EP3494764A1

EP3494764A1 - Printed circuit board and sensor

Info

Publication number: EP3494764A1
Application number: EP17739252.9A
Authority: EP
Inventors: Erich Mattmann; Robert Peter; Waldemar Brinkis; Martin Maasz; Burkhard Dasbach
Original assignee: Continental Automotive GmbH
Current assignee: Vitesco Technologies GmbH
Priority date: 2016-08-02
Filing date: 2017-07-12
Publication date: 2019-06-12
Also published as: US20190200456A1; CN109644565A; KR102163147B1; KR20190023107A; US10791630B2; CN109644565B; WO2018024451A1; DE102016214277A1

Abstract

The invention relates to a printed circuit board comprising conductor tracks (2) formed on one side of a substrate (1), wherein the substrate (1) can be connected integrally to a covering to protect the conductor tracks (2) on a contact surface (2). The substrate comprises a step (3), which forms a barrier with respect to an additive for promoting the integral connection, in order to prevent wetting of the conductor tracks with the additive. The invention further relates to a sensor comprising such a printed circuit board, for example for use in a fuel level measuring system of a vehicle.

Description

description

Circuit Board and Sensor The present invention relates to a circuit board and a sensor having such a circuit board.

According to the prior art, so-called magnetic, passive position sensors are known, which are used in a fuel tank of a motor vehicle for fuel level detection. Such sensors are also known as MAPPS (MAgnetic Passive Position Sensor). Such a sensor includes a printed circuit board which is equipped on one side of a substrate with conductor tracks and a contact spring structure, wherein the contact spring structure is contacted depending on the fuel level of the tank by means of a magnet with the conductor tracks.

The interconnects and the contact spring structure are very fine and therefore protect against contamination and corrosion. For this reason, stocked with the conductor tracks and the contact spring structure side of the substrate is liquid ^¬ tight manner and hermetically sealed off. Therefore, such a sensor is independent of the fuel composition and thus equally suitable for all types of fuel. Also provides a sensor of a so-called closed system. Conventional open systems, however, without such a con ^¬ tact spring structure are protected by special alloys to corrosion in order to use them in an aggressive medium, such as gasoline or diesel. The alloys are matched to the fuels of the respective region and their share of sulfur, ethanol or methanol.

Such a sensor or MAPPS is known for example from the patent EP 0844459 Bl, which is hereby incorporated by reference in this application. For hermetic encapsulation of the MAPPS, the circuit board is materially connected to a cover or a cover, for example by soldering. When soldering a flux is added as an adjuvant for cohesive connection, which allows a better wetting of the contact or connecting surface of the circuit board or the substrate of the circuit board with a solder. However, the use of such an adjuvant may result in undesirable wetting of other surfaces of the circuit board side to be encapsulated than the said contact or connection surface, which undesired wetting may impair the contacting of the interconnects by contact spring structure.

An object of the present invention is therefore to prevent such impairments.

This object is achieved by claim 1. The claims 13, 14 and 15 provide a sensor with such a circuit board, a fuel level measuring system with such a sensor and a vehicle with such a fuel level measurement system under protection. Advantageous embodiments of the invention are the subject of the dependent claims.

It is proposed a printed circuit board with formed on one side of a substrate tracks, wherein the substrate is integrally connected to a contact or connection surface with a cover for protecting the printed conductors or to protect the populated substrate side. The cohesive connection can - as in the MAPPS - be designed so that it ensures a hermetic seal of the assembled substrate side, so that this page is absolutely free of contamination and corrosion. In this case, the substrate has a gradation which, compared to an auxiliary material, promotes the cohesive connection Barrier forms to prevent wetting of the interconnects or the populated substrate side with the excipient. Thus, the above-mentioned undesirable wetting of other not intended for wetting surfaces of the stocked substrate side is omitted.

