DE29703892U1 - Potentiometers in thick-film technology, circuit board and grinder for this - Google Patents

Description

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"Potentiometer in thick film technology, circuit board and wiper for this"

State of the art

The invention is in the field of potentiometers using thick-film technology. The invention primarily relates to a potentiometer using thick-film technology with a carrier plate on which a resistance layer, conductor tracks and tapping and connection surfaces are arranged and with a pivoting wiper for tapping the resistance layer (general term of protection claim 1). The invention is also based on a circuit board with a resistor applied to the circuit board base material using thick-film technology (general term of protection claim 2).

It is known to apply a resistance layer to an insulating carrier. For example, DE-C2 29 32 714 discloses an adjustable rotary resistor using thick-film technology with a carrier plate to which a pivoting wiper lever is assigned, which interacts with a wiper track that is formed from a series of adjacent conductor tracks with gaps that are connected to a resistance layer outside the wiper track. The conductor tracks are each designed to be about 0.2 mm wide - and the distance between them about the same - because then a particularly high measurement value resolution can be achieved with little manufacturing effort. Further refinement of the conductor track pattern leads to a higher resolution, but also to an increase in manufacturing costs, while a coarser

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Conductor track pattern results in a lower resolution but also lower manufacturing costs. Based on this, in order to achieve a high measurement value resolution with low manufacturing costs, the subject of DE-4-1 ^4 39 829 provides a second wiper track that is electrically separated from the first wiper track, the conductor tracks of which are connected to a further resistance layer and aligned so that they lie opposite the spacing gaps of the first wiper track, with the wiper lever having a wiper for each wiper track, which are electrically connected to one another.

Since the resistive tracks are generally applied to the carrier plate when the resistive layer is applied, there is a possibility that the thickness of the resistive layer will vary slightly as a result. At such locations, an increase in friction is therefore achieved which opposes the sliding of a movable contact arm or brush over the surface of a resistive layer. The brush moves with uniform contact pressure as it traverses the tracks or track, and the contact resistance varies, causing an error to be created between the movement of the brush and the corresponding resistance value formed by the relevant portion of the resistive layer. There is also a risk of damage to the brush because the thickness changes in the layer lead to high friction between the brush and the layer. In order to increase the accuracy of the aforementioned precision resistors, a variable thick-film resistor is known from DE-Al 30 25 155, in which a section of conductive material is electrically connected to the peripheral edge of the resistance layer on at least one peripheral edge of the resistance layer. This makes it possible _to determine the resistance value formed by the resistance layer between the section of conductive material and the end section of the resistance layer.

Furthermore, rotary resistors with non-linear characteristics are also known. For example, a thick-film resistor with a trumpet-shaped and arc-shaped resistance layer and a series of parallel resistors is known from DE-Ül 85 Ö4 477.6. During production, three layers, a silver layer, a resistance layer and a covering lacquer, are printed on top of each other. The conductor track sections or surfaces form the 1st layer, which consists of cermet silver due to the high technical requirements in the professional field and is printed in one operation on a carrier plate measuring 2 x 2 cm using screen printing with a contour accuracy of ±0.05 mm. The 2nd layer, made of an electrically conductive lacquer, which takes extreme mechanical and electrical requirements into account, includes the resistors* '-..^, conductor track bridges and position markings. . The position markings are used for the precise setting of the screen printing screen.

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in order to maintain the coverage accuracy of ±0.1 mm of the 1st and 2nd layers. The 2nd layer is printed onto the 1st layer in one operation using the screen printing process and partially overlaps it. The 3rd layer, consisting of the two covering lacquer parts on the resistance layer and the position markings, which are necessary for the precise setting up of the screen printing screen with the desired coverage accuracy, is printed onto the 2nd layer in one operation using the screen printing process.

Finally, an SMD (Surface-Mounted-Device) assembly with ohmic resistors is known from DE-Al 42 15 553. High-quality and cost-effective miniature components can be manufactured using SMD technology. In the course of miniaturizing SMD assemblies, it is also important to reduce the size of conventional soldered SMD resistors accordingly. Conventional SMD resistors are positioned on the circuit board using the placement machine and then wave- or reflow-soldered.

In the subject matter of DE-Al 42 15 553, the SMD assembly is implemented using screen-printed resistors. Polymer resistor pastes, such as epoxy and phenol based ones, are usually used to produce screen-printed resistors on circuit board base materials. The resistor pastes are printed onto the circuit boards using a screen or a stencil with appropriate configurations using a screen printing machine and then hardened by applying heat. The resistance values are determined by the so-called output resistance of the resistor paste, decadal from 100 kO to 1 μΩ per unit area, and the geometry of the printed and hardened resistors.

