JP2001339143A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliabile wiring board which can effectively prevent the migration of metals that form an interconnection conductor. SOLUTION: The wiring board is a substrate 1, the upper face of which is formed with a plurality of interconnection conductors 2 which contain silver, aluminum, or an alloy of these metals, and are arranged parallelly at an interval of 10 to 100 μm. The interconnection conductor 2 is covered by one and the same protective layer 3 which is chiefly made of epoxy resin. The protective layer 3 contains a poly 4-methly pentene resin filler 4 of the grain diameter 0.5 to 5.0 μm, by 12 to 30 wt.% for the regions between the adjacent wiring conductors 2, 2, and 6 to 18 wt.% for the regions above the wiring conductors 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring board used for forming a head substrate such as an LED array head.

[0002]

2. Description of the Related Art Hitherto, a wiring substrate has been used to constitute a head substrate such as an LED array head.

In such a conventional wiring board, as shown in FIG. 2, for example, a plurality of wiring conductors 12 are adhered in a predetermined pattern on an upper surface of a substrate 11 made of glass, ceramic or the like, and these wiring conductors 12 are simply formed. It has a structure covered with one protective layer 13.

The material of the wiring conductor 12 is silver (A).
g) or a conductive material containing a metal such as aluminum (Al) is used. Such a wiring conductor 12 is formed by adding a predetermined conductive paste obtained by adding and mixing a suitable organic solvent and a solvent to silver powder, for example. A predetermined pattern is printed and applied on the upper surface of the substrate 11 by printing or the like.
It is formed by baking at a temperature of 00 ° C.

The protective layer 13 for covering the wiring conductors 12 is for preventing the wiring conductors 12 from being oxidized and corroded by contact with moisture or the like contained in the air. Epoxy resins have been suitably used from the viewpoints of ease of handling and moisture resistance.

[0006]

However, in this conventional wiring board, since the relative permittivity of the epoxy resin forming the protective layer 13 is relatively high at 4 to 7, the plurality of wiring conductors 12 are interposed. When a plurality of wiring conductors 12 are selectively applied to each of a plurality of wiring conductors 12 in use of a wiring board at a high density at intervals of about 10 μm to 100 μm, a large amount of power is applied between adjacent wiring conductors 12. A potential difference may occur, in which case, silver, aluminum, etc. forming the wiring conductor 12 cause migration,
There is a disadvantage that adjacent wiring conductors are electrically short-circuited.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and a wiring board according to the present invention has a plurality of wirings containing silver, aluminum, or an alloy of these metals on the upper surface of the substrate. In a wiring board in which conductors are juxtaposed at intervals of 10 μm to 100 μm and these wiring conductors are commonly covered with a protective layer mainly composed of epoxy resin, the protective layer has a particle size of 0 μm. 0.5 μm to 5.0 μ
m, wherein the poly (4-methylpentene) resin filler is contained at 12 wt% to 30 wt% in a region between adjacent wiring conductors and 6 wt% to 18 wt% in a region on the wiring conductor.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a wiring board according to one embodiment of the present invention, wherein 1 is a substrate, 2 is a wiring conductor, 3 is a protective layer, and 4 is a poly-4-methylpentene resin filler.

The substrate 1 is made of an electrically insulating material such as alumina ceramics, mullite, aluminum nitride, glass ceramics, quartz, alkali glass, alkali-free glass, etc., and has a plurality of wiring conductors 2 and a protective layer 3 on its upper surface. It functions as a supporting base material for supporting.

When the substrate 1 is made of, for example, alumina ceramics, an appropriate organic solvent and a solvent are added to and mixed with a ceramic raw material powder of alumina, silica, magnesia or the like to form a slurry. A ceramic green sheet (ceramic green sheet) is obtained by employing a doctor blade method, a calendar roll method, or the like, and thereafter, the green sheet is punched into a predetermined shape and fired at a high temperature (about 1600 ° C.). Be produced.

A plurality of wiring conductors 2 are attached and formed on the upper surface of the substrate 1. The wiring conductor 2 is made of silver (A
g), a conductive material containing, for example, 85 wt% or more of aluminum (Al) or an alloy of these metals, and is arranged at a high density on the upper surface of the substrate 1 with a space of 10 μm to 100 μm between adjacent wiring conductors. Is established.

When a wiring board is used, these wiring conductors 2 are connected to the wiring conductors 2 by a switching transistor (not shown) or the like.
The power of mW to 15 mW is selectively applied individually.

