JP2761113B2 - Printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having a printed circuit provided on an insulating film.

[0002]

2. Description of the Related Art Printed wiring boards for inverter circuits and power circuits for power supplies have also been developed to have high density mounting, multilayer structure, thinning, and miniaturization. It was started. Therefore, recently, as shown in FIG. 5, a metal-substrate type printed wiring board having a metal substrate 1 under an insulating film 2 provided with a printed circuit 3 is often used. This is because the metal-substrate type printed wiring board is excellent in heat dissipation.

[0003]

However, the metal-substrate type printed wiring board has a problem that the insulating film 2 is liable to cause dielectric breakdown and has low reliability. The thickness of the insulating film 2 is small, and the electric circuit 1 in the metal substrate 1 and the printed circuit 3
When a voltage is applied during the period 3, electric field concentration occurs at the edge 13a of the electric circuit 13 on the insulating film 2 side, and dielectric breakdown starts therefrom. In the case of the insulating film 2 using a resin material, dielectric breakdown is particularly likely to occur. If the thickness of the insulating film 2 is increased, dielectric breakdown is less likely to occur, but heat dissipation is reduced or the thickness of the insulating film 2 is reduced. Therefore, increasing the thickness of the insulating film 2 is not an appropriate measure.

In view of the above circumstances, it is an object of the present invention to provide a printed wiring board in which dielectric breakdown of an insulating film is less likely to occur without increasing the thickness of the insulating film.

[0005]

According to a first aspect of the present invention, there is provided a printed wiring board.
A high-dielectric-constant insulating material is applied to at least the insulating-film-side edge of an electric circuit in a printed circuit provided on the insulating film . High-dielectric insulating material, the dielectric constant, not greater than the dielectric constant of the insulation Enmaku.

As the type of the printed wiring board, for example ,
Although metal substrate type printed circuit board with a metal substrate underneath the insulation Enmaku the like, in addition to this, the laminate-type printed wiring board may be a ceramic plate type printed circuit board or the like.
Examples of the printed circuit include a metal foil formed by etching and patterning, a conductive paste printed thereon, and a plating circuit formed by an additive method.

Hereinafter, the present invention will be described more specifically.
In FIG. 5, when the insulating film 2 is made of an epoxy resin-impregnated glass cloth, when a voltage is applied in the air, the electric field concentration is doubled at the insulating film 2 side edge 13a. Assuming that the insulating film 2 has a substantially uniform dielectric strength, the printed wiring board has only half the withstand voltage of the insulating film 2. The electric field in the insulating film 2 is calculated using the finite element method, using the electric circuit and the metal base as conductor electrodes. Assuming that there is no space charge in an electrostatic field, Laplace's equation "div (εgr
adφ) = 0 ”, and thus“ E = −gradφ ”
It was determined by this. Where φ is a potential and ε is a dielectric constant. The thickness of the insulating film 2 is 100 μm, ε _r = 5 to 6,
Assuming that the applied voltage is 10 kV, the electric field intensity at the edge 13a reaches about 200 kV / mm. In FIG. If the electric field in the element is constant and the potential is continuous at the element boundary, the electric field in the electric field concentration area A will be the average of the electric fields around it. The dielectric constant in the insulating film 2 is constant, and when the dielectric constant in the region B near the edge 13a increases,
Since the electric field is inversely proportional to the dielectric constant, the electric field in the vicinity area B decreases, and accordingly, the electric field in the electric field concentration area A also decreases. As a result, the electric field concentration is reduced.

Specific examples of application of a high dielectric constant insulating material to the insulating film side edge 13a include the following. As shown in FIG. 1, the high dielectric constant insulating material 5 is applied so as to just cover the side surface including the edge 13 a of the electric circuit 13. As shown in FIG. 2, the high dielectric constant insulating material 5 is applied so as to cover not only the edge 13 a of the electric circuit 13 but the entire exposed surface.

As shown in FIG. 3, the high dielectric constant insulating material 5 is moved from the edge 13 a of the electric circuit 13 to the upper surface 13 b of the electric circuit 13.
To cover a part of As shown in FIG. 4, the high dielectric constant insulating material 5 is applied so as to cover only the vicinity of the edge 13a of the electric circuit 13. Not limited to the above, a high dielectric constant insulating material may be applied to the entire surface of the printed wiring board,
It is desirable to apply only the electric circuit portion by screen printing (not limited to this) or the like so as to reduce interference between adjacent electric circuits. In addition, it is desirable that after application of the high dielectric constant insulating material, defoaming is performed to remove voids, and then the applied material is cured by heating or the like.

