DE102015214953B4 - Device for the electrical connection of connection pads of several stretch marks - Google Patents

Abstract

Device for the electrical connection of connection pads (1.1 - 8.4) of several strain gauges (1 - 8), towards which a flexible printed circuit board (L; L1 - L3) with vias (D1 - D3) interconnecting the strain gauges (1 - 8) to form a measuring bridge the connection pads (1.1 - 8.4) of the strain gauges (1 - 8) is placed, characterized in that the flexible printed circuit board (L) consists of several conductor foils (L1 - L3) placed one on top of the other with conductor tracks (9; 9.1 - 9.5), which have predetermined, mutually aligned vias (D1 - D3) to at least one other conductor foil (L1 - L3) and / or to the connection pads (1.1 - 8.4) of the strain gauges (1 - 8).

Description

The invention relates to a device for electrically connecting connection pads of several strain gauges, on which a flexible printed circuit board with vias to the connection pads of the strain gauges is placed, interconnecting the strain gauges to form a measuring bridge.

To record deformations or tensile and compressive forces as well as torques, strain gauges are used, which consist of an insulating layer, the so-called carrier, and a measuring grid attached to the carrier, which changes its electrical resistance even with slight deformations. If strain gauges are attached to components that deform minimally under load, deformation of the components referred to as spring or deformation bodies as a result of tensile and compressive forces leads to a change in the resistance of the strain gauges, which is used to record the change in electrical resistance in quarters -, half and full bridges can be interconnected by means of thin, insulated strands or enameled wires, whereby additional circuits or resistance wires can be integrated to adjust the bridge circuits.

For this purpose, the strain gauges are pre-tinned and coated with flux. The insulated strands or enamelled wires are heated on one side and also pre-tinned, soldered on one side, bent several times according to a circuit diagram, cut to length, pre-tinned again and soldered on. In addition to the considerable time required for this and the precision required for the wiring, there is a risk of mixing up the connection pads of the strain gauges and damaging the insulated strands or enameled wires with a bending tool, such as tweezers, and thus of short circuits or faulty electrical connections. In addition, strong tensile forces can be exerted on the strain gauges during bending, as a result of which connection pads of the strain gauges are torn off or damaged.

These dangers exist in particular in the case of deformation bodies to which a large number of strain gauges are applied, such as for force transducers for measurement in 5 axes, namely 3 Cartesian axes and 2 axes of rotation. For this purpose, instead of the otherwise usual 2 to 4 strain gauges for normal force transducers, 8 strain gauges are to be provided, the connection pads of which have to be wired to one another and to contacts of an evaluation device.

From the DE 40 12 077 A1 a flexible printed circuit board for a transducer with at least one measuring sensor is known, which is provided with contact points for connecting lines and with contact points for components of a balancing circuit formed on the printed circuit board and with contact zones for connection to the measuring sensor. In order to enable automated assembly, the contact zones of the circuit board correspond to the contact surfaces of the measuring sensors and interact with the measuring sensors attached to them, each contact zone having at least one connection element and via this contact can be made directly with the corresponding contact surface.

From the DE 36 34 123 C1 a force transducer is known with a measuring spring designed as a double bending beam, on the upper and lower surface of which wire strain gauges are arranged to form a measuring bridge. The connection of the measuring spring with force introduction components is carried out by means of contact surfaces that engage behind one another and run transversely to the longitudinal direction and in a cross-sectional plane. The wiring of the strain gauges to form a measuring bridge is designed as a flexible print film and extends over outer surfaces that are not provided with contact surfaces and an end surface of the measuring spring.

From the DE 10 2007 026 827 A1 a force-torque transducer is known which consists of a metallic carrier which is deformed under the action of a force or moment, the deformation being detected by means of applied strain gauges. For the automated production of the force-torque transducer, the carrier consists of a conventional printed circuit board, which is divided into a rigid and a deformable area and on whose copper lamination the strain gauges are arranged directly. The wiring of the strain gauges and the electronic signal processing electronics are also arranged on the circuit board.

