JP4097069B2 - Printed circuit board manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a printed circuit board in which conductor layers are electrically connected using via holes, and is particularly suitable for use in manufacturing a high frequency substrate such as a passive component built-in substrate for a power amplifier module, and is excellent in mass productivity. The present invention relates to a printed circuit board manufacturing method.
[0002]
[Prior art]
Conventionally, when forming a via hole in this type of printed circuit board, a hole having a diameter of 100 to 50 μm is formed at a predetermined position of the interlayer insulating resin layer using a carbon dioxide gas laser, a UV-YAG laser, etc. The thermal metamorphic layer (smear) is removed by etching using a desmear treatment solution such as sodium permanganate or potassium permanganate. Also, in the build-up method or the like, the surface of the interlayer insulating resin layer is etched in this step to increase the surface roughness, and the adhesion of the conductor layer formed in the next step is ensured.
[0003]
Japanese Patent Laid-Open No. 2000-22337 discloses a technique for forming a via hole in an interlayer insulating resin layer with a carbon dioxide gas laser.
[0004]
[Problems to be solved by the invention]
By the way, when the material of the interlayer insulating resin layer is a highly reliable resin having excellent electrical characteristics such as vinyl benzyl, for example, the thermal metamorphic layer dissolves to some extent in the desmear treatment liquid, but the resin itself is insoluble. In addition, an intermediate layer that hardly dissolves between the surface portion of the heat-denatured layer and the resin layer remains, which may cause a serious problem in reliability. In addition, when the base conductor is formed by electroless plating by a build-up method, etc., the resin surface is generally roughened at the same time as wet desmearing to ensure adhesion between the substrate and the plated copper, but the resin is etched. Therefore, the surface of the interlayer insulating resin layer cannot be roughened in this step.
[0005]
There is a method of forming a conductor layer on the surface of a smooth interlayer insulating resin layer while ensuring a certain degree of adhesion by a dry method such as sputtering or vapor deposition, but generally the adhesion is insufficient, and mass production Is significantly reduced.
[0006]
In view of the above points, the present invention can form a highly reliable interlayer connection with a high-frequency substrate having excellent characteristics, and can ensure the adhesion between the insulating resin layer and the conductor layer, and realize them with high productivity. An object of the present invention is to provide a method for manufacturing a printed circuit board.
[0007]
Other objects and novel features of the present invention will be clarified in embodiments described later.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 of the present application is a printed circuit board manufacturing method using an interlayer insulating resin layer having a Q of more than 150 at 1 GHz.
The interlayer insulating resin layer contains spherical silica as a filler in vinylbenzyl resin,
After forming holes having a diameter of 200 μm or less and 30 μm or more by UV-YAG laser in the interlayer insulating resin layer,
Forming via holes from which smear has been removed by dry etching with a reactive gas containing at least oxygen and having reactivity with vinylbenzyl resin and filler ,
The resin and filler on the surface of the interlayer insulating resin layer are etched at different etching rates during the dry etching so that the average height of the filler protruding from the resin surface is at least 1/4 of the average particle diameter of the filler. It is characterized by.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a printed circuit board manufacturing method according to the present invention will be described below with reference to the drawings.
[0015]
FIG. 1 shows an embodiment of a method for producing a printed circuit board according to the present invention. First, an interlayer insulating resin layer 2 having a Q of more than 150 at 1 GHz is applied and formed on a copper foil 1 serving as a first conductor layer. Prepare a substrate. Here, as the interlayer insulating resin layer 2 having a Q of more than 150 at 1 GHz, for example, several 10 spherical silica fillers of 1 to 30 μm are added to a vinylbenzyl resin (relative dielectric constant 2.5, Q value at 1 GHz is 260). What mixed by volume% etc. can be used. The thickness of the interlayer insulating resin layer 2 is several tens of μm to several hundreds of μm.
[0016]
The reason why the interlayer insulating resin layer 2 having a Q exceeding 150 at 1 GHz is to produce a high frequency substrate such as a passive component built-in substrate for a power amplifier module, and when the Q at 1 GHz is 150 or less, This is because the high frequency characteristics are deteriorated and become unsuitable for use. Resins having a Q of more than 150 at 1 GHz are chemically stable as seen in vinylbenzyl, and many materials cannot be sufficiently obtained by wet desmear treatment when drilled with a laser.
