TWI446845B - Method for forming blind via of circuit board by laser - Google Patents

Description

Method for forming a blind hole of a circuit board by using a laser

SUMMARY OF THE INVENTION The present invention is directed to a method of forming a blind via of a circuit board, and more particularly to a method of forming a blind via a laser using a laser.

In the field of circuit board technology today, a multi-layer circuit board usually has a plurality of conductive blind via structures, and by these conductive blind via structures, multilayer circuits in a multilayer circuit board can be Electrically connected between adjacent layers. In order to meet the current trend of reducing the line width and line spacing and increasing the line density of the circuit board, these conductive blind hole structures are generally formed by laser drilling.

The multilayer wiring of a typical multilayer circuit board is usually made of copper foil. Since the thermal conductivity of the copper foil is large, the heat conduction effect is quite good. Therefore, when the copper foil is directly irradiated with the laser beam, the copper foil will quickly disperse the heat energy generated by the laser beam, thereby causing the heat energy to be less likely to accumulate in the copper foil. The dielectric layer below. Thus, it is difficult for the laser beam to directly perform a direct laser drilling process from the surface of the copper foil.

In order to solve the above problems, in the conventional laser drilling process, the copper foil is first subjected to a lithography and etching process to form a conformal mask having a plurality of openings, and the openings are exposed to copper. The dielectric layer under the foil. Thereafter, the openings are illuminated with a laser beam to melt the dielectric layer within the openings. In this way, a plurality of blind holes are formed. Next, via filling plating is performed to form a plurality of conductive blind via structures.

However, since these openings are formed by lithography and etching processes, that is, the openings need to be formed by processes such as upper photoresist, exposure, and development, the above-described laser drilling process is too complicated. In addition, in the process of lithography, the alignment error will occur, and the error will cause the relative positions of the openings to be offset from the laser beam, except that the laser beam is not completely melted and the exposed dielectric layer is exposed. In addition to forming a blind hole with a complete hole shape, it is even easy to cause the laser beam to damage the circuit board, thereby reducing the process yield of the circuit board.

In view of the above disadvantages, an improved laser drilling process has been proposed which is illustrated in Figures 1A-1E. 1A to 1E are schematic cross-sectional views showing a flow of a conventional laser drilling process. Referring to FIG. 1A, first, a dielectric layer 120 and a copper foil 130 are laminated on an inner circuit board 110. The inner circuit board 110 includes a dielectric layer 112 and a copper circuit layer 114. The electrical layer 120 is located between the copper foil 130 and the copper wiring layer 114.

Referring to FIG. 1A and FIG. 1B, the copper foil 130 is then blackened to form a copper oxide layer 140. Since the blackening treatment oxidizes the surface of the copper foil 130, after the blackening treatment, a part of the copper foil 130 becomes a copper oxide layer 140 due to a chemical oxidation reaction. In order to blacken the copper foil 130, the thickness T1 of the copper foil 130 shown in FIG. 1A needs to exceed 6 micrometers.

Referring to FIG. 1B and FIG. 1C, next, the copper oxide layer 140 is irradiated with a laser beam L1. Since the thermal conductivity of the copper oxide layer 140 is smaller than that of the copper foil 130, the thermal energy generated by the laser beam L1 is accumulated in the dielectric layer 120. Thus, a plurality of blind holes B1 (only one is shown in FIG. 1C) are formed.

Referring to FIG. 1C and FIG. 1D, the copper oxide layer 140 is removed to expose the copper foil 130. Referring to FIG. 1E, a hole filling process and a lithography and etching process of the copper foil 130 are performed to form a plurality of conductive blind via structures 150 and a copper wiring layer 130'.

However, the laser drilling process shown in FIGS. 1A to 1E needs to be subjected to a blackening process, and the copper foil 130 (shown in FIG. 1D) after removing the copper oxide layer 140 may have a rough surface, resulting in a rough surface. The uniformity of the thickness of the copper foil 130 is deteriorated. This will reduce the stability of the process, which in turn affects the yield of the board process.

The present invention provides a method of forming a blind via of a circuit board using a laser, which is applied to a conductive blind via structure for fabricating a circuit board.

The invention provides a method for forming a blind hole of a circuit board by using a laser to improve the yield of the circuit board process.

The present invention provides a method of forming a blind via of a circuit board using a laser. First, a substrate is provided, which includes a first conductive layer, a second conductive layer, and an insulating layer disposed between the first conductive layer and the second conductive layer. Next, a layer of low thermal conductivity material is deposited on the first conductive layer, wherein the layer of low thermal conductivity material has a thermal conductivity that is less than the thermal conductivity of the first conductive layer. Thereafter, a layer of low thermal conductivity material is irradiated with a laser beam to form at least one blind via, wherein the blind via extends from the layer of low thermal conductive material to the second conductive layer.

In an embodiment of the invention, the material of the low heat conductive material layer is selected from the group consisting of zinc, nickel, chromium, and tin.

In one embodiment of the invention, the low thermal conductivity material layer has a thickness between 0.01 microns and 3 microns.

In an embodiment of the invention, the first conductive layer has a thickness of less than 6 microns.

In one embodiment of the invention, the low thermal conductivity material layer covers the first conductive layer in its entirety after deposition of the low thermal conductivity material layer.

In an embodiment of the invention, the low thermal conductivity material layer partially covers the first conductive layer after depositing the low thermal conductivity material layer.

In an embodiment of the invention, after forming the blind via, the layer of low thermal conductivity material is further removed.

The present invention further provides a method of forming a blind via of a circuit board using a laser. First, a circuit substrate is formed, which includes a first circuit layer, a second circuit layer, an insulating layer disposed between the first circuit layer and the second circuit layer, and a low layer disposed on the first circuit layer A layer of thermally conductive material. The first line and the second line are buried in the insulating layer, and the surface of the first line is substantially aligned with the surface of the insulating layer, and the heat transfer coefficient of the low heat conducting material layer is smaller than the heat transfer coefficient of the first circuit layer. Next, a layer of low thermal conductivity material is irradiated with a laser beam to form at least one blind via, wherein the blind via extends from the layer of low thermal conductive material to the second wiring layer.

In an embodiment of the invention, the method for forming a circuit substrate includes first depositing a layer of a low thermal conductive material and a first conductive layer on a carrier substrate. Next, the first conductive layer is patterned to form a first wiring layer. Thereafter, the carrier substrate is laminated to the second wiring layer by half of the cured film, wherein the first wiring layer is opposite to the second wiring layer. Next, the carrier substrate is removed to expose a layer of low thermal conductivity material.

In an embodiment of the invention, the material of the low heat conductive material layer is selected from the group consisting of zinc, nickel, chromium, and tin.

In one embodiment of the invention, the low thermal conductivity material layer has a thickness between 0.01 microns and 3 microns.

In an embodiment of the invention, after forming the blind via, the layer of low thermal conductivity material is further removed.

The present invention employs a layer of low thermal conductivity material such that the insulating layer is heated by the laser beam. As such, the low heat conductive material layer and the first conductive layer (or the first wiring layer) are blasted outward to form a blind hole. Compared with the prior art, the first conductive layer (or the first circuit layer) of the present invention has a relatively flat surface and a relatively uniform thickness. Thus, the present invention can greatly improve the stability of the process, thereby improving the yield of the circuit board process.

The above described features and advantages of the invention will be apparent from the following description.

[First Embodiment]

2A to 2E are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a first embodiment of the present invention. Please refer to FIG. 2A. First, a substrate 210 is provided. The substrate 210 includes a first conductive layer 212a, a second conductive layer 212b, and an insulating layer 214. The insulating layer 214 is disposed on the first conductive layer 212a and the second conductive layer. Between 212b.

The substrate 210 of this embodiment may be a copper foil substrate (CCL) or other substrate that can be used to fabricate a circuit board. The material of the first conductive layer 212a and the second conductive layer 212b may be copper, aluminum or other suitable metal material, and the insulating layer 214 is, for example, a prepreg, and the insulating layer 214 may include a resin and a glass fiber.

