JPH073663Y2 - Printed wiring board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a printed wiring board comprising an insulating film and a conductive vapor-deposited metal layer forming a circuit.

(Prior Art) A flexible printed wiring board generally has a structure in which an insulating film and a conductive metal foil such as copper are laminated via an insulating adhesive and then a circuit is formed. As one method for satisfying the requirement for high flexibility of formation and wiring board itself, there is a method in which a conductive metal layer is directly formed on the surface of an insulating film by vapor deposition, and the circuit conductor is formed by the vapor deposited metal layer. This is a printed wiring board in which a metal layer is an extremely thin vapor-deposited layer, so that a fine circuit can be easily formed in an etching process and the flexibility is extremely high.

FIG. 3 is a schematic cross-sectional view of a main part of a conventional printed wiring board. In FIG. 3, 1 is an insulating film and 2 is a circuit conductor made of a vapor-deposited metal layer. Generally, a flexible protective film 3 made of an insulating resin film or the like is provided on the circuit conductor 2 except for the parts where components are mounted. Reference numeral 4 denotes an opening of the protective film, and the circuit conductor 2 is exposed at this portion. When mounting a component, the component is mounted on the circuit conductor 2 exposed in the opening 4 and connected by soldering.

By the way, since the thickness of the vapor-deposited metal layer forming the circuit conductor 2 is usually about 1 to 5 μm, an alloy layer with a dissimilar metal cannot be formed, and soldering to the circuit conductor 2 during component mounting is extremely difficult. is there. Therefore, usually, the plating layer 5 made of the same metal as the vapor-deposited metal layer is formed on the exposed portion of the circuit conductor 2 for mounting components, which enables the formation of an alloy layer at the time of soldering.

(Problems to be Solved by the Invention) In such a printed wiring board as described above, after the protective film 3 having the opening 4 for mounting a component is provided on the circuit conductor 2, as described above. Exposed circuit conductor 2
Since the plating layer 5 is formed on the upper surface of the circuit conductor 2 by electrolytic plating, the circuit conductor 2 has a thin portion including only the vapor-deposited metal layer and a thick portion including the vapor-deposited metal layer and the plating layer. 6 naturally coincides with the boundary of the opening portion of the protective film.

Therefore, there is no problem as long as the components are mounted and the circuit conductor in the opening and the components are connected by soldering, but when the wiring board is subsequently distorted or bent, the stress is applied to the protective film. It is not only the boundary of the opening part of 3 and the boundary 6 of the thickness of the metal layer, but it is easy to cause a crack in this part, which not only causes the cutting / breaking of the circuit,
It becomes easy for the parts to drop off together with the plating layer from the insulating film. In particular, such an accident is likely to occur frequently in a wiring board on which an extremely fine circuit is formed. Such a problem is not limited to the soldering as described above and is the same in the connection mode such as the connector portion.

(Means and Actions for Solving the Problems) The present invention has been made to solve the above problems. The plating layer as described above is wider than the periphery of the exposed portion of the circuit conductor by 0.1 mm or more to the outside. A structure in which the peripheral portion is extended and covered with a protective film, that is, a boundary portion between a thin portion of the circuit conductor consisting only of the vapor-deposited metal layer and a thick portion of the vapor-deposited metal layer covered with the plated layer is covered with the protective film. The structure is reinforced by being torn.

By adopting the structure as described above, it is possible to prevent stress concentration due to the deformation of the wiring board from being directly applied to the opening of the protective film at the boundary portion of the thickness of the circuit conductor, and this part is protected by the protective film. Therefore, cracks are unlikely to occur.

(Embodiment) FIG. 1 (a) is a schematic sectional view of a main part of an embodiment of a printed wiring board according to the present invention. In the figure, 1 is an insulating film, 2 is a vapor-deposited metal layer forming a circuit conductor, 3 is a protective film, 4 is an opening of the protective film, and 5 is a plating layer. The plating layer 5 extends from the outer periphery of the opening 4 to a range indicated by a, and a is 0.1 mm or more, and this portion is covered with the protective film 3. FIG. 1B is a plan view of the above printed wiring board as seen from above.

In order to explain the method for manufacturing the above-mentioned printed wiring board, FIGS. 2 (a) to (e) show schematic cross-sectional views of a main part in the order of manufacturing steps of the above-mentioned printed wiring board. First, as shown in (a), the circuit conductor 2 is formed on the insulating substrate 1 by the vapor-deposited metal layer, and as shown in (b), the plating resist 7 intended only for masking the plating process is formed, and the protective film formed later. Formed with a larger opening than the opening,
A plating process is performed as shown in (c) to form a plating layer 5, and the plating resist 7 is removed as shown in (d).
As shown in (e), the protective film 3 is provided so as to cover the peripheral portion of the plating layer 5 to obtain a printed wiring board as shown in FIG.

(Effects of the Invention) In the printed wiring board of the present invention, the plated layer of the circuit conductor by the plating treatment of the opening portion used for mounting the soldering component is provided wider than the opening portion, and the thin portion and the thick portion of the circuit conductor are formed. The boundary part of is located outside the opening of the protective film, and the stress concentration due to the deformation of the wiring board is not directly concentrated on the above-mentioned boundary part, and the boundary part which is the weak point is Since it is reinforced by the protective film, cracks are less likely to occur, and it is possible to prevent disconnection / breakage of the circuit or dropping of mounted components.

[Brief description of drawings]

1 (a) is a schematic cross-sectional view of the main part of the printed wiring board according to the present invention, (b) is a plan view seen from above (a),
FIGS. 4A to 4E are sectional views showing the main part of the printed wiring board shown in FIG. 1 in the order of manufacturing steps, and FIG. 3 is a schematic sectional view of the main part of the conventional printed wiring board. 1: Insulating substrate, 2: Circuit conductor consisting of evaporated metal layer, 3: Protective coating, 4: Protective coating opening, 5: Plating layer.

Claims (1)

[Scope of utility model registration request] 1. A protective film having an opening for mounting a component is provided on a circuit conductor formed of a vapor-deposited metal layer on an insulating substrate, and a plating layer is formed on the surface of the circuit conductor exposed in the opening. In a printed wiring board provided, the plating layer is extended to 0.1 mm or more outside the peripheral edge of the opening, and the peripheral edge of the plating layer is covered with the protective film. Board.