From the U.S. 4,520,339 A a force transducer for converting a force into an electrical signal is known, which has a carrier to which strain gauges and a flexible printed circuit board are attached. On the flexible printed circuit board, conductor tracks and soldering ports are formed, which are provided on both sides of a bent section on which the flexible printed circuit board is bent for attachment to the carrier.

From the DE 43 27 560 A1 a method for contacting conductor tracks is known in which a second substrate is applied to a substrate with a conductor track arrangement and a contact point, the at least one substrate that can be connected to at least one connection area, the contact point of the has through-hole associated with the first substrate, the through-hole and the contact point being aligned with one another. Both substrates are fixed to one another and the through hole is filled with a filling such that the connection areas on the second substrate and the contact point of the first substrate are connected in an electrically conductive manner, so that stable contact is ensured for circuits with small dimensions regardless of the conductor track material and the ambient conditions.

The object of the present invention is to provide a device of the type mentioned at the beginning with which a large number of conductor tracks and links to the connection pads of several strain gauges with each other and with contacts of an evaluation device with little effort, without the risk of confusion or damage to connection pads and damage to electrical connection lines can be connected.

This object is achieved according to the invention with the features of claim 1.

The solution according to the invention of assembling the flexible printed circuit board from several conductor foils placed one on top of the other with conductor tracks connecting the vias, which have predetermined, mutually aligned vias to at least one other conductor foil and / or to the connection pads of the strain gauges interconnected to form a measuring bridge, also enables one larger number of strain gauges with little effort and without the risk of mixing up or damaging connection pads and damaging electrical connection lines.

By composing the flexible printed circuit board from several layers of flexible conductor foils or multilayers, a large number of conductor tracks and links to the connection pads of the strain gauges are possible, with line connections and connections to the connection pads being connected to one another via vias.

• - die flexible Leiterplatte wird mäanderförmig ausgebildet,
• - die Anschlusspunkte werden als Löt- oder Anschlussfahnen ausgebildet,
• - die Lötfahnen weisen einen maximalen Abstand zu den Leitungsbahnen der flexiblen Leiterplatte auf,
• - die flexible Leiterplatte weist mehrere Schlitzungen zwischen den Leitungsbahnen, Anschlusspunkten oder Anschlusskontakten zu einer Auswerteinrichtung und/oder den Anschlusspads auf,
• - an den Anschlusspunkten der flexiblen Leiterplatte ist nur jeweils eine Löt- oder Anschlussfahne der Folienleiter mit Anschlusspads eines Dehnungsmessstreifens durchkontaktiert,
• - über jedem Anschlusspad ist eine Durchkontaktierung derart vorgesehen, dass nach dem elektrischen Verbinden der Löt- oder Anschlussfahnen mit den Anschlusspads eine feste Verbindung auf beiden Seiten der Löt- oder Anschlussfahnen besteht.

Due to the multi-layer structure of the flexible printed circuit board, there is a risk that it will lose its flexibility and become correspondingly rigid, which leads to the risk of influencing the measured values of the strain gauges. In order to rule out this risk, the following measures are taken individually or in combination in a further development of the invention:

• - the flexible circuit board is designed in a meandering shape,
• - the connection points are designed as soldering or connection lugs,
• - the soldering lugs have a maximum distance from the conductor tracks of the flexible circuit board,
• - The flexible printed circuit board has several slots between the conductor tracks, connection points or connection contacts to an evaluation device and / or the connection pads,
• - At the connection points of the flexible circuit board, only one soldering or connection lug of the foil conductor is contacted through with connection pads of a strain gauge,
• - A through-hole plating is provided above each connection pad in such a way that after the electrical connection of the soldering or connection lugs with the connection pads, there is a fixed connection on both sides of the soldering or connection lugs.

