CIRCUIT BOARD

Abstract

A circuit board includes an inner circuit substrate and an outer circuit substrate electrically connected to the inner circuit substrate. The outer circuit substrate includes an outer dielectric layer and an outer circuit layer facing the inner circuit substrate embedded in the outer dielectric layer. A portion of the outer circuit layer facing away from the inner circuit substrate protruding from the outer dielectric layer. The circuit board can increase contact area between the outer circuit layer and the outer dielectric layer, improving adhesion between the outer circuit layer and the outer dielectric layer, and reducing a thickness of the outer circuit substrate, thereby reducing the overall thickness of the circuit board.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of patent application Ser. No. 17/335,059 filed on May 31, 2021, assigned to the same assignee, which is based on and claims priority to China Patent Application No. 202110402159.6 filed on Apr. 14, 2021, the contents of which are incorporated by reference herein.

FIELD

The subject matter herein generally relates to circuit boards, and more particularly, to a circuit board and a method for manufacturing the circuit board.

BACKGROUND

Circuit boards include dielectric layers and circuit layers formed on the dielectric layers. However, such a circuit board may be very thick. Furthermore, a contact area between the circuit layer and the dielectric layer is limited, which reduces adhesion between the circuit layer and the dielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by way of example only, with reference to the attached figures.

FIG. 1 is a cross-sectional view of an embodiment of an inner circuit substrate.

FIG. 2 is a cross-sectional view showing a single-sided copper-clad laminate covering the inner circuit substrate of FIG. 1.

FIG. 3 is a cross-sectional view showing the copper-clad laminate of FIG. 2 etched to form a groove.

FIG. 4 is a cross-sectional view showing an outer dielectric layer etched from the groove of FIG. 3 to obtain a circuit groove and a blind hole.

FIG. 5 is a cross-sectional view showing a copper-plated layer formed in the circuit groove and the blind hole and on a copper layer of FIG. 4.

FIG. 6 is a cross-sectional view showing the copper-plated layer and the copper layer of FIG. 5 etched to form an outer circuit layer.

FIG. 7 is a cross-sectional view of a product after processes of FIGS. 2 to 6 are repeated.

FIG. 8 is a cross-sectional view showing a solder mask with an opening formed on the outer circuit substrate of FIG. 7, thereby obtaining a circuit board.

FIG. 9 is a flowchart of an embodiment of a method for manufacturing a circuit board according to the present disclosure.

FIG. 10 is a sub-flowchart of blocks in the method of FIG. 9.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.

The term “comprising,” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like.

Some embodiments of the present disclosure will be described in detail with reference to the drawings. If there is no conflict, the embodiments and features can be combined with each other.

A method for the manufacturing of a circuit board 100 is provided in accordance with an embodiment. The method is provided by way of example, as there are a variety of ways to carry out the method. Referring to FIG. 9, the method can begin at block 1.

In block 1, referring to FIG. 1, an inner circuit substrate 10 is provided.

The inner circuit substrate 10 can be a flexible circuit board, a rigid circuit board, or a rigid-flexible circuit board.

The inner circuit substrate 10 includes an inner dielectric layer 12 and a number of first conductive pillars 14. Each first conductive pillar 14 penetrates opposite surfaces of the inner dielectric layer 12.

The inner dielectric layer 12 can be made of at least one of polyimide (PI), liquid crystal polymer (LCP), modified polyimide (MPI), polypropylene (PP), and polytetrafluoroethylene (PTFE).

The inner circuit substrate 10 can further include at least one inner circuit layer (not shown) electrically connected to the first conductive pillar 14. That is, the inner circuit substrate 10 can be a single-layer circuit substrate, a double-layer circuit substrate, or a multi-layer circuit substrate.

In block 2, referring to FIG. 2, a single-sided copper-clad laminate 20 is formed on the inner circuit substrate 10. The single-sided copper-clad laminate 20 includes an outer dielectric layer 22 and a copper layer 24 stacked in sequence. The copper layer 24 is disposed on a surface of the outer dielectric layer 22 facing away from the inner circuit substrate 10.

The single-sided copper-clad laminate 20 can be formed on one surface of the inner circuit substrate 10. The single-sided copper-clad laminate 20 can also be formed on each surface of the inner layer circuit substrate 10.

In block 3, referring to FIGS. 3 and 4, the single-sided copper-clad laminate 20 is etched to form a circuit groove 244. The circuit groove 244 penetrates the copper layer 24 and a portion of the outer dielectric layer 22.

