WO2023126667A1

WO2023126667A1 - Cover, enclosure and manufacturing method thereof, for electromagnetic shielding

Info

Publication number: WO2023126667A1
Application number: PCT/IB2021/062480
Authority: WO
Inventors: Pedro Miguel DE SOUSA BERNARDO; Susana SILVA; Anibal PORTINHA; Ricardo Freitas; Gustavo DIAS; Carlos Ribeiro
Original assignee: Bosch Car Multimedia Portugal S.A; Universidade Do Minho
Priority date: 2021-12-29
Filing date: 2021-12-30
Publication date: 2023-07-06

Abstract

Cover for an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding, the cover comprising: Continuous Fibre Reinforced Thermoplastic, CFRTP, skin and an injection-moulded electrically-conductive thermoplastic sub-cover overmoulded on the CFRTP skin; Respective enclosure, container and manufacturing method thereof.

Description

D E S C R I P T I O N

COVER, ENCLOSURE AND MANUFACTURING METHOD THEREOF, FOR ELECTROMAGNETIC SHIELDING

TECH NICAL FI ELD

[0001] The present disclosure relates to a cover and an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding comprising a thermoformed electrically-conductive Continuous Fibre Reinforced Thermoplastic, CFRTP, skin, and other injectable thermoplastics with a polymeric matrix based on thermoplastic material which are electrically conductive and thermally conductive, and modified with specific fillers.

BACKGROU ND

[0002] Document US2019/0159371A1 refers a housing that contains an electronic module inside is composed by a polymer that exhibits a thermal conductivity of lW/mK and an electromagnetic shielding effectiveness of about 20dB or more for the range of 1GHz.

[0003] Document US2011/0103021A1 shows heat sinks made of thermally conductive plastic material, comprising of an expanded graphite in an amount of at least 20 wt. %, relative to the total weight of the thermally conductive plastic material and/or has an in-plane thermal conductivity All at least 7.5 W /m- K. The heat sink can be produced from the thermally conductive plastic material by injection moulding of the thermally conductive plastic material, optionally followed by applying a coating layer.

[0004] Document US2011/0235255A1 reports a carbon laminate enclosure that comprises a Thermally conductive carbonaceous member partially or completely encapsulated within one or more electrically conductive materials.

[0005] WO2016/198923A1 discloses a mechanical fastening for point joining of metal sheet parts uses a clamp or clamps deformable against a recess or cavity. The fastening comprises a recess cavity on the first metal sheet; a cut-out clamp on the second metal sheet; wherein said cut-out clamp comprises one or two tongues cut-out from the second metal sheet, wherein the tongue or tongues are plastically inclinable in the direction of the recess cavity, and wherein the tongue or tongues deform plastically and laterally when the tongue or tongues are inclined to be embedded into the recess cavity. The tongue or tongues may diminish in width towards the end of the tongue. The clamp may have two tongues cut-out from the second metal sheet arranged symmetrically and extending towards each other. A metal chassis comprising said fastening may be used as an automotive radio chassis. It may have mating guiding rails and mating stoppers.

[0006] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.

GENERAL DESCRIPTION

[0007] As discussed, the present disclosure relates to a cover and an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding comprising a thermoformed electrically-conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, skin over injection moulded electrically and thermally conductive thermoplastics.

[0008] The exploration of alternative solutions to maximize mass savings has been investigated along the last years. The aerospace industry has been a pioneer in these applications due to the potential of cost savings induced by weight reduction and more flexible design options. The strategy used is replacing conventional light alloys or steel components by polymeric composite materials.

[0009] The interest in Continuous Fibre Reinforced Thermoplastics (CFRTPs) has grown rapidly across multiple industries, including automotive, aerospace, and sporting goods, because of intrinsic advantages over thermoset counterparts (Vaidya & Chawla, 2008; Hou, 1997; 6 Mairtin et al., 2001; Parton et al., 2005). The CFRTPs materials have been less technically explored and less used than thermoset composites (Parlevliet et al., 2007).

[0010] Thermoplastics have gained significant attention as polymeric matrices, they do not need a curing stage and they have less hazardous chemical compositions, improved recycling and mass production capability compared with conventional thermosetting resins (Yao et al., 2018).

[0011] In carbon fibre (CF) reinforced composites, the polymer (the matrix) usually acts as the continuous phase, and the carbon fibres (CF) serves as the discontinuous phase. The low through thickness electrical conductivity has limited the application of CFRPTPs (Fujita & Nagano, 2017; Wang & Chung, 2006).

