JPH10117058A - Method for working printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work method for securely and electrically connecting an inner layer circuit and an outer layer circuit. SOLUTION: At the time of burning and removing an insulating layer 3 by irradiating it with laser light, the peripheral walls 74 of a via hole (non- through hole) 7A are obliquely formed toward a center by making them face downward. Although the residual material 3B of the insulating layer 3 exists on an upper face 21 of the inner layer circuit 2 at the bottom of the via hole 7A, the resin residual material 3B on the upper face 21 of the inner layer circuit 2 is dissolved and removed, by cleaning the inner part of the via hole 7A solution which dissolves the resin of permanganate solution. Then, the upper face 21 of the inner layer circuit 2 is cleaned, and the via hole 7A is plated 70. Then, an outer circuit 71 is formed on the outer surface of the insulating layer 3 by etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a printed circuit board having a non-through hole in a multilayer printed circuit board.

[0002]

2. Description of the Related Art For substrates used in electronic devices, LSI packages and printed boards of various shapes and structures have been devised in order to meet demands for smaller and thinner electronic devices. Therefore, the diameter of the non-through hole or the through hole formed in the printed circuit board tends to be small. Conventional drilling of printed circuit boards is mainly performed by drilling, and the hole drilling is usually 0.1 mmφ in the hole minimum diameter is the minimum processing limit,
Generally, the processing limit for mass production is about 0.3 mmφ. As shown in FIG. 6, a hole is formed in a printed board by a drill d at an appropriate position on a board having copper foils b and c adhered to upper and lower surfaces of a plate-shaped insulating layer a made of resin or the like. (See (a)), plating f is applied to the surfaces of the copper foils b and c and the inner surface of the through hole e to electrically connect the copper foils b and c on the upper and lower surfaces of the insulating layer a (b). Then, the upper and lower surfaces of the insulating layer a are etched to perform plating f and copper foils b and c.
Are removed to form circuit patterns b ₁ and c ₁ (see C) connected to the upper and lower surfaces of the insulating layer a by the plating layer f ₁ .

FIG. 7 shows a multi-layer printed circuit board having a non-through hole. 2 made of resin, etc.
Copper foils b ₁ , c ₁ and b ₂ , c ₂ are attached to the upper and lower surfaces of the insulating layers a ₁ and a ₂ respectively, and a drill (not shown)
Thereby, holes e ₁ and e ₂ penetrating the insulating layers a ₁ and a ₂ respectively are formed (see (a)), and the copper foils b ₁ , c ₁ and b
₂ , c ₂ and the inner surfaces of the through holes e ₁ , e ₂ are plated f ₁ , f 2
₂ by subjecting the insulating layer a ₁ and is respectively electrically connected to the copper foil b ₁ of the upper and lower surfaces c ₁ and b ₂ and c ₂ of a ₂ (see B), thereafter the insulating layer a _1, a ₂ (7, insulating layer a ₁ is a top, a ₂ the lower surface only) top and bottom surfaces or one surface a part of the plating f _1, f ₂ and the copper foil b _1, c ₁ and b _2, c ₂ are etched After removal, the upper and lower surfaces or one surface of the insulating layers a ₁ and a ₂ (in FIG. 7, the insulating layer a ₁ is the upper surface and a ₂ is the lower surface only), and the plating layers f ₁₁ and f ₂₂ are provided with copper foil on the opposite side. Circuit patterns b ₁₁ and c ₂₂ (see c) connected to c ₁ and b ₂ are formed. The insulating layers a ₁ and a ₂ are connected to each other with the surfaces provided with the circuit patterns b ₁ and c ₂ facing each other and an adhesive sheet g such as a prepreg is interposed between the insulating layers a ₁ and a ₂ to form a multilayer structure. Form a printed circuit board. At this time, the holes e ₁ and e ₂ become non-through holes by closing one of the holes with the adhesive sheet g.

In order to further increase the density, 0.3 mmφ
A printed circuit board having the following non-through holes is required, so that hole processing by a photo method in which an insulating layer is formed of a photosensitive (photocurable) resin or hole processing by a laser beam is performed from conventional drilling. became. The hole processing by the photo method will be described with reference to FIG. 8. The one shown in (a) uses a photocurable resin, and an inner layer formed of copper foil on both surfaces of an insulating layer a made of a normal resin. A circuit h is provided, and insulating layers a ₀ , a ₀ made of a photocurable resin sandwich the inner layer circuit h.
Is bonded to both surfaces, a mask for shielding light at a predetermined position j is arranged, and the resin is cured by irradiating light k such as ultraviolet light, and then a portion m corresponding to the light shielding position j, that is, a portion m that is not cured is removed. Then, after the non-through hole n in which the inner layer circuit h is exposed is formed at the bottom (see C), the entire inner wall and bottom wall of the non-through hole n (exposed surface of the inner layer circuit h) and the entire outer surface of the insulating layer a are exposed. After the plating p is applied, a part of the plating p is removed by etching, and an outer layer circuit q is formed (see d). On the other hand, drilling using laser light (see b)
Irradiates a laser beam r from the surface of the insulating layer a to form an inner layer circuit h.
Is exposed.

[0005]

However, in the above-mentioned conventional method for processing a printed circuit board, a part of the insulating layer a may remain as a residual film s on the inner layer circuit h (see FIG. 9). In the case where the remaining film s of the insulating layer a is present on the inner layer circuit h as described above, even if the non-through hole n is plated p in order to connect the inner layer circuit h to the outer layer circuit q provided on the surface. As a result, a residual film s exists between the plating p and the inner layer circuit h (see FIG. 10), and there has been a problem that connection to the upper surface of the inner layer circuit h cannot be made or connection reliability is impaired. Further, as shown in FIG. 11, since the inner peripheral wall of the non-through hole n is formed substantially vertically, plating p is applied to the upper surface of the inner layer circuit h, the inner peripheral wall of the non-through hole n, and the upper surface of the insulating layer a. Then, it is difficult to obtain a uniform plating layer from the upper surface of the inner circuit h, which is the bottom of the non-through hole n, to the inner peripheral wall of the non-through hole n, and a plating layer p ₁ provided on the upper surface of the inner circuit h, plating p the junction between the plated layer p ₂ attached to the inside wall of non-through holes n is not sufficiently precipitated, plating p is reduced, or the gap at the junction of the plating layer p ₁ and the plating layer p ₂ There is a problem in that the reliability of the electrical connection is impaired due to the formation of the electrical connection. Furthermore, if the output of the laser light r is increased to prevent the residual film s from being generated, it is possible to remove the residual film s to some extent, but it is extremely difficult to remove all of the residual film s and the output of the laser light r Becomes larger, the peripheral wall of the non-through hole n is formed more vertically, and when the plating p is applied, the non-through hole n
Plating p does not sufficiently precipitate at the joint between the peripheral wall and the bottom surface of
There has been a problem that the plating p becomes thin and the reliability of electrical connection is impaired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of processing a printed circuit board capable of securely connecting an inner layer circuit and an outer layer circuit by a non-through hole in a multilayer printed circuit board.

[0007]

In order to achieve the above object, a method for processing a printed circuit board according to the present invention comprises the steps of: forming a substrate, an inner layer circuit provided on the surface of the substrate, and a surface of the substrate including the inner layer circuit. A method for processing a printed circuit board having an insulating layer to cover and an outer layer circuit provided on an outer surface of the insulating layer, wherein a non-through hole exposing the upper surface of the inner layer circuit is formed at the bottom by irradiating a laser beam. After the installation, the non-through hole is washed to remove the remaining insulating layer, so that the resin residue on the surface of the inner layer circuit can be removed, and the contact between the plating and the inner layer circuit is ensured. And the reliability of the electrical connection can be improved. Also, weaken the output of the laser light,
By inclining the peripheral wall of the non-through hole toward the bottom toward the center, the angle formed between the bottom surface of the non-through hole (the upper surface of the inner layer circuit) and the peripheral wall becomes obtuse. In addition to dissolving the resin residue, the throwing power of the plating is improved, and the plating having a uniform thickness can be obtained on the inner wall of the non-through hole.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. In FIG. 5, a printed circuit board to which the processing method of the present invention is applied will be described. An inner layer circuit 2 is previously formed on one side surface of the printed circuit board 1, a resin layer 3 serving as an insulating layer is provided at an appropriate position thereon, and a pad 20 which is a conductor of the inner layer circuit 2 is exposed. It is covered with an insulating layer 3.

In this embodiment, the IC bare chip 4 is placed between the pads 20 of the inner layer circuit 2 which is arranged to face each other.
The IC bare chip 4 and the pad 20 are connected by bonding using the bonding wire 5. Note that the pads 20 of the inner layer circuit 2 are not limited to those provided on both sides of the IC bare chip so as to be opposed to each other. The good is natural.

A step due to the thickness of the insulating layer 3 is formed around the IC bare chip 4 to form a flow prevention dam. When the sealing agent 6 such as resin is poured over the portion where the IC bare chip 4 is mounted, This prevents the sealant 6 from flowing out to unnecessary parts. The sealant 6 covering the portion where the IC bare chip 4 is mounted is poured in, and the IC bare chip 4, the bonding wires 5 and the pads 20 are covered and protected by the sealant 6. In order to connect the outer surface of the insulating layer 3 and the inner layer circuit 2, via holes 7 are formed at predetermined positions of the insulating layer 3.
After the inner circuit 2 is exposed in the via hole 7, the inner circuit 2 in the via hole 7 and the outer surface of the insulating layer 3 are electrically connected by plating 70,
An outer circuit 71 connected to the plating 70 is provided on the outer surface of the insulating layer 3.
Is provided.

