Method of providing a lead to an end of a capacitor and a capacitor manufactured according to this method

The invention relates to a method of providing a lead to an end of a capacitor which is formed of two metal foils which are wound together and between which an insulating material is provided, in which at one end of the capacitor the edge of one foil projects from the edge of the other, and at the opposite end of the capacitor the edge of the latter foil projects from the edge of the former, viewed in the direction perpendicular to the longitudinal direction of the foils. According to the invention the projecting ends of the foils are coated with a metal layer. Next, the end of a lead is pressed onto the metal layer at each end of the capacitor, while heating the lead and/or the metal layer. The said end has two substantially contiguous portions which are pressed against the outside of the metal layer and are interconnected by a connecting portion which is offset from the plane of symmetry of the contiguous portions and is pressed into the metal layer.

BACKGROUND OF THE INVENTION 
The invention relates to a method of providing a lead to an end of a 
capacitor which is formed of two metal foils which are wound together and 
between which an insulating material is provided, in which at one end of 
the capacitor the edge of one foil projects from the edge of the other, 
whereas at the other end of the capacitor the edge of the latter foil 
projects from the edge of the former, viewed in the direction 
perpendicular to the longitudinal direction of the foils. 
The German Patent Application No. 2,717,382 discloses a method in which a 
lead is provided by urging a plate-shaped member which carries the lead 
against one end of the capacitor formed by the wound foils. In this 
method, the plate-shaped member has projecting ribs which are brought into 
contact with the projecting edge of a foil on the relevant side of the 
capacitor. The shape of the plate-shaped member substantially corresponds 
to the cross-section of the capacitor. The plate-shaped member is bonded 
to the capacitor by melting the insulating material so that an adhesive 
layer is formed between the end of the capacitor and the plate-shaped 
member. 
The plate-shaped member is relatively heavy and the leads connected thereto 
and extending in a perpendicular direction to this plate-shaped member 
hamper the incorporation of the capacitor, or require relatively much 
room. 
Moreover, there is the possibility of molten insulating material 
penetrating between the ribs of the plate-shaped member and the metal 
foils, thereby adversely affecting the formation of a satisfactory contact 
between the leads and the metal foils. 
SUMMARY OF THE INVENTION 
According to the invention the projecting ends of the foils are coated with 
a metal layer onto which the end of a lead is pressed, while heating the 
lead and/or the metal layer, which end has two substantially contiguous 
portions which are interconnected by a connecting portion which is & 
offset from the plane of symmetry and which is symmetrical relative to a 
plane of symmetry which extends halfway between the facing ends of the 
contiguous portions and perpendicularly to the longitudinal axis of these 
portions, the connecting portion being pressed into the metal layer over 
such a distance that the contiguous portions lie against the outside of 
the metal layer. 
The metal layer ensures a satisfactory connection between the edge portions 
of the foils and, consequently, between the foils and the lead provided on 
the metal layer. In securing the lead, the connecting portion which 
interconnects the contiguous portions is pressed into the metal layer 
which is softened by heating, and the flattened portions come to rest on 
the outside of the metal layer such that an even well-defined penetration 
of the connecting portion into the metal layer is obtained. 
Moreover, the leads can readily be provided parallel to the end faces of 
the capacitor, which usually facilitates the future incorporation of the 
capacitor in a limited space. 
The invention will now be explained in more detail by means of an exemplary 
embodiment of the construction according to the invention which is shown 
schematically in the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a view of a capacitor 1 which is formed of two metal foils 2 and 
3 between which an insulating material 4 is provided. The foils 2 and 3 
which are in shown cross-section in FIG. 2 are formed by elongated strips 
which are wound together such that during winding the capacitor 1 can be 
given any desired cross-section. This cross-section may be, for example, 
circular, oval or elongated. The capacitor may also be formed of foils of 
insulating material on which metal layers are provided by vacuum 
evaporation, and which serve as electrodes. 