Referring to FIG. 2B, a low thermal conductive material layer 220 is deposited on the first conductive layer 212a. The method of depositing the low thermal conductive material layer 220 may include electroplating, electroless plating or chemical vapor deposition ( Chemical Vapor Deposition (CVD), or may also include Physical Vapor Deposition (PVD), such as evaporation or sputtering.

The low heat conductive material layer 220 comprehensively covers the first conductive layer 212a, and the heat transfer coefficient of the low heat conductive material layer 220 is smaller than the heat transfer coefficient of the first conductive layer 212a, and the material of the low heat conductive material layer 220 may be metal, or ceramic, oxidized. Object or other non-metallic material. The thickness T2 of the low heat conductive material layer 220 may range from 0.01 micrometers to 3 micrometers. Of course, in order to meet different product designs and requirements, the thickness T2 of the low thermal conductive material layer 220 may also be 3 microns or more.

Under the premise that the material of the first conductive layer 212a is copper and the material of the low thermal conductive material layer 220 is metal, the material of the low thermal conductive material layer 220 is a metal material having a thermal conductivity lower than that of copper, such as zinc, nickel, chromium or tin. Therefore, the material of the low heat conductive material layer 220 may include zinc, nickel, chromium, tin or other suitable metal, or any combination of these metals.

Referring to FIG. 2B and FIG. 2C, next, the low heat conductive material layer 220 is irradiated with a laser beam L2 to form at least one blind hole B2, wherein the blind hole B2 extends from the low heat conductive material layer 220 to the second conductive layer 212b. The laser beam L2 can be provided by a carbon dioxide laser or other suitable laser station.

Since the thermal conductivity of the low thermal conductive material layer 220 is smaller than the thermal conductivity of the first conductive layer 212a, the thermal energy generated by the laser beam L2 can be accumulated in the insulating layer 214 via the transfer of the low thermal conductive material layer 220 and the first conductive layer 212a. . This causes the insulating layer 214 to vaporize and expand due to local heat, and the low heat conductive material layer 220 and the first conductive layer 212a are blasted outward because they cannot withstand the expansion of the insulating layer 214. In this way, the blind hole B2 is formed.

Further, after the blind holes B2 are formed, some glue remains in these blind holes B2. Therefore, in the present embodiment, the blind hole B2 can be desmear to remove the slag in the blind hole B2 and clean the surface of the second conductive layer 212b exposed by the blind hole B2.

It is worth mentioning that the material of the low heat conductive material layer 220 may be selected from materials having low chemical activity or good corrosion resistance, such as chromium. In this way, it is ensured that the low heat conductive material layer 220 does not deteriorate or deteriorate before being irradiated by the laser beam L2 to improve the stability of the process.

Referring to FIG. 2C and FIG. 2D, after the blind via B2 is formed, the low thermal conductive material layer 220 may be removed to expose the first conductive layer 212a. The above method of removing the low thermal conductive material layer 220 may include an etching process, a grinding process, or other suitable method.

Referring to FIG. 2D and FIG. 2E, a hole-fill plating process and a portion of the first conductive layer 212a and a portion of the second conductive layer 212b may be removed. Thus, the conductive blind via structure 230, the first wiring layer 212a', and the second wiring layer 212b' are formed, and a circuit board 200 is substantially completed.

It should be noted that although the conductive blind hole structure 230 shown in FIG. 2E fills the entire blind hole B2, in other embodiments not shown, the conductive blind hole structure 230 may cover only the hole wall of the blind hole B2. The blind hole B2 is not filled. Therefore, the conductive blind via structure 230 shown in FIG. 2E is merely illustrative and not limiting.

It should be noted that the circuit board 200 shown in FIG. 2E is a double sided circuit board, but the embodiment can also be applied to manufacturing a multilayer circuit board having three or more layers, and is familiar with The method of the present invention can easily understand how to apply the method of using the laser to form a blind hole of a circuit board in a circuit board for manufacturing three or more layers according to FIGS. 2A to 2E and the above contents. . Therefore, it is emphasized herein that FIGS. 2A through 2E are merely illustrative and not limiting.

