Tantalum chip capacitor

1 2

FIG. 1 is an isometric preassembly view of the com

TANTALUM CHIP CAPACITOR ponents of the capacitor;

. , T„ FIGS. 2, 3 and 4 are vertical sectional views through

BACKGROUND OF THE INVENTION the capadtor components ^grammatically illustrating

1. Field of the Invention 5 progressive stages of manufacture thereof;

The present invention is in the field of capacitors, and FIG. 5 is a side elevational view diagrammatically

more particularly relates to an improved tantalum chip illustrating a further operation in the manufacture of the

capacitor. device;

2. The Prior Art FIG. 6 is a perspective view of a finished capacitor in Tantalum chip capacitors, also known as solid elec- 1° accordance with the invention.

trolytic capacitors, have recently come into widespread Referring now to the drawings, there is shown at 10

use, especially in so-called thick film circuitry applica- a tantalum chip capacitor subassembly, the manufactur

tions. Tantalum chip capacitors have the known advan- in8 stePs of which are known in the art, being described

tage of providing a relatively high capacitance per bnefly hereinbelow for illustrative purposes only, since

given volume. By way of example, capacitor devices of 15 the principal advance of the present invention resides in

the type described and related types of capacitors are the method of terminating and encapsulating the subject

shown in U.S. Pat. Nos. 3,855,505; 3,349,294; 3,341,752; known capacitor.

3,356,911; 3,308,350; and 3,337,428. Such capacitors are The capacitor subassembly 10 is comprised of a tanta

known to be fragile, non-uniform in outside dimension, lum Powder Pressed mt0 a Pellet> mt0 which a lead is

and have high susceptibility to moisture penetration. 20 ^edded.The Pellet is heated to temperatures of about

2000 C under high vacuum conditions to produce a

SUMMARY OF THE INVENTION sponge-like tantalum anode. A dielectric surface is

The present invention may be summarized as directed formfd on the tantal«m, the surface being composed of

to an improved capcitor, and particularly an improved „ tanta!um Pf*oxide formed in situ by electrolytically

capacitor of the tantalum chip type and method of mak- 25 anod.zing the spongy tan alum pellet in a bath of phos

in the same phone acid. The part is cleaned and dried, and thereaf

ml 6 m' . tU •„.„,„♦; :„ A-.^t^A *~ „ ter impregnated in Manganous nitrate, the pellet being

Broadly stated, the invention is directed to a means K. °, . , . , .. *\, .t f

- ix- • ii4 -i * thereafter heated to about 300 C, converting the nitrate

for encapsulating and forming output terminals on tan- . ., 6

x , , . °.. J :r *t. J • i t0 Manganous dioxide.

talum chip capacitors, the product of a method involv- ,n ° . ■ . . , , „i. „

J . \ , I , . , <• . • r 30 This pyrolysis step is repeated a number of times with

ing inserting into a tubular .meta case which ,s prefera- intermit^nt ;iectrolytic reformations, to heal the di

bly rectangular m transverse section, a tantalum capaci- ... which ig d d by ^ ^ t ature

tor subassembly, the subassembly including a body por- excursions

tion the outer surface of which defines the cathode, an After ^ ocedure is completed) the part is washed anode and an anode lead. A first electrical connection is J5 and dried and a layer u of ^ Ued as an effected between the cathode and the case adjacent a ous suspension. After drying, the graphite is coated first end of the case through the use or solder or con- with a conductive iayer, such as a silver paint or copper ductive epoxy. A second connection is effected by layer 12, it being appreciated that the layer 12 forms the welding, etc. between the anode lead and the case adja- cathode connection or terminal to the subassembly 10, cent a second end of the case. The voids withm the case ^ ^ the lead 13 defines the anode connection. are thereafter filled, preferably through the second end, As the specific procedure in the formation of the with an insulating liquid polymeric material which, subassembly 10 is fully expounded in one or more of the through cooling or polymerization, etc. thereafter above referenced patents, further description is omitted, hardens. As noted above, the principal contribution of the The final step of manufacture includes removing a 45 instant invention resides in terminating (providing outcontinuous band of the casing at an area in registry with put terminals for) and encapsulating the capacitor dethe hardened polymeric material, whereby direct cur- vice. Such method and the resultant capacitor are illusrent flow through the case between the ends thereof is trated in FIGS. 1 to 6.

interrupted, the polymeric material nonetheless bond- The anode lead 13 may be welded as at 14 to a tanta

ing the case halves together to form a durable, rugged 50 lum, nickel or Kovar cross bar 15, which will in a subse

and relatively moisture impervious capacitor device, quent step be electrically connected to define the anode

the terminals of which are defined by the portions of the terminal of the capacitor, it being understood that a

case to either side of the groove, band or gap. direct connection between the riser or lead 13 may be

It is accordingly an object of the invention to provide optionally effected. The use of a tantalum, nickel or

a tantalum chip capacitor. 55 Kovar cross bar is optional but preferred, due to their

A further object of the invention is to provide a ca- compatible welding characteristics, pacitor of the type described which is highly resistant to The subassembly 10, with the bar 15 attached, is ingress of moisture and which is sufficiently rugged to thereafter inserted into a metallic case 16 which is prefpermit manual or automatic handling without special erably formed of extruded metal, such as, by way of precautions, in contrast to conventional capacitors of 60 preferred example, KOVAR (the trademark of Westhis type which require the use of vacuum handling tinghouse Electric Corporation for a high electrical apparatus, cushioned tweezers or the like. conductivity, relatively low thermal expansion mateStill a further object of the invention is the provision rial), of an improved capacitor device. With the insert 10 positioned within the case 16, as To attain these objects and such further objects as 65 shown in FIG. 2, the case is placed in an upright posimay appear herein or be hereinafter pointed out, refer- tion, with the anode or silver coating 12 uppermost, and ence is made to the accompanying drawings, forming a a layer 17 of solder or conductive epoxy is flowed into part hereof, in which: the area between the coating 12 and lower end 18 of the 4,085

3

case, providing the cathode connection of the capacitor. The quantity of solder or conductive epoxy 17 is preferably sufficient to fill the interstices between the case and the subassembly, providing a tight seal adjacent the end 18. 5

As the next step, the cross bar 15 is electrically connected to the case 16 adjacent the upper end 19 thereof, effecting the anode connection. Such electrical connection, by way of example, is effected by a capacitive discharge welding device 20, one electrode 21 of which 10 is grounded to the case, the other electrode 22 of which is connected to the "hot" side of the weld current output.