As is shown in FIG. 2, on one side of the capacitor (in FIG. 2 the 
left-hand side) the edge of the metal foil 2 projects from the metal foil 
3, whereas on the other side (in FIG. 2 the right-hand side) the edge of 
the metal foil 3 projects from the metal foil 2. 
After the metal foils 2 and 3 have been wound together, metal layers 5 and 
6, respectively, are applied to the ends of the metal foils in such a way 
that the projecting edge of the foil 2 is embedded in the metal layer 5 
and the projecting edge of the foil 3 is embedded in the metal layer 6. 
Such metal layers 5 and 6 can be provided efficaciously by spraying on a 
suitable metal, the so-called metal spraying. An useful thickness of such 
a layer is 200-300 micrometer, and a material which can suitably be used 
is a mixture of Zn and Sn. 
Subsequently, the leads 7 can be provided. Such leads, which often have a 
circular cross-section with a diameter of 0.6 mm are flattened at the ends 
to a thickness of .+-.0.3 mm. Such a flattened end is formed in the way 
shown in FIG. 4, i.e. the end has two flattened elongated contiguous 
portions 8 and 9 which are interconnected by a connecting portion which is 
formed of three portions 10-12 which lie at an angle to each other. 
As is shown in FIG. 4, both portions 10 and 12 are bent through an angle of 
approximately 45.degree. relative to the portions 8 and 9, such that with 
respect to the facing ends of the portions 8 and 9 they extend in facing 
directions. The ends of the portions 10 and 12 facing away from the 
portions 8 and 9 are interconnected by a portion 11 which runs parallel to 
the portions 8 and 9. 
FIG. 4 shows that the connecting portion which comprises the portions 10-12 
is constructed so that it is symmetrical with respect to a plane of 
symmetry which is perpendicular to the plane of the drawing, which plane 
of symmetry is situated halfway between the facing ends of the flattened 
portions 8 and 9. 
In order to secure the lead to the capacitor, the portion 11 of the 
connecting portion is positioned against the outside surface of a metal 
layer 5 or 6 and is urged against the said metal layer 5 or 6 by means of 
two electrodes 13, while current is simultaneously applied via these 
electrodes. Consequently, the connecting portion 10-12 and the metal layer 
5 or 6 below the connecting portion will be heated, thereby softening the 
metal layer such that the connecting portion can be pressed into the metal 
layer. The contiguous flattened portions 8 and 9 will also contact the 
outside surface of the metal layer, thereby limiting the extent to which 
the flattened end of the lead can be pressed into the metal layer. 
Moreover, the flattened portions 8 and 9 which are situated on either side 
of the portion 10-12 which is pressed into the metal layer 5 or 6 prevent 
the end of the lead from being obliquely pressed into the metal layer, not 
only because the portion pressed into the metal layer is supported on 
either side by the flattened portions 8 and 9 but also because these 
portions act as heat dissipators and, consequently, the temperature of the 
free end of the portion pressed into the metal layer is not substantially 
higher than that of the other end of the portion. 
The length of the straight portion 11 is mainly determined by the 
dimensions of the electrodes 13 to be used and by the necessary interval 
between these electrodes. 
The distance between one end of the horizontal portion 11 and the end of a 
flattened portion 8 or 9 which is connected to this end amounts to 
approximately twice the thickness of the metal spraying layer, measured in 
the longitudinal direction of these flattened portions 8 and 9. 
In FIG. 4, the distance between the underside of a flattened portion 8 or 9 
and the underside of the portion 11 amounts to approximately 0.5-1 times 
the thickness of the metal spraying layer. 
The length of the freely projecting flattened portion 9 is preferably 
greater than the length of a bevelled portion 10 or 12. 
The exemplary embodiment of a lead shown in FIG. 5 largely corresponds to 
that shown in FIG. 3. Consequently, all corresponding components of FIGS. 
5 and 3 bear the same reference numerals. In this embodiment, however, the 
free end 14 of the lead is not flattened as is free of the lead shown in 
FIG. 3 the end 9 but has a circular shape instead. Also in this embodiment 
favourable results can be obtained.