Staging in the sense of this application is a variation of a substrate thickness, which can be increased and / or reduced by the variation. In other words, the grading can thus be carried out substrate reinforcing and / or Sub ^¬ stratabschwächend. Positive grading increases substrate thickness, whereas negative grading reduces substrate thickness. An adjuvant in the sense of this application is one of the material ^¬ positive connection by means of a connecting material to be ^¬ a given substance, the better wetting of the contact or connection surface of the circuit board or the substrate of the printed circuit board to the connection material for the cohesive connection between the circuit board and Cover or allows a lid. In the connecting material, it can thereby be a filler material, such as a solder, Schweißzu ^¬ the filler metal or glue. In principle, however, a cohesive connection can also be achieved without such an additional material in that the surfaces to be joined together merge. In this case, at least one of the materials of the surfaces represents the connecting substance. For example, a flux is one such excipient.

A flux is an additive added during soldering in the context of this application, which effects a better wetting of a surface or contact surface of the substrate to be bonded with a solder as a bonding substance. It removes superficial oxides by chemical reaction. The same applies to oxides produced during a soldering operation by the sow ^¬ erstoff the air. Such a solder joint is only one possibility for cohesive connection. In addition or as an alternative to this, the cohesive connection between the substrate and the cover can also be achieved by gluing and / or welding. Correspondingly, a connecting substance may also be an adhesive and / or a welding filler material.

According to one embodiment, the gradation with respect to the substrate is disposed inwardly of the contact surface of the substrate. This prevents the previously described undesired wetting of other non-wetting surfaces of the assembled substrate side.

According to a further embodiment, the grading is designed to reinforce the substrate, ie that the grading in the sense of a positive grading increases the substrate thickness or thickness. According to a further embodiment, the grading comprises the contact surface of the substrate. That is, the contact surface goes directly into the gradation. In other words, the grading follows directly on the contact surface. This allows a very space-saving design of the ^{circuit board ¬} . In principle, however, a spacing of the graduation to the contact surface or layer is also conceivable. The graduation can be formed from one or more layers ^¬. The same or different materials can be used for the layers.

According to one embodiment, the grading comprises a first layer, a second layer and a third layer, wherein the first and second layers form the contact layer and the third layer forms the barrier.

The grading can be metal-containing. As a result, the grading is suitable for example for soldering with a metallic or at least metallized contact surface of the cover. According to one embodiment, the stepping is formed from a silver-containing sintering paste. In principle, the sintering paste can be any conceivable, preferably metal-containing, sintering paste which is suitable for producing such a grading.

Such a sintering paste, which may be printed on an alumina ceramic substrate, compacts and solidifies into a solid material upon drying and sintering in a sintering furnace.

By sintering or sintering is meant a solidification and compression of a sintering paste into a compact material as a result of a temperature treatment in a sintering furnace.

According to a further embodiment, the gradation is formed circumferentially around the conductor tracks. In this case, the gradation may be formed continuously encircling, so that - if necessary, such as in the MAPPS - a hermetic seal of the covered substrate side to be covered can be achieved.

Depending on how the substrate side to be covered is to be executed, the gradation can be formed along the edges of the substrate. This allows a very space-saving design of the circuit board.

The substrate may be formed from a sintered ceramic. In principle, the substrate can be made of any conceivable material which is suitable for a printed circuit board, for example in connection with the MAPPS.

It is also proposed a sensor with a cover having a circuit board of the type described above.

Furthermore, a fuel level measuring system is proposed with a sensor of the type described above.

In addition, a vehicle is proposed with a fuel level measuring system of the type described above. In the following, the invention will be explained in detail with reference to figure representations. From the subclaims and the following description of preferred embodiments, further advantageous developments of the invention result. Show:

1 shows a circuit board according to the prior art, Fig. 2 shows a modified circuit board according to the invention, Fig. 3 shows a possible step education and

Fig. 4 is a schematic representation of an arrangement of a printed circuit board and a cover or a lid. Identical or equivalent features are denoted by the same reference numerals across all figures.

