Method for manufacturing a heat dissipation structure of a printed circuit board

A method for manufacturing a heat dissipation structure of a printed circuit board includes: forming a barrier layer on the dimple in the first copper plating layer; forming a nickel plating layer; removing the nickel plating layer and the barrier layer on the dimple; forming a second copper plating layer to make the total height of the first copper plating layer and the second copper plating layer in the second opening higher than that of the first copper plating layer in the first opening; filling the dimple in the second copper plating layer with an etching-resistant material; removing the second copper plating layer; removing the nickel plating layer and the etching-resistant material to make the second copper plating layer in the second opening being at the same height as the first copper plating layer in the first opening; and forming the heat dissipation structure by photolithography.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for manufacturing a heat dissipation structure of a printed circuit board, and more particularly to a method for manufacturing a heat dissipation structure of a printed circuit board for improving the filling capability of plating copper, and improving the uneven surface caused by performing the copper plating process for many times using a nickel plating process.

2. The Prior Arts

FIGS. 1A to 1Fare cross-sectional views illustrating the steps of a conventional method for manufacturing a heat dissipation structure of a printed circuit board. Referring toFIG. 1A, a printed circuit board1is provided. The printed circuit board1includes a first substrate10, two second substrates15respectively disposed on the upper and lower surfaces of the first substrate10, two inner copper layers21each disposed between the first substrate10and the second substrate15, and two outer copper layers23each disposed on one outer surface of the second substrates15. Referring toFIG. 1B, a plurality of openings are formed in the upper layers of the printed circuit board1to expose a portion of the inner copper layers21. The openings include at least one first opening31and at least one second opening33. The first opening31is smaller than the second opening33, and the size of the second opening33is larger than or equal to 150×100 μm2. Referring toFIG. 1C, at least one first copper plating layer25is formed on the printed circuit board1. The first opening31is fully filled up with the first copper plating layer25, but the second opening33is not fully filled up with the first copper plating layer25such that the first copper plating layer25filling in the second opening33has a first dimple40on its top.

Referring toFIG. 1D, a copper plating layer60is formed by performing a copper plating process at least once. The copper plating layer60is thick so that the dimple40can be fully filled up with the copper plating layer60. A chemical mechanical planarization process is then performed to planarize the surface of the copper plating layer60.

Referring toFIGS. 1E and 1F, a patterned dry film50is formed on the surface of the copper plating layer60. After an etching process and a removal of the dry film process, a heat dissipation structure70including the first copper bumps71, the second copper bumps73, and the copper pads75is formed. The heat dissipation structure70and the inner copper layers21are electrically connected to each other.

In the prior art, because the size of the opening is larger than or equal to the size of 150×100 μm2, the opening is not easily to be fully filled up by performing the copper plating process only once, and thereby the copper plating process must be performed for many times in order to fill up the opening. However, there exists an uneven surface problem caused by the interface between the two adjacent copper plating layers when the copper plating process is performed for many times, which results in the variation of the resistance values. The resistance value will be increased for each copper plating process. Therefore, a polishing process is needed in order to meet the specification of the resistance value, but the polishing process is not easily controlled so that the resistance value cannot be standarized.

SUMMARY OF THE INVENTION

In the present invention, a method for manufacturing a heat dissipation structure of a printed circuit board is provided, which is characterized in that: forming a barrier layer on the first copper plating layer; removing the barrier layer except the barrier layer formed on a surface of the first dimple in the first copper plating layer; forming a nickel plating layer on the first copper plating layer and on the barrier layer formed on the surface of the first dimple; removing the nickel plating layer formed on the barrier layer on the surface of the first dimple, followed by removing the barrier layer formed on the surface of the first dimple; forming a second copper plating layer on the nickel plating layer and on the surface of the first dimple to make a total height of the first copper plating layer and the second copper plating layer in the second opening higher than a height of the first copper plating layer in the first opening, the second copper plating layer in the second opening having a second dimple; filling the second dimple with an etching-resistant material; removing the second copper plating layer uncovered by the etching-resistant material; removing the nickel plating layer and the etching-resistant material to make a top surface of the second copper plating layer filling in the second opening being at the same height as a top surface of the first copper plating layer filling in the first opening; forming a patterned dry film on the top surface of the first copper plating layer and on the top surface of the second copper plating layer; and etching the top layer of the printed circuit board uncovered by the photoresist and removing the dry film to form a heat dissipation structure layer comprising a plurality of first copper bumps, a plurality of second copper bumps, and a plurality of copper pads.