[0012] Dopped thermoplastic matrices with conductive fillers, viz. with carbonaceous types for injection molded has been identified as a promising strategy to enhance the electrical and thermal properties. In this field, several studies have been reported showing the type of fillers used and the significant improvements (Cheng et al., 2018) (Gordeyev et al., 2000; Markov et al., 2006; Nurul & Mariatti, 2013; Gulrez et al., 2014; Wieme et al., 2019). Recent studies have focused on the preparation and characterization of nanoparticle-filled CF/thermoplastic composites as a means of achieving significantly improved mechanical and electrical properties (Yao et al., 2018).

[0013] Nowadays, at the market are available injection composite materials that actually answer to these specific needs, the electrical, thermal and mechanical performance.

[0014] However, there is a need for achieving enhanced thermal and electrical behaviour simultaneously, that are also easier to process and inexpensive to manufacture. Carbon fillers have been used to assure the electrical performance, while hybrid materials, usually a combination of carbon and ceramic fillers guarantee the heat dissipation. Suitable surface treatments and preparation methods of fillers are important for achieving a uniform dispersion in polymer matrices and for increasing the interfacial adhesion between the fillers and matrix (Rong et al., 2006) (Supova et al., 2010). [0015] Traditional approaches resort to metallic materials (US 5,256,833) that must present folding and openings specifically conceived for such a purpose (US 8,541,696 B2, WO 2014/145594 Al and US 2007/0297160 Al, both focused on electromagnetic compatibility shielding).

[0016] Alternatives include the usage of other materials (such as polymers) with an added electrically-conductive EMI shielding layer (for example, sprayed -- US6,763,576 B2 or overmolded or coupled on top -- US 6,807,731 B2) or the overmolding of an electrically conductive wire mesh screen (US 2014/0347831 Al) or wire (US 6,137,050) or the use of other conductive inserts (US 4,880,679).

[0017] Other options include an electrically conductive polymer (US 2007/0297160, US 2012/0285738, WO 2017/001888). As the Shielding Effectiveness (SE) is measured in dB (represented in a logarithmic scale), the requirements for higher shielding levels represents exponential decrease in maximum allowable openings. High SE requirements result in very small acceptable openings.

[0018] This leads to the use of gaskets or similar additional components to ensure for proper closing (US2477267 A, US 3783173 A, US7402761 B2, US 6,355,878 Bl, US 7,889,515 B2 -- conductive gaskets - US 7,078,614 Bl, US 7,527,506 B2 -- metal springs or WO 2008/153917 Al, US 5,265,833 -- solutions including several alternatives).

[0019] Alternative geometries are also patented for competent closing - US 5,565,656. In the case of polymers (particularly US 2007/0297160), the characteristic shape flexibility of polymers leads to a configuration of the edges developed in order to ensure maximum contact between parts of the casing and, thus, a good conduction while reducing or eliminating the need of gaskets or other alternatives.

[0020] A chassis that assumes the function of assuring electrostatic discharge (ESD) immunity is particularly in need of a proper contact between printed circuit board (PCB) and casing (US 4,494,651). The high variability in terms of PCB thickness results in the use of flexible conductive elements with this purpose (US 8,472,203 B2).

[0021] The disclosure includes the development of a lighter solution than conventional ones maximizing the weight saving, by using the lightest materials together with the best performing material while assuring the requirements of EMI shielding, thermal and mechanic behaviour in an economic competitive way.

[0022] The disclosure includes the implementation of an integrated design taking in account the EMC, grounding and the superficial electrical contact needs in this kind of products to answer the high and lower frequencies requirements. From the physics point of view at high frequencies it is more important the material properties attenuation in terms of EMI shielding while at lower and medium ones the geometrical and contact behaviour between parts surfaces takes more influence.

[0023] The surface electrical resistivity improvements can be assured in different ways, namely by the processing conditions of parts, adequate design features able to promote the contacts with localized surface improvements.

[0024] Replacing metals by polymeric materials have been widely investigated by automotive industries.

[0025] In this disclosure, the application product preferably selected was a central computer which traditionally comprises a magnesium and steel enclosure and aluminium heat sinks. Inside, includes several Printed Circuit Boards (PCBs) that are necessary to control all the functions, and they should be protected physically and shielded from electromagnetic fields as well as supress their interference on external devices. Assuming a challenging scenario, all the integrated circuits (ICs) working at the same time, generating a severe thermal environment, an excess of 95W, or more, must be dissipated.