Fig. 1 illustrates a known in the art circuit board 10 of a MAPPS (MAgnetic Passive Position Sensor). The printed circuit board 10 comprises a substrate 1, which is formed from an alumina sintered ceramic. The substrate 1 is printed on one side with conductor tracks 2 which can be applied in the Template ^¬ nendruck- or screen printing process. In addition, the substrate 1 has along its edges a continuous circumferential contact surface 2 or layer, which surrounds the conductor tracks 2. Both the conductor tracks 2 and the contact surface 2 or layer are formed from a metal-containing sintered paste. This is expediently the same material, such as a silver-containing sintering paste. The thickness of these layers is suitably identical. The contact surface 2 or layer is cohesively connectable to a corresponding metallic or at least metallized cover such that the printed substrate side can be hermetically sealed and consequently remains free from contamination and corrosion. 2 illustrates a further developed printed circuit board 10, in which on the side of the substrate 1 to be covered both printed circuit traces 2 made of the metal-containing sintering paste and a resistance track 8 or layer-which is not shown as such in FIG. 1-are printed. Both the tracks 2 and the resistance track 8 can be applied in stencil printing or screen printing.

Analogously to FIG. 1, the conductor tracks 2 and the resistance track 8 are surrounded by the continuous peripheral contact surface 2 or layer, which is printed along the edges of the substrate 1 in order to ensure a hermetic seal with a correspondingly ver ^¬ bindable cover. This contact surface 2 consists of the same sintering paste, which is also used for the tracks 2. At this contact surface 2 further includes a gradation 3, which is arranged with respect to the substrate 1 inwardly opposite the contact surface 2 and the surface analogous to the contact 2 is formed continuously encircling so that it surrounds the tracks 2 and the resistance track 8.

The grading 3 acts as a barrier or dam against a flux with which the contact surface 2 is wetted to promote the cohesive connection between the contact surface 2 and a corresponding contact surface of the cover by means of a solder.

FIG. 3 illustrates the edge region 7 of the substrate 1 shown in FIG. 2 in a cross-sectional view. In detail a possible execution of the graduation 3 is to be seen. The grading 3 in this case comprises the contact surface 2 or layer of the sintering paste, ie, the s the contact surface directly merges into the grading. In other words, the grading follows directly onto the contact surface, so that the substrate thickness increases or intensifies. Starting from the edge of the substrate 1, the thickness of the sintering paste changes as a result of an essentially positive step. Flank jump from Y to Y '. The width of the sintered paste corresponds to X and the width of the step corresponds to X '. In this example, Y = 0, 015mm, Y '= 0, 025mm, and X = 1, 2mm, X' = 0.7mm. The sintering paste including the contact surface portion and the gradation is formed in a single layer. For this purpose, the sintering paste is printed by means of a corresponding template or by means of a corresponding screen on the ceramic substrate. The template or the screen is formed correspondingly fine mesh, so that it or it allows such a stepped imprint on the substrate. Alternatively, the sintering paste can also be applied in layers or in layers (see Fig. 4).

FIGS. 3 and FIG. 4 illustrate this a particularly simple and at the same time effective executing a sub ^¬ stratverstärkenden grading which has the shape of a substantially positive amplification stepped substrate having at least one step or edge. In principle, however, other gradations with both positive or substrate-enhancing as well as negative or substrate weakening sections are conceivable in order to prevent the aforementioned unwanted wetting of other not intended for wetting surfaces of the assembled substrate side.

4 illustrates a multilayer structure of a sintered paste printed along the edges of the substrate 1. In this case, this sintering paste comprises a first layer 2, a second layer 2 'or reinforcing layer and a third layer 3, wherein the first and second layers 2, 2' form the contact surface section on which the third layer 3 is printed in order to act as a barrier or dam to act. The thickness of the first layer 2 corresponds to the layer thickness of the indicated conductor track 2, over which an indicated contact spring element 4 extends. The stepped sintered paste ^¬ section 2, 2 ', 3 and the conductor 2 exist suitably from the same material, for example from the aforementioned silver-containing sintering paste.

Such a printed alumina sintered ceramic, which is already sintered before the printing of the sintering pastes 2, 2 ', 3, finally passes through a sintering furnace, in which the sintering pastes 2, 2', 3 are dried and sintered. In the process, the sintering pastes 2, 2 ', 3 compact and solidify to form a physically strong structure and enter into a cohesive connection with the aluminum oxide sintered ceramic.

Such a substrate or carrier material is suitable for a high-temperature or Sinterprozes s according to the so-called LTCC (Low Temperature Cofired Ceramics) or HTCC (High Temperature Cofired Ceramics) technology, i. for a treatment at about 950 ° C or at about 1500 ° C.

An indicated cover 5 is connected by means of a solder 6 with the contact surface 2 'cohesively. The lid 5 does not touch the barrier 3, even if it could. The solder 6 is attached to the substrate edge and thus spaced to the barrier 3. In principle, however, the solder can also rest against the barrier. A barrier according to FIG. 3 or FIG. 4 effectively prevents the wetting of the conductor track 2 and thus also the wetting of the contact spring element 4 by the flux. Thus, a bonding of the contact spring element 4 is omitted with the conductor 2 as a result of such wetting.

Although exemplary embodiments have been explained in the foregoing description, it should be understood that a variety of modifications are possible. In addition, it should be noted that the exemplary embodiments are merely examples of the scope of protection, the

Applications and the structure should in no way limit. Rather, the person skilled in the art by the preceding description a guide is given for the implementation of at least one exemplary embodiment, wherein various changes, in particular with regard to the function and arrangement of the described components, can be made without departing from the scope as it results from the claims and these equivalent combinations of features.

Claims

Printed circuit board with conductor tracks (2) formed on one side of a substrate (1), wherein the substrate (1) can be connected in a conclusive manner to a contact surface (2) with a cover for protecting the conductor tracks (2)

characterized in that the sub strate ^¬ has a graduation (3) which forms a barrier to an adjuvant for promoting cohesive Ver ^¬ bond, to prevent wetting of the conductor tracks with the excipient.

Printed circuit board according to claim 1, dadurchge ^¬ indicates that the gradation (3) with respect to the substrate (1) on the inside surface relative to the contact

(2) of the substrate (1) is arranged.

Printed circuit board according to claim 1 or 2, characterized in that the step (3) is formed sub ^¬ stratverstärkend.

Printed circuit board according to one of the preceding claims, characterized in that the grading

(3) comprises the contact surface (2).

Printed circuit board according to one of the preceding claims, characterized in that the gradation (3) is formed at least in one layer.

Circuit board according to claim 5, dadurchge ^¬ indicates that the gradation (3) comprises a first layer (2), a second layer (2 ') and a third layer (3), wherein the third layer forms the barrier.

Printed circuit board according to one of the preceding claims, characterized in that the gradation (3) contains metal.

Printed circuit board according to claim 7, characterized in that the gradation (3) is formed from a silver-containing sintering paste.

Printed circuit board according to one of the preceding claims, characterized in that the gradation (3) is formed circumferentially around the conductor tracks (2).

Printed circuit board according to claim 9, characterized in that the gradation (3) is formed continuously encircling.

Printed circuit board according to one of the preceding claims, characterized in that the gradation (3) along the edges of the substrate (1) is formed.

Printed circuit board according to one of the preceding claims, since you rchgekennzeichnet that the Sub ^¬ strat (1) is formed of a sintered ceramic.

Sensor with a cover and with a printed circuit board one of claims 1 to 12.

Fuel level measuring system with a sensor according to claim 13.

15. Vehicle with a fuel level measuring system according to claim 14.