In the present invention, when the substrate has the openings with different sizes and the copper cannot be plated in the openings once, the nickel plating layer is formed as a barrier layer to avoid the uneven surface caused by performing the copper plating process for many times. Furthermore, by sandwiching the nickel plating layer between the copper plating layers, the resistance value of the plated copper layer can be easily controlled, and thereby the problems in the prior art can be solved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constituted a part of this specification. The drawings illustrate an embodiment of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 2is a flowchart showing the steps of the method for manufacturing a heat dissipation structure of a printed circuit board according to the present invention.FIGS. 3A to 3Lare cross-sectional views illustrating the steps of the method for manufacturing a heat dissipation structure of a printed circuit board according to one embodiment of the present invention. Referring toFIG. 2, the method for manufacturing the heat dissipation structure of the printed circuit board of the present invention (S1) comprises: a step of preparing a printed circuit board (S11), a step of performing a drilling process (S13), a step of performing a first copper plating process (S15), a step of forming a barrier layer (S17), a step of removing the barrier layer (S19), a step of performing a nickel plating process and a chemical removal process (S21), a step of performing a second copper plating process (S23), a step of forming an etching-resistant layer (S25), a step of performing an etching process (S27), a step of performing an removing process and a thinning process (S29), a step of forming a dry film (S31), and a step of forming a heat dissipation structure (S33).

Referring toFIG. 3A, in the step of preparing a printed circuit board (S11), a printed circuit board1is provided. The printed circuit board1includes a first substrate10, two second substrates15respectively disposed on the upper and lower surfaces of the first substrate10, two inner copper layers21each disposed between the first substrate10and the second substrate15, and two outer copper layers23each disposed on one outer surface of the second substrates15. The printed circuit board1of the present invention is a three layer printed circuit board, and however, this is just an example and should not be seen as to limit the scope of the present invention. Referring toFIG. 3B, in the step of performing a drilling process (S13), a plurality of openings are formed in the upper layers of the printed circuit board1to expose a portion of the inner copper layers21. The openings include at least one first opening31and at least one second opening33. The first opening31is smaller than the second opening33, and the size of the second opening33is larger than or equal to 150×100 μm2. Referring toFIG. 3C, in the step of performing a first copper plating process (S15), at least one first copper plating layer25is formed on the printed circuit board1. The first opening31is fully filled up with the first copper plating layer25, but the second opening33is not fully filled up with the first copper plating layer25such that the first copper plating layer25filling in the second opening33has a first dimple40on its top.

Referring toFIGS. 3D and 3E, in the step of forming a barrier layer (S17), a barrier layer52is formed on the first copper plating layer25. In the step of removing the barrier layer (S19), the barrier layer52is removed by a chemical mechanical planarization process, but the barrier layer52formed on the surface of the first dimple40is remained. Referring toFIG. 3F, in the step of performing a nickel plating process and a chemical removal process (S21), a nickel plating layer27is formed on the first copper plating layer25and the barrier layer52, and then the remaining barrier layer52formed on the surface of the first dimple40and the nickel plating layer27formed on the remaining barrier layer52on the surface of the first dimple40are removed by a chemical removal process so that there is no nickel plating layer27above the first dimple40.

Referring toFIG. 3G, in the step of performing a second copper plating process (S23), a second copper plating layer29is formed on the nickel plating layer27and on the first copper plating layer25formed on the surface of the first dimple40to make the total height of the first copper plating layer25and the second copper plating layer29in the second opening33higher than the height of the first copper plating layer25in the first opening31. The second copper plating layer29in the second opening33has a second dimple42. Referring toFIG. 3H, in the step of forming an etching-resistant layer (S25), the second dimple42is filled with an etching-resistant material54. In the step of performing an etching process (S27), the second copper plating layer29is removed except the portion of the second copper plating layer29which is covered by the etching-resistant material54. Referring toFIG. 3I, in the step of performing an removing process and a thinning process (S29), the nickel plating layer27and the etching-resistant material54are removed by a chemical mechanical planarization process or a chemical stripping process. Because the height of the second copper plating layer29filling in the second opening33is higher than the height of the first copper plating layer25in the first opening31, when the chemical mechanical planarization process is performed, a portion of the second copper plating layer29is removed, and after that the top surface of the second copper plating layer29filling in the second opening33will be at the same height as the top surface of the first copper plating layer25in the first opening31, as shown inFIG. 3J. Further, the thickness of the first copper plating layer25can be thinned, which depends on the need of the required resistance value.

Referring toFIG. 3K, in the step of forming a dry film (S31), a patterned dry film or a photoresist56is formed on the surface of the two outer copper layers23, the first copper plating layer25and the second copper plating layer29. Referring toFIG. 3L, in the step of forming a heat dissipation structure (S33), after the two outer copper layers23uncovered by the photoresist56are etched and the dry film is removed, a heat dissipation structure80including a first copper bump81, a second copper bump83, and a copper pad85is formed on the surface of the printed circuit board1. The heat dissipation structure80and the inner copper layers21are electrically connected to each other.

In the present invention, when the substrate has the openings with different sizes and the copper cannot be plated in the openings once, the nickel plating layer is formed as a barrier layer to avoid the uneven surface caused by performing the copper plating process for many times. Furthermore, by sandwiching the nickel plating layer between the copper plating layers, the resistance value of the plated copper layer can be easily controlled, and thereby the problems in the prior art can be solved.