JPH0328041B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a chip resistor in which a resistor chip having a metal foil resistor adhered to an insulating substrate is exteriorized with resin, and external connection terminals are exposed to the mounting surface of the exterior resin to the printed circuit board. It is related to vessels.

(Background of the invention) A metal foil resistor containing nickel, chrome, etc. is attached to an insulating substrate such as alumina or glass.
Conventionally, there is a metal foil resistor in which a resistance pattern is formed on the metal foil resistor by photo-etching or the like to form a resistor chip, a lead wire is connected to the resistor, and then the whole is covered with resin.

In this type of resistor, by matching the linear expansion coefficient of the substrate and the temperature coefficient of resistance of the resistor, it is possible to suppress fluctuations in resistance value with respect to temperature and obtain a highly accurate resistor. That is, changes in the resistance value of the resistor due to temperature rise are offset by applying stress to the resistor using linear expansion of the substrate, thereby reducing the temperature coefficient of resistance.

It has been considered that such metal foil resistors are chip-shaped, with external connection terminals facing the mounting surface of the exterior resin on the printed circuit board.

Such chip resistors are often subjected to stress when mounted on a printed circuit board. For example, when a resistor is temporarily attached to a printed circuit board with adhesive, the adhesive is heated and cured, and then soldered in a jet soldering bath (dip flow method), or the resistor is temporarily attached with cream solder and soldered using an infrared oven. In the case of heating and melting (reflow method), residual stress is applied to the resistor after soldering due to the difference in thermal expansion coefficient between the board and the resistor or solder.

In particular, high-precision products such as metal foil resistors that utilize the difference in coefficient of linear expansion between an insulating substrate and a metal foil resistor are said to lose their accuracy when such mechanical stress is applied from the outside. There was a problem.

(Objective of the Invention) The present invention was made in view of the above circumstances, and even if stress is applied from the external connection terminal side during mounting on a printed circuit board, stress will not be applied to the resistor itself, especially the resistance chip. It is an object of the present invention to provide a chip resistor that can be made difficult to maintain a highly accurate resistance value in a mounted state.

(Structure of the Invention) According to the present invention, this purpose is to cover an insulating substrate with a metal foil resistor attached to one side in two layers with a flexible inner resin and a hard outer resin, In a chip resistor in which a plate-shaped external connection terminal faces the mounting surface of the exterior resin to the printed circuit board, the external protruding end is attached to the other side of the insulating substrate and is attached to the mounting surface of the exterior resin to the printed circuit board. a pair of plate-shaped external connection terminals that protrude outward from a surface other than the surface and are bent toward the mounting surface with a gap between them and the exterior resin; each of these plate-shaped external connection terminals and the resistor; This is achieved by a chip resistor characterized by comprising a lead wire that connects the resistor and the resistor within the exterior resin.

(Example) Fig. 1 is a sectional view of an embodiment of the present invention, Fig. 2 is an exploded perspective view showing the assembly process, and Figs. 3 and 4 are illustrations of the mounting process using the dip flow method and the reflow method, respectively. be.

In these figures, reference numeral 10 denotes an insulating substrate, for which alumina, glazed alumina, borosilicate glass, soda glass, diamond, sapphire, steatite, or the like is used. 12 is a metal foil resistor made of nickel, chrome, copper,
The foil is made by rolling an alloy containing aluminum, etc., and then heat-treated in a vacuum (approximately 10 ^-6 Torr) to remove the processing strain caused by rolling and obtain the desired resistance-temperature characteristics. This resistor 12 is adhered to one surface of the substrate 10 with an adhesive 14. Here, as the adhesive 14, an adhesive with good heat resistance is suitable.

After the resistor 12 is bonded to the substrate 10 in this manner, a resistor pattern is formed on the resistor 12 by a method such as photo-etching to form a resistor chip 16. One ends of lead wires 18, 18, such as gold wires, are connected to this resistor 12 by ultrasonic welding or the like.

Reference numerals 20 and 20 denote a pair of external connection terminals, which are made of metal plates such as tin plated annealed copper plates. The widened end portions of the external connection terminals 20 are arranged facing each other as shown in FIG.
2 (FIG. 1). A thermosetting epoxy resin, a rubber adhesive, or the like can be used as the chip fixing resin 22, and it is particularly preferable to use a rubber adhesive because stress is not directly applied to the substrate 10 by the external connection terminals 20. The other end of the lead wire 18 is connected to the external connection terminal 20 by ultrasonic welding or the like (see FIG. 2B).

After being assembled in this manner, the periphery of the substrate 10 is double coated with a rubber resin 24 having appropriate elasticity and a hard resin 26. As a result, the plate-shaped external connection terminal 20 protrudes to the outside from the side surface of the exterior resin 26, that is, the side surface that is substantially perpendicular to the mounting surface 26a to the printed circuit board 30. The externally protruding portion of the terminal 20 is bent into a U-shape with a gap between it and the exterior resin 26 so as to face the lower surface of the exterior resin 26, that is, the mounting surface 26a to the printed circuit board 30. Further, a convex portion 28 is formed near the center of the lower surface of the exterior resin 26, and the terminals 20, 20 face each other with this convex portion 28 in between. Chip resistor 32 is produced in this way.