The flexible printed circuit board or the conductor foils or multilayers preferably consist of print foils with conductor tracks and vias or connection contacts for the evaluation device printed thereon.

• - die Dehnungsmessstreifen vorverzinnt und mit einem Flussmittel bestrichen werden,
• - eine die Dehnungsmessstreifen zu einer Messbrücke verschaltende und Anschlusspunkte aufweisende flexible Leiterplatte mit vorgegebenen Durchkontaktierungen zu Anschlusspads der Dehnungsmessstreifen auf die Dehnungsmessstreifen aufgelegt wird und
• - die Durchkontaktierungen über den Anschlusspads der Dehnungsmessstreifen mittels Lötzinn derart erhitzt werden, dass der Lötzinn durch die Durchkontaktierungen von den Anschlusspunkten der flexiblen Leiterplatte zu den Anschlusspads der Dehnungsmessstreifen läuft.

A method for electrically connecting connection pads of several strain gauges is characterized in that

• - the strain gauges are pre-tinned and coated with a flux,
• a flexible printed circuit board, which interconnects the strain gauges to form a measuring bridge and has connection points, with predetermined vias for connection pads of the strain gauges, is placed on the strain gauges, and
• - The plated-through holes over the connection pads of the strain gauges are heated by means of tin solder in such a way that the solder runs through the plated-through holes from the connection points of the flexible printed circuit board to the connection pads of the strain gauges.

To produce the flexible printed circuit board, several conductor foils are placed on top of one another, on which predetermined conductor tracks, connection pads and vias are arranged, the inner wall of which is provided with a conductive coating, the conductor foils placed on top of one another being electrically connected to one another at the vias by means of flowing solder. In order to increase the flexibility of the circuit board or the To obtain conductor foils, the flexible printed circuit board or conductor foil provided with the conductor tracks and vias is cut or punched in a meandering shape.

• 1 eine schematische Abwicklung des Umfangs eines Feder- oder Verformungskörpers zur Messung von Zug- oder Druckkräften mit acht auf den Umfang des Verformungskörpers applizierten Dehnungsmessstreifen;
• 2 eine vergrößerte schematische Abwicklung der acht Dehnungsmessstreifen mit die Anschlusspads und Anschlusspunkte der acht Dehnungsmessstreifen verbindenden Leitungsbahnen;
• 3 eine schematische Darstellung einer mäanderförmigen flexiblen Leiterplatte mit aufgedruckten Leitungsbahnen, Durchkontaktierungen und Anschlussfahnen zu den Anschlusspads der Dehnungsmessstreifen und
• 4 bis 6 eine schematische Darstellung einer oberen, mittleren und unteren Lage einer dreilagigen flexiblen Leiterplatte mit Leitungsbahnen, Durchkontaktierungen, Anschlussfahnen zu den Anschlusspads der Dehnungsmessstreifen und Kontakten für die Auswerteinrichtung.

The idea on which the invention is based and further variants of the invention that can be derived therefrom are to be explained in more detail using an exemplary embodiment shown in the drawing. Show it:

• 1 a schematic development of the circumference of a spring or deformation body for measuring tensile or compressive forces with eight strain gauges applied to the circumference of the deformation body;
• 2 an enlarged schematic development of the eight strain gauges with the conductor tracks connecting the connection pads and connection points of the eight strain gauges;
• 3 a schematic representation of a meandering flexible printed circuit board with printed conductor tracks, vias and connection lugs to the connection pads of the strain gauges and
• 4th to 6th a schematic representation of an upper, middle and lower layer of a three-layer flexible printed circuit board with conductor tracks, vias, connection lugs to the connection pads of the strain gauges and contacts for the evaluation device.

