JP3259156B2 - Circuit board surface treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of a circuit board, and more particularly, to irradiating a circuit board having a substrate made of an organic material and a conductor formed by laminating a metal material on the substrate with laser light. The present invention relates to a method for treating a surface of a circuit board, which treats a conductor portion.

[0002]

2. Description of the Related Art Conventionally, PGA (Pin Grid Array), QF
P (Quard Flat Pakage), COB (Chip On Board)
In various semiconductor package products called
A conductor portion made of a metal material layer such as copper or gold is formed on a circuit board made of a synthetic resin or the like, and various electronic components such as a semiconductor chip are electrically joined to the conductor portion so that the electronic components or The connection between electronic components and external circuits is achieved. The conductor formed on such a circuit board for a semiconductor package requires extremely fine processing in accordance with a semiconductor chip and the like, and a weak current or a high-frequency current is applied to the conductor. Requires extremely high performance.

However, due to the influence of the atmosphere in which the circuit board is manufactured and various other effects on the manufacturing process, the surface of the conductor on the circuit board becomes contaminated or the surface of the conductor becomes metallically inactive. As a result, the insulation resistance value on the surface of the conductor part increases, or the reliability of the electrical connection decreases. Such a decrease in the reliability of the performance of the conductor portion surface will cause fatal damage to the characteristics of the entire circuit board.

Accordingly, various methods have been proposed for improving the reliability of the performance of the conductor surface by cleaning the circuit board or modifying the surface of the conductor. As a conventional method for cleaning a conductor, a wet chemical method using a chemical such as chlorofluorocarbon is generally used in many cases. However, in recent years, a cleaning method using chlorofluorocarbon has become a problem due to global environmental problems and the like, and a method not using chlorofluorocarbon has been demanded. Therefore, instead of cleaning with chlorofluorocarbon, a cleaning method using pure water and a cleaning method using a surfactant have been proposed.

However, these cleaning methods cannot completely remove contaminants present on the conductor surface.
In addition, there is a problem that the cleaning agent remains on the surface of the conductor portion and rather deteriorates the characteristics of the conductor portion. Further, these methods can be used as long as contaminants adhere to the surface of the conductor portion. However, the cleaning method as described above can be applied to the case where the surface of the conductor portion has become metallically inactive. Cannot recover the reliability of the electrical connection.

Therefore, as a dry surface treatment method which replaces the wet cleaning method as described above, in recent years, the surface of the conductor has been irradiated with a laser beam to remove organic contaminants and improve the performance reliability. There has been proposed a method of restoring the metallic activity of the surface to improve the reliability of the electrical connection. As one example, a method of irradiating a laser beam having a pulse width of 1 μsec to a conductor portion composed of a plurality of metal material layers to form an alloy layer having good solder wettability on the surface is disclosed in Japanese Patent Application Laid-Open No. Hei.
No. 256249. In this conventional circuit board surface treatment method, a high-density laser beam instantaneously melts and solidifies the surface of the conductor to form a uniform alloy layer with good wettability, and also removes foreign substances such as organic substances. Evaporate to obtain a clean metal layer.

[0007]

However, the conventional dry surface treatment method using a laser beam as described above has a problem that the reliability of the electrical connection of the conductor surface is not sufficiently improved. Specifically, since laser light having a long pulse width is used, an intermetallic compound is formed between a plurality of metal material layers, which causes a problem that the resistance value of the entire conductor portion increases. In addition, the formation of an alloy layer requires a sufficient amount of laser heat input with sufficient energy, which affects the area of the circuit board other than the conductor section, for example, the resin section, etc., thereby affecting the properties of the resin section and the like. There is also the problem of changing.

Further, since the surface of the conductor portion is usually formed by plating, and the surface shape has irregularities and changes individually, there is a case where the electrical connection reliability is not sufficient only by removing the dirt on the surface. Many. Therefore, it has been found that if only the very surface layer is smoothed, the electrical bonding reliability can be improved. An object of the present invention is to provide a surface treatment method for a circuit board that can improve the reliability of electrical connection of the surface without affecting a region other than the conductor on the conductor on the circuit board. Is to do.

[0009]

According to a method of treating a surface of a circuit board according to the present invention, a laser beam is applied to a circuit board having a substrate made of an organic material and a conductor formed by laminating a metal material on the substrate. In the method of irradiating the conductor portion by irradiating, a laser irradiation step of irradiating the circuit board with a short pulse laser beam from a light source to smooth the surface irregularities of the conductor portion (a)
Contains. In the above method, the outermost surface of the conductor portion is made of gold having a thickness of 0.2 μm or more,
The irradiation energy density of the laser beam in (a) is 0.6 to 3.
0 J / cm ² , and the number of laser beam irradiations is 1 to 50 times.

[0010] In the above method, the first with respect to the circuit board.
A first laser irradiation step (b) of irradiating the laser beam to remove foreign matter adhering to the conductor portion; and after the first laser irradiation step,
The second laser irradiation step (a) of irradiating the circuit board with a second laser light having an intensity equal to or higher than the first laser light to surface-treat the conductor portion. In the above method, the first laser beam has an irradiation energy density of 0.2 to
An excimer laser beam of 0.6 J / cm ² , and the second laser beam has an irradiation energy density of 0.6 to 3.0 J / cm 2.
^2. Excimer laser light.

In the above method, the method further includes the step of placing the circuit board under a reduced pressure atmosphere, and in each laser irradiation step, the circuit board placed under the reduced pressure atmosphere can be irradiated with laser light through an optical window. .

The above method may further include a plasma generating step of generating plasma under a reduced pressure atmosphere. The above method may further include a plasma control step of controlling the power of the plasma generated in the plasma generation step.

