The present invention relates to an electronic device having a pair of plate or strip terminals and, more particularly, to an improvement in the pair of terminals of an electronic device such as a capacitor and a resistor.
Along with a recent increase in the packaging density of electronic circuits, the electronic devices incorporated in the circuit have become small. In particular, it is demanded that electronic devices, which are to be mounted on a printed circuit board, be compact. For this reason, the pair of terminals of each electronic device must be designed to be suitable for high-density mounting.
Under these circumstances, an electronic device having a pair of plate or strip terminals recently replaces an electronic device having a pair of metal wire terminals or round metal rod terminals. More specifically, a pair of plate or strip terminals are mounted along a device body to make the entire device compact. In order to realize still higher density mounting, a leadless electronic device (so-called a chip type electronic device) on which a pair of terminals are mounted along a device body, not extending from the device body, is already available.
FIG. 1 shows a conventional electronic device, e.g., a capacitor. This capacitor has capacitor element 1 in which insulating films 2 and deposition metal layers 3 are alternately stacked, and sprayed metal layer 4 formed of a low-melting point metal is formed on capacitor element 1. A pair of plates or strip terminals 5 are overlaid and connected to capacitor element 1 by spot-welding or soldering through metal layer 4.
When terminal 5 is spot-welded, resistive heating occurs at the contact surfaces thereof since terminal 5 is energized while being urged against metal layer 4, and the surface of metal layer 4 is slightly melted. As a result, terminal 5 is slightly embedded in metal layer 4.
When terminal 5 is soldered, a solder is heated and melted at about 360.degree. C., and terminal 5 is placed on the melted solder.
However, the capacitor in which terminal 5 is welded to metal layer 4 of the capacitor element has the following drawbacks (1) to (4).
(1) Since its welding strength is low, terminal 5 is easily peeled from metal layer 4.
(2) If a welding current is increased to improve a welded joint strength, insulating films 2 arranged below metal layer 4 are deteriorated by the welding heat, reducing a contacting property with corresponding deposition metal layer 4, and dielectric loss tangent tan.delta. of the capacitor increases.
(3) In order to prevent deterioration of insulating films 2 due to heating, metal layer 4 must be much thicker than is necessary for connecting terminal 5, and the capacitor is inevitably bulky.
(4) If metal layer 4 is melted and plate or strip terminal 5 is embedded in it in order to improve a welded joint strength, a molten metal projects and is scattered from the peripheral portion of terminal 5, changing the dimensions of the capacitor and impairing the outer appearance of the capacitor.
The capacitor, in which terminal 5 is soldered to metal layer 4 of the capacitor element, has the following drawbacks (1) to (4).
(1) Automation of manufacturing the capacitor is difficult to achieve, and a manual operation is required to produce the capacitor, resulting in low productivity.
(2) The manual operation is performed over a relatively long time, and the entire process is prolonged, resulting in high cost.
(3) Insulating films 2 below metal layer 4 are degraded due to heating during soldering, and dielectric loss tangent tan.delta. of the capacitor increases.
(4) In order to prevent degradation of insulating films 2 due to heating, metal layer 4 must be much thicker than is necessary for connecting terminal 5, and as a result, the capacitor becomes bulky.