DE3147770A1 - Fusible conductor and method of producing it - Google Patents

Abstract

A fusible conductor for a fuse device, in particular for a semiconductor fuse, comprises a thin conductor element composed of a nobler metal which is situated in a narrow region between at least two conductor sections containing baser metal. It is intended that such a fusible conductor should be relatively simple and cheap to produce and nevertheless contain only a relatively small proportion of the nobler metal. The invention provides for the fusible conductor (21) to contain a conductor element (13) extending over its entire length (L) and composed of the nobler metal, which conductor element is connected outside the at least one narrow region (23) on at least one side to the baser metal of the conductor sections (22). Said fusible conductor (21) can advantageously be produced by first producing a conductor preproduct containing at least one conductor part composed of baser metal and one conductor part composed of nobler metal, then deforming said conductor preproduct so as to produce a composite conductor and, finally, removing, for example etching off, the baser metal at the planned narrow region (23) of said composite conductor. <IMAGE>

Description

Fusible link and process for its manufacture

The invention relates to a fuse element for a fuse device, in particular for a semiconductor fuse between at least two less noble Metal-containing conductor pieces each in a narrow point area from a thin The ladder element is made of noble metal. The invention also relates to a method for the production of this fuse element. Such a fuse element is, for example, off from DE-PS 1 161 987 known.

To protect power semiconductor components, e.g.

Silicon diodes or thyristors because of their low heat capacity are very sensitive to overcurrent, special, extremely fast safety devices, so-called semiconductor fuses, are provided. These backups have the generally at least one mostly band-shaped fusible link that is connected to a or several bottleneck areas are provided where the conductor cross-section is significant is decreased. The bottleneck areas can, for example, be through holes or openings be formed in the fusible link. The fusible conductor has a predetermined one Melting I2t value which, when exceeded, leads to melting in the at least one Bottleneck area leads. The sizes 1 and t are the one through the fusible link current passed through or the time during which the conductor with the current maximum may be charged (see e.g.

"The Electronics Technician", Volume 14, Issue 3, March 1975, Pages 7 bis 14).

Because of its resistance to oxidation, scale resistance and its The favorable ratio of melting I2t value to electrical conductivity is silver particularly advantageous for fusible conductors of semiconductor fuses.

However, these properties of a fuse element are only used for its bottleneck area required.

To meet the demand for pure silver for fusible conductors in semiconductor fuses To reduce this, fusible conductors were therefore developed that are only used in the bottleneck area contain a thin conductor element made of silver, while the remaining conductor pieces E.g. made of copper. Silver wires can be used as thin conductor elements (DE-PS 1 161 987).

However, these silver wires must be used in the known embodiment in a relatively complex process to the remaining conductor sections of the fusible conductor, which can consist of copper, which is less noble than silver, connected, for example be soldered on.

The object of the present invention is therefore to provide the aforementioned To improve fusible conductors to the effect that it is relatively simple and inexpensive can be produced and yet only a relatively small proportion of the nobler one Has metal.

According to the invention, this object is achieved in that the fusible conductor a conductor element made of the more noble metal and extending over its entire length contains that outside of the at least one bottleneck area on at least one Side is connected to the at least one base metal of the conductor pieces.

The advantages of the inventive design of the fusible conductor are especially to be seen in its relatively simple manufacturability. The fusible link namely consists essentially of only one composite conductor with one with the less noble one Metal of its conductor pieces connected thin conductor element from the comparatively nobler metal. You only need in the at least one bottleneck area to remove the less noble metal. This is based on methods known per se easy way possible.

The need for contacting the individual conductor element from the more noble metal, as in the case of the known fusible conductor, is therefore omitted. Included can advantageously compare the cross-sectional proportion of this thin conductor element be kept relatively small to the cross section of the entire composite conductor. In addition, the cross-sectional dimensions of the thin conductor element are also wide Limits selectable, so that fusible conductors can be produced that practically the have the same properties as known fusible conductors made of pure silver.

A ribbon shape of the fusible conductor is also a good option for heat dissipation to the environment and to ensure high mechanical stability.

The fusible conductor can be manufactured particularly advantageously by that first a ladder pre-product with at least one ladder part made of less noble Metal and is formed with a conductor part made of noble metal that then this Conductor pre-product is deformed into a composite conductor and that subsequently to the provided at least one bottleneck area of this composite conductor is the less noble Metal is removed. Preferably, the less noble metal in the at least removed a constriction area in an etching step.

Further advantageous embodiments of the fusible conductor according to the invention and the method for its production are based on the remaining subclaims emerged.

To further explain the invention and its in the subclaims marked further developments, reference is made to the schematic drawing, 1 to 7 show a method for producing a fusible conductor according to FIG the invention is explained below. 8 to 10 each show a conductor pre-product of such a fusible conductor, while in FIG. 11 a further method of production a composite conductor illustrated as a preliminary stage of a fusible conductor according to the invention is.

For the production of a fusible conductor according to the invention, as it is in particular can be provided for semiconductor fuses, a composite conductor is assumed. This composite conductor should have a thin, continuous ribbon-shaped conductor element made of a more noble metal such as pure silver, that on at least one of its two flat sides with a less noble metal like e.g. copper is connected. Under a thin conductor element, all are elongated Understood flat or curved conductor parts, the thickness of which is at most 0.5 mm.

The cross-sectional proportion of the thin conductor element in the total cross-section of the composite conductor is advantageous about 2 to 40%, preferably about 5 to 20.

The production of a corresponding copper-silver composite conductor with a thin central band-shaped conductor core made of silver, which is in a copper Matrix is embedded, can be carried out according to known methods. According to an embodiment of such a method as described in the Cross Sections 1 to 5 is shown schematically, is first a silver rod or -wire 2 inserted into a copper tube 3 (Fig. 1). This resulting coat wire 4 is then subjected to a suitable deformation treatment such as hammering, Wire drawing or rolling to form a jacket band 5 with an approximately rectangular cross-section deformed (Fig. 2).

Since the silver content of this cladding band 5 is still relatively high is, it is placed between two equally wide copper strips 6 and 7 (Fig. 3) and introduced into a corresponding hollow profile body 8 with these copper strips (Fig. 4). This hollow profile body 8 is either also made of copper or is advantageous made of a non-scaling material such as a special copper alloy. Appropriate I-copper alloys are in particular copper-germanium, copper-aluminum and copper Magnesium or copper-tin.

Subsequently, this conductor pre-product 10 produced in this way is made by means of a suitable deformation step such as hammering, rolling or wire drawing given the desired final ribbon shape of a single-core composite conductor 11 (Fig. 5).

After the deformation step, the in Fig. 5 has then schematically as Ribbon-shaped single-core composite conductors (all) shown in cross-section in general a thickness D from 0.1 to 0.5 mm and a width B between 10 and 70 mm. A ratio of thickness to width of the cross section of smaller than i: 50, preferably smaller than 1: 100.

In this manufacturing process, an intermediate annealing can also be used if necessary at about 700 ° C. for several hours before, during or after the deformation for improvement the connection of the single thin conductor element with the matrix material is required be.

This is the conductor core in its matrix 12 made of the less noble metal thin conductor element 13 embedded from the nobler metal. This ladder element also has the shape of a strip due to the previous rolling step.

Its width b and thickness d are dependent on the cross-sectional portion of the original silver rod on the overall cross-section of the conductor pre-product.

While the thickness d is generally less than 0.1 mm, according to 5 shows the width b almost the value of the width B of the entire single-core composite conductor 11 have. As can also be seen from FIG. 5, the matrix 12 is in a form-fitting manner a sheath 14 made of a non-scaling material such as a special copper alloy surround.

In this band-shaped single-core composite conductor produced in this way then the necessary bottleneck areas are formed. This can be advantageous a known shape etching process can be provided. Accordingly, according to the top view of the EiK core composite conductor of length L shown in FIG. 6 in one provided with a mask 16 suitable lacquering or photoresist processes. Of the masked composite conductor is generally designated by 17 in the figure. It contains for example three areas 18 covered with this mask, between which two non-masked areas 19 are kept free, which are the later bottlenecks determine. These non-masked areas 19 are then immersed in the ribbon-shaped conductor 17 in a selective etchant exposed to the etchant alone. A selective etchant is particularly suitable for copper-silver composite conductors Copper III chloride or aqua regia, a mixture of hydrochloric acid and nitric acid in a ratio of 3: 1.

The etchant only dissolves the copper matrix 12 and its possibly existing shell 14, so that in the constriction areas 19 then only the continuous Silver core remains. The single-core composite conductor can then be used in one Polishing bath cleaned, the protective layers formed on the silver core removed.

Instead of the shape etching process described in accordance with the exemplary embodiment can be used to produce the narrow areas of the fusible conductor according to the invention If necessary, also physical etching processes such as ion etching or plasma etching can be used.

The single-core composite fusible conductor produced in this way is shown in FIG. 7 as Supervision indicated in its final form. This ladder 21 contains wide, unetched conductor pieces 22 from the matrix of at least one less noble metal and the single thin conductor element 13 made of noble metal embedded therein, wherein the conductor pieces 22 through the thin conductor element 13 in constriction areas 23 with one another are connected.

While for the more noble metal of the thin conductor element e.g. also a silver alloy can be selected, can be used as a matrix material instead of Copper also use a copper alloy. It can also be used as a matrix material also provide nickel or nickel alloys.

In addition, aluminum or an aluminum alloy is used as a matrix material particularly suitable.

If necessary, one can make an interdiffusion of silver and copper to prevent the conductor element from the nobler metal in the composite conductor respectively surrounded by a special diffusion-inhibiting cladding tube.

This is done, for example, in the manufacture of the preliminary conductor product the silver wire first in a cladding tube and then with the cladding tube in a copper tube inserted. The cladding tube expediently consists of one in both the matrix material as well as metal which is largely insoluble in the conductor core material. Suitable materials are e.g. niobium, tantalum, molybdenum or zirconium. When etching the bottleneck areas of the composite conductor, the cladding tube is then selectively etched away in these areas.

Deviating from the described method for producing a tape-shaped With a suitable choice of the hollow profile body 8, single-core composite conductors can also be used another number of copper strips 6 and 7 selected or on these copper strips can be dispensed with entirely. In addition, the copper-silver cladding tape can also be used for the layering 5 can be replaced by a silver band of suitable thickness, provided that a good connection is achieved between the copper and the silver is taken care of.

Is used in the copper-silver clad wire 4 according to FIG Copper pipe 3, which is so thick-walled that the silver content is already that for the end product corresponds to the desired silver to copper ratio, it can be done by flat rolling alone this jacket wire to the desired thickness a single composite conductor tape produce. In general, the band-shaped silver Rern will not get over it extend the entire width of the composite conductor.

Finally, the hollow profile body 8 according to FIG. 4 can also be dispensed with will. As can be seen from the schematic cross section shown in FIG. 8, namely, a silver tape 25 can be unilaterally applied to the flat side of a copper tape Apply 26 of a predetermined thickness. This can e.g. done by roll cladding. The resulting conductor pre-product 27 then becomes a composite conductor deformed to the desired thickness, for example rolled.

In addition to this asymmetrical arrangement of the silver ribbon 25 on the Copper tape 26 can in a corresponding manner also according to the schematic shown in FIG. 9 Cross-section of a conductor pre-product 22 can be created in which a silver ribbon 30 is symmetrical is arranged between two copper strips 31 and 32 of predetermined thickness.

According to the schematic cross section according to FIG. 10, a band-shaped Conductor preliminary product 33 can also be produced by forming a copper strip 34 by profile rolling with liner continuous recess, in which a silver band 35 or a copper-silver jacket tape is inserted. This structure is then followed by another Copper tape 36 covers, the one with the profiled, the silver ribbon 35 containing copper tape can still be welded or soldered. Through the following The desired strip thickness of the composite conductor is achieved by flat rolling. The bottleneck areas can then be generated in the manner described.

Another option for making a composite conductor with a central band-shaped silver core in a copper matrix can use a double roller technique are provided. This technique is used in a simplified manner during manufacture amorphous ribbons are used (see e.g.

"Rev.Sci.Lnstr, PB, Vol. 41, 1970, pages 1237 ff. Or" Z.Metallkde. " Vol. 69, 1978, H.4, pages 212 to 220).

According to the longitudinal section shown in Fig. 11 is for a symmetrical Structure of a conductor pre-product or composite conductor such as that shown in Fig. 9, respectively a jet 40 and 41 of liquid copper from heated crucibles 42 and 43 onto the cold surfaces of two counter-rotating rollers 45 and 46 applied.

Between the copper strips 48 and 49 solidifying on these rollers a jet 51 of liquid silver is injected from a further heated crucible 50. A suitable setting of the process parameters can then achieve that behind the rollers 45 and 46 the finished composite conductor with defined layer thicknesses and predetermined bandwidth exits. An asymmetrical structure like him, for example from Fig. 8, when using only one copper beam 40 or 41 reach.

In order to increase the mechanical stability of the composite fusible conductor, you can use the finished, initially flat strip-shaped fusible link or the yet unetched composite conductor to a shape that increases its mechanical stability to bend. For example, can the fusible conductor has a V-shaped cross-sectional shape are given. The finished fusible conductor can also be made into a tube, for example to bend.

According to a specific exemplary embodiment for the production of a fusible conductor according to the invention according to FIGS. 1 to 7, a Cu-Ag sheathed wire is first produced by inserting an Ag rod with a diameter of 5 mm into a 10 mm × 2.5 mm Cu tube . This structure is then formed into a shell wall with the cross-sectional dimensions 0.5 mm x 14 mm by rolling. This cladding strip and two equally wide Cu strips 0.75 mm thick are annealed at 5000C for one hour and then thoroughly cleaned. 50 cm long pieces of the Cu strips are then inserted together with the jacket strip arranged between them into a Cu hollow profile body, also shortened to 50 cm in length, the outer dimensions of which are 4 mm x 16 mm and inner dimensions 2 mm x 14 mm. This preliminary conductor product is then rolled to a thickness of 0.2 mm, if necessary with intermediate annealing. The thickness of the Ag layer in the composite conductor obtained in this way is then approximately 0.02 mm. Finally, four bottleneck areas with a distance of 10 mm and a length of 2 mm are machined out of the composite conductor cut to a length of 70 mm by etching. Here, the composite material is first covered with photoresist, which is removed in the area of the later constrictions by appropriate exposure and development. During the subsequent etching in iron-111-chloride, the copper is selectively ntPerut at the areas free of the Sotolac, so that only the thin Ag layer remains here.

Claims (21)

Patent claim 1. Fusible conductor for a safety device, in particular for a semiconductor fuse between at least two base metals Ladder pieces each in a narrow area made of a thin conductor element consists of more noble metal, that it is not indicated that this one Fusible conductor (21) a conductor element extending over its entire length (L) (13) made of the more noble metal that is outside the at least one constriction area (23) on at least one side with the at least one less noble metal of the conductor pieces (22) is connected. 2. Fusible conductor according to claim 1, g e k e n n -z e i c h n e t through a band shape (Figs. 5, 8 to 10). 3. Fusible conductor according to claim 2, d a d u r c h g e k e n n z e i c h n e t that the ratio of thickness (D) to width (B) of the cross-section of the Conductor pieces (22) smaller than 1:50, preferably smaller than 1: 100. 4. Fusible conductor according to claim 1, g e k e n n -z e i c h n e t through a tube shape. 5. Fusible conductor according to one of claims 1 to 4, d a d u r c h g e k e n n n z e i c h n e t that the cross-sectional portion of the conductor element (13) between 2% and 40%, preferably between 5% and 20% of the total cross section the conductor pieces (22) is. 6. Fusible conductor according to one of claims 1 to 5, d a d u r c h g It is not possible to say that the nobler metal is silver or a silver alloy is. 7. Fusible conductor according to one of claims ~ 1 to 6, d a d u r c h g It is not noted that the less noble metal is copper or a copper alloy or nickel or a nickel alloy or aluminum or an aluminum alloy is. 8. Fusible conductor according to one of claims 1 to 7, d a d u r c h g e k e n n n e i n e t that the less noble metal (12) of the conductor pieces (22) of a shell (14) made of a non-scaling material is positively surrounded. 9. Fusible conductor according to claim 8, g e k e n n -z e i c h n e t through a sheath (14) made of a copper alloy. 10. Fusible conductor according to one of claims 1 to 9, d a d u r c h it is not noted that the thin conductor element is made of the more noble metal of the conductor pieces each of at least one cladding tube from a diffusion between the more noble and the less noble metal hindering material are surrounded. 11. Fusible conductor according to claim 10, g e k e n n -z e i c h n e t through Cladding tubes made of niobium or tantalum or molybdenum or zirconium. 12. A method for producing a fusible conductor according to one of the Claims 1 to 11, d a d u r c h g e k e n n n z e i c h n e t, that first a conductor pre-product (10; 27; 29; 22) with at least one conductor part (3, 6 to 8; 267 31, 32 34s 36) made of less noble metal and with a ladder part (2; 25; 30; 35) is made of more noble metal that then this conductor precursor to a composite conductor (11) is deformed and that then to the intended at least one bottleneck area (19, 23) of this composite conductor (11) is the less noble Metal is removed. 13. The method according to claim 12, d a d u r c h g e -k e n n z e i c That is to say, before, during or after the deformation step of the preliminary conductor product at least one annealing step is provided. 14. The method according to claim 12 or 13, d a d u r c h g e k e n n indicates that the less noble metal is in the at least one constriction area (19, 23) is removed in an etching step. 15. The method according to claim 14, g e k e n n -z e i c h n e t through a shape etching step. 16. The method according to claim 14, g e k e n n -z e i c h n e t through a physical etching step. 17. The method according to any one of claims 12 to 16, d a d u r c h g e k e n n n n e i n e t that the conductor intermediate product (10; 29S 33) by inserting a band-shaped conductor part (5s 30, 35) made of or with the more noble metal between at least two conductor parts (6 to 8; 31, 32; 35, 36) made of the less noble metal will. 18. The method according to claim 17, d a d u r c h g e k e n n z e i c h n e t that the band-shaped conductor part (35) made of the more noble metal in a corresponding pre-profiled band (34) made of the less noble metal is inserted (Fig. 10). 19. The method according to any one of claims 12 to 16, d a d u r c h & It is noted that the conductor intermediate product 27) by plating a band-shaped conductor part (26) made of the less noble metal with a layer (25) the nobler metal is formed (Fig. 8). 20. The method according to any one of claims 12 to 16, d a d u r c h g It is not noted that the composite conductor (53) is produced by injecting a jet (51) of liquid noble metal between solidifying bands (48, 49) of rays (40, 41) is formed from liquid, less noble metal with simultaneous rolling (Fig. 11). 21. The method according to any one of claims 12 to 20, d a d u r c h g e k e n n n n e i n e t that the finished band-shaped fusible conductor (21) or the corresponding composite conductor (11) before the method step for removing the of less noble metal (12, 14) in the constriction area (19, 23) to one of its mechanical Stability-increasing shape is bent.