From the above, it is known that the laser beam L2 can be heated to vaporize the insulating layer 214 by the low heat conductive material layer 220. Thus, the low heat conductive material layer 220 and the first conductive layer 212a are blasted outward, and the blind hole B2 is formed. Compared to the conventional laser drilling process using blackening treatment (please refer to FIG. 1A to FIG. 1E), the thickness of the first conductive layer 212a may be less than 6 micrometers (as shown in FIG. 2A), and the first conductive The surface of layer 212a is relatively flat and relatively uniform in thickness.

[Second embodiment]

3A to 3B are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a second embodiment of the present invention. Referring to FIG. 3A and FIG. 3B, the present embodiment is similar to the first embodiment, so only the difference between the two is described below, in which the low thermal conductive material layer 220' of the present embodiment partially covers the first conductive layer after deposition. 212a.

In detail, the low heat conductive material layer 220' may cover only where it is required to be irradiated by the laser beam L2, i.e., the low heat conductive material layer 220' may be distributed only where the blind hole B2 is to be formed. Therefore, the low heat conductive material layer 220' can be used to mark the place to be illuminated by the laser beam L2.

After deposition of the low heat conductive material layer 220', the low heat conductive material layer 220' is irradiated with the laser beam L2. In this way, the blind hole B2 is formed. After the blind hole B2 is formed, the subsequent process is the same as that of the first embodiment, and therefore the description will not be repeated.

[Third embodiment]

4A to 4H are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a third embodiment of the present invention. Referring to FIG. 4E, first, a circuit substrate 310 is formed, which includes a first circuit layer 312a, a second circuit layer 312b, an insulating layer 314, and a low thermal conductive material layer 316.

The insulating layer 314 is disposed between the first circuit layer 312a and the second circuit layer 312b, and the first line 312a and the second line 312b are buried in the insulating layer 314, wherein the surface of the first line 312a and the surface of the insulating layer 314 Essentially aligned. That is to say, the circuit substrate 310 can basically be regarded as an embedded circuit board. The low heat conductive material layer 316 is disposed on the first wiring layer 312a, and the low heat conductive material layer 316 has a heat transfer coefficient smaller than that of the first wiring layer 312a. In addition, the second wiring layer 312b may be one of the multilayer wirings of the wiring substrate 310.

In this embodiment, the material of the first circuit layer 312a and the second circuit layer 312b may be copper, aluminum or other suitable metal material, and the material of the first circuit layer 312a is made of copper, and the layer of low heat conductive material is The material of 316 is a metal material with a thermal conductivity lower than that of copper. Thus, the material of the low thermal conductivity material layer 316 may comprise zinc, nickel, chromium, tin or other suitable metal, or any combination of these metals. Further, the thickness of the low heat conductive material layer 316 may be between 0.01 micrometers and 3 micrometers. Of course, the thickness of the low thermal conductivity material layer 316 may also be above 3 microns in response to different product designs and requirements.

There are many methods of forming the wiring substrate 310, and in the present embodiment, the method of forming the wiring substrate 310 may include the following steps. Referring first to FIG. 4A, first, a low thermal conductive material layer 316 and a first conductive layer 312a' are sequentially deposited on a carrier substrate 320, wherein the low thermal conductive material layer 316 can cover the surface of the carrier substrate 320 in a comprehensive manner. The deposition method of the low heat conductive material layer 316 and the first conductive layer 312a' is the same as the low heat conductive material layer 220 in the first embodiment, and the carrier substrate 320 may be a metal plate such as an aluminum plate. Of course, the carrier substrate 320 can also be made of plastic, ceramic or other non-metallic materials.