The outer circuit 71 has external pads 72 on the outer surface of the insulating layer 3 for connecting to electronic components and the like.
The legs of the electronic component 8 are soldered to the external pad 72 and the electronic component mounting pad 73 separately provided on the outer surface of the insulating layer 3. In this embodiment, the case where the IC bare chip is provided only on one side of the printed board has been described. However, the inner layer circuits are provided on both side faces of the printed board, and the IC bare chip is provided in the same manner as in the above embodiment. Of course, it can be provided. Further, instead of the electronic component 8, an IC bare chip can be connected.

An example of the processing method of the present invention will be described with reference to the drawings. In FIG. 2, an inner layer circuit 2 which is a conductor circuit adapted to component mounting is provided on the surface of a printed circuit board 1.
Is formed by etching or the like, and an insulating resin is applied thereon to form an insulating layer 3 over the entire surface of the substrate 1, and then a necessary portion of the insulating layer 3 is removed. A rectangular portion on which the IC bare chip 4 is mounted as a portion for removing the insulating layer;
The portion of the inner circuit 2 to be exposed (the via hole 7 of the inner circuit 2 and the like) is determined.

Here, processing of the via hole 7 will be described as a portion where the inner layer circuit 2 needs to be exposed at the bottom. Insulating layer 3 at the site where via hole 7 is formed
Is irradiated with a laser beam R having a normal output or a reduced output from the laser irradiation device 9 to burn off the removed portion 3A, and the upper surface 21 of the inner layer circuit 2 is formed at the bottom. Exposed via hole (non-through hole) 7
A is formed (see FIG. 3).

Here, an example of laser processing will be described. In laser processing for forming a hole having a diameter of 0.1 to 0.2 mm, the wavelength of a laser beam is a CO ₂ gas laser of 9.2 to 10.6 μm and an output of 10 W to 300 W. Laser light output from a laser oscillator having
Irradiation is performed on the insulating layer 3 with a pulse diameter of 16 μs to 80 μs on the insulating layer 3 with a spot diameter of about 0.2 mmφ. The continuous output at this time is 2.0 W to 0.3 W, and the burnout depth of the insulating layer resin per pulse is about 0.01 to 0.05 mm, and 2 pulses to 2 W
By forming one non-through hole 7A with 10 pulses, from the upper surface of the insulating layer 3 toward the upper surface of the inner layer circuit 2,
The peripheral wall 74 of the non-through hole 7A can be inclined toward the center of the hole.

Note that the inclination angle θ of the peripheral wall 74 is
Is the angle formed by the peripheral wall 74 with respect to the normal VL to the upper surface of
θ = 15 ° to 25 ° is suitable (see FIG. 4), and θ is 1
When the angle is smaller than 5 ° (θ <15 °), the peripheral wall becomes almost vertical, and it becomes difficult to uniformly form the plating layer. When the angle θ is larger than 25 ° (θ> 25 °), the diameter of the bottom becomes small. If they are the same, there is a problem that the upper end opening of the hole becomes excessively large and the printed circuit board becomes large. Conversely, if the upper end openings are the same, there is a problem that the diameter of the bottom becomes small, the connection area becomes small, and there is a possibility that a defect occurs in the electrical connection.

As described above, when the normal output or low output laser beam R is applied to burn and remove the portion 3A of the insulating layer 3 (see FIG. 2), the peripheral wall 74 of the via hole 7A is removed.
Are formed diagonally downward toward the center, that is, inclined so that the area of the bottom is smaller than the upper opening (see FIG. 3), and the permanganate is formed in the via hole 7A. The inside of the via hole 7A is washed by spraying a solution that dissolves the resin such as a solution or by immersing it in a solution that dissolves the resin such as a permanganate solution.

In the case of only laser processing, the hole 7 for the via hole is used.
Residues 3B of the resin forming the insulating layer 3 are present on the upper surface 21 of the inner circuit 2 at the bottom of A (see FIG. 3), but the resin such as permanganate solution is dissolved in the via hole 7A. By washing with a solution, the resin residue 3B on the upper surface 21 of the inner circuit 2 is dissolved and removed, and the upper surface 21 of the inner circuit 2 is removed.
After cleaning (see FIG. 4), as shown in FIG. 1, plating 70 is applied to the via hole 7A, and an outer layer circuit 71 is provided on the outer surface of the insulating layer 3, and the plating 70 and the outer layer circuit 71 are provided. To electrically connect the inner layer circuit 2 and the outer layer circuit 71 to form a via hole 7.

