GB2627230A

GB2627230A - A printed circuit board assembly

Info

Publication number: GB2627230A
Application number: GB2302181.9A
Authority: GB
Inventors: Attila Fodor Tamás; László Hegedüs-Fuchs Gergely; Farkas Daniel
Original assignee: Rolls Royce Deutschland Ltd and Co KG
Current assignee: Rolls Royce Deutschland Ltd and Co KG
Priority date: 2023-02-16
Filing date: 2023-02-16
Publication date: 2024-08-21
Also published as: GB202302181D0

Abstract

A variety of printed circuit board assemblies are shown, each having one or more ribs 21,22 attached to the PCB improve resilience to shock and vibration loading that may cause unwanted bending (fig 17). The figure shows a side view of PCB 1 mounted to a base or housing 4 via fasteners 33, the ribs directly fixed to a face of the PCB via connectors 34. Figure 3 here shows gaps 51, 52 under portions of the ribs, in contrast to figures 1, 2 which have a flat rib in contact with the PCB. Figure 5 shows an alternative where fixtures (32) connect ends of opposing ribs without passing through the PCB. Figure 7 shows a variation of figure 5 with a joint (234) replacing one end fixture. The ribs may be various shapes such as straight or curved (figure 9), or may comprise an interconnected grid (figure 10) or H shape (figure 11). Figure 12 shows that a rib might be indirectly mounted, possibly by clipping to, guide rails (6) on the PCB. Figures 13, 14 shows the ribs (263) may also be attached at the ends by the fixings 33 to the PCB 1 and base 4. The ribs may be moulded or 3-d printed, either as a solid body or one with openings or lattice work. The ribs may be a thermally conductive plastic.

Description

A PRINTED CIRCUIT BOARD ASSEMBLY

Field of the disclosure

The present disclosure generally relates to printed circuit board assemblies.

Background

Printed circuit boards used in electric drives or other harsh environments need to be robust against environmental loads such as mechanical shock and vibrations in order to protect sensible components they carry such as power semiconductor modules. The use of holding down clamps represents an effective means to increase stiffness of a printed circuit board. However, holding down clamps require a counterpart that provides a counterforce which may limit its application.

The problem underlying the present invention is to provide for a printed circuit board assembly which comprises improved resilience against mechanical loads.

This problem is solved by a printed circuit board assembly with the features of claim 1.

Embodiments of the invention are identified in the dependent claims.

Summary of the disclosure

According to an aspect of the invention, a printed circuit board assembly is provided which comprises a printed circuit board having an upper side and a lower side. At least one rib is arranged at the upper side or at the lower side of the printed circuit board.

Aspects of the disclosure are thus based on the idea of increasing the resilience of a printed circuit board against mechanical loads by providing at least one rib arranged at the printed circuit board, wherein such rib provides for an additional stiffening of the printed circuit board.

A rib within the meaning of the present disclosure is any structure which has a primarily longitudinal extension (meaning that the longitudinal dimension is larger than the transverse dimension). Such rib naturally has two longitudinal ends. Also, such rib typically comprises a constant height at least over sections of the rib. However, a rib may alternatively have a varying height.

It is pointed out that the language "upper side" and "lower side" of the printed circuit board only serves to discriminate the two sides of a printed circuit board. Depending on the orientation of the printed circuit board in space, the upper side may run oblique or across the horizontal direction.

In an embodiment, the at least one rib is directly attached to the upper side or to the lower side of the printed circuit board. Direct attachment of the rib to the printed circuit board means that a lower side of the rib is in direct contact with the respective side of the printed circuit board. As will be discussed below, alternatively, the rib may be attached to the circuit board indirectly, i.e., by means of intermediate elements, without having a contact surface to the printed circuit board.

Depending on the space on the circuit board for placing one or several ribs, ribs may be attached to the upper side and/or lower side of the circuit board.

In an embodiment, at least one upper rib is directly attached to the upper side and at least one lower rib is directly attached to the lower side of the circuit board. Providing ribs on both sides further stiffens the printed circuit board.