[0017]
Silica filler is used as the filler mixed in the interlayer insulating resin layer 2 because it can be selectively etched (or left selectively) because the etching rate in the dry etching process described later is different from that of the resin. is there. Also, the reason why the silica filler particle size is 1 to 30 μm is that it is difficult to obtain particles having a particle size of less than 1 μm, and the effect of forming irregularities on the surface of the interlayer insulating resin layer 2 in the dry etching process is reduced. If the particle diameter exceeds 30 μm, the thickness of the interlayer insulating resin layer varies, and the unevenness on the surface of the interlayer insulating resin layer 2 becomes excessive compared to the thickness of the resin layer. Further, the spherical shape of the silica filler is preferable for reducing the loss of high frequency because the surface area is small.
[0018]
As shown in FIG. 1A, the substrate is irradiated with a UV-YAG laser at a via-hole forming position to form holes 3 having a diameter of 200 μm or less and 30 μm or more. At that time, a thermal metamorphic layer (smear) 2 a of the interlayer insulating resin layer 2 is formed on the inner side surface of the hole 3 and around the hole. Here, the reason why the UV-YAG laser is used is that, as shown in FIG. 2A, the heat-transformed layer 2a generated when the hole 3 is formed in the interlayer insulating resin layer 2 by laser processing is hardly formed on the bottom surface of the hole. Because. On the contrary, in the carbon dioxide laser that has been widely used in the past, when the hole 3 is formed in the interlayer insulating resin layer 2 as shown in FIG. The metamorphic layer 2a (or resin) remains at the bottom of the hole, and there is a strong possibility that a problem in reliability occurs when the conductor layers are connected to each other by a via hole. Resin that can be removed by dry etching and the thickness of its thermal metamorphic layer is limited to 2 μm. If the thermal metamorphic layer 2a is left at the bottom of the hole, it may cause problems such as disconnection of conductor connection due to via holes and loose contact. It becomes. The diameter of the hole 3 (referred to here as the opening diameter of the hole 3) is in the range of 30 μm to 200 μm. If the diameter is less than 30 μm, the hole diameter is too small compared to the thickness of the interlayer insulating resin layer. This is because the reliability of via hole connection cannot be ensured when the upper conductor layer is formed, and if it exceeds 200 μm, via holes can be formed by a method that is less expensive than laser processing.
[0019]
A dry etching process using a gas (for example, a mixed gas of O ₂ and CF ₄ ) having reactivity with the interlayer insulating resin layer 2 and the filler on the substrate having the holes 3 formed by laser processing as described above. As shown in FIG. 1B, the thermal metamorphic layer 2a is removed (desmear treatment), and at the same time, the surface of the interlayer insulating resin layer 2 is roughened. When a mixed gas of O ₂ + CF ₄ is used in the dry etching process, increasing the O ₂ ratio increases the resin etching rate, and increasing the CF ₄ ratio increases the silica filler etching rate. Therefore, the surface of the interlayer insulating resin layer 2 can be appropriately roughened by changing the mixing ratio of O ₂ and CF ₄ in the mixed gas and appropriately setting the etching rate of the resin of the interlayer insulating resin layer 2 and the silica filler. .
[0020]
By this dry etching process, the via hole 10 is formed by removing the inner side surface of the hole 3 and the thermal transformation layer 2a around it, and the interlayer insulating resin layer 2 has a roughness suitable for forming the second conductor layer in the next step. The surface of can be roughened.
[0021]
Thereafter, as shown in FIG. 1C, the underlying conductor layer 11 of the second conductor layer is formed on the interlayer insulating resin layer 2 and on the inner surface of the via hole 10 by electroless copper plating or the like. Electrical connection is made between the first conductor layer 1 and the underlying conductor layer 11 of the second conductor layer. Although not shown, a plated conductor layer is formed on the underlying conductor layer 11 by electrolytic plating such as copper so as to have a required thickness, thereby forming a second conductor layer.
[0022]
Note that at least one of the first conductor layer and the second conductor layer is patterned to have a predetermined wiring pattern.
