EP0841668A1 - Electrical resistor and method of manufacturing the same - Google Patents

Abstract

Electrical measuring or power resistor comprises a laminated structure of a resistance alloy metal foil(2), a substrate(1) with good heat conductivity and an adhesive layer(3) between them of an electrically insulating material, preferably a plastic containing a heat conducting powder. In a process for manufacturing a number of resistors the resistance foil(2) is etched and pressed at elevated temperature with the substrate(1) and an intervening adhesive layer(3) before the entire laminate is cut into individual resistors. In a process for manufacturing resistors with connector contact layers(4) on the outer side of the resistance foil(2) the specific areas at which connector contacts are to be positioned are formed by a lithographic process on the outer side of the resistance foil facing away from the substrate(1) and these areas are then coated with metal. The partially metallised resistance foil(2) is then etched to create the resistance structures. In a process for separating the laminate into individual resistors the substrate(1) is etched through to the adhesive layer(3) along the desired parting lines and then pressure is applied to the side of the laminate facing away from the substrate so that the adhesive layer bridges(52) still remaining are broken through and the resistors separated.

Description

The invention relates to an electrical resistor according to the preamble of claim 1, preferably with on the Arranged side of the resistance film facing away from the substrate Terminal contact surfaces, and method for producing such Resistances.

Low-resistance measuring power resistors of this type, their resistance values are often in the milliohm range, for some applications but also up to orders of magnitude of more than 100 Ohm can be enough, are often required in SMD design, so that they like the well-known chip components with their flat Connection contacts directly on flat connection conductors from PCBs soldered or with their substrate flat on the Surface of a heat sink can be soldered or glued. The resistors can also be used together with power semiconductors and other passive components in so-called power hybrid circuits are used, with the connection contact layers the resistors external leads be attached ("bonding"). A major advantage of this Surface mounting is next to a possible downsizing and better use of space the good heat dissipation from the resistance element. In many cases, it also becomes more and more extensive Miniaturization of measuring or power resistors demands. On the other hand, the burdens of higher and higher Resistors and correspondingly higher operating temperatures required. Add to that the resistances with possible should be easy to manufacture and reusable, since the circuits to be populated are often very cost-sensitive are. These requirements are met by the previously known SMD or chip resistors are not always sufficiently met.

A known from DE-GM 90 15 206 SMD resistor The type mentioned at the beginning has a compact connection contact Pearl made of solder. First of all, to make it a composite body by pressing an aluminum substrate (e.g. made of AlMg3 sheet) with a foil made of a resistance alloy, between which there is an adhesive film. Then the resistance foil is photo-etched into the desired one Form with the required path structures. After this The surface of the resistor foil carrying the resistance foil is etched Composite body in the screen printing process with a layer of Solder mask coated, the later connection contact areas defined and left out, which are then screen printed be printed with a solder paste from which finally through a remelting process the connection contact forming solder pearl is created.

From DE 43 39 551 C1 is also a low-resistance measuring resistor known in SMD design, the connecting contacts not on the side of the resistance film facing away from the substrate located, but formed by the substrate itself will. For the production, a copper sheet is first a polyimide film covered with an adhesive and the resistance film formed a relatively large laminate that the so-called "benefit" forms from which after etching the required Resistance structure, then generating the Resistance foil with copper layers connecting the copper sheet and etching through the copper sheet to separate the connection contacts formed by the substrate, for example about 2000 resistors can be separated.

Proceeding from this, the object of the invention is a suitable as a power resistor for current measurements To create resistance that is even more resilient than before and easy to manufacture and reuse in large quantities is without the required precision and reliability resistance is impaired.

This object is achieved through the features of the claims solved.

The invention enables the production of a large number of Resistors with the properties mentioned above from the prefabricated Triple composite laminate made of resistance film, adhesive layer and substrate with little effort. If it extreme miniaturization is important, for example 8000 resistors from a "benefit" of 300 x 400 mm produce. The resistors can be used as needed SMD components for printed circuit boards or as internal elements used for other types of resistance, e.g. built into housing or attached to thicker copper supports, heat sinks, etc. be etc.

According to a first aspect of the invention is the use a relatively strong resin adhesive filled with ceramic powder preferably in the form of a film as an adhesive layer of the laminate advantageous, both in the manufacture, in particular when separating the resistors, as well as when manufacturing Component. This adhesive layer is mechanical and thermal resilient and so far in the manufacture of resistors used polyimide adhesive films with regard to the derivation of the Superior heat loss of the resistance foil. Those with ceramic powder or other thermally conductive, but electrically insulating granular material are filled plastic adhesive layers known per se, namely for gluing semiconductor components on heat-dissipating housing parts or heat sinks. In which however, they have resistance described here in the known case non-relevant advantages such as brittleness and easy breakability.

Furthermore, it is advantageous if according to another Aspect of the invention which is preferably a good heat conductor Substrate containing metal such as copper or aluminum Separate the laminate from its resistance film etched away from the back along the dividing lines becomes. Then there is only the material of the adhesive layer, because at the separation points before when etching the resistance structures and if necessary the connection contact layers also removed all metal from the other side had been. In particular, the above-mentioned filled adhesive is relatively brittle and can easily separate the resistors be broken through, conveniently in a single operation with a rubber elastic pressed onto the resistance side of the laminate Mat covering the entire surface of the "benefit" covered.

According to another aspect of the invention, essential in particular procedural advantages, that the contact layers are not as before after Etching of the resistance structure, but by partial Pre-metallization of the resistance foil are applied, either on the top or e.g. in previously etched Cutouts in the resistance foil. If the connection contact layers larger to simplify the procedure can be formed as desired later, the resistance and contact structures can be combined in a single Operation can be etched. This advantage also applies to Use of other adhesive layers without ceramic filling. On the other hand there are advantages of using the filled Adhesive even for resistors whose resistance foil does not have pre-metallized contact layers, but only Terminal contact surfaces, which only occur when the resistance is isolated be contacted.

The invention is particularly suitable for extremely small resistors, but also for large components with side lengths of a few cm.

Fig. 1A und 1B

zwei Ausführungsformen des zu erzeugenden Widerstands in schematischer Darstellung;

Fig. 2A bis 2G

schematische Darstellungen zur Erläuterung aufeinanderfolgender bzw. alternativer Verfahrensschritte bei der Herstellung der Widerstände; und

Fig. 3

eine Darstellung zur Erläuterung von Vorteilen der bevorzugten Vereinzelungsmethode bei dem beschriebenen Verfahren.

The invention is explained in more detail in a preferred exemplary embodiment. The drawing shows:

1A and 1B

two embodiments of the resistor to be generated in a schematic representation;

2A to 2G

schematic representations for explaining successive or alternative process steps in the manufacture of the resistors; and

Fig. 3

a representation to explain the advantages of the preferred separation method in the described method.

The resistance shown in Fig. 1A essentially exists from a substrate 1 made of a metal such as copper or Aluminum, the resistance foil 2 made of metal such as one of the CuNi alloys known for precision measuring resistors and an interposed adhesive layer 3 with which the Resistance film 2 is attached to the substrate 1. The Substrate 1 is usually thicker than the resistance film and can serve as a heat sink in addition to the supporting function. The resistance foil is in the usual way for the one you want Structured resistance value, for example in a four-pole version (see FIG. 2B) and / or in the form of a meander track, and has on its surface facing away from the substrate opposite ends each at the edge of the resistor its electrical connection to external circuits separate contact pads. In the illustrated Examples are metallized on these surfaces Terminal contact layers 4, but not always necessary are. The connection contacts can each consist of several Layers consist of different metals, e.g. out a lower layer 5 made of copper, which has a low resistance Creates contact transition, and a layer thereon 6 made of nickel, which makes subsequent external contacting easier, So depending on the application, a soldered connection or that Connect connecting wires.

Important for the production and properties of the described here Resistance is the adhesive layer 3, which is is a flexible plastic film that e.g. a thickness can be on the order of 75 or 100 µm. she should on the one hand in addition to the required electrical insulation firm and permanently reliable adhesion of the resistance foil on the substrate even at high mechanical and thermal Load and on the other hand the best possible thermal conductivity guarantee. For these reasons, layer 3 consists of a plastic adhesive such as Epoxy resin or polyimide material, which is filled with a heat-conducting powder, preferably with ceramic powder, e.g. Alumina, boron nitride or the same as is known per se for other purposes. How has already been mentioned, this will result in the described here Resist the heat dissipation from the resistance film into the Substrate compared to that used to make resistors previously used plastic adhesive layers significantly improved. The degree of filling (e.g. 60-70%, based on the plastic weight) is chosen so that there is good heat conduction (high degree of filling) still sufficient adhesion of the resistance film 2 on the substrate 1 results.

1B shows a modified embodiment of the resistor, whose connection contact layers 4 'in recesses 8th are arranged on the side edges of the resistor into the upper side of the resistance film facing away from the substrate 1 2 'are incorporated, as will be explained in more detail. Here, too, the connection contact layer 4 'can be made from or at Several different metal layers are required. As can be seen from Fig. 1 and also from the following described method results, there are the contact layers 4 completely within the outer circumference of the Resistance layer, which in turn is inside the outer circumference of the substrate.

The resistance element shown schematically can then provide protective layers in the usual way and / or easily in housing or other external Arrangements are installed.

To produce the resistors, the laminate shown in FIG. 2A is first made from a metal sheet forming the substrate 1, which can be, for example, a 0.5 mm thick copper sheet, the adhesive layer 3 and the metallic resistance film 2 in a several thousand resistors resulting size generated. The adhesive is either applied in several layers using the screen printing process, for example to the substrate, or transferred as a prefabricated dry film in a tempered press. The actual bonding of this triple bond is then carried out in a vacuum press at high temperature (for example in the order of 180 ° C) and high pressure (for example in the order of 20 bar = 20 x 10 ⁵ Pa). Vacuum may be necessary to avoid air pockets, which would greatly reduce the adhesive strength and heat dissipation through the adhesive.

To generate the individual resistors are now in one first step in the known from photolithography Way with the help of a photo mask and a photosensitive Laminated film areas defined that the later Contact areas of the resistors includes. As can be seen in Fig. 2B regions 42 are defined which are larger than the later contact areas 23 of the finished resistor, because that is easier than exactly the desired contact layers corresponding photolithographic definition. The resistance structure to be generated later is indicated at 22. A galvanic or chemical metallization carried out, the between the Areas 42 lying during metallization with a part Photoresist or other protective layer can be covered. However, the partial metallization can also take place by that first the entire surface is coated and then that of the Contact areas complementary area is selectively etched (without attacking the underlying resistance metal).

As can also be seen from FIG. 2B, the resistance structure 22 for two separate pads be formed at their opposite ends, as at 23 is indicated. As is well known, this four-pole design can two connection contacts for the power connection and the serve the other two for the voltage connection, as it is for Measurement purposes is required.

Fig. 2C shows a section through Fig. 2B along the plane A-A. The metallization of the areas 42 can be with or according to Fig. 2C several layers are carried out. The bottom, Layer 5 preferably made of copper (see also FIG. 1A) is used to make this area less resistive, while the uppermost layer 6, preferably made of nickel later contacting made easier, as already mentioned.

If the resistance values are extremely low, one must be used accordingly thick resistance foil can be used, which in turn results has that a correspondingly thick copper layer as a contact layer must be deposited to the desired To achieve effect. Especially in these cases the Resistance film in the defined areas 42 before Metallization etched by an amount thinner, approximately corresponds to the later thickness of the copper layer. The has the advantage that the subsequent operations are not through a step from the coated to the uncoated area be hindered. The etched trough-like depressions or recesses are in the (corresponding in Fig. 2C) 2D at 43 recognizable. Again, this can be done in the Recesses 43 introduced copper preferably a thinner Nickel layer 6 are metallized.

Only after the partial precoating described Resistance side of the laminate (the "benefit") becomes the real one Structure of the resistors and the contact areas defined another photolithography process and by etching generated. The etching is advantageously carried out in one Operation, being in the area of the actual resistance only the resistance material and in the contact area the resistance foil etched through with their metallization up to the adhesive layer 3 as shown in Fig. 2E using the example of (to Fig. 2C alternative) embodiment according to Fig. 2D can be seen. The There are etched edges on the edges of the later resistors designated with 44.

Deviating from the method described here, there is Possibility to produce resistors without connection contact layers. In this case, only the desired structure of opposition photolithographically defined and etched. Depending on the application can make the necessary connections later when reusing of the individual, essentially finished resistors will.

After etching the resistance structure and after removing the auxiliary layers required for etching and cleaning of the laminate the resistors are now ready to be separated. If needed, can do a comparison of the resistance values beforehand, ie while still "using" in a known manner e.g. through incisions in the resistance foil be performed.

The resistors could be e.g. in the so far usual way (DE 43 39 551 C1) with a coordinate punch are punched out in order. The ceramic filling of the preferably used in the method described here However, glue can have a highly abrasive effect on the punching tools have, which are therefore constantly reworked must, for example after every less than 1000 work steps, so that not even the resistances of a "benefit" could be separated without reworking the punch. There is also the risk of punching in the edge area the resistances where a material feed occurs during punching, a more or less wide detachment of adhesive takes place, as in 3 is shown at 30 for explanation. The edge area 31, by means of which the adhesive can be detached from the substrate be more than 0.5 mm. This danger arises in particular in the one used here, due to the high degree of ceramic filling relatively brittle adhesive and limits the desired miniaturization of resistance.

One way to avoid this difficulty would be Separating the resistors by cutting, especially with a laser cutting system, which is relatively complex and is slow and also the electrical properties of the Components can affect.

The method described here is less complex and more gentle separation method applied. As in 2F is shown, the metal substrate 1 of its the back of the resistance film 2 facing away in one narrow area etched following the outline of the resistance, so that the continuous up to the adhesive layer 3 Incisions 50 and consequently side surfaces etched on the substrate 1 51 of the component to be produced, similar to the etched side surfaces 44 (FIG. 2E) of the resistance foil 2 and the connection contact surfaces 5 and 6. Since the contour of the Separation lines or incisions 50 photolithographically and etching defined and generated, it can easily be almost arbitrarily complex. It is also particularly advantageous that this also desired other recesses as required or creates holes in the resistor with no extra effort can be.

Because this etching process is still "useful" for all resistors is carried out simultaneously results in a comparison with the individual processing of the individual components correspondingly reduced effort.

After the etching, the resistors hang over the adhesive layer 3 still in "use", that is, in the original large laminate together so that further handling is possible without any problems. On the other hand, since the one explained above with reference to FIG. 2E Structural etching also the resistance metal up to within the Dividing lines had been removed, as can be seen in FIG. 2F, are the resistances after etching the incisions 50 only still connected by the short adhesive layer bridges 52 which can easily be broken due to their brittleness. The Separation is done by a simple press cycle a plate press. On the resistance side is the whole area placed on the "benefit" a silicone mat 54 so that when The press is closed by the material flow of the silicone The adhesive is sheared off or broken over the outer edge, as can be seen at the breaking points 55 in FIG. 2G.

The resistors of the type described here, which are made of foils, are suitable for both SMD assembly and for contacting via bond wires and can be used above all as measuring resistors with resistance values in the milliohm range (typically between 1 and 500 mOhm). They are highly resilient and, due to their extremely low internal thermal resistance (typically less than 1 K / W x cm ² ), can also be considerably overloaded for a short time.

To produce resistors according to the invention with the filled Glue between its resistance film and its substrate methods other than those described above are also suitable. For example, the resistors could be known per se Isolated by cutting the laminate with a laser will. On the other hand, the described method can also Have advantages over comparable known methods, if adhesive films without ceramic powder filling are used.

Claims (18)

Electrical, in particular low-resistance, with a metal foil (2) consisting of a resistance alloy, a highly thermally conductive substrate (1) and an adhesive layer (3) of insulating material located between the resistance foil (2) and the substrate (1) and firmly connecting them to one another, characterized in that the adhesive layer (3) consists of a plastic material filled with powder of thermally conductive insulating material. Resistor according to Claim 1, characterized in that the adhesive layer (3) consists of an epoxy resin or polyimide plastic filled with ceramic powder. Resistor according to claim 1 or 2, characterized in that the degree of filling of the powder is about 60-70%. Resistor according to one of Claims 1 to 3 with connection contact layers (4) arranged on the side of the resistance film (2) facing away from the substrate (1), characterized in that the connection contact layers (4) consist of a galvanically or chemically applied metallization, for example made of copper and / or nickel. Resistor according to one of the preceding claims, characterized in that it contains connection contacts arranged in recesses (43) in the resistance film (2) in its surface facing away from the substrate (1). Resistor according to one of the preceding claims, characterized in that the metallic side faces (44; 51) extending transversely to the layer planes are formed by etching. Method for producing electrical, in particular low-resistance, resistors with a resistance foil (2) which is located entirely within the circumference of a substrate (1) of the individual resistors, a metal foil (2) made of a resistance alloy using a thermally conductive adhesive layer (3) made of insulating material is glued to a substrate (1) consisting of a good heat-conductive material, the resistance film (2) being etched to produce a large number of individual resistance elements, and the laminate consisting of the etched resistance film, the substrate and the adhesive layer located between them into the individual resistors is separated, characterized in that the resistance film (2), the substrate (1) and the layer (3) arranged between them made of a plastic adhesive, which is filled with a powder of thermally conductive insulating material, are heated and pressed together in a press. A method according to claim 7, characterized in that the bonding is carried out by pressing the laminate (1, 2, 3) in a vacuum. A method according to claim 7 or 8, characterized in that the adhesive layer (3) is applied by screen printing or is arranged as a prefabricated dry film between the resistance film (2) and the substrate (1). Method for producing electrical, in particular low-resistance, resistors with a resistance film which is located entirely within the circumference of a substrate (1) of the individual resistors, and with connection contact layers (4) located on the surface of the resistance film (2) facing away from the substrate (1) , wherein a metal foil (2) made of a resistance alloy is glued by means of a thermally conductive adhesive layer (3) made of insulating material onto a substrate (1) consisting of a good thermally conductive material, the resistance foil (2) being etched to produce a large number of individual resistance elements, and wherein the laminate consisting of the etched resistance film, the substrate and the adhesive layer located between them is separated into the individual resistors, characterized in that first on the surface of the resistance film (2) facing away from the substrate (1) at the points at which the connection contact layers are located (4) of the resistances to be produced, limited surface areas (42) containing at least the surfaces (23) of the desired connection contacts are formed by photolithography, and these limited areas (42) are then coated with connection contact metal, and then the partially metallized resistance foil (2) is etched to produce the resistor structures (22). Method according to Claim 10, characterized in that the limited metallized surface areas (42) are initially larger than the desired connection contact areas (23), and in that the desired connection contact layers (4) are produced by etching at the same time as the resistance structures (22) are produced. A method according to claim 10 or 11, characterized in that the connection contact metal is applied by galvanic or chemical metallization. Method according to claim 12, characterized in that two layers (5, 6) made of different metals (eg Cu, Ni) are applied as the connection contact metal. Method according to one of claims 10 to 13, characterized in that for the partial metallization of the resistance foil (2) at the limited surface areas (42), recesses (43) are first formed in the surface of the resistance foil (2) facing away from the substrate (1) and this Recesses (43) are then filled with contact metal (5). A method according to claim 14, characterized in that the recesses (43) are etched in. Method for producing electrical, in particular low-resistance, resistors with a resistance foil (2) which is located entirely within the circumference of the substrate (1) of the individual resistors, a metal foil (2) made of a resistance alloy using a thermally conductive adhesive layer (3) made of insulating material is glued to a substrate (1) consisting of a good heat-conductive metal, the resistance foil (2) being etched to produce a large number of individual resistance elements, and the laminate consisting of the etched resistance foil, the substrate and the adhesive layer located in between in the individual resistors is separated, characterized in that to separate the laminate, the substrate (1) is etched along the dividing lines from the surface facing away from the resistance film (2) to the adhesive layer (3) and then onto the side of the substrate facing away from the substrate (1) Laminate pressure is exerted the remaining adhesive layer bridges (52) are broken and the resistors are separated. Method according to one of claims 7-16, characterized in that a film made of a plastic adhesive which is filled with ceramic powder is used as the adhesive layer (3) to form the laminate. Method according to claim 16 or 17, characterized in that the pressure for separating the resistors in a press is exerted by a rubber-elastic mat (54) covering the entire surface of the laminate (1, 2, 3).

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