The wiring conductor 2 is attached and formed in a predetermined pattern on the upper surface of the substrate 1 by employing a conventionally known thick film method. That is, the wiring conductor 2 is formed by printing and applying a predetermined conductive paste obtained by adding and mixing an appropriate organic solvent and a solvent to, for example, silver powder on the upper surface of the substrate 1 by a conventionally known screen printing or the like. This is baked at a high temperature (350 ° C. to 800 ° C.) to form a thickness of, for example, 2 μm to 30 μm.

Further, the plurality of wiring conductors 2 are commonly covered by a single protective layer 3. The protective layer 3 is made of an epoxy resin having a moisture absorption of less than 0.01%, and its thickness is set to 10 μm to 50 μm, for example, when the thickness of the wiring conductor 2 is 2 μm to 30 μm.

The protective layer 3 has a particle size of 0.5 μm.
m-5.0 μm poly 4-methylpentene resin filler 4
Is 12 wt% to 3% in the area of 2-2 between adjacent wiring conductors.
0 wt%, 6 wt% to 18 wt% in the region on the wiring conductor 2
It is contained.

The above poly 4-methylpentene resin filler 4
Is for effectively lowering the dielectric constant of the protective layer 3, and the content of the filler 4 is reduced between adjacent wiring conductors 2-2.
Is set to 12 wt% to 30 wt% in the region, the relative dielectric constant of the protective layer 3 in the region is set to 2.5 to 3 wt%.
It can be as low as 8. Thereby, 10 μm to 1 μm
Wiring conductors 2, 2 juxtaposed at an interval of 00 μm
Even when electric power is selectively applied to each of the wiring conductors 2, a large potential difference does not occur between the adjacent wiring conductors 2 and 2, and migration of silver, aluminum, and the like contained in the wiring conductor 2 can be effectively prevented. become able to.

The content of the poly-4-methylpentene resin filler 4 in the region 2-2 between adjacent wiring conductors is 1
If the content is less than 2 wt%, the dielectric constant of the protective layer 3 becomes relatively high, so that the potential difference between the adjacent wiring conductors 2-2 cannot be sufficiently suppressed, and the content is 30 wt%.
Is greater than the maximum value, large irregularities corresponding to the outer shape of the filler 4 are formed on the surface of the protective layer 3 located between the wiring conductors 2-2. When the area in contact with the protective layer 3 is increased, a large amount of moisture in the air may enter the protective layer 3 to create an environment where migration is likely to occur.

Therefore, it is important that the content of the poly (4-methylpentene) resin filler 4 in the region between adjacent wiring conductors 2-2 is set to 12 wt% to 30 wt%.

On the other hand, the poly 4-
If the content of the methylpentene resin filler 4 is less than 6 wt%, the thermal expansion coefficient of the protective layer 3 is largely different between the region between the wiring conductors 2-2 and the region on the wiring conductor 2, and thus the wiring substrate When heat is applied to the protective layer 3 in accordance with the use of, for example, cracks due to thermal stress may occur near the boundary between the two regions described above, and the content is 18 watts.
If it exceeds t%, large irregularities corresponding to the outer shape of the filler 4 are formed on the surface of the protective layer 3 located on the wiring conductor 2, so that the surface roughness of the protective layer 3 in this portion becomes large, and When the area in contact with the moisture increases, a large amount of moisture in the air infiltrates into the protective layer 3, and the wiring conductor 2 may be oxidized and corroded in a relatively short time due to contact with the infiltrated moisture.

Therefore, the poly in the region on the wiring conductor 2
The content of 4-methylpentene resin filler 4 is from 6 wt%
It is important to set it to 18 wt%.

The protective layer 3 has a particle size of, for example, 0.5 μm to 1.5 μm in a liquid epoxy resin precursor.
12 wt% of poly 4-methylpentene resin filler 4
A first varnish to which 〜30 wt% is added, and a second varnish to which 6 wt% to 18 wt% of a poly-4-methylpentene resin filler 4 having a particle size of 0.5 μm to 1.5 μm are added in the precursor are prepared. , The first varnish is placed in the area between adjacent wiring conductors 2-2, and the second varnish is placed in the wiring conductor 2
The upper region is formed by printing and applying each by conventionally known screen printing or the like, and heating and heating the precursor at a temperature of 60 ° C. to 200 ° C. to thermally cure the precursor. In this case, the poly 4- to be contained in the precursor of the epoxy resin
The content of the methylpentene resin filler 4 is 12 wt% or more.
If it is set within the range of 18 wt, it can be used as any one of the first varnish and the second varnish.
The varnish can be applied to both the region 2 and the region on the wiring conductor, which has the advantage of improving the productivity of the wiring board. Therefore, poly 4-methylpentene resin filler 4 contained in the precursor of epoxy resin
Is preferably set in the range of 12 wt% to 18 wt%.

