DE102021203904A1 - Process for encapsulating an electronic assembly - Google Patents

Abstract

The present invention relates to a method for encapsulating an area (12) to be encapsulated of an electronic assembly (10), wherein the area (12) to be encapsulated comprises at least part of an electrical circuit (14) arranged on a substrate (18) and having at least one electrical Component (16), characterized in that the method has the following method steps: a) Attaching an encapsulation boundary (20) on the substrate (18) in such a way that the encapsulation boundary (20) separates the region (18) to be encapsulated from the substrate ( 18) sealingly at least partially, with a filling opening (22) remaining in particular between the substrate (18) and the encapsulation boundary (20);b) introducing encapsulation material (28) into the filling opening (22);c) degassing of the encapsulation material (28 ) by applying a vacuum to the fill port (22); andd) closing the filling opening (22).

Description

The present invention relates to a method for encapsulating an electronic assembly. The present invention relates in particular to a method with which an electrical circuit of an electronic assembly can be encapsulated in an improved manner with an encapsulation material, in particular without tools.

Electronic assemblies comprising a printed circuit board with an applied circuit arrangement usually include electronic components that are combined on a carrier printed circuit board to form an electrical circuit arrangement, and mechanical components, for example, on which sensors are installed. Alternatively, the electronic components can also be connected to a stamped grid, which is located in an enclosure. According to the prior art, these assemblies are mounted on a base plate, for example made of aluminum, using connecting elements, which serves to mechanically stabilize and cool the assembly. Such assemblies are used, for example, as control units in motor vehicles, for example as a transmission control unit.

Control units are usually protected from external influences by means of covers. In this case, seals, adhesive bonds or material connections are used between the carrier circuit board and the cover.

However, it is also known to provide electrical circuits with an encapsulation material in order to enable protection against external influences. Molding processes for encapsulation are currently usually tool-related. A melted plastic mass is pressed into a metal mold. With this process, a so-called insert, such as electronics, is provided on one or both sides with a plastic coating that increases its robustness. This process is also known as "overmolding". There are also processes known as liquid molding or potting. These relate to gravity potting at ambient conditions or in a vacuum.

• - eine Mehrzahl elektronischer Bauteile, und
• - zumindest ein mechanisches Einlegeteil zur mechanischen Fixierung zumindest eines elektronischen Bauteils.

EP 3 257 339 B1 describes a mechatronic assembly, comprising a carrier circuit board with at least one populated flat side, on which the following components are arranged:

• - a plurality of electronic components, and
• - At least one mechanical insert for mechanically fixing at least one electronic component.

According to this document, a one-piece encapsulation is provided, which surrounds all components arranged on the populated flat side of the carrier circuit board in a form-fitting and material-locking manner. This document also relates to a method for producing a mechatronic assembly.

However, solutions known from the prior art can still be further improved, in particular with regard to a cost-effective and simple application of protection for electronic circuits.

It is the object of the present invention to provide a solution which is able to at least partially overcome at least one disadvantage of the prior art. It is in particular an object of the present invention to provide a solution with the aid of which it is possible to apply protection for electrical circuits of an electronic assembly in a cost-efficient and simple manner.

The solution of the present invention is achieved by a method with the features of claim 1. The solution of the present invention is achieved by an electronic assembly with the features of claim 10. Preferred developments of the invention are described in the dependent claims, in the description or in the figures. Wherein further features described or shown in the subclaims or in the description or the figures, individually or in any combination, may constitute a subject matter of the invention if the context does not clearly indicate the contrary.

1. a) Befestigen einer Verkapselungsbegrenzung auf dem Substrat derart, dass die Verkapselungsbegrenzung den zu verkapselnden Bereich zu dem Substrat dichtend teilweise einschließt, wobei insbesondere zwischen dem Substrat und der Verkapselungsbegrenzung eine Einfüllöffnung verbleibt;
2. b) Einbringen von Verkapselungsmaterial in die Einfüllöffnung;
3. c) Entgasen des Verkapselungsmaterials durch Anlegen eines Vakuums an die Einfüllöffnung; und
4. d) Verschließen der Einfüllöffnung.

