JPS624885A - Method and device for local etching of cu circuit pattern on printed circuit board - Google Patents

Abstract

PURPOSE:To correct the defect of Cu circuit pattern on a printed circuit board by bringing the surface of a workpiece contg. a part to be etched into contact with an etching liquid so that only the part irradiated with a laser beam has the etching capacity and irradiating the laser beam on the part to be etched. CONSTITUTION:The defect part 9 of a Cu pattern on the printed circuit board 4 is projected on the cathode-ray tube 13 of a TV video monitor 12 with a TV camera 11 via a half mirror 10 set on the same axis as a laser beam and displayed in the intersection of the lines 14, 15. While watching the TV video monitor 12, an operator operates an X-Y mobile table 1 mounted with the printed circuit board 4 immersed in an etching liquid 2 stored in a tank 3 so that only the part irradiated with the laser beam has the etching capacity and positions it. Then the laser beam is irradiated from a laser beam generator 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an etching method and apparatus, and more particularly to a method and apparatus for locally etching a Cu circuit pattern on a printed circuit board.

[Conventional technology]

As a method of forming a fine Cu circuit pattern on a printed circuit board by etching without using a mask, the printed circuit board is immersed in an etching solution (for example, CuCla + FeCt3 solution), and at the same time, the parts to be etched are etched.
A technique has been published in which the etching solution is irradiated with a laser beam having a wavelength that does not absorb energy, and selectively etches only the irradiated area.

This utilizes the reaction acceleration phenomenon caused by an increase in reaction rate due to heating of the portion to be etched by a laser beam and a reduction in the diffusion layer of Cu ions due to local heating.

However, in this conventional method, laser beam irradiation
The etching rate of the irradiated area is accelerated and a higher etching rate is observed than that of the non-laser irradiated area, but this is because an etching solution that originally has the ability to etch the Cu pattern is used.

Parts that were not irradiated with the laser were also back etched, and side etching also occurred, making it difficult to perform fine patterning. As a means to prevent this, a method was considered in which the etching solution was diluted to about 1/10 times the concentration. However, although this method reduces the amount of back-etching in the areas not irradiated with the laser beam, it Since the etching speed of the laser beam also decreases significantly, there is a drawback that the effect of increasing the etching speed by laser beam irradiation can hardly be expected. On the other hand, focusing on the fact that the etching reaction is rate-determined by environmental temperature, which can be approximated by the arenium equation, the temperature of the entire etching solution is kept low enough to inactivate the etching, and only the portion irradiated with the laser beam is selectively heated. Methods have also been considered, but forced turbulent convection occurs due to local heating of the laser beam, and the laser beam energy does not work effectively due to dispersion of local heating energy. Therefore, there was a drawback that the back etching and side etching amounts were not reduced as much as expected.

Due to the drawbacks mentioned above, the etching method and apparatus based on laser beam irradiation have not yet reached the stage of practical use.

[Problem that the invention seeks to solve]

An object of the present invention is to eliminate the drawbacks of the prior art as described above, to eliminate almost no back etching in areas other than the laser beam irradiation area, and to cause almost no side etching in the laser beam irradiation area, and to eliminate the problem of conventional CuCl2+ FeC43 in the laser beam irradiation area.
A method and apparatus for etching a Cu circuit pattern on a printed circuit board, preferably a method and apparatus for etching a Cu circuit pattern on a printed circuit board, using a laser beam and having a local etching property that is one order of magnitude better than that of a Cu etching solution. We are in the process of providing equipment.

[Means for solving problems]

This invention is originally a solution that shows no or almost no etching properties for Cu, and moreover, when irradiated with laser beam energy of an appropriate wavelength, only that part undergoes a photochemical reaction or thermal decomposition reaction. It has a selective etching ability, and furthermore, by energy acceleration caused by laser beam irradiation, only the portion irradiated by the laser beam can be etched selectively and at high speed.

The local area of the Cu circuit pattern on the printed circuit board is characterized by using a solution having characteristics such that the etching ability is immediately lost as soon as the etching is completed, and no back etching in one periphery or side etching in the etched area occurs. The present invention relates to a selective etching method and apparatus.

〔Example〕

As a method of implementing an etching solution that can achieve this invention, 2
There is a way.

That is, it absorbs the energy of the laser beam and is effective in etching Cu through a photochemical reaction (all lu" is generated. After the etching reaction of Cu by Cu"+ is completed, Cu2+ is reduced to Cu+, so the etching ability is lost. However, this Cu+ becomes Cu”+ again due to laser light reaction.
One method uses an etching solution that has a regenerating photochemical reaction loop that regenerates the Cu surface. One side has a hydrophilic adsorption group (e.g. NH2) and one side has a lipophilic reactive group (e.g.

-R-) is added in several ppm to several percent.

While this organic acid coats the Cu surface and prevents back etching, this organic acid is locally decomposed by the heat supplied by the laser beam energy, and only the laser beam irradiated area is locally etched.

After etching, the etched area is quickly coated with organic acid again, so this method uses an additive that has a mechanism that prevents side etching from occurring.

As a method of irradiating the etching solution with a laser beam,
A tube with an inner diameter several times to several hundred times the beam diameter of the laser beam and a composition that does not react with the machining fluid is immersed vertically into the workpiece with a small gap so as not to come into contact with the workpiece. When processing is performed by passing a laser beam through the center of the tube and irradiating the laser beam onto the part to be processed, the heating effect of the laser causes the etching liquid to be stirred turbulently by thermal convection in the tube, and the etching liquid is rapidly jetted from the bottom end of the tube. be done. Therefore, only the processing liquid excited or reacted by the laser beam is supplied to the part to be processed, so that extremely efficient etching processing can be achieved.

FIGS. 1 and 2 show C of the printed circuit board according to the present invention.
FIG. 6 shows a block diagram of an embodiment of a circuit pattern local etching apparatus. Defects in the Cu circuit pattern that occurred after wet etching of the Cu circuit pattern on the printed circuit board (
Fig. 1 shows an embodiment of a locally selective etching apparatus in which the etching liquid according to the present invention is used to correct (remaining copper), and Fig. 1 shows a case in which point-like pattern defects are removed by etching.
Figure 2 is.

This figure shows the case where a linear tube-turn defect is removed by etching.

In FIG. 1, a tank 3 containing an etching solution 2 is placed on an X-Y movable table 1 that is movable in the X-Y direction, and a printed circuit board 4 is immersed in the solution.

The laser beam generated by the laser beam generator 5 is modulated by an optical modulator 6 to a frequency effective for optical heating reactions and evaporation reactions, and is focused into the shape of a point defect 9 by a condensing lens 7 and a beam slit 8. Ru.

The defective portion 7 of the Cu pattern to be corrected is projected onto a cathode ray tube 13 of a television image monitor 12 by a television camera 11 through a half mirror 10 coaxial with the laser beam. The correction position is indicated by the intersection of lines 14 and 15.

The operator positions the X-Y moving table 1 while viewing the television image monitor 12.

In this example, the laser beam is focused to a diameter of 50 μm in TEMoo mode with a beam intensity of Gaussian distribution, but if the Cu pattern defect 7 is smaller than the laser beam diameter, it is shaped by the beam slit 8. Point irradiation with laser beam.

FIG. 2 shows a case where the pattern defect portion is linear.

If the Cu pattern defect 16 is larger than the laser beam diameter, etching is performed by optically vibrating the half mirror 10 (galvano mirror) and continuously examining the linear defect 16.

The laser beam generated by the laser beam generator 8 is modulated by the optical modulator 6 to a frequency effective for the above-mentioned photochemical reaction and thermal decomposition reaction. The light is focused on the shape.

In this case, the wavelength of the laser beam is such that it has an absorption of 10% or more for o, which is necessary to achieve the photochemical reaction or thermal decomposition reaction of the etching solution according to the present invention, and heats the local portion of the Cu pattern to be etched. However, it is necessary to select a wavelength that has sufficient characteristics to remove the Cu ion diffusion layer. This wavelength will be explained later.

In the first method, which uses photochemical reactions, wavelengths in the ultraviolet region are effective.
44 nm, the second method is effective for wavelengths in the infrared region and N
d: The fundamental wavelength of YAG laser was 1.06 μm. Further, the energy level in this case is preferably in the range of 102 W/crn2 to 105-2 for both methods. At an energy level lower than this, the reaction progresses slowly and the laser energy cannot be used effectively, and at an energy level higher than this, the printed circuit board itself (glass epoxy resin, polyimide resin, etc.) will be damaged.

The laser beam thus formed is passed through the tube 17 immersed in the etching solution to the defective part of the Cu circuit pattern to be repaired on the printed circuit board immersed in the tank containing the etching solution according to the present invention. irradiated. When processing is performed while passing a laser beam through the center of this tube 17 and irradiating the laser beam to the part to be processed,
Due to the heating effect of the laser in the tube, the etching liquid is turbulently stirred by thermal convection, and the etching liquid is rapidly injected from the lower end of the tube. Therefore, only the processing liquid excited or reacted by the laser beam is supplied to the part to be processed, so that extremely efficient etching processing can be achieved.

