JP2516606Y2 - Surface mount electronic components - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin surface mount type electronic component, and more particularly to an electronic component in consideration of mounting on a printed wiring board.

[0002]

2. Description of the Related Art With the miniaturization of electronic devices, it is required that electronic components have a low overall height and be mounted on a printed wiring board at a high density, and that the mounting is performed by an automatic machine. There is. In order to meet this demand, there is an urgent move to make electronic parts thinner and leadless chip type. Generally, chip type electronic parts are
It is possible to reduce the volume, including the total height, as compared with an electronic component using a hermetically sealed container represented by a popular crystal unit. FIG. 3 is a side view showing a state in which the chip-type resistor is attached to the printed wiring board. Such a chipped electronic component is provided with a lead electrode on the lower surface thereof. It was connected to an external electrode such as a printed wiring board. In FIG. 3, 3 is a chip resistor, 41 and 42 are lead electrodes, S is solder, and P is a printed wiring board. Usually, the extraction electrode is formed by baking silver-palladium with molten glass on the extraction electrode portion of the resistor. The connection with the printed wiring board is a flow of automation of electronic device assembly, and electro-mechanical joining of electronic components to the printed wiring board is often performed by reflow soldering. Reflow soldering is a method in which an appropriate amount of solder (for example, Pb-Sn system solder) is supplied in advance to the joint portion, the solder is melted by an external heat source, and soldering is performed, which is suitable for surface mounting. It is a joining method.

[0003]

[Problems to be solved by the invention] Chip type electronic parts are
As described above, the electro-mechanical bonding to the printed wiring board is often performed firmly by the reflow soldering. However, the lead electrode is joined to the printed wiring board by the combination of silver-palladium and solder, but as shown in FIG. 4, focusing on the surface of the lead electrode 42 and the solder S layer, a metal of silver or palladium is used. The molecules P move to the solder layer side (indicated by arrow A) and become in a eutectic state with the metal forming the solder, and the conductor particles on the surface of the extraction electrode, that is, silver palladium, decrease.
Such a state is not a problem in the case of normal reflow soldering, but when trying to reconnect the electronic component due to a connection error, etc. Due to the decrease in reconnection, reconnection sometimes became impossible.

The present invention has been made in order to solve the above-mentioned problems, and the conductive connection between the printed wiring board and the electronic component can be surely performed, and even if the electronic component is reconnected, the conductive component is electrically connected. It is an object of the present invention to provide a surface mount electronic component that does not deteriorate the connectivity.

[0005]

In order to solve the above problems, a surface mount type electronic component according to the present invention is provided with a plurality of extraction electrodes on the bottom surface, and these extraction electrodes and electrode pads of a substrate to be mounted. In a chip-type electronic component mounted on a substrate by soldering, a metal film made of high melting point solder having a melting point higher than at least the soldering temperature is formed on the uppermost layer of the extraction electrode. It is a thing. Further, when performing solder joining at a relatively high temperature, even if a metal film is formed of high melting point solder and a metal thin film having a higher melting point such as nickel is formed on at least the upper surface of the high melting point solder film. Good.

[0006]

