Abstract
A circuit having a printed circuit board and at least one multilayer ceramic capacitor (MLCC) is described, characterized in that the printed circuit board has at least one opening in the region of the projection of the MLCC on the printed circuit board. The opening is not filled with any material and in the event of the MLCC malfunctioning it essentially prevents heat from accumulating between the MLCC and the printed circuit board
Claims
1. A circuit having a printed circuit board and at least one multilayer ceramic capacitor (MLCC), wherein the printed circuit board has at least one opening in a region of a projection of the MLCC on the printed circuit board.
2. The circuit according to claim 1, wherein the at least one opening is elongated in a direction parallel to a row of contacts of the MLCC.
3. The circuit according to claim 1, wherein at least one boundary of the at least one opening coincides with the projection of the MLCC on the printed circuit board.
4. The circuit according to claim 1, wherein the at least one opening (16) has an area of at least 20% and/or at most 50% of the projection of the MLCC on the printed circuit board.
5. The circuit according to claim 1, wherein the at least one opening has at least one curved boundary.
6. The circuit according to claim 1, wherein the at least one opening has at least two parallel boundaries.
7. The circuit according to claim 1, wherein the printed circuit board consists of FR4 material.
8. The circuit according to claim 1, wherein there are a plurality of MLCCs and the at least one opening extends over the projection of two or more MLCCs.
9. The circuit according to claim 1, wherein further components are mounted on the printed circuit board.
10. The circuit according to claim 1, wherein the printed circuit board has strip conductors.
11. The circuit according to claim 1, wherein the at least one opening is not coated.
12. The circuit according to claim 1, wherein the circuit is designed for a 12V and/or 48V operating voltage.
13. The circuit according to claim 1, wherein the at least one opening is free from any material.
14. A vehicle, in particular an electric vehicle or hybrid vehicle, having at least one circuit according to claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Embodiments of the invention shown by way of example in the drawings will be described in more detail below. The drawings show the following:
[0027] FIG. 1 shows a perspective view of a section of the circuit according to the invention;
[0028] FIG. 2 shows a plan view of the section according to FIG. 1 without the MLCC;
[0029] FIG. 3 shows a plan view of an alternative embodiment in which several MLCCs are electrically connected to one another in parallel;
[0030] FIG. 4 shows a further plan view of the embodiment in FIG. 1, in which the position of an opening with respect to contact blocks can be seen;
[0031] FIG. 5 shows two views and dimensions of a typical MLCC package;
[0032] FIG. 6 shows the embodiment in FIG. 1 with its surroundings on a printed circuit board;
[0033] FIG. 7 shows the section in FIG. 6 with an MLCC;
[0034] FIG. 8 shows the implementation of the embodiment in FIG. 3 with three places for MLCCs and the surroundings thereof on a printed circuit board;
[0035] FIG. 9 shows the section in FIG. 8 with two MLCCs;
[0036] FIG. 10 shows a block diagram with an MLCC, which is provided in a typical arrangement with an EMC filter in power supply lines;
[0037] FIG. 11 schematically shows the structure of the internal layers of an MLCC;
[0038] FIG. 12a to c show the development of a fault in the surroundings of an MLCC;
[0039] FIG. 13a to c show the prevention of such a fault as according to the invention;
[0040] FIGS. 14 and 15 show a current and voltage diagram in the event of a fault in a conventionally used MLCC; and
[0041] FIG. 16 shows a current and voltage diagram in the event of a fault in an MLCC built in according to the invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0042] As is shown in FIG. 1, an MLCC 10 is mounted on a printed circuit board 12 in such a way that the contacts thereof, which are not visible in FIG. 1 and which extend in parallel on the left and right outer edges, are contacted on blocks 14 of the printed circuit board 12. Parallel to and between the blocks 14, the end of an opening 16 can be seen in FIG. 1, which is easier to see in FIG. 2.
[0043] FIG. 2 reveals the substantially rectangular design of the blocks 14 and the elongated design of the opening 16 parallel thereto. In the case shown, the opening has two parallel side edges, which are substantially parallel to the longer edges of the blocks 14. The ends of the opening 16 are substantially formed by a semi-circle, such that the opening 16 can be efficiently created by means of a drill or end mill, the diameter of which substantially corresponds to the distance between the parallel edges.
