JPH0883971A - Filling ink for printed-wiring board - Google Patents

Abstract

PURPOSE: To obtain a filling ink which is excellent in a thermal shock-resistant property, which prevents the generation of a crack in a solder resist film covering a part near a boundary between a pattern circuit and the filling ink and which can ensure airtightness inside a through hole. CONSTITUTION: A filling ink 1 is composed of a mixture of an epoxy resin and a silica powder. The filling ink 1 is filled into the inside of a through hole 90 in a printed-wiring board 10 and into a gap between adjacent pattern circuits 61, 62. The average particle size of the silica powder is set at 0.001 to 0.50μm. It is desirable that the silica powder in 0.3 to 5wt.% is contained in the filling ink. It is desirable that a coupling treatment is executed to the surface of the silica powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hole filling ink for a printed wiring board, and more particularly to a hole filling ink for filling the inside of through holes and the gaps between pattern circuits.

[0002]

2. Description of the Related Art A ball grid type printed wiring board is provided with through holes for electrically connecting each pattern circuit provided on the front and back sides or for dissipating heat. As shown in FIG. 14, this through hole 90 is formed so as to penetrate through the insulating substrate 9 that constitutes the printed wiring board. The metal plating film 3 is applied to the inner wall of the through hole 90.

The through hole 90 is filled with hole filling ink 19. The hole-filling ink 19 prevents flux, solder cleaning liquid, and the like from seeping out through the through holes 90 when the printed wiring board is soldered to the mother board, and the pattern circuit 61 and various electronic components provided on the front surface of the insulating substrate 9. Plays a role in preventing pollution. The hole filling ink 19 is an epoxy resin impregnated with a filler, and as shown in FIG. 15, in the through hole 90 having a high aspect ratio (the thickness of the insulating substrate 9 (a) / the diameter of the through hole 90 (b)). Even when used, it exhibits excellent thermal shock resistance.

Further, as shown in FIG. 14, the gap filling 60 between adjacent pattern circuits 61 is also filled with the filling ink 17. The filling ink 17 is used for filling the solder resist film 7 in order to form a flat surface in the gaps 60 between the pattern circuits 61 without forming dents.

[0005]

By the way, there is a desire to simplify the manufacturing method of a printed wiring board by filling the hole filling inks 19 and 17 into the gaps 60 between the through holes and the pattern circuits in one step. There is.

Therefore, it is possible to fill the inside of the through hole 90 and the gap 60 between the pattern circuits 61 with the same kind of filling ink by one application, but it is suitable for any environment. Filling ink has never existed before. That is, when the filling ink for filling the inside of the through hole is also filled between the pattern circuits, as shown in FIGS. 16A and 16B, during the heat cycle, the pattern circuit 61 and the filling ink 17 are filled. The solder resist film 7 covering the boundary with
May occur.

On the contrary, when the through holes are filled with the filling ink for filling the gaps 60 between the pattern circuits 61, as shown in FIG. 15, during the heat cycle, the filling ink in the through holes is filled. A crack 199 is generated at. Therefore, the hermeticity of the through hole 90 cannot be maintained, and the pattern circuit on the insulating substrate 9, the semiconductor chip, and the like may be damaged such as corrosion.

In view of such conventional problems, the present invention is excellent in thermal shock resistance, prevents cracks in the solder resist film covering the upper surface of the pattern circuit and the hole-filling ink, and improves the hermeticity in the through hole. The aim is to provide a hole-filling ink for printed wiring boards that can be secured.

[0009]

The present invention relates to a hole filling ink which is made of a mixture of epoxy resin and silica powder and is used for filling the inside of through holes in a printed wiring board and the gaps between adjacent pattern circuits. The silica powder has an average particle diameter of 0.001 to 0.050 μm in a hole-filling ink for printed wiring boards.

What is most noticeable in the present invention is that the filling ink has an average particle size of 0.001 to 0.050 μm.
That is, it is impregnated with silica powder. When the average particle diameter of the silica powder is less than 0.001 μm, the silica powder is liable to float, which may be difficult to handle, and the cost may increase. On the other hand, when the average particle diameter exceeds 0.050 μm, cracks occur in the filling ink in the through holes due to thermal shock, and it becomes difficult to maintain the airtightness between the front and back surfaces of the insulating substrate.

The silica powder is preferably contained in the hole filling ink in an amount of 0.3 to 5% by weight.
If the amount is less than 0.3% by weight, the strength of the filling ink decreases, and thermal shock may cause cracks in the filling ink in the through holes. On the other hand, if it exceeds 5% by weight, cracks are likely to occur in the epoxy resin due to the difference in thermal expansion between the silica powder and the epoxy resin in the ink for filling the gaps between the pattern circuits.