The poly-4-methylpentene resin filler 4 added to the varnish is first prepared by polymerizing a monomer of the poly4-methylpentene resin at a predetermined temperature as shown in the following formula 1. A lump of pentene resin is formed, and then a lump having a predetermined particle size (0.5 μm
１．５1.5 μm).

[0023]

Embedded image

It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the spirit of the present invention.

For example, the present invention can be applied to a case where a wiring conductor or a protective layer is further laminated on the protective layer 3 in the above-described embodiment to form a multilayer wiring board.

[0026]

[Experimental Example] Next, the operation and effect of the present invention will be described based on an experimental example. First, a plurality of wiring conductors containing 85% by weight of silver were placed on a substrate made of alumina ceramics.
The wiring conductors 2 were juxtaposed at an interval of 0 μm, and these wiring conductors 2 were covered with eight kinds of epoxy resin protective layers having different contents of the poly4-methylpentene resin filler in the region between the adjacent wiring conductors. Eight types of wiring board samples (sample Nos. 1 to 8) were prepared.
The diameter of the poly-4-methylpentene resin filler present in the protective layer of each wiring board sample was 0.5 μm or more.
It was confirmed by a metal microscope equipped with a length measuring device that it was within the range of 5.0 μm.

Then, each of these samples was heated at 85 ° C. for 8 hours.
It is placed in a constant temperature and humidity chamber of 5% Rh, and one of the adjacent wiring conductors is maintained at a potential of 5 V and the other is connected to a ground (GND) potential for 500 hours to check whether or not migration has occurred. did. Further, for each sample, the impedance between adjacent wiring conductors was measured using an oscilloscope. Table 1 shows the results.

[0028]

[Table 1]

According to Table 1, Sample No. 1 in which the content of the poly-4-methylpentene resin filler in the protective layer is less than 12 wt%. 1, No. In No. 2, the occurrence of migration between the adjacent wiring conductors was confirmed, and the impedance between the wiring conductors was as small as 2.3 × 10 ² Ω or less in any of the wiring board samples, resulting in an electrical short circuit.

On the other hand, in Sample No. 1 in which the content of the poly-4-methylpentene resin filler in the protective layer was set to a value larger than 30 wt%. 7, No. 8, migration between adjacent wiring conductors was confirmed.
Also in these wiring board samples, the impedance between the wiring conductors is as small as 3.8 × 10 ⁵ Ω or less, and they are electrically short-circuited.

On the other hand, in Sample No. 1 in which the content of the poly-4-methylpentene resin filler in the protective layer was set to 12 wt% to 30 wt%. 3-No. In No. ⁶ , no migration occurred between adjacent wiring conductors, and the impedance of each of these wiring board samples was in the range of 2.6 × 10 ⁶ Ω to 9.25.3 × 10 ⁹ Ω. This is a relatively large value, and no electrical short circuit occurs between adjacent wiring conductors.

Therefore, according to the results of these experiments, 50
In order to keep the impedance high without causing migration between the wiring conductors arranged in parallel at intervals of μm, the content of the poly-4-methylpentene resin filler present in the protective layer must be 12 wt% or less. It turns out that it must be set to 30 wt%.

In the above experiment, the effect was confirmed using a sample in which the distance between adjacent wiring conductors was set to 50 μm.
It was confirmed by other experiments that the same result as the above-mentioned experiment was obtained when the sample set to μm and the sample set to 100 μm were used.

Next, a plurality of wiring conductors 2 containing 85% by weight of silver are arranged side by side at intervals of 50 μm on a substrate made of alumina ceramics, and poly 4 in the region on each wiring conductor 2 is formed. -Eight types of wiring board samples covered with eight types of epoxy resin protective layers with different contents of -methylpentene resin filler (Sample No.
9-No. 16) was prepared. In addition, it was confirmed with a metal microscope equipped with a length measuring device that the diameters of the poly-4-methylpentene resin fillers present in the protective layer of each wiring board sample were all within the range of 0.5 μm to 5.0 μm.