[0044] This also applies to the embodiment in FIG. 3, in which the opening 16 extends under a plurality of MLCCs 10 which are indicated by dashed lines. The dashed lines essentially indicate the projection of the respective MLCC on the printed circuit board. Furthermore, the respective blocks 14 are shown, which correspond to those of FIG. 2, only the opening 16 is longer, corresponding to the plurality of MLCCs. According to FIG. 3, the opening protrudes slightly beyond the projection of the uppermost and lowermost MLCC according to FIG. 3, but the respective end may coincide with the edge of the projection, or the opening 16 may be shorter.
[0045] It should be noted by way of example that the longer sides of the blocks 14 can be between 1.5 and 2.8 mm long and can be spaced apart from one another by between 1.5 and 2 mm. The parallel edges of the opening 16 may in this case be spaced apart from one another by between 0.9 and 1 mm, and the opening 16 may have an overall length of 2.6 to 3.9 mm. This applies, for example, to an MLCC having a width (as measured from left to right in FIGS. 2 and 3) of 3.0 to 3.4 mm. According to FIG. 3, the blocks of adjacent MLCCs may be spaced apart by 0.8 mm, for example. In particular, the advantages according to the invention can be achieved particularly well with the dimensioning rule described.
[0046] FIG. 4 shows for the embodiment in FIG. 1 the two blocks 14, the projection of an MLCC 10 and the opening 16 between the blocks 14. This substantially corresponds to the situation in the surroundings of one of the three MLCCs shown by way of example in FIG. 3, and the exemplary dimensions set out above apply.
[0047] FIG. 5 shows in the upper part thereof a plan view of a typical MLCC, the contacts of which are shown hatched. In the lower part, a side view is shown, not to scale, but it should be noted that depending on the design L can be between 3.0 and 3.4 mm, S between 1.5 and 2.3 mm, W between 1.4 and 2.7 mm, and T between 0.25 and 0.75 mm. In particular, the aforementioned exemplary dimensions of the blocks and opening apply to such measurements. The table below shows advantageous dimensions according to FIGS. 4 and 5 depending on the type of MLCC.
TABLE-US-00001 EIA Inch L [mm] S [mm] W [mm] T [mm] G [mm] X [mm] M [mm] N [mm] Code min max min max min max min max min max min max min max min max 1206 3.0 3.4 1.5 2.3 1.4 1.8 0.25 0.75 1.5 2 1.5 1.9 0.9 1.1 2.6 3 1210 3.0 3.4 1.5 2.3 2.3 2.7 0.25 0.75 1.5 2 2.4 2.8 0.9 1.1 3.5 3.9
[0048] In FIG. 6 it can be seen on the basis of the embodiment in FIG. 1 that on the printed circuit board 12 strip conductors 18 follow the blocks 14, which strip conductors may be connected to further electronic components. FIG. 7 shows the section in FIG. 6 in this case with one MLCC 10. This substantially corresponds to the situation shown in FIG. 1, wherein according to FIG. 7 at both ends the opening 16 protrudes slightly beyond the projection of the MLCC 10.
[0049] FIG. 8 shows a similar section for the embodiment in FIG. 3, wherein in this case three pairs of blocks 14 and a correspondingly long opening 16 are provided.
[0050] As can be seen in FIG. 9, such an embodiment is suitable for three MLCCs, of which only two are shown in FIG. 9. In the surroundings thereof, strip conductors 18 can again be seen.
[0051] According to FIGS. 13A and B, the development in the event of a leakage current in the case of the solution according to the invention is initially identical to that described with reference to FIG. 12, but on account of the opening 16 in the printed circuit board 12 in the region below the MLCC 10, charring of the printed circuit board 12 and the combustion thereof can be prevented.
[0052] As can be seen from FIG. 16, in particular when compared with FIG. 15, there is no current flow through the printed circuit board, and the current and voltage fall to safe levels, such that only the MLCC is damaged, but no charring, delamination or flame propagation takes place.
