DE102021130128A1 - Assembly for connecting at least one component to a printed circuit board - Google Patents

Abstract

The invention relates to an assembly (1) for connecting at least one component (2) to a printed circuit board (3), comprising - the at least one component (2) with at least one contact surface (4), - the printed circuit board (3). at least one connection surface (5), - a cover foil (7) with at least one through hole (8), the cover foil (7) being glued to the surface (6) of the printed circuit board (3) by means of a foil adhesive (9) in such a way that the at least one through hole (8) is located on the at least one connection surface (5), and - a conductive adhesive (10), which is designed to produce an electrical and mechanical connection between the at least one component (2) and the printed circuit board (3), wherein the film adhesive (9), the conductive adhesive (10), the at least one contact surface (4) and the at least one connection surface (5) are designed and arranged in such a way that the at least one contact surface (4) with the at least one connection surface (5) is connected by means of the conductive adhesive (10) and that the film adhesive (9) at least partially touches the conductive adhesive (10) and the at least one connection surface (5).

Description

The invention relates to an assembly for connecting at least one component to a printed circuit board.

Field devices in process and automation technology are used to monitor and/or determine at least one, for example chemical and/or physical, process variable of a medium. Within the scope of the present application, in principle all measuring devices that are used close to the process and that supply or process process-relevant information are referred to as field devices. A large number of such field devices are manufactured and sold by companies in the Endress+Hauser Group.

The process variable to be determined by the field device can be the fill level, the flow rate, the pressure, the temperature, the pH value, a redox potential, or the conductivity of the respective medium. The different, possible measurement principles on which the determination of the process variable is based are known from the prior art and are not explained further here. Field devices for measuring the filling level are designed in particular as microwave filling level measuring devices, ultrasonic filling level measuring devices, time-domain reflectometric filling level measuring devices (TDR), radiometric filling level measuring devices, capacitive filling level measuring devices, conductive filling level measuring devices and vibronic filling level measuring devices. Field devices for measuring the flow, on the other hand, work, for example, according to the Coriolis, ultrasonic, vortex, thermal and/or magnetically inductive measuring principle. Pressure measuring devices are preferably so-called absolute, relative or differential pressure devices. In addition to the measuring devices and actuators mentioned above, field devices also include remote I/Os, radio adapters or devices in general that are arranged at the field level.

A field device typically includes a sensor that comes into contact with the process at least partially and/or at least temporarily, and an electronics unit that is used, for example, for signal acquisition, signal evaluation and/or signal feeding. The electronics unit of the field device is typically arranged in a housing and also has at least one connection element for connecting the electronics unit to the sensor and/or an external unit and for transmitting data and/or energy. The connection element can be any connection, a wireless connection can also be used. The electronics unit and the sensor of the field device can be designed in the form of separate units with separate housings or as a common unit with one housing. As a rule, at least the electronics unit has at least one printed circuit board with components arranged thereon.

In some cases, a printed circuit board is connected to a piezo drive, for example, which has at least one piezoelectric element. This is used, for example, to excite the oscillating unit of a vibronic level gauge. In addition to one or more soldered connection(s), one or more conductive adhesive connection(s) is/are additionally used for the mechanical and electrical connection of the printed circuit board to the piezo drive. While solder paste is used for the solder connection, a conductive adhesive is used for the conductive adhesive connection. It has been shown that the quality and mechanical strength of the conductive adhesive connection is heavily dependent on the printed circuit board used. Slight differences in the manufacture of the circuit board can significantly affect the adhesion of the conductive adhesive between the circuit board and the piezo drive. In addition, the adhesion of the conductive adhesive to the printed circuit board or to an electrically conductive connection surface of the printed circuit board is often rather weak.

The object of the present invention is therefore to specify an assembly in which a reproducible and stable electrical and mechanical conductive adhesive connection is ensured between a component and a printed circuit board.

