# Patent

## Title
Manufacturing method of metal structure of flexible multi-layer substrate

## Abstract

A metal structure manufacture method for a multi-layer substrate comprises coating a photoresist layer on a first dielectric layer; proceeding a photolithography process to the photoresist layer to define a specific position for a first metal layer; removing the photoresist layer at the specific position; and forming the first metal layer at the specific position, wherein a base area of the first metal layer is larger than a top area thereof, and wherein the embedded base and the main body are formed in a same process and are monolithic formed. Said manufacturing method can be employed to manufacture a pad or a metal line of the flexible multi-layer substrate, and the manufactured metal structure cannot easily be delaminated or separated from the contacted dielectric layer.

## Background
CROSS REFERENCE TO RELATED APPLICATION
This application is a divisional application of U.S. patent application Ser. No. 12/830,321, filed Jul. 4, 2010, which issued as U.S. Pat. No. 8,373,070 on Feb. 12, 2013.


BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a metal structure of a multi-layer substrate and the manufacturing method thereof, and more particularly to a metal structure of a flexible multi-layer substrate and the manufacturing method thereof.
2. Description of Prior Art
A multi-layer substrate can be utilized for manufacturing a package substrate, a printed circuit board, a flexible package substrate or a flexible printed circuit for realizing miniaturization of all electronic products is an inevitable trend in this modern world. Particularly, a flexible multi-layer substrate can be utilized for manufacturing a flexible package structure to apply in kinds of products to meet miniaturization demands more efficiently. As the thickness of the flexible multi-layer substrate gets thinner, the routing density of the multi-layer substrate becomes higher. Accordingly, the requirements of the metal structure size of the flexible multi-layer substrate become smaller and more meticulous. Traditional flexible multi-layer substrates according to prior arts can only be manufactured with two or three layers. The thickness of each layer is about 50 ̃60 μm and the thickness of the metal layer is about 30 μm.
Please refer to FIG. 1, which depicts a diagram showing a bubble generated at a side of a metal structure of a multi-layer substrate according to prior arts. The multi-layer substrate according to prior arts can be flexible comprises a metal layer 100 and a dielectric layer 102 covering the metal layer 100. Generally, an etching or a build-up process is utilized to form the metal layer 100 of the flexible multi-layer substrate according to prior arts. When the metal layer 100 is employed as a metal line or a pad, the sectional appearance of the metal layer 100 shows a rectangular figure. A common problem which often occurs is that a bubble generated at the side the metal layer 100. As shown in FIG. 1, a phenomenon of bad adhesion or delamination in layers exists due to the bubble. As a result, a lower manufacturing yield of the flexible multi-layer substrate happens. Particularly, as the metal layer 100 becomes thinner as long as the thickness of the flexible multi-layer substrate gets thinner, the influence of the aforesaid phenomenon of bad adhesion or delamination in layers unavoidably turns to more obvious.
Please refer to FIG. 2, which depicts a diagram showing a metal structure of a multi-layer substrate stripped off with a ball mount due to an external force according to prior arts. As aforementioned, as the metal layer 100 is employed as a metal line or a pad, the sectional appearance of the metal layer shows a rectangular figure. As the metal layer 100 is utilized as a metal layer for package of an IC (Integrated Circuit), the dielectric layer 102 covering the metal layer 100 above is going to be opened a hole and a metal material 106 is formed in for connecting with the solder ball mount 108. As previously mentioned, the flexible multi-layer substrate is utilized as a flexible package substrate or a flexible printed circuit. Generally, it is applied for a constantly bent device. Namely, when the flexible multi-layer substrate is bent, the metal layer 100 may be stripped off with the solder ball mount 108 due to a bending external force as shown in FIG. 2 because the bonding strength between the metal layer 100 and the solder ball mount 108 is too strong. Similarly, as the metal layer 100 becomes thinner as long as the thickness of the flexible multi-layer substrate gets thinner, the aforesaid stripped-off phenomenon unavoidably becomes more possible and happens more easily.
In conclusion, there is a need to develop a metal structure of a flexible multi-layer substrate and manufacturing method which is still valid for resolving the aforesaid problems when the thickness of the flexible multi-layer substrate is manufactured thinner and accordingly the metal layer also has to be thinner, wherein the metal structure cannot easily be delaminated or separated from the contacted, adjacent dielectric layers and a higher reliability of the metal structure can be achieved.
SUMMARY OF THE INVENTION
An objective of the present invention is to provide a metal structure of a multi-layer substrate and manufacturing method thereof. The metal structure of the present invention can be employed as a pad or a metal line in a thin, flexible multi-layer substrate in which delamination and separation from the contacted dielectric layers cannot easily happen.
Another objective of the present invention is to provide a metal structure of a multi-layer substrate and manufacturing method thereof. Especially, for a flexible substrate package to a general IC (a hard, firm IC), the metal structure of the present invention can allow the thin, flexible multi-layer substrate to be utilized for a constantly bent device and achieving a higher reliability.
The metal structure of a multi-layer substrate of the present invention comprises a first metal layer and a dielectric layer. The first metal layer has an embedded base and a main body positioned on the embedded base. The base area of the embedded base is larger than the base area of the main body. The dielectric layer covers the embedded base and the main body and has a hole at a specific position of the first metal layer. Therefore, the first metal layer can connect with a second metal layer above the dielectric layer. The main body and the embedded base can be monolithic formed. The main body and the embedded base can be formed by the same material or different material. Alternatively, the main body and the embedded base can be formed by different processes. A first process is to form embedded base and then, a second process is to form the main body on the embedded base thereafter.
The present invention also provides a manufacturing method of a metal structure of a flexible multi-layer substrate. The manufacturing method comprises steps below:

    
    
        coating at least one photoresist layer on a first dielectric layer;
        proceeding a photolithography process to the photoresist layer to define a specific position for a first metal layer;
        removing the photoresist layer at the specific position; and
        forming the first metal layer at the specific position, wherein a base area of the first metal layer is larger than a top area thereof to form the metal structure having an embedded base and a main body positioned thereon.
    
    


The present invention further provides another manufacturing method of the metal structure of the multi-layer substrate. The manufacturing method comprises steps below:

    
    
        coating a first photoresist layer on a first dielectric layer;
        proceeding a photolithography process to the first photoresist layer to define a specific position for a first metal layer;
        removing the first photoresist layer at the first specific position;
        forming an embedded base of the first metal layer;
        coating a second photoresist layer after removing first photoresist layer on the first dielectric layer;
        proceeding a photolithography process to the second photoresist layer to define the second specific position for the first metal layer;
        removing the second photoresist layer at the second specific position; and
        forming a main body of the first metal layer on the embedded base and a base area of the embedded base is larger than a base area of the main body.
    
    


Specifically, the metal structure of the multi-layer substrate according to the present invention can be flexible and not only applied in the field of package substrates. Meanwhile, the present invention also can be applied in the technical field of manufacturing print circuit boards and flexible package substrates. Significantly, the manufacturing method of the present invention attends to provide a metal structure comprising an embedded base and a main body. When the second dielectric layer is formed to cover thereon, such a metal structure of the thin and flexible multi-layer substrate cannot easily be delaminated or separated from the contacted, adjacent dielectric layers. The metal structure of the present invention employed as a pad or a metal line of the thin and flexible multi-layer substrate can achieve a higher reliability.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts a diagram showing a bubble generated at a side of a metal structure of a multi-layer substrate according to prior arts.
FIG. 2 depicts a diagram showing a metal structure of a multi-layer substrate stripped off with a ball mount due to an external force according to prior arts.
FIG. 3 depicts a diagram of a first embodiment of a metal structure of a multi-layer substrate according to the present invention.
FIG. 4 depicts a diagram of a second embodiment of a metal structure of a multi-layer substrate according to the present invention.
FIG. 5 depicts a diagram for explaining a manufacturing method for the first embodiment of the metal structure of the multi-layer substrate according to the present invention.
FIG. 6 depicts a diagram for explaining a manufacturing method for the second embodiment of the metal structure of the multi-layer substrate according to the present invention.



