conductive posts 51 and a block 59a are disposed on a carrier 50 through a patterning process.

[0064] In an embodiment, the carrier 50 is metal, a semiconductor or an insulating substrate.

[0065] The first conductive posts 51 and the block 59a are made of metal, such as copper. The first conductive posts 51 and the block 59a can be made of the same or different materials.

[0066] Referring to FIG. 5B, a first insulating layer 53 is formed on the carrier 50 to encapsulate the first conductive posts 51 and the block 59a. The surfaces of the first conductive posts 51 and the block 59a are flush with the surface of the first insulating layer 53 so as to be exposed from the first insulating layer 53. The block 59a penetrates the first insulating layer 53.

[0067] In an embodiment, the first insulating layer 53 serves as a rigid portion and is formed on the carrier 50 by molding, coating or lamination. The first insulating layer 53 is made of a dielectric material, such as an epoxy resin containing a molding compound or a primer, such as an epoxy molding compound. The epoxy molding compound contains 70 to 90 wt % of a filler.

[0068] Referring to FIG. 5C, a substrate body 55 is disposed on the first insulating layer 53 and electrically connected to the first conductive posts 51.

[0069] In an embodiment, the substrate body 55 is coreless and formed through a circuit built-up process. The substrate body 55 has at least a dielectric layer 550 formed by coating, a circuit layer 551 bonded to the dielectric layer 550, and a plurality of conductors 552 formed in the dielectric layer 550 and electrically connected to the circuit layer 551.

[0070] In another embodiment, the substrate body 55 is formed by molding. In yet another embodiment, a circuit layer 551 is formed on the first insulating layer 53 and then a plurality of conductive posts 551 are disposed on the circuit layer 551. Thereafter, the dielectric layer 550 is formed by molding to encapsulate the circuit layer 551 and the conductive posts. The conductive posts serve as the conductors 552.

[0071] The dielectric layer 550 serves as a soft portion. The dielectric layer 550 and the first insulating layer 53 can be made of the same or different materials. In an embodiment, the dielectric layer 550 and the first insulating layer 53 are made of the same or different kinds of epoxy resin.

[0072] Referring to FIG. 5D, a plurality of second conductive posts 52 and a block 59b are disposed on the substrate body 55 and a second insulating layer 54 is formed on the substrate body 55 to encapsulate the second conductive posts 52 and the block 59b. The surfaces of the second conductive posts 52 and the block 59b are flush with the surface of the second insulating layer 54 so as to be exposed from the second insulating layer 54. The block 59b penetrates the second insulating layer 54.

[0073] In an embodiment, the second conductive posts 52 and the block 59b are made of metal, such as copper. The second conductive posts 52 and the block 59b can be made of the same or different materials.

[0074] Further, the second insulating layer 54 serves as a rigid portion and is formed by molding, coating or lamination. The second insulating layer 54 is made of a dielectric material, such as an epoxy resin containing a molding compound or a primer, such as an epoxy molding compound. The epoxy molding compound contains 70 to 90 wt % of a filler.

[0075] Further, the second insulating layer 54 and the first insulating layer 53 can be made of the same or different materials, and the second insulating layer 54 and the dielectric layer 550 can be made of the same or different materials.

[0076] Referring to FIGS. 5E and 5G, the carrier 50 is removed by stripping and the blocks 59a, 59b are removed by etching. As such, a first through hole 530 is formed in the first insulating layer 53 and a second through hole 540 is formed in the second insulating layer 54. The substrate body 55 is exposed from the first and second through holes 530, 540 to serve as a flexible section F, wherein the first through hole 530 and the flexible section F form a cavity, and the second through hole 540 and the flexible section F form another cavity. The first conductive posts 51 and the first insulating layer 53 can be regarded as an additional element 5a, and the second conductive posts 52 and the second insulating layer 54 can be regarded as another additional element 5b.

[0077] In an embodiment, when the block 59a is removed, a portion of the substrate body 55 is also removed and hence the first through hole 530 extends into the substrate body 55. Similarly, the second through hole 540 extends into the substrate body 55.

[0078] Subsequently, a surface treatment layer 56 can be formed on the first and second conductive posts 51, 52 according to the practical need.

[0079] Therefore, the substrate body 55 is directly formed on the first insulating layer 53 (i.e., the dielectric layer 550 is coated on the first insulating layer 53) to replace the conventional lamination or attachment process. At the rigid-flexible interface of the flexible substrate 5, two layers of epoxy resin are directly bonded so as to overcome the conventional drawbacks such as adhesive overflows, shorts and bulges and increase the interlayer alignment accuracy to +/25 um.

[0080] Further, the coreless substrate body 55 greatly reduces the overall thickness of the flexible substrate 5. Compared with a conventional four-layer board (generally having a thickness of a bout 0.25 mm), a four-layer board according to the present disclosure has a thickness D less than 0.2 mm. In an embodiment, the four-layer board has a thickness of 0.16 mm.