• - das mindestens eine Bauteil mit mindestens einer Kontaktfläche, welche elektrisch leitfähig ausgestaltet ist,
• - die Leiterplatte mit mindestens einer Anschlussfläche, welche auf einer Oberfläche der Leiterplatte angeordnet und elektrisch leitfähig ausgestaltet ist,
• - eine Deckfolie mit mindestens einem Durchgangsloch, wobei die Deckfolie mittels eines Folienklebers auf die Oberfläche der Leiterplatte geklebt ist, derart dass das mindestens eine Durchgangsloch auf der mindestens einen Anschlussfläche liegt, und
• - einen Leitkleber, welcher dazu ausgestaltet ist, eine elektrische und mechanische Verbindung zwischen dem mindestens einen Bauteil und der Leiterplatte herzustellen, wobei der Folienkleber, der Leitkleber, die mindestens eine Kontaktfläche und die mindestens eine Anschlussfläche derart ausgestaltet und angeordnet sind, dass die mindestens eine Kontaktfläche mit der mindestens einen Anschlussfläche mittels des Leitklebers verbunden ist und dass der Folienkleber mindestens teilweise den Leitkleber und die mindestens eine Anschlussfläche berührt.

According to the invention, the object is achieved by an assembly for connecting at least one component to a printed circuit board, comprising

• - the at least one component with at least one contact surface, which is designed to be electrically conductive,
• - the printed circuit board with at least one connection surface, which is arranged on a surface of the printed circuit board and designed to be electrically conductive,
• - a cover film with at least one through-hole, the cover film being glued to the surface of the printed circuit board by means of a film adhesive in such a way that the at least one through-hole lies on the at least one connection surface, and
• - a conductive adhesive, which is designed to create an electrical and mechanical connection between the at least one component and the printed circuit board, wherein the foil adhesive, the conductive adhesive, the at least one contact surface and the at least one connection surface are designed and arranged in such a way that the at least one contact surface with the at least one connection surface is connected by means of the conductive adhesive and that the film adhesive at least partially touches the conductive adhesive and the at least one connection surface.

According to the invention, when connecting the printed circuit board and the at least one component, the foil adhesive is at least partially in contact with the conductive adhesive and the conductive adhesive connects the at least one contact surface and the at least one connection surface. The conductive adhesive is thus at least partially in contact with and touches the at least one contact surface, the at least one connection surface and the foil adhesive. This triple contact on the conductive adhesive improves the adhesion of the conductive adhesive compared to conventional connections in assemblies in which the conductive adhesive is only arranged between the at least one contact surface and the at least one connection surface and touches both of them. In particular, the contact between the conductive adhesive and the foil adhesive ensures additional adhesion and/or crosslinking between the conductive adhesive and the foil adhesive, which improves the mechanical resilience of the connection of the printed circuit board to the at least one component by means of the conductive adhesive.

According to the invention, the film adhesive is not only partially in contact with the conductive adhesive, but also with the at least one connection surface. The adhesion of the film adhesive to the at least one connection surface and the adhesion of the conductive adhesive to the film adhesive and to the at least one connection surface achieves better adhesion of the conductive adhesive to the printed circuit board compared to conventional assemblies.

The at least one through hole may have a circular, rectangular, or other shaped perimeter. Likewise, the at least one connection surface and the at least one contact surface can form different geometric shapes. The at least one through-hole is, for example, punched, etched or lasered into the cover film. The cover foil is designed to enable access to the at least one connection surface by means of the at least one through hole and to cover further defined areas of the surface of the printed circuit board. The conductive adhesive is - at least in the hardened state - electrically conductive and has a defined adhesive strength within the framework of the assembly. For example, adhesive strengths of the conductive adhesive of at least 4 N are achieved with the assembly according to the invention. The printed circuit board typically has conductor tracks which run on the surface or inside the printed circuit board and which make contact with at least one connection area.

In one configuration, the dimensions of the at least one connection area are equal to or larger than the dimensions of the at least one through hole. In this way, a possible distance between the film adhesive and the connection surface and between the film adhesive and the conductive adhesive is reduced and it is ensured that the film adhesive touches the at least one connection surface and/or the conductive adhesive.

In a further embodiment, the film adhesive is applied to the surface of the printed circuit board in a defined layer thickness. A defined layer thickness of the film adhesive is thus set between the surface of the printed circuit board and the cover film. A defined layer thickness increases the reproducibility of the mechanical load capacity of the assembly, since the film adhesive is always available with the same layer thickness. In particular, higher layer thicknesses facilitate contact with the conductive adhesive, since more foil adhesive is available for contact with the conductive adhesive. Layer thicknesses that are too thick are in turn disadvantageous because this requires a large amount of film adhesive, as well as conductive adhesive and other connecting means such as soldering paste, which are used, for example, to further connect the circuit board to at least one component or to other components arranged on the circuit board.

The defined layer thickness of the film adhesive is preferably between 30 μm and 45 μm. This layer thickness represents an optimum between the stated advantages and disadvantages of lower and higher layer thicknesses.

In a development, the film adhesive emerges partially from under the cover film, so that an end area of the film adhesive is arranged between the at least one connection surface and the conductive adhesive. In this development it is provided that the film adhesive is not arranged completely between the cover film and the at least one connection surface, but rather that it extends outside the cover film in the direction of the at least one connection surface and thus also in the direction of the conductive adhesive. The film adhesive forms a bulge in the area of the at least one connection surface, as a result of which the area of contact between the film adhesive and the conductive adhesive is increased.

In one development, the at least one component is a piezoelectric element.

The conductive adhesive advantageously comprises at least one conductive material. By means of the conductive material of the conductive adhesive, an electrical connection between the printed circuit board and the min at least one component can be produced. As a rule, the conductive adhesive consists of at least 60%, in particular at least 80%, in particular at least 90%, of the conductive material. The conductive material is present, for example, in the form of flakes, powder or particles randomly distributed in the conductive adhesive. Due to the high proportion of conductive material in the conductive adhesive, there is always contact between the individual flakes, powder or particles of the conductive material, so that at least one conductive connection forms between the at least one connection surface and the at least one contact surface. The conductive adhesive can have other components in addition to the conductive material.

In one embodiment, the conductive material is silver.

In a further configuration, the conductive adhesive comprises at least one adhesive. The adhesive ensures a mechanical connection between the printed circuit board and the at least one component. The proportion of adhesive in the conductive adhesive is often significantly lower than other components of the conductive adhesive, such as the conductive material.

Preferably the adhesive is epoxy resin.

In a development, the film adhesive is an acrylate adhesive.

In a further embodiment, the conductive adhesive touches the film adhesive in an edge area, with the edge area being arranged in particular along the circumference of the at least one through-hole. The adhesion increases in particular if the contact between the conductive adhesive and the film adhesive does not only take place at one or a few points, but rather the contact between the film adhesive and the conductive adhesive extends over an edge area. The edge area is arranged in the area of the circumference of the at least one through hole.

In a further development, the cover film is a solder resist film.

The at least one connection surface advantageously has a coating of at least one electrically conductive metal, in particular nickel and/or gold. In particular, the at least one electrically conductive metal interacts with the film adhesive in such a way that the film adhesive changes at least partially with regard to its chemical and/or physical properties. The at least one connection surface is coated with the at least one electrically conductive metal after the film adhesive and the cover film have been applied. For example, the internal crosslinking of the foil adhesive is broken up in those areas of the foil adhesive in which the at least one electrically conductive metal touches the foil adhesive and/or penetrates into the foil adhesive. This happens in particular during the process of coating the at least one connection surface. As a result of the change in the film adhesive, it adheres better to the at least one connection surface than an original, unmodified film adhesive.

• 1: eine schematische Darstellung der Leiterplatte als einen Ausschnitt der erfindungsgemäßen Baugruppe.
• 2: eine schematische Darstellung der erfindungsgemäßen Baugruppe.