DETAILED DESCRIPTION OF THE INVENTION
Please refer to FIG. 3, which depicts a diagram of a first embodiment of a metal structure of a multi-layer substrate according to the present invention. In the first embodiment, the metal structure of the multi-layer substrate is employed as a pad and the multi-layer substrate can be flexible and utilized to package an IC (Integrated Circuit, not shown). The metal structure of the flexible multi-layer substrate comprises a first metal layer 300 and a second dielectric layer 308. The first metal layer 300 comprises a main body 302 and an embedded base 304. The flexible multi-layer substrate further comprises a first dielectric layer 200 under the main body 302 and the embedded base 304. As shown in FIG. 3, the main body 302 is on the embedded base 304 and a base area of the embedded base 304 is larger than a base area of the main body 302. The second dielectric layer 308 covers the embedded base 304 and the main body 302. After the second dielectric layer 308 is covered, the embedded base 304 is clamped by the first dielectric layer 200 and the second dielectric layer 308.
A hole of the second dielectric layer 308 is formed on the specific position of the main body 302 to allow the main body 302 connect with the solder ball mount 310 for package of an IC (not shown in FIG. 3). If a bubble generates at one side of the first metal layer 300, the embedded base 304 can reduce the affect of the phenomenon of bad adhesion or delamination in layers caused by the bubble. Moreover, although the adhesion between the first metal layer 300 and the first dielectric layer 200 has certain strength. The issue that the first metal layer 300 is stripped off with the solder ball mount 310 from the multi-layer substrate due to a bending external force can be efficiently prevented because the present invention utilizes the clamped strength of the embedded base 304 by the first dielectric layer 200 and the second dielectric layer 308. Especially, as the multi-layer substrate of the present invention can be flexible and manufactured up to six, seven layers, or even 10 layers, and the thickness of each layer can be so thin about 10 μm. The thickness of the first metal layer 300 is even merely about 5 μm which is far thinner than the possible thickness made by prior arts. It's totally necessary to avoid the foregoing phenomenon of the bubble generated at the side of the metal structure, bad adhesion or delamination in layers. In this embodiment, though, the metal structure is employed as a pad of the flexible multi-layer substrate. Similarly, as the metal structure is employed as a metal line in the flexible multi-layer substrate and connects with another metal line above through a via, the aforesaid phenomenon of bad adhesion or delamination in layers also can be prevented. Accordingly, the metal structure of the flexible multi-layer substrate according to the present invention can solve the problems of prior arts and efficiently promote the reliability of the flexible multi-layer substrate.
Please refer to FIG. 4, which depicts a diagram of a second embodiment of a metal structure of a multi-layer substrate according to the present invention. In the second embodiment, the metal structure can be flexible an also employed as a pad. The flexible multi-layer substrate is utilized for package of an IC (Integrated Circuit, not shown). The metal structure of the flexible multi-layer substrate comprises a first metal layer 400 and a second dielectric layer 308. The first metal layer 400 comprises a main body 402 and an embedded base 404. The flexible multi-layer substrate further comprises a first dielectric layer 200 under the main body 402 and the embedded base 404. As shown in FIG. 4, the main body 402 is on the embedded base 404 and a base area of the embedded base 404 is larger than a base area of the main body 402. The second dielectric layer 308 covers the embedded base 404 and the main body 402. After the second dielectric layer 308 is covered, the embedded base 404 is clamped by the first dielectric layer 200 and the second dielectric layer 308. A hole of the second dielectric layer 308 is formed on the main body 402 for connecting with the solder ball mount 310 for package of an IC (not shown in FIG. 4).
As shown in FIG. 4, the difference of the second embodiment from the first embodiment is that the main body 402 and the embedded base 404 can be formed by the same metal material or different metal materials. Moreover, the main body 402 and the embedded base 404 can be monolithic formed like the first embodiment. In the second embodiment, the embedded base 404 is formed first and then, the main body 402 can be formed on the embedded base 404 by two processes. Similarly, the metal structure in the second embodiment also can be employed as a metal line in the flexible multi-layer substrate and connects with another metal line above.
The second embodiment of the present invention also can reduce the affect of the phenomenon of delamination or separation in layers caused by the bubble generated at one side of the first metal layer 400 or the phenomenon of bad adhesion, delaminated or separated in layers from the contacted, adjacent dielectric layers. Therefore, the metal structure of the flexible multi-layer substrate according to the present invention is capable of resolving the problems of prior arts. The metal material for forming the metal layers in the first, second embodiment can be copper. The material for forming dielectric layers can be polyimide.
Please refer to FIG. 5, which depicts a diagram for explaining a manufacturing method for the first embodiment of the metal structure of the multi-layer substrate according to the present invention. Please also refer to FIG. 3 at the same time. The manufacturing method of the metal structure of the flexible multi-layer substrate according to the present invention comprises the steps below.