[0026] The research and development focus of the disclosure was to redesign and replace metallic parts from an enclosure by composite polymeric based materials. In more detailed, an ultrathin CFRTP material with EMI-SE characteristics was combined with a multi-functional injectable thermoplastic material, as exemplified in figures 1 to 5. The heat sinks were substituted by a thermoplastic injectable material capable to conduct the heat, for example, in different directions (20 w/mK or more in longitudinal and 6W/mk or more in through thickness). [0027] The requirements were defined with the purpose of providing a composite enclosure design with sufficient durability and various functionalities as well as more lightweight characteristics as compared with metallic widely-used for conventional electronics enclosures.

[0028] It is disclosed a cover for an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding, the cover comprising: a thermoformed electrically-conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, skin; an electrically- or thermally-conductive thermoplastic sub-cover overmoulded by injection on CFRTP skin.

[0029] In an embodiment, the subcover is arranged to cover gaps of the CFRTP skin.

[0030] In an embodiment, the CFRTP skin is arranged to cover gaps of the subcover.

[0031] In an embodiment, the CFRTP skin comprises a thermoplastic matrix and continuous carbon fibres.

[0032] In an embodiment, the thermoplastic sub-cover is the electrically-conductive and the cover further comprises an injection-moulded thermally-conductive thermoplastic material to provide a heatsink to the electronic equipment.

[0033] In an embodiment, the thermally-conductive thermoplastic material comprises ceramic, metallic and/or graphite fillers for heat dissipation.

[0034] In an embodiment, the cover is a top cover of the enclosure.

[0035] it is also disclosed an enclosure comprising the cover according to any of the described embodiments.

[0036] An embodiment of the enclosure further comprises a bottom cover.

[0037] An embodiment of the enclosure further comprises a back cover.

[0038] An embodiment of the enclosure further comprises a chassis, or a fan, or a chassis and a fan. [0039] It is also disclosed an electronic device comprising an enclosure according to any of the described embodiments and electronic equipment contained within said enclosure.

[0040] It is also disclosed a method for manufacturing the cover according to any of described embodiments, comprising the steps of: thermoforming an electrically conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, Skin; injection-overmoulding an electrically-conductive thermoplastic sub-cover on the CFRTP skin; optionally, overmoulding an thermally-conductive thermoplastic, on the assembly of the CFRTP skin and electrically-conductive thermoplastic subcover.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0042] Figure 1: Schematic representation of an embodiment of the top cover of the present disclosure.

[0043] Figure 2: shows a schematic representation of an embodiment of the heat sink and heat sink of the present disclosure.

[0044] Figure 3: shows a schematic representation of an embodiment of a back cover, heat sink, fan, fan protection and chassis of the present disclosure.

[0045] Figure 4: Schematic representation of an embodiment of a bottom cover of the present disclosure.

[0046] Figure 5: Schematic representation of an embodiment of the top cover of the present disclosure, comprising a thermoformed electrically-conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, sheet and an injection-moulded electrically- conductive thermoplastic sub-cover, which has been overmoulded by injection on the sheet (or skin), and an injection-moulded thermally-conductive thermoplastic material to provide a heatsink to the electronic equipment.

[0047] Figure 6: Schematic representation of an embodiment of a manufacturing sequence wherein the CFRTP sheet is thermoformed, then placed in an injection mould where the electrically-conductive material is overmoulded, and where subsequently this sub-assembly is subjected to another moulding where a thermal heat-pad is overmoulded, resulting the final form of a top/bottom cover.

DETAILED DESCRIPTION

[0048] As discussed, the present disclosure relates to a cover and an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding comprising a thermoformed electrically-conductive Continuous Fibre Reinforced Thermoplastic, CFRTP, skin.

[0049] In particular, Figure 1 shows a schematic representation of an embodiment of the top cover 4 of the present disclosure.

[0050] Further, Figure 2 shows a schematic representation of an embodiment of a first heat sink 1 and a second heat sink 2 included in the present disclosure.

[0051] Figure 3 shows a schematic representation of an embodiment of a back cover 8, heat sink 9, fan 2, fan protection 7 and a chassis 5 of the present disclosure.

[0052] Figure 4 illustrates a schematic representation of an embodiment of a bottom cover 10 of the present disclosure.

