DE102017209297A1 - Method for producing an electrical conductor track on a plastic carrier and sensor module comprising a plastic carrier with a conductor track produced in this way - Google Patents

Abstract

The invention relates to a method for producing an electrical conductor track (5) on a plastic carrier (1), in which in a first method step (201) a copper conductor track (2) is applied to the plastic carrier (1) by means of a jet-bonded thermal spraying method. It is proposed to coat the copper conductor track (2) after its production on its side facing away from the plastic carrier (1) (21) with a continuous layer (3) made of tin or a tin-containing metal alloy.

Description

State of the art

Various forms of electrical connection techniques using printed conductors on plastic carriers are known in the prior art. In particular in electronic control units, control modules are increasingly being used which, in addition to the electrical wiring of circuit components, also use sensors or actuators which are to be contacted via conductor tracks. This is increasingly used, for example, in transmission control technology. The known control devices use, inter alia, conventional printed circuit boards with a carrier material made of glass-fiber-reinforced epoxy resin having printed conductors on several layers of the carrier material. Furthermore, control modules are known which use flexible printed circuit boards or plastic encapsulated stamped grid. Furthermore, control devices are known which use a two-component MID (Molded Interconnect Device), in which injection-molded plastic components are provided with metallic conductor tracks.

For some time, alternative methods for the production of electrical conductors on plastic carriers have become known, in which a thermal injection process is used. For example, this describes US 5,891,527 a mask-bound plasma spraying process for producing printed conductors on plastic substrates.

In the last ten years, methods for the production of electrical conductors on plastic carriers have also been discussed which apply conductor tracks to a plastic carrier by means of a jet-bonded thermal spraying method. In a beam-bound method, a directed material flow is deliberately guided over the plastic carrier. At the place of impact of the material flow, the conductor path is formed. In this sense, the material is applied quasi by "sputtering" on the plastic carrier. Here, especially copper is used. But also tin and other metals are used. The metal particles are applied by means of a special spray head and by means of kinetic energy and heat to the plastic carrier. Mask steps are not used. The process is also commonly referred to as thermal spraying. The heated metal particles can be partially or completely melted. Due to their kinetic momentum, the particles can at least partially penetrate into the surface of the plastic carrier. These methods include, but are not limited to, flame spraying, cold gas spraying and, more particularly, plasma spraying.

Disclosure of the invention

The invention relates to a method for producing an electrical conductor on a plastic carrier, wherein in a first method step by means of a jet-bonded thermal spraying method, a copper conductor is applied to the plastic carrier. According to the invention, the copper conductor track is coated after its production on its side remote from the plastic carrier side with a continuous layer of tin or a tin-containing metal alloy. Furthermore, the invention relates to a sensor assembly, comprising a plastic carrier as a sensor dome with an electrical conductor produced on the outside of the plastic carrier according to said method.

Advantages of the invention

The copper conductor tracks produced on plastic carriers by means of the known jet-bonded thermal spraying methods are relatively porous due to their production. The electrical conductivity of the copper interconnects is therefore only 10-20% of the electrical conductivity of pure copper. As a result, the ability of this trace to conduct strong currents is relatively low and the electrical resistance quite large. In addition, despite the porosity, the electrical conductivity of tin conductor tracks which are produced by means of the known jet-bonded thermal spraying method is still 50% of the electrical conductivity of pure tin, but the tin conductor tracks can not be further contacted by soldering because the tin melted during soldering droplets forms and can dissolve again from the plastic carrier. Due to the porosity of the tracks, they can be severely attacked by aggressive media. The latter is very disadvantageous especially for transmission control modules, since they are often exposed directly to the aggressive transmission fluid.

The proposed method avoids these disadvantages by coating a copper conductor track after its production on its side facing away from the plastic carrier with a continuous layer of tin or a tin-containing metal alloy. This advantageously increases the electrical conductivity and allows the attachment of Lötkontaktierungen on the conductor track. In addition, the continuous layer provides better protection against aggressive media in relation to a porous surface.

Advantageously, the method for producing an electrical conductor on a plastic carrier can be used in many ways. In addition to the production of multi-conductor printed circuit boards is electronic The method is particularly suitable for mounting printed conductors on plastic carriers of sensors, plug parts or actuator assemblies and in particular offers a cost-effective alternative to the relatively expensive and technically complex two-component MID method.

Advantageous embodiments and further developments of the invention are made possible by the features contained in the dependent claims.

In the first method step, a plasma spraying method for application of the copper conductor track can advantageously be used as the beam-bonded thermal spraying method. In a jet-bonded plasma spraying process, a spray head movable relative to the plastic carrier is filled with a shaping gas, for example N ₂ H ₂ . The carrier gas nitrogen N _{2 is} supplied to the spray head, which is mixed with powdered copper particles. The spray head includes a plasma torch which generates a highly heated plasma while supplying electrical energy and forming gas. In the plasma, the pulverulent copper particles sprayed into the spray head are completely or partially melted. The plasma stream of the spray head entrains the molten copper particles and throws them onto the plastic carrier to be coated. The method is known as such and can be used inexpensively.

In a first embodiment of the method, the copper conductor track can, after its production, particularly advantageously be on its side remote from the plastic carrier in a second jet-bonded spray method, which may also be a jet-bonded plasma spray method, with a tin layer, for example 20 to 500 micrometers thick In a subsequent process step, this tin layer is subsequently melted and compacted so that a continuous layer of tin or a tin-containing metal alloy is formed. The tin-melted by heating condenses, whereby the original porosity is removed.

The heating can be carried out advantageously example meadow in a reflow oven, wherein the tin melts and arranges in a dense microstructure on the underlying copper conductor cock. The heating in the reflow oven can be done if the plastic carrier can withstand the high temperatures in the range of, for example, about 232 ° C. However, the melting and densification can also be carried out by means of a laser beam directed via the conductor track or another suitable heat source, which travels the same path which the plasma spray head, which is used for the application of the copper layer or tin layer, has previously traveled. In this case, only the metal of the conductor track is advantageously heated and not additionally the plastic of the carrier material next to the conductor track. Furthermore, the conductor can also be heated in a vapor phase soldering, in which the tin melts. This has the advantage that the related heat transfer oil condenses only on the tin layer of the conductor track and transfers the heat there, while the condensation on the plastic support due to the lower heat capacity and thermal conductivity is lower, so that the plastic is less stressed.

In a second advantageous embodiment of the method, it is provided to provide the copper interconnect after its production on its side facing away from the plastic carrier side in a wave soldering with a continuous layer of a tin-containing metal alloy, in particular with a solder layer. For this purpose, the plastic carrier part is preferably designed to be relatively flat, so that the soldering wave can be guided over the surface of the plastic carrier part. For a three-dimensional geometry, a relatively small solder wave can be used to achieve a localized solder application. For this purpose, the plastic carrier member is moved by means of a device over the solder wave, that the copper conductor tracks come into contact with the solder wave.

In a third advantageous embodiment of the method, it is provided to coat the copper conductor track after its production on its side facing away from the plastic carrier side galvanically with a continuous layer of tin or a tin-containing metal alloy. As with a printed circuit board manufacturing process, the workpiece is coated with the copper conductor in tin plating technique, wherein the tin is deposited in dense form on the copper conductor.

It is particularly advantageous if the electrical conductor track on its side facing away from the plastic carrier over the continuous layer of tin or an alloy containing tin in a further process step is provided with a protective cover. The protective cover preferably covers the electrical conductor on its side facing away from the plastic carrier side and their side surfaces completely to the outside. As a result, aggressive substances can not come into direct contact with the conductor track and it is avoided that an aggressive medium penetrates into any possibly still locally existing porous area.

Preferably, a solder mask is used as a protective cover, which on the Plastic carrier adheres well. This is the case in particular when a thermoset or epoxy resin substrate is used as the plastic carrier.

In the plastic carrier, an electrical connection element of an electrical component can be embedded, which is exposed at one end flush to the outside of the plastic carrier. The copper conductor track can advantageously be applied to the plastic carrier over the exposed end such that the copper conductor track is electrically conductively connected to the electrical connection element. This is particularly appropriate if the method produces a sensor module which comprises a plastic carrier as a sensor dome with an electrical conductor track produced on the outside of the plastic carrier.

list of figures

• 1a to 1c show cross sections through an electrical assembly in which according to a first embodiment of the method according to the invention an electrical conductor is applied to a plastic carrier,
• 2 shows a flow chart of the method,
• 3 shows a sensor assembly with a plastic carrier as a sensor dome and with an electrical conductor produced on the outside of the plastic carrier according to the inventive method.

Embodiments of the invention

The 1a to 1c show for a first embodiment of the method according to the invention various stages of the production of an electrical conductor on a plastic carrier. 2 shows an associated flowchart of the method. This is done first at the starting point 200 of the process a plastic carrier 1 , For example, a support plate made of thermoset or epoxy resin provided. As in 1 is shown in a first step 201 on a surface 11 of the plastic carrier 1 by means of a jet-bonded thermal plasma spraying method, a copper conductor track 2 produced. For this purpose, a movable spray head 100 in the direction of the arrow a in 1a emotional. The particle beam provided with copper particles 101 beats on the surface 11 down and forms a extending in the direction of arrow a copper conductor track 2 whose thickness is perpendicular to the surface 11 between 5 and 100 microns can be.

In a subsequent second process step 202 will after the production of the copper track 2 on the of the plastic carrier 1 opposite side 21 the copper interconnect in a second jet-sprayed a tin layer 3. ' applied, whose thickness can be between 20 and 500 microns.

In the following process step 203 becomes this tin layer 3. ' by heat, as in 3c represented by the reference symbol W, melted and compacted, which is in 3c due to the smaller thickness of the tin layer 3 is symbolized. The heating can be done for example in a reflow oven, by heat input by means of a guided over the conductor track laser beam or in a vapor phase soldering. Warming turns the tin layer 3. ' transformed from a porous structure into a compacted, compact structure having no cracks or gaps. The fact that tin can be melted at a relatively low temperature, the porosity of the tin layer 3. ' be easily eliminated. Since tin adheres well to copper and also forms intermetallic phases, the molten tin runs exactly on the copper conductor 2 together. The end result is a coherent layer 3 of tin or a tin-containing metal alloy over the copper track. Connected in this context means that the metal structure corresponds to the metallic structure of pure tin or the metallic structure of a tin-containing alloy without cracks, gaps and porous intermediate areas. The copper track 2 with the contiguous tin layer disposed above 3 forms the in 1c illustrated electrical conductor 5 , which is ready for power line.

The tin layer 3 can the copper track 2 on her from the plastic carrier 1 opposite side 21 in particular completely cover. In this case, the copper track is 2 completely covered with tin or a tin-containing alloy in the direction of their longitudinal extension over their entire length.

Alternatively to the in the 1a to 1c In the embodiment shown, the copper conductor track 2 after its production on its side facing away from the plastic carrier side 21 also be provided in a wave soldering with a continuous layer of a tin-containing metal alloy, in particular with a solder layer, or are galvanically coated with a continuous layer of tin or a tin-containing metal alloy.

In the last procedural step 204 of the 2 becomes the electrical conductor 5 on her from the plastic carrier 1 opposite side over the continuous layer 3 of tin or a tin-containing alloy with a protective cover 4 Mistake. The protective cover 4 can the electrical conductor 5 on her from the Plastic carrier 1 cover the opposite side and their side surfaces completely outwards. This can be done for example by painting. The protective cover 4 may include, for example, a solder mask. Epoxy resin solder resists offer particularly high chemical resistance to aggressive substances.

With the method presented here for producing an electrical conductor on a plastic carrier, a single or multiple conductor tracks can be applied to the same plastic carrier.

3 shows one on a circuit board 40 mounted sensor module 60 , For example, it may be a speed sensor. The sensor assembly 60 includes a plastic carrier 1 acting as sensor dome 10 is trained. The sensor dome 10 includes an electrical component designed as a sensor ASIC 20 attached to one of the circuit board 40 repellent end of the sensor dome 10 in the plastic of the sensor dome 10 injected. In the sensor dome 10 and thus in the plastic carrier 1 are electrical connection elements 25 of the electrical component 20 embedded with theirs of the components 20 repellent ends flush (that is largely without steps and edges) on a circumferential outer side 11 of the sensor dome 10 exposed. As with the enlarged section of the 3 is clearly visible, is a copper conductor produced by the method described above 2 so on the outside 11 of the sensor dome 10 over the respective exposed end of a connection element 25 applied that to the copper conductor 2 with the electrical connection element 25 is electrically connected. Over the copper track 2 is the coherent layer 3 made of tin or a tin-containing metal alloy. The copper track 2 and the coherent layer 3 Of tin or a tin-containing metal alloy together form an electrical conductor 5 , This track 5 is with a protective cover 4 , For example, a paint, especially a solder mask or a polymer coating against short circuits and covered as protection against contact.

The sensor assembly can be on a printed circuit board 40 be attached, which of the connecting elements 25 opposite end of the track 5 with a conductor track arranged on the printed circuit board 41 or a contact surface arranged there by means of a solder application 42 on one not with the protective cover 4 provided end portion of the conductor track 5 can be electrically connected. The circuit board 40 can continue with a potting material 50 Be covered, for example, a thermosetting or epoxy resin potting, with the device 20 provided end of the sensor dome 10 from the potting material 50 protrudes.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5891527 [0002]

Claims (11)

Method for producing an electrical conductor track (5) on a plastic carrier (1), in which in a first method step (201) a copper conductor track (2) is applied to the plastic carrier (1) by means of a jet-bonded thermal spraying method, characterized 2) after its production on its side facing away from the plastic carrier (1) side (21) with a continuous layer (3) of tin or a tin-containing metal alloy is coated. Method according to Claim 1 , characterized in that a plasma spraying method is used as the beam-bonded thermal spraying method. Method according to Claim 1 , characterized in that the copper conductor track (2) after its production on its side facing away from the plastic carrier (1) side (21) in a second jet-sprayed method (202) with a tin layer (3 ') is provided and this tin layer (3') is melted and compacted in a subsequent process step (203) and thus forms the continuous layer (3) of tin or a tin-containing metal alloy. Method according to Claim 3 , characterized in that the following step (203) of melting and compacting the tin layer (3 ') by a heating process in a reflow oven or by heat input by means of a guided over the conductor track laser beam or in a vapor phase soldering. Method according to Claim 1 , characterized in that the copper conductor track (2) after its preparation on its side remote from the plastic carrier (1) (21) in a wave soldering with a continuous layer (3) of a tin-containing metal alloy, in particular with a solder layer is provided. Method according to Claim 1 , characterized in that the copper conductor track (2) after its preparation on its side facing away from the plastic carrier (1) side (21) is galvanically coated with a continuous layer (3) made of tin or a tin-containing metal alloy. Method according to one of the preceding claims, characterized in that the electrical conductor track (5) on its side facing away from the plastic carrier (1) (21) over the continuous layer (3) made of tin or an alloy containing tin in a further process step (204 ) is provided with a protective cover (4). Method according to Claim 7 , characterized in that the protective cover (4) covers the electrical conductor track (5) on its side facing away from the plastic carrier (1) side and their side surfaces completely outwards. Method according to Claim 7 or 8th Characterized in that the protective cover (4) is a solder resist. Method according to one of Claims 1 to 9 , characterized in that in the plastic carrier (1) an electrical connection element (25) of an electrical component (20) is embedded, which is flush with one end on the outer side (11) of the plastic carrier (1) and in that the copper conductor track (2) in such a way on the plastic carrier (1) over the exposed end is applied, that the copper conductor track (2) with the electrical connection element (25) is electrically connected. Sensor assembly (60), comprising a plastic carrier (1) provided sensor dome (10) with one on the outside (11) of the plastic carrier (1) according to the method of one of Claims 1 to 10 produced electrical conductor (5).

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