Capacitor and method of manufacturing same

A capacitor having at least one dielectric layer present between each time a flat electrode and an opposite electrode, in which the electrode(s) and the opposite electrode(s) are staggered with respect to each other so that in the plane of each time one of two opposing end faces of the capacitor they terminate in the same plane and are contacted there by means of external connection contacts, in which at least one electrode in its end area adjacent the external connection contact associated with it comprises a window and that the non-contacted end(s) of the opposite electrode(s) extend(s) in the area of the window(s).

BACKGROUND OF THE INVENTION 
The invention relates to a capacitor having at least one dielectric layer 
present between a flat electrode and an opposite flat electrode, in which 
the electrode(s) and the opposite electrode(s) are staggered with respect 
to each other in such a manner that in the plane of each time one of two 
oppositely located end faces of the capacitor they terminate and are 
contacted there by means of external connection contacts. 
Capacitors, for example, ceramic multilayer capacitors, are produced in 
large numbers since, on the basis of their properties, they are 
particularly suitable for automatic printed circuit board mounting (SMD 
technology with surface mounted devices). Multilayer capacitors have a 
high volume capacity, i.e. they are not very bulky, they have the 
advantage of a large range of the capacity from pF to .mu.F and they can 
be manufactured in standardized dimensions. 
In order to ensure the cost reduction and quality improvement which can be 
achieved by means of SMD techniques, high requirements are imposed upon 
all components used as regards rejection rate and units of the permissible 
capacity tolerances. 
Ceramic multilayer capacitors are manufactured in known manner in that a 
foil is rolled or drawn from a suspension of a dielectric ceramic powder 
with a binder. The said foil is cut into individual plates, on which 
electrodes are provided by means of a metal paste in a silk screening 
method. 
The printed green ceramic foils are stacked and packed under a high 
pressure. From the said sandwich pack individual capacitor bodies in the 
form of a sandwich stack are punched or cut before the binder is cured and 
the sandwich stack is sintered. According to this sintering process the 
contacting of the electrode layers is done by metallizing the opposing end 
faces of the capacitor body. 
Associated with this method of manufacturing is that inhomogeneous starting 
materials or variable process parameters, such as time, temperature, 
composition of the sintering atmosphere or tolerances within the automatic 
production machines, for example, upon aligning tool and workpiece, lead 
to a deviation of the capacity from the desired value. By optimizing the 
manufacturing process, these error sources can be removed only partly not 
in the least because the price calculated on the market per component is 
limited and a large series manufacture may not be arbitrarily expensive. 
Known multilayer capacitors are constructed as is shown in FIG. 3. 
Reference numeral 2 denotes the electrodes, 4 denotes the opposite 
electrodes, 6 are the outer connection contacts at the end faces of the 
capacitor and 8 denotes the dielectric layers. When the individual 
electrodes move with respect to each other in the x and in the y 
direction, as is shown in FIG. 4, the surface covered in common with the 
opposite electrodes following in the sandwich stack also vary so that 
according to the known laws of physics a capacity change occurs. This 
problem is not restricted to multilayer capacitors, but generally extends 
to flat capacitors having electric connections (external connection 
contacts) provided from oppositely located end faces, so, for example, 
plate capacitors. 
According to the prior art the expert is capable of considerably 
compensating for shifts of the electrodes 2 in the y direction as shown in 
FIG. 4, in that each opposite electrode 4 is widened within the sandwich 
stack. FIG. 5 is a sectional view in the y direction through a sandwich 
stack having two electrodes 2 which are widened (FIG. 5a). The capacity of 
a multilayer capacitor constructed in such a manner varies only slightly 
so long as the opposite electrode 4, in spite of a movement about the 
length .DELTA.y, fully remains within the common overlapping area of its 
adjacent electrodes 2 (FIG. 5b). However, it is particularly desirable to 
also compensate for a lateral staggering of individual electrodes 2 in the 
x direction as is shown in FIG. 4, since the said lateral staggering in 
the x direction very essentially influences the values for the capacity. 
SUMMARY OF THE INVENTION 
It is the object of the invention to improve the quality of capacitors and 
in particular to show a way how undesired capacity changes as a result of 
an electrode shift in the direction towards the external connection 
contacts, so in the x direction, which shift can be avoided only with 
difficulty in the manufacture of such capacitors, can be substantially 
avoided. 
According to the invention this object is achieved in that at least one 
electrode in its end area adjacent the external connection contact 
associated with it comprises a window and that the non-contacted end(s) of 
the opposite electrode(s) extend(s) in the area of the window(s). 
According to an advantageous further embodiment of the capacitor according 
to the invention at least one opposite electrode comprises a window in its 
end area adjacent the external connection contact associated with it. 