[0053] Figure 5 shows a schematic representation of an embodiment of the top cover 4 of the present disclosure, comprising a thermoformed electrically-conductive Continuous Fibre Reinforced Thermoplastic, CFRTP, sheet 1, an injection-moulded electrically-conductive thermoplastic sub-cover 2, which has been overmoulded on the CFRTP sheet 1, and an injection-moulded thermally-conductive thermoplastic material 3 to provide a heatsink to the electronic equipment at the top cover 4. [0054] The present work presents a lightweight electronic enclosure as presented in Figure 1 with improved EMI-SE (electromagnetic interference shielding effectiveness). The enclosure contains thermoplastic composite materials that protects the electronic components inside and guarantee their structural integrity. Polymeric systems based on thermoplastic matrices were selected, taking into account the weight reduction, design flexibility and the environmental impacts at every stage of the product, from extraction and production, product use up to end of life.

[0055] To meet the growing demand for low emissions, electronic enclosures made from these compounds are significantly lighter and their counterparts, thereby reducing the overall vehicle weight.

[0056] Light weighting for fuel efficiency has been a dominant theme in automotive industries, however, there are many other performance requirements that drive products developments, such as electrical, thermal and mechanical performance.

[0057] The goal is to ensure a good EMI-SE behaviour of an electronic improve EMI-SE behaviour of an electronic enclosure, typically using an ultrathin skin (0.1-0.5 mm) of CFRTP Combined with a more structural parts in a thermoplastic composite material, as detailed in Figure 5.

[0058] The technical performance, in particular EMI Shielding, electrical contact between the counterparts is ensured by the materials properties combined with processing technologies and dedicated design features specially designed for the purpose as explained by Figures 1, 3 and 4. These novelties can be described as:

The applied material (thin sheets of CFRTP) ensures the global EMI-SE performance of the device combined with composite thermoplastic for the specific areas where CFRTP is not present, due to their attenuation capacity of electrical field.

The combination of different processing technologies (thermoforming of the thin CFRTP sheets and overmoulding) fulfil the mechanical and thermal requirements of the device. Dedicated design approach, including special features, together with processing conditions, ensure the grounding conditions needed.

[0059] In order to promote a proper compatibility between materials, due to the different chemical properties of the chosen materials, the design was adjusted to enhance quality and reduce manufacturing costs as represented in Figure 5.

[0060] The present disclosure can be proved by using the similar materials and same approaches and especial features in electronic protection enclosures traditionally built- in conventional materials or a different combination of traditional and other combinations of polymeric materials with metallic inserts like metallic foils or meshes.

[0061] The present disclosure can be used in all electronic enclosures despite the application, where the EMI shielding is a key factor to be ensured, as well a good thermal management needs to be ensured. Some examples are, these new automotive central computers, infotainment systems, ECU's, battery enclosures and other electrical devices.

[0062] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0063] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable. The following claims further set out particular embodiments of the disclosure.

[0064] References

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Claims

C L A I M S Cover for an enclosure for containing electronic equipment, with electromagnetic interference, EMI, shielding, the cover (4) comprising: a thermoformed electrically-conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, skin (1); an electrically- or thermally-conductive thermoplastic sub-cover (2) overmoulded by injection on the CFRTP skin (1). Cover according to the previous claim wherein the subcover (2) is arranged to cover gaps of the CFRTP skin (1). Cover according to any of the previous claims wherein the CFRTP skin (1) is arranged to cover gaps of the subcover (2). Cover according to any of the previous claims wherein the CFRTP skin (1) comprises a thermoplastic matrix and continuous carbon fibres. Cover according to any of the previous claims wherein the thermoplastic subcover (2) is electrically-conductive and the cover further comprises an injection- moulded thermally-conductive thermoplastic material (3) to provide a heatsink to the electronic equipment. Cover according to the previous claim wherein the thermally-conductive thermoplastic material (3) comprises thermally conductive ceramic, metallic or graphite fillers for heat dissipation. Cover according to any of the previous claims wherein the cover is a top cover of the enclosure. Enclosure comprising the cover according to any of the previous claims. Enclosure according to the previous claim further comprising a bottom cover. Enclosure according to claim 6 or 7 further comprising a back cover. Enclosure according to any of the claims 8-10 comprising a chassis, or a fan, or a chassis and a fan. Electronic device comprising an enclosure according to any of the claims 8-11 and electronic equipment contained within said enclosure. Method for manufacturing the cover according to any of the claims 1-7 comprising the steps of: thermoforming the electrically-conductive Continuous Fibre Reinforced ThermoPlastic, CFRTP, skin (1); injection-overmoulding an electrically-conductive thermoplastic sub-cover (2) on the CFRTP skin (1). Method for manufacturing according to the previous claim comprising the subsequent step of injection-overmoulding a thermally-conductive thermoplastic on the previous apparatus.