In a variant of that embodiment, the upper rib and the lower rib are attached to the printed circuit board facing each other, wherein the lower rib is a counter rib to the upper rib. The upper rib and the lower rib, accordingly, have a corresponding form and length. Such arrangement of an upper rib and a lower rib strongly reduces the bending of the printed circuit board upon external forces independent of the direction of the external forces.

In a further variant, the upper rib and the lower rib are connected directly to each other at at least one longitudinal end by means of a fastening element. Accordingly, in this embodiment, the upper rib and lower rib are not (or not only) connected to the printed circuit board, but are connected directly to each other. Such a direct connection of the ribs may be adjacent to the edge of the printed circuit board, avoiding connection space on the printed circuit board. In such embodiment, the upper rib and the lower rib pinch the circuit board between themselves.

In another embodiment, the upper rib and the lower rib are connected at one of their longitudinal ends by a joint and at the other of their longitudinal ends by a fastening element. For example, the upper rib and the lower rib are be formed as a single U-shaped part, wherein the joint is formed by a flexible area between the legs of the U-shaped part, or the upper rib and the lower rib may be formed by two L-shaped parts which are connected by a joint. Again, in such embodiment, the upper rib and the lower rib pinch the circuit board between themselves.

In an embodiment, the at least one rib is attached to the circuit board by means of screws or other fastening elements. For example, a screw with a male thread is screwed through the printed circuit board into the material of the rib which comprises a corresponding female thread. In another embodiment, snap fit connectors are used, wherein such snap fit connectors comprise elements extending from the circuit board onto which the rib is snap fit.

The at least one rib may extend longitudinally in various ways. In one embodiment, the at least one rib is formed straight. In another embodiment, the at least one rib comprises at least one section which is curved.

In a further embodiment, a plurality of ribs are provided on the upper side and/or the lower side of the printed circuit board. The plurality of ribs may be arranged in various ways. For example, the plurality of ribs may be formed as a grid or arranged parallel to each other.

In a further embodiment, the printed circuit board is mounted to a mounting base by means of a plurality of mounting elements such as mounting screws. Such mounting base may be the housing of a device in which the printed circuit board is arranged. In such case, it may be provided that the at least one rib is connected to the circuit board also by means of the mounting elements, wherein the mounting elements connect both the rib to the circuit board and the circuit board to the mounting base. This way, the total amount of screws or other mounting elements can be minimized.

In a further embodiment, the at least one rib comprises at least one section in which it forms a recess in which the rib is at a distance from the circuit board. The provision of such recess allows to place electrical components on the printed circuit board below the rib. To put it differently, such recess allows the rib to bridge an area in which a component is attached to the printed circuit board.

In an embodiment, several ribs, in a view onto the printed circuit board, form a double-T-beam. Such a structure provides for additional resilience against bending.

The at least one rib may have a rectangular cross-section which has a good resilience against bending moments. However, other cross-sections are possible as well such as a double-T-cross-section.

In a further embodiment, the at least one rib is made out of a thermally conductive material which has a thermal conductivity that lies, e.g., in the range from 1 W/(m*K) to 500 W/(m*K), in particular in the range from 1 W/(m*K) to 100 W/(m*K). Examples of such materials are thermally conductive plastic materials (wherein thermally conductive additives such as graphite are added to a plastic material), ceramics and coated metal, the coating providing for electrical insulation.

By implementing the rib by a thermally conductive material, it is possible to conduct heat produced by electrical components located on the printed circuit board by means of the ribs to a heat sink. Further, the one or several ribs themselves may serve as a heat sink that radiates heat and/or provides for convective heat transfer.

In a further embodiment, the ribs are made out of a material that does not comprise heat-conducting properties (wherein the thermal conductivity lies below 1 W/(m*K)), such as regular plastic materials.

The at least one rib may be formed as a solid part or, alternatively, may comprise openings and/or cavity volume. In one embodiment, the at least on rib is formed by a 3D printed lattice structure to reduce the weight of the rib while keeping its stiffness.