[0010]

In the printed wiring board of the present invention, the high dielectric constant insulating material is applied to the insulating film side edge of the electric circuit in the printed circuit on the insulating film, so that the electric field concentration in the insulating film side edge region is reduced. In addition, dielectric breakdown does not easily occur without increasing the thickness of the insulating film.

When the dielectric constant of the high dielectric constant insulating material is higher than the dielectric constant of the insulating film, the degree of reduction of the electric field concentration is large, and the dielectric breakdown of the insulating film is less likely to occur.

[0012]

Embodiments of the present invention will be described below. -Example 1-The printed wiring board of Example 1 has a configuration shown in Fig. 3.
The metal substrate 1 is an aluminum square plate having a thickness of 1 mm, a length of 70 mm and a width of 70 mm. The insulating film 2 is a 100 μm thick epoxy resin film (ε _r = 3.9). The electric circuit 13 is a copper foil disk having a thickness of 35 μm and a diameter of 25 mm. High dielectric constant insulating material 5 is made of epoxy resin containing rutile (titanium oxide) 4
0 volume% was added (ε _r = 10).

The electric circuit 13 is formed by etching and patterning a copper foil on the insulating film 2.
After the formation, an epoxy resin obtained by adding 40% by weight of rutile (titanium oxide) to the epoxy resin is applied to the edge 13a, followed by performing a void removal treatment by defoaming, and curing by heating. Example 2 Example 2 was the same as Example 1 except that the insulating film 2 was a 150 μm thick epoxy resin film (ε _r = 6.0) containing 50% by volume of an alumina filler.

Example 3 A solder resist (solar ink ε) was used instead of epoxy resin to which rutile (titanium oxide) was added by 40% by weight.
_This example is the same as Example 1 _{except that r} = 3.5) was used. -Example 4-Example 4 is the same as Example 2 except that a solder resist (solar ink) is used instead of epoxy resin to which rutile (titanium oxide) is added by 40% by weight.

Comparative Example 1 The same as Example 1 except that the high dielectric constant insulating material 5 was not applied. Therefore, the area near the edge is air (ε _r =
1.0). - other not subjected to comparative example 2 high-dielectric insulating material 5 is the same as Example 2. Therefore, the area near the edge is air (ε _r =
1.0).

A Vt test was performed on each of the six printed wiring boards obtained. In the Vt test, a voltage of AC 4 kV was applied between the electric circuit 13 and the metal substrate 1 in an oil bath, and the time until dielectric breakdown was measured. The measurement results (average) are shown below together with the electric field concentration obtained by simulating with the finite element method. Example 1 Time to destruction: 130 hours Electric field concentration 1.55 Example 2 Time to destruction: 150 hours Electric field concentration 1.61 Example 3 Time to destruction: 50 hours Electric field concentration 1.73 Example 4 Time to destruction: 70 hours Electric field concentration 1.83 Comparative Example 1 Time to destruction: 5 hours Electric field concentration 2.00 Comparative Example 2 Time to destruction: 9 hours Electric field concentration 2.07 Print Examples In a wiring board, dielectric breakdown of an insulating film is extremely unlikely to occur. The results of the simulation of the degree of concentration of the electric field also well support that the fact that the dielectric breakdown became less likely is due to the relaxation of the concentration of the electric field.

[0017]

As described above, in the printed wiring board of the present invention, since the electric field concentration near the insulating film side edge of the electric circuit in the printed circuit is reduced, the dielectric breakdown of the insulating film increases the thickness of the insulating film. It is unlikely to occur even without. When the dielectric constant of the high-dielectric-constant insulating material is higher than the dielectric constant of the insulating film, the degree of reduction of electric field concentration is large, and dielectric breakdown of the insulating film is less likely to occur.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first configuration example of a printed wiring board according to the present invention.

FIG. 2 is a sectional view showing a second configuration example of the printed wiring board of the present invention.

FIG. 3 is a sectional view showing a third configuration example of the printed wiring board of the present invention.

FIG. 4 is a cross-sectional view illustrating a fourth configuration example of the printed wiring board of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration example of a conventional printed wiring board.

[Description of sign]

 DESCRIPTION OF SYMBOLS 1 Metal substrate 2 Insulating film 3 Printed circuit 5 High dielectric constant insulating material 13 Electric circuit 13a Insulating film side edge

Claims (2)

(57) [Claims] 1. A printed wiring board comprising a printed circuit provided on an insulating film, wherein a dielectric constant is insulated at least at an edge of the printed circuit on an insulating film side of an electric path.
A printed wiring board provided with a high dielectric constant insulating material having a dielectric constant higher than a dielectric constant of a film . 2. A method according to claim 1 Symbol placement of the printed circuit board insulating film is formed on the metal substrate surface.