Electricity: electrical systems and devices – Electrolytic systems or devices – Solid electrolytic capacitor
Patent
1992-04-06
1993-12-07
Reynolds, Bruce A.
Electricity: electrical systems and devices
Electrolytic systems or devices
Solid electrolytic capacitor
361538, 29 2503, H01G 1005, H01G 114, H01G 910
Patent
active
052688224
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns the manufacture of electrolytic capacitors, more particularly the lead frames for electrolytic capacitor anodes.
At present, electrolytic capacitors are generally made using an aluminium or tantalum anode and an electrolyte which may be solid or liquid.
A process of manufacture of capacitors with aluminium and with a solid electrolyte comprises several stages, a similar process being usable for capacitors with tantalum and a solid electrolyte. These stages are principally: by etching, folding or rolling of a sheet of aluminium, or by sintering; (oxidation);
The manufacturing process of these capacitors is rather complicated and the problems presently encountered during the manufacture of electrolytic capacitors are of several types.
The connection of the anode block to the tab of the lead frame, which is performed by soldering, is subject to dimensional constraints to be respected to take into account the different phases of manufacture.
To deposit the electrolyte and then the graphite, the anodized blocks are soaked in different solutions which have good wettability, and it can be observed that the conducting electrolyte and graphite rise by capillary action around the solder. There is therefore a risk of short-circuiting between the non-oxidized anode and the cathode constituted by the electrolyte. This rise by capillarity is not controllable and varies depending on the materials and their surface states.
To prevent such short-circuiting, dimensions are imposed: a minimum height for the oxidation of the tab of the lead frame and a lower minimum height for electrolytic impregnation and graphitization, taking into account the capillary rise. There is therefore an oxidized part of the anode which is not impregnated and which is inactive from a capacitive point of view.
SUMMARY OF THE INVENTION
The present invention proposes a mechanical means to eliminate this capillary effect, while enabling the necessary dimensions to be reduced. By reducing the height of oxidation with respect to that of impregnation and graphitization, it decreases the loss of active volume.
The invention consists of a lead frame for electrolytic capacitor anodes, characterized by the fact that it comprises, for each anode to be connected, a tab with, close to its free end, a means preventing the rise by capillary action, without hindering the soldering of the anode block.
The invention also concerns a process for manufacture of an electrolytic capacitor using such a lead frame.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other advantages will appear on reading the description of a preferred mode of embodiment, with reference to the appended drawings of which:
FIG. 1 represents a lead frame for electrolytic capacitors according to the prior art;
FIG. 2 represents a lead frame for electrolytic capacitors according to the invention; and
FIG. 3 represents a variant embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 shows part of a lead frame 1. This frame can be made of aluminium or tantalum or any other metal compatible with the anode of the capacitor. It is provided with tabs 2 of the same material. On one of them has been soldered the connecting wire 3 from an anode block 4. This soldering 5 is performed before soaking the anode in the various baths for oxidation of the anode block, then the deposition or impregnation of the electrolyte and finally the graphitization. After soaking in these baths, a rise by capillarity 6 is seen around the solder 5, to a height which is not controllable. If the height Y represents the tolerance for the bath level in the impregnation and graphitization phases, then the height X is the height lost for the active volume of the capacitor. For safety reasons, the oxidation must go up to the limit h on FIG. 1, which for given external dimensions reduces the active volume of the capacitor.
A mode of embodiment of the present invention is represented in FIG. 2. In this case, t
REFERENCES:
patent: 4483062 (1984-11-01), Irikura
patent: 4539623 (1985-09-01), Irikura et al.
patent: 5007149 (1991-04-01), Schnabel
Besnard Patrice
Delalande Francois
Compagnie Europeenne de Composants Electroniques - LCC
Plottel Roland
Reynolds Bruce A.
Switzer Michael O.
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