[0023]
In FIG. 3, when the filler is protruded from the resin surface by dry etching the interlayer insulating resin layer 2 containing the spherical silica filler and selectively etching the vinylbenzyl resin on the surface of the interlayer insulating resin layer 2, The average protrusion height / filler average particle size} and the peel strength of the second conductor layer are shown. From this figure, it can be seen that if the average protrusion height of the filler is 1/4 or more of the average particle diameter of the filler, a peel strength of 90% or more of the upper limit value can be obtained.
[0024]
In the dry etching process, the mixing ratio of the mixed gas of O ₂ + CF ₄ is changed so that the spherical silica filler is selectively etched, and the spherical silica filler portion is etched on the surface of the interlayer insulating resin layer. Then, the surface may be roughened by making it depressed. It is preferable to roughen the resin surface simultaneously with desmear during dry etching. However, when it is difficult to set conditions, the resin surface can be processed under conditions effective for surface roughening after being processed under conditions effective with desmear. Further, the order of processing steps may be reversed. The above process can be performed in the same batch of dry etching.
[0025]
According to this embodiment, the following effects can be obtained.
[0026]
(1) Since a high-Q material such as vinylbenzyl (Q is greater than 150 at 1 GHz) is used as the interlayer insulating resin layer 2 interposed between the conductor layers, the high-frequency characteristics are excellent.
[0027]
(2) When a low-loss filler such as spherical silica is mixed in the interlayer insulating resin layer 2, the Q is increased and the high frequency characteristics are further improved.
[0028]
(3) The desmear (thermal metamorphic layer removal) after drilling by laser is performed by dry etching, so the reliability is good. In the case of wet etching, a highly reliable resin such as vinylbenzyl having excellent electrical characteristics leaves an insoluble intermediate layer between the surface portion of the heat-denatured layer and the resin layer, resulting in insufficient reliability.
[0029]
(4) Since the interlayer insulating resin layer is roughened simultaneously with the desmear process, the process is short and the mass productivity is excellent.
[0030]
(5) Since the surface of the interlayer insulating resin layer 2 after the treatment has fine irregularities similar to the particle size of the filler, the adhesiveness of the conductor layer formed thereon is excellent. In particular, the peel strength can be sufficiently increased by setting the average protrusion height of the filler from the resin surface to ¼ or more of the average particle diameter of the filler.
[0031]
(6) Since the irregularities on the surface of the interlayer insulating resin layer are determined by the particle size of the filler, it is easy to control the roughening. That is, when increasing the surface roughness of the surface, the particle size of the filler is increased. Moreover, what is necessary is just to raise the mixing rate of a filler, when raising the total number of unevenness | corrugations.
[0032]
(7) A similar idea to the above is also wet desmear processing. That is, a filler that is easily etched, such as calcium carbonate, is mixed in the resin, and the filler is dissolved by chemical treatment such as desmear to form irregularities. In this case, the filler inside may be dissolved by the permeation of the treatment liquid, and in this case, an interlayer insulation failure occurs. In the present invention, since the resin or filler on the surface layer is etched by dry etching (since etching is limited to the surface layer), insulation failure does not occur.
[0033]
(8) When the particle size of the filler is about 1 μm, a conductor layer having excellent adhesion and good high frequency characteristics can be formed on the interlayer insulating resin layer. That is, when the conductor layer is copper, the skin depth is about 2 μm at 1 GHz, and the unevenness on the surface of the interlayer insulating resin layer is preferably smaller than the skin depth from the viewpoint of high frequency characteristics.
[0034]
(9) By drilling with a UV-YAG laser, there are few thermal metamorphic layers 2a around the holes 3 in the interlayer insulating resin layer 2, and almost no thermal metamorphic layer is formed on the bottom of the holes (see FIG. 2 (A)), there is no trouble such as disconnection of the conductor connection due to the via hole, loose contact or the like.
[0035]
【Example】
Hereinafter, the manufacturing method of the printed circuit board concerning the present invention is explained in full detail in an example.