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A key advantage of this process is that the screen-printed resistors require less space on the circuit board than conventional SMD resistors, thus allowing a higher packing density of an SMD assembly. Due to their low height (approx. 12 μm) and significantly smaller dimensions (L x W), screen-printed resistors can be placed under large-area components, which further reduces the size of the circuit board. Resistors made in this way enable a very cost-effective design.

problem

Although the manufacturing process for such precision resistors or potentiometers is known, this manufacturing technology has not been taken into account in the design of circuit boards for machine assembly with components. This is due to problems with

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Circuit board layout and different contact pressure levels are expected. In order to get these problems under control, the component, i.e. resistor or potentiometer itself, was always optimized and the size and connection position of the components were taken into account in the " circuit board layout.

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are solved starting from a potentiometer in accordance with DE-C2 2932 714 in that the resistance layer is applied directly to a circuit board to be equipped with the potentiometer instead of to the carrier plate and that the circuit board has a recess in the area of the resistance layer for fastening the wiper.

Furthermore, these problems are solved, starting from a circuit board with a resistor applied to the circuit board base material according to DE-Al 42 15 553, by accommodating both electronic components and the resistance layer as well as tapping and connection surfaces of at least one potentiometer and by a recess for attaching a wiper of the potentiometer for tapping on the resistance layer and the tapping surface.

Advantageous effects of the invention

The invention ensures that the layout of the potentiometer can be taken into account in the circuit board layout, so that overall the manufacturing costs can be reduced considerably. While a commercially available potentiometer costs 15 pfennigs, the invention costs 3 pfennigs for the screen printing of the resistance layer, 3 pfennigs for the surface treatment of the circuit board and 3 pfennigs for the wiper, a total of 100 pfennigs. A further saving is achieved by the fact that the assembly costs are also reduced compared to assembly with commercially available potentiometers.

Further development of the invention

Advantageous embodiments of the invention are set out in claims 3
specified

The further development according to claim 3 has the advantage that both rotary resistors and sliding resistors can be manufactured in a simple manner.

In a preferred embodiment of the invention according to claim 4, the slider is designed as an electrical spring contact, which has at least two

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spring arms and an inner spring designed as a fastening part in the area of the spring base. The advantage here ^is that a commercially available, highly conductive spring sheet can be used, which is cut out and shaped accordingly. The level of the contact pressure is thereby essentially determined by the spring. 5 is influenced by the spring stiffness and can be dimensioned differently for the resistance track and the wiper track. Only small and constant transition resistances arise between the wiper and the tapping surface. The material of the tapping surface and the wiper can be selected in such a way that the wiper has good and constant sliding properties with little wear. Since the contact pressure on the resistance mass is not critical and no uneven wiper track is created,.

Ij (; cheap printing pastes, e.g. carbon layer pastes, can be used. To adjust such a potentiometer only small torques 'iff &psgr;&idigr; are required and the noise resistance, which is due to the contact of the wiper J[|f:J15 with the resistance layer and the tapping surface, remains

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III || To reduce the axial play of the grinder, in a further embodiment

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j|| I 25 6 provided that the inner spring at the insertion end in the radial edge area

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ll &iacgr;&idiagr;|: Preferably, according to claim 7, snap rings are used as retaining elements

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Isii' The embodiment of the invention according to claim 8, in which a spring arm as

ll:!|| Counterholder has the advantage of low radial

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Pl^i, Finally, according to claim 9, in the area of the spring base a

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Description of the invention

Further parts, features and details of the invention can be found in the following description of an embodiment of the invention with reference to the drawing. The drawing shows

FIG. 1 is a plan view of a circuit board with rotary and sliding resistor layout,

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a partial side view through a rotary resistor according to the invention with a longitudinal center section in the plane I-I in FIG. 1 and

FIG. 3 is a plan view of a grinder according to the invention.

FIG. 1 shows a top view of a circuit board with a rotary and sliding resistor layout. According to the invention, the resistance layer W and the tapping and connection surfaces A of a potentiometer P are applied directly to a circuit board L to be fitted with the potentiometer. The circuit board L has a recess LA in the area of the resistance layer W for fastening the wiper S (FIG. 2). For the sliding resistor, the recess LA is designed as a slot, and for the rotary resistor as a hole in the circuit board L. In the usual way, the circuit board layout contains conductor tracks, soldering points and holes for fitting the

Components, according to the invention, the resistance layer is part of the circuit board and when assembling, only the wiper S (FIG. 2) has to be inserted into the respective recess in the circuit board.