The above method may further include a gas flow forming step of forming a gas flow near the optical window under a reduced pressure atmosphere. In the above method, before the laser irradiation, the method further includes a step of determining whether or not the conductor portion of the circuit board is larger than one laser irradiation region. In the laser irradiation step, it is determined that the conductor portion is larger than the laser irradiation region. At this time, it is possible to irradiate the laser beam to the mixed portion of the conductor portion that is mixed with the non-conductor portion on the circuit board, and then to irradiate the laser beam to the conductor portion excluding the mixed portion.

In the above method, in the laser irradiation step,
The laser beam emitted from the light source is driven by driving two mirrors, and the laser beam deflected can be scanned on the circuit board. In the above method, in the laser irradiation step, disposed between the light source and the mirror, a mask to limit the irradiation position,
A lens for forming an image of the mask on the circuit board can be moved in the optical axis direction in synchronization with the mirror.

In the above method, in the laser irradiation step,
Laser light can be emitted between the light source and the circuit board via two lenses disposed at a distance of the sum of their focal lengths. In the above method, the method further includes an irradiation position detecting step of detecting an irradiation position of the laser light irradiated on the circuit board in the laser irradiation step, and a correcting step of correcting the irradiation position of the laser light according to the detected irradiation position. Can be.

In the above method, in the irradiation position detecting step, the detection laser light irradiated from the detection light source is irradiated to the same position as the laser light irradiated from the light source, and the irradiation position of the irradiated detection laser light is detected. Can be. In the above method, the conductor portion of the circuit board is composed of a plurality of plating layers, and further includes an evaluation step of evaluating plating adhesion by a state of the conductor portion after the conductor portion is irradiated with laser light in the laser irradiation step. You can be in.

[0017]

In the method for treating a surface of a circuit board according to the present invention,
In the laser irradiation step, the circuit substrate is irradiated with short-pulse laser light from a light source. Here, by irradiating a short-pulse laser beam onto the circuit board, the energy of the laser beam can be applied only to the surface of the conductor portion, so that the surface of the conductor portion can be heated without affecting the area other than the conductor portion. Foreign matter can be removed, and the surface of the conductor can be smoothened without melting any pinholes or irregularities by melting only the surface of the conductor without forming intermetallic compounds between multiple metal material layers. Mechanical joining reliability can be improved.

The outermost surface of the conductor portion is made of gold having a thickness of 0.2 μm or more, the laser beam irradiation energy density in the laser irradiation step is 0.6 to 3.0 J / cm ² , and the number of laser beam irradiations is 1 If the number of times is up to 50 times, even if a plurality of metal materials are stacked, foreign matter on the surface of the conductor portion can be removed and the surface of the conductor portion can be smoothed without affecting the metal material stacked under the gold.

The circuit board is irradiated with a first laser beam to remove foreign matter adhering to the conductor, and subsequently, the circuit board is irradiated with a second laser beam to surface-treat the conductor. For example, since the first laser beam is used to remove foreign matter such as dirt from the organic substance on the surface of the conductor portion, and then the second laser beam is used to melt the surface of the conductor portion, the electrical connection reliability can be further improved.

The first laser beam is an excimer laser beam having an irradiation energy density of 0.2 to 0.6 J / cm ² ,
The second laser beam has an irradiation energy density of 0.6 to 3.0.
In the case of excimer laser light of J / cm ² , foreign matter can be removed without exerting thermal influence on the circuit board with the weak excimer laser light, and then the surface of the conductor can be melted with the strong excimer laser light. Mechanical joining reliability can be further improved.

When a short-pulse laser beam is applied to a circuit board placed under a reduced-pressure atmosphere through an optical window, the laser beam is applied under a reduced-pressure atmosphere. Thereby, the collision between the scattered particles and the atmospheric gas is reduced, and the adhesion of the scattered particles to the conductor can be suppressed. For this reason, even if the conductor portion and the other region are irradiated with the laser beam over a large area, the electrical connection reliability can be secured.

In a state where plasma is generated under a reduced pressure atmosphere, if a short pulse laser beam is irradiated to the circuit board,
The laser light is irradiated in the plasma atmosphere, so that the foreign matter attached to the optical window is removed by the collision of the gas ionized by the plasma, and the scattered particles are gasified and exhausted, so that the amount adhered to the optical window And the deterioration of the laser transmittance of the optical window is suppressed. In addition, the scattered matter slightly attached to the conductor surface due to the collision of the ionized gas can be removed, and the electrical connection reliability can be further improved.

If the amount of generated plasma is controlled, it is possible to reliably prevent the laser transmittance of the optical window from deteriorating and to remove a small amount of scattered matter adhering to the surface of the circuit board, thereby further improving the electrical connection reliability. it can. If a gas flow is formed in the vicinity of the optical window under a reduced-pressure atmosphere, scattered substances are less likely to adhere to the optical window, and the laser transmittance of the optical window is less likely to deteriorate. Therefore, a laser beam having a uniform energy density is always applied to the circuit board, and high quality surface treatment can be performed.

Before the laser irradiation, it is determined whether or not the conductor portion of the circuit board is larger than a single laser irradiation area. By irradiating the laser light to the mixed part mixed with the non-conductor part and then irradiating the laser light to the conductor part except the mixed part, if the conductor part is larger than the irradiation area, the laser light is irradiated first from the mixed part Therefore, even if particles scattered from a region other than the conductor portion in the mixed portion adhere to the conductor portion excluding the mixed portion, the scattered particles adhered to the mixed portion can be reliably removed, and the electrical connection reliability can be improved.

By driving the two mirrors with the laser light emitted from the light source and scanning the laser light on the circuit board, the laser light is scanned. Can be processed, and by limiting the scanning area, only an arbitrary portion of the circuit board can be surface-treated.