In a further embodiment, the at least one rib is connected indirectly to the printed circuit board, meaning that the lower face of the rib is not directly contacting the printed circuit board but arranged at a distance to the plane of the printed circuit board. In such case, the at least one rib is connected to guide posts or guide rails directly mounted to the printed circuit board. Naturally, in such embodiment, the rib has a greater longitudinal dimension than the guide posts or guide rails. This embodiment reduces the space required on the printed circuit board to accommodate the at least one rib. The stiffness of the rib is transformed onto the printed circuit board by means of the guide posts or guide rails.

In an embodiment, the at least one rib is snap fit onto an upper part of the mentioned guide posts or guide rails, thereby allowing an easy assembly of the fastening rib.

As mentioned before, the printed circuit board assembly may comprise a plurality of ribs. The plurality of ribs may be individual ribs or all or some of the ribs may be formed as one part. For example, three ribs forming a double-T structure may be formed as one part.

The skilled person will appreciate that except where mutually exclusive, a feature or parameter described in relation to any one of the above aspects may be applied to any other aspect. Furthermore, except where mutually exclusive, any feature or parameter described herein may be applied to any aspect and/or combined with any other feature or parameter described herein.

Brief description of the disclosure

The invention will be explained in more detail on the basis of exemplary embodiments with reference to the accompanying drawings in which: Figure 1 is a sectional view of an embodiment of a printed circuit board assembly comprising a stiffening rib attached to a printed circuit board; Figure 2 is a sectional view of a further embodiment of a printed circuit board assembly, wherein an upper rib and a lower rib are attached to both sides of a printed circuit board; Figure 3 is a variant of the embodiment of Figure 2, wherein recesses are formed in the upper rib and in the lower rib; Figure 4 is a top view on a printed circuit board assembly that comprises stiffening ribs; Figure 5 is a sectional view of the embodiment of Figure 4; Figure 6 is a top view on a further printed circuit board assembly that comprises stiffening ribs; Figure 7 is a sectional view of the embodiment of Figure 6; Figure 8 is a top view on a printed circuit board assembly that comprises a stiffening rib formed in a straight manner; Figure 9 is a top view on a printed circuit board assembly that comprises a stiffening rib in a curved manner; Figure 10 is a top view on a printed circuit board assembly that comprises a stiffening ribs arranged in a grid; Figure 11 is a top view on a printed circuit board assembly that comprises stiffening ribs arranged as a double-T-beam; Figure 12 is a sectional view along lines A-A of the printed circuit board assembly of Figure 11; Figure 13 is a sectional view along lines B-B of the printed circuit board assembly of Figure 11; Figure 14 is a partly sectional view in the direction C of the printed circuit board assembly of Figure 11; Figure 15 is a top view on a further printed circuit board assembly that comprises stiffening ribs arranged as a double-T-beam; Figure 16 shows schematically a stiffening rib formed as a 3D printed lattice structure; 25 and Figure 17 shows a printed circuit board not in accordance with the present disclosure mounted to a mounting base and amenable to bending.

Detailed description

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

Figure 17 shows a printed circuit board 1 not in accordance with the principles of the present disclosure. The printed circuit board 1 has a generally flat extension and comprises an upper side 11 and a lower side 12. At its sides, the printed circuit board 1 is connected by means of mounting screws 33 or other fastening means to a counterpart 4 such as a housing which represents a mounting base for the printed circuit board 1. In case of a force acting perpendicular on the printed circuit board 1, the printed circuit board 1 is prone to bending, as schematically shown by bending distance D. Figures 1 to 16 depict embodiments of printed circuit board assemblies which have an improved resilience against mechanical loads, thereby reducing or avoiding any bending of the printed circuit board in case of mechanical loads.

According to Figure 1, a stiffening rib 21 -generally referred to as rib -is attached to the upper side 11 of the printed circuit board 1. To this end, screws 31 or other types of connectors fasten the rib 21 to the printed circuit board 1. In the depicted embodiment, a screw head 310 of the screws 31 lies against the lower side 12 of the printed circuit board 1, wherein a screw shaft 311 extends through the printed circuit board 1 and into respective openings in rib 21 which comprise a female thread corresponding to the male thread of the shaft 311. However, this manner of connecting the rib 21 to the printed circuit board 1 is to be understood as an example only, and other means of connection may be provided instead.