The invention is further illustrated by the following figures 1-2 explained in more detail. They show:

• 1 : a schematic representation of the circuit board as a section of the assembly according to the invention.
• 2 : a schematic representation of the assembly according to the invention.

The assembly according to the invention can be used in all types of field devices, some of which were listed in the introduction in a non-limiting manner.

In 1 a printed circuit board 3 is shown, which is used in the assembly 1 according to the invention. For clarity, the circuit board is 3 in 1 shown without the at least one component 2. In 2 Finally, the assembly 1 according to the invention including the at least one component is shown. The configurations of the printed circuit board 3 described below 1 are looking for the assembly 1 according to the invention 2 transferable.

The circuit board 3 in 1 has on a surface 6 of the printed circuit board 3 at least one connection surface 5, which is designed to be electrically conductive. In addition, a cover film 7 is provided with at least one through hole 8, which is shown hatched. The cover film 7 is glued to the surface 6 of the printed circuit board 3 by means of a film adhesive 9 in such a way that the at least one through-hole 8 lies on the at least one connection surface 5 . For example, the dimensions of the at least one connection surface 5 are the same size or larger than the dimensions of the at least one through hole 8. The through hole 8 does not touch the at least one connection surface 5, but is spaced from it by means of the cover film 7 and the film adhesive 9. If the at least one through-hole 8 and the at least one connection surface 5 are each circular in shape, the at least one through-hole 8 and the at least one connection surface 5 are in particular arranged concentrically. The two are also in the case of other geometries of the at least one connection surface 5 and the at least one through hole 8 on top of each other or overlap completely. The through hole 8 has a circumference 13 . The cover film 7 is a solder resist film, for example.

Optionally, the foil adhesive 9 is applied to the surface 6 of the circuit board 3 in a defined layer thickness, the defined layer thickness being in particular between 30 μm and 45 μm. The film adhesive 9, which is in particular an acrylate adhesive, exits under the cover film 7, for example, so that an end region 11 of the film adhesive 9 lies between the at least one connection surface 5 and the (in 2 shown) conductive adhesive 10 is arranged.

The at least one connection surface 5 optionally has at least one coating 14 with an electrically conductive metal, in particular nickel and/or gold. The coating 14 of the at least one connection surface 5 with the at least one electrically conductive metal takes place after the film adhesive 9 and the cover film 7 have been applied to the surface 6 of the printed circuit board 3. During the production process of the coating 14, there may be a reaction or interaction of the at least one electrically conductive metal come with the film adhesive 9, which leads to a change in the chemical and / or physical properties of the film adhesive 9. In particular, the interaction between the at least one electrically conductive metal and the film adhesive 9 affects the internal crosslinking of the film adhesive 9, such that the polarity of the film adhesive 9 in the area of the at least one connection surface 5 is increased and improved adhesion of the film adhesive 9 to the at least one pad 5 is reached.

In 2 the assembly 1 according to the invention is shown schematically. In addition to the printed circuit board 3, the cover film 7 and the film adhesive 9, the assembly 1 according to the invention has at least one component 2 which has a contact surface 4 designed to be electrically conductive. The at least one component 2 is a piezoelectric element, for example. A conductive adhesive 10 is provided for the electrical and mechanical connection of the at least one component 2 to the printed circuit board 3 . The conductive adhesive 10 comprises, for example, at least one conductive material, in particular silver. In addition, the conductive adhesive 10 can include at least one adhesive, in particular epoxy resin. The film adhesive 9, the conductive adhesive 10, the at least one contact surface 4 and the at least one connection surface 5 are designed and arranged in such a way that the at least one contact surface 4 is connected to the at least one connection surface 5 by means of the conductive adhesive 10 and that the film adhesive 9 is at least partially touches the conductive adhesive 10 and the at least one connection surface 5 .