If the mask and the lens move in the direction of the optical axis in synchronization with the movement of the mirror, since the mask is arranged,
Laser light is not irradiated to the part other than the conductor part, so that the generation of scattered particles can be suppressed, and the mask and lens are moved in synchronization with the mirror, so that the image changes according to the change in the optical path length due to the driving of the mirror The position can always be set on the board,
High-precision surface treatment can be performed.

If the two lenses are arranged apart from each other by the sum of the focal lengths, the laser beam can be made incident perpendicularly on the circuit board, and even if a mask is arranged, the image blur will be small,
Even if there is a step on the circuit board, surface treatment can be performed with high accuracy. The irradiation position of the laser light applied to the circuit board is detected, and according to the detected irradiation position, if the irradiation position of the laser light is corrected, the irradiation position is detected, and the irradiation position is corrected accordingly. Therefore, accurate surface treatment can be always performed.

When the detection laser light emitted from the detection light source is irradiated to the same position as the laser light emitted from the light source and the irradiation position of the emitted detection laser light is detected, for example, visible light is used as the detection laser light. For example, since the irradiation position can be detected by an inexpensive detection means such as a CCD camera, the irradiation position can be easily detected at low cost.

If the plating adhesion is evaluated based on the state of the conductor after the conductor is irradiated with the laser beam, the quality can be inspected simultaneously with the surface treatment, thereby improving the productivity and improving the reliability of the circuit board. it can.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. 2 and 3 show a PGA substrate as a specific example of the circuit substrate. The circuit board 10 has a structure in which two types of conductive portions made of conductive metal are laminated on a rectangular plate-shaped resin base material 11 made of a modified polyimide resin. On the upper surface of the resin base material 11, cavities 12, which are first conductor portions, which are recessed in a rectangular shape, are formed at equal intervals, for example, at four locations in the vertical and horizontal directions. In this cavity 12,
A semiconductor chip (not shown) on which an integrated circuit is formed is accommodated. Around the four sides of the cavity 12, a large number of inner leads 13, which are small conductive strips, are formed. The inner lead 13 is connected to a conductor circuit connected to a terminal pin (not shown). Each terminal of the semiconductor chip housed in the cavity 12 is connected to the inner lead 13 by a bonding wire. The inner lead 13 is
As shown in FIG. 2, for example, the resin base material 11 is mixed in an area of 1 mm × 15 mm, and a mixed area in which a conductor portion is mixed in the resin base material 11. Also, cavity 1
2 is, for example, an area of 15 mm × 15 mm, which is an area where only the conductor portion exists.

As schematically shown in FIG. 3, the cavities 12 and the inner leads 13 as the conductors are formed on the resin base material 11.
Has a structure in which an electrolytic copper plating layer 15, a nickel plating layer 16, and a gold plating layer 17 are laminated in this order on a copper foil layer 14 adhered to the upper surface of the substrate. The gold plating layer 17 is formed, for example, by gold plating having a thickness of 0.2 μm or more, and preferably by gold plating having a thickness of 0.5 μm or more. Here, the reason why the thickness of the gold plating layer 17 is set to 0.2 μm or more is that the thickness of the gold plating layer 17 is set to 0.2 μm or less.
This is because there is a possibility that the thermal effect may occur.

FIG. 1 shows the entire structure of a surface treatment apparatus used for carrying out one embodiment of the present invention. The surface treatment device includes an excimer laser irradiation device 30 and an XY table 60. Many circuit boards 10 are mounted on the XY table 60. The circuit board 10 is irradiated with a short pulse excimer laser beam R from an excimer laser irradiation device 30. The laser light R is applied to the circuit board 10 via the mirror 32 and the imaging lens 34. The laser light R is a KrF excimer laser light having a wavelength of 248 nm. As shown in FIG. 4, the pulse width is about 30 nsec, and the repetition frequency when processing the circuit board 10 with a plurality of pulses is 1 to 200 Hz ( The cycle is 1 sec
５5 msec). The irradiation energy density is
It is set to about 0.6 to 3.0 J / cm ² , and the irradiation area is, for example, 3 mm □.

As described above, when a short-pulse laser beam is applied to a conductor, the heat capacity is small due to short-time irradiation, so that the energy of the laser beam acts only on the pole surface of the conductor. As a result, heat is not transferred deep into the conductor, and even when the conductor is formed of a plurality of metal layers, an intermetallic compound is less likely to be formed between the layers, and the resistance of the entire conductor is reduced. The increase is not increased, and the reliability of the electrical connection of the conductor is improved. Further, as shown in FIG. 3 (b), the organic substances adhering to the surface of the conductor are evaporated and removed, and the metal adhering substances on the surface of the conductor are diffused into the conductor to reduce the amount of impurities on the surface. it can. Furthermore, since only the polar surface of the conductor can be melted, the surface can be smoothed, the number of pinholes on the surface can be reduced, and the surface can be softened. Furthermore, since only the conductor is heated, the resin base 11 is less likely to be affected by heat, and the characteristics of the resin base 11 are not easily changed.

As described above, the short pulse laser beam causes
The contaminant removal on the conductor part surface and the melting of the conductor part pole surface are performed to perform a surface modification action to smooth the pole surface and activate the metal. Laser beam R
The following method is employed as the irradiation method. Oscillation of the short pulse laser is continuously repeated at a constant interval (for example, 1 to 200 Hz) by the laser irradiation device 30 (for example, 1 to 200 Hz).
50 times) and the circuit board 10 is moved. The circuit board 10 is also continuously moved while performing such oscillation,
The entire area of the irradiation pattern of the circuit board 10 is irradiated with the laser beam R. By employing such a method, the work can be performed efficiently without interrupting the irradiation of the laser beam R.