When an electronic component is mounted on a printed wiring board, a thick metal film made of at least a high melting point solder is formed on the extraction electrode, so that it is very well compatible with the solder applied on the printed wiring board. It is considered that this is because the interface between the upper layer of the high melting point solder and the solder layer on the side of the printed wiring board which is in contact with the high melting point solder is made of the same kind of metal, and the metal bonding is performed firmly. Also when reconnecting, since no binder such as molten glass is used, metal particles at the interface portion do not decrease. The high melting point solder can be easily formed by a method such as screen printing even after completion of the electronic component. Further, by forming a metal thin film having a high melting point, for example, a thin film made of nickel, on the upper surface of this thick film, it is possible to prevent melting of the thick film layer when joining at a relatively high temperature.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings, taking a chip type crystal oscillator as an example. The same structural parts as in the conventional example will be described with the same numbers. The same applies to the other embodiments described below. FIG. 1 is a bottom perspective view showing an embodiment of the present invention, and FIG. 2 is a side view. The chip-type crystal unit 1 has a package made of alumina, and a crystal vibrating piece (not shown) having electrodes formed therein is housed in the internal space, and the electrodes pulled out from the vibrating units are extraction electrodes 21, 22, 23. , 24 electrically connected. Each extraction electrode 21, 22, 23, 24
Respectively contact the package with the tungsten layer 21.
a, 22a, 23a, 24a (partly not shown) are provided, and the nickel thin film layers 21b, 22b, 23 are provided on the upper surfaces thereof.
b, 24b (partly not shown) are plated, and metal films 21c, 22c, 23 made of high melting point solder are further formed on the upper surface thereof.
c and 24c (partly not shown) are provided. The high melting point solder may be set to a melting temperature higher than the melting temperature at which the extraction electrode is soldered. For example, when using a well-known eutectic solder having a melting point of 183 ° C., However, it is only necessary to use a high melting point solder that is several tens of degrees Celsius higher than this, especially when soldering is performed using the reflow soldering method as described above, the degree to which melting does not occur at the reflow set temperature (for example, 230 ° C) It is necessary to choose a high melting point solder. Thus, high melting point solder is Pb-S
The so-called Pb rich which increases the ratio of Pb in the n-based solder, or similarly Ag is added, or a solder other than the Pb-Sn solder is used (for example, Pb-Sn).
In type) and the like. The metal films 21c, 22c, 23c and 24c made of high melting point solder are formed by, for example, forming a thick film of solder paste by a screen printing technique and then vaporizing the binder at around 250 ° C. In this embodiment, the tungsten layer is about 10 μm, the nickel layer is several tens of μm, and the metal film made of high melting point solder is 100 μm.
Although the thickness is set to μm, if it is necessary to increase the distance between the electronic component and the printed wiring board, for example, to improve the cleaning property, the metal film may be thickened to about 400 μm. Although not shown, the bonding with the printed wiring board is performed at a relatively high temperature (for example, 250
When performed at a temperature of not less than 0 ° C.), a thin film layer such as nickel plating may be provided on the upper surface of the metal film in order to protect the metal film made of high melting point solder.

[0008]

[Effect of the Invention] When an electronic component is mounted on a printed wiring board, a metal film made of at least a high melting point solder is formed on the extraction electrode, so that the familiarity with the solder applied on the printed wiring board becomes extremely good. , Electronic components can be connected in a highly reliable and highly reliable state.
Such an improvement in solderability is effective even during reflow soldering, and highly reliable soldering can be performed. Also, when reconnecting, since the extraction electrode is a high melting point solder that does not use a binder such as molten glass, the metal particles at the interface portion do not decrease, and the bondability does not decrease. Further, the high melting point solder can be easily formed by a method such as screen printing even after the electronic component is completed, the thickness thereof can be easily adjusted, and the degree of freedom in design is improved. Further, by forming a metal thin film having a high melting point on the upper surface of the metal film made of the high melting point solder, for example, a thin film made of nickel, it is possible to induce melting of the metal film even when joining at a relatively high temperature. Since there is no problem, there is no problem such as collapse of the shape of the extraction electrode,
The reliability of electronic parts can be improved.

[Brief description of drawings]

FIG. 1 is a bottom perspective view showing a chip-type electronic component according to the present invention.

FIG. 2 is a side view of FIG.

FIG. 3 is a side view showing a conventional example.

FIG. 4 is a partially enlarged view of FIG.

[Explanation of symbols]

 1 Chip type crystal unit (electronic component) 21, 22, 23, 24 Lead electrode 3 Chip resistor 41, 42 Lead electrode

Claims (2)

(57) [Scope of utility model registration request] 1. A plurality of extraction electrodes are provided on a bottom surface,
These lead electrodes and the electrode pads on the board
In a chip-type electronic component mounted on a substrate by soldering, a high melting point solder having a melting point higher than at least the soldering temperature is formed on the uppermost layer of the extraction electrode.
A surface-mount type electronic component having a metal film formed thereon. 2. A higher melting point is formed on the upper surface of the high melting point solder film.
The surface mount type electronic component according to claim 1, wherein at least one high metal thin film is formed .