GB2563206A

GB2563206A - Electronic arrangement and method for overmolding same

Info

Publication number: GB2563206A
Application number: GB1708795.8A
Authority: GB
Inventors: Alexandru Gabriel; Katkar Rohit
Original assignee: Conti Temic Microelectronic GmbH
Current assignee: Conti Temic Microelectronic GmbH
Priority date: 2017-06-02
Filing date: 2017-06-02
Publication date: 2018-12-12
Also published as: GB201708795D0

Abstract

Electronic arrangement (1) and method for overmolding the same, the electronic arrangement (1) comprises a printed circuit board (2) which further comprises solder pads (4), wherein one or more electronic components (3) are soldered onto at least part of the solder pads (4). A thermal interface material (5) is arranged on one or more areas of the printed circuit board (2), wherein an overmoulding process is performed in which an overmold material (6) is applied to the printed circuit board (2). A curing process is performed in which the electronic arrangement (1) is cooled down. These areas may encompass the one or more electronic components (3). A structural and thermal simulation may take into account different coefficients of thermal expansion. The overmould material (6) may be applied by compression or transfer moulding. The thermal interface material (5) may be silicone and may be able to withstand temperatures above 200 degrees.

Description

Electronic arrangement and method for overmolding same

It is known in the art to overmold electronic assemblies, i.e. a printed circuit populated with electronic components is encapsulated by a thermoset or thermoplastic material in a molding process. The overmolding process is usually performed by compression or transfer molding at relatively high temperatures, e.g. 180 °C to 200 °C. The overmolding process is followed by a curing process and the electronic arrangement 1 is cooled down, e.g. to room temperature thus cooling down all components from about 180 °C to about 22 °C.

It is an object of the present invention to provide an improved method for overmolding an electronic arrangement and an improved electronic arrangement overmolded by such a method.

The object is achieved by a method according to claim 1 and by an electronic arrangement according to claim 8.

Exemplary embodiments of the invention are given in the dependent claims .

According to the invention, a method is provided for overmolding an electronic arrangement comprising a printed circuit board comprising solder pads and one or more electronic components soldered onto at least some of the solder pads. The method comprises arranging a thermal interface material on one or more critical structural and thermal areas of the printed circuit board, wherein subsequently an overmolding process is performed in which an overmold material is applied to the printed circuit board, wherein subsequently a curing process is performed in which the electronic arrangement is cooled down.

Due to the use of the thermal interface material, cracks and integrity of the electronic components and their connection to the solder pads during the overmolding process and/or during the subsequent curing process can be avoided. Without the thermal interface material, the different coefficients of thermal expansion of the electronic components and the printed circuit board and/or the solder pads may result in stresses and strains developed in the solder joints when heating and cooling the electronic arrangement during the overmolding process and the subsequent curing process and compromise integrity of the electronic components and solder joints.

In an exemplary embodiment, the one or more critical structural and thermal areas encompass the one or more electronic components .

In an exemplary embodiment, the one or more critical structural and thermal areas are identified by a structural and thermal simulation taking into account different coefficients of thermal expansion between the one or more electronic components and the printed circuit board and/or the solder pads during the overmolding process and/or during the subsequent curing process .

In an exemplary embodiment, a thermal interface material capable of withstanding temperatures above 200 °C is used. These temperatures may typically occur during application of the overmold material.

In an exemplary embodiment, the thermal interface material is not applied outside the critical structural and thermal areas. This way, sealing capabilities of the overmold material are maintained and fewer thermal interface material is needed.

In an exemplary embodiment, the thermal interface material is cured prior to application of the overmold material.

In an exemplary embodiment, the overmold material is applied by compression or transfer molding. Compression reduces the flow rate of the overmold material on the thermal interface material.

In an exemplary embodiment, the thermal interface material is silicone .

According to an aspect of the invention, an electronic arrangement overmolded by the above described method is provided, comprising a printed circuit board comprising solder pads wherein one or more electronic components are soldered on at least some of the solder pads, wherein a thermal interface material is arranged on one or more critical structural and thermal areas of the printed circuit board, wherein an overmold material is arranged on the printed circuit board over the thermal interface material.

In an exemplary embodiment, the thermal interface material is not arranged outside the critical structural and thermal areas.

In an exemplary embodiment, the thermal interface material is silicone .

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

Brief Description of the Drawings

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

Figure 1 is a schematic view of an exemplary embodiment of an electronic arrangement,

Figure 2 is another schematic view of the electronic arrangement,

Figure 3 , is a schematic detail view of the electronic ar rangement and

Figure 4 is a schematic exploded view of the electronic arrangement .