FIG. 5 is a schematic view showing an embodiment in which the laser beam is irradiated in two divided steps. In the circuit board, organic dirt 20 adheres to the surface of the conductor portion 12 (13) in any process. Therefore, first, the first laser light is irradiated to remove the organic dirt 20. Thereby, connection reliability of wire bonding is improved. Since the first laser beam has a low energy density, the influence on the conductor is small. Therefore, laser light irradiation is performed until organic substances are completely removed. Here, the irradiation energy density of the first laser light is 0.2 to 0.6 J / cm ² , and the number of irradiations is 1
５００500 times. The irradiation interval is the same as described above and is 1 to 200 Hz.

As shown in FIG. 3, a plating layer is usually formed on the surface of the conductor portion, and the surface condition (crystal grain size of the plating, surface irregularities, amount of impurities in the plating) varies from lot to lot. Therefore, by irradiating the second laser beam to melt the surface of the conductor portion, the variation in the surface state is reduced, and the wire bonding characteristics (electrical bonding reliability) are improved. That is, after removing the dirt, the very surface of the conductor portion is melted in a very short time with the high-density second laser light, and the surface is smoothed and softened without impurities such as organic substances diffusing inside. Form a surface with few pinholes. Here, the irradiation energy density of the second laser light is
0.6 to 3.0 J / cm ² , and the number of irradiations is 1 to 50
Times.

Although it is possible to remove organic dirt with the second laser beam, when the thickness of the dirt 20 is large, the dirt cannot be completely removed if the number of laser irradiations is small. In addition, when the number of laser irradiations is increased, a thermal effect occurs on the circuit board, and the electrical characteristics of the circuit deteriorate. Therefore, the organic contaminants 20 can be removed by increasing the number of laser irradiations with a laser beam having a low energy density and improving the surface state by reducing the number of laser irradiations with a laser having a high energy density. Without deteriorating the electrical connection reliability. Further, in the above two embodiments, a mask for limiting the irradiation pattern to the conductor portion is arranged between the mirror 32 and the laser irradiation device 30,
The mask may be moved in synchronization with the XY table 60.

FIG. 6 shows an embodiment in which a circuit board arranged in a vacuum chamber is irradiated with short pulse laser light. Usually, since the conductor is formed only on a necessary portion of the resin substrate 11 on the circuit board 10, the conductor and the resin substrate 11 are mixed. For this reason, when trying to irradiate only the conductor with the laser light, the control of the laser light irradiation system becomes complicated. In addition, when only the conductor is irradiated, the area that can be irradiated at a time becomes small, and there is a problem from the viewpoint of productivity. Therefore, in this embodiment, the range that can be irradiated at a time is 3 mm square, and the conductor portion and the resin base material 11 are collectively irradiated so that a large area can be processed at a time.

The surface treatment apparatus used for carrying out this embodiment has a box-shaped vacuum chamber 1 in which an optical window 4 is arranged on the upper outer wall. A vacuum pump 2 is connected to the vacuum chamber 1, and the inside thereof is maintained at a degree of vacuum of about 0.1 to 0.01 Torr by the vacuum pump 2. A laser irradiation device 30 is arranged above the optical window. Here, the mirror 32 and the imaging lens 34 are used.
Is not shown. Inside the vacuum chamber 1,
The substrate holding part 5 for holding the circuit board 10 is an optical window 4.
Are arranged to face each other.

When the conductor R and the resin base 11 are collectively irradiated with the laser beam R, the scattered matter generated from the resin base 11 collides with the atmospheric gas and adheres to the surface of the conductor. In order to prevent this, in a state where the circuit board 10 is placed in a reduced-pressure atmosphere in the vacuum chamber 1, short-pulse laser beams having a wide irradiation range are collectively irradiated onto the circuit board 10. In addition,
The atmosphere gas may be air, but may be He, Ar, or N gas. When the circuit board 10 is placed in a reduced-pressure atmosphere in this way, even if the scattered matter from the resin base material 11 jumps out of the board 10 at high speed, it is difficult to collide with the atmospheric gas, and the amount of adhesion to the conductor is reduced.

FIG. 7 shows an embodiment in which a circuit board is irradiated with short-pulse laser light while generating plasma in a reduced-pressure atmosphere. Irradiation with laser light in a reduced-pressure atmosphere causes a problem that scattered matter from the resin substrate 11 adheres to the optical window 4 and the laser transmittance of the optical window 4 decreases. Therefore, in this embodiment, plasma is generated under a reduced-pressure atmosphere, and the adhesion of flying matter to the optical window 4 is reduced by chemical action and physical action.

The surface treatment apparatus includes a plasma electrode 7 disposed between the optical window 4 and the substrate holder 5 in addition to the apparatus shown in FIG. The plasma electrode 7 is connected to a high-frequency plasma power supply 9 arranged outside the vacuum chamber 1. The plasma electrode 7 is made of stainless steel.
It is a coil-shaped electrode having a winding diameter of 0 to 250 mm and a length of 50 mm. The high-frequency plasma power supply 9 applies a high-frequency voltage to the plasma electrode and outputs 20 to 500 W from the plasma electrode 7.
To generate plasma.

In this embodiment, the laser light R is applied to the circuit board 1
When illuminated to 0, scattered matter is generated from the resin substrate 11 and adheres to the optical window and the conductor. Even if this scattered matter adheres to the optical window 4, it is physically removed by etching by collision with the ionized atmospheric gas. Further, the scattered matter scattered in the plasma is gasified and exhausted, so that the amount attached to the optical window 4 is reduced. As a result, the laser transmittance of the optical window 4 hardly decreases, and the laser light R
Reaches the circuit board 10 stably over a long period of time, and a stable surface treatment becomes possible.

Further, the scattered matter slightly attached to the conductor can be removed by the etching action. The slight adhesion of the scattered matter to the conductor has little effect on the wire bonding. However, as shown in FIG. 8, when the semiconductor chip 22 is die-bonded to the cavity 12, the attached matter may be dissolved in the solvent 21 of the die bond, and the viscosity of the solvent 21 may be reduced to facilitate the flow. When the solvent 21 flows to the inner lead 13, a problem such as a short circuit occurs. Therefore, by removing such a small attached matter, the electrical bonding reliability can be further improved.

