WO2019166232A1

WO2019166232A1 - Electronic circuit for generating, preparing and/or processing high-frequency signals

Info

Publication number: WO2019166232A1
Application number: PCT/EP2019/053702
Authority: WO
Inventors: Dietmar Birgel; Bernhard Michalski; Mario Leonhardt; Alexander Bannwarth
Original assignee: Endress+Hauser SE+Co. KG
Priority date: 2018-03-01
Filing date: 2019-02-14
Publication date: 2019-09-06
Also published as: DE102018104662A1

Abstract

The invention relates to an electronic circuit with improved signal transmission properties for generating, preparing and/or processing high frequency signals comprising frequencies of 20 GHz or higher, having a circuit board (1) and one or more HF components (3) each designed for a frequency range of 20 GHz or higher and soldered to the circuit board (1), wherein the connections (5) of the HF components are connected by means of a respective first solder joint (7) to an associated circuit board connection (9) arranged on the circuit board (1), the electronic circuit being characterized in that the first solder joints (7) are each formed as a generated first solder joint (7) by means of a lead-free first solder comprising a bismuth content of 50% or more by means of a reflow soldering method, specifically by vacuum soldering or by vapour phase soldering.

Description

Electronic circuit for generating, processing and / or processing high-frequency signals

The invention relates to an electronic circuit for generating, processing and / or processing of frequencies greater than or equal to 20 GHz, high-frequency signals, with

a circuit board, and

one or more in each case designed for a frequency range of greater than or equal to 20 GHz, soldered on the circuit board RF components whose RF component connections each by means of a first soldering with an associated on the circuit board

arranged printed circuit board connection are connected.

Circuits of the type mentioned in the introduction are e.g. used in measuring devices that are used, for example, in industrial measurement and control technology.

An example of this are fill level measuring devices operating according to the transit time principle for measuring a filling level of a filling material located in a container. These gauges generate high-frequency signals that are transmitted through an antenna or along a

Waveguide are sent in the direction of the medium and their reflected on a surface of the product echo signals are received after a dependent on the level of the filling material term as received signals, based on which then the duration or the level is determined. Depending on the meter type, it will be very high-frequency

Transmit signals, such as Microwave signals with frequencies greater than or equal to 20 GHz, used.

In these measuring devices are electronic circuits of the type mentioned for generating the transmission signals, as well as for the preparation and / or processing of

Reception signals used.

In circuits of the type mentioned above, it applies through the circuit, esp. Their transmission behavior and / or their dynamics, in terms of the function of

Circuit unwanted changes generated by the circuit,

processed and / or processed high-frequency signals as low as possible.

In that regard, the frequency-dependent attenuation of high-frequency signals, which is caused by the dynamics of the circuit, plays an important role in the measuring devices mentioned above as an application example, since the attenuation directly affects the achievable

Measuring accuracy affects. To improve the signal transmission characteristics are in these circuits today particularly suitable for use in high-frequency engineering

PCB materials used. Additionally, the circuit layout is optimized to minimize circuit-related unwanted signal variations. The latter, however, is the more difficult the higher frequency the signals are.

Investigations by the applicant have shown, however, that not only the printed circuit board material used and the circuit layout, but in addition also provide the provided on the circuit board, the electrical connection of the individual components causing soldering on the transmission behavior of the circuit. It has been found, inter alia, that circuits whose components are manufactured using a lead-free solder commonly used today, e.g. a well-known under the name SAC-Lot tin-silver-copper solder have been soldered, a significantly larger frequency-dependent attenuation of transmitted via the soldering high-frequency signals cause identically constructed circuits whose components

Use of a lead-containing solder have been soldered.

For the protection of the environment and of persons, the use of heavy metals, e.g. Lead or mercury to avoid in electronic circuits. The RoHS Directive (Restriction of Certain Hazardous Substances) of the

European Union, which prohibits the use of certain dangerous substances, such as Lead, banned in the electrical industry. Accordingly, all components used in circuits of the type mentioned above are soldered today using a lead-free solder.

It is an object of the invention to provide a circuit for generating, processing and / or processing frequencies of equal to 20 GHz high-frequency signals having improved signal transmission characteristics.

This object is achieved by an electronic circuit for generating, processing and / or processing frequencies of equal to 20 GHz, high-frequency signals, with

a circuit board, and

arranged printed circuit board connection are connected

solved, which is characterized in that the first solders are each formed as a first soldering produced by means of a reflow soldering method, namely a bismuth component of greater than or equal to 50%, by means of a reflow soldering method, namely by vacuum soldering or by vapor phase soldering.

Circuits according to the invention have the advantage that, due to the high proportion of bismuth in the first solder and the reflow soldering method used to produce them, their first solderings transmit only a relatively small amount of attenuation over the respective soldering in a comparatively large frequency range

cause high-frequency signals.

A first development is characterized in that the first solders are formed as first solders produced by means of an indium portion of greater than or equal to 2% and / or an indium portion of 2% to 10% comprising the first solder.

Preferred embodiments are characterized in that the first solderings

are formed by means of a tin, bismuth and silver comprehensive lead-free, first solder produced first solder, or

are formed by means of a tin, bismuth and indium comprehensive lead-free, first solder produced first soldering.

A second development is characterized in that the circuit comprises at least one further component, the terminals of which are each connected by means of a soldering process carried out by means of a lead-free second solder soldering process with an associated arranged on the circuit board PCB connection, wherein the second Lot has a melting temperature that is greater than one

Melting temperature of the first solder is.

An embodiment of the second development is characterized in that the further components comprise at least one soldered by means of a reflow soldering and / or designed as an SMD component component.

An embodiment of the second development is characterized in that the second solderings are formed as second solderings produced by means of a tin, silver and copper SAC solder.

A refinement of the second development is characterized in that its HF components are arranged on a front side of the printed circuit board and its further components on a rear side of the printed circuit board opposite the front side of the printed circuit board. Another embodiment is characterized in that the circuit is formed as part of a working according to the transit time principle level gauge.

Furthermore, the invention comprises a method for producing a

according to the invention, characterized in that the first solderings are produced by:

the printed circuit board connections provided on the printed circuit board for the HF components are each printed with the first solder provided as solder paste,

the circuit board is equipped with the RF components of the circuit, and

the first solderings are produced by means of a reflow soldering method, namely by vacuum soldering or by vapor phase soldering.

A first development of the method is characterized in that the

melted first solder during the reflow soldering process for a period greater than or equal to 100 seconds or a period of

For 100 seconds to 150 seconds at temperatures above its liquidus temperature.

A second development of the method for producing a circuit according to the second embodiment is characterized in that the other components are soldered to the circuit board before the RF components are soldered onto the circuit board.

A further development of the last-mentioned further development is characterized in that printed circuit board connections provided on the back side of the printed circuit board for additional components of the circuit to be soldered on the back side are each printed with the second solder provided as solder paste, the rear side of the printed circuit board with the soldering on it further components is fitted and the associated second soldering is produced by means of a reflow soldering process,

the circuit board is turned, and

arranged on the front of the circuit board, for on the front

aufzulötende RF components of the circuit provided printed circuit board connections are each printed with the provided as solder paste first solder, the front of the circuit board is mounted with the aufzulötenden RF components and the associated first soldering be produced by vacuum soldering or by vapor phase soldering.

The invention and further advantages will now be explained in more detail with reference to the figure of the drawing, in which an embodiment is shown.

Fig. 1 shows: a section of an electronic circuit. The invention relates to an electronic circuit for generating, processing and / or processing of frequencies greater than or equal to 20 GHz, high-frequency signals comprising a printed circuit board 1 and at least one designed for a frequency range greater than 20 GHz RF component 3.

1 shows by way of example a section of such an electronic circuit, which shows a printed circuit board region of a printed circuit board 1, on which at least one HF component 3 is arranged. Of course, the circuit may comprise further arranged on the circuit board 1 RF components 3.

In the present case, signals which comprise frequencies of greater than or equal to 20 GHz are referred to as high-frequency signals. These high-frequency signals can, for example, frequencies in a frequency range of

20 GHz to 100 GHz.

In the present case, high-frequency components designed for a frequency range greater than or equal to 20 GHz are referred to as HF components 3. These include e.g. for the production,

Transmission, modulation, filtering and / or processing of high-frequency signals components such. designed for this frequency range and / or operating in this frequency range oscillators, mixers, amplifiers, filters and / or duplexers.

The RF components 3 of the circuit are each formed as soldered onto the circuit board 1 components whose RF component terminals 5 are each connected by means of a first soldering 7 with an associated on the circuit board 1 PCB connection 9. According to the invention, the first solders 7 are each in the form of first soldering 7 produced by means of a lead-free first bismuth component of greater than or equal to 50% by means of a reflow soldering method, namely by vacuum soldering or by vapor phase soldering.

Since the first solder used is a lead-free solder which has a bismuth content of greater than or equal to 50%, the first solderings 7 produced by means of the first solder also have a correspondingly high proportion of bismuth.

The percentages used herein to quantify proportions of individual solder components contained in a lot each denote the weight fraction of each component in the total weight of the solder.

The circuit has the aforementioned advantage. In this case, the first solderings can be formed, for example, as solderings produced by means of a tin, bismuth, and silver, lead-free, first solder.

Optionally, the signal transmission characteristics of circuits according to the invention for frequencies greater than or equal to 20 GHz can be further improved by providing the first solders 7 as lead-free first by means of an indium content greater than or equal to 2% and / or from 2% to 10% Lots produced first Lötungen 7 are formed. An example of this are first solders 7 produced by means of tin, bismuth and indium-comprising, lead-free, first solder.

The HF components 3 of the circuit are preferably each formed as SMD components. The well-known under the English name 'Surface Mounted Devices' SMD components offer over wired components the advantage that through their

Using the high frequency signals under circumstances changing inductors, as e.g. can be reduced by connecting wires of leaded components.

Alternatively or additionally, the RF components 3 of the circuit are preferably all arranged on a front side of the printed circuit board 1. In terms of manufacturing technology, this offers the advantage that the first solderings 7 of the circuit can all be soldered in a single reflow soldering process. Alternatively, however, it is also possible to use the HF components 3 of circuits which have at least one on the front side and / or at least one on the front side opposite the rear side of the

Circuit board 1 arranged RF component 3 comprehensive, to solder selectively.

Optionally, the circuit according to the invention may comprise at least one further component 11 in addition to its at least one HF component 3. As an example of this, FIG. 1 shows, by way of example, three further components 1 1 soldered onto the printed circuit board 1.

In these circuits, the other components 1 1 each include terminals 13, which are each connected by means of a second solder produced by means of a second solder 15 with an associated circuit board connection 17. In this case, to produce the second solder 15, preferably a lead-free solder is used as the second solder, which has a higher melting temperature than the first solder used to produce the first solder 7. It is to be assumed that the melting point is less than or equal to 140 ° C for the first lot due to the contained therein, the melting point, high bismuth proportion of greater than or equal to 50%. Correspondingly, suitable solders comprising tin, silver and copper are suitable as the second solder, for example under the abbreviation SAC-Lot. Circuits which, in addition to their at least one HF component 3, comprise at least one further component 1 1, are preferably designed such that their RF components 3 are each arranged on a front side of the printed circuit board, and their further components 1 1 each on one of Front of the circuit board 1 opposite the back of the circuit board 1 are arranged. In this case, the other components 1 1 are preferably formed as soldered onto the circuit board 1 SMD components.

Circuitries according to the invention are preferably produced by printing the printed circuit board connections 9 provided on the printed circuit board 1 for which their HF components 3 are each printed with the first solder provided as solder paste. Subsequently, the circuit board 1 is equipped with the RF components 3 of the circuit and the first solder 7 produced by means of a reflow soldering.

As a reflow soldering method, a vapor-phase soldering method or a vacuum soldering method is preferably used. In vapor phase soldering, the printed circuit board is exposed to an initially gaseous medium which condenses on the surface of the printed circuit board 1, where its heat of condensation contributes to the heating of the solder joint.

In the vacuum soldering process, the assembled printed circuit board is placed in a vacuum soldering furnace, where the solder joints are heated by radiant heat.

These methods offer over other soldering methods, e.g. convection soldering, the advantage that this can produce relatively smoother first soldering 7 with smoother surfaces that form more homogeneous transitions to the joining partners. Both lead to frequencies greater than or equal to 20 GHz signals to improve the signal transmission characteristics of the first Soltungen 7, esp. To reduce the frequency caused by the first Solder 7 frequency-dependent attenuation of transmitted over the first Soltungen 7 signals.

In addition, the comparatively low melting temperature of the first solder offers the advantage that the reflow soldering process is correspondingly lower

Process temperatures can be performed. The latter offers the advantage that during the solidification of the first solderings 7 less defects, such as e.g. Voids or

Shrinking cracks, form, as would be the case at higher process temperatures.

This in turn also contributes to the formation of advantageous for the signal transmission characteristics of the circuit smooth surfaces of the first solder 7.

In this context, an indium-containing first solders offer the additional advantage that indium the ductility of the first solder and / or the first Soldering increased. Higher ductility promotes the formation of smoother surfaces and counteracts the formation of shrinkage cracks.

In addition, lower process temperatures offer the advantage that the HF components 3 are subjected to lower thermal and, if appropriate, lower thermomechanical loads both during soldering and during the subsequent solidification of the solder joint.

In carrying out the reflow soldering method, it is preferable to carry out such a method that a temperature profile is passed through in which the first solder is melted and subsequently held at temperatures above its liquidus temperature for a period of time. In connection with highly bismuth-containing solders, it is preferable to use a comparatively long period of time, e.g. a period of greater than or equal

100 seconds, e.g. a period of 100 seconds to 150 seconds.

This comparatively long period offers the advantage that comparatively much time is available to the molten first solder for wetting the HF component connections 5 and the associated printed circuit board connections 9. This leads to an im

Substantially complete or at least almost complete wetting of the

Surfaces of these connections. As a result, after the termination of the soldering process exposed and thus the signal transmission characteristics of the circuit adversely affecting pads are largely avoided.

In addition, a longer period of time over which the first solder is maintained above its liquidus temperature promotes the formation of more homogeneous first solders 7 and reduces the formation of voids trapped in the first solders 7.

In the production of at least one RF component 3 and at least one further component 1 1 comprehensive circuit is preferably such method, in a first

Step further, the other components 1 1 are soldered to the back of the circuit board 1. For this purpose, arranged on the back of the circuit board 1, provided for the other components 1 1 PCB connectors 17 are each printed with the solder provided as a second solder. Subsequently, the back of the circuit board 1 is equipped with the other components 1 1 of the circuit and generates the second solder 7 by means of a reflow soldering.

Here, too, such a method is preferably carried out such that a temperature profile is run through, in which the second solder is melted and then kept at temperatures above its liquidus temperature for a period of time. there In connection with the aforementioned SAC solders, a comparatively short period of time, such as a period of less than or equal to 50 seconds, eg a period of 10 seconds to 50 seconds, is preferably used. Subsequently, the circuit board 1 is turned and soldered in a second process step, the RF components 3 in the manner described above on the front of the circuit board 1. In this case, the higher melting temperature of the second solder prevents the previously produced second solderings 15 from being damaged.

Where a division of the components to be arranged on the circuit board 1 in the on

Front arranged RF components 3 and arranged on the back of further component 1 1 can not or only incomplete can be made, single or all RF components 3 following the soldering of the other components 1 1 as needed selectively to the appropriate positions the front and / or the back of the circuit board 1 are soldered.

Circuits according to the invention can e.g. as part of a after the

Runtime principle working level gauge to be formed. After this

Runtime operating level gauge, such. the in the

The level gauges described in the introduction, which comprise one or more circuits according to the invention, offer the advantage that they have the signal transmission characteristics improved therein due to the first solders 7

used circuit or the circuits used therein and / or the

comparatively low attenuation of transmitted over the first solder 7

Signals have improved measurement accuracy.

LIST OF REFERENCE NUMBERS

I circuit board

3 RF component

5 HF component connection

7 first soldering

9 PCB connection

I I another component

13 connection

15 second soldering

17 PCB connection

Claims

claims

1. Electronic circuit for generating, processing and / or processing of

Frequencies greater than or equal to 20 GHz, high-frequency signals, with

a printed circuit board (1), and

one or more in each case designed for a frequency range greater than or equal to 20 GHz, soldered on the circuit board (1) RF components (3) whose RF component connections (5) each by means of a first soldering (7) with an associated on the Printed circuit board (1) arranged PCB connection (9) are connected,

characterized in that

the first solders (7) are in each case formed as first soldering (7) produced by means of a reflow soldering method, namely by means of vacuum soldering or by vapor phase soldering, by means of a lead-free, a bismuth component of greater than or equal to 50%.

2. An electronic circuit according to claim 1, characterized in that the first solderings (7) as by means of an indium portion of greater than or equal to 2% and / or an indium portion of 2% to 10% comprising first solder produced first solderings ( 7) are formed.

3. Electronic circuit according to claim 1 to 2, characterized in that the first solderings (7)

are formed by means of a tin, bismuth and silver comprehensive lead-free, first solder produced first solderings (7), or

are formed by means of a tin, bismuth and indium comprehensive lead-free, first solder produced first soldering (7).

4. An electronic circuit according to claim 1 to 3, characterized in that the circuit comprises at least one further component (1 1), the terminals (13) in each case by means of a second soldering (15) generated by means of a lead-free second solder soldering process an associated on the circuit board (1) arranged printed circuit board connection (17) are connected, wherein the second solder a

Melting temperature which is greater than a melting temperature of the first solder.

5. An electronic circuit according to claim 4, characterized in that the further components (1 1) comprise at least one soldered by means of a reflow soldering and / or formed as an SMD component component.

6. An electronic circuit according to claim 4 to 5, characterized in that the second Lötungen (15) as formed by means of a tin, silver and copper SAC solder second Lötungen (15) are formed.

7. An electronic circuit according to claim 4 to 6, characterized in that the RF components (3) on a front side of the printed circuit board (1) and its further components (1 1) on one of the front side of the printed circuit board (1) opposite the back of the circuit board (1) are arranged.

8. An electronic circuit according to claim 1 to 7, characterized in that the circuit as part of a working according to the transit time principle

Level gauge is designed.

9. A method for producing an electronic circuit according to claim 1 to 8, characterized in that the first solderings (7) are produced by:

the printed circuit board connections (9) provided on the printed circuit board (1) for the HF components (3) are each printed with the first solder provided as solder paste; the printed circuit board (1) is equipped with the HF components (3) of the circuit , and the first solderings (7) by means of a reflow soldering, namely by

Vacuum brazing or by vapor phase soldering produced.

10. The method according to claim 9, characterized in that the molten first solder during the reflow soldering over a period of greater than or equal to 100 seconds or a period of

For 100 seconds to 150 seconds at temperatures above its liquidus temperature.

1 1. A method according to claim 9 to 10 for producing a circuit according to claim 4 to 7, characterized in that the further components (1 1) are soldered to the circuit board (1) before the RF components (3) on the circuit board ( 1) are soldered.

12. The method according to claim 1 1, characterized in that

on the back of the circuit board (1) arranged, for on the back

aufzulötende other components (1 1) of the circuit provided printed circuit board connectors (17) are each printed with the solder provided as solder second solder, the back of the circuit board (1) with the aufzulötenden further components (1 1) is fitted and the associated second Solderings (15) are produced by means of a reflow soldering process,

the circuit board (1) is turned, and on the front side of the printed circuit board (1) arranged for on the front aufzulötende RF components (3) of the circuit provided printed circuit board connectors (17) are each printed with the provided as solder paste first solder, the front of the circuit board (1) with the mounted on it to be soldered RF components (3) and the associated first soldering (7) are produced by vacuum soldering or by vapor phase soldering.