Then, these samples were put into a thermal shock tester, and (25 ° C.) − (85 ° C.) − (25 ° C.) −
After 100 cycles of (−25 ° C.) temperature cycle,
The occurrence of cracks in the protective layer was confirmed with a metallographic microscope.

Thereafter, the above sample was heated at 85 ° C. and 85 ° C.
The sample was kept in a constant temperature / humidity bath of 500% Rh for 500 hours, and thereafter, the resistivity of the wiring conductor of each sample was measured by a digital multimeter. Table 2 shows the results.

[0037]

[Table 2]

According to Table 2, the content of the poly-4-methylpentene resin filler in the protective layer was less than 6 wt%. 9, No. In No. 10, the occurrence of cracks was confirmed, and each resistivity was a large value of 2.1 × 10 ⁻³ Ω · cm or more. It is considered that the increase in the resistivity is mainly caused by the fact that the moisture in the thermo-hygrostat contacts the wiring conductor through the cracks and causes the wiring conductor to be significantly oxidized and corroded in a short time.

On the other hand, in Sample No. 1 in which the content of the poly-4-methylpentene resin filler in the protective layer was set to a value larger than 18 wt%. 15, No. In 16,
Although no generation of cracks was confirmed, each resistivity was a large value of 4.8 × 10 ⁻⁴ Ω · cm or more. This increase in resistivity is due to the large amount of poly.
A large amount of moisture in the thermo-hygrostat penetrates from the surface of the protective layer, which contains a 4-methylpentene resin filler and has many large irregularities, which contacts the wiring conductor and oxidizes the wiring conductor in a short time. The main cause is considered to be corrosion.

On the other hand, in Sample No. 3 in which the content of the poly-4-methylpentene resin filler in the protective layer was set to 6 wt% to 18 wt%. 11-No. In No. 14, no crack was found in the protective layer, and the resistivity of each of these wiring board samples was 3.7 × 10
^-6 Ω · cm to 6.3 × 10 ^-6 Ω · cm was a relatively small value.

Therefore, according to these experimental results, in order to effectively prevent the oxidative corrosion of the wiring conductor and the occurrence of cracks in the protective layer, the content of the poly-4-methylpentene resin filler present in the protective layer must be reduced. It turns out that it is necessary to set to 6 wt%-18 wt%.

In the above experiment, the effect was confirmed using a sample in which the distance between adjacent wiring conductors was set to 50 μm.
It was confirmed by other experiments that the same result as the above-mentioned experiment was obtained when the sample set to μm and the sample set to 100 μm were used.

[0043]

According to the present invention, a plurality of wiring conductors containing silver, aluminum, or an alloy of these metals are juxtaposed on the upper surface of a substrate with an interval of 10 μm to 100 μm therebetween. Is commonly coated with a protective layer made of resin, the protective layer has a particle size of 0.5 μm
By containing a 5.0 μm poly 4-methylpentene resin filler in an area between adjacent wiring conductors of 12 wt% to 30 wt%, the dielectric constant of the protective layer in this area can be effectively reduced, and the wiring conductor can be reduced. It is possible to reduce the intrusion of moisture into the protective layer located therebetween, thereby effectively preventing the migration of silver, aluminum, or the like forming the wiring conductor.

According to the present invention, a poly-4-methylpentene resin filler having a particle size of 0.5 μm to 5.0 μm is provided in the protective layer in an area of 6 wt% to 18 wt% in a region on the wiring conductor.
By containing it, the penetration of moisture into the protective layer located on the wiring conductor is reduced, the wiring conductor is maintained in a good state with little corrosion, and the thermal stress inside the protective layer is well relaxed and protected. The formation of cracks in the layer can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a wiring board according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional wiring board.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Wiring conductor, 3 ... Protective layer, 4
... Poly-4-methylpentene resin filler

Claims (1)

[Claims] A plurality of wiring conductors containing silver, aluminum, or an alloy of these metals are interposed between a plurality of wiring conductors having a thickness of 10 μm on an upper surface of a substrate.
A wiring board in which these wiring conductors are commonly covered with a protective layer containing epoxy resin as a main component while being juxtaposed at intervals of m to 100 μm, wherein the protective layer has a particle size of 0.5 μm to 5 μm. 0.0 μm poly 4-
Methylpentene resin filler is added in an amount of 12 wt% to 30 wt% in an area between adjacent wiring conductors, and
A wiring board, characterized in that the content is from 18 wt% to 18 wt%.