According to advantageous further embodiments of the invention the 
electrode(s) and/or the opposite electrode(s) in the area of its (their) 
window(s) comprise a widened area or the window(s) is (are) divided in 
such a manner that at least one central bridge of electrode material is 
formed which extends in the longitudinal direction of the electrode(s) 
and/or the opposite electrode(s). 
The dielectric layers preferably consist of ceramics in which the 
electrodes/opposite electrodes are preferably metal layers, for example, 
of nickel or chromium/nickel. 
A method of manufacturing capacitors formed according to the invention in 
which at least one dielectric layer is provided with each time a flat 
electrode and an opposite flat electrode and the electrode(s) and the 
opposite electrode(s) are staggered with respect to each other in such a 
manner that in the plane each time of one of two opposing end faces of the 
capacitor they terminate in the same plane, after which the external 
connection contacts contacting the electrode(s)/opposite electrode(s) are 
provided at the end faces, is characterized in that a window is provided 
in at least one electrode in its end area adjacent the external connection 
contact associated with it and that the electrode(s) is (are) provided so 
that the non-contacted end(s) of the opposite electrode(s) extend(s) in 
the area of the window(s). 
According to an advantageous further embodiment of the method according to 
the invention the capacitor is constructed from at least one foil of 
unburnt green ceramic as a dielectric layer having provided thereon 
metallic layers for the electrode(s) and the opposite electrode(s), is 
then sintered and provided with the external connection contacts. 
According to a further advantageous embodiment of the method according to 
the invention the layers for the electrode(s) and opposite electrode(s) 
are provided on the dielectric layer(s) in the form of a suspension of 
metal powder in an organic binder while using at least one mask which 
covers the areas of the dielectric layer(s) not to be coated with the 
suspension and in particular the areas corresponding to the windows to be 
formed. 
The invention provides the particular advantage that the capacity of 
capacitors of the above-described type remains considerably uninfluenced 
also when individual electrodes or opposite electrodes move undesirably 
with respect to each other in the direction of the external connection 
contacts, so in the x direction, with respect to the opposite electrodes 
adjacent same.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention suggests forms of electrodes and opposite electrodes, 
for example, for multilayer capacitors which make the capacity 
substantially independent of a shift of the electrodes and/or the opposite 
electrodes in the direction of the two external contacts contacting the 
electrodes and opposite electrodes. The principle solution of this problem 
is shown in FIGS. 1a to 2b. 
According to the embodiment shown in principle in FIG. 1 of an electrode 3 
on a dielectric layer 1 a window 7 is recessed in the electrode 3 in its 
area adjacent the external connection contact 11. The electrode 3 has a 
widened surface 13 in its area adjoining the window 7. FIG. 1b is a 
sectional view of this embodiment. In the embodiment shown a window 7 is 
provided in each electrode 3 in the sandwich stack (compare FIG. 1), so 
that the non-contacted end 15 of the opposite electrode 5 following next 
in the sandwich stack lies in the area of the window 7. So long as this 
condition is fulfilled the capacity of such a multilayer capacitor changes 
only very inconsiderably as compared with multilayer capacitors having 
electrodes which do not comprise (a) window(s) when a shift of the 
electrodes 3 and/or opposite electrodes 5 in the direction of the outer 
connection contacts 11 (so in the x direction), occurs. The stability of 
the capacity values significantly improved in this manner is maintained so 
long as the surface covered in common by the electrodes 3 and opposite 
electrodes 5 remains unchanged. 
As a result of the formation of windows, however, the charge transport is 
inhibited and moreover the danger exists that an electrode or opposite 
electrode is detached from the external connection contact 11 because one 
or both bridges 17 (compare FIG. 2) of remained electrode material are 
interrupted above or below the window 7. Therefore, the expert must choose 
the dimensions of the window 7 with respect to the remaining electrode 
material surrounding same in such a manner that the two said disadvantages 
are in a sensible relationship with the advantage of the stabilization of 
the capacity value achievable by a window in the electrode/opposite 
electrode. 
When using electrodes which are wider as compared with the opposite 
electrodes for compensating lateral shifts of the electrodes in the 
direction of the outer surfaces of the sandwich stack not provided with 
external connection contacts, so a shift in the y direction (compare FIG. 
5b), it is sensible to provide the wider electrodes with a window because 
more area remains there after the formation of the window than when the 
window is provided in the narrower opposite electrodes. 
