JP3366815B2 - Large current circuit board - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large current circuit board in which circuit conductors are provided on a circuit pattern formed on an insulating substrate. 2. Description of the Related Art Conventionally, to reduce the size and weight of devices, the space of circuit boards has been reduced, and circuit patterns for large currents and circuit patterns for small currents are mounted on the same substrate. A provided large current circuit board has been proposed. FIG. 3 shows an example of a conventional large current circuit board. This large-current circuit board forms a large-current copper foil circuit pattern 21a and a minute-current copper foil circuit pattern 21b on the surface of an insulating substrate 11 made of a glass epoxy material or the like by pattern etching. A metal plate circuit conductor 31 formed by punching a copper plate or the like is joined on a copper foil circuit pattern 21a for use via a solder layer 41a. In this large current circuit board, the size of the metal plate circuit conductor 31 is larger than the width of the large current copper foil circuit pattern 21a in order to facilitate the arrangement of the metal plate circuit conductor 31 on the copper foil circuit pattern 21a. It is formed small. Further, the metal plate circuit conductor 31, the copper foil circuit pattern 21a, and the insulating substrate 11 are provided with through-holes penetrating the three components, and the holes 51 provided in the metal plate circuit conductor 31 are provided with the copper foil circuit pattern. 21a and the hole 61 of the insulating substrate. Hole 6 in insulating substrate 11
1 serves as a vent path. In addition, the metal plate circuit conductor 3
By forming the hole 51 in the hole 1, the inside of the hole is filled with solder when soldering, so that the bonding of the metal plate circuit conductor 31 is strengthened. However, in such a circuit board, the size of the metal plate circuit conductor 31 is changed to the copper foil circuit pattern 2.
1a, the conductor cross-sectional area is limited, and the width of the copper foil circuit pattern 21a must be increased in order to increase the current carrying capacity, which hinders the space saving of the circuit board. . In addition, the fact that the size of the metal plate circuit conductor 31 is smaller than the copper foil circuit pattern 21a means that the area where the metal plate circuit conductor 31 and the copper foil circuit pattern 21a are in contact with each other is also small, and the bonding strength may be insufficient. There is. Further, holes must be provided in the metal plate circuit conductor 31, the copper foil circuit pattern 21a and the insulating substrate 11 for degassing and increasing the bonding strength,
Therefore, there is a problem that a circuit pattern cannot be arranged on the opposite surface of the circuit board in some cases. Another example of a conventional large current circuit board is shown.
There is a circuit board in which the circuit conductor 32 of the circuit board shown in FIG. 4 is made of a metal foil circuit conductor having a small thickness (FIG. 4). However, in this circuit board, since the thickness of the circuit conductor 32 is small, when soldering the circuit pattern 22 a and the circuit conductor 32, a sufficient amount of solder is applied to the joint surface and the side surface of the metal foil circuit conductor 32. However, there is difficulty in the bonding strength.
Further, since the thickness of the metal foil circuit conductor 32 is small, the solder easily rises along with the flux on the upper surface of the metal foil circuit conductor 32 (42b in FIG. 4), and the finished appearance may be impaired. Generally, components mounted on a circuit board for a large current are heavy. Therefore, for example, even if a large current circuit board is installed vertically and a large load is applied to the joint between the circuit conductor and the circuit pattern, the circuit conductor is not separated from the circuit pattern by vibration or heat shock. Strong bonding is required between the patterns. SUMMARY OF THE INVENTION An object of the present invention is to provide a long-term reliability in which the joint strength between a circuit conductor and a copper foil circuit pattern is improved while realizing an increase in current carrying capacity and space saving. An object of the present invention is to provide a high high-current circuit board. [0008] That is, the present invention relates to a large current circuit board in which a circuit pattern for a large current is formed on the surface of an insulating substrate and a circuit conductor is provided on the circuit pattern. Another object of the present invention is to provide a large current circuit board in which a side end of a circuit conductor is bent in a direction away from a circuit pattern, and a fillet is formed between the side end of the circuit conductor and the circuit pattern. In the present invention, the joint strength between the circuit conductor and the circuit pattern can be increased by the fillet formed between the side end of the circuit conductor and the circuit pattern. In addition, gas generated between the circuit pattern and the circuit conductor when the circuit conductor and the circuit pattern are joined is easy to escape because the distance between the side end of the circuit conductor and the circuit pattern is large. It is not necessary to provide it. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In this large current circuit board, a circuit pattern 20a is formed on an insulating substrate 10, and a circuit conductor 30 whose side end 30a is bent away from the circuit pattern 20a is formed on the circuit pattern 20a via a solder layer 40a. It is provided. A fillet 40c is formed between the side end 30a of the circuit conductor 30 and the circuit pattern 20a.
Although FIG. 1 shows the copper foil circuit pattern 20b for a minute current, this is shown as an example, and the present invention is applicable to a large current circuit board having no circuit pattern for a minute current. It is of course applicable. The degree of bending of the side end 30a of the circuit conductor in the present invention is, as shown in FIG. 2, a vertical line and a horizontal line extending from the lower end b of the edge a of the circuit conductor from the point at which the circuit conductor separates from the horizontal plane. 0.7m distance d to the intersection
It is appropriate that m ≦ d ≦ 1.7 mm, and the distance h from the lower end b of the edge a of the side end 30 a to the horizontal plane be h ≦ 2.9 mm. As the circuit conductor, a foil of copper or the like having high conductivity and good workability can be used after being processed into a predetermined shape having a thickness and a width corresponding to the current carrying capacity. Is used. As a method for producing a circuit conductor, there is a method in which a metal foil or a metal plate is punched by a mold, and then a side end is bent or cut off with a blade. The selection is made in consideration of the type, thickness, and the like. In the production using a mold, first, a flat circuit conductor is punched, and then a side end is bent. In the case of a copper foil having a thickness of 50 to 300 μm, a method of punching by parting with a big blade or the like can be applied. According to the punching process using the big blade, the punch-out formed in the circuit conductor at the time of the punching process can be directly used as the side end of the circuit conductor in the present invention, and is preferable in that it is simple and inexpensive. The large current circuit board of the present invention is manufactured in the same procedure as a normal circuit board. When the circuit pattern and the circuit conductor are joined by soldering, usually, cream solder is screen-printed on the circuit pattern of the insulating substrate, and then the circuit conductor is arranged on the pattern and reflowed to complete the soldering. At this time, the melted cream solder is filled between the side end 30a of the circuit conductor 30 and the circuit pattern 20a by the action of capillary action, and forms a solder fillet 40c by surface tension. [0015] Melting of the cream solder can be easily carried out by using a copper foil having a small heat capacity as a circuit conductor by passing the copper solder through a reflow furnace. When a metal made of a metal having a large specific heat is used or a copper plate having a small specific heat is made of a thick plate, the heating is performed by bringing a heating device into close contact with the substrate and hot pressing. A jig having a heating surface having substantially the same shape as the flat portion excluding the side end of the conductor circuit is attached to the heating device, and the jig is placed on the circuit board when the heating device is placed on the circuit board. Are arranged so that the heating surface of the jig contacts the flat portion of the circuit conductor. It is sufficient that the width of the heating surface is 50% or more of the width of the flat portion of the circuit conductor. By changing the jig attached to the heating device, it is possible to cope with various types of substrates. The bonding between the circuit pattern and the circuit conductor may be performed by providing an adhesive or an adhesive tape in advance along the center line of the width of the circuit pattern. In order to electrically connect to the circuit conductor and form a fillet, it is necessary to apply cream solder or conductive paste to the outer periphery of the circuit pattern. In the case where components other than the circuit conductors are passed through the solder bath at the time of mounting components, there is no need for a process for imparting conductivity between the circuit patterns and the circuit conductors in the joining step between the circuit patterns and the circuit conductors. According to the large current circuit board of the present invention, since the fillet is formed between the side end of the circuit conductor and the circuit pattern, the conductor circuit and the conductor pattern are joined sufficiently firmly. It has excellent vibration resistance and heat shock resistance. In addition, when the thickness of the circuit conductor is small, even if the solder is slightly larger when joining the circuit conductor, it is absorbed between the side end of the circuit conductor and the circuit pattern, so that the solder flows around the upper surface of the circuit conductor. This makes it possible to reduce defects such as poor appearance. Furthermore, at the time of joining the circuit conductor and the circuit pattern, gas generated between the circuit pattern and the circuit conductor easily escapes from the gap between the side end of the circuit conductor and the circuit pattern,
Since it is not necessary to take any special measures such as providing a hole for venting gas, it is possible to simultaneously increase the current carrying capacity and save space.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view showing one embodiment of a large current circuit board according to the present invention. FIG. 2 is a schematic sectional view of a thick circuit conductor side end according to the present invention. FIG. 3 is a schematic sectional view showing a conventional large current circuit board. FIG. 4 is a schematic sectional view showing another conventional large current circuit board. [Description of Signs] 10 Insulating substrate 20a Metal foil circuit pattern 20b for large current Metal foil circuit pattern 30 for small current Circuit conductor 30a for large current Side end 40a Solder layer 40c Fillet 90 Horizontal plane 11 Insulated substrate 21a Large current Copper foil circuit pattern 21b for small current Copper foil circuit pattern 31 for small current Metal circuit conductor 41a for large current Solder layer 51 Hole 61 Gas vent hole 12 Insulating substrate 22a Copper foil circuit pattern 22b for large current For small current Copper foil circuit pattern 32 Circuit conductor 42a for large current Solder layer 42b Bleed of solder layer

Claims (1)

(57) [Claim 1] In a large current circuit board in which a circuit pattern is formed on a surface of an insulating substrate and a circuit conductor is provided on the circuit pattern, a side end of the circuit conductor is formed. A large current circuit board that is bent away from the circuit pattern and has a fillet formed between the side end of the circuit conductor and the circuit pattern.