Patent Application
20240268027
The disclosure relates to a circuit board that allows for effective use of all the regions of a circuit board.
The practice of producing circuit boards from a multiplicity of prepregs (“pre-impregnated fibers”) and copper layers that are connected to one another and structured by laminating and etching processes is known. According to the standard EN IEC 60664-1, which relates to the design of air clearance and creepage distances, it is possible to assume a solid insulation between individual prepreg layers, and it is therefore unnecessary to comply with air clearance and creepage distances in this case. However, owing to delamination, for example, failure phenomena may occur along a prepreg layer, making it impossible to assume solid insulation between two potentials within a layer. Instead, a creepage distance is assumed in accordance with the standard mentioned. Here, the creepage distance is the shortest allowed distance between two conductive parts along the surface of an insulating material.
In this case, creepage distances between the layers of a circuit board are also maintained with respect to the circuit board edge. A housing or a heat sink may be situated adjacent to the circuit board edge, or there are additional creepage distances with respect to contact surfaces on the circuit board surfaces via the circuit board edge. Maintaining creepage distances in the layers of a circuit board, including toward the circuit board edge, disadvantageously leads to a relatively large unused edge region of the circuit board.
Moreover, an unused edge region also has a limiting effect on the thermal spread within a circuit board. If active components are integrated into or soldered onto the circuit board, it is advantageous to form a copper layer that is as sheet-like as possible below the component in which heat arises, which layer spreads this heat into the surface and thus increases the heat transfer surface via which heat may be transferred to a heat sink. On account of the creepage distance that has to be maintained with respect to the edge region, it is also not possible for a heat-spreading copper layer of this kind to extend as far as the edge region, and this limits heat transfer to a heat sink.
Known circuit board designs therefore require two-fold over-dimensioning. On the one hand, over-dimensioning of the circuit board in order to maintain the necessary air clearance and creepage distances with respect to the edge region. On the other hand, over-dimensioning of the assembly and/or of the heat sink due to limited thermal transfer.
The disclosure is based on the object of providing a circuit board that allows effective use of all the regions of a circuit board.
The scope of the present disclosure is defined solely by the appended claims and is not affected to any degree by the statements within this summary. The present embodiments may obviate one or more of the drawbacks or limitations in the related art.
Accordingly, a circuit board is disclosed that has a plurality of circuit board layers arranged one above the other. The plurality of circuit board layers includes an uppermost circuit board layer and a lowermost circuit board layer, wherein the uppermost circuit board layer forms an upper side of the circuit board, and the lowermost circuit board layer forms a lower side of the circuit board. The circuit board layers together form a circuit board end-face edge, which runs perpendicularly to the upper side and the lower side of the circuit board. The circuit board edge has a height that is substantially equal to the thickness of the circuit board.
The circuit board end-face edge is provided with a coating of an insulating material.
The disclosure is based on the concept of reducing or even completely avoiding air clearance and creepage distances that have to be maintained with respect to the edge of the circuit board by the targeted application of a coating of an insulating material to the end-face edge of the circuit board. The applied coating forms a materially integral solid insulator on the circuit board end-face edge which prevents the formation of creepage currents. The applied coating on the circuit board end-face edge provides a solid insulation within the individual layers of the circuit board.
As a result, the circuit board may be provided with a smaller unused edge region or no such edge region and may be reduced in size overall, thus enabling the required installation space and the use of material to be reduced. Moreover, there is the possibility that a heat-spreading copper layer in a circuit board of this kind extends further toward the circuit board end-face edge and, accordingly, forms a larger total surface, improving the thermal connection by increasing the proportion of copper in the circuit board and thereby allowing the achievement of smaller components. In this way, it is possible to minimize the necessary spacing between the copper layer around the circuit board edge as soon as it is possible to assume a solid insulation at the edge of the circuit board.
Another advantage associated with the disclosure includes increasing the robustness of the circuit board with respect to environmental influences at the critical circuit board edge, which is milled or scored, for example. For example, the edge coating with insulating material prevents moisture penetration into the circuit board on account of its inherent properties of low permeability to moisture and air.
As disclosed herein, an insulating material may refer to any non-conductor and thus any material, the electrical conductivity of which at 20° C. is less than 10−8 S·cm−1 (or which has a specific resistance at 20° ° C. of over 108 Ω·cm). Here, “S” is the unit of measure of the electrical conductivity. Refinements envisage that the resistance to creepage current provided by the insulating material has a CTI value (Comparative Tracking Index) that is at least 175, in the range of 175 to 600, or in the range of 400 to 600.
In one embodiment, the circuit board end-face edge is over-molded with the insulator in such a way that the coating extends over the circuit board edge onto the upper side and/or the lower side of the circuit board. For this purpose, provision is made, for example, for the coating to be formed in an edge strip on the lower side and/or in an edge strip on the upper side of the circuit board in addition to the circuit board end-face edge. An edge strip coated with insulating material on the upper side and/or on the underside of the circuit board protects the circuit board edge in an improved manner against environmental influences, e.g., the penetration of moisture. Moreover, the coated edge strips result in additional mechanical compressive stresses being applied to the circuit board edge, and these may counteract delamination of the circuit board starting from the edge, further increasing the life of the circuit board.
In another embodiment, the edge region of the circuit board is structured in such a way that it forms hollow structures filled with the insulating material at a distance from and/or adjacent to the circuit board end-face edge. In this case, the hollow structures may be configured as channels running perpendicularly to the upper side and the lower side of the circuit board and are spaced apart from the circuit board end-face edge, or for the hollow structures to be configured as channels running perpendicularly to the upper side and the lower side of the circuit board and extending as far as the circuit board end-face edge. The hollow structures may be introduced into the circuit board by standard processes in the manufacture of circuit boards, such as milling or drilling. The hollow structures filled with the insulating material improve the adhesion of the insulating material applied at the edge.
In principle, the insulating material used as a coating may be any insulating material. In certain embodiments, the insulating material is formed by a material that includes silicone, polyurethane, an epoxy resin, or a plastic.
In one embodiment, the coating of insulating material includes a material belonging to the material group of parylenes. Parylenes are hydrophobic, chemically resistant polymeric coating materials with a good barrier effect. One example of a parylene material is a plastic with the basic building block poly-p-xylylene, also referred to as parylene N. In certain examples, halogenated parylenes may be used.
One refinement of the disclosure provides that the insulating material provides insulation that meets the requirements of protection class 2 according to IEC 60664-3 and/or DIN VDE 0100-410 (VDE 0100-410):2018-10. According to one refinement, therefore, the coating is a coating of protection class 2. This provides materially integral solid insulation on the circuit board edge.
In principle, the coating of the circuit board end-face edge with an insulating material may be provided by numerous methods. In one embodiment, the coating of insulating material has been produced by chemical gas phase deposition. Such a method may be employed, for example, when using parylenes as an insulating material, wherein the parylene material is deposited in the gas phase. Here, there is the possibility of coating the circuit board edge in an electrically insulating manner with a homogeneous layer thickness.
In further embodiments, the coating of insulating material is produced by thermal spraying (e.g., including direct spraying from the side), nozzle coating using a nozzle through which the insulating material is applied directly to the surface of the circuit board end-face edge, or multicomponent injection molding, wherein the material is injection-molded onto the circuit board end-face edge.
According to one embodiment, the insulating material may extend in the circumferential direction of the circuit board along the entire circuit board end-face edge. According to this refinement, therefore, the circuit board end-face edge is provided with insulating material over its entire periphery. In other refinements, the insulating material may be formed only on some section or sections or points of the circuit board end-face edge, e.g., on edges of the circuit board or in sections in which components subject to high stresses are arranged or contacted.
As already observed, the circuit board may have at least one sheet-like copper layer formed and arranged in such a way that the layer spreads into the surface the heat of an active component integrated into the circuit board or is soldered onto the latter. In this case, the sheet-like copper layer extends substantially as far as the circuit board end-face edge, thereby improving the thermal connection of the circuit board.
The thickness of the coating of the circuit board end-face edge with insulating material is fundamentally dependent on the materials used, the temperatures which occur, the voltages applied, and other parameters. Refinements envisage that the layer thickness of the coating is in the range of 10 μm to 3 mm. For example, the layer thickness in the case of coating with parylene or an epoxy resin may be in the range of 10 μm to 50 μm, e.g., 30 μm. In the case where the edges are over-molded with polyurethane, the layer thickness may be in the millimeter range.
The disclosure is explained in greater detail below by a plurality of exemplary embodiments and with reference to the Figures of the drawing, in which:
For a better understanding of the background of the present disclosure, a circuit board arrangement is described on the basis of
The individual circuit board layers 10 are formed, for example, by prepreg layers, (e.g., glass fiber mats impregnated with epoxy, and copper layers), which are connected to one another and structured in a manner known per se by laminating and etching processes. The contours of the circuit board 1 are achieved by milling and drilling processes. According to the standard EN IEC 60664-1, which relates to the design of air clearance and creepage distances, it is assumed that there is solid insulation between individual prepreg layers (in the vertical direction in
Creepage distances 71 that have to be taken into account within a layer 10 is also maintained in each layer 10 with respect to the end-face edge 15 of the circuit board 1. Accordingly, an edge region A of the circuit board 1 may be kept free from components, conductor tracks, and contacts toward the end-face edge 15. This leads to a relatively large unused edge region A of the circuit board 1.
The edge region A to be kept free also has a limiting influence on the “thermal spread” within the circuit board 1, as explained with reference to
The end-face edge 15 of the circuit board is provided with a coating 2 of an insulating material 3. The insulating material 3 provides solid insulation at the edge of the circuit board 1. As a result, the formation of a creepage current is prevented, and the robustness of the circuit board 1 with respect to environmental influences is improved.
In principle, the insulating material 3 may be formed by any desired non-conductor. For example, this is a coating 2 of silicone, polyurethane, or an epoxy resin. The insulating material 3 provides an insulator that meets the requirements of protection class 2 according to IEC 60664-3.
In one exemplary embodiment, the insulating material 3 is formed from a material that belongs to the material group of parylenes. Accordingly, the coating 2 is a parylene coating. This may be deposited in the gas phase and offers the possibility of coating the circuit board edge 15 in an electrically insulating manner with a homogeneous layer thickness in the range of 10 μm to 100 μm, for example.
Owing to its insulating properties, such a coating 2 prevents the formation of a current. Moreover, it is resistant to environmental influences such as moisture, noxious gases, and temperature, and offers very high gap penetration in order to coat even micro cracks in the edge of the prepreg layers. Hydrophobic properties of the coating material and low permeability to moisture and air protect the circuit board 1 from the penetration of unwanted moisture and other noxious gases. Particularly at the edge 15 of the circuit board 1, which may be milled, it is possible for damaged glass fibers or microscopic delamination to form, starting from which the circuit board 1 degrades if it is formed without a protective coating 2.
According to
In principle, the coating 2 of the insulating material 3 may be applied by many coating methods. Examples thereof are chemical gas phase deposition, thermal spraying, nozzle coating, or multicomponent injection molding.
The coating 2 of insulating material 3 may be formed at the end-face edge 15 along the entire periphery of the circuit board 1, or alternatively may be formed only in some section or sections or points.
By such a refinement, the robustness of the circuit board 1 with respect to environmental influences is further improved. Moreover, the situation is such that the edge coating 21, 22 of the upper side 11 and of the underside 12 lead to the introduction of mechanical compressive stresses into the circuit board edge which additionally counteract any possible delamination of prepreg layers starting from the circuit board edge.
The application of the coating 2 with the coating regions 21, 22 may be accomplished by deposition from the gas phase, as explained with reference to
Attention is drawn to the fact that
On the right-hand side of
On the left-hand side of
The disclosure is not limited to the embodiments described above, and various modifications and improvements may be made without departing from the concepts described here. It is furthermore to be noted that any of the features described may be used separately or in combination with any other features, provided that they are not mutually exclusive. The disclosure extends to and includes all combinations and sub-combinations of one or more features which are described here. If ranges are defined, these ranges therefore include all the values within these ranges as well as all the partial ranges that lie within a range.
It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend on only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.
While the present disclosure has been described above by reference to various embodiments, it may be understood that many changes and modifications may be made to the described embodiments. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 115 851.6 | Jun 2021 | DE | national |
The present patent document is a § 371 nationalization of PCT Application Serial No. PCT/EP2022/066361, filed Jun. 15, 2022, designating the United States, and this patent document also claims the benefit of German Patent Application No. 10 2021 115 851.6, filed Jun. 18, 2021, which are incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/066361 | 6/15/2022 | WO |