The following embodiments of the electrodes/opposite electrodes according 
to the invention are advantageous: 
As is shown in FIG. 1a the electrodes 3 and/or the opposite electrodes 5 
may comprise a widened area 13 in the area of the windows 7. As a result 
of this it is ensured that a sufficient contacting with the external 
connection contacts 11 is formed because the bridges of electrode material 
formed as a result of this above and below the windows 7 may be 
comparatively wide. 
As is shown in FIG. 2a both the electrodes 3 and the opposite electrodes 5 
may be provided with windows 7. This provides two advantages: in order to 
compensate for a given shift .DELTA.x in the x direction with respect to 
the capacity values, small window widths in the x direction suffice as 
compared with the embodiment having only windows in each electrode 3 or 
opposite electrode 5. This reduces the danger that the electrodes 3 or 
opposite electrodes 5, as a result of interrupted bridges 17, have no 
sufficient contact with the external connection contact 11 contacting 
same. On the other hand in the case of wider window dimensions in the x 
direction which correspond to the widths of windows which are each 
provided only in the electrodes 3 or only in the opposite electrodes 5, a 
larger shift .DELTA.x can be compensated for. 
As is shown in FIG. 2b, the windows 5 may also be severed so that a central 
bridge 9 of electrode material extending in the longitudinal direction of 
the electrodes 3 or also of the opposite electrodes 5 is obtained. As a 
result of this the danger of an unsatisfactory contact with the external 
connection contacts 11 is also effectively reduced. 
The electrodes or opposite electrodes for multilayer capacitors formed 
according to the invention occupy a part of the electrical field between 
the electrodes/opposite electrodes through the windows which, however, 
provide the advantage of a stabilization of the capacity value. As a 
result of this the volume capacity of multilayer capacitors formed 
according to the invention reduces inconsiderably as compared with known 
multilayer capacitors of the same dimensions but with electrodes and 
opposite electrodes without windows. In order to achieve the same volume 
capacity values with multilayer capacitors formed according to the 
invention as with known multilayer capacitors of the same construction, 
the sandwich stack can be expanded, if so desired, by one 
electrode/dielectric layer. 
The effectivity of the measures suggested according to the invention will 
be described in greater detail with reference to a numerical example. 
The following capacity calculation is based on the known formula for the 
plate capacitor 
##EQU1## 
.epsilon.=.epsilon.o.epsilon.r dielectric constant, A=area covered by both 
plates in common, 
d=plate spacing. 
In this calculation only the field between the plates and within the area 
covered in common is taken into account. The inclusion of edge effects 
would influence all the calculated results in the same manner 
(inconsiderably), the qualitative expression is not varied by it. 
Multilayer capacitors having a sandwich stack of five electrodes I to V and 
inbetween arranged dielectric layers of a relative dielectric constant of 
.epsilon..sub.r =133 and a spacing of d=20 .mu.m between adjacent 
electrodes/opposite electrodes, will be considered hereinafter. These and 
all remaining values are oriented to the real order of magnitude of 
typical multilayer capacitors. All results are rounded down to one decimal 
behind the decimal point. 
1. Multilayer capacitor having equally formed electrodes without window: 
the electrodes I, III and V are considered to be contacted with the first 
external connection contact and the electrodes II and IV are considered to 
be contacted with the second external connection contact. 
With an overlap area between adjacent electrodes/opposite electrodes of A=2 
mm.times.1 mm it follows that 
##EQU2## 
When one of the electrodes 2, 3 or 4 is moved in the x direction and in the 
y direction so that an average overlap area of A=1.75.times.0.09 between 
adjacent electrodes/opposite electrodes is obtained, it follows that 
##EQU3## 
The capacity variation hence amounts to 10.6%. When one of the electrodes I 
or V is shifted a capacity variation of 5.3% is obtained in a 
corresponding manner. 
2. A multilayer capacitor with unequally formed electrodes, i.e. provided 
with windows and widened electrodes: the electrodes I, III and V are 
considered again to be contacted with the first external connection 
contact and provided with windows in the area of their end area adjacent 
the external connection contacts, into which windows the adjacent opposite 
electrodes II and IV extend up to approximately the centre of the window 
with their end faces not contacted with the second external connection 
contact. The electrodes I, III and V are additionally considered to be 
widened with respect to the opposite electrodes II and IV. 
With A=2 mm.times.1 mm as an overlap area between adjacent 
electrodes/opposite electrodes the same capacity as according to example 1 
is obtained for 
##EQU4## 
When one of the electrodes I, III or V or one of the opposite electrodes II 
or IV is moved in the x and/or in the y direction over a length .DELTA.x 
lying within the window area or by a length .DELTA.y lying in the range of 
the widths of the electrodes I, III and V larger as compared with the 
widths of the electrodes II and IV, the overlap area between adjacent 
electrodes does not vary and the capacity value remains constant.