It will be understood that the edge portion 23 of the cross bar 15 is sandwiched against the side of the casing" by pressure exerted between the electrodes 21 and 22, and, upon passage of a welding current, is fused to the case.

Alternative means to that shown in FIG. 3 for effecting an electrical connection between the lead 13 and case adjacent the end 19 may be employed. However, an advantage of the utilization of the tantalum bar and Kovar case is that, due to the coordinated coefficients of thermal expansion of the two metallic components, 2J the likelihood of separation of the parts when the capacitor is subsequently heated in the course of incorporation into an electronic circuit is substantially reduced.

In accordance with the illustration of FIG. 4, the next step in the manufacture of the device involves introduc- jQ ing into the voids between the inner walls 24 and the capacitator subassembly 10 a polymeric insulating material 25. The material 25 must, of course, have high electrical insulation properties, is preferably shrink-resistant in the course of hardening or polymerizing, and prefera- 35 bly forms a strong adhesive bond with the engaged interior surfaces 24 of the case and external surfaces of the subassembly 10.

A preferred material is an epoxy mixture such as an epoxy potting compound, it being understood that any 40 of a variety of thermosetting or thermoplastic resinous materials having the above recited properties may be suitably employed.

Preferably, the epoxy or like liquid resinous material may be added in an vacuum environment, whereby 45 improved sealing properties and evacuation of voids are accomplished.

It will be recognized that, as presently constituted, the capacitor elements are shunted by the metal case 16.

After hardening of the resinous materials, the next 50 step, illustrated in FIG. 5, involves cutting or etching a groove or gap 26 completely about the case, whereby current flow between the ends 18 and 19 of the case is precluded. While the formation of such gap 26 may be effected in any of a plurality of ways, such as by grind- 55 ing, broaching, etc., it is preferred to form the groove by the use of a sandblasting technique, known per se.

As diagrammatically shown in FIG. 5, a fine nozzle carries a stream of abrasive particles, such as sand entrained in a high speed air blast, against an increment of 60 the side portion of the case, a relative movement between the case 16 and the nozzle 27 being effected, whereby the metallic material is completely removed about a zone or area circling the case. The use of sandblasting techniques is preferred since it has been discov- 65 ered that the resulting cutting action is preferential as respects the metal, and will cut into the epoxy material at a slower rate.

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4

The capacitor resulting from the manufacturing steps hereinabove described is shown in FIG. 6.

It will be understood that the case 16 has now been divided into two separate parts, 16' defining the cathode terminal and 16" defining the anode terminal of the capacitor. The hardened epoxy material 25 mechanically bonds together the two components of the case, at the same time tightly sealing the case and assuring that the capacitor will not be harmed in the course of handling. Electrical connections may be made to any portion of the terminals 16', 16".

While the capacitor has been illustrated as having been ecapsulated within a rectangular (in this instance, a square) tubular metal member preferably comprising a secion cut from an extended extruded length, it will be readily recognized that other cross sectional shapes may be suitably employed. The rectangular shape has the advantage, however, of permitting mounting of the device on a flat surface.

From the foregoing description it will be understood that there has been described and illustrated an improved method of making a capacitor, and particularly a tantalum chip capacitor. A principal advance inhering in the method of the present invention is considered to reside in the concept of disposing a capacitor subassembly within an integral conductive sleeve, effecting connections between the electrodes of the subassembly and sleeve at spaced positions, introducing into the interior of the case or sleeve a polymeric dielectric material which is permitted or caused to harden, and electrically isolating end portions of the sleeve, thereby to define the terminals of the capacitor, while assuring co-planar alignment of the respective surfaces. Such alignment facilitates connection of the terminals to spaced conductor portions, e.g. on a flat circuit board.

The term "electrical isolation" as used herein and in the claims is intended to refer to the interruption of the direct conductive relationship through the casing without regard to the capacitive connection between the terminals, which is obviously the result of the process as, described.

It will be further recognized that variations in the steps, manner of executing the same, and sequence in which they are carried out will occur to those skilled in the art who have been familiarized with the instant disclosures. For instance, two or more capacitors may be disposed in a single metal case and electrically isolated by the formation of two or more circumferential peripheral gaps. Likewise, an internal connection may be effected between the cathodes, for instance, of the capacitors, the common terminal being the central band isolated from the ends (anode terminals) by peripheral gaps.

Further, while the present invention has been described as encapsulating a tantalum capacitor, it will be appreciated that the encapsulating concept may be used with other capacitive devices, particularly of the film forming material type.

Accordingly, the invention hereof is to be broadly construed within the scope of the appended claims.

Having thus described the invention and illustrated its use, what is claimed as new and is desired to be secured by Letters Patent is:

1. A capacitor device comprising, in combination, a solid electrolyte chip capacitor subassembly having an outer cathode end portion, an anode body projecting axially from the cathode end portion, and an anode lead extending axially from said anode body, a tubular metal