JPH05183291A - Manufacture of emi shield printed wiring board - Google Patents

Abstract

PURPOSE:To reduce specific resistance by a method wherein a coated metal paste for magnetic shield is heated in a vacuum oven and cured. CONSTITUTION:After through holes 5 are formed in a board 6, a conductor circuit 1 is formed by plating a metal. A resin insulating layer 2 is formed on the conductor circuit 1 except the through holes 5, and coated with metal paste for magnetic shield. Said metal paste is heated at 50-140 deg.C in a vacuum oven and precured, and then finally cured at 150-220 deg.C in a vapor phase soldering vessel or a far infrared furnace. Thereby specific resistance can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an EMI shielded printed wiring board, and more particularly, to an E having a small specific resistance and a small sheet resistance without impairing the EMI shielding characteristics.
We propose a method for manufacturing printed wiring boards with MI shield measures.

[0002]

2. Description of the Related Art Generally, electronic devices emit electromagnetic waves specific to them, that is, electromagnetic waves from each electromagnetic energy source. Therefore, it inevitably affects other electromagnetic devices (electromagnetic interference). In order to prevent such a so-called "electromagnetic interference" (electromagnetic interference, hereinafter abbreviated as "EMI" in the present invention), a casing of an electromagnetic device is conventionally magnetically shielded by a conductive plastic or the like. The way to do is taken.

However, such a magnetic shield method is
It is not used so much because of problems such as cost and size increase. Moreover, it is necessary to individually magnetically shield electronic components such as printed wiring boards to which the present invention is applied. In response to such a demand, recently, some techniques for shielding the printed wiring board itself have been already proposed and put into practical use. EMI like this
An example of the shield printed wiring board is shown in FIG.

The shielded printed wiring board shown in FIG.
A conductor circuit 1 is formed directly on a substrate 6 having through holes 5 by an additive method or a subtractive method, a resin insulating layer 2 is further formed, and an EMI shield such as Cu or Ag is formed on the resin insulating layer 2. The shield layer 3 is formed of a hardened layer of a metal paste for, and then an overcoat layer 4 is formed so as not to expose the metal paste of the shield layer 3.

In such a conventional EMI shield multilayer printed wiring board, as a metal paste curing method for forming the shield layer 3, it is known to use a blower oven or a far infrared furnace for the metal paste. There is. The one having the shield layer 3 thus formed can reduce the radiation noise by 10 to 20 dB and also reduce the crosstalk noise.

[0006]

However, the above-mentioned E
Although the MI shield printed wiring board can reduce EMI interference, its specific resistance is 5 to 20 × 10 ^-5 Ω · cm, which is considerably higher than that of Cu foil. To further enhance the shielding effect, this specific resistance should be minimized. It is desired to make it smaller. An object of the present invention is to establish a hardening treatment technique for a metal paste that is effective in reducing the specific resistance in such an EMI shielded printed wiring board.

[0007]

As a result of intensive studies aimed at achieving such an object, the present inventors have found that, in the printed wiring board of this type, the applied metal paste is hardened in forming the EMI shield layer. The inventors of the present invention have come to the present invention by discovering that the goodness and badness of the effect strongly influence the sheet resistance and the like.

That is, according to the present invention, a conductor circuit is formed on a substrate, a resin insulating layer is formed, and a metal paste is applied on the resin insulating layer and then cured to form a magnetic shield layer. In a method of manufacturing an EMI shielded printed wiring board in which an overcoat layer is formed on a layer, when curing the applied magnetic shield metal paste, the first step is to heat and cure the metal paste in a vacuum oven. This invention is also an invention, and this metal paste is pre-cured by heating it in a vacuum oven at a temperature of 50 to 140 ° C, and then in a vapor phase soldering tank or far infrared furnace at a temperature of 150 to 220 ° C. Curing is the second invention.

[0009]

According to the manufacturing method of the present invention, for a single-sided printed wiring board, a double-sided printed wiring board, a multilayer printed wiring board, etc., a magnetic shield metal paste is applied onto a conductor circuit formed on the substrate and then cured. Is a technique applied when the EMI shield layer is formed. For example, it is applied to a printed wiring board in which the conductor circuit 1 is provided by a method of directly electroless plating on an epoxy resin substrate or by forming a resin insulating layer on a copper clad laminate and then etching the same. That is, in the method of the present invention, first, the through hole 5 is formed by drilling, then Cu plating is performed to form the conductor circuit 1, and the resin insulating layer 2 is formed on the conductor circuit 1 other than the through hole 5. Form. Then, a metal paste is applied to the resin insulating layer 2 for magnetic shielding, and a curing process is performed at a temperature of 150 to 220 ° C. in a vacuum oven to form the shield layer 3.