A negative photoresist layer 306 is coated on a first dielectric layer 200. A photolithography process is proceeded to the negative photoresist layer 306 to define a specific position of the first metal layer 300. Then, the negative photoresist layer 306 at the specific position is removed (such as a developing process). Because the top of the negative photoresist layer 306 receives more light than the bottom, the fringe of the negative photoresist layer 306 adjacent to the specific position is formed a top-protruding appearance as shown in FIG. 5. After that, the first metal layer 300 having a main body 302 and an embedded base 304 is formed by physical vapor deposition, like vacuum evaporation, at the specific position as shown in FIG. 5. Moreover, due to the top-protruding appearance of the negative photoresist layer 306, the embedded base 304 of the first metal layer 300 can extend out to reach the bottom of the negative photoresist layer 306 when the first metal layer 300 is formed. As shown in FIG. 5, a base area is larger than a top area of the first metal layer 300, i.e. the base area (or the occupied area) of the embedded base 304 is larger than a base area (or the occupied area) of the main body 302.
As shown in FIG. 3, after the negative photoresist layer 306 is removed, the second dielectric layer 308 covers the main body 302 and the embedded base 304 of the first metal layer 300. The embedded base 302 is now clamped by the first dielectric layer 200 and the second dielectric layer 308. After that, a via of the second dielectric layer 308 is opened at the specific position of the first metal layer 300. The first metal layer 300 can be connected with a second metal layer (such as a solder ball mount 310 or another metal line). If the first metal layer 300 is employed as a pad, and will connect with the solder ball mount 310 for package. If the first metal layer 300 is employed as metal line, and will connect with another metal line to realize an interconnection of the flexible multi-layer substrate.
Please refer to FIG. 6, which depicts a diagram for explaining a manufacturing method for the second embodiment of the metal structure of the multi-layer substrate according to the present invention. The second embodiment of the metal structure according to the present invention can have two manufacturing methods. In one manufacturing method, at least two photoresist layers with different photolithography rates, such as a bottom photoresist layer 406 and a top photoresist layer 408 are formed are coated. The bottom photoresist layer 406 and the top photoresist layer 408 can be both positive photoresist or both negative photoresist. Then, a photolithography process is proceeded to the bottom photoresist layer 406 and the top photoresist layer 408 at the same time but due to the different photolithography rates of the bottom photoresist layer 406 and the top photoresist layer 408, respective holes s with different sizes are formed as shown in FIG. 6. The hole of the bottom photoresist layer 406 is larger than the hole of the top photoresist layer 408. Accordingly, as the first metal layer 400 is manufactured by physical vapor deposition, like vacuum evaporation, a metal structure having a main body 402 and an embedded base 404 is formed. Same metal material can be utilized to form the main body 402 and the embedded base 404 in the manufacturing method of the present invention.
Please also refer to FIG. 4 with FIG. 6, as the second embodiment of the metal structure is manufactured with another manufacturing method, the manufacturing method of the metal structure of the multi-layer substrate according to the present invention comprises the steps below.
A first photoresist layer 406 is coated on a first dielectric layer 200. A photolithography process is proceeded to the first photoresist layer 406 to define a first specific position for the first metal layer 400. Then, the first photoresist layer 406 at the first specific position is removed (such as a developing process). The embedded base 404 of the first metal layer 400 is formed by physical vapor deposition, like vacuum evaporation, at the first specific position. A second photoresist layer 408 is coated after the rest first photoresist layer 406 is removed. A photolithography process is proceeded to the second photoresist layer 408 at a second specific position of the first metal layer 400. Then, the second photoresist layer 408 is at the second specific position is removed (such as a developing process). Meanwhile the hole of the second photoresist layer 408 is controlled to be smaller than the hole of the first photoresist layer 406. After that, the main body 402 is formed on the embedded base 404. A metal structure which a base area of the embedded base 404 is larger than a base area of the main body 402 is completed. Alternatively, forming the embedded base 404 and the main body 402 by etching also can be illustrated. In this case, the step of forming the embedded base 404 and the main body 402 of the first metal layer is proceeded in advance. Then, coating the first photoresist layer 406 or the second photoresist layer 408 at the first specific position and the second specific position is proceeded for covering the first metal layer. With one or two etching steps, the first metal layer except the position of the first photoresist layer 406 and the position of the second photoresist layer 408 can be removed and the same embedded base 404 and the main body 402 shown in FIG. 6 can be obtained.
As shown in FIG. 4, the second dielectric layer 408 covers the main body 402 and the embedded base 404 of the first metal layer 400. The embedded base 402 is now clamped by the first dielectric layer 200 and the second dielectric layer 408. After that, a via of the second dielectric layer 408 is opened at the specific position of the first metal layer 400. The first metal layer 400 can be connected with a second metal layer (such as a solder ball mount 310 or another metal line). If the first metal layer 400 is employed as a pad, and will connect with the solder ball mount 310 for package. If the first metal layer 400 is employed as a metal line, and will connect with another metal line to realize an interconnection of the flexible multi-layer substrate. According to the present invention, the embedded base 404 is formed first and then, the main body 402 can be formed on the embedded base 404 by two independent processes. The main body 402 and the embedded base 404 can be formed by the same metal material. Alternatively, the main body 402 and the embedded base 404 also can be formed by two different metal materials.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative rather than limiting of the present invention. It is intended that they cover various modifications and similar arrangements be included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.

