EP1283528B1 - Low impedance electrical resistor and method of making it - Google Patents

Abstract

Low impedance electrical resistor comprises a flat rectangular metal element (1') made of a resistor alloy, and connecting contacts (4', 4'') galvanized on opposite ends of the main surface of the metal element. The end faces of the metal element and the connecting contacts on these ends and the side surface (8) of the metal element perpendicular to the end faces and the connecting contacts are aligned with each other perpendicular to the plane of the main surface of the metal element. An Independent claim is also included for a process for producing the above low impedance electrical resistor using photolithographic production of a covering mask formed by parallel strips, galvanization of a layer only on the surface supporting the covering mask, and separation of the galvanized layer. Preferred Features: The metal element is a foil fixed on a substrate with its side facing away from the connecting contacts.

Description

The invention relates to a low-resistance electrical resistor and a method for its production according to the preamble of the independent claims. In particular acts low-resistance precision resistors for current measurement purposes in SMD or chip design.

In a method for manufacturing known from EP 0841668 A1 of SMD measuring resistors with resistance values in the milliohm range is first a laminate from a as a substrate serving copper sheet, a foil made of a resistance alloy based on Cu and a thermally conductive between them Adhesive film formed. On the free top of the alloy foil then become contact areas for the individual Resistors defined photolithographically, galvanically copper-plated and coated with nickel. After the galvanic metallization will the actual structure of the resistors and their connection contacts generated by etching. The resistance structure can have the usual four-pole and / or meandering shape. The separation of the resistors can be done with a laser cutting machine or preferably by breaking the adhesive film after double-sided Etching through the metal layers along the intended Separation lines are made. This known method is relative consuming. Above all, however, it is hardly possible thanks to this necessary etching resistors with precisely defined resistance values to create. It is particularly difficult to apply the alloy foil galvanized connection contacts by etching structure without the underlying alloy metal attack, with the precision also by the for the etching Typical undefined shape of the end faces of the connection contacts is affected, which is not exactly perpendicular to Surface, but more or less concave down to the alloy surface run.

In another method known from EP 0484756 B1 Connection contacts are used to manufacture SMD measuring resistors a bonded to a substrate, structured in the usual way Resistance foil if necessary after galvanic pre-tinning the connection areas as a paste using the screen printing process applied to the film and then melted into compact "beads". The desired precise resistance value can also be found here can only be achieved by subsequent adjustment. The In practice, these resistors are separated by stamping, as is also the case with comparable other known components is common.

The invention has for its object a method for Specify the manufacture of precision resistors of the type under consideration, that is easier than comparable known methods and in particular the formation of the connection contacts without etching allows.

This object is achieved by the specified in claim 6 Procedure solved.

The invention also provides a low-resistance resistor with the features of claim 1 provided.

Particular embodiments of the invention are defined in the dependent claims.

According to the invention, precision resistances can be done with a few simple operations be made in the milliohm range that with resistance tolerances of max. ± 5% no subsequent Require adjustment. Neither the connection contacts nor the Alloy areas have to be etched, with the disadvantages the etching structuring, namely the Formation of leaking, non-vertical etching flanks leading to large fluctuations in the resistance value and poor reproducibility to lead.

The fact that according to the invention is more photolithographic has an advantageous effect Definition of the deposition areas the comparative thick copper contact layers very precisely galvanically can be deposited, in particular the to Main surface of the sheet or one of the resistance layers Slide vertical training and the position of the active Flanks facing resistance are important.

The second requirement for the production according to the invention is more precise Resistance is the creation of a defined width. This is preferably done by sawing the galvanized resistance layer reached.

Sawing results in much higher accuracy and reproducibility of the resistances than with other separation methods such as etching, stamping and z. B. also in itself possible use of lasers. In addition, by sawing is the number that can be produced for a given usable area Resistances are maximized.

The process is suitable for for the production of extremely low-resistance Resistors in the range of about 0.5, for example Large quantities of mΩ to 5 mΩ, but resistors can also be used with even lower or higher resistance values be, e.g. B. 0.01-50 mΩ. With a modified design with particularly thin resistance foils, the resistance value can also be easily raised, e.g. up to 100 mΩ. The resistors are also flexible and can be almost any size depending on the desired load capacity or be made small. Since the manufactured according to the invention Resistance consists essentially only of metal and the organic used in the known methods mentioned Adhesive layer either completely eliminated or, if available, does not have to dissipate heat, it has the advantage of high temperature resistance and high resilience. In the for this resistance typical applications, it is sufficient to use the heat loss derived via the connection contacts, for example in a Circuit board, on the surface of which the resistors according the SMD technology.

Fig. 1

die verschiedenen Schritte oder Stufen des Verfahrens;

Fig. 2

eine schematische schrägbildliche Darstellung eines erfindungsgemäß hergestellten Widerstands, und

Fig. 3

eine modifizierte Bauform des Widerstands.

The invention is explained in more detail using the exemplary embodiments illustrated in the drawing. Show it

Fig. 1

the different steps or stages of the procedure;

Fig. 2

is a schematic oblique representation of a resistor produced according to the invention, and

Fig. 3

a modified design of the resistor.

According to FIG. 1A), a bare is in the first step rectangular sheet 1 made of a metallic resistance alloy covered with a photoresist layer 2, which in the Photolithography usual way through a photomask (not shown) can be exposed. The sheet 1 can be practical Cases a usable area of z. B. have about 300 x 400 mm and be between 0.1 and 1 mm thick. It preferably exists made of one of the proven Cu-based resistance alloys such as z. B. CuMn12Ni or the like.

In the next step according to FIG. 1B) is also in itself known way by partially removing the photolithographic Structure of the photoresist layer 2 is formed. This as Mask serving structure consists of a multitude of themselves over the entire width or length of the upper one in the drawing Surface of the sheet 1 or at least the surface to be used extending parallel strip 2 ', as a rule the same width and same, over the entire length of the strip have constant mutual distances.

Before, after or simultaneously with the photolithographic Structuring the photoresist layer 2 is the bottom of the Sheet 1 covered with a protective film 3, which in the subsequent Galvanizing is a metallization of the sheet metal underside prevented.

1C) shows the process stage after the galvanic deposition of copper on the between the strips 2 'of the mask blank sheet metal strip. The secluded Copper strips 4 consequently also extend with one another same width and same, over the entire length of the strip constant mutual distances across the entire Width or length of the panel surface 1.

The photoresist strips are in the process stage according to FIG. 1D) 2 'removed and replaced by protective lacquer. The protective lacquer strips 5 can, for example, by hand Spatulas or squeegees can be applied. You prevent one Metallization of the areas between the copper strips 4 of the sheet 1 in a subsequent galvanic reinforcement the copper strip and later protect as well like the protective film 3, the surface of the alloy area of the finished resistance.

According to FIG. 1E), further copper can be galvanically applied to the copper strip 4 Copper to strengthen the contacts and / or an additional one Metal to be deposited. Through a layer of tin 6 the copper surface is protected from tarnishing and that later soldering the resistor onto a circuit board or The like. Relieved. Form the strips 4 with the tin layer 6 the connection contacts of the individual resistors to be generated.

Now the precision resistors that have already been completed can be used be isolated. For this purpose, the Connection contacts provided sheet 1 longitudinally perpendicular to the Sheet surface and groups running perpendicular to each other separated from cutting planes. The cutting planes of one of these both groups run parallel to the copper strips 4 and thus to one of the edges of the sheet 1 through the entire sheet and are each in the middle of one of the copper strips 4, the thereby being cut into two equal strips, along the arrows 7 in Fig. 1E) and in Fig. F). In Fig. F) as the last or penultimate stage of the process the isolated resistance or one along the second group of cutting planes shown strips to be divided. The cutting planes of the second group also run parallel to the other sheet edge through the entire sheet along the side edges of the individual resistors.

This separation of the resistors is best done by sawing at the individual cutting levels. Sawing has the advantage that the required dimensions of the Resistors with levels exactly perpendicular to the sheet level Cut surfaces can be guaranteed. Suitable for this Precision sawing machines, e.g. B. optically with the galvanized Sheet can be aligned (referenced) and with high Working accuracy in the µm range are known per se and commercially available. The sheet is useful for sawing glued to a base, of which the isolated layer of adhesive Resistors can then be easily solved. Appropriately, the galvanized sheet is first along one sawn the two groups of cutting planes into individual strips, which then in turn form the individual resistances be sawn. Depending on the type of sawing machine could theoretically sawn or sawn several strips at the same time become. From a sheet with the example mentioned above 300 x 400 mm can be used on the one described here Saw out several 10,000 resistors.

The single resistance created after the last process step is shown schematically (not to scale) in Fig. 2. The finished resistor consists of the rectangular one Alloy sheet metal piece 1 ', at the opposite ends of which rectangular connection contacts 4 'and 4' 'with the tin layers 6 ', 6' 'are electroplated. The by galvanic cutting of copper, possibly in several layers are preferably relatively thick, i.a. for good Input and output of the current in or out of the alloy guarantee. For example, the thickness of the copper can be approximate 50-100 µm.

As can be seen, the resistance has the opposite Ends of flat end faces 9 of the connection contacts and the sheet metal piece 1 'itself, which is exactly perpendicular to the Align the sheet level with each other. The same applies to the two lateral end faces 8 of the contacts and the sheet metal piece 1'. The is between the connection contacts Protective lacquer layer 5 ', while the surface facing away from the contacts of the resistance is still covered by the protective film 3 ' can be.

The modified resistor shown in Fig. 3 differs differs from the design according to FIG. 2 only in that instead of the relatively thick sheet metal piece covered with the protective film 3 ' 1 'a much thinner resistance film 11 has been used is that on a double-sided adhesive serving as a protective film Adhesive film 13 has been attached. The resistance foil 11 whose thickness is less than 100 µm e.g. down to 20 µm is for the purpose of manageability, i.e. for mechanical Stabilization using the protective and adhesive film 13 been fixed on a substrate 18, for example can be a 0.5 mm thick aluminum sheet.

The connection contacts 14 with the tin layers 16 and Protective lacquer layer 15 correspond to the embodiment according to FIG. 2, and also the manufacture of the modified resistor takes place essentially according to that described with reference to FIG. 1 Method with the proviso that instead of in the step of FIG. 1A of the relatively thick sheet 1 from the thin resistance film 11, the double-sided adhesive film 13 and the substrate 18 existing laminate is used, the adhesive film 13 and the substrate 18 can replace the protective film 3. The values of the resistors produced in this way can typically in the order of 50 or 100 mΩ.

Instead of the glued-on aluminum substrate 18, the Manageability of a possibly very thin resistance film like that 3 in FIG. 3 also by means of mechanical stabilization suitable non-metallic substrate of the film so that there is a resistance that thinner piece of film instead of sheet 1 'and the thicker non-metallic substrate instead of the protective film 3 'the embodiment 2 corresponds (or the embodiment 3, in which the adhesive film 13 and the substrate 18 are replaced by a single substrate layer on which the Resistance film 11 can be glued).

Claims (12)

1. A low-impedance electrical resistor comprising a flat, rectangular metal member (1', 11) of a resistive alloy and connector contacts (4', 4", 14) electroplated onto one main surface of the metal member at opposite ends, whereby the end surfaces (9) of the metal member (1', 11) and of the connector contacts (4', 4", 14) at these ends and the side surfaces (8), perpendicularly adjoining these end surfaces (9), of the metal member (1') and of the connector contacts (4', 4", 14) are in alignment with one another perpendicular to the plane of the main surface of the metal member (1', 11).
2. A resistor as claimed in Claim 1, characterised in that its resistance is between about 0.5 mΩ and about 5.0 mΩ.
3. A resistor as claimed in Claim 1 or 2, characterised in that the metal member is a film (11), which is secured to a substrate on its side remote from the connector contacts (14).
4. A resistor as claimed in Claim 3, characterised in that the film (11) is less than 100 µm thick.
5. A resistor as claimed in Claim 3 or 4, characterised in that its resistance is greater than 10 mΩ and preferably greater than 50 mΩ.
6. A method of producing low-impedance electrical resistors, in which a metal to form connector contacts (4) for a plurality of individual resistors is galvanically deposited on photolithographically defined regions of a layer comprising a metallic resistive alloy in the form of a plate (1) or a film (11) and the layer (1, 11) provided with the connector contacts (4) is divided into the individual resistors, characterised by the following method steps

   photolithographically producing a shielding mask, which is constituted by a plurality of uniformly spaced parallel strips (2') extending over one surface of the layer (1, 11);

   galvanising the layer (1, 11) only on its surface carrying the shielding mask to deposit the connector contact metal on the resistive strips situated between the parallel mask strips (2'); and

   severing the galvanised layer (1, 11) along groups of cut planes, which extend perpendicular to its surface and perpendicular to one another and of which the one cut planes (7) sever a respective one of the connecting contact strips parallel to the connecting contact strips whilst the other cut planes separate the resistors from one another at their edges extending transverse to the connector contact strips (4), whereby the galvanised layer (1, 11) is severed by sawing or with a laser to separate the resistors.
7. A method as claimed in Claim 6, characterised in that the rear surface of the layer (1) is covered with a protective film (3) before the galvanising process.
8. A method as claimed in one of Claims 6 or 7, characterised in that after the deposition of the connector contact metal, the mask strips (2') are removed and a protective lacquer (5) is applied in their place.
9. A method as claimed in one of Claims 6 to 8, characterised in that at least one additional layer (6) of the same metal or of a different metal is applied galvanically to the connector contact strips (4) before separating the resistors.
10. A method as claimed in one of Claims 6 to 9, characterised in that a sheet (1) or a film (11) of a Cu alloy is plated with copper to form the connector contact strips and the copper strips (4) are plated with tin.
11. A method as claimed in one of Claims 6 to 10, characterised in that the length, width and thickness of the sheet portions (1') remaining after separating the resistors and the spacing of the remaining connector contacts (4', 4") are dimensioned for resistive values of between about 0.1 mΩ and about 5 mΩ.
12. A method as claimed in one of Claims 6 to 10, characterised in that the shielding mask is produced on a film less than 100 µm thick and consisting of the resistive alloy, which is rendered handleable by connection to a substrate (18) and that the length, width and thickness of the film portions (11) remaining after separation of the resistors are dimensioned for resistive values of more than 10 mΩ and preferably more than 50 mΩ.

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