The outer dielectric layer 22 can be made of at least one of polyimide, liquid crystal polymer, modified polyimide, polypropylene, and polytetrafluoroethylene.

In at least one embodiment, the single-sided copper-clad laminate 20 is etched to form the circuit groove 244. During the etching process, the copper layer 24 is first etched, and then the portion of the outer dielectric layer 22 adjacent to the copper layer 24 is etched to form the circuit groove 244. That is, the circuit groove 244 penetrates the copper layer 24 but does not penetrate the outer dielectric layer 22.

In some embodiments, a blind hole 245 is also formed together with the circuit groove 244, and first conductive pillar 14 is partially exposed from the blind hole 245.

In some embodiments, referring to FIG. 10, the formation of the circuit groove 244 and the blind hole 245 may be carried out as follows.

In block 301, referring to FIG. 3, the copper layer 24 is etched to form a slot 242, and the outer dielectric layer 22 is exposed from the slot 242.

In block 302, referring to FIG. 4, the outer dielectric layer 22 exposed from the slot 242 is etched by a plasma etching process to form the circuit groove 244 and the blind hole 245. A depth of etching of the circuit groove 244 and the blind hole 245 can be controlled by the etching time or the power applied in the plasma etching process.

In block 4, referring to FIG. 5, a copper-plated layer 30 is formed in the circuit groove 244 and on a surface of the copper layer 24.

The copper-plated layer 30 may be formed by electroplating.

In some embodiments, the copper-plated layer 30 further infills the blind hole 245 and is connected to the first conductive pillar 14.

In block 5, referring to FIG. 6, the copper-plated layer 30 and the copper layer 24 are etched to form an outer circuit layer 42, thereby obtaining the circuit board 100.

A portion of the outer circuit layer 42 facing the inner circuit substrate 10 is embedded in the outer dielectric layer 22. A portion of the outer circuit layer 42 away from the inner circuit substrate 10 protrudes from the outer dielectric layer 22. A portion of the outer circuit layer 42 is embedded in the outer dielectric layer 22, which increases the contact area between the outer circuit layer 42 and the outer dielectric layer 22, thereby improving adhesion therebetween. In addition, the outer circuit substrate 40 is reduced in thickness, thereby reducing the overall thickness of the circuit board 100.

In some embodiments, the copper-plated layer 30 in the blind hole 245 forms a second conductive pillar 44. The second conductive pillar 44 is connected to the first conductive pillar 14 and the outer circuit layer 42.

The outer dielectric layer 22, the outer circuit layer 42 and the second conductive pillar 44 cooperatively form an outer circuit substrate 40. The outer circuit substrate 40 is electrically connected to the inner circuit substrate 10.

In some embodiments, referring to FIG. 7, other circuit layers can be built up and formed. The building-up process can be carried out by repeating the processes of blocks 2 to 5.

In some embodiments, the method for forming the circuit board 100 may further include the following blocks.

In block 6, referring to FIG. 8, a solder mask 50 is applied to cover a surface of the outer circuit substrate 40 facing away from the inner circuit substrate 10, and an opening 52 is formed on the solder mask 50, so that a portion of the outer circuit layer 42 is exposed from the opening 52. Then, the circuit board 100 is obtained.

The solder mask 50 covers a surface of the outer dielectric layer 22 away from the inner circuit substrate 10, and the solder mask 50 further covers the outer circuit layer 42. The portion of the outer circuit layer 42 away from the inner circuit substrate 10 is embedded in the solder mask 50. The opening 52 penetrates the solder mask 50. The portion of the outer circuit layer 42 exposed from the opening 52 is a solder pad 422. The soldering pad 422 can allow connections to a conductor (not shown), so as to be electrically connected to other circuit boards (not shown) through the conductor.

In some embodiments, when the outer circuit layer 42 is formed, the copper-plated layer 30 and/or the copper layer 24 are also etched, so that a surface of the portion of the outer circuit layer 42 exposed from the opening 52 has several planes. For example, the surface of the portion of the outer circuit layer 42 can be step-shaped or have grooves at various depths. The portion of the outer circuit layer 42 exposed from the opening 52 forms the solder pad 422, to increase a contact area between the solder pad 422 and the conductor and improve adhesion between the conductor and the solder pad 422. In some embodiments, the opening 52 is combined with the outer circuit substrate 40 to form a groove 55. When the circuit board 100 is electrically connected to another circuit board, liquid solder can be injected into the groove 55. During a soldering process, the groove 55 confines the liquid solder and thus prevents undesired electrical connections between the two circuit boards.