In another embodiment of the present invention, the metal paste coating layer is pre-cured in a vacuum oven at a temperature of 50 to 140 ° C. and then vapor phase which is usually used for curing. Main baking is performed at a temperature of 150 to 220 ° C in a soldering layer or a far infrared furnace.

An overcoat layer 4 is formed on the shield layer 3 of the metal paste obtained by hardening the metal paste by the above-mentioned treatment, for protection thereof. As a means for forming the overcoat layer 4, a known coating method can be applied as it is.

In the method of the present invention, the reason why the vacuum oven is used for hardening the metal paste is as follows. That is, by performing the curing treatment in vacuum,
This is because the sheet resistance, which had been a problem, is reduced because the metal paste is not oxidized.
Must be 100 Torr or less. This is because if it is more than that, the sheet resistance is increased due to oxidation.

Further, in the other application example of the present invention described above, the reason for first pre-curing at a low temperature of 50 to 140 ° C. is that the metal paste such as Cu or Ag contains a solvent. If heated rapidly, the metal paste may be hardened without completely evaporating the solvent.In this case, the metal paste may not be dense and the sheet resistance may be increased, or blistering may occur. Because.
Also, if the temperature is 50 ° C or lower, the evaporation of the solvent is insufficient,
If it is over, the sheet resistance becomes large due to the above-mentioned problems, so the pre-curing temperature must be in the temperature range of 50 to 140 ° C.

[0014]

[Example] Glass epoxy substrate (G-10, plate thickness 1.0 mm)
Then, a hole of 0.6 mmφ was drilled, electroless and electrolytic Cu plating was performed, a photosensitive laminate film was formed, and an etching process was performed to form a conductor circuit layer. Next, after forming a resin insulating layer using a printing method, a Cu paste is applied on the resin insulating layer to a thickness of 20 to 60 μm, and
Cured by vacuum oven treatment under the conditions shown in
Alternatively, after pre-curing in a vacuum oven, main baking treatment was further performed in a vapor phase soldering tank. Then, an overcoat layer was formed on the resin insulating layer with a solder resist to obtain a printed wiring board.
Table 1 shows the results of measuring the specific resistance of such a printed wiring board.

[0015]

From Table 1, it can be seen that the printed wiring board under the No. 1 processing condition of the present invention has a specific resistance of 4.0 × 10 ⁻⁵ Ω · cm, which is extremely higher than that of the printed wiring board cured in a blower oven or a vapor phase soldering tank. The specific resistance was small, and particularly, the pre-cured printed wiring board showed a good value of 3.5 × 10 ⁻⁵ Ω · cm.

[0017]

As described above, according to the method of the present invention, it is possible to obtain an EMI shielded printed wiring board having a small specific resistance, so that it is possible to provide a shield substrate useful as an EMI countermeasure for electronic equipment.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an EMI shield substrate.

[Explanation of symbols]

 1 Conductor Circuit 2 Resin Insulation Layer 3 Shield Layer 4 Overcoat Layer 5 Through Hole 6 Board

Claims (2)

[Claims] 1. A magnetic shield layer is formed by directly or indirectly forming a conductor circuit on a substrate and forming a resin insulating layer, applying a metal paste on the resin insulating layer, and then curing the paste to form a magnetic shield layer. In a method for manufacturing an EMI shielded printed wiring board having an overcoat layer formed on a shield layer, when curing the applied magnetic shield metal paste, the metal paste is heated and cured in a vacuum oven. Manufacturing method of EMI shielded printed wiring board. 2. The method of manufacturing an EMI shielded printed wiring board according to claim 1, wherein when curing the magnetic shield metal paste applied to the substrate, the metal paste is first heated in a vacuum oven at 50 to 140 ° C. A method for producing an EMI shielded printed wiring board, which comprises heating to a temperature to pre-cure, and then main curing at a temperature of 150 to 220 ° C. in a vapor phase soldering tank or a far infrared furnace.