KR20230073594A - Dry desmear process method for micro-hole smear removal - Google Patents

Abstract

The present invention relates to a method for removing the smear inside PCB micro-holes using plasma treatment, and more specifically, to a dry desmear method for removing the smear created inside fine holes after machining the fine holes in a PCB manufacturing process using an optimized plasma treatment process. The dry desmear method according to the present invention can be usefully used to reduce the problem of defects such as swelling of or damage to a substrate by making the surface properties of the substrate hydrophilic and cleanly removing the smear inside fine holes of 150 um or less.

Description

Dry desmear process method for micro-hole smear removal}

The present invention relates to a method for removing smear inside a fine hole in a PCB using plasma treatment, and more particularly, cleanly removes smear inside a hole of 150 um or less in a PCB through plasma treatment, which is a new dry method rather than the conventional wet method It's about a possible process.

In general, in the PCB process, it is soaked in potassium permanganate to remove the smear generated inside the hole after hole processing (polymer residue remaining on the inner wall of the hole after hole processing, if this remains, it causes poor conduction during through-hole plating). removing smear.

However, due to the high specification, high multi-layering, and fine patterning of the PCB, even the necessary holes in the PCB have been miniaturized and become very small in micro size. Since the hole size is very small and the thickness of the board is thick, even if it is immersed in a chemical for a wet process to remove smear after hole processing, the chemical does not penetrate properly into the hole, so smear often remains.

If the chemical exposure time is lengthened to remove all the remaining smear, there is a problem that the substrate swells or the substrate is damaged, so the existing wet desmear process has reached its limit.

Accordingly, the inventors of the present invention have made efforts to develop a method for removing smear inside PCB fine holes. As a result, a new dry method rather than the existing wet method, plasma treatment, developed a process that can cleanly remove smear inside a hole of 150 um or less. By doing so, the present invention was completed.

Republic of Korea Patent No. 10-0484573 Republic of Korea Patent No. 10-1748054 Republic of Korea Patent Publication No. 10-2021-0103022

An object of the present invention is to provide a method for removing smear inside microholes of a PCB through plasma treatment.

Another object of the present invention is to provide a PCB in which smear inside the microholes is removed according to the present invention.

In order to achieve the above object, the present invention

A dry desmear method for removing smear generated inside the fine hole after processing the fine hole in a printed circuit board (PCB) manufacturing process using plasma,

here,

The plasma provides a dry desmear method, characterized in that the treatment for 40 to 50 minutes at a power intensity of 4.5 to 8 kW.

In addition, the present invention

i) A dry desmear step of removing smear generated inside the fine hole after processing the fine hole in the printed circuit board (PCB) manufacturing process by treating with plasma,

At this time, a dry desmear step characterized in that the plasma is treated for 10 to 20 minutes at a power intensity of 4.5 to 8 kW; and

ii) a wet desmear step of removing smear remaining inside the hole by treating the inside of the micro hole with a potassium permanganate solution after step i);

In addition, the present invention

Provided is a printed circuit board in which fine holes are desmeared by the method according to the present invention.

The desmear method using plasma according to the present invention can cleanly remove smear inside a hole of 150 μm or less.

In particular, in the present invention, optimization of the etching degree and surface properties of the substrate was established through optimization of plasma process conditions.

In addition, the dry and wet combined desmear method according to the present invention removes some of the smear by drying and changes the characteristics of the surface of the substrate, and then allows the wet chemical to penetrate well into the hole, so that the hole is very small and the substrate thickness is thick. For holes where wet chemicals do not permeate well, the smear inside the hole is completely removed and the desmear process time can be significantly reduced.

1 is a picture showing a picture of smear and plating defects generated thereby.
2 is a graph showing the etching degree of prepreg according to plasma desmear process conditions.
3 is a diagram showing changes in physical properties of prepreg and copper foil before and after the plasma desmear process.
4 is a diagram showing surface changes of prepreg and copper foil before and after the plasma desmear process.

Hereinafter, the present invention will be described in detail.

In describing the present invention, detailed descriptions of related known configurations or functions may be omitted. Terms or words used in this specification and claims should not be construed as being limited to ordinary or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical details of the present invention. The embodiments described in this specification and the configurations shown in the drawings are preferred embodiments of the present invention, and do not represent all of the technical spirit of the present invention, so various equivalents and modifications that can replace them at the time of this application are There may be.

the present invention

A dry desmear method for removing smear generated inside the fine hole after processing the fine hole in a printed circuit board (PCB) manufacturing process using plasma,

here,

The plasma provides a dry desmear method, characterized in that the treatment for 40 to 50 minutes at a power intensity of 4.5 to 8 kW.

In the above method, the plasma is preferably treated at a temperature of 40 to 50 °C.

In the method, the plasma is preferably treated at a vacuum degree of 0.2 to 0.3 Torr.

In the above method, the plasma is preferably treated with a gas composition of 0.4 to 0.6 O ₂ gas, 0.2 to 0.4 N ₂ gas, and 0.2 to 0.4 CF ₄ gas.

In the above method, the plasma is a plasma processing device comprising a reaction vessel, a gas for generating plasma introduced into the reaction vessel, an electrode for generating plasma in the reaction vessel under pressure, and a moving means including a conveying roller and a winding roller. can be performed by

The plasma processing apparatus introduces a gas for plasma generation into a reaction vessel through a gas inlet, flows the gas for plasma generation from top to bottom in the reaction vessel, and introduces the plasma generation gas into a discharge space, and then pulses or alternating current between electrodes by a power source. When a voltage is applied and a discharge is generated in the discharge space under the pressure by the application of the voltage, plasma is generated by the discharge, and the plasma is treated by the plasma jet to convert the smear remaining on the surface of the substrate or in the hole into active species of the plasma. The desmear treatment is carried out by decomposing or oxidizing and simultaneously blowing or removing. At this time, by circulating a refrigerant such as water in the flow path of the work table, the processing target substrate can be cooled and thermal damage can be reduced.

In the above method, the principle of removing the smear using plasma is as follows. When electrical energy is applied to the gas molecules inside the low-vacuum chamber, the outermost electrons of the molecule or atom are deviating from the orbit due to the collision of the accelerated electrons, generating ions or highly reactive radicals. is accelerated by continuous collision and electrical attraction and collides with the surface of the material, breaking molecular bonds in a region within several micrometers to remove the smear generated inside during hole processing. In particular, since ions or radicals collide inside the hole to create fine surface irregularities, the adhesion of copper plating can be improved during the through-hole copper plating process.

In addition, the present invention

i) A dry desmear step of removing smear generated inside the fine hole after processing the fine hole in the printed circuit board (PCB) manufacturing process by treating with plasma,

At this time, a dry desmear step characterized in that the plasma is treated for 10 to 20 minutes at a power intensity of 4.5 to 8 kW; and

ii) a wet desmear step of removing smear remaining inside the hole by treating the inside of the micro-hole with a potassium permanganate solution after step i);

In the above method, the plasma is preferably treated at a temperature of 40 to 50 °C.

In the method, the plasma is preferably treated at a vacuum degree of 0.2 to 0.3 Torr.

In the above method, the plasma is preferably treated with a gas composition of 0.4 to 0.6 O ₂ gas, 0.2 to 0.4 N ₂ gas, and 0.2 to 0.4 CF ₄ gas.

In addition, the present invention provides a printed circuit board in which fine holes are desmeared by the method according to the present invention.

Process optimization in the desmear method using plasma according to the present invention can provide a substrate from which 100% of the smear inside the fine holes of 150 μm or less is completely removed.

In particular, the dry and wet combined desmear method according to the present invention removes some parts and changes the surface characteristics by drying, and then allows the wet chemical to permeate well into the hole, so that the hole is very small and the thickness of the substrate is thick, so that the wet chemical permeates It is possible to provide a substrate from which the smear inside the hole is completely removed for the hole that does not work well.

Hereinafter, the present invention will be described in more detail through examples.

These examples are only for explaining the present invention in more detail, and it is obvious to those skilled in the art that the scope of the present invention is not limited by these examples according to the gist of the present invention. .

< Example 1> prepreg Etching degree/ plasma Desmear

Ten sheets of FR-4 prepreg 10 cm X 10 cm were prepared as substrates and treated under the following plasma process conditions. The etching amount (average) was measured as the average of the difference in weight before and after treatment, and it was assumed that the smear removal ability was proportional to the weight reduction (Epoxy etch rate) of FR-4. The higher the etching power, the faster the smear removal rate.

Power [kW] 3, 4.5, 6, 7 Time [min] 10, 20, 40, 50 Temp [℃] 45 Vacuum degree [Torr] 0.25 Gas
conditions O ₂ 0.4, 0.6, 0.8 N ₂ 0.1, 0.2, 0.35 CF ₄ 0.1, 0.15, 0.35

As a result, as shown in FIG. 2, the smear etching power increased as the plasma power increased, and in particular, it significantly increased when the plasma power was 6 and 7 kW. In addition, the longer the plasma process time, the higher the smear etching power, especially at 40 and 50 minutes. In addition, the higher the O ₂ gas concentration, the lower _the smear etching power, the change in N ₂ gas concentration does not change significantly, and the higher the CF ₄ gas concentration, the higher the smear etching power. , it was found that the optimum condition was when the N ₂ gas concentration was 0.2 to 0.35 and the CF ₄ gas concentration was 0.15 to 0.35 (FIG. 2).

< Example 2> Surface properties

After treating the surface of prepreg (FR-4) and copper foil with plasma, the change in surface properties was confirmed by measuring the contact angle.

Plasma conditions were performed as follows: plasma power 4.5 kW, Time 20, Temp 45 degrees, vacuum degree 0.25, Gas O ₂ /N ₂ /CF ₄ =0.6/0.2/0.2.

The contact angle was measured with Phoenix 300 (manufacturer SIO, Korea), the measurement solvent was DI water, the measurement temperature was 23 ° C, and the measurement method was static.

As a result, as shown in FIG. 3, it was confirmed that when prepreg (FR-4) and the copper foil surface were treated, the surface changed from hydrophobic to hydrophilic (FIG. 3).

< Example 3> hole processing substrate processing

After processing 100 holes of 115 um on a 3T 20-layer board (hole processing method: CNC drilling), 5 of them were processed for each of the following conditions, and then the degree of smear removal was determined.

wet process
process dry only
use
(10 minutes) dry only
use
(20 minutes) dry only
use
(40 minutes) 5 minutes dry + 20% wet process 10 minutes dry + 40% wet process 10 minutes dry + 30% wet process smear
degree of removal 90% 80% 95% 100% 95% 100% 100% swelling
occurrence frequency 30% 0% 0% 0% 0% 3% 0%

As a result, as shown in FIG. 4, the frequency of swelling during wet treatment was high. On the other hand, when using only the dry method (plasma method), a long process time of about 40 minutes was required. When smear is removed by using wet after dry (plasma method), smear is removed well, and swelling does not occur well and it is possible to proceed quickly. After the dry (plasma method) treatment, the surface was changed from hydrophobic to hydrophilic, and the smear removal chemical solution went well into the microholes, so there was almost no smear removal defect.

The process conditions were set to use only the dry method for smear removal, but the smear was well removed when there were few holes, but as the number of holes increased, the smear was not 100% removed and some remained. Doing so had the downside of being a butler and taking a long time. On the other hand, in view of the fact that the surface is changed from hydrophobic to hydrophilic during plasma treatment, a dry process was performed to partially remove and change the surface characteristics so that the wet chemical penetrates well into the hole.

As the hole became very small and the thickness of the board became thick, there was a hole in which the wet chemical did not penetrate well into the hole, and smear removal defects were occurring in some holes. Since the two processes were used together, the smear inside the hole was also removed cleanly and the time was tolerated to some extent. It was possible to progress to the level that could be done.

Claims (10)

A dry desmear method for removing smear generated inside the fine hole after processing the fine hole in a printed circuit board (PCB) manufacturing process using plasma,
here,
The plasma is a dry desmear method, characterized in that for 40 to 50 minutes at a power intensity of 4.5 to 8 kW.
According to claim 1,
The plasma is a dry desmear method, characterized in that the treatment at a temperature of 40 ~ 50 ℃.
According to claim 1,
The plasma is a dry desmear method, characterized in that the processing at a vacuum degree of 0.2 ~ 0.3 Torr.
According to claim 1,
The plasma is a dry desmear method, characterized in that the O ₂ gas concentration is 0.4 to 0.6, the N ₂ gas concentration is 0.2 to 0.4, and the CF ₄ gas concentration is treated with a gas composition of 0.2 to 0.4.
According to claim 1,
The fine hole is a dry desmear method, characterized in that the hole has a diameter of 10 ~ 150 um.
i) A dry desmear step of removing smear generated inside the fine hole after processing the fine hole in the printed circuit board (PCB) manufacturing process by treating with plasma,
At this time, a dry desmear step characterized in that the plasma is treated for 10 to 20 minutes at a power intensity of 4.5 to 8 kW; and
ii) a wet desmear step of removing the smear remaining inside the hole by treating the inside of the fine hole with a potassium permanganate solution after step i);
Desmear method.
According to claim 6,
Desmear method, characterized in that the plasma is treated at a temperature of 40 ~ 50 ℃.
According to claim 6,
The plasma is a desmear method, characterized in that the processing at a vacuum degree of 0.2 ~ 0.3 Torr.
According to claim 6,
The plasma is a desmear method, characterized in that the O ₂ gas concentration is 0.4 to 0.6, the N ₂ gas concentration is 0.2 to 0.4, and the CF ₄ gas concentration is treated with a gas composition of 0.2 to 0.4.
A printed circuit board on which fine holes are desmeared by the method according to any one of claims 1 to 9.

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