The present invention relates to a method for encapsulating an area of an electronic assembly to be encapsulated, the area to be encapsulated comprising at least part of an electrical circuit arranged on a substrate and having at least one electrical component, the method having the following method steps:

1. a) Fastening an encapsulation boundary on the substrate in such a way that the encapsulation boundary partially encloses the region to be encapsulated in a sealing manner relative to the substrate, with a filling opening remaining in particular between the substrate and the encapsulation boundary;
2. b) introducing encapsulation material into the filling opening;
3. c) degassing of the encapsulation material by applying a vacuum to the filling opening; and
4. d) Closing the filling opening.

Such a method allows significant advantages over the solutions from the prior art, in particular with regard to a simple method sequence and improved variability of the encapsulation of the electronic assembly.

The method described here is therefore used to encapsulate an area of an electronic assembly that is to be encapsulated. The area to be encapsulated comprises at least part of an electrical circuit arranged on a substrate. The electrical circuit has at least one electrical component, but can also have a plurality of electrical components.

In principle, the substrate can be a printed circuit board, which is designed as a circuit carrier, for example, with the electronic components being able to be arranged directly on the printed circuit board in the form of unhoused semiconductor components, which can also be referred to as “bare dies”, and/or as housed semiconductor components. Unpackaged semiconductor components are electrically connected to the substrate and thereby to other electronic components arranged thereon by means of electrical connection elements, such as bonding wires and conductive adhesive connections. Housed semiconductor components are electronic components that are protected against external influences by means of an overmolding or a housing and are connected to the substrate and thus to other components via any connection using soldering or plugging processes.

In order to place the electronic components on the substrate, such as the carrier circuit board, they can thus be applied directly to the substrate in the form of housed and/or unhoused components. On the other hand, it is conceivable to assemble the unhoused components on a printed circuit board element, e.g.

In order to protect the electronic components and also the electronic connections, such as the bonding wires, against external influences, they are encapsulated with an encapsulation material.

For this purpose, the method according to method step a) comprises the in particular cohesive attachment of an encapsulation boundary on the substrate in such a way that the encapsulation boundary partially encloses the region to be encapsulated in a sealing manner relative to the substrate.

The encapsulation boundary is an element intended to spatially confine the encapsulation and thus close off the formed encapsulation on the side opposite the circuit. To this end, the encapsulation boundary is sealed on the substrate so that encapsulation material located within the encapsulation boundary cannot flow through between the substrate and the encapsulation boundary.

However, it is important that a filling opening remains, in particular between the substrate and the encapsulation boundary. Such a fill opening is an area through which encapsulation material can be filled into the area between the substrate and the encapsulation boundary. For example, the fill port may be an area where the encapsulation stopper is not attached to the substrate. Alternatively, it is also within the meaning of the present invention that the filling opening can be part of the encapsulation boundary. In the latter case, the encapsulation boundary is attached to the substrate in a sealing manner, completely encompassing the area to be encapsulated.

Correspondingly, according to method step b), encapsulation material is introduced into the filling opening. The encapsulation material can in particular be a fluid which assumes its ready-to-use configuration through a curing step.

The encapsulation material is therefore preferably hardenable, so that the positive and material connection between the encapsulation and the components can be produced particularly easily. For example, the hardenable encapsulation material is a thermosetting plastic, which has electrically insulating properties, so that a short circuit between the electronic components is avoided. The thermoset is, for example, an epoxy-based polymer.

The encapsulation material is preferably provided with at least one, for example inorganic, filler. Silicon dioxide or aluminum oxide, for example, are particularly suitable as inorganic fillers. A thermal expansion coefficient of the encapsulation material or the encapsulation formed can thus be adapted to the substrate, in particular to the materials which the substrate, ie the circuit board, for example, comprises such that warping of the encapsulation can be avoided or at least reduced. Likewise, the thermal expansion of the encapsulation can be adjusted via the thermal properties, in particular thermal expansion, rigidity and glass transition temperature.