FIG. 9 shows an embodiment in which a short pulse laser beam is irradiated while controlling the plasma. The surface treatment apparatus according to this embodiment is provided with a moving mechanism 7a for moving the plasma electrode 7 up and down in addition to the apparatus of the embodiment shown in FIG. As the moving mechanism 7a, for example, a driving mechanism such as a motor may be used. By raising and lowering the plasma electrode 7 in this manner, appropriate plasma power can reach both the optical window 4 and the circuit board 10. In addition to controlling the plasma by changing the position of the plasma electrode, the plasma may be controlled by applying a bias voltage to the circuit board or applying a magnetic field to the plasma.

In this embodiment, since the plasma can be controlled more appropriately than the embodiment shown in FIG. 7, the scattered matter adhering to the optical window 4 and the conductor can be further removed, and the electrical connection reliability can be further improved. FIG. 10 shows an embodiment in which laser light is irradiated while forming a gas flow near the optical window.

FIG. 7 shows a surface treatment apparatus according to this embodiment.
A nozzle 18 is arranged around the optical window 4 in addition to the apparatus of the embodiment shown in FIG. A gas cylinder 19 filled with an atmospheric gas (for example, clean air) is connected to the nozzle 18. In this embodiment, a gas is caused to flow in the vicinity of the optical window 4 to suppress the attachment of flying substances to the optical window 4. At this time, the inside of the vacuum chamber 1 is constantly evacuated by the vacuum pump 2,
Atmospheric pressure should not be increased by gas inflow. At this time, the gas flow rate may be such that the degree of vacuum (atmospheric pressure) in the vacuum chamber 1 is not affected. Specifically, it is desirable to be about 1 liter / minute, though it is related to the exhaust capacity. Further, the degree of vacuum in the vacuum chamber 1 is set to 0.
05 Torr may be used. It should be noted that any type of gas is effective in preventing the attachment of flying matter. However, a reactive gas may react with the circuit board 10 and corrode the circuit board 10. Therefore, an atmosphere gas (air) or an inert gas is desirable.

In this embodiment, the adhesion of the scattered matter to the optical window 4 by the gas flow is suppressed, so that the laser transmittance does not easily decrease, and the circuit board 10 is always irradiated with the laser light having a uniform energy density. To provide high quality surface treatment. FIG. 11 shows an embodiment in which the inner lead 13 and the cavity 12 are separately irradiated by the surface treatment apparatus shown in FIG. The area where the inner leads 13 are formed is
As shown in FIG. 2, it is a region where the conductor portion and the resin base material 11 are mixed. When irradiating the inner lead 13, both are illuminated simultaneously by laser light. However, since the cavity 12 has only the conductor, the resin substrate 11 is not irradiated when the cavity 12 is irradiated.

Therefore, as shown in FIG.
In step S1, it is determined whether or not the conductor portion has a larger laser beam irradiation area (one irradiation area). If it is determined that the conductor is large, the process proceeds to step S2,
The XY table 60 is controlled so as to irradiate only the mixed area where the inner leads 13 are formed. Thereby, the resin component is scattered from the resin base material 11 in the mixed area. The scattered resin adheres to the cavity 12. In step S3, the XY table 60 is controlled so that the cavity 12 is irradiated with laser light. Thereby, the resin scattered matter attached to the cavity 12 is removed, and the metal surface layer is melted and reformed. On the other hand, if it is determined that the conductor is smaller than the irradiation area, the process proceeds from step S1 to step S4.
1 and the whole is irradiated. When the laser beam is scanned by the galvano scanning mechanism, the galvano scanning mechanism may be controlled in steps S2 and S3.

By irradiating a laser beam in such a procedure, the resin component does not dissolve in the solvent for die bonding as described with reference to FIG. 8, and a short circuit due to the solvent can be prevented. FIG. 12 shows an embodiment in which a laser beam is scanned. The surface treatment apparatus of this embodiment has an optical window 4 on the upper outer wall.
And a laser irradiation device 30 disposed above the vacuum chamber 1. A laser scanning mechanism 31 is arranged between the vacuum chamber 1 and the laser irradiation device 30. Laser scanning mechanism 31
Has a condenser lens 34 disposed below the laser irradiation device 30 and two rotatable galvanometer mirrors 36 and 37 for scanning the collected laser light. The rotation angles of the galvanometer mirrors 36 and 37 are controlled by a servo mechanism (not shown), so that the irradiation angle of the circuit board 10 can be set arbitrarily based on the laser light emission angle with respect to each of the mirrors 36 and 37. Here, a large area can be processed at high speed without moving the circuit board 10, and surface control can be performed only at an arbitrary place by controlling the mirrors 36 and 37.

FIG. 13 shows an embodiment in which a mask is arranged between the laser irradiation device and the circuit board, and the conductor is accurately surface-treated. A laser scanning mechanism 31 of the surface treatment apparatus includes a mask 38 arranged opposite to the laser irradiation apparatus 30 and a lens 34 arranged facing the mask 38.
And two rotating galvanometer mirrors 36 and 37. The mask 38 and the lens 34 are moved by a moving mechanism 38 that moves in the optical axis direction in synchronization with the galvanometer mirrors 36 and 37.
a and 34a.

Normally, when surface treatment is performed by forming an image of the mask 38, the distance a from the mask 38 to the lens 34 and the processing point (the surface of the circuit board 10) from the lens 34
Between the distance b and the focal point f of the lens 34, the following relational expression holds: 1 / a + 1 / b = 1 / f.

