Method for manufacturing a conductivity sensor

The present application is related to and claims the priority benefit of German Patent Application No. 10 2015 121 857.7, filed on Dec. 15, 2015, the entire contents of which are incorporated herein by reference.

The present disclosure relates to a method for manufacturing a sensor, in particular a conductivity sensor.

Known from the state of the art are conductive conductivity sensors comprising at least two electrodes, which are immersed for measuring in the measured medium. For determining the electrolytic conductivity of the measured medium, the resistance or conductance of the electrode measuring path in the measured medium is determined. In the case of a known cell constant, the conductivity of the measured medium can then be ascertained.

Shown in DE 10 2006 024 905 A1 is an electrode arrangement of a conductive conductivity sensor, in the case of which an inner and an outer electrode are separated from one another and insulated relative to one another by a shaped seal and a seal support body. The shaped seal serves to avoid penetration of measured medium into an annular gap between the electrodes.

Such an electrode arrangement with additional seals is constructively relatively complex. This is the case especially for conductivity sensors destined for application in foods technology or in the pharmaceutical industry. High hygienic requirements are placed on such sensors. For example, the probes of such sensors, to the extent that they come in contact with the measured medium, are not permitted to have any difficultly accessible gaps, in order that a cleaning and/or sterilizing of the total probe surface contacting the measured medium is possible. Conventional seals or a shaped seal according to DE 10 2006 024 905 A1 can, indeed, basically fulfill these requirements, but they involve complex construction with correspondingly increased effort for their assembly.

An object of the present disclosure is to provide a method for manufacturing a conductivity sensor and a corresponding conductivity sensor, which fulfills high hygienic requirements and, in spite of this, is simple to manufacture.

The object is achieved by the subject matter of the present disclosure, including a method for manufacturing a conductivity sensor, including a conductive conductivity sensor, comprising method steps of producing a thermoplastic sensor body of a plastic, which is doped at least partially with a laser activatable, metal compound as an additive, structuring the doped sensor body by means of a laser, so that conductive metal nuclei form from the metal compound, immersing the sensor body in a metal plating bath, until at least one conductive trace forms on the sensor body, wherein at least one of the conductive traces serves as an electrode of the conductivity sensor.

The structuring of the doped sensor body by means of a laser produces an MID (Molded Interconnect Device). MIDs are injection molded, plastic components with specially applied metal conductive traces to serve as circuit supports for electronic or mechatronic assemblies.

Integration of conductive traces and metallized contact feedthroughs in the sensor body leads to a miniaturizing of the conductivity sensor. Furthermore, the number of components and mounting steps are reduced.

Laser direct structuring (LDS) utilizes a thermoplastic plastic doped with a non-conductive, laser activatable, metal compound as an additive. A laser beam writes the paths of the subsequently applied conductive traces on the plastic. Where the laser beam strikes the plastic, the surface of the plastic matrix is decomposed into volatile, cracking, or splitting products, such that the surface is slightly removed. At the same time, metal nuclei are split off from the additive. These metal nuclei lie finely distributed in the micro roughened surface, and, as metal particles, form the nuclei for the subsequent metallizing. Upon immersion into an electroless copper bath, sharply defined conductive trace layers form on the lasered surface portions. Following this, layers of copper, nickel and a gold finish can be sequentially applied.

The subject matter of the present disclosure further includes a conductivity sensor produced using a method of the present disclosure, wherein the at least one conductive trace is arranged on an area of the sensor body facing the measured medium.

In a further development, the sensor body includes at least one plug contact for producing an electrical contact to the at least one conductive trace.

In a variant, the sensor body includes at least one metallized contact feedthrough, which electrically connects the at least one conductive trace with the at least one plug contact.

In at least one embodiment, the sensor body includes a recess with a temperature sensor for measuring the temperature of the measured medium.

In a further embodiment, at least one of the conductive traces is injection mold coated for insulation.

The present disclosure will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

FIG. 1 shows a longitudinal section of a conductivity sensor according to the present disclosure.

FIG. 2 shows a perspective view of a longitudinal section of a conductivity sensor according to the present disclosure.

FIG. 3 shows a perspective view of the interior of a conductivity sensor according to the present disclosure.

FIG. 1 shows a longitudinal section of a conductive conductivity sensor 6 produced according to a method of the present disclosure. Conductivity sensor 6 includes a sensor body 1 having conductive traces 3 , wherein the conductive traces 3 are arranged on an area of the sensor body 1 facing the measured medium. The sensor body 1 includes, furthermore, plug contacts 4 for establishing electrical contact with an electronics unit (not shown) capable of supplying the conductive traces 3 with electrical voltage, in order to determine the conductivity of the medium. Metallized contact feedthroughs 2 provide electrical connection between the conductive traces 3 and the plug contacts 4 . Furthermore, the sensor body 1 includes a recess equipped with a temperature sensor 5 for measuring the temperature of the measured medium.

The sensor body 1 is produced by injection molding of a thermoplastic plastic doped with a laser activatable, metal compound. The resulting sensor body 1 is structured by means of a laser using the LDS method. The structuring produces conductive metal nuclei from the metal compound. The sensor body is then immersed in a metal plating bath to form the conductive traces 3 on the sensor body 1 , wherein the conductive traces 3 serve as electrodes of the conductivity sensor 6 .

After the above manufacturing steps, the sensor body 1 is injection mold coated with plastic, in order to make the conductivity sensor 6 even more hygienic and so to assure optimum process compatibility.

FIG. 2 shows a perspective view of a longitudinal section of a conductivity sensor 6 of FIG. 1 from a side of the sensor body 1 facing the measured medium. The conductive traces 3 are circularly and annularly embodied.

The manufacturing process for a conductive conductivity sensor 6 makes unnecessary the applying of conductive traces and metallized contact feedthroughs in some alternate procedure producing an additional layer on the contact feedthroughs 2 . The LDS method means that no additional layers are applied on the sensor body 1 . Therefore, no gaps result, which are difficult to clean and to sterilize. For this reason, the conductivity sensor manufactured by means of the LDS method is more hygienic than conventional conductivity sensors from the state of the art.

FIG. 3 shows a plan view onto the interior of a conductivity sensor of FIG. 1 .