FIG. 2 shows a partial side view through a rotary resistor with a longitudinal center section in plane II in FIG. 1 and FIG. 3 shows the top view of a wiper according to the invention. In the embodiment shown in the drawing ^, the wiper S is designed as an electrical spring contact; other designs such as a rolling contact are possible within the scope of the invention. The spring contact S has at least two spring arms FA and an inner spring FI designed as a fastening part in the area of the spring base. The inner spring ^FI is provided with funnel- or triangular-shaped cuts FIA at the insertion end. In the area of the cuts FLA, bending slots extending over the entire length of the same, which engage behind the lugs L , are arranged. As a result of this design, the spring contact S is guided into the recess LA of the circuit board L when inserted.

In an embodiment not shown in the drawing, the inner flange Fl has constrictions in the radial edge area at the insertion end and can be locked by means of holding elements that engage in the constriction, whereby

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preferably snap rings with a convex surface are provided as retaining elements. '

Furthermore, an additional spring arm is designed as a counterholder FH and in the area of the spring base there is a through hole FL into which an actuating device for the potentiometer P engages.

The invention is particularly characterized by the fact that a large number of differently designed potentiometers can be manufactured in a simple manner. Essentially, for a new potentiometer series, only the wiper needs to be redesigned and the boundary conditions for the circuit board layout that must be observed when using commercially available potentiometers are largely eliminated. All of the possible designs shown and described, as well as their combination with one another, are essential to the invention. It would also be possible to arrange several resistance layers with different resistance values per unit area in parallel to one another or to provide a switching function by interrupting the resistance path (covering varnish of the same layer thickness) or to use a gold coating instead of cermet silver or to manufacture the circuit boards in multiple use (e.g. 4-way circuit boards), i.e. to punch the contour of the circuit board and to separate it by scoring, etc.

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Claims (9)

1. Potentiometer in thick-film technology with a carrier plate, ■ on which a resistance layer (W), conductor tracks and tapping and connection surfaces (A) are arranged, and with a pivoting wiper (S) for tapping on (Jer _H resistance layer, characterized in that instead of on the carrier plate, the resistance layer (W) is applied directly to a circuit board (L) to be equipped with the potentiometer (P) and that the circuit board (L) has a recess (LA) in the area of the resistance layer (W) for fastening the wiper (S). 2. Printed circuit board with a resistor in diaphragm technology applied to the printed circuit board base material, characterized by the accommodation of both electronic components and the resistance layer (W) as well as tapping and connection surfaces (A) of at least one potentiometer (P) and by a recess (LA) for fastening a wiper (S) of the potentiometer (P), for tapping on the resistance layer (W) and the tapping surface (A). ■A 3. Potentiometer or circuit board according to claim 1 or 2, characterized in that when the potentiometer (P) is designed as a rotary resistor, the recess (LA) in the circuit board (L) is designed as a bore and when it is designed as a sliding resistor, the recess (LA) in the circuit board (L) is designed as a slot. &Agr;&Igr;:.- '■M'M'f,'"!!'', i &igr;, 4. Grinder for a potentiometer or a circuit board according to claim 1 or 2, characterized in that the grinder (S) is designed as an electrical spring contact and that the spring contact (S) has at least two spring arms (FA) and an inner spring (FI) designed as a fastening part in the region of the spring base. ■ 5. Grinder according to claim 4, characterized in that the Irmen spring (FI) has funnel-shaped or triangular bent cuts (FIA) at the insertion end and bending slots extending over the entire length of the cuts (FIA) in the region of the same, which engage behind the circuit board (L). O.Grinder according to claim 4 or 5, characterized in that the Irmenfe,(1er,(FI) has constrictions at the insertion end in the radial edge region and can be locked by means of holding members which can engage in the constriction. 7, Grinder according to claim 6, characterized in that snap rings with a convex surface are provided as holding members. 8. Grinder according to one of claims 4 to 7, characterized in that a spring arm is designed as a counterholder (FH). 9. Grinder according to one of claims 4 to 8, characterized in that a through hole (FL) is arranged in the region of the spring base, into which an actuating device for the potentiometer (P) engages. ;j IT,-f! ,':,;■ j,-| ;■■ Sii* |,i ''3'1"Vi' Ii Ulli I)','"I ₁ , Hi! i'ii" f: ¹ i'l»'ill."' ¹ Ik' Hm &euro;,