Corresponding parts are marked with the same reference symbols in all figures.

Detailed Description

Figures 1 and 2 are schematic views of an exemplary embodiment of an electronic arrangement 1. Figure 3 is a schematic detail view of the electronic arrangement 1. Figure 4 is a schematic exploded view of the electronic arrangement 1.

The electronic arrangement 1 comprises a printed circuit board 2 populated by a plurality of electronic components 3 which are soldered onto solder pads 4. A thermal interface material 5 is arranged on a part of the printed circuit board 2, in particular on the electronic components 3 and other critical structural and thermal areas.

In an exemplary embodiment, the critical structural and thermal areas in which a mismatch of thermal expansion may occur due to different coefficients of thermal expansion between the electronic components 3 and the printed circuit board 2 and/or the solder pads 4, in particular during an overmolding process and/or a subsequent curing process may be identified by a structural and thermal simulation.

The thermal interface material 5 is chosen such that after the thermal interface material 5 has been cured it can withstand temperatures above 200 °C which may occur in a subsequent overmolding process.

The thermal interface material 5 does not have to be added in keep-out areas in which a mismatch of thermal expansion is less likely or unimportant, in particular in areas without electronic components 3. This way, sealing capabilities of a subsequently applied overmold material 6 are maintained.

Subsequently, an overmolding process is performed in which an overmold material 6, e.g. a thermoset or thermoplastic material is applied to the printed circuit board 2, e.g. by compression or transfer molding at relatively high temperatures in the range from 180 °C to 200 °C.

Compression reduces the flow rate of the overmold material 6 on the thermal interface material 5.

The overmolding process is followed by a curing process in which the electronic arrangement 1 is cooled down, e.g. to room temperature at about 22 °C.

Due to the thermal interface material 5, cracks and integrity of the electronic components 3 and their connection to the solder pads 4 during the overmolding process and/or during the subsequent curing process can be avoided.

In an exemplary embodiment, the thermal interface material 5 has a low stiffness in order to be able to absorb a part of the stress developed in the solder joints during heating or cooling. In an exemplary embodiment, the thermal interface material 5 is silicone .

Table 1 shows reaction forces in solder joints for overmolded electronic arrangements 1 with and without thermal interface material 5. The same model was used for both cases.

Table 1:

Those of skill in the art will understand that modifications (additions and/or removals) of various components of the apparatuses, methods and/or systems and embodiments described herein may be made without departing from the full scope and spirit of the present invention, which encompass such modifications and any and all equivalents thereof.

reference list 1 electronic arrangement 2 printed circuit board 3 electronic component 4 solder pad 5 thermal interface material 6 overmold material

Claims

Patent claims

1. A method for overmolding an electronic arrangement (1) comprising a printed circuit board (2) comprising solder pads (4) wherein one or more electronic components (3) are soldered onto at least some of the solder pads (4), wherein a thermal interface material (5) is arranged on one or more critical structural and thermal areas of the printed circuit board (2), wherein subsequently an overmolding process is performed in which an overmold material (6) is applied to the printed circuit board (2), wherein subsequently a curing process is performed in which the electronic arrangement (1) is cooled down.

2. The method of claim 1, wherein the one or more critical structural and thermal areas encompass the one or more electronic components (3).

3. The method according to claim 1 or 2, wherein the one or more critical structural and thermal areas are identified by a structural and thermal simulation taking into account different coefficients of thermal expansion between the one or more electronic components (3) and the printed circuit board (2) and/or the solder pads (4) during the overmolding process and/or during the subsequent curing process.

4. The method according to any one of the preceding claims, wherein a thermal interface material (5) capable of withstanding temperatures above 200 °C is used.

5. The method according to any one of the preceding claims, wherein the thermal interface material (5) is not applied outside the critical structural and thermal areas.

6. The method according to any one of the preceding claims, wherein the overmold material (6) is applied by compression or transfer molding.

7. The method according to any one of the preceding claims, wherein the thermal interface material (5) is silicone.

8. An electronic arrangement (1) overmolded by a method according to any one of the preceding claims, comprising a printed circuit board (2) comprising solder pads (4) wherein one or more electronic components (3) are soldered on at least some of the solder pads (4) , wherein a thermal interface material (5) is arranged on one or more critical structural and thermal areas of the printed circuit board (2) , wherein an overmold material (6) is arranged on the printed circuit board (2) over the thermal interface material (5).

9. The electronic arrangement (1) of claim 8, wherein the one or more critical structural and thermal areas encompass the one or more electronic components (3).

10. The electronic arrangement (1) of claim 8 or 9, wherein the thermal interface material (5) is not arranged outside the critical structural and thermal areas.