With this configuration, the resin residue 3B on the upper surface 21 of the inner layer circuit 2 can be removed, the contact between the plating 70 and the inner layer circuit 2 can be ensured, and the reliability of the electrical connection can be improved. Performance can be improved. In addition, since the peripheral wall 74 of the via hole 7A is inclined, the angle formed between the bottom surface (the upper surface 21 of the inner layer circuit 2) and the peripheral wall 74 becomes obtuse. Thing 3B
Can be dissolved, the throwing power of the plating 70 is improved, and a plating having a uniform thickness can be obtained.

[0019]

EXAMPLE By forming a hole having a shape in which the peripheral wall is inclined by laser light, cleaning and melting are facilitated, the plating thickness on the surface of the insulating layer, the peripheral wall of the hole and the bottom of the hole are made uniform, and the residual film is sufficiently removed. The following results were obtained by dissolving and washing.
In each of the tests described below, a printed circuit board having a durable electrical connection of 100 cycles or more or 500 hours or more was obtained. [Example product pattern]: Insulation layer thickness 80 μm Hole diameter 150 μm (Insulation layer surface opening diameter 170 μm) (Hole bottom diameter 140 μm) Plating thickness 20 μm (1) Thermal shock test (in liquid) a. Repeat the following steps sequentially (→→→
→→ ・ ・ ・), and repeat as 100 cycles as 1 cycle. Immerse in liquid at -40 ° C for 30 minutes Leave at room temperature for 5 minutes Immerse in liquid at 125 ° C for 30 minutes Leave at room temperature for 5 minutes b. The following operations are sequentially repeated, and → is defined as one cycle, and 100 cycles are repeated. Immersion in a liquid at -65 ° C for 30 minutes Immersion in a liquid at 125 ° C for 30 minutes (2) High-temperature storage test (in the air) The device is left in an atmosphere at a temperature of 125 ° C for 500 hours. (3) Low temperature test (air) The sample is left in an atmosphere at a temperature of -40 ° C for 500 hours. (4) Constant Temperature and Humidity Test (Air) The sample is left for 500 hours in an atmosphere at a temperature of 85 ° C. and a humidity of 85%. (5) Oil dip test The following operations are sequentially repeated, and 100 cycles are repeated with → as one cycle. Immerse in oil at a temperature of 260 ° C for 10 seconds. Immerse in oil at a temperature of 10 ° C for 10 seconds. Note) The time required for movement with work is 15 seconds.

[0020]

Since the present invention is configured as described above, it has the following effects. After irradiating a laser beam to form a non-through hole exposing the upper surface of the inner layer circuit at the bottom, the non-through hole is washed and the remaining insulating layer is removed to remove the resin on the surface of the inner layer circuit. Residue can be removed, and contact between the plating and the inner layer circuit can be ensured. Also, by weakening the output of the laser beam and inclining the peripheral wall of the non-through hole toward the center toward the bottom, the angle formed between the bottom surface of the non-through hole (the upper surface of the inner layer circuit) and the peripheral wall becomes obtuse. As a result, the cleaning property is improved, sufficient resin residue can be dissolved, the throwing power of the plating is improved, the plating having a uniform thickness can be obtained, and the reliability of the electrical connection can be obtained. Can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a printed circuit board according to the present invention.

FIG. 2 is a cross-sectional view of the printed circuit board of the present invention during laser processing.

FIG. 3 is a cross-sectional view of the printed circuit board of the present invention at the end of laser processing.

FIG. 4 is a sectional view of the printed circuit board of the present invention after cleaning.

FIG. 5 is a cross-sectional view illustrating an example of a surface-mount LSI package to which the present invention is applied.

FIG. 6 is an explanatory view showing a conventional drilling process.

FIG. 7 is an explanatory view showing processing of a conventional non-through hole.

FIG. 8 is an explanatory view showing a conventional photo method and laser processing.

FIG. 9 is a cross-sectional view of a conventional printed circuit board at the end of laser processing.

FIG. 10 is a cross-sectional view of a conventional printed circuit board when plating is completed.

FIG. 11 is a cross-sectional view of a conventional printed circuit board when plating is completed.

[Explanation of symbols]

1 substrate, 2 inner layer circuit, 3 insulating layer, 4 IC bare chip 5 bonding wire, 6 sealant, 7 via hole, 20 pad 71 outer layer circuit

Claims (2)

[Claims] A substrate, an inner layer circuit provided on the surface of the substrate, an insulating layer covering the surface of the substrate including the inner layer circuit,
A method of processing a printed circuit board having an outer layer circuit provided on an outer surface of an insulating layer, the method comprising: irradiating a laser beam to form a non-through hole exposing an upper surface of an inner layer circuit at a bottom portion; A method for processing a printed circuit board, comprising cleaning a through hole to remove a remaining insulating layer. 2. The method for processing a printed circuit board according to claim 1, wherein the output of the laser beam is reduced, and the peripheral wall of the non-through hole is inclined toward the center toward the bottom.