Referring to FIGS. 6 to 8, a circuit board 100 includes an inner layer circuit substrate 10 and an outer circuit substrate 40, and the outer circuit substrate 40 is disposed on the inner layer circuit substrate 10.

The inner circuit substrate 10 can include an inner dielectric layer 12, an inner circuit layer, and a number of first conductive pillars 14. Each first conductive pillar 14 penetrates the inner dielectric layer 12, and the inner circuit layer is disposed on the surface of the inner dielectric layer 12 electrically connected to the first conductive pillar 14.

In some embodiments, the inner circuit substrate 10 can be a single-layer circuit substrate, a double-layer circuit substrate, or a multi-layer circuit substrate. When the inner circuit substrate 10 is a multi-layer circuit substrate, the inner circuit substrate 10 further includes other circuit layers embedded in the inner dielectric layer 12.

The outer circuit substrate 40 can include an outer dielectric layer 22, an outer circuit layer 42, and a second conductive pillar 44, the outer circuit substrate 40 being electrically connected to the inner circuit substrate 10. A portion of the outer circuit layer 42 facing the inner circuit substrate 10 is embedded in the outer dielectric layer 22. A portion of the outer circuit layer 42 away from the inner circuit substrate 10 protrudes from the outer dielectric layer 22. A portion of the outer circuit layer 42 is embedded in the outer dielectric layer 22, which increases the contact area and thus improving adhesion between the outer circuit layer 42 and the outer dielectric layer 22. In addition, part of the outer circuit layer 42 is embedded in the outer dielectric layer 22, improving adhesion between the outer circuit layer 42 and the outer dielectric layer 22. A thickness of the outer circuit substrate 40 is reduced, reducing the overall thickness of the circuit board 100.

The second conductive pillar 44 penetrates the outer dielectric layer 22 and is connected to the first conductive pillar 14 to electrically connect the outer circuit substrate 40 and the inner circuit substrate 10. The second conductive pillar 44 is further electrically connected to the outer circuit layer 42.

Referring to FIG. 8, in some embodiments, the circuit board 100 further includes a solder mask 50. The solder mask 50 is disposed on the outer circuit substrate 40 away from the inner circuit substrate 10. The solder mask 50 covers the outer dielectric layer 22 and the outer circuit layer 42. A portion of the outer circuit layer 42 away from the inner circuit substrate 10 is embedded in the solder mask 50.

The solder mask 50 includes an opening 52. The outer circuit layer 42 includes solder pads 422. The solder pads 422 are exposed from the opening 52. The solder pad 422 allows electrical connections to other circuit boards. In some embodiments, when the circuit board 100 is electrically connected to other circuit boards, liquid solder can be injected into the opening 52 first. During the soldering process, a periphery of the opening 52 prevents the liquid solder from escaping and causing undesired connections between the two circuit boards.

A surface of the solder pad 422 exposed from the opening 52 can have several planes, including but not limited to being step-shaped or having grooves at various depths, which increases a contact area between the solder pad 422 and the conductor for electrical connections, and improves adhesion between the conductor and the solder pad 422. In the embodiment, the surface of the solder pad 422 exposed from the opening 52 is step-shaped.

In some embodiments, the inner circuit substrate 10 and the outer circuit substrate 40 can also be provided with other circuit substrates electrically connected to each other as required.

It is to be understood, even though information and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present embodiments, the disclosure is illustrative only; changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.

Claims

1. A circuit board, comprising:

an inner circuit substrate; and

an outer circuit substrate electrically connected to the inner circuit substrate, and the outer circuit substrate comprising: an outer dielectric layer; and an outer circuit layer facing the inner circuit substrate embedded in the outer dielectric layer, a portion of the outer circuit layer facing away from the inner circuit substrate protruding from the outer dielectric layer.

2. The circuit board of claim 1, further comprising a solder mask, wherein the solder mask is disposed on the outer circuit substrate away from the inner circuit substrate; the solder mask comprises an opening, the outer circuit layer comprises a solder pad exposed from the opening.

3. The circuit board of claim 2, wherein a surface of the solder pad exposed from the opening is not on a same plane.

4. The circuit board of claim 3, wherein the surface of the solder pad is step-shaped or have grooves at various depths.

5. The circuit board of claim 1, wherein the inner circuit substrate comprises an inner dielectric layer and a first conductive pillar, and the first conductive pillar penetrates the inner dielectric layer; the outer circuit substrate further comprises a second conductive pillar electrically connected to the outer circuit layer; the second conductive pillar is connected to the first conductive pillar.