After the encapsulation material has been introduced, the encapsulation material is degassed according to method step c) by applying a vacuum to the filling opening. As a result, gas bubbles introduced during the filling of the encapsulation material can be removed. As a result, the stability of the encapsulation can be increased, which can improve the mechanical protection of the encapsulated electrical circuit. In addition, the gas bubbles can be prevented from forming a porous structure through which any corrosive fluids can get through the encapsulation. The protective effect can thus be significantly improved by degassing the encapsulation material that has been filled in and has not yet hardened.

Degassing is possible in particular by applying a vacuum to the filling opening. For this purpose, a vacuum pump can be applied directly to the filling opening, or the substrate together with the encapsulation boundary and the encapsulation material that has been filled in can be arranged in a volume which is provided with a vacuum.

When the encapsulation material has been degassed, the filling opening is closed or sealed according to method step d). This can be realized, for example, in that the encapsulation boundary is sealingly fastened to the substrate, such as in particular the printed circuit board, in particular before any necessary hardening of the encapsulation material in the area of the filling opening. The encapsulation material can then be cured as necessary.

Alternatively, the filling opening can be closed directly, for example, by the hardening of the encapsulation material.

This allows the encapsulation to be completed.

It can be seen from the above that the encapsulation limitation is advantageously flexible in order to enable mobility or deformability, for example when the encapsulation material is filled in.

After the encapsulation has been produced, the encapsulation or the encapsulation material at least partially surrounds the electrical circuit. In particular, it can be advantageous if the encapsulation material completely and in one piece surrounds all components on the populated flat side of the substrate, in particular the carrier circuit board, so that both the electronic components and all other connecting elements for electrical contacting of the electronic components are protected from external influences, such as are protected from chips, gear oil, corrosive gases or liquids.

Due to a possible one-piece design of the encapsulation within the encapsulation boundary, the gaps between the electronic components are also closed, so that open interfaces are avoided. By means of the encapsulation, an optimal combination of electronics protection and a housing concept with a small installation space requirement is thus made possible for the electronic assembly. Furthermore, due to the encapsulation, a sealing function is significantly improved compared to the use of a plurality of housings that have to be sealed off from one another.

By using the encapsulation limitation, it can also be achieved that encapsulation is possible without tools, ie without the use of tools into which the encapsulation material is pressed. As a result, the disadvantages of tool-related methods, such as high investment costs, can be avoided. In addition, prototype processes according to the prior art are not possible or only possible with great difficulty or at high cost. This can also be overcome according to the invention, since a desired adaptation of the encapsulation limitation also enables prototypes or small series to be carried out without any problems and at low cost, even with a short lead time, also referred to as “lead time”.

Rejects due to so-called over-injection, when tolerances can occur in tool-based processes, for example, do not occur or occur to a very limited extent. This also offers advantages for large series.

Furthermore, the process steps for encapsulation can optionally offer in terms of occupational safety, process reliability and/or contamination. In particular, it can be prevented that foaming over occurs during degassing, which could lead to contamination of tools. In addition, evaporations released into the environment can be avoided, which protects personnel and equipment. In principle, direct contact with the encapsulation material can also be avoided.

Advantages can continue in terms of weight and shape advantages compared to conventional tool-free encapsulation, such as the so-called liquid molding or Potting can be achieved. This is possible, for example, since the encapsulation material can be made very thin due to the encapsulation limitation. Additionally, pre-contouring through the encapsulation constraint may also be possible, as described below.

In addition, with regard to corresponding shaping processes of the encapsulation material or the encapsulation, a high degree of precision can be achieved, which equates the applicability to the solutions from the prior art.