Further, the depth of the etching solution to the printed circuit board at this time is preferably 5I+I+I+ or less. This is because the energy required for the photochemical reaction or thermal decomposition reaction of the etching solution must be absorbed from the laser beam.

Since the etching liquid used has a property of absorbing at least 10% of the laser beam, if the depth of the liquid is deeper than this, the entire laser beam will be absorbed by the etching liquid, making it necessary to modify the Cu circuit pattern. without reaching the site,
The effect of etching using a laser beam is lost. When using the etching apparatus with the above configuration, although there is a slight difference in etching speed between the first method and the second method, the etching speed is an order of magnitude faster than the conventional etching apparatus that does not use a laser, at a maximum of 10 μm/min. In addition to being able to obtain a high etching speed, the amount of back etching and side etching can be kept to 1/10 or less of the conventional etching rate despite the increased speed.

Below, specific etching solution embodiments of the present invention are discussed in detail.

This is an illustration for clarifying this invention in more detail.

This invention is not particularly limited.

(Example 1) Cu is formed on glass epoxy resin with a thickness of 0.1 mm.
1-OX 1-OX 0.035t of circuit pattern
50μ in diameter and 35μ in depth at the center of Cu hat part of trn
Form a through hole of m.

As a solution, I M is added to an aqueous suspension of CuC4(S).
O-25Motl as HClO4 and Ct concentration in oz
An etching solution with Cu"+ concentration of 25 m Mot was used. What is the etching rate of this solution at room temperature (20°C) (without laser irradiation)?

This solution hardly causes back etching or side etching when immersed at 0.001 μm/sec. This is due to the Cu2 required for Cu etching.
This is because there is almost no +.

This solution is Nd: YAG laser double wavelength wave 244
Light with a wavelength of n is pulsed at I KHz using an optical modulator and has an average energy of 600 W/LM2.

C that causes a lower reaction and is effective for etching Cu.
uCl2 is generated only in the area irradiated by the laser beam.

Etching progresses through the following reactions.

CuC1(B)+CC1-CuC121o, K=-
0,31CuC1z+Ct CuCl3” # =
−0,292CuC7(8) Cu +Cu(s)
l-2Cz' = -0,75Cu +C6-
-ΔCuC1' = 0-36CuC6+ C
1CuCta' = -0,14 (K: reaction equilibrium determination) CuO+Cu"+6C22Cu(:t3"Also, as can be seen from the above reaction formula, once Cu2+ etches the Cu pattern, the above reaction produces Cu effective for etching. "+" is reduced to Cu+, so the etching ability is not lost, and the area below the laser irradiation area is not etched, and back etching and side etching do not occur. The temperature is shown in FIG. 3, and the etching rate in this case is shown in FIGS. The side etching amount was maxQ, 1 μm/min.

(Example 2) The same object as in Example 1, that is, 1. of the Cu circuit patterns formed on glass epoxy resin with a thickness of 0.1 rtrm. OX 1. A through hole with a diameter of 50 μm and a depth of 35 μm is formed at the center of the Cu pad at OX O, 35.

As the solution, a CuCl2 solution with a concentration of 30% was used.

This is originally a Cu etching solution, and it is movable at room temperature.
．． It has a back etch characteristic of 0 μm/min. but,
To this, a corrosion inhibitor having amine acid amide as the aforementioned hydrophilic group (an adsorption group with the Cu pattern) was added.
．． When approximately 0% is added, the amount of back etching can be reduced to 0.1 μm/min or less, as shown in FIG.

In this solution, the fundamental wave of the Nd:YAG laser is 1.06 μm.
When pulse modulated with a Q switch and irradiated with a pulsed laser with a pulse m90n8 frequency I KHz, the laser energy is absorbed and the hydrophilic group of the amino acid amide is cut only in the laser irradiated part, so only this part is selectively cut. is etched at high speed.

This thermal decomposition of the amino acid amide is achieved at a temperature of about 80°C or higher, but the average laser irradiation energy in this case is about 4
This corresponds to 10' W/cm2, and above this energy very fast etching (approximately 10 μm/m1n) is selectively achieved.

Furthermore, since the area around the pattern after etching where the inhibitor has been destroyed is rapidly protected by new inhibitor in the gap between pulsed laser oscillations, the amount of back etching or side etching does not increase due to local laser destruction of the inhibitor.

