GB2140031A - Anodic oxidation of tantalum - Google Patents
Anodic oxidation of tantalum Download PDFInfo
- Publication number
- GB2140031A GB2140031A GB08313797A GB8313797A GB2140031A GB 2140031 A GB2140031 A GB 2140031A GB 08313797 A GB08313797 A GB 08313797A GB 8313797 A GB8313797 A GB 8313797A GB 2140031 A GB2140031 A GB 2140031A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tantalum
- anode
- anodising
- anodisation
- anode body
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 title claims abstract description 21
- 229910052715 tantalum Inorganic materials 0.000 title claims abstract description 18
- 230000003647 oxidation Effects 0.000 title description 3
- 238000007254 oxidation reaction Methods 0.000 title description 3
- 239000003990 capacitor Substances 0.000 claims abstract description 17
- 238000002048 anodisation reaction Methods 0.000 claims abstract description 10
- 239000007787 solid Substances 0.000 claims abstract description 5
- 238000000034 method Methods 0.000 claims description 23
- 238000007743 anodising Methods 0.000 claims description 8
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- 239000000843 powder Substances 0.000 claims description 5
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- 238000002425 crystallisation Methods 0.000 abstract description 4
- 239000010410 layer Substances 0.000 description 4
- 230000007423 decrease Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- NUJOXMJBOLGQSY-UHFFFAOYSA-N manganese dioxide Chemical compound O=[Mn]=O NUJOXMJBOLGQSY-UHFFFAOYSA-N 0.000 description 2
- 239000002344 surface layer Substances 0.000 description 2
- 101100457021 Caenorhabditis elegans mag-1 gene Proteins 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 101100067996 Mus musculus Gbp1 gene Proteins 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000010407 anodic oxide Substances 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
- H01G9/00—Electrolytic capacitors, rectifiers, detectors, switching devices, light-sensitive or temperature-sensitive devices; Processes of their manufacture
- H01G9/0029—Processes of manufacture
- H01G9/0032—Processes of manufacture formation of the dielectric layer
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
- C25D11/02—Anodisation
- C25D11/26—Anodisation of refractory metals or alloys based thereon
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Fixed Capacitors And Capacitor Manufacturing Machines (AREA)
- Powder Metallurgy (AREA)
Abstract
An anode body 11 from a tantalum solid electrolytic capacitor is anodised at a temperature below 5O DEG C. It is then treated to a further anodisation at a reduced voltage and for a short period up to 200 seconds at 85 DEG to 100 DEG C. This reduces the leakage current of the anode without introducing the risk of field crystallisation. <IMAGE>
Description
SPECIFICATION
Anodic oxidation of tantalum
This invention relates to a process for the anodic oxidation of tantalum and in particular to a process for forming capacitor anodes in the manufacture of tantalum by electrolytic capacitors.
The tantalum solid or dry electrolytic capacitor is widely used in a variety of applications where its combination of high capacitance and small physical size are of considerable advantage. These capacitors comprise a porous sintered tantalum anode body whose surface is anodised to form an oxide film. This oxide film provides the capacitor dielectric.
The anodes are pressed from tantalum powder, the processing and the surface condition of which determines the anode surface area and hence the capacitance of the finished capacitor. Recently the so-called 'high gain' tantalum powders have been introduced.
These powders, which contain phosphorus, have a very high surface area and thus provide a high capacitance per unit volume.
A disadvantage of these 'high gain' powders is their tendency to exhibit excessively high leakage currents. Attempts have been made to overcome this problem by extending the anodisation process at a high temperature, e.g. above 70"C. It has been found however that the extended period for which the anode is maintained at a high temperature during the anodisation process introduces a serious risk of field crystallisation.
The object of the present invention is to minimise or to overcome these disadvantages.
According to the invention there is provided a process for anodising a tantalum capacitor anode body, the process including anodising the body at a temperature below 50"C, and further anodising the body at a reduced voltage and at a temperature of 85"C to 100"C for a period of up to 200 seconds.
As the anode body is exposed to a high temperature for a short period only the risk of field crystallisation is substantially eliminated.
The short high temperature anodisation significantly improves the integrity of the dielectric film without producing an excessive increase in thickness. Thus the electrical leakage of the film is reduced without adversely affecting the capacitance of the finished capacitor.
An embodiment of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a schematic cross-sectional view of a tantalum solid electrolytic capacitor;
and Figure 2 illustrates the leakage current characterisitics of tantalum anode bodies treated by the process described herein.
Referring to Fig. 1, a tantalum solid electrolytic capacitor typically comprises a porous anode body 11 formed by pressing and sintering in vacuum either tantalum metal powder or a powdered refractory material coated with tantalum. Contact to the anode body 11 is provided by a tantalum wire 1 2 embedded therein. The surface of the body is coated with a dielectric layer 1 3 of anodic oxide whose thickness determines the capacitance value of the capacitor. This oxide layer 1 3 is in turn coated with a semiconductive layer 14 typically comprising manganese dioxide formed by thermal decomposition of manganous nitrate. The various techniques for forming this semiconductive layer will be apparant to those skilled in the art.
The anode structure is surrounded by a quantity of graphite 1 5 contained in a metal, e.g. aluminium, can 1 6 providing the cathode terminal of the capacitor and contacted by lead 18. Shorting between the capacitor terminals is prevented by an insulating sleeve 1 7 surrounding the anode lead 1 2 at the point where this lead protrudes through the can 16.