1 shows an enlarged representation of the development of eight strain gauges arranged on a deformation body for measuring tensile and compressive forces 1 to 8 whose central axes are spaced 45 ° from each other, so that the strain gauges 2 , 4th , 6th and 8th by 90 ° each and the strain gauges 1 and 5 as 3 and 7th are offset from each other by 180 °. The strain gauges 1 to 8 according to the in 2 enlarged development of the strain gauges 1 to 8 alternately differently shaped and aligned measuring grids for the detection of expansion and compression as well as four connection pads each, of which only a part of the connection pads is designated in more detail for the purpose of better visibility.

The connection pads 1.1 - 8.4 the strain gauge 1 to 8 are by means of ducts 9 , of which only the conductor tracks are also used for better visibility 9 to 9.3 are designated in more detail, connected to one another and to connection points A1 to A 10 for connection to contacts of an evaluation device. The connection pads are usually used to establish the connections 1.1 - 8.4 the strain gauge 1 to 8 with each other and partly with the contacts K1 to K10 for connection to the evaluation device by means of thin, insulated strands or enameled wires interconnected by the strain gauges 1 to 8 Pre-tinned and coated with flux and insulated strands or enameled wires heated on one side and also pre-tinned, soldered on one side, bent several times according to a circuit diagram, cut to length, pre-tinned again and soldered on.

This time-consuming wiring, which is associated with the risk of making faulty connections as a result of mixing up connection pads or damage to the lacquer insulation, is illustrated by the following based on the 3 to 6th features described and explained in more detail.

3 shows an enlarged view of a meandering flexible printed circuit board L. with ducts 9 , Soldering or connection lugs F1 to F12 with vias D1 to the connection pads 1.1 - 8.4 of the eight strain gauges 1 to 8 , Vias D2 for connecting conductor tracks and plated-through holes D3 to the contacts K1 to K10 in a contact area 10 for connection to an evaluation device. This will place the solder on the top of the flexible circuit board L. heated at the vias so that it flows down into the vias and connects on the underside with a connection pad, a conductor path or a contact for an evaluation device, so that a solid, conductive connection is created.

To the multitude of ducts 9 with the required distance to each other on the flexible circuit board L. to arrange the flexible circuit board L. in this embodiment according to the 4th to 6th made of three conductor foils or multilayer with an upper conductor foil L1 , a middle conductor foil L2 and a lower conductor foil L3 leading to the strain gauges. Vias D1 to D3 serve to connect cable tracks 9 the 3 Conductor foils L1 , L2 and L3 with each other, the connection lugs F1 to F 12th with the connection pads of the strain gauges and the conductor tracks 9 with the connection points of the flexible printed circuit board or the contacts K1 to K 10 the evaluation device. The vias connect D1 the ducts 9 with the connection lugs F1 to F12 for the connection pads of the strain gauges, the vias D2 the corresponding ducts 9 the 3 Conductor foils L1 , L2 and L3 to each other and the vias D3 the ducts 9 with the connection points K1 to K10 the flexible printed circuit board.

Here, too, the solder is on the top of the conductor foil L1 and L2 heated on the vias so that it flows down into the corresponding vias and connects on the underside with a connection pad, a conductor path or a contact for an evaluation device and creates a solid, conductive connection.

For a better understanding, some connections are described below with reference to the 4th to 6th explained in more detail.

The one on the terminal lug F1 of the upper conductor foil L1 provided vias to the connection pads 1.1 and 1.2 of the first strain gauge 1 are inside the upper conductor foil L1 via a duct 9 connected directly to contact K9.

A through-hole connection of the upper conductor foil L1 to the connection pad 6.2 of the sixth strain gauge 6th is via a duct 9 and a via D2 , to the lower conductor foil L3 and via a conductor path 9 and a via with the connection pad 8.1 of the eighth strain gauge 8th electrically connected, so that with reference to the schematic representation of the 2 a conductive connection between the connection pad 6.2 of the sixth strain gauge 6th to the connection pad 8.1 of the eighth strain gauge 8th will be produced.

The through-hole connection to the connection pad 2.1 of the second strain gauge 2 on the middle conductor foil L2 is via a duct 9 and a via D2 with the lower one, to the strain gauges 1 to 8 leading conductor foil L3 and a conductor path 9 and a via with the connection pad 4.2 of the fourth strain gauge 4th electrically connected, so that with reference to the schematic representation of the 2 a conductive connection between the connection pad 2.1 of the second strain gauge 2 to the connection pad 4.2 of the fourth strain gauge 4th will be produced.

The strain gauges are used for the respective interconnection 1 to 8 pre-tinned and coated with flux. Thereupon the three conductor foils L1 , L2 and L3 with that of the strain gauges 1 to 8 leading lower conductor foil L3 on the arrangement of the strain gauges 1 to 8 and the plated-through holes by means of solder D1 above each connection pad, the vias D2 the connections of the ducts 9 of the three conductor foils L1 , L2 and L3 with each other and the vias D3 to the contacts K1 to K 10 heated so that the solder through the vias D1 , D2 and D3 running.

• - die flexible Leiterplatte L bzw. die Leiterfolien L1, L2 und L3 mäanderförmig ausgebildet,
• - die Anschlusspunkte zu den Anschlusspads der Dehnungsmessstreifen 1 bis 8 als Löt- oder Anschlussfahnen F bis F12 ausgebildet,
• - die Löt- oder Anschlussfahnen F1 bis F12 mit maximalem Abstand zu den Leitungsbahnen angeordnet,
• - die flexible Leiterplatte L bzw. die Leiterfolien L1, L2 und L3 mit Schlitzungen 11 zwischen den Kontakten K1 bis K10, Schlitzungen 12, 13, 14 zwischen den Leitungsbahnen 9 und Schlitzungen 15 zwischen den Löt- oder Anschlussfahnen F3, F5, F9 und F12 zu den Anschlusspads der Dehnungsmessstreifen 1 bis 8 versehen,
• - an den Anschlusspunkten der flexiblen Leiterplatte L bzw. den Leiterfolien L1, L2 und L3 nur jeweils eine Löt- oder Anschlussfahne zu den Anschlusspads eines Dehnungsmessstreifens durchkontaktiert,
• - über jedem Anschlusspad nur eine Durchkontaktierung vorgesehen, so dass nach dem elektrischen Verbinden der Löt- oder Anschlussfahnen mit den Anschlusspads eine feste Verbindung auf beiden Seiten der Löt- oder Anschlussfahnen besteht.

Disadvantageous in the composition of the flexible printed circuit board L. from a multi-layer structure with in this embodiment 3 Conductor foils L1 , L2 and L3 is that the flexible printed circuit board becomes stiff, which leads to the danger of influencing the measured values. To prevent this, will or will be

• - the flexible circuit board L. or the conductor foils L1 , L2 and L3 meandering,
• - the connection points to the connection pads of the strain gauges 1 to 8 designed as soldering or connection lugs F to F12,
• - the soldering or connection lugs F1 to F12 are arranged at a maximum distance from the conductor tracks,
• - the flexible circuit board L. or the conductor foils L1 , L2 and L3 with slots 11 between contacts K1 to K10 , Slits 12th , 13th , 14th between the ducts 9 and slots 15th between the soldering or connection lugs F3, F5, F9 and F12 to the connection pads of the strain gauges 1 to 8 Mistake,
• - at the connection points of the flexible printed circuit board L. or the conductor foils L1 , L2 and L3 only one soldering or connection lug is plated through to the connection pads of a strain gauge,
• - Only one through-hole contact is provided above each connection pad, so that after the electrical connection of the soldering or connection lugs with the connection pads, there is a firm connection on both sides of the soldering or connection lugs.

List of reference symbols

1 - 8

Strain gauges

1.1 - 8.4

Connection pads of the strain gauges

9, 9.1-9.5

Ducts

10

Fasteners 10 , 11 , 12th

11

Slots between the contacts

12-14

Slots between the ducts

15th

Slits between the soldering or connection lugs

D1

Vias to the connection pads

D2

Vias for connecting conductor tracks

D3

Vias to the contacts

F1 - F12

Solder or connection lugs

K1 - K10

Contacts to an evaluation device

L.

flexible circuit board

L1

Upper conductor foil

L2

Medium conductor foil

L1

Lower conductor foil leading to the strain gauges

Claims (10)

Device for the electrical connection of connection pads (1.1 - 8.4) of several strain gauges (1 - 8), towards which a flexible printed circuit board (L; L1 - L3) with vias (D1 - D3) that connects the strain gauges (1 - 8) to form a measuring bridge the connection pads (1.1 - 8.4) of the strain gauges (1 - 8) is placed, characterized in that the flexible printed circuit board (L) consists of several conductor foils (L1 - L3) placed one on top of the other with conductor tracks (9; 9.1 - 9.5), which have predetermined, mutually aligned vias (D1 - D3) to at least one other conductor foil (L1 - L3) and / or to the connection pads (1.1 - 8.4) of the strain gauges (1 - 8). Device according to Claim 1 , characterized by a meandering flexible printed circuit board (L; L1 - L3) with connection points designed as soldering or connection lugs (F1 - F12) to the connection pads (1.1 - 8.4) of the strain gauges (1 - 8). Device according to Claim 2 , characterized in that the soldering or connection lugs (F1 - F12) have a maximum distance from the conductor tracks (9; 9.1 - 9.5) of the flexible printed circuit board (L; L1 - L3). Device according to at least one of the preceding Claims 1 to 3 , characterized in that the flexible printed circuit board (L; L1-L3) has several slots (11-15) between the conductor tracks (9; 9.1-9.5) and / or the connection points of the soldering or connection lugs (F1-F12). Device according to at least one of the preceding Claims 1 to 4th , characterized in that at the connection points of the flexible printed circuit board (L; L1 - L3) only one soldering or connection lug (F1 - F12) of the conductor foil (L1 - L3) to connection pads (1.1 - 8.4) of a strain gauge (1 - 8 ) is plated through. Device according to at least one of the preceding Claims 1 to 5 , characterized in that a through-hole (D1 - D3) is arranged above each connection pad (1.1 - 8.4) of a strain gauge (1 - 8) in such a way that, after electrical connection, a fixed connection on both sides of the soldering or connection lugs (F1 - F12 ) consists. Device according to at least one of the preceding Claims 1 to 6th , characterized in that the flexible printed circuit board (L1-L3) or the conductor foils (L1-L3) is or are designed as print foils. Method for electrically connecting connection pads of several strain gauges, characterized in that - the strain gauges (1-8) are pre-tinned and coated with a flux, - a flexible printed circuit board (L; L; L1 - L3) with specified vias (D1 - D3) to connection pads (1.1 - 8.4) the strain gauges (1 - 8) are placed on the strain gauges (1 - 8) and - the vias (D1 - D3) over the connection pads (1.1 - 8.4) the strain gauges (1 - 8) are heated with solder in such a way that the solder passes through the vias (D1 - D3) from the connection points of the flexible circuit board (L; L1 - L3) to the connection pads (1.1 - 8.4) of the strain gauges (1 - 8) is running. Procedure according to Claim 8 , characterized in that for the production of the flexible printed circuit board (L) several conductor foils (L1 - L3) are placed on top of one another, that predetermined conductor tracks (9; 9.1 - 9.5) are arranged on the conductor foils (L1 - L3) that on the conductor foils ( L1 - L3) predetermined vias (D1 - D3) are arranged, the inner wall of which is provided with a conductive coating and that the conductor foils (L1 - L3) placed on top of one another are electrically connected to one another at the vias (D1 - D3) by means of flowing solder. Procedure according to Claim 8 or 9 , characterized in that the flexible printed circuit board (L) or the conductor foils (L1-L3) is or are cut or punched in a meandering shape.

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