[0081] Furthermore, since the circuit layer 551 is formed by electroplating instead of metal etching, the edge of the circuit layer 551 is flat and straight, thereby overcoming the conventional foot problem caused by etching and facilitating impedance control. Further, the width/pitch of the circuit layer 551 can be reduced to be less than 20/20 um.

[0082] In addition, the flexible section F is fabricated by image transfer in combination with pattern electroplating copper (blocks 59a, 59b) and etching of copper (blocks 59a, 59b). Therefore, the shape, size and accuracy of the flexible section F are not limited by the conventional mechanical machining process, thereby improving the freedom of the structural design. In an embodiment, a plurality of flexible sections F having any shape can be fabricated at the same time. Further, the blocks 59a, 59b and the first and second conductive posts 51, 52 can be fabricated together to reduce the fabrication cost.

[0083] Furthermore, the outermost conductive pads of the flexible substrate 5 are copper posts (i.e., the first and second conductive posts 51, 52) and the dielectric material (i.e., the first and second insulating layers 53, 54) is used to replace the conventional solder mask layers. As such, the present disclosure strengthens the bonding between the conductive pads and the dielectric material, increases the subsequent wire bonding strength, and improves the product reliability and packaging capability.

[0084] FIGS. 6A to 6C are schematic cross-sectional views showing a method for fabricating a flexible substrate 6 according to a second embodiment of the present disclosure. The second embodiment differs from the first embodiment in the number of the through holes.

[0085] Referring to FIG. 6A, a substrate body 55 is formed on a carrier 50. The dielectric layers 550 serve as a soft portion. They are formed on the carrier 50 by coating.

[0086] Referring to FIG. 6B, a plurality of conductive posts 62 and a block 69 are formed on the substrate body 55, and an insulating layer 64 is formed on the substrate body 55 to encapsulate the conductive posts 62 and the block 69. The surfaces of the conductive posts 62 and the block 69 are flush with the surface of the insulating layer 64 so as to be exposed from the insulating layer 64.

[0087] In an embodiment, the conductive posts 62 and the block 69 are made of metal, such as copper. Further, the conductive posts 62 and the block 69 can be made of the same or different materials.

[0088] Furthermore, the insulating layer 64 serves as a rigid portion and is formed by molding, coating or lamination. The insulating layer 64 is made of a dielectric material, such as an epoxy resin containing a molding compound or a primer, such as an epoxy molding compound. The epoxy molding compound contains 70 to 90 wt % of a filler.

[0089] In an embodiment, the dielectric layers 550 and the insulating layer 64 can be made of the same or different materials. In another embodiment, the dielectric layers 550 and the insulating layer 64 are made of the same or different kinds of epoxy resin.

[0090] Referring to FIG. 6C, the block 69 is removed to form a through hole 640 in the insulating layer 64. As such, a portion of the substrate body 55 is exposed from the through hole 640 to serve as a flexible section F, wherein the through hole 640 and the flexible section F form a cavity. Thereafter, the carrier 50 is removed. The conductive posts 62 and the insulating layer 64 can be regarded as an additional element 60.

[0091] In an embodiment, when the block 69 is removed by etching, portions of the conductive posts 62 are also removed so as to have end surfaces lower than the surface of the insulating layer 64. Further, a portion of the substrate body 55 can be removed to increase the depth of the through hole 640.

[0092] Further, when the carrier 50 is removed, an exposed portion of the electroplated copper layer (a portion of the circuit layer 551) of the flexible substrate body 55 can serve as an electromagnetic shielding layer 651, thereby eliminating the need to attach a silver adhesive conductive film as an electromagnetic shielding layer.

[0093] Subsequently, a surface treatment layer (not shown) can be formed on the conductive posts 62 according to the practical need.

[0094] Therefore, the substrate body 55 is directly formed on a single side of the carrier 50 and the number of the layers of the soft portion (the dielectric layer 550) or the rigid portion (the insulating layer 64) is optional and not limited by the symmetric additional layers on the two opposite sides of the core layer as in the prior art.

[0095] Further, the flexible substrate 6 has a rigid-flexible interface at a single side of the substrate body 55. At the rigid-flexible interface, two layers of epoxy resin (i.e., the dielectric layer 550 and the insulating layer 64) are directly bonded together so as to overcome the conventional drawbacks such as adhesive overflows, shorts and bulges and reduce flexural variations.

[0096] Furthermore, the coreless substrate body 55 greatly reduces the overall thickness of the flexible substrate 6. A four-layer board according to the present disclosure has a thickness d less than 0.2 mm, significantly less than the conventional four-layer board.

