Active solid-state devices (e.g. – transistors – solid-state diode – Lead frame – Of specified material other than copper
Reexamination Certificate
2000-08-17
2001-09-25
Graybill, David E. (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Lead frame
Of specified material other than copper
C257S741000, C257S772000, C257S779000
Reexamination Certificate
active
06294826
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a resin-molded electronic component having lead terminals, and more particularly, to a chip type solid electrolyte capacitor having solder plated lead terminals, and a process for manufacturing the same.
2. Description of the Related Art
As the weight and size of electronic equipment is progressively reduced, and as surface mounting technology has advanced, the chip type component such as a solid electrolyte capacitor featuring a small size and high capacity has enjoyed an increasingly expanded market scale and is used in various applications.
Conventionally, as shown in
FIG. 8
, a chip type solid electrolyte capacitor has a capacitor element
1
having a cathode layer
3
, an anode lead
2
, an anode lead terminal
8
connected to the anode lead
2
by welding or the like, and a cathode lead terminal
9
connected to the cathode layer
3
.
Moreover, the cathode layer
3
and the cathode lead terminal
9
are connected by a conductive adhesive
10
such as silver paste. The capacitor is packaged by resin
6
, leaving portions of the anode and cathode lead terminals
8
and
9
exposed. In addition, the anode and cathode lead terminals
8
and
9
are bent along the outer surface of the resin package
6
. Since these lead terminals
8
and
9
are pre-plated with a plating layer of solder or the like by a direct current plating method using a linear current waveform as shown in
FIG. 9
, it has the following disadvantages (1) and (2).
(1) Organic components contained in a plating solution such as a brightener or dispersant are incorporated into the plating layer. As a result, the plating layer of solder or the like formed on the anode and cathode lead terminals
8
and
9
contains a considerable amount of the following organic substances.
Sample: Plating film formed by direct current plating
Detected components: Dichlorotoluene,
N,N,2,6-tetramethylbenzeneamine,
trichlorobenzene,
chlorobenzenemethanol,
dichlorobenzaldehyde,
dichlorobenzenemethanol,
lauric acid methyl
When such pre-plated lead terminals are employed in a resin-molded type electronic component, the organic substances in the plating layer of solder or the like are vaporized by thermal stress when mounting the component to generate a considerable amount of gas.
The gas thus generated in an adhering interface between the conductive adhesive
10
and the cathode lead terminal
9
affects connection reliability, and reduces the connection strength between the conductive adhesive
10
and the cathode lead terminal
9
. In a worst case, the cathode lead terminal may peel off to result in an electrically open circuit.
(2) The plated solder on the lead terminals
8
and
9
in the resin package
6
tends to elute from the resin package to form a solder ball
7
. This occurs when an excessive amount of an organic substance is generated due to thermal stress in mounting the electronic component. The resulting solder ball
7
can short circuit conductive patterns when the component is mounted on a printed circuit board.
To avoid the foregoing disadvantages, it is possible to plate only the exposed portion of the lead terminals. But such selective plating increases production cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electronic component such as a solid electrolyte capacitor which maintains good connection reliability at its connecting portion using conductive adhesive and prevents the generation of a solder ball, and a process for manufacturing the same without resorting to a selective plating method.
The above objective of the present invention is achieved by emptying electroplated lead terminals which contain organic substances in an amount of 0.03 wt % or less. In the case of a solid electrolyte capacitor, a pre-plated anode lead terminal is welded to an anode lead of a capacitor element and pre-plated cathode lead terminal is connected to a cathode layer of the capacitor element by using a conductive adhesive. The capacitor element is encapsulated by an insulating member so as to leave a portion of anode and cathode lead terminals exposed. Both of the encapsulated and exposed portions of the pre-plated anode and cathode lead terminals have a pre-plated layer containing organic substances in an amount of 0.03 wt. % or less.
Such a small amount of the organic substances in the electroplated loyer can be achieved by using a special pulse plating method with a current waveform having a counter pulse. ON time and OFF time of the current waveform is selected to be about 10 to 500 msec and the OFF time includes a counter (negative) current pulse which has an amplitude that is from ½ to {fraction (1/50)} that of the ON time pulse and a duration of 2 to 20 msec.
REFERENCES:
patent: 4589962 (1986-05-01), Sagga et al.
patent: 4631116 (1986-12-01), Ludwig
Patent Abstracts of Japan, vol. 14, No. 566 (C-0789), Dec. 17, 1999 (corresponds to JPA 02-243791).
Patent Abstracts of Japan, vol. 95, No. 11, Dec. 26, 1995 (corresponds to JPA 07-202100).
Tijdschrift Voor Oppervlaktetechinieken van Materialen, vol. 29, No. 2, Feb. 1985, pp. 44-47.
Ida Yoshio
Tainaka Akiyoshi
Graybill David E.
NEC Corporation
Sughrue Mion Zinn Macpeak & Seas, PLLC
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