When laser scanning is performed using a galvanomirror, the optical path length b is determined between the central portion A and the peripheral portion B on the circuit board 10.
Therefore, the pattern image of the mask 38 may be blurred and accurate processing may not be performed. Therefore, in this embodiment, the mask 38 and the lens 34 are moved according to the change in the optical path length b so that the pattern image of the mask 38 is not always blurred. For example, the central part A and the peripheral part B
If the optical path length differs by 10 mm, the mask 38 and the lens 34 may both be moved by 10 mm with respect to the mirror 36.

FIG. 14 shows that even if the conductor has a step,
This shows an embodiment in which a conductor portion is surface-treated with high accuracy. This surface treatment device includes a laser irradiation device 30, a mirror 36, and two lenses 34, which convert the irradiated laser light into parallel light.
39. The two lenses 34 and 39 are arranged between the mirror 36 and the circuit board 10. A cavity 12 is recessed in the circuit board 10, and there is a step between the inner lead 13 and the cavity 12.

In general, the irradiation position with respect to the optical path length of the circuit board 10 changes with the increase in the number of layers of the circuit board 10, so that a step is generated within one pulse of the laser light, and high-precision surface treatment becomes difficult. Become. Therefore, in this embodiment, the laser beam is set so that it enters the circuit board 10 vertically.
The optical system was arranged such that the lenses were combined and the energy density was constant even with respect to the steps of the circuit board 10. Assuming that the focal lengths of the two lenses 34 and 39 are f1 and f2 and the distance is L, the two lenses 34 and 39 are arranged so as to satisfy the following relationship.

F1 + f2 = L Here, since the laser beam is perpendicularly incident on the circuit board 10, even if the circuit board 10 has a step, a highly accurate surface treatment can be performed. Actually, when a lens having a focal length of f1 = 400 and f2 = 100 with respect to a step of 1 mm was used, a highly accurate surface treatment could be performed up to a step of 2 mm.

FIGS. 15 to 17 show an embodiment in which the laser irradiation position is detected and the position is corrected. In general, in a laser optical system, an optical path length changes due to a change in ambient temperature or a change with time, and thus a laser irradiation position may change.
Also, depending on the discharge state of the laser oscillator and changes in the resonator,
The processing position may be different due to a change in the laser emission position. Therefore, in these embodiments, the laser irradiation position is directly observed on the circuit board 10 and correction is made so that the irradiation position changes when the irradiation position changes.

The embodiment shown in FIG. 15 shows a case where the circuit board 10 is moved to fix the irradiation position of the laser beam. This surface treatment apparatus includes a mask 38 and a detector 50 disposed on an XY table 60 and having a sensitivity characteristic to the wavelength of excimer laser light. In addition,
The lens 34 has the same function as the lens 34 (FIG. 1) in FIG. The detector 50 is arranged so that the irradiation position can be seen. Other configurations are the same as those of the embodiment shown in FIG. The detection and correction timing may be performed, for example, once per hour.

When the KrF excimer laser is irradiated, the detector 50 and its optical system should preferably be of an ultraviolet type. Here, when the irradiation position is shifted in the field of view of the detector 50, the position of the XY table 60 may be corrected according to the shift amount. The embodiment shown in FIG. 16 shows a case where the circuit board 10 is fixed by scanning with laser light. This surface treatment apparatus is obtained by adding a detector 50 to the apparatus of the embodiment shown in FIG. The detector 50 includes a scanner control system 5 that controls the galvanometer mirrors 36 and 37.
The rotation is controlled in synchronism with 1. When the irradiation position changes, the shift amount is detected, and the irradiation position is corrected by the scanner control system 51 according to the detected shift amount.

FIG. 17 shows an embodiment in which an ordinary visible light camera is used as a detector instead of a special detector such as an ultraviolet detector. This surface treatment apparatus uses He-Ne laser light (wavelength 633n), which is visible light for irradiation position detection.
m), and further includes a detection laser irradiation device 52 for irradiating m), a mirror 54, a mirror 53, and a detector 50. The mirror 54 is disposed so as to face the detection laser irradiation device 52,
It transmits e-Ne laser light and reflects KrF excimer laser light. The mirror 53 is arranged facing the laser irradiation device 30 and reflects the excimer laser light toward the mirror 54. The detector 50 comprises, for example, a CCD camera,
The laser irradiation position is arranged so as to be the center in the visual field. Note that the two irradiation devices 3 are set so that the optical axis of the laser irradiation device 30 and the optical axis of the detection laser irradiation device 52 match.
0 and 52 are arranged.

Here, since the visible light is applied to the laser irradiation position, the cost of the detector is reduced and the irradiation position can be easily detected. Further, even if the wavelength of the processing laser light changes, the irradiation position can be detected reliably. FIG.
Shows an example in which plating adhesion can be evaluated by performing surface treatment with a laser beam.

In the circuit board 10 in which the conductor portion is formed by a plurality of plating layers, when the adhesion between the plating layers is weakened by the impurities 26, the plating is peeled off by laser irradiation (FIG. 18B). Also, if impurities are present between the plating layers even if they are not peeled, they will diffuse to the plating surface in the long term, and the electrical bonding reliability of the circuit board will be reduced. Thus, by setting the irradiation energy density and the number of times of laser irradiation, it becomes possible to evaluate the plating adhesion of the circuit board by laser light irradiation.

In this embodiment, in order to simultaneously evaluate the surface treatment and the plating adhesion of the circuit board 10 using the apparatus shown in FIG. 1, an irradiation energy density of 1.0 to 1.4 J using a KrF excimer laser. / Cm ² , laser irradiation frequency 1
Evaluation of plating adhesion was performed under irradiation conditions of 5 shots. As shown in FIG. 18, the circuit board 10 has a structure in which a copper foil 14 is adhered on a resin substrate 11 made of a glass cloth substrate-modified polyimide resin, and an electrolytic copper plating layer 15, a nickel plating layer 16, and a gold plating Layers 17 were each laminated. The thickness of each plating layer is 10 μm for the copper plating layer 15, 5 μm for the nickel plating layer 16, and 1 μm for the gold plating layer 17.
The place where the impurities 26 are attached and the plating is peeled off is mainly between the gold plating layer 17 and the nickel plating layer 16.