[0097] In addition, the outermost conductive pads of the flexible substrate 6 are copper posts (i.e., the conductive posts 62) and the dielectric material (i.e., the insulating layer 64) is used to replace the conventional solder mask layer. As such, the present disclosure strengthens the bonding between the conductive pads and the dielectric material, increases the subsequent wire bonding strength, and improves the product reliability and packaging capability.

[0098] Furthermore, the flexible section F is fabricated by image transfer in combination with pattern electroplating copper (block 69) and etching of copper (block 69). Therefore, the shape, size and accuracy of the flexible section F are not limited by the conventional mechanical machining process, thereby improving the freedom of the structural design. For example, a plurality of flexible sections F having any shape can be fabricated at the same time. Further, the block 69 and the conductive posts 62 can be fabricated together to reduce the fabrication cost.

[0099] FIGS. 7A and 7B are schematic cross-sectional views showing a method for fabricating a flexible substrate 7 according to a third embodiment of the present disclosure. The third embodiment differs from the second embodiment in the fabrication of the through holes.

[0100] Referring to FIG. 7A, following FIG. 6A, an insulating layer 77 is formed on the substrate body 55. The insulating layer 77 has a plurality of openings 771 exposing the circuit layer 551 and at least an open area 770 exposing the dielectric layer 550. In an embodiment, the carrier 50 is a metal sheet.

[0101] Referring to FIG. 7B, a portion of the carrier 50 corresponding in position to the open area 770 is removed to form a through hole 700 penetrating the carrier 50 and exposing a portion of the substrate body 55. The carrier 50 having the through hole 700 serves as an additional element 70 (a rigid portion), and the exposed portion of the substrate body 55 serves as a flexible section F, wherein the through hole 700 and the flexible section F form a cavity.

[0102] Therefore, a metal sheet is used as the carrier 50 so as for a built-up process to be performed thereon. Further, a portion of the carrier 50 is retained and not removed to serve as an additional element 70 for supporting the rigid area and facilitating heat dissipation.

[0103] Further, the flexible substrate 7 has a rigid-flexible interface at a single side of the substrate body 55. At the rigid-flexible interface, the dielectric layer 550 and the carrier 50 made of metal are directly bonded together, and a portion of the carrier 50 is removed to form the through hole 700 penetrating the carrier 50. As such, the present disclosure overcomes the conventional drawbacks such as adhesive overflows, shorts and bulges at the rigid-flexible interface.

[0104] Furthermore, the flexible section F is fabricated by metal etching (removing a portion of the carrier 50). Therefore, the shape, size and accuracy of the flexible section F are not limited by the conventional mechanical machining process, thereby improving the freedom of the structural design. For example, a plurality of flexible sections F having any shape can be fabricated at the same time.

[0105] The coreless substrate body 55 greatly reduces the overall thickness of the flexible substrate 7. A four-layer board according to the present disclosure has a thickness R less than 0.2 mm, significantly less than the conventional four-layer board.

[0106] The present disclosure further provides a flexible substrate 5, 6, 7, which has a coreless substrate body 55 having a flexible section F and an additional element 5a, 5b, 60, 70 formed on the substrate body 55 and having a through hole 640, 700 (first and second through holes 530, 540) exposing the flexible section F.

[0107] In an embodiment, the substrate body 55 has at least a dielectric layer 550 and a circuit structure (for example, a circuit layer 551 and/or conductors 552) bonded to the dielectric layer 550.

[0108] In an embodiment, the additional element 5a, 5b, 60 has an insulating layer 64 (first and second insulating layers 53, 54) and a plurality of conductive posts 62 (first and second conductive posts 51, 52) embedded in the insulating layer 64. For example, the insulating layer 64 (the first and second insulating layers 53, 54) is made of a molding compound or a primer.

[0109] In an embodiment, the additional element 70 is a metal sheet.

[0110] According to the present disclosure, the coreless substrate body facilitates to reduce the overall thickness of the flexible substrate so as to meet the thinning requirement.

[0111] Further, at the rigid-flexible interface, the dielectric material is directly bonded to the additional element so as to overcome the conventional drawbacks such as adhesive overflows, shorts and bulges and improve the interlayer alignment accuracy.

[0112] Furthermore, since the circuit layer is formed through a semi-additive process without metal etching, the present disclosure facilitates impedance control and reduces the line width/pitch to meet the fine pitch/circuit requirement.

[0113] In addition, since the flexible section is defined by metal etching, the shape, size and accuracy of the flexible section F are not limited by the conventional mechanical machining process, thereby improving the freedom of the structural design.

[0114] The above-described descriptions of the detailed embodiments are only to illustrate the implementation according to the present disclosure, and it is not to limit the scope of the present disclosure. Accordingly, all modifications and variations completed by those with ordinary skill in the art should fall within the scope of present disclosure defined by the appended claims.