This resistor 32 is mounted on the printed circuit board 30 by the steps shown in FIG. 3, for example, according to the dip flow method. First, adhesive is applied to a predetermined position on the printed circuit board 30 (FIG. 3A), and the convex portion 2 of the resistor 32 is applied to the adhesive from a feeder or the like.
8 and adhere it (B in the same figure). After inspecting the mounting position of the resistor 32 and confirming that it is correctly mounted (C in the same figure), the adhesive is cured with ultraviolet rays and heated with far infrared rays (D in the same figure). After applying flux, it is soldered in a jet solder tank or a flat static solder tank (E in the same figure), and then cooled, washed, and dried (F in the same figure). As a result, as shown in FIG.
Fixed by 4.

In addition, when mounting by reflow method, as shown in Fig. 4, cream solder is applied on the printed circuit board 30 (Fig. 4A), and external connection of the resistor 32 supplied by a feeder etc. After attaching the terminal 20 (B in the same figure) and inspecting the attached state (C in the same figure), cream solder is heated and melted in an infrared heating furnace (D in the same figure). Then, by cooling, washing, and drying (E in the same figure), soldering is performed as shown in FIG.

The resistor 32 is soldered to the printed circuit board 30 in this heated state, but stress in the direction of expansion and contraction is applied to the two external connection terminals 20 and 20 when the resistor 32 is cooled down due to temperature changes. However, external connection terminal 2
0, a portion 20a substantially perpendicular to the mounting surface 26a of the exterior resin 26 is formed with a slight gap between it and the exterior resin 26. Therefore, the stress in the expansion/contraction direction is applied to this almost vertical portion 20a of the exterior resin 26.
It is absorbed by deforming toward or away from the object. Therefore, this stress in the direction of expansion and contraction is not applied directly to the exterior resin 26, but is applied to the internal resistance chip 16.
The stress applied to it also becomes significantly smaller. As a result, the accuracy of the resistance value when the resistor 32 is mounted on the printed circuit board 30 is improved.

In the above embodiment, the external connection terminal 20 is made to protrude outward from the side surface of the exterior resin 26 that is substantially upright with respect to the mounting surface 26a to the printed circuit board 30, and the external connection terminal 20 is bent toward the mounting surface 26a. A substantially vertical portion 20a was formed. However, in the present invention, external connection terminals may be made to protrude from another surface, for example, the upper surface opposite to the mounting surface 26a, and may be bent toward the mounting surface 26a. In other words, the external connection terminal is attached to the mounting surface 26.
Any material may be used as long as it protrudes to the outside from a surface other than a and is bent toward the mounting surface with a gap between it and the exterior resin.

(Effects of the Invention) As described above, the present invention allows the external connection terminal to protrude outside from the surface of the exterior resin other than the mounting surface to the printed circuit board, and mounts the external connection terminal with a gap between this protruding portion and the exterior resin. Since it is bent in the plane direction, even when a resistor is soldered to a printed circuit board, stress is absorbed by slight deformation of the externally protruding portion of the external connection terminal. Therefore, no large stress is applied to the resistor, and the accuracy of the resistance value when mounted on a printed circuit board is improved. In particular, since the external connection terminal is made to protrude to the outside from a surface other than the mounting surface, the external connection terminal becomes sufficiently long, and the stress during soldering can be well absorbed by utilizing the elasticity of the external connection terminal itself. In addition, both external connection terminals were attached to the opposite side of the insulating substrate to which the metal foil resistor was attached, and these external connection terminals and the resistor were connected by lead wires within the exterior resin. Therefore, even if stress is applied to the external connection terminal, that stress will not be applied to the resistor, further improving the accuracy of the resistance value.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is an exploded perspective view showing the assembly process, and FIGS. 3 and 4 are illustrations of the mounting process using a dip flow method and a reflow method, respectively. 10...Substrate, 12...Metal foil resistor, 20...
...External connection terminal, 26...Exterior resin, 26a...
Mounting surface, 30... Printed circuit board, 32... Resistor.

Claims (1)

[Claims] 1. An insulating substrate with a metal foil resistor pasted on one side is covered with two layers of a flexible inner resin and a hard outer resin, and a printed circuit board of this outer resin is used. In a chip resistor having a plate-shaped external connection terminal facing the mounting surface of the chip resistor, the chip resistor is affixed to the other side of the insulating substrate, and its external protruding end is exposed to the outside from a surface other than the mounting surface of the exterior resin to the printed circuit board. A pair of plate-shaped external connection terminals that protrude and are bent toward the mounting surface with a gap between them, and each of these plate-shaped external connection terminals and the resistor are placed within the exterior resin. A chip resistor comprising a connecting lead wire.