When laser irradiation is performed under such conditions, the surface can be modified to improve the electrical bonding reliability, and the plating adhesion can be evaluated. Can be sorted out as good products Here, laser irradiation makes it possible to detect impurities and defects between plating layers, which were difficult to detect in the past, and to detect in advance low-reliability circuit boards that are difficult to maintain for a long period of time. Reliability can be improved. Further, since the quality inspection can be performed simultaneously with the surface modification, the productivity is also improved.

[0065]

In the method for treating the surface of a circuit board according to the present invention, by irradiating the circuit board with a short-pulse laser beam, the energy of the laser beam can be applied only to the surface of the conductor section. It is possible to remove foreign substances on the conductor surface without affecting the area other than
Without forming intermetallic compounds between multiple metal material layers, only the surface of the conductor can be melted to eliminate pinholes and irregularities, making the surface smoother and improving the electrical connection reliability of the conductor surface. it can.

The outermost surface of the conductor is made of gold having a thickness of 0.2 μm or more, the laser beam irradiation energy density in the laser irradiation step is 0.6 to 3.0 J / cm ² , and the number of laser beam irradiations is 1 If the number of times is up to 50 times, even if a plurality of metal materials are stacked, foreign matter on the surface of the conductor portion can be removed and the surface of the conductor portion can be smoothed without affecting the metal material stacked under the gold.

If the surface of the conductor is melted with the second laser light after removing foreign matters such as stains by organic substances on the surface of the conductor with the first laser light, the electrical connection reliability can be further improved. The first laser beam has an irradiation energy density of 0.2 to
An excimer laser beam of 0.6 J / cm ² , and the second laser beam has an irradiation energy density of 0.6 to 3.0 J / cm 2.
^{In the case} of the excimer laser light of No. ² , foreign substances can be removed by the excimer laser light having a low intensity without affecting the circuit board thermally, and then the surface of the conductor can be melted by the excimer laser light having a high intensity, and the electrical connection reliability can be improved. Performance can be further improved.

If laser light irradiation is performed in a reduced-pressure atmosphere, the collision between the particles scattered by the irradiation of the region other than the conductor and the ambient gas is reduced, and the adhesion of the scattered particles to the conductor can be suppressed. For this reason, even if the conductor portion and the other region are irradiated with the laser beam over a large area, the electrical connection reliability can be secured.

When a laser beam is irradiated in a plasma atmosphere, foreign matter adhering to the optical window is removed by collision of gas ionized by the plasma, and scattered particles are gasified and exhausted to the optical window. Is reduced, and deterioration of the laser transmittance of the optical window is suppressed. In addition, the scattered matter slightly attached to the conductor surface due to the collision of the ionized gas can be removed, and the electrical connection reliability can be further improved.

If the amount of generated plasma is controlled, a small amount of scattered matter adhering to the surface of the circuit board can be reliably removed, and the reliability of electrical connection can be further improved. If a gas flow is formed in the vicinity of the optical window under a reduced-pressure atmosphere, scattered substances are less likely to adhere to the optical window, and the laser transmittance of the optical window is less likely to deteriorate. Therefore, a laser beam having a uniform energy density is always applied to the circuit board, and high quality surface treatment can be performed.

If the conductor portion is larger than the irradiation area and the laser light is irradiated from the mixed portion first, particles scattered from the region other than the conductor portion in the mixed portion adhere to the conductor portion excluding the mixed portion even if they adhere. The scattered particles can be reliably removed, and the electrical connection reliability can be improved. By scanning with a laser beam, a large area can be processed at a high speed without moving the circuit board, and the surface can be processed only at an arbitrary position on the circuit board by limiting the scanning region.

If a mask is arranged, laser light is not irradiated to portions other than the conductor portion, and the generation of scattered particles can be suppressed. In addition, by moving the mask and lens in synchronization with the mirror, the mirror can be driven. An imaging position that changes according to a change in the optical path length can always be set on the substrate, and highly accurate surface treatment can be performed.

If the two lenses are arranged apart from each other by the sum of the focal lengths, the laser beam can be made incident perpendicularly on the circuit board, and even if a mask is arranged, the imaging blur will be small.
Even if there is a step on the circuit board, surface treatment can be performed with high accuracy. If the irradiation position is detected and the irradiation position is corrected accordingly, highly accurate surface treatment can always be performed.

If, for example, visible light is used as the detection laser beam, the irradiation position can be detected by an inexpensive detection means such as a CCD camera, so that the irradiation position can be easily detected at low cost.
By performing the quality inspection simultaneously with the surface treatment, the productivity can be improved and the reliability of the circuit board can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a surface treatment apparatus used for carrying out a method of the present invention.

FIG. 2 is a plan view illustrating an example of a circuit board.

FIG. 3 is an enlarged cross-sectional view of a circuit board.

FIG. 4 is a graph showing a repetition period and a pulse width of an embodiment in which laser irradiation is repeated with short pulses.

FIG. 5 is a schematic view showing an irradiation procedure of an embodiment in which laser irradiation is performed twice.

FIG. 6 is a schematic sectional view showing an embodiment in which laser irradiation is performed in a reduced-pressure atmosphere.

FIG. 7 is a schematic sectional view showing an embodiment in which laser irradiation is performed while generating plasma in a reduced-pressure atmosphere.

FIG. 8 is a diagram showing an influence when a flying matter adheres to a cavity.