Along its edge (and possibly at other locations as well), the printed circuit board 1 is connected by mounting screws 33 or other fastening means to a counterpart 4 such as a housing which represents a mounting base for the printed circuit board 1.

It is pointed out that rib 21 is connected directly to the printed circuit board 1 in the sense that a lower face 211 of the rib 21 is in direct contact with the upper side 11 of the printed circuit board 1. Rib 21 may have a rectangular cross-section such that lower face 211 is 30 rectangular.

Rib 21 may be formed of a thermally conductive material such as a thermally conductive plastic material. The thermally conductive material may have a thermal conductivity that lies in the range from 1 W/(m*K) to 100 W/(m*K), or from 1 W/(m*K) to 500 W/(m*K). Rib 21 may be a mold part. By being formed of a thermally conductive material, rib 21 distributes heat received from the printed circuit board 1. In further embodiments, rib 21 may be formed by a ceramic material or an electrically insulated metal.

Printed circuit board 1 is depicted in a purely schematical manner, without showing components attached to the printed circuit board. Such components may be heat sinks and/or power semiconductor modules in case of electric drive applications. Rib 21 extends around or between areas in which components are attached to the printed circuit board 1.

Figure 2 depicts an embodiment in which an upper rib 21 is directly connected to the upper side 11 and a lower rib 22 is directly connected to the lower side 12 of the printed circuit board 1 in a manner that the upper rib 21 and the lower rib 22 directly face each other, wherein the lower rib 22 is a counter rib to the upper rib 21. The two ribs 21, 22, accordingly, have a corresponding form and length. For connection of the upper rib 21 and the lower rib 22 to the printed circuit board 1 and to each other, connectors 34 are provided which may be an integrated part of the upper rib 21 or lower rib 22. In an embodiment, the connectors 34 are of a snap-fit nature, such that the upper rib 21 and the lower rib 22 can be connected to each other and to the printed circuit board 1 by means of snap-fit connections. In Figure 2, the connectors 34 are depicted schematically only, and various ways are possible to implement the connectors 34.

Figure 3 depicts an embodiment which differs from the embodiment of Figure 2 in that both the upper rib 21 and the lower rib 22 comprise recesses 51, 52 in which a section of the rib 21, 22 runs at a distance from the printed circuit board 1. This allows to arrange components (not shown) on the printed circuit board 1 in such recesses 51, 52.

Figures 4 and 5 show in a top view and in a sectional view an embodiment of a printed circuit board assembly which is similar to the embodiment of Figure 2 except that the upper rib 21 and the lower rib 22 are also directly connected to each other at their longitudinal ends by means of fastening elements 32 such as mounting screws which extend through both ribs 21, 22. The longitudinal ends of the ribs through which the fastening elements 32 extend are located beyond the edge of the printed circuit board 1, such that the fastening elements 32 do not pass through the printed circuit board 1. The fastening elements 32 are external to the printed circuit board 1.

By directly connecting the ribs 21, 22 through fastening elements 32, the ribs 21, 22 pinch or clamp the circuit board 1 between themselves, thereby providing additional steadiness of the connection. In embodiments, in such case, direct attachment of the ribs 21, 22 to the circuit board 1 by connectors 34 is avoided and replaced by only clamping the circuit board 1. However, in the embodiment of Figures 4 and 5 the clamping connection by means of fastening elements 32 is in addition to the use of connectors 34.

Figures 6 and 7 show in a top view and in a sectional view an embodiment of a printed circuit board assembly which is similar to the embodiment of Figures 4 and 5 except that the upper rib 21 and the lower rib 22 are replaced by a one-piece U-shaped rib 23 which has an upper leg 231, a lower leg 232 and a connecting part 233. In the connecting part 233, rib 23 forms a joint 234 which may be formed, e.g., by a material recess. Along joint 234, the upper leg 231 and the lower leg 232 can be bended apart to attach rib 23 to the printed circuit board 1. At the other end, the upper leg 231 and the lower leg 232 are connected by a fastening element 32 as in Figure 5.

In an alternative embodiment, rib 23 is not formed by a single U-shaped part, but instead is formed by two parts such as two L-shaped ribs which are connected at one of their ends by a joint 234.