The dielectric surface layer 1 3 on the anode body is provided by the following technique.
The pressed and sintered anode bodies are anodised in dilute phosphoric acid at a temperature of 50"C or less. The anodisation is preferably a constant current process so that the voltage rises until a predetermined maximum value is reached at which the current is allowed to fall. Typically the current density for this stage of the process is 35 to 45 mAg - 1 and the limiting voltage is 70 to 100 volts. After this forming stage the anodes are then subjected to a short further forming by a second anodisation for a period of 30 to 200 seconds in dilute phosphoric acid maintained at a temperature of 85 to 100"C. The effect of this further or secondary forming stage is to enhance the integrity of the dielectric surface layer and thus significantly reduce the leakage current.The results of this treatment are illustrated in Fig. 2 of the accompanying drawings. Under an applied voltage leakage current slowly decreases with time and then rises again after about 100 seconds. As can be seen from Fig. 2 a successive increase in the secondary anodisation period provides a corresponding decrease in the leakage current.
Current A shows the leakage time characteristic of an anode treated by the conventional high temperature process. Current B is the characteristic of an anode formed by anodising at 50"C only whilst curves C, D, E and F show the effects of an anodisation at 50"C followed by treatment at 85"C for periods of 10 sec, 20 sec, 30 sec and 40 sec respectively. As can be seen the two stage treatment provides a significant decrease in the leakage current. In each case the leakage was measured at embient temperature with an applied voltage of 70 volts. We have also found that for periods in excess of 40 seconds no subsequent rise in leakage current is observed.
However this period should not be extended beyond 200 seconds as the risk of field crystallisation may then be reintroduced.
Claims (9)
1. A process for anodising a tantalum capacitor anode body, the process including anodising the body at a temperature below 50"C, and further anodising the body at a reduced voltage and at a temperature of 88 to 1 00 C for a period of up to 200 seconds.
2. A process as claimed in claim 1, wherein said anode comprises a sintered body of a refractory powder coated with metallic tantalum.
3. A process as claimed in claim 1 or 2, wherein said body is anodised in phosphoric acid.
4. A process as claimed in claim 1, 2 or 3, wherein said first anodisation process is a constant current process.
5. A process as claimed in claim 4, wherein the current density is 35 to 45 mAg-'.
6. A process as claimed in claim 4, wherein the anodisation is carried out at a limiting voltage of 70 to 100 volts.
7. A process for anodising a tantalum capacitor anode body substantiaily as described herein with reference to the accompanying drawings.
8. A tantalum anode body treated by a process as claimed in any one of claims 1 to 7.
9. A tantalum solid electrolytic capacitor incorporating an anode body as claimed in claim 8.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08313797A GB2140031B (en) | 1983-05-18 | 1983-05-18 | Anodic oxidation of tantalum |
| DE19843418086 DE3418086A1 (en) | 1983-05-18 | 1984-05-16 | ANODIC OXIDATION OF TANTAL |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08313797A GB2140031B (en) | 1983-05-18 | 1983-05-18 | Anodic oxidation of tantalum |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8313797D0 GB8313797D0 (en) | 1983-06-22 |
| GB2140031A true GB2140031A (en) | 1984-11-21 |
| GB2140031B GB2140031B (en) | 1985-11-20 |
Family
ID=10542990
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08313797A Expired GB2140031B (en) | 1983-05-18 | 1983-05-18 | Anodic oxidation of tantalum |
Country Status (2)
| Country | Link |
|---|---|
| DE (1) | DE3418086A1 (en) |
| GB (1) | GB2140031B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1117110A2 (en) * | 2000-01-12 | 2001-07-18 | Nec Corporation | Fabrication method of solid electrolytic capacitor |
| WO2003064731A1 (en) * | 2002-01-28 | 2003-08-07 | Medtronic, Inc. | Methods of anodizing sintered valve metal anodes |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB958669A (en) * | 1959-08-28 | 1964-05-21 | Philips Electrical Ind Ltd | Improvements in or relating to a method of manufacturing solid electrolytic capacitors |
| GB1006536A (en) * | 1963-06-24 | 1965-10-06 | Ciba Ltd | Process for the manufacture of dry electrolytic condensers |
-
1983
- 1983-05-18 GB GB08313797A patent/GB2140031B/en not_active Expired
-
1984
- 1984-05-16 DE DE19843418086 patent/DE3418086A1/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB958669A (en) * | 1959-08-28 | 1964-05-21 | Philips Electrical Ind Ltd | Improvements in or relating to a method of manufacturing solid electrolytic capacitors |
| GB1006536A (en) * | 1963-06-24 | 1965-10-06 | Ciba Ltd | Process for the manufacture of dry electrolytic condensers |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1117110A2 (en) * | 2000-01-12 | 2001-07-18 | Nec Corporation | Fabrication method of solid electrolytic capacitor |
| EP1117110A3 (en) * | 2000-01-12 | 2006-04-19 | Nec Tokin Corporation | Fabrication method of solid electrolytic capacitor |
| WO2003064731A1 (en) * | 2002-01-28 | 2003-08-07 | Medtronic, Inc. | Methods of anodizing sintered valve metal anodes |
| US6802951B2 (en) | 2002-01-28 | 2004-10-12 | Medtronic, Inc. | Methods of anodizing valve metal anodes |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2140031B (en) | 1985-11-20 |
| GB8313797D0 (en) | 1983-06-22 |
| DE3418086A1 (en) | 1984-11-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |