EP3087579B1 - Fuse conductor, fuse protection, method for producing fuse protection, smd fuse protection and smd switch - Google Patents

Description

The present invention relates to a fuse, a fuse, a method of manufacturing a fuse, an SMD fuse and an SMD circuit.

For many circuit applications, for example in automotive engineering, measurement and control technology, etc., small, surface-mounted device (SMD) device fuses or fuses are required. For example, the publications describe WO 99/16097 A1 . DE 10 2005 002091 A1 . US 5 900 798 A and US 5,898,357 A Fuses in which a fusible conductor and a support each comprise materials which diffuse upon passage of electrical current through the fusible conductor. For technical reasons and for cost reasons, such device fuses are implemented as usual in printed circuit board technology. SMD fuses, which include fuses, are usually automatically positioned and placed on FR4 boards by pick-and-place machines. Subsequently, the SMD fuses are soldered by means of reflow soldering or wave soldering on the circuit board. As base materials for SMD fuses, for example, FR4 printed circuit board materials or Al ₂ O ₃ ceramics are used, ie all common base materials for printed circuit board production.

Fuses include a fusible conductor disposed on a base support, which comprises, for example, copper. The fusible conductor usually serves to protect overcurrents and thereby protects downstream electronic components.

Fuses have the disadvantage that the base supports usually have limited operating temperatures. For example, the operating temperature of a base carrier made of FR4 base material is only 200 ° C. Higher temperatures damage the FR4 base material. In the process, the material delaminates and dissolves the fusible link, which generally consists of a copper foil, from the base carrier. After a short time decomposition and charring of the material occur. By charring again arise conductive layers with a low electrical resistance in comparison, which then produce impermissibly low insulation resistance.

To counteract this problem, it is known to produce the base support from an Al ₂ O ₃ ceramic, which can endure much higher temperatures than for example 200 ° C without being damaged. However, it has the disadvantage that the Coefficient of Thermal Expansion (CTE) of this Al ₂ O ₃ ceramic is usually less than 8 ppm / K and thus differs greatly from the coefficient of thermal expansion CTE of copper, which is 17 ppm / K , Due to this high difference between the expansion coefficients of the base support made of Al ₂ O ₃ ceramic and copper, mechanical stresses occur between the copper fusible conductor and the ceramic base support. This results in an increased risk of breakage. In addition, ceramic substrates are very brittle in themselves and extract a lot of heat energy from the fusible link. Thus, fuses with low rated currents and nimble characteristics are difficult to realize on this Al ₂ O ₃ ceramic. In addition, these ceramic fuses break often as soon as the fusible conductor is subjected to torsion or bending.

There is a disadvantage in the prior art that thermal fuses can not be soldered on an SMD basis by, for example, reflow soldering. The reason for this is to be found in the fact that the known thermal fuses trigger immediately at the high temperatures occurring in a range of 240 ° C to 265 ° C.

It is an object of the present invention to provide a fuse, a fuse, a method of manufacturing a fuse, an SMD fuse, and an SMD circuit in which the aforementioned problems are solved.

This object is achieved by a fusible conductor according to claim 1.

According to the invention, the fusible conductor comprises two connection contacts and an interconnected conductor track, the conductor track having at least sections a reduced conductor cross-section in relation to the connection contacts, furthermore comprising at least one support, wherein the fusible conductor and the support each comprise materials which, when a predetermined ambient temperature and at Conducting an electric current through the fusible conductor to enter a diffusion.

As a result, a fusible conductor is created in a surprisingly simple manner, which does not trigger in the occurring during soldering high temperatures, but in the Operation at high ambient temperatures, for example, more than 200 ° C will trigger.

This advantage is achieved by a diffusion process which is activated as soon as the ambient temperature exceeds a predetermined temperature, for example 200 ° C., and additionally an electric current (eg rated current) flows through the fusible conductor. This diffusion process takes place in a region in which the at least one support communicates with the fusible conductor (also called the diffusion zone). Under these circumstances, the diffusion process involves diffusing the atoms of the material of the fusible conductor into the material from the overlay. As a result, an alloy of these two materials is formed. Due to the diffusion process, the diffusion zone becomes high-impedance with high power dissipation P = I _n ² xR even at rated current. As a result, in turn, the melting temperature of the diffusion zone of 1080 ° C drops to about 500 ° C. Within this diffusion zone, therefore, the reduced melting temperature of about 500 ° C even at low currents (eg rated current) is reached, whereby the fusible conductor is triggered and advantageously the circuit is reliably interrupted. In addition to the new feature of the fuse to protect against overheating, the fuse retains under original conditions the property continues to act as a fuse to protect against overcurrent. An essential advantage of the inventive fusible conductor is that the fusible conductor in operation at predetermined high ambient temperatures (over-temperature threshold) of, for example, more than 200 ° C triggers, even if no overcurrent flows. The term triggering here means a melting or burning through of the fusible conductor.

The line cross section of the conductor track is reduced at least in sections in a plane perpendicular to the longitudinal direction of the fusible conductor in relation to the line cross section of the connection contacts. This relation has a value less than 1 (<1). For example, the cable cross-sections of the terminal contacts in relation to each other are constant. Thus, a fusible conductor is created which has an H-profile in plan view. Of course, the fusible conductor can also have a different profile, as long as the surfaces of the terminal contacts in relation to the conductor track are possible large. The areas of the terminal contacts may be rectangular, circular, elliptical or triangular. The fusible conductor may be formed by punching out a one-piece material. Alternatively, the fusible conductor can be formed by cutting, for example by means of a laser.

The respective ambient temperature at which the fusible conductor triggers can be predetermined by selecting the relation of the line cross-section of the conductor track to the line cross-section of the connection contacts. By appropriate selection of the aforementioned relation, an overcurrent threshold value can also be defined, from which the fusible conductor will be triggered.

Another significant advantage is that provided with such a fusible fuse SMD-based by, for example, a Reflow soldering process can be connected to the circuit board without the fuse element is triggered at the high temperatures occurring here. Since no current flows in the course of this process (reflow soldering process), these high temperatures cause no change in the fusible conductor. Thus, a fuse provided with this fusible conductor can be easily soldered by a reflow soldering process according to JEDEC standard (240 ° C to 265 ° C, 10s) on the circuit board.

Preferably, the at least one support is at least partially disposed within the conductor track. As a result, it is reliably ensured that in the case of a tripping of the fusible conductor, ie during melting or burning through of the conductor track of the fusible conductor, no current will flow between the connection contacts. By appropriate selection of the respective extension of the support provided to the fusible conductor (eg length, width and thickness in relation to the fusible conductor), tripping characteristics of the conductor track of the fusible conductor can be determined. According to the invention, the at least one support within the conductor track is arranged adjacent to one of the connection contacts of the fusible conductor. As a result, the diffusion zone can be placed particularly close to an adjacent electronic component (eg power transistor) to be protected with regard to overcurrent and excess temperature. It may be provided a support adjacent to a terminal contact or it may be two Pads may be provided adjacent to the two terminal contacts. Fuses are increasingly needed for the protection of power transistors on printed circuit boards for use in high-energy equipment, such as automotive, heating and ventilation technology, renewable energy, etc. High-energy applications are optimally regulated today, for example, to reduce energy consumption. In this case, the power transistors often operate in pulsed mode. In fault-free operation, the maximum thermal load of the power transistors in pulsed operation is not exceeded. If, on the other hand, the power transistors are driven with a constant signal in the event of a fault or the power transistor is damaged, high temperatures of, for example, more than 200 ° C. occur in the power transistor. This creates a fire hazard. However, this danger is prevented by the fusible conductor according to the invention, which triggers immediately when it exceeds a predetermined high temperature. This advantageous effect is further increased by the fuse is mounted in the immediate vicinity of the power transistor. By arranging the diffusion zone, ie the support, in a region of the conductor adjacent to one of the terminal contacts of the fusible conductor, ie by providing the diffusion zone near the contacts of the fusible conductor and thus as close as possible to the power transistor, the reliability of the fusing of the fusible conductor can be further increased become.

A further advantage of this arrangement is that a base support underlying the fusible conductor has a reduced heat dissipation capability at the edge region, ie adjacent to one of the terminal contacts of the fusible conductor, than, for example, in the middle region. By thus placing the diffusion zone in as far as possible an off-center region of the base support, ie in a region adjacent to one of the contacts of the fusible conductor, the exceeding of a predetermined ambient temperature, for example 200 ° C., is detected more quickly and reliably and thus immediately triggers lead the fusible conductor. This effect is supported by, viewed in plan view of the fusible conductor, the surface of a respective terminal contact in relation to the conductor track is formed as large as possible. As a result, the connection contacts in relation to the conductor track on better properties for heat dissipation. When viewed in the longitudinal direction of the fusible conductor, the highest temperature values will thus advantageously occur in the middle of the conductor track. By selecting the relation between the respective width of the terminal contacts and the width of the conductor track, viewed in the longitudinal direction of the fusible conductor, one of several design parameters is given, by which a triggering of the fusible conductor can be predetermined at over-temperature and / or overcurrent. Another design parameter is given by the choice of one or two editions.

Preferably, the conductor cross-section of the conductor path progressively increases over the line cross-section of the connection contacts. The conductor cross section of the conductor can increase linear or non-linear. In this embodiment, the conductor cross-section of the conductor increases gradually at each of the two ends of the conductor track with a minimum line cross-section and grows to a maximum line cross-section, which is equal to the line cross-section of the connection contacts. The cable cross-section of the connection contacts can be constant starting from this section. In this embodiment, the fusible conductor assumes a bone shape that appears in plan view.

Preferably, the at least one support is arranged at least in sections within the conductor track in a region of the stepwise increasing line cross section. This provides a further design parameter by which it is possible to set from which temperature and / or from which current value the fusible conductor is to be triggered.

The at least one support is preferably arranged in a region of the conductor track with a gradually increasing conductor cross-section adjacent to a section of the conductor track with a minimum conductor cross-section. As a result, the fusible conductor triggers reliably at over-temperature and / or overcurrent.

Preferably, the fusible conductor further comprises at least one introduced into the conductor track recess in which the at least one support is arranged. This is the diffusion zone is diluted as a whole, so that a diffusion of the atoms of the material of the fusible conductor into the material of the support which is necessary or sufficient for triggering the fusible conductor takes place more rapidly. With decreasing material thickness of the conductor track of the fusible conductor in the region of the recess, resp. as the depth of the recess increases, the temperature threshold for triggering the fusible conductor decreases. Also, the current threshold drops to trip on overcurrent. Thus, the extent of the recess is an important design parameter by which the temperature threshold and the current threshold are set.

Preferably, the at least one recess is aligned transversely to the longitudinal direction of the conductor track. The fusible conductor is usually formed as an elongate, thin strip body. The recess is introduced on the surface and perpendicular to the current direction in the material of the conductor track. In the case of tripping of the fusible conductor, the current flow can thus be completely interrupted. The recess is introduced, for example, by means of photolithography, a laser, etc. in the conductor track. This recess is then filled with the material of the support, for example by means of a galvanic process. The recess can be partially or completely filled. The recess can also be filled over the edge of the recess away with the material of the pad. It may be one or more recesses may be provided, which are each filled with a support.

Preferably, the material of the fusible conductor comprises copper and the material comprises the support tin. Conventional fused conductors for overcurrent protection are usually formed of copper. With the selection of tin as the material of the overlay an excellent material is found which undergoes diffusion with the copper as the material of the fusible conductor in case of excess temperature and current flow through the fusible conductor. In the case of the diffusion process, the copper atoms diffuse into the tin and thus a copper-tin alloy is formed. In normal operation, for example, when passing a nominal current through the fusible conductor at ambient temperatures of 125 ° C for an extended period of time, this load on the fusible conductor does not cause any change.

The above object is also achieved by a fuse comprising a fuse element according to any one of claims 1 to 8 and further comprising a base support made of an electrically insulating material, wherein the fuse element is disposed on a surface of the base support. As a base support, for example, a FR4 base material or an Al ₂ O ₃ ceramic can be used. An advantage of this fuse is that it reliably protects not only against overcurrent but also against overtemperature. In contrast to known thermal fuses, however, the fuse according to the invention does not trigger during soldering, for example by means of a reflow soldering process. Conventional thermal fuses would trigger immediately at the necessary high temperatures of for example 240 ° C - 265 ° C, so far so expensive Countermeasures are taken, such as the provision of wire terminations. Due to the particular advantage of the fuse according to the invention, an automatic assembly is possible and is also the cost of this greatly reduced in contrast to the prior art, since, for example, can be dispensed with the provision of wire terminations. In addition, the inventive fuse is cheaper and much smaller than previously known thermal fuses. The fuse also complies with all known approvals (IEC 60127 and UL248-14 standard). In addition, the fuse is resistant to strong current pulses.

Preferably, the fusible conductors are disposed on opposite surfaces of the base support. As a result, a fuse based on a multilayer construction with two fuse elements can be provided in parallel. For example, the diffusion zones of the individual fusible conductors can be arranged in mutually offset positions in relation to the longitudinal direction. This ensures a more reliable triggering of the fuse in the event of overheating.

Preferably, the fuse further comprises two base contacts, which are electrically connected to each of the base support opposite terminal contacts of the fuse element. Thus, a fuse is provided in a simple manner, which comprises parallel connected fuse element. These base contacts may also be formed of copper.

Preferably, the base carrier comprises a Rogers 4000 material. Conventional fuses are usually composed of base carriers, which comprise, for example, FR4 base materials, or circuit board materials, or Al ₂ O ₃ ceramics. The FR4 base material is made of glass fabric reinforced with epoxy resin. This material has good coefficients of expansion in the x and y directions. These coefficients of expansion are in the range of 14 to 17 ppm / K and come very close to the coefficient of expansion of copper as the material of the fusible conductor at 17 ppm / K. Copper foils having various thicknesses, for example 6, 9, 12, 18, 35, 70, 120 and 240 μm, are pressed on the FR4 base material under pressure and temperature and form the basis for the fusible conductor. However, the limited operating temperatures of the FR4 base materials, which have a max. 200 ° C. Even higher temperatures damage the FR4 base material. In the process, the FR4 base material delaminates and a copper foil provided, for example, as a fusible conductor separates from the FR4 base material. This is followed by decomposition and charring of the FR4 base material. The charring causes conductive, relatively low-resistance layers, which thus produce impermissibly low insulation resistances.

As described above, it is also known to provide an Al ₂ O ₃ ceramic as a material of the base support. This ceramic withstands higher temperatures than the FR4 base material. However, the expansion coefficient of this ceramic is less than 8 ppm / K very low, so that mechanical stresses (risk of breakage) between the melt conductor of copper and the ceramic arise. In addition, ceramic substrates are very brittle and extract much heat energy from the fusible link. A fuse with low rated currents and nimble characteristic is thus difficult to realize based on Al ₂ O ₃ ceramic as the material of the base carrier. In addition, such a fuse easily breaks upon stress of the fusible conductor on torsion or bending.

By using Rogers4000 material as the material of the base support, as proposed, all advantages of the Al ₂ O ₃ ceramic and the FR4 base material are advantageously combined. The Rogers4000 material is therefore excellently suited as the material of the base carrier of the fuse. This applies to all types and sizes of the basic carrier. The Rogers4000 material is also compatible with all board processes and is durable even at temperatures up to 300 ° C.

The at least one fusible conductor is preferably coated with a protective lacquer, in particular a polymer protective lacquer. As a result, the fusible conductor is reliably protected against environmental influences.

The above-mentioned object is likewise achieved by a method for producing a fuse, wherein the method comprises the steps of providing at least one fuse conductor comprising two connection contacts and an interconnected conductor track, such that the conductor track reduces at least in sections one in relation to the connection contacts Line cross-section has; Providing a base carrier; Providing the fusible conductor with at least one support, the fusible conductor and the support each being selected from materials which diffuse when a predetermined ambient temperature is exceeded and an electric current is passed through the fusible conductor; and arranging the at least one fusible conductor on the base support. By the method according to the invention a fuse is produced, which triggers quickly and reliably at excess temperature. In addition, this fuse can be produced inexpensively by only a few steps.

By respective selection of the relation between the conductor cross section of the conductor track and the line cross section of the connection contacts, the ambient temperature (overtemperature threshold value) at which the fusible conductor is to be triggered is predetermined. This selection of the relation can also be used to define an overcurrent threshold at which the fusible conductor will be triggered. The line cross section of the conductor track is reduced in a plane perpendicular to the longitudinal direction of the fusible conductor in relation to the line cross section of the connection contacts. Thus, a fusible conductor is provided which has an H-profile in plan view. Alternatively, the line cross-section of the fusible conductor can increase linearly or non-linearly to the line cross-section of the connection contacts. Thus, a fusible conductor is created, which corresponds to a bone profile in plan view. The fusible conductor is in Trap of overtemperature and / or overcurrent always in the section with reduced line cross-section, ie in the course of the conductor, trigger. The fusible conductor is formed, for example, by punching a one-piece material. Alternatively, the fusible conductor is formed by cutting, for example by means of laser. The at least one support is preferably arranged at least in sections within the conductor track of the fusible conductor. When the fuse element is triggered, ie when the printed conductor melts or burns through, the current flow between the connecting contacts is thus reliably interrupted. According to the invention, the at least one support within the conductor track is arranged adjacent to one of the connection contacts of the fusible conductor. By arranging the support in a region adjacent to one of the terminal contacts of the fusible conductor, the diffusion zone can thus be arranged in close proximity to an electronic component to be protected, for example a power transistor. By the closest possible proximity to this electronic component, the reliability can be further increased, with which the fusible conductor is triggered quickly and reliably when a predetermined temperature is exceeded.

Preferably, the step of providing the fusible conductor with the at least one support comprises arranging the support in at least one recess introduced in the conductor track. Depending on the size of the recess (length, width and geometry in Longitudinal direction of the fusible conductor considered) and the depth of the recess, a temperature threshold can be determined or defined, beyond which the fuse is triggered. Thus, tripping characteristics of the fuse conductor can be easily determined.

The aforementioned object is also achieved by an SMD fuse, which comprises a fuse according to one of claims 9 to 13. This makes it possible to assemble an SMD printed circuit board with an SMD fuse as a thermocouple.

The aforementioned object is also achieved by an SMD circuit comprising an SMD fuse according to claim 17. As a result, an SMD circuit is provided which comprises at least one SMD fuse for thermal monitoring of individual electronic components.

• Figur 1 eine Schmelzsicherung gemäss der Erfindung in Perspektivdarstellung;
• Figur 2 die in Figur 1 gezeigte Schmelzsicherung gemäss der Erfindung in einer Schnittansicht;
• Figur 3 einen Schmelzleiter gemäss einer ersten Ausführungsform der Erfindung in Perspektivdarstellung;
• Figur 4 den in Figur 3 gezeigten Schmelzleiter gemäss der ersten Ausführungsform der Erfindung in einer Schnittansicht;
• Figur 5 einen Schmelzleiter gemäss einer zweiten Ausführungsform der Erfindung in Perspektivdarstellung; und
• Figur 6 den in Figur 5 gezeigten Schmelzleiter gemäss der zweiten Ausführungsform der Erfindung in einer Schnittansicht.

Embodiments of the present invention will be explained in more detail below with reference to figures. Show it:

• FIG. 1 a fuse according to the invention in perspective view;
• FIG. 2 in the FIG. 1 shown fuse according to the invention in a sectional view;
• FIG. 3 a fuse element according to a first embodiment of the invention in perspective view;
• FIG. 4 the in FIG. 3 shown fuse element according to the first embodiment of the invention in a sectional view;
• FIG. 5 a fuse element according to a second embodiment of the invention in perspective view; and
• FIG. 6 the in FIG. 5 shown fuse according to the second embodiment of the invention in a sectional view.

Referring to Figures 1 and 2 For example, a fuse 10 according to the invention comprises two fuse elements 12 ', 12 ", which are each arranged on opposite surfaces of a base support 14 viewed in the longitudinal direction of the fuse 10. The base support 14 is made of an electrically insulating material, which is also at high temperatures, for example up to to 300 ° C. It is particularly preferred to use Rogers 4000 material as the material of the base support 14. The fusible conductors 12 ', 12 "lying on the base support 14 are each provided on their outer surface facing surface with a support 16', 16" The supports 16 ', 16 "each extend in a region of the fuse elements 12', 12", which extends transversely to the current direction.

Respective ends of the opposite fusible conductors 12 ', 12 ", also referred to as connection contacts, which are viewed in the longitudinal direction of the fuse 10 on a plane, are electrically connected to each other via base contacts 18', 18". These base contacts The fuse elements 12 ', 12 "and the base contacts 18', 18" are formed, for example, from copper Current exceeds a predetermined or defined current value (current threshold), in the usual way, one of the fusible conductor 12 ', 12 "melt or burn. Because of the thus reduced line cross-section, the further fusible conductor will then likewise melt or burn out directly. The current path is thus interrupted.

In addition to this protection against overcurrent, the fuse 10 also provides protection against overheating. In this case, if the ambient temperature exceeds a predetermined temperature threshold value, for example 200 ° C., and an additional electric current flows through the fusible conductors 12 ', 12 ", a diffusion process is activated according to the invention, in which the atoms of the material of the fusible conductor (copper) diffuse into the material of the support 16 ', 16 ", for which purpose the material of the support 16', 16" made of tin is chosen as the diffusion partner. In this example, a copper-tin alloy is formed by diffusing the copper atoms into the tin overlay. As explained in more detail below, the support 16 ', 16 "in order to enhance the diffusion process in a in the material of the fusible conductor 12', 12" introduced recess 20 ', 20 "filled.

As soon as the ambient temperature reaches or exceeds the predetermined temperature threshold, the copper layer diffuses completely into the tin layer. Even at rated current, a high-impedance diffusion zone with high power dissipation P = I _n ² xR is produced. In this case, the melting temperature of the diffusion zone drops from, for example, 1080 ° C. to about 500 ° C. The diffusion zone is designed by appropriate choice of design parameters, such as size, choice of material, etc., such that the reduced melting temperature of about 500 ° C even at relatively low currents is achieved and the circuit thus reliably by triggering or Thus, the fuse 10 will trip even at predetermined ambient temperatures (overtemperature), for example, more than 200 ° C., when no overcurrent flows, the operation and advantage of the fuse 10 will be explained below after closer inspection of the fusible link.

FIGS. 3 and 4 show in detail a fuse element 12_1 according to a first embodiment of the invention in each case in a perspective view and in a sectional view. The fusible conductor 12_1 is assembled in one piece from two connection contacts 24_1 ', 24_1 "and a conductor track 26_1 arranged between the connection contacts 24_1', 24_1", wherein the conductor track 26_1 has a continuously reduced conductor cross-section in relation to the connection contacts 24_1 ', 24_1 " the conductor 26_1 is over the total extension of the conductor 26_1 away constant. In addition, the connection contacts 24_1 ', 24_1 "in relation to the conductor track 26_1 have a very large surface area. <br/><br/> This embodiment makes possible a significantly higher heat dissipation in the area of the connection contacts 24_1', 24_1" than in the area of the conductor track 26_1 itself. Viewed in the longitudinal direction of the fusible conductor 12_1, the temperature is highest approximately in the middle of the conductor track 26_1 and decreases in the direction of both connection contacts 24_1 ', 24_1 ".

When viewed in plan view, the outer shape of the fusible conductor 12_1 assumes an H-profile. The connection contacts 24_1 ', 24_1 "are of rectangular design, wherein the connection contacts 24_1', 24_1" can also take on other forms, as long as the total considered in a plane perpendicular to the longitudinal direction of the fuse conductor, the conductor cross section of the conductor 26_1 in relation to the line cross section of the connection contacts By way of example, the fusible conductor 12_1 is formed by punching out a one-piece material (eg copper) Alternatively, the fusible conductor 12 may be formed by cutting, for example by means of a laser.

The support 16_1 is filled in the recess 20_1, which is introduced in the material of the conductor track 26_1. Although in FIGS. 3 and 4 not shown, can be provided at both end portions of the conductor track 26_1, at the transitions to the terminal contacts 24_1 ', 24_1 ", recesses each with filled-in. By reduced in the region of the recess 20_1 Conductor cross section of the trace 26_1 is one of the design parameters for setting the temperature threshold value. With decreasing line cross section of the conductor 26_1 (copper), the temperature threshold is increasingly reduced. Thus, the geometric shape of the recess 20_1 as a whole allows a possibility for setting or defining the temperature threshold value. As soon as the outside temperature exceeds this temperature threshold, this results in a melting or burning through of the fusible conductor 12_1 in the region of the conductor track 26_1. As a further design parameter for setting or defining the temperature threshold value, the amount of material of the support 16_1, ie the amount of tin used. Another design parameter for setting or defining the temperature threshold is shown by the choice of material composition of the two diffusion partners. In addition to the diffusion partners copper and tin presented here, other suitable diffusion partners can also be selected.

To protect the fusible conductor 12_1 against damaging external influences, this can be coated with a protective lacquer 22_1, for example a polymer protective lacquer (see FIG. 4 ).

FIGS. 5 and 6 show in detail a fuse element 12_2 according to a second embodiment of the invention in each case in a perspective view and in a sectional view. The fusible conductor 12_2 is made in one piece from two connection contacts 24_2 ', 24_2 "and a conductor track arranged between the connection contacts 24_2', 24_2" 26_2 composed equal to the one in FIGS. 4 and 5 shown construction of the fusible conductor 12_1 of the first embodiment.

The fusible conductor 12_2 according to the second embodiment differs from the fusible conductor 12_1 according to the first embodiment in that the conductor cross-section of the conductor track 26_2 approaches the larger conductor cross-section of the connection contacts 24_2 ', 24_2 "at both end sections in a stepped manner Line cross section of the conductor 26_2 not over the entire extent of the conductor 26_2 away constant.

As in FIG. 5 to recognize the line cross-section increases linearly. The conductor track 26_2 thus comprises, viewed in plan view, at each of its two ends portions of the shape of an isosceles trapezoid. When viewed in plan view, the outer shape of the fusible conductor 12_2 thus assumes a bone-shaped profile. Alternatively, the line cross section of the conductor track 26_2 can also increase non-linearly, whereby the end sections of the conductor track 26_2, viewed in plan view, are given a different geometric shape from the isosceles trapezoid.

The connection contacts 24_2 ', 24_2 "are further rectangular in plan view, wherein they can also assume other geometric shapes, as long as the total conductor cross-section of the conductor 26_2 decreases in relation to the line cross-section of the terminals 24_2', 24_2" to the center of the fusible conductor 12_2 extending ,

Unlike the in FIGS. 3 and 4 According to the second embodiment, the fusible conductor 12_2 comprises two recesses 20_2 ', 20_2 "which are introduced in the material of the conductor track 26_2. The recesses 20_2', 20_2" are respectively arranged in those regions of the conductor track 26_2 in which the conductor cross-section is like previously described increases. In other words, the recesses 20_2 ', 20_2 ", as viewed in plan view, are respectively disposed on the blunt tips of the trapezoidal end portions of the track 26_2.

In the recesses 20_2 ', 20_2 "pads 16_2', 16_2" are filled. By thus in the region of the recesses 20_2 ', 20_2 "reduced line cross section of the conductor track 26_2 and additionally by the respective trapezoidal geometry of the end portions of the conductor track 26_2 in plan view, is one of a variety of design parameters for setting or defining the temperature By selecting the geometric shape of the recesses 20_2 ', 20_2 ", an overall possibility for setting or defining the temperature threshold value is given. To protect against damaging external influences, the fusible conductor 12_2 is coated with a protective lacquer 22_2.

In the Figures 1 and 2 shown fuse 10 may be single-sided or double-sided with one or more fuse elements 12_1 of the first embodiment (see FIGS. 3 and 4 ) or one or more fusible conductors 12_2 of the second embodiment (see FIGS. 5 and 6 ). There are also combinations possible.

Overall, therefore, a reliable fuse 10 for thermal and electrical monitoring of, for example, sibling power transistors is created. One advantage is that the fuse 10 despite thermal fuse feature is suitable to be soldered by a direct reflow soldering on the circuit board without triggering. Since, in the course of this reflow soldering process, no current flows through the fusible conductor 12, the high temperatures which occur in this process do not trigger the fusible conductor 12 either. Only in the operating state, i. when passing a current, such as rated current, the fuse element 12 triggers even at excess temperatures, which may be lower than the temperatures occurring during the reflow soldering process.

Thus, a hitherto unprecedented SMD fuse is created, which can be automatically populated and soldered on SMD basis. Due to the small form factor of the SMD fuse, it can advantageously be placed very close to a highly heat-generating electrical component, for example a power transistor. As soon as this component assumes a temperature which exceeds a predetermined temperature threshold, eg caused by a defect of the component itself or a defect in the circuit, the SMD fuse triggers rapidly, whereby the current flow is reliably interrupted at this defective component.

The fuse 10 has a smallest possible form factor (for example, 0201, 0402, 0603, 1206, 1812, 2010, 2512, 4018, etc.). In addition, the fuse 10 has a high pulse load capacity, since the fusible conductor 12 is fixed on the base support 14.

A multilayer construction with one or more fusible conductors 12; In order to protect against environmental influences, the fusible conductor 12, 12 ', 12 "is completely covered by a protective lacquer 22; 22 ', 22 "By appropriate selection of the above mentioned design parameters, it is possible to use them in maximum ambient temperatures of up to 280 ° C. Also, currents in the range of a few mA to several hundred A can be protected Advantageously, the fuse 10 can be placed particularly close to highly heat-generating electrical components, such as power transistors, thereby permitting good thermal coupling, which immediately detects elevated temperatures, for example an elevated temperature of the power transistor caused by a malfunction of the power transistor As the fuse 10 triggers immediately when the defined excess temperature is exceeded, the risk of a fire development is thus eliminated In comparison with conventionally known thermal fuses, the fuse 10 offers a considerable overall improvement in terms of reliability, cost, size, weight, processing, pulse resistance, vibration resistance, response, etc.

It is a fuse 10 created that previously known properties of fuses in terms of current-time behavior, temperature behavior, pulse resistance, breaking capacity, insulation resistance, i2t values, material and manufacturing costs improved and expanded.

Claims (18)

1. A fuse element (12_1; 12_2), comprising two connecting contacts (24_1', 24_1"; 24_2', 24_2") and an interposed conductive track (26_1; 26_2), wherein the conductive track (26_1; 26_2) has a reduced line cross-section in relation to the connecting contacts (24_1', 24_1"; 24_2', 24_2") at least in some sections, further comprising at least one overlay (16_1; 16_2', 16_2"), wherein the fuse element (12_1; 12_2) and the overlay (16_1; 16_2', 16_2") each comprise materials which undergo diffusion when a predetermined ambient temperature is exceeded and when an electric current is conducted by the fuse element (12_1; 12_2), wherein the at least one overlay (16_1) is arranged within the conductive track (26_1) adjacent to one of the connecting contacts (24_1', 24_1") of the fuse element (12_1).
2. The fuse element (12_1; 12_2) according to claim 1, wherein the at least one overlay (16_1; 16_2', 16_2") is arranged at least in sections within the conductive track (26_1; 26_2).
3. The fuse element (12_2) according to claim 1 or 2, wherein the line cross-section of the conductive track (26_2) increasingly converges step-by-step to the line cross-section of the connecting contacts (24_2', 24_2").
4. The fuse element (12_2) according to claim 3, wherein the at least one overlay (16_2', 16_2") is arranged at least in sections within the conductive track (26_2) in a region of the gradually increasing line cross-section.
5. The fuse element (12_2) according to claim 3 or 4, wherein the at least one overlay (16_2', 16_2") is arranged in a region of the conductive track (26_2) with a gradually increasing line cross-section adjacent to a section of the conductive track (26_2) with minimal line cross-section.
6. The fuse element (12_1; 12_2) according to one of the preceding claims, further comprising at least one recess (20_1; 20_2', 20_2") which is introduced into the conductive track (26_1; 26_2) and in which the at least one overlay (16_1; 16_2', 16_2") is arranged.
7. The fuse element (12_1; 12_2) according to claim 6, wherein the at least one recess (20_1; 20_2', 20_2") is oriented in a continuously transverse manner in relation to the longitudinal direction of the conductive track (26_1; 26_2).
8. The fuse element (12_1; 12_2) according to one of the preceding claims, wherein the material of the fuse element (12_1; 12_2) comprises copper and the material of the overlay (16_1; 16_2', 16_2") comprises tin.
9. A fuse (10), comprising at least one fuse element (12; 12', 12") according to one of the preceding claims and further comprising a base support (14) made of an electrically insulating material, wherein the fuse element (12; 12', 12") is arranged on a surface of the base support (14).
10. The fuse (10) according to claim 9, wherein the fuse element (12', 12") is arranged on opposite surfaces of the base support (14).
11. The fuse (10) according to claim 9 or 10, further comprising two base contacts (18', 18") which are each electrically connected to connecting contacts of the fuse elements (12', 12") which are opposite the base support (14).
12. The fuse (10) according to one of the claims 9 to 11, wherein the at least one fuse element (12; 12', 12") is coated with a protective lacquer (22; 22', 22").
13. The fuse (10) according to claim 12, wherein the protective lacquer (22; 22', 22") comprises a polymer protective lacquer.
14. A method for producing a fuse (10) according to one of the claims 9 to 13, comprising the steps of:

    providing at least one fuse element (12; 12', 12") having two connecting contacts (24', 24") and an interposed conductive track (26), such that the conductive track (26) has a reduced line cross-section in relation to the connecting contacts (24', 24") at least in some sections;

    providing a base support (14);

    providing the fuse element (12; 12', 12") with at least one overlay (16; 16', 16") which is arranged within the conductive track (26) adjacent to one of the connecting contacts (24', 24") of the fuse element (12; 12', 12"), wherein the fuse element (12; 12', 12") and the overlay (16; 16', 16") are each selected from materials which undergo diffusion when a predetermined ambient temperature is exceeded and when an electric current is conducted by the fuse element (12; 12', 12"); and

    arranging the at least one fuse element (12; 12', 12") on the base support (14).
15. The method according to claim 14, wherein the at least one overlay (16; 16', 16") is arranged at least in sections within the conductive track (26) of the fuse element (12; 12', 12").
16. The method according to claim 14 or 15, wherein the step of providing the fuse element (12; 12', 12") with the at least one overlay (16; 16', 16") comprises arranging the overlay (16; 16', 16") in at least one recess (20; 20', 20") introduced into the conductive track (26).
17. An SMD fuse, comprising a fuse (10) according to one of the claims 9 to 13.
18. An SMD circuit, comprising an SMD fuse according to claim 17.

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