JPH0320043B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a method for packaging a resistor chip with a metal foil resistor adhered to an insulating substrate with resin, and attaching external connection terminals to the resin-covered printed circuit board. It concerns a chip resistor exposed to the surface.

(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 resistance temperature coefficient 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.

In such a chip resistor, the chip resistor supplied from a feeder or the like is pressed onto a printed circuit board to fix it, and then soldered in a solder bath or cream solder is melted by heating.

However, when chip resistors are automatically supplied by a feeder or the like and mounted on a printed circuit board, if the pressing force is uneven for each resistor, the stress applied to the external connection terminal becomes uneven for each resistor. In particular, with high-precision products such as metal foil resistors that utilize the difference in linear expansion coefficient between an insulating substrate and a metal foil resistor, there is a problem that accuracy decreases when such mechanical stress is applied from the outside. It was hot.

(Purpose of the Invention) The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a chip-type metal foil resistor that can be mounted on a printed circuit board using a feeder or the like by pressing the resistor against the printed circuit board. Another object of the present invention is to provide a chip resistor that does not apply excessive stress to external connection terminals or a resistor chip, and can maintain high accuracy in resistance value when mounted on a printed circuit board.

(Structure of the Invention) According to the present invention, this object is achieved by manufacturing a chip in which an insulating substrate having a metal foil resistor adhered to one side is coated with two layers of flexible inner resin and hard outer resin. In the resistor, a pair of plate-shaped external connection terminals that are affixed to the other side of the insulating substrate and whose external protruding ends are folded back to the mounting surface of the exterior resin to the printed circuit board, and each of these plate-shaped external connections. A lead wire connecting the terminal and the resistor within the exterior resin, and a convex portion integrally molded on the mounting surface of the exterior resin so as not to interfere with each of the plate-shaped external connection terminals, This is achieved by a chip resistor characterized in that the external protruding end of the plate-shaped external connection terminal and the convex portion facing the printed circuit board are located on substantially the same plane.

(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. It is.

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, a portion of the plate-shaped external connection terminal 20 protrudes from the exterior resin 26 to the outside. The externally protruding portion of the terminal 20 is bent into a U-shape 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 the convex portion 28 in between. The portions of the terminals 20, 20 and the convex portion 28 that face the printed circuit board 30 are located on substantially the same plane.

The resistor 32 configured in this manner is mounted on the printed circuit board 30 by the steps shown in FIG. 3, for example, according to the dip flow method. First, an adhesive is applied to a predetermined position on the printed circuit board 30 (FIG. 3A), and the convex portion 28 of the resistor 32 supplied from a feeder or the like is pressed onto the adhesive to bond it (FIG. 3B). 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, the external connection terminal 20 and the printed circuit board 30 are fixed by the solder 34 as shown in FIG.

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.

As described above, since the mounting surface 26a of the resistor 32 is formed with the convex portion 28 located substantially on the same plane as the external connection terminals 20, 20, when the resistor 32 is pressed and bonded to the printed circuit board 30, Convex portion 28
comes into contact with the printed circuit board 30. Therefore, excessive force is not applied to the external connection terminal 20. As a result, excessive stress is not applied to the resistor chip 16, and the accuracy of the resistance value in the mounted state can be maintained at a high level.

5 is a front view of another embodiment of the present invention, FIG. 6 is a bottom view, FIG. 7 is a side view, and FIG. 8 is a sectional view taken along the line -- in FIG. 7.

In this example, the mounting surface 26Aa of the exterior resin 26A
A concave groove 40 for loading adhesive is formed in the protruding portion 28A.

According to this embodiment, when bonding the resistor 32A to the printed circuit board 30A using the dip flow method, a sufficient amount of adhesive enters the groove 40, thereby ensuring the bonding of the resistor 30A. In FIGS. 5 to 8, the same parts as those in the embodiment shown in FIGS. 1 and 2 are indicated by the same reference numerals with "A" added thereto, so the explanation thereof will not be repeated.

(Effects of the Invention) As described above, the present invention forms a convex portion on the mounting surface of the exterior resin to the printed circuit board, and aligns the convex portion and the portion of the external connection terminal facing the printed circuit board on substantially the same plane. Because of this position, even if the resistor is pressed against the printed circuit board when mounting it on the printed circuit board, the protrusion will come into contact with the printed circuit board and receive the pressing force, which will prevent excessive stress from being applied to the external connection terminals. There is no. In addition, both external connection terminals are attached to the opposite side of the insulating substrate to which the metal foil resistor is attached, and these external connection terminals and the resistor are 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. It is possible to prevent excessive external stress from being applied to the resistor chip from the external connection terminal, and it is possible to maintain high accuracy of the resistance value in the mounted state of the resistor.

[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 the dip flow method and the reflow method, respectively. 5 is a front view of another embodiment of the present invention, FIG. 6 is a bottom view, FIG. 7 is a side view, and FIG. 8 is a sectional view taken along the line -- in FIG. 7. 10, 10A... Board, 12, 12A... Metal foil resistor, 20, 20A... External connection terminal, 2
6,26A...Exterior resin. 26a, 26Aa...
Mounting surface, 28, 28A...Protrusion, 30, 30A...
...Printed circuit board, 32,32A...resistor.

Claims (1)

[Scope of Claims] 1. A chip resistor in which an insulating substrate having a metal foil resistor adhered to one side is coated with two layers of a flexible inner resin and a hard outer resin, comprising: a pair of plate-shaped external connection terminals that are affixed to the other side of the board and whose external protruding ends are folded back to the mounting surface of the exterior resin to the printed circuit board; and each of these plate-shaped external connection terminals and the resistor. A lead wire connected within the exterior resin, and a convex portion integrally molded on the mounting surface of the exterior resin so as not to interfere with each of the plate-shaped external connection terminals, A chip resistor characterized in that portions of the protruding end and the convex portion that face the printed circuit board are located on substantially the same plane.