## Claims

1. A manufacturing method of a metal structure of a multi-layer substrate, comprising:
coating at least one photoresist layer on a first dielectric layer;
proceeding a photolithography process to the at least one photoresist layer to define a specific position for a first metal layer;
removing the at least one photoresist layer at the specific position;
forming the first metal layer at the specific position, wherein a base area of the first metal layer is larger than a top area thereof to form the metal structure having an embedded base and a main body positioned thereon, and wherein the embedded base and the main body are formed in a same process and are monolithic formed; and
forming a second dielectric layer to cover the main body and the embedded base of the first metal layer after the step of forming the first metal layer, wherein the step of forming the second dielectric layer comprises clamping the embedded base by the first dielectric layer and the second dielectric layer.

2. The manufacturing method of claim 1, further comprising a step of opening a hole on the specific position of the first metal layer for connecting with a second metal layer above the second dielectric layer after the step of forming the second dielectric layer.

3. The manufacturing method of claim 2, wherein a material of the second metal layer is copper.

4. The manufacturing method of claim 2, wherein a material of the second metal layer is solder.

5. The manufacturing method of claim 4, wherein the second metal layer is a solder ball mount for package.

6. The manufacturing method of claim 1, wherein the multi-layer substrate is flexible.

7. The manufacturing method of claim 1, wherein a material of the first dielectric layer and the second dielectric layer is polyimide.

8. The manufacturing method of claim 1, wherein a material of the first metal layer is copper.

9. The manufacturing method of claim 1, wherein the step of coating the at least one photoresist layer comprises coating a negative photoresist layer.

10. The manufacturing method of claim 1, wherein the at least one photoresist layer comprises top and bottom photoresist layers with different development rates, and the step of coating the at least one photoresist layer on the first dielectric layer comprises coating the top and bottom photoresist layers with different development rates sequentially on the first dielectric layer, and wherein the development rate of the top photoresist layer is smaller than that of the bottom photoresist layer.