With regard to a shaping process or with regard to shaping, it can be preferred if the encapsulation boundary rests against a mold on the side opposite the encapsulation material during or after method step b), optionally with the application of pressure. For example, a mold die can be pressed against the encapsulation boundary as a negative mold or vice versa, in order to introduce a mold into the encapsulation. This can take place in particular before or during or even after curing. This configuration can be realized, for example, by pad printing, for example essentially without pressure, using a respectively adapted shaping stamp.

The particularly flexible encapsulation delimitation can thus rest against a corresponding negative mold in a state in which it is completely filled with encapsulation material. This is preferably possible before or during curing of the encapsulation material, with the mold manifesting its shape as a result of the curing. In this configuration, the inflow of encapsulation material into the encapsulation boundary is limited not only by the encapsulation boundary but also by the negative mold, so that the negative mold can determine the shape of the encapsulation.

Alternatively, shaping can also be carried out using a heated shaping die and, if appropriate, under the action of pressure, which can also be advantageous during hardening.

Alternatively or additionally, it may be preferred that the encapsulation material is formed in that the encapsulation boundary has a defined preform. In this embodiment, the form of encapsulation to be achieved is thus already achieved when the encapsulation boundary is completely filled with the encapsulation material. In this configuration, encapsulation and also the formation of the geometric shape can therefore take place completely without tools, which can make the advantages described above particularly effective.

The shape can be necessary, for example, but in no way limiting, in order to introduce reinforcement structures, such as stiffening ribs, into the encapsulation.

The stiffening ribs are designed, for example, in the form of a honeycomb structure or in the form of crossed ribs. Alternatively, other geometries and/or multiple stiffening ribs are also conceivable. The stiffening ribs enable the assembly to be stiffened, as a result of which the base plate described in the prior art, in particular the aluminum base plate, can be omitted. Mechanical stability of the electronic assembly is thus ensured even under high mechanical stress during assembly and/or during operation.

Alternatively or additionally, it is also possible to arrange another stiffening structure, for example metal grids or plates overmoulded with plastic.

More preferably, the encapsulation boundary can be formed as a film. This allows easy attachment of the encapsulation border to the substrate and equally easy complete filling with the encapsulation material. Examples of suitable films include, for example, polyethylene terephthalate (PET) or another material, particularly thermoplastic, which has a melting/softening point above the hardening temperature of the encapsulating material and which is particularly electrically insulating.

It is further preferred that the encapsulation boundary is glued or welded to the substrate. This refinement enables an equally safe and process-technically simple and cost-effective possibility to attach the encapsulation boundary to the substrate.

The encapsulation material can be degassed and the filling opening can be closed or sealed in a coherent work step. This configuration can have advantages in terms of process technology, since an additional process step can be dispensed with.

Alternatively, the encapsulation material can be degassed in a first step and the filling opening can be closed in a separate method step.

This step can be particularly advantageous if excessive degassing takes place, which could damage a mechanism for separating a sacrificial volume or for sealing the filling opening. Thus, degassing in a first chamber and sealing in a second chamber can protect the corresponding mechanics.

In principle, sealing, that is to say preferably fastening the encapsulation boundary to the substrate in a vacuum, can be advantageous since in this way no air is drawn into the inner volume, which can further reduce the risk of damage to the electronic components.

Furthermore, it can be advantageous if an encapsulation limitation with an electrically insulating matrix and with an electrically conductive structure is used. The electrically conductive structure can be present in or on the matrix, ie it can be surrounded by the matrix or formed on the surface of the matrix. For example, as has already been explained above, the encapsulation boundary can be in the form of a film made of an electrically insulating polymer, with the electrically conductive structure being arranged in the film.

In this configuration, the encapsulation limitation can thus be functionalized with regard to the electrical or electromagnetic properties, which can result in clear advantages.

For example, the encapsulation limitation can be optimized with regard to an electrostatic discharge (ESD) or provide protection against it. Furthermore, it is possible to improve the electromagnetic compatibility (EMC) or to design the encapsulation limitation as an antenna, which is connected to the substrate, such as the printed circuit board (PCB), in a signal-conducting manner. Applications for such an antenna include, for example, wireless communication, for example for existing sensors, for example when used in a transmission.