When the carrier substrate 320 is an aluminum plate and the first conductive layer 312a' is made of copper, the first conductive layer 312a' cannot be directly attached to the carrier substrate 320. Therefore, the first conductive layer 312a' can be formed by the low heat conductive material layer 316. To adhere to the carrier substrate 320. That is, the low thermal conductive material layer 316 can serve as an adhesive layer between the first conductive layer 312a' and the carrier substrate 320, and in order to enable the first conductive layer 312a' to adhere to the carrier substrate 320, The material of the heat conductive material layer 316 may be zinc.

Referring to Figures 4A and 4B, next, the first conductive layer 312a' is patterned to form a first wiring layer 312a. The method of patterning the first conductive layer 312a' may employ a lithography and etching process.

Referring to Figures 4B and 4C, the carrier substrate 320 is then laminated to the second wiring layer 312b by a half cured film 314', wherein the first wiring layer 312a is opposite the second wiring layer 312b. Referring to FIG. 4C and FIG. 4D, after the carrier substrate 320 is pressed, the prepreg film 314' is cured to become the insulating layer 314.

Referring to FIGS. 4D and 4E, the carrier substrate 320 is then removed to expose the low thermal conductivity material layer 316. As such, the circuit substrate 310 is formed. Further, in the present embodiment, the method of removing the carrier substrate 320 may include an etching process.

Referring to FIG. 4E and FIG. 4F, after forming the circuit substrate 310, the low heat conductive material layer 316 is irradiated with the laser beam L2 to form at least one blind hole B3, wherein the blind hole B3 extends from the low heat conductive material layer 316 to the second line. Layer 312b. After the blind hole B3 is formed, the blind hole B3 may be desmeared to remove the slag in the blind hole B3 and clean the surface of the second wiring layer 312b exposed by the blind hole B3.

Referring to FIG. 4F and FIG. 4G, after forming the blind via B3, the low thermal conductive material layer 316 may be removed, and the low thermal conductive material layer 316 may be removed by an etching process or a grinding method.

Please refer to FIG. 4G and FIG. 4H. Next, a hole filling plating process can be performed. As such, the conductive blind via structure 330, the first wiring layer 312a, and the second wiring layer 312b are formed, and a circuit board 300 is substantially fabricated. Although the conductive blind hole structure 330 shown in FIG. 4H fills the entire blind hole B3, in other embodiments not shown, the conductive blind hole structure 330 may cover only the hole wall of the blind hole B3 and not fill the blind hole. B3. Therefore, the conductive blind via structure 330 shown in FIG. 4H is merely illustrative and not limiting.

It must be noted that the circuit board 300 shown in FIG. 4H is a multilayer circuit board having two or more lines. However, the present embodiment can also be applied to the manufacture of a double-sided circuit board having only two layers of lines, and those skilled in the art to which the present invention pertains can easily understand how to utilize the present embodiment based on FIGS. 4A to 4H and the above. The method of laser forming a blind via of a circuit board is applied to the manufacture of a double-sided circuit board. Therefore, it is emphasized herein that FIGS. 4A through 4H are merely illustrative and are not intended to limit the invention.

In summary, the present invention utilizes a layer of low thermal conductivity material to enable the laser beam to be heated to vaporize the insulating layer. As such, the low heat conductive material layer and the first conductive layer (or the first wiring layer) are blasted outward to form a blind hole. Compared with the conventional laser drilling process using the blackening process, the first conductive layer (or the first circuit layer) of the present invention has a relatively flat surface and a relatively uniform thickness. Thus, the present invention can greatly improve the stability of the process, thereby improving the yield of the circuit board process.

