Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Reexamination Certificate
2001-10-22
2003-05-06
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
C361S524000
Reexamination Certificate
active
06560090
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrolytic capacitor used for various electronic apparatus, and particularly, to a surface-mounted type solid electrolytic capacitor having terminals for external connection, and a method of manufacturing same.
BACKGROUND OF THE INVENTION
As conventional solid electrolytic capacitors having terminals for external connection, surface-mounted type tantalum solid electrolytic capacitors are representative ones, which are used for various electronic apparatus in large quantities. This type of tantalum solid electrolytic capacitor is described as an example in the following. The configuration of such conventional tantalum solid electrolytic capacitor includes a capacitor element portion and lead frame portion. As a material for the lead frame, nickel-base alloy or copper-base alloy is mainly used. Particularly, nickel-base alloy such as 42 alloy is used when the terminal of the lead frame portion is required to have a repeated bending strength or the terminal is required to have a mechanical strength enough to endure actual device installation. Also, copper-base alloy such as copper-nickel-tin alloy is used when the lead frame portion is required to have specially high processability.
A conventional tantalum solid electrolytic capacitor of this type will be described in the following with reference to FIG.
12
and FIG.
14
.
FIG. 12
is a sectional view showing the configuration of a conventional tantalum solid electrolytic capacitor. In
FIG. 12
, the conventional tantalum solid electrolytic capacitor comprises a capacitor element
12
and positive electrode lead wire
13
. The capacitor element
12
comprises a porous positive electrode body, and a dielectric oxide film layer, solid electrolytic layer and negative electrode layer (all of these are not shown) which are sequentially formed on the outer surface of the positive electrode body. The porous positive electrode body is formed by sintering a compact of tantalum powder. One end of the positive electrode lead wire
13
is exposed. One end of positive electrode terminal
14
is connected by welding or the like to the positive electrode lead wire
13
of the capacitor element
12
. The other end of the positive electrode terminal
14
is led out of outer jacket resin
17
described later and is bent along the outer jacket resin
17
. In this way, a terminal for external connection is formed. One end of negative electrode terminal
15
is connected to the negative electrode layer of the capacitor element
12
via conductive bonding agent
16
, and the other end of the negative electrode terminal
15
is led out of the outer jacket resin
17
described later and is bent along the outer jacket resin
17
. In this way, a terminal for external connection is formed. The capacitor element
12
is coated with the outer jacket resin
17
capable of electrical insulation so that each of the positive electrode terminal
14
and negative electrode terminal
15
is partially exposed to the outside.
FIG. 13
is a plan view showing the lead frame which forms the positive electrode terminal
14
and the negative electrode terminal
15
.
FIG. 14
is a sectional view of the line
14
A—
14
A portion of FIG.
13
. In FIG.
13
and
FIG. 14
, lead frame
18
is formed of a strip-form metallic member made of nickel-base alloy (such as 42 alloy) or copper-base alloy (such as copper-nickel-tin alloy). The positive electrode terminal
14
and the negative electrode terminal
15
are formed at the lead frame
18
. Silver-plated layer
20
is disposed at element fixed portion
19
. Guide hole
21
for transport is formed in the lead frame
18
. As an undercoat layer
22
, a copper or copper alloy plated layer of 0.3 &mgr;m in thickness is disposed on the positive electrode terminal
14
and the negative electrode terminal
15
. For soldering in actual device installation, plated layer
23
for soldering, formed from tin or tin-lead alloy, is disposed on the undercoat layer
22
.
Next, a method of manufacturing a conventional tantalum solid electrolytic capacitor having such configuration as described above.
First, the capacitor element
12
is disposed at element fixed portion
19
located between the oppositely disposed positive electrode terminal
14
and negative electrode terminal
15
extending from the lead frame
18
. The positive electrode lead wire
13
of the capacitor element
12
is connected by welding or the like to the positive electrode terminal
14
formed at the lead frame
18
. The negative electrode layer of the capacitor element
12
is bonded by conductive bonding agent
16
of silver paste to silver plated layer
20
disposed on the negative electrode terminal
15
formed at the lead frame
18
. The conductive bonding agent
16
is hardened under heat to establish electrical connection. The bonding agent
16
is heated at temperatures of 170° C. to 180° C. for about one hour for hardening.
Next, with each of the positive electrode terminal
14
and negative electrode terminal
15
partially exposed to the outside, the capacitor
12
is coated by outer jacket resin
17
capable of electrical insulation. Thus, the outer jacket resin
17
is heat-treated at 170° C. to 180° C. for about six hours for complete hardening. In this way, the outer jacket resin
17
is improved in cross-linking ability, and as a result, the tantalum solid electrolytic capacitor will be, for example, improved in moisture resistance. After that, thermal screening is performed in a furnace at 240° C. to 260° C. for about 60 sec. Thus, excessive current leakage or shorting trouble that may cause hindrance to the user during actual reflow soldering, for example, can be prevented from occurrence. After that, unnecessary portions of the lead frame
18
are removed, and thereafter, the characteristic and appearance inspections are performed before delivery of the finished product.
In the assembling process of a conventional tantalum solid electrolytic capacitor manufactured by such manufacturing method as described above, the capacitor will be subjected to severe heat history in the atmosphere. Therefore, the plated film is required to be heat resisting adhesion even after application of such heat history, and further, it is required to ensure excellent solder wettability, for example, during reflow soldering performed by the user.
Also, in this way, for making the plated film heat resistant and realizing excellent solder wettability, it is necessary for the copper or copper alloy plated layer disposed as the undercoat layer
22
for the above conventional positive electrode terminal
14
and negative electrode terminal
15
to have a thickness of 0.3 &mgr;m at least. The thickness of the undercoat layer
22
is closely related to the heat resisting adhesion of the tin or tin-lead alloy plated layer as the plated layer
23
for soldering which is disposed on the undercoat layer
22
. Also, the adhesion of the tin plated layer or tin-lead alloy plated layer depends upon the forming volume of thermal diffusion layer in connection with the copper or copper alloy plated layer that is the undercoat layer
22
, and the copper or copper alloy plated layer acts to promote the formation of the thermal diffusion layer.
Thus, since the copper or copper alloy plated layer provided as the undercoat layer
22
contributes to heat resisting adhesion, the state of plated film is preferable to be very dense. To achieve the purpose, it is necessary to perform the plating under appropriate conditions with respect to the current density and plating bath control. Due to such severe conditions for plating bath control, it is possible to realize a plating thickness of 0.3 &mgr;m or over. If such conditions are not satisfied, for example, performing the plating at excessive current density, then the copper or copper alloy plated layer formed will become porous. Accordingly, the layer is insufficient in adhesion. Also, even when the plated film of the copper or copper alloy plated layer is very dense, sufficient heat resisting
Higuchi Yoshihiro
Kadoya Masashi
Nakamura Tsuneshi
Omori Minoru
Uenishi Yoshitsugu
McDermott & Will & Emery
Reichard Dean A.
Thomas Eric
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