In principle, the above effects can be achieved by providing the film with an optionally structured, electrically conductive, for example metallic, coating or by laminating a corresponding electrically conductive structure between two films. Examples include printed structures and/or network structures, meander structures or other structures.

An antenna can, for example, be applied using 3D-MID technology (3D Mechatronic Integrated Device) or by means of a functionalized metal-coated surface. Contact can be made by electrically conductively connecting the structure to the printed circuit board, such as by soldering, gluing or welding. A wire can be attached to the structure on the foil surface, which is connected to the circuit board.

With regard to further advantages and technical features of the method, reference is made to the description of the electronic assembly, to the figures and to the description of the figures, and vice versa.

Also disclosed is an electronic assembly comprising a substrate on which is disposed electrical circuitry and is at least partially encapsulated by an encapsulation material, the encapsulation material being bounded by an encapsulation border, the encapsulation border being sealed to the substrate.

Such an electronic assembly can in particular have advantages with regard to manufacturability and can also be particularly adaptable with regard to the specific application.

For example, the encapsulation boundary, such as a film, can lie directly against the encapsulation material and thus immediately surround it and seal it off from the outside. The encapsulation boundary can be attached to the encapsulation material, for example in a materially bonded manner.

Specific areas of application for such electronic assemblies include, for example, control units or other electronic components for dual clutch transmissions, manual transmissions, automatic torque converters, drives with high performance data, such as boat drives, transfer cases for all-wheel drives, commercial vehicle applications and/or inverter or power electronics in general.

A control device, in particular a transmission control device, for a motor vehicle with an electronic assembly within the meaning of the present disclosure is also described.

With regard to further advantages and technical features of the control unit and/or the electronic assembly, reference is made to the description of the method, to the figures and to the description of the figures, and vice versa.

• 1 zeigt schematisch einen ersten Schritt eines Verfahrens gemäß der vorliegenden Erfindung;
• 2 zeigt schematisch einen weiteren Schritt eines Verfahrens gemäß der vorliegenden Erfindung;
• 3 zeigt schematisch einen weiteren Schritt eines Verfahrens gemäß der vorliegenden Erfindung; und
• 4 zeigt schematisch zeigt schematisch einen weiteren Schritt eines Verfahrens gemäß der vorliegenden Erfindung.

The invention is explained in more detail below with reference to the figures, wherein one or more features of the figures can be a feature of the invention, either alone or in combination. Further the figures are only to be seen as exemplary but not restrictive in any way.

• 1 shows schematically a first step of a method according to the present invention;
• 2 shows schematically a further step of a method according to the present invention;
• 3 shows schematically a further step of a method according to the present invention; and
• 4 shows schematically shows a further step of a method according to the present invention.

1 shows a first step of a method for encapsulating an area 12 to be encapsulated of an electronic assembly 10. In FIG 1 It is indicated that the area 12 to be encapsulated comprises an electrical circuit 14, wherein the electrical circuit 14 comprises at least one electrical component 16 that is arranged and connected on a substrate 18 designed as a printed circuit board.

According to method step a), an encapsulation boundary 20 is fastened to the substrate 18 in such a way that the encapsulation boundary 20 at least partially encloses or surrounds the region 12 to be encapsulated in relation to the substrate 18 in a sealing manner. For this purpose, for example, a film as an encapsulation boundary 20 can be materially attached to the substrate 18, for example the printed circuit board, for example by means of gluing or welding.

It is appropriate 1 provided that a filling opening 22 remains between the substrate 18 and the encapsulation boundary 20 .