Secondly, since the present invention can form a blind via without blackening, the thickness of the first conductive layer does not need to exceed 6 μm, so the present invention can be applied to the first conductive layer having a small thickness. Thus, the present invention can reduce the overall thickness of the circuit board to meet the trend of thinning current circuit boards.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

110. . . Inner circuit board

112, 120. . . Dielectric layer

114, 130’. . . Copper circuit layer

130. . . Copper foil

140. . . Copper oxide layer

150, 230, 330. . . Conductive blind hole structure

200, 300. . . Circuit board

210. . . Substrate

212a, 312a’. . . First conductive layer

212a’, 312a. . . First circuit layer

212b. . . Second conductive layer

212b’, 312b. . . Second circuit layer

214, 314. . . Insulation

220, 220’, 316. . . Low thermal conductivity material layer

310. . . Circuit substrate

314’. . . Semi-cured film

320. . . Carrier substrate

B1, B2, B3. . . Blind hole

L1, L2. . . Laser beam

T1, T2. . . thickness

1A to 1E are schematic cross-sectional views showing a flow of a conventional laser drilling process.

2A to 2E are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a first embodiment of the present invention.

3A to 3B are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a second embodiment of the present invention.

4A to 4H are schematic cross-sectional views showing the flow of a method of forming a blind via a laser using a laser according to a third embodiment of the present invention.

212a. . . First conductive layer

212b. . . Second conductive layer

214. . . Insulation

220. . . Low thermal conductivity material layer

L2. . . Laser beam

T2. . . thickness

Claims (11)

A method for forming a blind via hole by using a laser, comprising: providing a substrate comprising a first conductive layer, a second conductive layer, and a first conductive layer and the second conductive layer disposed between the first conductive layer and the second conductive layer An insulating layer; depositing a low thermal conductive material layer on the first conductive layer, wherein the low thermal conductive material layer has a thermal conductivity smaller than a thermal conductivity of the first conductive layer, and the low thermal conductive material layer is selected from the group consisting of zinc a population of nickel, chromium, and tin; and irradiating a layer of the low heat conductive material with a laser beam to form at least one blind via, wherein the blind via extends from the layer of low thermal conductive material to the second conductive layer. A method of forming a blind via a laser using a laser as described in claim 1, wherein the low heat conductive material layer has a thickness of from 0.01 micrometer to 3 micrometers. A method of forming a blind via a laser using a laser as described in claim 1, wherein the first conductive layer has a thickness of less than 6 micrometers. The method of using a laser to form a blind via of a circuit board according to claim 1, wherein the low thermal conductive material layer comprehensively covers the first conductive layer after depositing the low thermal conductive material layer. A method of forming a blind via a laser using a laser as described in claim 1, wherein the low thermal conductive material layer partially covers the first conductive layer after depositing the low thermal conductive material layer. The method for forming a blind hole of a circuit board by using a laser according to claim 1, wherein after the blind hole is formed, the method further comprises: removing the blind hole Low thermal conductivity material layer. A method for forming a blind via a laser using a laser, comprising: forming a circuit substrate comprising a first circuit layer, a second circuit layer, and a first circuit layer and the second circuit layer An insulating layer and a low thermal conductive material layer disposed on the first circuit layer, wherein the first line and the second line are buried in the insulating layer, and a surface of the first line and the insulating layer The surface is substantially aligned, the heat transfer coefficient of the low heat conductive material layer is less than the heat transfer coefficient of the first circuit layer; and the low heat conductive material layer is irradiated with a laser beam to form at least one blind hole, wherein the blind hole is from the A layer of low heat conductive material extends to the second circuit layer. The method for forming a blind hole of a circuit board by laser according to claim 7, wherein the method for forming the circuit substrate comprises: sequentially depositing the low thermal conductive material layer and a first conductive layer on a carrier substrate. Patterning the first conductive layer to form the first circuit layer; pressing the carrier substrate on the second circuit layer by half-curing film, wherein the first circuit layer is opposite to the second circuit layer; And removing the carrier substrate to expose the layer of low thermal conductivity material. The method for forming a blind hole of a circuit board by laser according to the seventh aspect of the invention, wherein the material of the low heat conductive material layer is selected from the group consisting of zinc, nickel, chromium and tin. The method for forming a blind hole of a circuit board by using the laser according to claim 7, wherein the low heat conductive material layer has a thickness of 0.01 μm. Up to 3 microns. A method of fabricating a blind via of a laser using a laser according to claim 7, wherein after the blind via is formed, the layer of low heat conductive material is further removed.