JPS62126517A - Small size fuse for printed wiring board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a method for connecting fuse elements of a small fuse for a printed wiring board (hereinafter referred to as a printed board). Here, the term "small fuse" refers to a case in which the dimensions of the housing case are, for example, about IOX 8 XIO to 4 Dragon 3, and the maximum current carrying capacity of the fuse element is about 5 amperes.

(Prior art and problems to be solved) Figure 1 is a cross-sectional view showing an example of the structure of a conventional small fuse for printed circuit boards.
This figure shows that a fuse element (fuse wire) is installed at the bent ends of the two lead wires 3 and 4 introduced into the fuse case l, and this fuse element is fixed to the lead wire hardware. . Methods for fixing the fuse element to the lead wire hardware include l) soldering, 2) caulking, 3) applying conductive paint such as silver paste after caulking, and 4) spotting. However, these methods have the following problems.

(1) Soldering.

a) It is necessary to wrap the fuse wire around the lead wire hardware. So-called cleats are unreliable and cannot be used.

b) Solder and flux must be supplied each time. C) The amount of solder cannot be kept constant. d) The heating and melting time is long (and not constant); e) For a) and b), in the case of small fuses, mass production is difficult and the number of man-hours increases. f
) If the fuse element is thin, the number of cleaning steps will increase to avoid corrosion. g) Due to variations in the spread of solder, the effective length of the element varies, causing variations in fuse characteristics. h) Element materials that are easily susceptible to solder diffusion, such as copper, silver, and their alloys, cause so-called "solder eating" and thin wires of 100 μm or less cannot be used because they will break and deteriorate.

(2) Mere caulking.

The connection between the lead wire hardware and the thin wire fuse element is electrically incomplete, increases the resistance value, has large variations, and changes over time, so it cannot be used for small fuses.

(3) Caulking and conductive paint.

The application and drying process of conductive paint is required, and electrical connection using 4-electrode paint has significantly lower performance and reliability than soldering or spot bonding for heat-generating components such as fuses.

(4) Spotting a) It is necessary that the difference in melting point between the lead wire hardware and the fuse element be small, and the selection of materials is extremely limited. b) It is necessary that the difference in heat capacity between the lead wire hardware and the fuse element be small, but spotting cannot be done stably with thin wires. C) Thin wires cannot be used because the fuse element in the spot portion is greatly deformed and the mechanical strength is significantly reduced.

(Means for Solving the Problems) In the present invention, as means for solving the above-mentioned conventional problems, 1) the lead wire hardware is coated with a low melting point metal by plating in advance; 2) the fuse element is coated with the lead wire hardware. Temporarily secure it by crimp it between the folded parts.

3) Connect the fuse element and lead wire hardware by resistance welding.

Each method is used in turn.

(Structure and operation of the invention) The manufacturing process of the fuse of the present invention using the above-mentioned means will be explained in detail with reference to the embodiment shown in FIG.

(1) First, the lead wire hardware (actually manufactured from a thin plate with a width of 0.7 fl and a thickness of about 0.4 mm, but hereinafter simply referred to as a terminal) is pressed into a thin metal plate as shown in Figure 2 (a). to form a set of two.

(2) Perform low-fusion metal plating on each terminal. The low alloy metal is Sn, which is used for soldering and has a melting point of 350°C or lower.

Sn alloy + S n P b + I nl I n
It may be made of metal such as an alloy and has a thickness of about 2 to 10 μm.

(3) Bend a part of the terminal. The state is shown in Figure 2(b)
Either the head part may be bent as shown in FIG. 2(C), or a part of the middle may be bent as shown in FIG. 2(C).

(4) Continuously caulk and fix the fuse element. Figure 2 (dl) combines steps (4) and (5); 5 in the figure is a continuous line of the fuse element, 6 is caulking, 7 is spot welding, and 8 is a line other than between a pair of terminals. 3 shows each step of removing extra element lines.

The caulking should be light enough to temporarily secure the element. Also, the fuse element is copper.

Copper alloy, nickel, nickel alloy, silver, silver alloy.

Alternatively, a material that can be soldered with nickel or other plating and a wire diameter of 100 μm or less can be used. Furthermore, since the terminal and the fuse element have a sandwich structure, the precision of the position of the fuse element and the spot electrode is rough (and deformation of the fuse element is also protected).

(5) Spot and cut off the excess fuse element length. Regarding spot welding, an AC or DC spot welding machine and its setting conditions are appropriately selected depending on the combination of the terminal and the fuse element.

Unlike conventional spotting, this spotting does not require the formation of nuggets between bonded metals, so it is not limited by the materials and dimensions of the fuse element and terminal. Furthermore, because the heating time is spot-on, the heating time is short and constant, so there is no thermal deterioration of the fuse element. In addition, in the joints created by this type of processing, there is only an extremely thin diffusion layer between the terminal and the fuse element, so even if the temperature of the joint is raised above the melting point, the soldering will not loosen, as in the case of soldering. Suitable for connecting fuse elements that generate heat during use.

Furthermore, if infrared heating or soldering with a soldering iron is used instead of spot bonding, not only will the above-mentioned problem due to FRA 7x occur, but also problems due to diffusion and thermal deterioration of the fuse element will occur due to increased heating time. .

(6) Assemble into the housing and separate. As shown in FIG. 2 (el), a housing (or case) 9 is placed over the pair of terminals and assembled into the housing, and then cut away from the metal plate 11, leaving a drawn-out portion 10 long enough to serve as a lead terminal. After cutting, fit the housing bottom plate etc. so that the fuse element does not come out from the housing 9.

(Effect of the invention) By implementing the present invention, the following effects can be obtained.

■) Thin fuse elements that could not be used in the past: 15 μmφ Ni wire, 25 μmφ limiter wire, 2
Ag wires up to 0 μmφ can now be used. Previously, such thin lines could only be prototyped by hand, and there was no hope of mass production.

2) A small, lightweight, and highly reliable fuse for printed circuit boards housed in a housing of about 4 m3 can now be obtained at low cost.

3) In the end, the current carrying capacity is maximum 5A and minimum 0. Fuses of IA or lower are now available as mass-produced products in the form of 2).

[Brief explanation of drawings]

Figure 1 is an example of the structure of a conventional small fuse for printed circuit boards.
FIG. 2 is an explanatory diagram of the manufacturing process of a fuse according to the present invention. 1.9... Fuse housing (outer box), 2.5.
... Fuse element, 3.4 ... Terminal hardware (terminal board), 6 ... Caulking process of the bent terminal part, 7 ... Spot welding process,
8...Excess fuse element removal process, 10.
...3.4 drawer terminal part.

Claims (1)

[Claims] After coating and fixing a low melting point metal having a melting point lower than the melting point of the fuse element on the surfaces of a pair of metal terminals at regular intervals, which also serve as the fuse element support and lead wire, by surface treatment such as plating or coating, A fuse element is connected between a pair of terminals by sandwiching the fuse element between a terminal and a member having the same quality and surface treatment as the terminal, and melting the coating metal on the terminal surface by pressure heating such as spot welding. A small fuse for printed wiring boards characterized by a