[0036]
The board | substrate used for the present Example apply | coats the vinyl benzyl resin as an interlayer insulation resin layer on the copper foil as a 1st conductor layer. The vinylbenzyl resin is mixed with 40 volume% of 1-30 μm spherical silica filler. The film thickness of the vinyl benzyl resin used as the interlayer insulating resin layer is about 0.1 mm.
[0037]
A 605DLX laser processing machine manufactured by Mitsubishi Electric was used for laser processing of the via hole formed in the interlayer insulating resin layer. The type of laser processing machine is UV-YAG. The laser processing conditions are a frequency: 30 kHz, a pulse width: 200 μs, a mask: a diameter of 0.9 mm, a pulse energy: 0.5 mJ, and a shot number: 20.
[0038]
An SEM (scanning electron microscope) photograph of the hole laser-processed in the interlayer insulating resin layer under the above conditions is shown in (photo 1) of FIG. In FIG. 4 (photo 2), scattered matter (smear) is attached in the vicinity of the processing hole (near A in photo 1). 4 (Photo 3) is a position away from the processing hole (near B in Photo 1), and no scattered matter is seen.
[0039]
The apparatus used for the dry etching process for removing the scattered material around the inner surface of the hole by the laser processing and for roughening the surface of the interlayer insulating resin layer is a versatile plasma apparatus SYSTEM400 manufactured by TELPA AG. The gas type is O ₂ + CF ₄ , and the etching conditions are O ₂ : 700 cc / min, CF ₄ : 100 cc / min, pressure: 100 Pa, plasma output: 1 kW, RF bias: 100 W, etching time: 10 minutes. . A surface SEM image of the substrate etched under the above conditions is shown in FIG. It can be seen that the spherical silica filler remains on the surface of the interlayer insulating resin layer without being etched.
[0040]
RF as the bias: 100W, etching time: the substrate was dry-etched with 10 minutes, where the underlying conductor processing in the next step was to measure the peel strength is performed by electroless plating of copper, about 0.6 kgf / cm ² ( About 6 × 10 ⁴ N / m ² ). This is because the peel strength of low profile copper foil coated with vinylbenzyl is about 0.4 kgf / cm ² (about 4 × 10 ⁴ N / m ² ). In comparison, it can be seen that it is the same or higher.
[0041]
Although the embodiments and examples of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited thereto and various modifications and changes can be made within the scope of the claims. I will.
[0042]
【The invention's effect】
As described above, according to the method of manufacturing a printed circuit board according to the present invention, it is possible to form an interlayer connection by a via hole having excellent reliability in a high-frequency substrate having excellent characteristics, and to ensure adhesion between the insulating resin layer and the conductor layer. Therefore, they can be realized with high productivity.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an embodiment of a method for producing a printed circuit board according to the present invention.
FIG. 2 shows a state of a heat-denatured layer (smear) generated during drilling with a UV-YAG laser and a carbon dioxide gas laser, where (A) is a UV-YAG laser and (B) is a carbon dioxide laser. It is explanatory drawing of.
FIG. 3 is a graph showing the relationship between {filler average protrusion height / filler average particle size} on the surface of an interlayer insulating resin layer and peel strength of a second conductor layer formed on the interlayer insulating resin layer.
FIG. 4 is a photographic view of the periphery of a hole after laser drilling for an interlayer insulating resin layer.
FIG. 5 is a photograph of the surface of an interlayer insulating resin layer after dry etching.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Copper foil 2 Interlayer insulation resin layer 2a Thermal metamorphic layer 3 Hole 10 Via hole 11 Base conductor layer

Claims (1)

In a method for manufacturing a printed circuit board using an interlayer insulating resin layer having a Q exceeding 150 at 1 GHz,
The interlayer insulating resin layer contains spherical silica as a filler in vinylbenzyl resin,
After forming holes having a diameter of 200 μm or less and 30 μm or more by UV-YAG laser in the interlayer insulating resin layer,
Forming via holes from which smear has been removed by dry etching with a reactive gas containing at least oxygen and having reactivity with vinylbenzyl resin and filler ,
The resin and filler on the surface of the interlayer insulating resin layer are etched at different etching rates during the dry etching so that the average height of the filler protruding from the resin surface is at least 1/4 of the average particle diameter of the filler. A printed circuit board manufacturing method characterized by the above.

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