Figure 8 depicts an embodiment in which a single rib 21 is depicted which is formed straight. The cross-section of rib 21 may be rectangular.

In Figure 9, an embodiment is depicted in which a single rib 24 is provided which is curved throughout its length. In other embodiments, rib 24 may be curved in particular sections only. By providing a curved rib 24, rib 24 can be more easily attached to the printed circuit board 1 without interfering with components 7 attached to the printed circuit board 1. Further, the bended form may extend into a three-dimensional form as well, in particular in case of flexible printed circuit boards.

In a further embodiment (not shown), one or several ribs are attached to a printed circuit board 1 which comprises components such as components 7 which are pressed against a heat sink. Such components may be power semiconductor modules. In an area in which the printed circuit board is pressed against a heat sink it is already prohibited from bending. In such embodiments, ribs are attached to areas of the printed circuit board different to those areas which are pressed against a heat sink.

Figure 10 depicts an embodiment in which several ribs 21, 25 are provided which form a rectangular grid. By forming a grid of ribs, the stiffness of the printed circuit board 1 can be further improved. The individual ribs 21, 25 may be formed as one part or as individual parts.

In the above embodiments, the one or several ribs are connected directly to the printed circuit board, i.e., a lower face of the ribs directly contacts the surface of the printed circuit board. This way, bending of the printed circuit board is prevented in the most efficient manner. Also, heat conduction from the printed circuit board to the ribs is most efficient.

However, there may be instances in which the printed circuit board is so crowded with components located on the printed circuit board that it is not possible to attach over a longer distance a rib directly to the printed circuit board. In such case, one or several ribs may be arranged at a distance to the printed circuit board. Such embodiment is shown in Figures 11 to 15, wherein Figures 11 to 14 depict a first embodiment and Figure 15 depicts a second embodiment.

In the embodiment of Figures 11 to 14, Figure 11 is a top view, Figure 12 is a sectional view along line A-A of Figure 11, Figure 13 is a sectional view along line B-B of Figure 11, in Figure 14 is a partly sectional view in the direction C in Figure 11. Reference is made in the following to these Figures in conjunction.

A rib arrangement 26 is provided which is formed as a double-T-beam, having a central rib 261 and two side ribs 262, 263. Rib 26 arrangement is connected to the printed circuit board 1 indirectly by means of guide rails 6 and additionally directly through mounting screws 33.

To provide for the indirect connection, a plurality of guide rails 6 are directly attached to the upper side 11 of the printed circuit board 1, wherein the longitudinal dimension of the guide rails 6 is less than the longitudinal dimension of the ribs 261, 262, 263. In the depicted embodiment, the guide rails 6 comprises a base part 61 directly attached (such as screwed or glued) to the printed circuit board 1, a top part 62 and an intermediate part 63 of reduced diameter. The top part 62 and the intermediate part 63 together provide for a snap fit element. A corresponding snap fit area 264 is formed on the underside of ribs 261, 262, 263 such that rib arrangement 26 can be connected to guide rails 6 by means of a snap fit connection, as shown in Figure 12. Respective guide rails 6 are arranged along each of ribs 261 to 263.

Instead of guide rails 6, guide posts of short length may be implemented instead, the guide posts being arranged in a distance to each other on the printed circuit board.

The direct connection of rib arrangement 26 to the printed circuit board 1 is through the mounting screws 33, wherein the mounting screws 33 connect both the ribs 262, 263 to the circuit board 1 and the circuit board 1 to a mounting base 4. The connection of the ribs 262, 263 by means of mounting screws 33 is at the longitudinal ends of ribs 262, 263, wherein the ribs 262, 263 form an area of reduced height 2620, 2630 at their longitudinal ends that can be directly connected to the printed circuit board 1.

Figure 15 shows an embodiment which is similar to the embodiment of Figures 11 to 14 except that there is no direct connection of the rib arrangement 26 to the printed circuit board 1 by means of mounting screws 33, which in this embodiment only serve to mount the circuit board 1 to a mounting base. Guide rails 6 for indirect attachment of the ribs 261, 262, 263 are provided for only. The sectional view along line A-A in Figure 15 is identical to the sectional view of Figure 12.