Optionally, the conductive adhesive 10 touches the foil adhesive 9 in an edge region 12 which is arranged in particular along the circumference 13 of the at least one through hole 8 . In 2 the edge area 12 is a circumferential edge area 12 following the circumference 13 of the through hole 8. The edge area 12 can also be designed in several parts, so that there are several edge areas 12 in which film adhesive 9 and conductive adhesive 10 touch. A larger edge area 12 generally ensures better adhesion of the at least one component 2 to the printed circuit board 3 than a smaller edge area 12.

As already in 1 shown, the film adhesive 9 can emerge under the cover film 7 in part, so that an end region 11 of the film adhesive 9 is arranged between the at least one connection surface 5 and the conductive adhesive 10 . The film adhesive 9 is therefore partially located between the at least one connection surface 5 and the conductive adhesive 10. In this example, as in 2 shown, come to the fact that the end portion 11 of the foil adhesive 9 (almost) completely comes into contact with the conductive adhesive 10, so that the edge portion 12 with the end portion 11 of the foil adhesive 9 at least partially overlaps. The conductive adhesive 10 can touch the cover film 7 or not.

Reference List

1

module

2

component

3

circuit board

4

contact surface

5

land

6

surface of the circuit board

7

cover sheet

8th

through hole

9

foil glue

10

conductive adhesive

11

end area of the film adhesive

12

edge area

13

Circumference of the through hole

14

coating

Claims (14)

Assembly (1) for connecting at least one component (2) to a printed circuit board (3). - the at least one component (2) with at least one contact surface (4) which is designed to be electrically conductive, - the circuit board (3) with at least one connection surface (5) which is arranged on a surface (6) of the circuit board (3) and is designed to be electrically conductive, - a cover film (7) with at least one through hole (8), the cover film (7) being bonded to the surface (6) of the printed circuit board (3) using a film adhesive (9), such that the at least one through hole (8) is located on the at least one connection surface (5), and - a conductive adhesive (10) which is designed to produce an electrical and mechanical connection between the at least one component (2) and the printed circuit board (3), the Foil adhesive (9), the conductive adhesive (10), the at least one contact surface (4) and the at least one connection surface (5) are designed and arranged in such a way that the at least one contact surface (4) can be connected to the at least one connection surface (5) by means of the Conductive adhesive (10) is connected and that the foil adhesive (9) at least partially touches the conductive adhesive (10) and the at least one connection surface (5). assembly claim 1 , wherein the dimensions of the at least one connection surface (5) are equal to or larger than the dimensions of the at least one through hole (8). Assembly according to at least one of Claims 1 - 2 , wherein the film adhesive (9) is applied in a defined layer thickness to the surface (6) of the printed circuit board (3). assembly claim 3 , wherein the defined layer thickness of the film adhesive (9) is between 30 and 45 µm. Assembly according to at least one of Claims 1 - 4 , wherein the film adhesive (9) under the cover film (7) emerges partially, so that an end region (11) of the film adhesive (9) is arranged between the at least one connection surface and the conductive adhesive. Assembly according to at least one of Claims 1 - 5 , wherein the at least one component (2) is a piezoelectric element. Assembly according to at least one of Claims 1 - 6 , wherein the conductive adhesive (10) comprises at least one conductive material. assembly claim 7 , where the conductive material is silver. Assembly according to at least one of Claims 1 - 8th , wherein the conductive adhesive (10) comprises at least one adhesive. assembly claim 9 , where the adhesive is epoxy resin. Assembly according to at least one of Claims 1 - 10 , wherein the film adhesive (9) is an acrylate adhesive. Assembly according to at least one of Claims 1 - 11 , wherein the conductive adhesive (10) touches the foil adhesive (9) in an edge area (12), the edge area (12) being arranged in particular along the circumference (13) of the at least one through hole (8). Assembly according to at least one of Claims 1 - 12 , wherein the cover film (7) is a solder resist film. Assembly according to at least one of Claims 1 - 13 , wherein the at least one connection surface (5) has a coating (14) made of at least one electrically conductive metal, in particular nickel and/or gold.

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