(Example 3) The same object as Example 1, that is, 1-O of the Cu circuit pattern formed on a glass epoxy resin with a thickness of O-1 mm.
A through hole with a diameter of 50 μm and a depth of 35 μm is formed at the center of the Cu pad portion of X 1−OX 0.035 am.

As the solution, an aqueous solution of cupric tetraammine chloride, which is a copper ammine complex, at a concentration of 5% was used.

Add N to this solution (1: YAG laser fundamental wave 1.06 μm)
is pulse-modulated with a Q switch to generate a pulsed laser with a pulse width of 9Qns and a frequency of IKH2 at an average energy of 10”W/
cm2 for approximately 60 seconds. In this case, as shown in FIG. 6, the effect is that the verticality of the side surfaces is high and pattern etching with extremely good pattern cutting is achieved.

In the above processing process, the surface brightness of the part to be processed that is irradiated with the laser is monitored using a TV monitor and a brightness monitor, and when the laser beam reaches the substrate during end etching.

It uses a control method that automatically ends the etching process by sensing a signal emitted by the substrate at high brightness.

〔Effect of the invention〕

According to the present invention, it is possible to provide a technology that can easily perform fine patterning with high resolution without using a mask (with less back etching and side etching), and can also achieve Cu pattern etching more than an order of magnitude faster than conventional etching. can.

The invention is particularly useful in electronics packaging and related technologies.

[Brief explanation of the drawing]

Figures 1 and 2 show C of the printed circuit board according to the present invention.
u A block diagram of an embodiment of a circuit pattern local etching apparatus, FIG. 3 shows the temperature rise characteristics of the etching solution according to the present invention due to laser irradiation, and FIGS. 4 and 5 show the laser irradiation of the etching solution according to the present invention. Figure 6 shows the etching properties of cupric tetraammine chloride, which is a copper ammine complex. 1... X-Y moving table 2... Etching liquid 4... Printed circuit board 5... Laser beam generator 6... Optical modulator. Figure 1 Figure 3

Claims (1)

[Claims] 1. A method of etching by bringing the surface of the workpiece including the part to be etched into contact with an etching solution and simultaneously irradiating the part to be etched with a laser beam,
The above-mentioned etching solution is characterized by using an etching solution that has the ability to selectively etch only the area irradiated with the laser beam, and which quickly loses its etching ability after the etching reaction is completed. A method for locally etching a Cu circuit pattern on a printed circuit board. 2. The Cu circuit of the printed circuit board according to claim 1, wherein the etching solution has a composition that absorbs 10% or more of energy with respect to the wavelength of the laser beam to be irradiated. A method of locally etching patterns. 3. The method for locally etching a Cu circuit pattern on a printed circuit board according to claim 1, wherein a copper ammine complex, preferably cupric tetraammine chloride, is used as the etching solution. 4. C of the printed circuit board according to claim 1, wherein the immersion distance between the etching solution and the surface of the workpiece including the portion to be etched is 5 mm or less.
U-circuit pattern local etching method. 5. As the average irradiation energy of the above laser beam, 10
Claim 1, characterized in that a material having an intensity of ^2W/cm^2 to 10^5W/cm^2 is used.
A method for locally etching a Cu circuit pattern on a printed circuit board as described in 1. 6. As for the above laser beam irradiation method, a tube with an inner diameter several times to several hundred times the beam diameter of the laser beam and a composition that does not react with the machining liquid is placed over the workpiece part with a small gap so as not to come into contact with it. A Cu circuit pattern of a printed circuit board according to claim 1, characterized in that a laser beam is passed through the center of the tube and the part to be processed is irradiated with the laser beam while being processed. Localized etching method. 7. In the above processing process, the surface brightness of the part to be processed that is irradiated with the laser is monitored using a TV monitor and a brightness monitor, and during end etching, when the laser beam reaches the substrate, the substrate emits high brightness. Claim 1 is characterized in that a control method is used to automatically terminate the etching process by sensing a signal that
A method for locally etching a Cu circuit pattern on a printed circuit board as described in 1. 8. An X-Y moving table movable in the X-Y direction, a tank placed on the X-Y moving table, an etching solution contained in this tank, and a print immersed in this etching solution. 1. An apparatus for locally etching a Cu circuit pattern on a printed circuit board, comprising a substrate, a laser beam generator facing the printed circuit board, and an optical modulator for controlling the laser beam generator. 9. An apparatus for locally etching a Cu circuit pattern on a printed circuit board according to claim 8, further comprising a tube provided above the printed circuit board through which a laser beam passes.