The filling opening 22 is used to introduce encapsulation material 28, such as an epoxy resin, into it according to method step b) and thus to convey it to the region 12 to be encapsulated. This is in the 2 shown, from which it can also be seen that the substrate 18 is supported on the one hand on a carrier 24 and, furthermore, a mold 26 is provided which defines the shape of the encapsulation 30 to be formed. The encapsulation material 28 is discharged through a nozzle 32, which should indicate that the encapsulation material 28 still has gas bubbles.

2 FIG. 12 further shows a clamping unit 34 by which encapsulation material 28 can be separated from the encapsulation border 20, as explained later.

In the 3 another process step is shown. In particular, in 3 and according to method step c), the encapsulation material 28 is degassed by applying a vacuum to the filling opening 22 . The application of the vacuum should be represented by the arrow 36. Accordingly, a vacuum is generated in the space enclosed by the encapsulation boundary 20 or in the region 12 to be encapsulated, so that air pockets within the encapsulation material 28 are displaced in the direction of the filling opening 22, and the circuit 14 or the component 16 degasses from a mold -Material designated encapsulation material 28 is surrounded. In particular, the air bubbles can accumulate in a sacrificial volume 38 outside of the area 12 to be encapsulated.

Then, as in the 4 is shown, according to method step d), the filling opening 22 is closed. For this purpose, the clamping unit 34 can have a cutting edge at its lower end, which cuts through the encapsulation material 28 . When using a curable encapsulation material 28 , it is cured beforehand or afterwards, for example by means of thermal influence, which is intended to be illustrated by the radiation 40 . The filling opening 22 is closed by the hardening of the encapsulation material 28 and thus the formation of the encapsulation 30 . In accordance with the design 4 the curing takes place in the arrangement in which the encapsulation material 28 was also previously filled into the filling opening 22 .

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• EP 3257339 B1 [0005]

Claims (11)

Method for encapsulating an area (12) to be encapsulated of an electronic assembly (10), wherein the area (12) to be encapsulated comprises at least part of an electrical circuit (14) arranged on a substrate (18) and having at least one electrical component (16). , characterized in that the method has the following method steps: a) Fastening an encapsulation boundary (20) on the substrate (18) in such a way that the encapsulation boundary (20) at least partially seals the area (12) to be encapsulated to the substrate (18). includes, wherein in particular between the substrate (18) and the encapsulation boundary (20) a filling opening (22) remains; b) introducing encapsulation material (28) into the filling opening (22); c) degassing the encapsulation material (28) by applying a vacuum to the fill port (22); and d) closing the filling opening (22). procedure after claim 1 , characterized in that the encapsulation material (28) is subjected to shaping in that the encapsulation boundary (20) on the side opposite the encapsulation material (28) rests against a mold (26) during or after method step b), optionally with the application of pressure. Procedure according to one of Claims 1 or 2 , characterized in that the encapsulation material (28) is subjected to shaping in that the encapsulation boundary (20) has a defined preform. Procedure according to one of Claims 1 until 3 , characterized in that the encapsulation limitation (20) is designed as a film. Procedure according to one of Claims 1 until 4 , characterized in that the encapsulation material (28) is curable and is cured after degassing. Procedure according to one of Claims 1 until 5 , characterized in that the encapsulation boundary (20) is glued or welded to the substrate (18). Procedure according to one of Claims 1 until 6 , characterized in that the encapsulation material (28) is degassed in a coherent work step and the filling opening (22) is closed. Procedure according to one of Claims 1 until 6 , characterized in that the encapsulation material (28) is degassed in a first step, and in a separate process step the filling opening (22) is closed. Procedure according to one of Claims 1 until 8th , characterized in that an encapsulation boundary (20) with an electrically insulating matrix and with an electrically conductive structure is used. Electronic assembly (10), having a substrate (18) on which an electrical circuit (14) is arranged and at least partially encapsulated by an encapsulation material (28), characterized in that the encapsulation material (28) is defined by an encapsulation boundary (20 ) is bounded, wherein the encapsulation boundary (20) is sealingly attached to the substrate (18). Transmission control device for a motor vehicle with an electronic assembly (10). claim 10 .

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