The surface of the silica powder is preferably subjected to a coupling treatment. By this,
The bonding strength between the silica powder and the epoxy resin is increased, and it is possible to prevent cracks from occurring in the epoxy resin near the silica powder even when a thermal shock is applied. Here, the coupling treatment is a treatment in which a coupling agent is added to and mixed with silica powder so that the surface of the silica powder forms a strong bond with an organic substance.

It is preferable that the inner wall of the through hole is covered with a metal plating film, and a roughened surface layer is formed on the surface of the metal plating film by a chemical surface treatment. In this case, the filling ink comes into close contact with the inner wall of the through hole. Therefore, even if a thermal shock is applied, the filling ink does not separate from the inner wall of the through hole. Therefore, the hermeticity in the through hole can be ensured more reliably.

As the chemical surface treatment, for example, a method of performing only blackening treatment, a method of sequentially performing blackening treatment and blackening reduction treatment, a method of sequentially performing blackening treatment, blackening reduction treatment and acid treatment, etc. There is.

As a method of performing only the blackening treatment, for example, the insulating substrate is dipped in a blackening treatment liquid in which sodium chlorite, trisodium phosphate, sodium hydroxide and the like are dissolved in water. . As a result, needle-like crystals are generated on the surface of the metal plating film. This crystal
A roughened surface layer is formed in the through holes and on the surface of the insulating substrate on the metal plating film.

As a method of sequentially performing the blackening treatment and the blackening reduction treatment, for example, the insulating substrate is immersed in the blackening treatment solution, and then sodium borohydride, sodium hydroxide, etc. are dissolved in water. The insulating substrate is immersed in the first reduction treatment liquid. Further, this is immersed in a second reduction treatment liquid in which sodium hydroxide, formaldehyde, methanol, etc. are dissolved in water. As a result, needle-like crystals are generated on the surface of the metal plating film, and the crystals are reduced.

As a method for sequentially performing the blackening treatment, the blackening reduction treatment and the acid treatment, for example, the insulating substrate is sequentially immersed in the blackening treatment liquid and the reduction treatment liquid, and then this is subjected to acid treatment. It is immersed in an acid treatment solution such as sulfuric acid. As a result, needle crystals are formed on the surface of the metal plating film, and the crystals are once reduced and then oxidized.

Next, the filling ink is filled in the inside of the through hole forming the roughened surface layer and the peripheral portion of the opening, and is cured. Next, the hole-filling ink protruding from the surface of the insulating substrate is polished and removed together with the roughened surface layer of the metal plating film on the surface of the insulating substrate by using a buff, a brush or the like. As a result, the surfaces of the metal plating film and the filling ink become smooth, and the entire surface of the insulating substrate becomes a smooth surface. Next, a pattern circuit is formed on the surface of the smooth insulating substrate.

[0019]

FUNCTION AND EFFECT In the hole filling ink according to the present invention, silica powder having the above average particle diameter is used. This silica powder has a smaller average particle size than the fillers used conventionally. Therefore, the silica powder can be uniformly dispersed in the hole-filling ink with a high density, and the strength of the hole-filling ink filled and cured can be improved.

When a thermal shock is applied to the filling ink, thermal stress is generated in the silica powder. This thermal stress is
The epoxy resin around the silica powder is absorbed by the epoxy resin due to the generation of minute cracks. Therefore, these minute cracks do not propagate throughout the epoxy resin. Therefore, in the through hole, no crack occurs in the whole filling ink. Therefore, the tightness of the through hole can be secured. Therefore, it is possible to prevent damage such as corrosion of the pattern circuit and the semiconductor chip on the insulating substrate.

In the gap between adjacent pattern circuits, the filling ink itself absorbs the stress of the solder resist film covering the boundary between the filling ink and the pattern circuit. Therefore, it is possible to prevent cracks from occurring in the solder resist film.

Therefore, according to the present invention, the thermal shock resistance is excellent, the generation of cracks in the solder resist film covering the upper surface of the pattern circuit and the filling ink is prevented, and the hermeticity in the through hole is secured. It is possible to provide hole filling ink for printed wiring boards.

