JPH0533598U - Electromagnetic wave shield printed wiring board - Google Patents

Abstract

(57) [Summary] [Object] To improve the radiation noise reduction effect and prevent the high frequency characteristics from deteriorating in a case where a predetermined area of a wiring pattern on a substrate surface is covered with a shield layer via an insulating layer. [Structure] A polymer paste containing iron powder was used as a material for forming the shield layer 5.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to improvement of an electromagnetic wave shield printed wiring board that is effective in reducing unnecessary radiation of electromagnetic waves from electronic circuit devices.

[0002]

[Prior Art]

 As one of countermeasures against electromagnetic interference, the following electromagnetic shielded printed wiring board disclosed in JP-A-2-76295 has been developed in order to reduce unnecessary radiation from the printed wiring board itself.

An insulating layer is formed so as to cover a predetermined area of a portion where a wiring pattern is formed in an ordinary printed wiring board, and a polymer paste containing Ni—Zn ferrite powder is formed on the insulating layer ( A shield layer made of ferrite paste) is formed by coating, and a part of the shield layer is connected to a part of the wiring pattern (ground part).

According to this structure, with respect to the electromagnetic wave generated from the wiring pattern in the portion covered with the shield layer, a reflection loss at the boundary surface of the shield layer and an absorption loss inside the shield layer occur, so that the electromagnetic wave is transmitted to the outside. Unnecessary radiation of electromagnetic noise is suppressed.

Further, an electromagnetic wave shield wiring board formed by coating copper paste as the shield layer is also known. In this case, unnecessary radiation of the electric field component is mainly suppressed by reflection loss at the boundary surface of the copper paste layer and absorption loss inside the copper paste layer.

[0006]

[Problems to be solved by the device]

 When forming a shield layer with a ferrite base, it is not possible to expect a sufficient shield effect unless the thickness is made a few millimeters. If the shield layer is thick, the entire board becomes thicker, which leads to problems such as difficult component mounting, increased weight, and increased cost.

When forming the shield layer with copper paste, since the conductivity of copper is extremely high, a large shield effect can be obtained with a thin shield layer, and the above-mentioned problems do not occur. However, the impedance of the bypass path due to the stray capacitance generated by forming the shield layer becomes too small, which causes another problem that the high-frequency characteristics deteriorate, such as the waveform of the pulse signal becoming blunt.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to obtain a sufficient radiation noise reduction effect with a thin shield layer by appropriately selecting the material of the shield layer. This is to prevent the high frequency characteristics of the circuit from being impaired.

[0009]

[Means for Solving the Problems]

 Therefore, in this device, the shield layer is formed of a material (iron paste) containing iron powder in the polymer paste.

[0010]

[Action]

 The conductivity of iron is higher than that of ferrite and lower than that of copper. Therefore, even if it is thinner than the ferrite paste / shield layer, a sufficient shielding effect is exhibited. Since the internal resistance of the iron paste shield layer is larger than that of the copper paste shield layer, the roundness of the waveform transmitted through the circuit is less than that of the copper paste shield layer.

[0011]

【Example】

 FIG. 1 shows the construction of an electromagnetic wave shield printed wiring board according to an embodiment of the present invention. The basic structure of the printed wiring board is the same as the conventional one, in which the wiring patterns 2 made of copper foil are printed on both sides of the glass epoxy board 1 and the through holes 3 are formed at the predetermined positions of the board 1. Its inner surface is plated.

A resin insulating layer (undercoat layer) 4 is formed so as to cover a predetermined area of a portion of the substrate 1 where the wiring pattern 2 is formed, and a shield layer 5 is formed on the insulating layer 4 with iron paste. The coating is formed in a predetermined pattern. The shield layer 5 is connected to a part (ground part) of the wiring pattern 2 without the insulating layer 4. Further, a resin insulating layer (overcoat layer) 6 is formed on the shield layer 5 by coating.

The iron paste for forming the shield layer 5 is a carbonyl-type condensed resin containing 60 to 90% by weight of carbonyl iron powder. This iron paste is applied to a substrate surface in a predetermined pattern and a predetermined thickness, dried with hot air at 150 to 160 ° C. for 30 minutes, and then heated with far infrared rays at 175 ° C. for about 4 minutes. This forms the shield layer 5.

A printed wiring board according to the present invention using the above-mentioned iron paste shield layer and a printed wiring board of a ferrite paste shield layer using a Ni—Zn-based ferrite material (other conditions are the same). As a result of a comparative test of the radiation noise reduction effect on the above, as shown in FIG. 2, the effect of the embodiment of the present invention was clearly superior.

[0015]

[Effect of the device]

 As described above in detail, in the electromagnetic wave shield printed wiring board of the present invention, the shield layer is formed by the iron paste containing the iron powder whose conductivity is larger than that of ferrite and smaller than that of copper. Even if it is thin, a sufficient shielding effect can be obtained. In addition, the impedance of the bypass path through the stray capacitance due to the shield layer is larger than that in the case of the copper paste shield layer, and the rounding of the signal waveform is small and a circuit with good high frequency characteristics can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of an electromagnetic shield printed wiring board according to an embodiment of the present invention.

FIG. 2 is a graph showing a comparative test of a radiation noise reduction effect of a printed wiring board according to the present invention and a conventional printed wiring board.

[Explanation of symbols]

 1 Glass Epoxy Substrate 2 Wiring Pattern 3 Through Hole 4 Insulating Layer (Undercoat Layer) 5 Shield Layer (Iron Paste Layer) 6 Insulating Layer (Overcoat Layer)

Claims (1)

[Scope of utility model registration request] 1. A predetermined area of a wiring pattern formed on a surface of a substrate is covered with an insulating layer, a shield layer is formed on the insulating layer, and a part of the shield layer is covered with the insulating layer. An electromagnetic wave shield printed wiring board, characterized in that the shield layer is a layered coating of a polymer paste containing iron powder.