FR2529378A1 - Multilayer ceramic dielectric capacitor with PCB cleaning device - has space under dielectric leaves which permits cleansing of substrate but which prevents ingress of connecting wire - Google Patents

Abstract

The interleaved dielectric leaves (10), coated partially with metal, are supported by metal end-pieces (11,12). These are soldered to metal sheets (21) on the insulating substrate (20) to make the electrical connections. A recess milled on the underside of the capacitor leaves space for cleansing of the substrate underneath (23) but is shallow enough to prevent accidental ingress of a substrate connecting wire. The process is applicable to leaves stacked horizontally or vertically. Preferably, the recess is in the region of the metallisations. To expose the largest possible area of substrate and to maintain a good mechanical rigidity, the size of the recess is pref. 1/20 to 1/5 the length of the capacitor.

Description

 The present invention relates to multilayer ceramic dielectric capacitors which are intended to be fixed and soldered directly to a flat substrate, that is to say capacitors without connection wires.

 Capacitors of this type have a generally parallelepiped shape, with two opposite metallized faces intended to be presented perpendicular to the substrate. Once the capacitor has been placed on the substrate, it suffices to make two solder points, for example by wave welding, between these faces and the corresponding conductive patterns of the substrate to establish the electrical connection.

 After welding, the substrate is subjected to a washing in order to remove the remnants of pickling resin, as well as the traces or overflows of solder which could adhere to the substrate there ot this one does not contain conductive patterns, and which risk by Therefore create bridges forming a short circuit between two conductive patterns.

 With capacitors of the aforementioned type, which are bonded directly to the substrate, there remains the risk that a short-circuit will form, under the capacitor, between the two conductive patterns leading to metallizations, for example due to a weld overflow outside the patterns. Washing will not eliminate this short circuit, due to the flat shape of the capacitor glued against the substrate.

 One of the aims of the invention is to provide a capacitor of the aforementioned type which overcomes this drawback, by authorizing the washing of the substrate under the capacitor.

 To this end, the capacitor according to the invention comprises, on its face facing the substrate, at least two over thicknesses by which the body of the capacitor rests on the substrate, and allowing the area of the latter located under the body to be washed. of the capacitor.

 Preferably, the height of the extra thicknesses is less than the average diameter of the connection wires used for wiring the substrate. In this way, a fragment of wire is prevented from entering and blocking between the capacitor and the substrate.

 Preferably, the extra thicknesses are produced in the vicinity of the metallizations, and extend over the entire width of the component; to reveal the largest possible surface of the substrate while retaining good mechanical rigidity of the capacitor, the width of each of the extra thicknesses is preferably between 1 / 20th and 1 / 5th of the total length of the capacitor.

 The extra thicknesses can be produced only on the face of the capacitor which will face the substrate; they can also be made on the opposite face: although in this case, these latter thicknesses will not play any functional role, they make it possible to make the capacitor symmetrical and to avoid any problem of positioning at the time of the positioning of the component , this implementation can be done either on one or the other side.

 The invention also proposes, in order to produce such a capacitor, to machine the latter by means of a tool with a profile complementary to that of the extra thicknesses, this tool correcting the capacitor by removing material in a dead zone of the capacitor; this operation is preferably carried out before sintering, but after a pre-firing, carried out at a temperature between 850 and 10,000 for ceramics sintering between 1,100 and 13,000.

 Indeed, a rectification carried out before sintering but without pre-cooking would risk destroying.

stacking, the only consistency of which is obtained by pressing the ceramic sheets. Furthermore, rectification after sintering would be made more difficult due to the compactness of the sintered material.

 In another production method, at least one dead ceramic sheet is added to the stack of ceramic sheets, obtained in known manner, at each location where the extra thicknesses are to be made; the assembly is then compressed, before sintering, by means of a punch with a profile complementary to that of the capacitor profile to be produced.

 Finally, it is also possible to stack ceramic sheets all having the same outline, this outline itself being identical to the profile of the capacitor to be produced. As will be explained later, this arrangement is particularly advantageous in microwave circuits, where it provides excellent reproducibility of performance.

Other characteristics and advantages of the invention will appear on reading the detailed description below, made with reference to the appended figures, in which
FIG. 1 is a perspective view of a capacitor according to the invention, soldered on its substrate,
FIGS. 2a and 2b are side views of this same capacitor showing two possible profiles,
FIGS. 3a and 3b are perspective views of the capacitor showing two ways of stacking the ceramic layers,
FIG. 4 illustrates the first method according to the invention, by machining the stack,
FIG. 5 shows the different ceramic sheets used in the second production method,
FIG. 6 illustrates the implementation of this second method,
Figure 7 shows the ceramic sheets used in the third manufacturing process.

 In the following, the direction perpendicular to the plane of the substrate will be called "vertical", and "horizontal" any direction parallel to this same plane, whatever the actual physical position of the substrate.

In FIG. 1, the capacitor 10 according to the invention is welded to the substrate 20: the capacitor has a generally parallelepiped shape, and has two opposite ends 11, 12 metallized forming an electrical connection common to each series of reinforcements of the capacitor
These two metallized faces are welded onto conductive patterns 21, 22 produced on the substrate, by means of solder points 31, 32; the electrical connection of the capacitor to the conductive patterns of the substrate is therefore made without any connection wire.

 According to the invention, the capacitor 10 comprises two extra thicknesses 13, 14, preferably located in the vicinity of the metallizations and extending over the entire width of the capacitor. The capacitor rests on these extra thicknesses or "washing feet" so as to leave a space between the body of the capacitor and the substrate 20, which allows, as indicated above, the washing of the region 23 of this substrate located below the capacitor.

 Figures 2a and 2b show the two possible profiles for the capacitor depending on whether the washing feet are formed respectively on two sides or on one side of the capacitor. In the first case, the capacitor has a symmetrical appearance and, although the washing feet 13 'and 14' identical to the feet 13, 14 formed on the opposite face play no functional role, they avoid an additional operation of positioning the capacitor with the washing feet down when it is attached to the substrate.

 The height h of the extra thicknesses is preferably less than the average diameter of the connection wires used for the wiring of the substrate, and the width 1 of each of the excess thicknesses can be between 1 / 20th and 1 / 5th of the total length L of the capacitor.

 FIG. 4 illustrates the first method of producing the capacitor according to the invention, in which a tool 50, for example a diamond grinding wheel or abrasive resinoid, rectifies the capacitor 10 previously positioned in a guide rail 40, by removing material in a dead zone 18 of this capacitor. The profile 50a of the tool 50 is complementary to the profile of the extra thicknesses that it is desired to form.

 This process lends itself as well to the formation of extra thicknesses for capacitors whose layers are stacked in horizontal planes (as shown for example in Figure 3a) as in vertical planes (Figure 3b).

 If it is desired to make extra thicknesses on the two faces of the capacitor (profile in FIG. 2a), it suffices to make a second pass under the rectification tool, the capacitor having been previously turned over.

 The preliminary pre-cooking step, as indicated above, gives the stack sufficient mechanical strength to undergo without damage the various manipulations and machining operations.

 For the implementation of the second manufacturing process, ceramic sheets are used having, once cut, the shape indicated in FIG. 5: in addition to the sheets 16 and 16 ′ carrying the offset conductive patterns which constitute, in known manner, the armatures of the capacitor, dead ceramic sheets 15 or 15 ′ are provided, having substantially the size of the extra thicknesses to be formed and arranged at the location thereof. Thus stacked (Figure 6): one or more dead ceramic sheets 15 '; one or more pairs of sheets 16, 16 'forming the capacitor proper; as well as (if one wants to obtain a symmetrical profile of the capacitor) one or more dead leaves 15. The assembly is placed in a matrix 60 and compressed between two punches 61, 62 having profiles 61a, 62a complementary to the profiles of the thicknesses to achieve. The stack thus compressed is then sintered in a conventional manner.

 This process allows capacitors to be produced, the sheets of which will be stacked horizontally, as shown in FIG. 3a, the dead ceramic sheets 15, 15 ′ making it possible to create extra thicknesses below and above the stack of sheets 16, 16 ′. , the latter sheets having the same shape in plan as in the prior art, that is to say having a rectangular shape for a parallelepiped capacitor.

 Finally, according to a third production method, instead of bringing back dead ceramic sheets to form the extra thicknesses, pairs of ceramic sheets 17, 17 ′ are stacked carrying the conductive patterns (FIG. 7), whose outline 17a, identical for all the sheets, is itself identical to the profile of the capacitor to be produced: in this way a capacitor such as that shown in FIG. 3b is obtained, all the ceramic sheets being located in vertical planes.

 This latter arrangement is particularly advantageous in microwave circuits: in fact, the current lines (shown in dashed lines) are identical for all the plates of the capacitor, while in the conventional arrangement (FIG. 3a) the current lines follow different paths. for each armature, which is the source of phase shift causing well known reproducibility problems in microwave.

Claims (10)

 1. Multilayer ceramic dielectric capacitor, capable of being fixed directly to a flat substrate (20) and of being welded thereto by metallizations (11, 12) produced on its lateral faces, characterized in that it comprises, on its face facing the substrate, at least two extra thicknesses (13, 14) by which the body of the capacitor rests on the substrate, and allowing the washing of the zone (23) of the latter located under the body of the capacitor.  2. Capacitor according to claim 1, characterized in that the height (h) of the extra thicknesses is less than the average diameter of the connection wires used for the wiring of the substrate.  3. Capacitor according to one of claims 1 and 2, characterized in that the width (1) of each of the extra thicknesses is between 1 / 20th and 1 / 5th of the total length (L) of the capacitor.  4. Capacitor according to one of claims 1 to 3, characterized in that the extra thicknesses are produced in the vicinity of the metallizations, and extend over the entire width of the capacitor.  5. Capacitor according to one of claims 1 to 4, characterized in that the extra thicknesses are also produced (13 ', 14') on the face of the capacitor opposite the substrate.  6. Method for producing a capacitor according to one of the preceding claims, characterized in that it consists in machining the capacitor by means of a tool (50) of profile (50a) complementary to that of the extra thicknesses, this tool rectifying the capacitor by removing material in a dead zone (18) thereof.  7. Method according to claim 6, characterized in that the rectification operation is carried out before sintering, but after a pre-cooking.  8. Method according to claim 7, characterized in that the pre-firing is carried out between 850 and 10000C for ceramics sintering between 1100 and 13000C.  9. A method of producing a capacitor according to one of claims 1 to 5, characterized in that it consists in adding to the stack of ceramic sheets (16, 16 '), at each location where must be carried out extra thicknesses, at least one sheet (15, 15 ') of dead ceramic, and to compress the assembly, before sintering, by means of a punch (61, 62) of profile (61a, 62a) complementary to that of the profile of the capacitor to be produced.  10. A method of producing a capacitor according to one of claims i to 5, characterized in that it consists in making a stack of ceramic sheets (17, 17'j all having the same outline (17a), this contour itself being identical to the profile of the capacitor to be produced.