[0023]

EXAMPLE A filling ink according to an example of the present invention will be described with reference to FIGS. As shown in FIG. 1, the printed wiring board 10 manufactured according to this example has through holes 90 penetrating the insulating substrate 9. The inner wall of the through hole 90 is covered with the metal plating film 3. The inside of the through hole 90 is filled with the filling ink 1. Further, pattern circuits 61 and 62 are formed on the front and back surfaces of the insulating substrate 9. The gap filling ink 1 is filled in the gap 60 between the adjacent pattern circuits 61 and the gap 60 between the adjacent pattern circuits 62.

Through hole 90 and pattern circuit 6 described above.
The filling ink 1 filled between 1 or 62 is made of a mixture of epoxy resin and silica powder. Silica powder is
The average particle diameter is 0.010 μm. The surface of silica powder is subjected to coupling treatment. Silica powder is
The filling ink contains 2% by weight.

The pattern circuit 6 is provided on the front surface of the insulating substrate 9.
1 and a die pad 63 for mounting a semiconductor chip are provided. A pattern circuit 62 and a heat dissipation pad 64 are provided on the back side surface of the insulating substrate 9. The die pad 63 and the heat radiation pad 64 are electrically connected to each other by the through hole 90 provided in the substantially central portion of the insulating substrate 9. Each pattern circuit 6 provided on the front and back surfaces of the insulating substrate 9
2, 1 and 62 are connected by the through hole 90 provided in the peripheral portion of the insulating substrate 9 as shown in FIG. The surface of the printed wiring board 10 excluding the bonding pad 610 and the motherboard mounting pad 620 is
It is covered with the solder resist film 7.

Next, a method of manufacturing a printed wiring board using the hole filling ink will be described with reference to FIGS. First, as shown in FIG. 3, through holes 90 are formed in the insulating substrate 9 having the copper foil 2 adhered to the front and back surfaces. Next, the metal plating film 3 is applied to the surface of the insulating substrate 9 and the inner wall of the through hole 90. The metal plating film 3 is copper.

Next, unnecessary portions of the copper foil 2 and the metal plating film 3 are removed by an etching resist method, and the pattern circuit 61, the bonding pad 610, and the die pad 63 are insulated on the front surface of the insulating substrate 9 by one-side insulation. A pattern circuit 62 and a heat dissipation pad 64 are formed on the back surface of the substrate 9.

Next, as shown in FIG.
The whole surface of the insulating substrate 9 including the inside of 0 is covered with the hole filling ink 1. Next, the filling ink 1 is cured by heating or ultraviolet irradiation.

Next, as shown in FIG. 5, the surface of the hardened hole-filling ink 1 is polished by a buff to form a pattern circuit 6
1, 62, the die pad 63, the heat radiation pad 64, and the pad forming portion for mounting the motherboard are exposed, and the filling ink 1 is left only in the gap 60 and the through hole 90 between them. Further, the surface of the metal plating film 3 exposed from the hole-filling ink 1 by the above polishing is made a smooth surface 39.

Next, as shown in FIG. 6, the solder resist film 7 is coated on the entire surface of the insulating substrate 9 except for the portions where the bonding pads 610, the die pads 63, and the pads for mounting the mother board are formed. Next, as shown in FIG. 7, the surface of the metal plating film 3 not covered with the solder resist film 7 is covered with the Ni / Au plating film 4. As a result, the die pad 63 and the bonding pad 610 are covered with the Ni / Au plating film 4. In addition, a pad 620 for soldering to the mother board is formed on the back surface of the insulating substrate 9. As a result, the printed wiring board 10 is obtained.

The printed wiring board 10 has an adhesive 59 on the die pad 63 as shown in FIG.
The semiconductor chip 5 is mounted and electrically connected to the bonding pad 610 by the wire 50. The pad 620 on the back side of the printed wiring board 10 is mounted on the pad 82 of the mother board 8 via the ball-shaped solder 81. Next, this is heated and both are soldered.

Next, the function and effect of this example will be described.
In this example, as shown in FIG.
Is a mixture of the silica powder 11 having the above-mentioned average particle diameter and the epoxy resin 12. This silica powder 11 is
The average particle size is smaller than that of the filler 191 used in the conventional hole filling ink 199 shown in FIG. for that reason,
It is dispersed in the epoxy resin 12 at high density and uniformly. Therefore, the strength of the hole filling ink 1 is improved.

When thermal shock is applied to the filling ink 1, stress is generated in the silica powder 11. This thermal stress is absorbed by the generation of minute cracks 121 in the epoxy resin 12 around the silica powder 11. The minute cracks 121 are formed by the conventional hole filling ink 1 shown in FIG.
Like 99, it does not propagate throughout the epoxy resin. Therefore, the thermal stress of the silica powder 11 is absorbed by the filling ink itself.