FIG. 9 is a schematic cross-sectional view showing an embodiment in which laser irradiation is performed while generating controlled plasma in a reduced-pressure atmosphere.

FIG. 10 is a schematic cross-sectional view showing an embodiment in which laser irradiation is performed while blowing gas around an optical window in a reduced-pressure atmosphere.

FIG. 11 is a flowchart illustrating an embodiment in which laser irradiation is performed first on an inner lead in a conductor portion.

FIG. 12 is a schematic sectional view showing an embodiment in which a laser beam is scanned by a galvano scan optical system.

FIG. 13 is a schematic cross-sectional view showing an embodiment in which an optical system including a mask and a lens is moved and laser light is scanned.

FIG. 14 is a schematic cross-sectional view showing an embodiment in which surface treatment can be performed accurately even when there is a step in the conductor portion.

FIG. 15 is a schematic view showing an embodiment for detecting an irradiation position and correcting the irradiation position.

FIG. 16 is a schematic view showing another embodiment for detecting an irradiation position and correcting the irradiation position.

FIG. 17 is a schematic diagram showing an embodiment in which an irradiation position is detected by visible light and the irradiation position is corrected.

FIG. 18 is a cross-sectional view for explaining an example in which surface treatment is performed while evaluating plating adhesion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Vacuum pump 4 Optical window 7 Plasma electrode 10 Circuit board 11 Resin base material 12 Cavity 13 Inner lead 17 Gold plating layer 18 Nozzle 19 Gas cylinder 20 Dirt 30 Laser irradiation device 31 Laser scanning mechanism 34, 39 Lens 36, 37 Galvano mirror 38 mask 50 detector 52 detection laser irradiation device

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshimitsu Nakamura 1048 Odomo Kadoma, Kadoma City, Osaka Inside Matsushita Electric Works, Ltd. (56) References JP-A-5-136569 (JP, A) JP-A-4-99292 (JP, A) JP-A-1-266983 (JP, A) JP-A-5-235520 (JP, A) JP-A-6-170570 (JP, A) JP-A-5-198950 (JP, A) ( 58) Fields surveyed (Int. Cl. ⁷ , DB name) H05K 3/00-3/26 B23K 26/00

Claims (13)

(57) [Claims] 1. A method of treating a surface of a circuit board, comprising: irradiating a laser beam to a circuit board having a substrate made of an organic material and a conductor formed by laminating a metal material on the substrate to treat the conductor. Wherein the outermost surface of the conductor is made of gold having a thickness of 0.2 μm or more.
Ri, irradiation with laser light of a short pulse from the light source with respect to the circuit board
Radiation energy density 0.6-3.0 J / cm ² , laser light
Concave and irradiation at times 1-50 times the surface of the conductor portion of the
A method for treating a surface of a circuit board, comprising a laser irradiation step (a) for smoothing convexities . 2. The method according to claim 1, further comprising : irradiating the circuit board with a short pulse laser beam from a light source before the laser irradiation step (a).
Irradiation at an irradiation energy density of 0.2 to 0.6 J / cm ²
Laser irradiation for removing foreign substances attached to the surface of the conductor portion
The method for treating a surface of a circuit board according to claim 1, further comprising a step (b) . 3. The method according to claim 1, further comprising the step of placing the circuit board under a reduced pressure atmosphere, wherein in each of the laser irradiation steps, the circuit board placed under the reduced pressure atmosphere is irradiated with the laser light through an optical window. Item 3. The method for treating a surface of a circuit board according to item 1 or 2 . 4. The surface treatment method for a circuit board according to claim 3 , further comprising a plasma generating step of generating plasma under said reduced pressure atmosphere. 5. The method for processing a surface of a circuit board according to claim 4 , further comprising a plasma control step of controlling power of plasma generated in said plasma generation step. Wherein said near the optical window in a reduced pressure atmosphere further comprising a gas flow formation step of forming a gas stream, the surface treatment method of a circuit board according to any of claims 3 to 5. 7. The method according to claim 1, further comprising, before the laser irradiation, determining whether or not the conductor portion of the circuit board is larger than a single laser irradiation area. When it is determined that the larger than the mixed portion, the mixed portion of the conductor portion mixed with the non-conductor portion on the circuit board is irradiated with laser light, and thereafter, the conductor portion excluding the mixed portion is irradiated with laser light. 2. The method for treating a surface of a circuit board according to claim 1. 8. The surface treatment method for a circuit board according to claim 1, wherein in the laser irradiation step, two mirrors are driven by the laser light irradiated from the light source to scan the laser light on the circuit board. . 9. In the laser irradiation step, a mask disposed between the light source and the mirror and defining an irradiation position, and a lens for forming an image of the mask on the circuit board are formed by the mirror. The surface treatment method for a circuit board according to claim 8 , wherein the circuit board is moved in an optical axis direction in synchronization with the method. 10. In the laser irradiation step, a laser beam is irradiated between the light source and the circuit board via two lenses arranged at a distance of a sum of their focal lengths. The surface treatment method for a circuit board according to the above. 11. An irradiation position detecting step for detecting an irradiation position of the laser light irradiated on the circuit board in the laser irradiation step, and a correcting step for correcting the irradiation position of the laser light according to the detected irradiation position. The method for treating a surface of a circuit board according to claim 1. 12. In the irradiation position detecting step, a detection laser beam emitted from a detection light source for irradiating the circuit substrate with the detection laser beam is irradiated to the same position as the laser beam emitted from the light source. by detecting the irradiation position of the detected laser light, the surface treatment method of a circuit board according to claim 1 1, wherein. 13. An evaluation step of evaluating a plating adhesion based on a state of the conductor after the conductor is irradiated with the laser beam in the laser irradiation step, wherein the conductor of the circuit board is composed of a plurality of plating layers. The surface treatment method for a circuit board according to claim 1, further comprising: