EP0562977B1 - Process for making ceramic insulated supports by piling up layers - Google Patents

Description

TECHNICAL AREA

The invention relates to a process for obtaining insulating ceramic inserts (for example, beads) serving as a sealed passage for electrically conductive wires or pins through an electrically conductive wall, generally metallic.

STATE OF THE ART

Insulating ceramic beads are generally in the form of cylindrical parts having an axial bore. The external side wall of the ceramic part and that of the axial bore are metallized separately from one another. Thus it is possible to braze the external surface on the metal wall to be crossed and to braze the conductive wire inside the pearl, so as to finally obtain a sealed electrical passage and electrically isolated from the metal wall.

• soit frittée par les techniques connues, puis, ou métallisée en partie séparément sur la surface latérale externe et dans l'alésage axial, ou métallisée totalement, un rodage des extrémités de la perle étant alors nécessaire pour isoler électriquement l'une de l'autre la surface latérale du passage axial,
• soit métallisée sur cru, partiellement ou en totalité comme précédemment, puis frittée, la métallisation étant alors cuite et cofrittée avec la céramique.

Ceramic beads are usually obtained by conventional sintering techniques. A ceramic powder containing a binder and a plasticizer is thus formed by pressing to obtain a green part which can then be

• either sintered by known techniques, then, or partially metallized separately on the external lateral surface and in the axial bore, or totally metallized, a lapping of the ends of the bead then being necessary to electrically isolate one from the other the lateral surface of the axial passage,
• either metallized on raw, partially or entirely as before, then sintered, the metallization then being fired and co-sintered with the ceramic.

FIG. 1 illustrates such a method of the prior art:
(1) represents the pearl shaped with its external lateral wall (2), the axial passage (3) comprising for example a central cylindrical part (3a) terminated at each end by a flare (3b); (4) represents the planar ends of the pearl; (5) represents the metallized pearl in part with the metallization layer of the lateral surface (6) and that of the axial bore (7b), separated from each other by the end surfaces (4) not metallic. In (8) the metallized pearl is shown in full; this pearl then undergoes a running-in intended to remove the metallization on the end faces (4) so as to obtain a pearl (9) identical to the pearl (5) where the metallization of the lateral surface (6, 10) is isolated that of the axial bore (7.11).

Metallization is generally done using metallization inks or pastes having a rheology adapted to the ceramic material and to the device for depositing said ink or paste.

Such a type of process, described for example in document FR-A-2,585,181, where the beads are shaped individually is long and not very productive. In addition with such beads, there are frequent hermeticity defects after performing the soldering of the electrical conductor wire in the axial bore, generally on the metallized flare (7b, 11b). Furthermore, the insulating distance separating the metallization layers from the lateral surface (6,10) and from the axial bore (7,11) is limited to the flat end surfaces (4) which are not metallized. This insulating distance directly conditions the current leaks and the risks of electric ignition between these two metallized surfaces (6,10) and (7,11); it is often insufficient and limits the electrical voltage of use of the pearls. In addition, by this process it is very difficult to obtain hermetic insulating inserts having any shape and comprising a plurality of metallized bores (3) as in (5) or (9), corresponding to as many hermetic passages of conductors electric.

Faced with these problems, the applicant has sought a process for manufacturing pearls, or more generally insulating inserts of any shape, which is more productive while also making it possible to avoid scrap by loss of hermeticity at the solder of the wire. crossing the pearl and increasing the breakdown tension between said wire and the metal wall in which the pearl is brazed, without increasing the dimension of the pearl.

DESCRIPTION OF THE INVENTION

The invention is a method of manufacturing insulating ceramic inserts (pieces or beads) comprising a ceramic body delimited by two planar end faces, an external lateral surface of any shape and at least one bore joining the two faces of end, said parts or beads being used as hermetic insulating passages of at least one electrically conductive wire or pin through a wall which is also electrically conductive. This process is characterized in that at least two flat sheets are poured from a slip of insulating ceramic powder to obtain at least two raw sheets, screen-shaped patterns are screen-printed on at least one side of a sheets using a conductive metallization ink or paste, the screen-printed sheet is pressed, then all the sheets are punched to obtain a plurality of holes (corresponding to as many bores), the holes of the screen-printed sheet agreeing with the inside of the crown and having a diameter smaller than that of the holes of the other sheets, the different sheets are stacked by making the axes of the different holes coincide and thus obtaining said bores, we press to agglomerate the sheets between they are cut around at least one bore to obtain the external lateral surface of desired shape and thus make pieces or beads c in the streets, the raw pieces or pearls are metallized either only on their external lateral surface or totally and in this case a lapping is then carried out to remove the metallization from the end faces, then heat treatment is carried out for baking and sintering.

FIG. 2 is an illustration of the invention which will make it easier to understand it. In (A) marks 1, 2 and 3 represent raw sheets poured, for example from a slip typically comprising a 94 to 96% pure alumina powder, a binder and a plasticizer, according to the known techniques of one skilled in the art. Each of these sheets may consist of a stack of elementary sheets.

The sheet (2) which, as will be seen below, comprises the cylindrical part of the axial bore and the screen-printed patterns, may advantageously be thicker than the others.

In (B), on each of the sides of the sheet (2), patterns have been screen printed, using an ink or a metallic paste (adapted to the ceramic support and to the subsequent solders made on the metallized surfaces) (9) corresponding to the bores of future pearls. These are generally circular rings whose inner circle (9a) has a diameter at most equal to that of the cylindrical part of the bore.

It is possible to screen-print only one of the faces of the sheet (2), for example to obtain a half-pearl; it is this face which will come into contact with the non-screen-printed sheet, as will be seen later.

When these patterns are screen printed on each of the two faces, they are located two by two on the same axis.

The screen-printed sheet is then subjected to pressing to perfect the adhesion of the metallic paste to the raw ceramic.

In (C) we see that we then made a punching in each of the sheets (1), (2), (3) to obtain a plurality of holes (11,21,31) which will constitute the bores (4) located in the center of the pearls. The holes (11,31) made in the non-screen-printed sheets have a diameter greater than that of the hole (21) made in the screen-printed sheet. We also see that we have positioned the sheets (1), (2), (3) so as to superimpose the axes of the holes (11), (21), (31).

The sheets are then brought into contact and pressed against each other to obtain a raw monolith as illustrated in (D), where the axial bores of the future pearls are seen, said bores comprising a cylindrical part (4a) in insulating ceramic, continued at both ends by the shoulders metallized (9) and by larger openings (4b) following them.

The screen-printed sheet comprising the cylindrical part of the bore is thus sandwiched between the two non-screen-printed sheets forming the end faces and comprising the openings. Usually the non-screen-printed sheets partially cover the metallized shoulders (9).

In (E), we see the cut made around an axial bore to obtain the external lateral surface (5), of any shape, of the pieces or beads; the ceramic body (10) of said pieces or pearls has acquired its final shape at this stage. Said cutout may include one or more bores; it can have any shape. For example when it only includes a bore it can be circular and coaxial with said bore to obtain a pearl; it can be rectangular and include a row of bores to finally obtain an insulating insert comprising as many hermetic electrical passages (for wires or pins), said insert possibly constituting a part of an encapsulation box.

• l'alésage (4) comprenant généralement, comme cela a été déjà vu, la partie centrale (4a) cylindrique en céramique, l'épaulement métallisé (9), sur lequel sera brasé le fil ou la broche conducteur traversant la pièce ou la perle, et l'ouverture (4b) en céramique (de diamètre supérieur à celui de la partie cylindrique (4a)) permettant d'accéder à l'épaulement métallisé (9) où sera effectuée la brasure ultérieure du fil ou de la broche conducteur ;
• la surface latérale externe (5) qui permettra après métallisation de fixer la pièce ou la perle dans la paroi à traverser ;
• les faces d'extrémité (6) planes, correspondant aux feuilles coulées (1) et (3).

It is noted, whether in the case of a pearl having a single bore or in the case where the cut includes several bores:

• the bore (4) generally comprising, as has already been seen, the central cylindrical ceramic part (4a), the metallized shoulder (9), on which the wire or the conductive pin passing through the part or the pearl will be brazed , and the ceramic opening (4b) (of diameter greater than that of the cylindrical part (4a)) providing access to the metallized shoulder (9) where the subsequent brazing of the wire or conductive pin will be carried out;
• the external lateral surface (5) which will allow, after metallization, to fix the part or the pearl in the wall to be crossed;
• the planar end faces (6), corresponding to the cast sheets (1) and (3).

From there it is preferable to first of all metallize the lateral surface (5) of the raw pearl then to bake and sinter, so that there is a co-sintering of the metallic ink and of ceramic, which improves their mutual adhesion.

Thus we see in (F) the selective metallization (7) of the lateral surface (5), made for example using an ink or metallic paste by methods known to those skilled in the art, after which it only remains to carry out the heat treatment for cooking and sintering to obtain the final insert (pearl with single bore or parts of any shape which may contain several bores).

It is also possible, as illustrated in (G1), to carry out a total metallization (8) of the raw ceramic part, for example by simple dipping in an ink or a metallic paste according to the techniques known to those skilled in the art, followed, in (G2), a lapping of the end faces (6) to remove the deposited metal and thereby electrically isolate the metallization (7) from the lateral surface (5) of the metallization (8) from the bore ( 4) and obtain a metallized pearl similar to that of the case illustrated in (F), except that, in case (G2), the cylindrical part (4a) of the bore (4) as well as the vertical part of the opening (4b) will be metallized.

But it is also possible, after obtaining the raw pearl such as in (E), to first carry out the heat treatment of cooking and sintering which is then followed by additional metallization as carried out in (F) or (G1), according to techniques known to those skilled in the art which may in particular include a treatment for baking inks or metallization pastes. Using the method according to the invention it is possible, as has already been said, to obtain half-pieces or -pearls of appearance different from those of FIG. (2) by screen printing only the upper face of the sheet (2), the final pearl obtained then having only one metallized shoulder (9) and of stacking only the sheets (1) and (2), one of the end faces being constituted by the face lower non-metallized sheet (2).

A ceramic insulating part or pearl according to the invention therefore comprises a sintered ceramic body (10), two end faces (6) which are not metallized, an external lateral surface (5) metallized (7) and of any shape, at least a bore (4) connecting the two end faces (6), which bore comprises a cylindrical central part (4a), preferably non-metallized, at least one metallized shoulder (9), on which a conductor will be brazed electric crossing the piece or pearl, and at least one ceramic opening, generally not metallized, giving access to said shoulder. This opening giving access to the shoulder and to said cylindrical part is delimited by one of the end faces (6) of the bead, and the vertical cylindrical wall (4b).

With the method according to the invention it is easy to obtain that this wall (4b) is not metallized, which has an undeniable advantage. Indeed the fact that it is not metallized increases the insulating distance separating the metallized shoulder (9) from the metallized external surface (7) which will cause a reduction in the leakage currents, and notable increase in the breakdown voltage between these two metallized parts intended to be brought to different potentials.

In addition to this advantage, the method according to the invention makes it possible to obtain a marked improvement in the seal at the level of the subsequent soldering of the conductor (wire or pin) on the metallized shoulder (9) thanks to very good adhesion of the metallization layer obtained during the compression phase of the metallization paste on the raw sheet carried out before punching, and at the burial between two ceramic layers of the metallized ring on part of its surface. This configuration makes it possible to improve the peel strength of the metallization and consequently increases its resistance to tensile-flexions exerted on the brazed wire.

Claims (7)

1. Process for making ceramic insulated supports, parts or pearls comprising a ceramic body (10) delimited by two flat outer sides, an external lateral surface (5) of any form and at least one bore linking the two outer sides, characterised in that at least two flat sheets (1, 2, 3) are cast from an insulating, ceramic powder casting slip to obtain at least two raw sheets (1, 2, 3), the patterns (9) are serigraphed in the shape of a ring on at least one side of one of the sheets with the assistance of ink or conducting metallising pulp, the serigraphed sheet is pressed then all the sheets are punched to produce a plurality of holes (11, 21, 31), corresponding to the bores (4), the holes of the serigraphed sheet corresponding with the inside of the ring and having a smaller diameter than the holes of the other sheets, the different sheets are piled up so that the axes of the different holes (11, 21, 31) coincide thus obtaining the bores (4), the sheets are pressed together so that they form a single unit, and are cut around at least one bore to obtain the external lateral surface (5) of the desired shape and raw parts or pearls are thus made, the parts or pearls are metallised either on their external lateral surface only or completely, and in this case grinding is necessary to remove the metallisation of the outer surfaces, then they are treated thermically for firing and sintering.
2. Process for making ceramic insulated supports, parts or pearls comprising a ceramic body (10) delimited by two flat outer sides, an external lateral surface (5) of any form and at least one bore linking the two outer sides, characterised in that at least two flat sheets (1, 2, 3) are cast from an insulating, ceramic powder casting slip to obtain at least two raw sheets (1, 2, 3), the patterns (9) are serigraphed in the shape of a ring on at least one side of one of the sheets with the assistance of ink or conducting metallising pulp, the serigraphed sheet is pressed then all the sheets are punched to produce a plurality of holes (11, 21, 31), corresponding to the bores (4), the holes of the serigraphed sheet corresponding with the inside of the ring and having a smaller diameter than the holes of the other sheets, the different sheets are piled up so that the axes of the different holes (11, 21, 31) coincide thus obtaining the bores (4), the sheets are pressed together so that they form a single unit, and are cut around at least one bore to obtain the external lateral surface (5) of the desired shape and raw parts or pearls are thus made, they are treated thermically for firing and sintering, the parts or pearls are metallised either on their external lateral surface only or completely, and in this case grinding is necessary to remove the metallisation of the outer surfaces.
3. Process according to either claim 1 or 2, characterised in that three ceramic sheets (1, 2, 3) are cast, the serigraphed sheet (2) is thicker than the other two, it is serigraphed on both sides, and when the sheets are piled up is inserted between the other two.
4. Process according to any one of claims 1 to 3 characterised in that the raw ceramic sheets (1, 2, 3) are obtained by piling up several elementary raw ceramic sheets.
5. Process according to any one of claims 1 to 4 characterised in that the serigraphed patterns (9) are circular rings, the central circle of which corresponds to the bore (4) of the parts or pearls.
6. Process according to any one of claims 1 to 5, characterised in that on piling up the raw sheets the serigraphed pattern (9) is partially covered.
7. Insulated part or pearl obtained according to any one of claims 1 to 6 characterised in that it comprises a sintered ceramic body (10) comprising two outer non-metallised sides (6), a lateral external metallised surface (7), at least one bore (4) linking the two outer sides, said bore comprising a central cylindrical section (4a) continued by at least one metallised shoulder (9) and at least one opening of a greater diameter to that of the central cylindrical section and providing access to said shoulder and to the cylindrical section of the axial passage.

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