Therefore, in the through hole,
No cracks occur in the entire hole filling ink 1. For this reason,
As shown in FIG. 1, the hermeticity of the through hole 90 can be ensured. Therefore, when the printed wiring board 10 is soldered to the mother board 8, flux, solder cleaning liquid, etc. do not seep through the through holes 90, and the pattern circuit 61, the bonding pad 610, the semiconductor chip formed on the front surface of the insulating substrate 9 It is possible to prevent damage such as corrosion from occurring in 5.

In the gap 60 between the adjacent pattern circuits 61 and 62, the hole filling ink itself absorbs the stress of the solder resist film 7 covering the boundary between the hole filling ink 1 and the pattern circuits 61 and 62. To do. Therefore,
It is possible to prevent cracks from occurring in the solder resist film 7.

Example 2 In this example, the thermal shock resistance of the hole-filling ink was evaluated. In the evaluation, filling inks (Samples 1, 2,
3,4,5, C1, C2) were prepared. Then, a printed wiring board was produced using each hole filling ink. The content of silica powder and the average particle size were changed as shown in Table 1. Others are the same as in the first embodiment.

In the evaluation of the filling ink in the through holes, the occurrence of cracks in the filling ink was examined. The results are shown in Table 1. In the table, ○ indicates a state in which some cracks are recognized around the silica powder. △
Indicates a state in which cracks are recognized to the extent that they connect adjacent silica powders mixed in the filling ink. ×
Indicates a state in which a thick and long crack that crosses the through hole is recognized.

In the evaluation of the hole filling ink that fills the gaps between the pattern circuits, the crack generation state of the solder resist film that covers the upper surfaces of the pattern circuit and the hole filling ink was examined. The results are shown in Table 1. In the table, ○
Is the same as ○ above. Δ is the same as the above Δ. A cross indicates a state in which a thick and long crack that crosses between adjacent pattern circuits is recognized.

In the table, the content of silica powder is 0.
4 to 4.0% by weight and an average particle size of 0.01 to
When the thickness was 0.030 μm (Samples 1 to 5), no crack was generated in the filling ink in the through hole. In addition, no crack was generated in the solder resist film covering the boundary between the pattern circuit and the filling ink. On the other hand, in the case of Samples C1 and C2, the generation of relatively long cracks was observed.

[0040]

[Table 1]

Example 3 In the printed wiring board of this example, as shown in FIG. 10, the surface of the metal plating film 3 covering the inner wall of the through hole 90 was
The printed wiring board of Example 1 is different in that the roughened surface layer 30 is formed by the chemical surface treatment. Other configurations are the same as those in the first embodiment.

A method of manufacturing the printed wiring board of this example will be described with reference to FIGS. 11 to 13. First, similarly to the first embodiment, the pattern circuits 61 and 62, the bonding pad 610, the die pad 63, and the heat dissipation pad 64 are formed on the insulating substrate 9 (see FIG. 3).

Next, as shown in FIG. 11, a roughened surface layer 30 is formed on the surface of the metal plating film 3 by a chemical surface treatment. The chemical surface treatment is performed by blackening treatment.
The blackening treatment is performed by immersing the insulating substrate 9 in the following blackening treatment liquid for 0.3 to 15 minutes. By this blackening treatment, copper needle crystals are formed on the surface of the metal plating film 3.

Blackening treatment liquid-ingredient (concentration in water) sodium chlorite. ． ． ． ． ． ． 20-70 g / liter, trisodium phosphate 12 water. ． ． ． 10 to 30 g / liter, sodium hydroxide. ． ． ． ． ． ． ． 10 to 30 g / liter, temperature. ． ． ． ． ． ． ． 70-98 ° C,

Next, as shown in FIG. 12, the whole surface of the insulating substrate 9 including the inside of the through hole 90 is covered with the hole-filling ink 1 similar to that of the first embodiment, and is cured by heating or UV irradiation. .

Next, as shown in FIG. 13, the surface of the hardened hole-filling ink 1 is buffed to expose the pattern circuits 61, 62, the die pad 63, the heat radiation pad 64, and the portion where the motherboard mounting pad is formed. Then, only inside the gap 60 and the through hole 90 between them,
Leave the hole-filling ink 1. The surface of the metal plating film 3 exposed from the hole-filling ink 1 is smoothed by the above polishing.
Set to 9.

Thereafter, as in the first embodiment, the insulating substrate 9 is covered with the solder resist film 7 (see FIG. 6), Ni /
The metal plating film 3 is covered with the Au plating film 4 (see FIG. 7). As a result, the printed wiring board shown in FIG. 10 is obtained.

In this example, as shown in FIG. 10, the surface of the metal plating film 3 formed on the inner wall of the through hole 90 is chemically surface-treated to form the roughened surface layer 30. The filling ink 1 is brought into close contact with the inner wall of the through hole 90 on the roughened surface layer 30. Therefore, even if a thermal shock is applied, the filling ink 1 will not be peeled off from the inner wall of the through hole 90. Therefore, through hole 9
It is possible to prevent moisture from entering from zero.

Therefore, even when the printed wiring board is mounted on the mother board by soldering, peeling does not occur between the metal plating film 3 in the through hole and the filling ink 1 due to the melting temperature of the solder.

The filling ink 1 is supplied not only to the inside of the through hole 90 but also to the peripheral portion of the opening. Therefore, even if the filling ink 1 contracts when the filling ink 1 is cured, the entire inside of the through hole 90 can be filled with the filling ink 1.

A roughened surface layer is formed on the metal plating 3 on the surface of the insulating substrate 9, which is then polished to form a uniform smooth surface. Therefore, even when the surface of the metal plating 3 is further covered with a plating film, a plating film having a uniform thickness can be formed. Therefore, the insulating substrate 9
It is possible to form the pattern circuit 61 and the die pad 63 on the surface of which are smooth and have a uniform layer thickness. In addition, also in this example, the same effect as that of the first embodiment can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a printed wiring board of Example 1 mounted on a motherboard.

FIG. 2 is an explanatory view showing the front and side surfaces of the printed wiring board of Example 1.

FIG. 3 is a cross-sectional view of an insulating substrate on which patterns such as through holes, pattern circuits, die pads, and heat dissipation pads are formed in the method for manufacturing a printed wiring board according to the first embodiment.

FIG. 4 is a sectional view of the insulating substrate filled with hole-filling ink, following FIG. 3;

FIG. 5 is a cross-sectional view of the insulating substrate after polishing the pattern filling ink on the pattern surface, which is continued from FIG. 4;

6 is a cross-sectional view of the insulating substrate on which a solder resist film is formed, following FIG.

FIG. 7 is a cross-sectional view of an insulating substrate having a Ni / Au plating film, following FIG.

FIG. 8 is an explanatory diagram showing silica powder in the hole filling ink of Example 1.

FIG. 9 is an explanatory diagram showing a problem in Example 1 when the filler in the hole filling ink has a large diameter.

FIG. 10 is a sectional view of a printed wiring board according to a third embodiment.

FIG. 11 is a cross-sectional view of an insulating substrate that has been subjected to a chemical surface treatment in Example 3.

FIG. 12 is a cross-sectional view of the insulating substrate filled with hole-filling ink, following FIG. 11;

FIG. 13 is a cross-sectional view of the insulating substrate subsequent to FIG. 12, in which the hole-filling ink on the pattern surface is removed by polishing.

FIG. 14 is a cross-sectional view of a main part of a printed wiring board of a conventional example.

FIG. 15 is an enlarged cross-sectional view around a through hole of a printed wiring board in a conventional example.

16A and 16B are cross-sectional views (a) and (a) in the vicinity of the boundary between the pattern circuit of the printed wiring board and the filling ink in the conventional example.
A sectional view taken along the line A-A of FIG.

[Explanation of symbols]

 1. ． ． Filling ink, 10. ． ． Printed wiring board, 11. ． ． Silica powder, 3. ． ． Metal plating film, 30. ． ． Roughened surface layer, 4. ． ． Ni / Au plating film, 5. ． ． Semiconductor chip, 60. ． ． Gap, 61, 62. ． ． Pattern circuit, 9. ． ． Insulating substrate, 90. ． ． Through hole,

Claims (4)

[Claims] 1. An inside of a through hole in a printed wiring board, comprising a mixture of epoxy resin and silica powder,
And a filling ink for filling a space between adjacent pattern circuits, wherein the silica powder has an average particle diameter of 0.001 to 0.050 μm. ink. 2. The silica powder according to claim 1,
A hole-filling ink for a printed wiring board, characterized in that the hole-filling ink contains 0.3 to 5% by weight. 3. The hole filling ink for a printed wiring board according to claim 1, wherein the surface of the silica powder is subjected to a coupling treatment. 4. The method according to claim 1, wherein
A hole filling ink for a printed wiring board, wherein an inner wall of the through hole is covered with a metal plating film, and a roughened surface layer is formed on the surface of the metal plating film by a chemical surface treatment.