The material of the ribs can be solid or include openings and/or hollow cavities. Figure 16 schematically depicts an embodiment in which a rib 27 is formed as a 3D printed lattice structure.

It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Also, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Various features of the various embodiments disclosed herein can be combined in different combinations to create new embodiments within the scope of the present disclosure. In particular, the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein. Any ranges given herein include any and all specific values within the range and any and all sub-ranges within the given range.

Claims

CLAIMS1. A printed circuit board assembly comprising a printed circuit board (1) having an upper side (11) and a lower side (12), wherein at least one rib (21-27) arranged at the upper side (11) or at the lower side (12) of the printed circuit board (1).
2. The printed circuit board assembly of claim 1, wherein the at least one rib (21-25) is directly attached to the upper side (11) or to the lower side (12) of the printed circuit board (1).
3. The printed circuit board assembly of claim 1 or 2, wherein at least one upper rib (21) is directly attached to the upper side (11) and at least one lower rib (22) is directly attached to the lower side (12) of the printed circuit board (1).
4. The printed circuit board assembly of claim 3, wherein the upper rib (21) and the lower rib (22) are attached to the printed circuit board (1) facing each other, wherein the lower rib (22) is a counter rib to the upper rib (21).
5. The printed circuit board assembly of claim 4, wherein the upper rib (21) and the lower rib (22) are connected directly to each other at at least one longitudinal end by means of a fastening element (32).
6. The printed circuit board assembly of claim 4, wherein the upper rib (231) and the lower rib (232) are connected at one of their longitudinal ends by a joint (234) and at the other of their longitudinal ends by a fastening element (32).
7. The printed circuit board assembly of any preceding claim, wherein the at least one rib (21-27) is attached to the printed circuit board (1) by means of screws (31-34) or other fastening elements.
8. The printed circuit board assembly of any preceding claim, wherein the at least one rib (21-23, 25-27) is formed straight.
9. The printed circuit board assembly of any one of claims 1 to 7, wherein the at least one rib (24) comprises at least one section which is curved.
10. The printed circuit board assembly of any preceding claim, wherein several ribs (21, 25) are provided which are formed as a grid.
11. The printed circuit board assembly of any preceding claim, wherein the printed circuit board (1) is mounted to a mounting base (4) by means of a plurality of mounting elements (33).
12. The printed circuit board assembly of claim 11, wherein the at least one rib (26) is connected to the circuit board (1) also by means of the mounting elements (33), wherein the mounting elements (33) connect both the rib to the circuit board (1) and the circuit board (1) to the mounting base (4).
13. The printed circuit board assembly of any preceding claim, wherein the at least one rib (21, 22) comprises at least one section in which it forms a recess (51, 52) in which the rib (21, 22) is at a distance from the circuit board (1).
14. The printed circuit board assembly of any preceding claim, wherein in a view onto the printed circuit board (1), the at least on rib (26) is formed as a double-T-beam.
15. The printed circuit board assembly of any preceding claim, wherein the at least one rib (21-27) comprises a rectangular cross-section.
16. The printed circuit board assembly of any preceding claim, wherein the at least one rib (21-27) is made out of a thermally conductive material which has a thermal conductivity that lies in the range from 1 W/(m*K) to 500 W/(m*K).
17. The printed circuit board assembly of any preceding claim, wherein the at least on rib (27) is formed by a 3D printed lattice structure.
18. The printed circuit board assembly of any preceding claim, wherein the at least one rib (26) is connected indirectly to the printed circuit board (1), wherein the at least one rib (26) is connected to guide posts or guide rails (6) mounted to the printed circuit board (1), wherein the at least one rib (26) extends at a distance to the plane of the printed circuit board (1).
19. The printed circuit board assembly of claim 18, wherein the at least one rib (26) is snap-fit to an upper part (62, 63) of the guide posts or guide rails (6).
20. The printed circuit board assembly of any preceding claim, wherein several ribs (21, 25, 26) are provided at the upper side (11) or lower side (12) of the printed circuit board (1), wherein the several ribs (21, 25, 26) are formed as one part.