Patent Application
20250048578
The invention relates to a circuit board for a field device of automation technology as well as to a field device of automation technology having such a circuit board.
In automation technology plants, especially in process automation plants, field devices are often applied, which serve for registering and/or influencing process variables. Serving for registering process variables are sensors, which are used, for example, in fill level measuring devices, flowmeters, pressure- and temperature measuring devices, pH-redox potential measuring devices, conductivity measuring devices, etc. for registering the corresponding process variables, fill level, flow, pressure, temperature, pH value, and conductivity. Serving for influencing process variables are actuators, such as, for example, valves or pumps, via which the flow of a liquid in a pipeline section, or the fill level in a container, can be changed. Referred to as field devices are, in principle, all devices, which are applied near to a process and which deliver, or process, process relevant information. In connection with the invention, the terminology, field devices, thus, refers also to remote I/Os, radio adapters, and, in general, devices, which are arranged at the field level. A large number of such field devices are manufactured and sold by the firm, Endress+Hauser.
In order to enable the electrical, or electronic, functionality of such field devices, corresponding circuit boards with electrical, or electronic, components are applied in the interior of the field device to form the field device electronics.
Field devices thus often have a sensor unit, especially a sensor unit at least at times and/or at least sectionally in contact with a process medium, in order to produce a signal dependent on the process variable. Furthermore, field devices often include an electronics arranged in a transmitter housing, wherein the electronics serves for processing and/or forwarding signals, especially electrical and/or electronic signals, produced by the sensor unit. Typically, the electronics includes at least one circuit board with components arranged thereon.
Field devices, especially their electronics, that are qualified to be operated in explosion endangered regions (Ex regions), must satisfy very high safety requirements regarding explosion protection. In such case, of concern, especially, is safely to prevent the forming of sparks or at least to assure that a spark arisen due to a malfunction has no effects reaching to the environment. For this, corresponding standards are defined with a series of associated protection classes, especially in European standard IEC 600079-11 and/or EN60079-11.
In the protection class, “increased safety” (Ex-e), explosion protection is obtained by spatial separation between two different electrical potentials sufficiently large that, due to the separation, a spark formation cannot occur, even in the case of malfunction. Use of a potting compound encapsulation of electronic components falls under the protection class “Ex-m” in the context of the above-mentioned standards. In the protection class, “intrinsic safety” (Ex-i), explosion protection is obtained using values for an electrical is variable (electrical current, voltage, power) lying in each case and at all times below predetermined limit values, in order that even in the case of malfunction no ignition sparks are produced.
Comparable protection classes are defined in the American standard FM3610 and/or the ANSI/UL 60079-11 and/or the Canadian standard CAN/CAS C22.2 No. 60079-11.
Another requirement is that the field devices in an explosive atmosphere are allowed to operate only when their surface temperature remains below an ignition temperature of the surrounding explosive mixture. For this, temperature classes are defined. For example, in the case of the temperature class T6, surface temperature must not exceed 85° C.
In order to be able to reduce the needed spatial separations mentioned in the above-mentioned standards, fixed insulation can be provided where required.
This is usually done with the aid of a potting compound. In order to apply this liquid potting compound on the circuit board, however, a potting compound container, or housing, is required, in order that the potting compound retains a desired shape until it becomes hardened.
According to the protection class “intrinsic safety” (Ex-i; EN60079-11), the covering with a potting compound must be at least 1 mm thick.
Disadvantageous in the use of a potting compound is that such changes its volume as a function of temperature. In the case of a decrease of temperature, the potting compound shrinks and in the case of an increase of temperature, the potting compound expands.
This has the result that forces arise in the potting compound container (to the extent that is the potting compound has no free space), in order to handle the volume change. Thus, there act, due to the contraction of the potting compound and supplementally also due to clinging effects, or adhesive bond effects, on wall- and/or cover regions of the potting compound container, upon temperature increase, compressive forces, and, upon temperature decrease, tensile forces on the electronic components. Tensile- or compressive forces that are too high can result in cracks in the potting compound, since, for example, silicone rubber as potting compound has a limited ability to strain.
Another disadvantage is that upon temperature decrease the necessary 1 mm covering required for EX-qualification can no longer be assured, due to deformation of the potting compound and/or crack formation.
In order to be able to accommodate the volume change associated with temperature changes and to avoid possible forces between the potting compound, the potting compound container and the circuit board, usually, an intermediate space between the potting compound container and the filled potting compound is kept free, such that upon a temperature rise the potting compound can expand and upon a temperature drop the potting compound can contract.
When an intermediate space between the potting compound container and the filled potting compound is kept free, it can, however, occur that the potting compound because of capillary forces climbs the side walls of the potting compound container in the direction of the potting compound cover and as soon as the potting compound reaches the potting compound cover, it can, at least partially, occupy the intermediate space. This, in turn, has the result that potting compound is missing in the central region, and, thus, the covering necessary for EX-qualification cannot be assured at all locations.
An object of the invention is, therefore, to provide measures for how, in the potting of electronic components on a circuit board with the aid of a potting compound container, a covering necessary for EX-qualification can be assured.
The object is achieved according to the invention by the circuit board as defined in claim 1 and the field device of automation technology as defined in claim 10.
The circuit board of the invention for a field device of automation technology comprises a plurality of electronic components and a potting compound container made of a plastic and having a peripheral side wall defining an outer contour of the potting compound container, a potting compound cover adjoining the side wall and an opening located on the potting compound cover far side, wherein the potting compound container is set via the opening over at least a part of the plurality of electronic components and filled with a potting compound in such a manner that electronic components covered by potting compound have a predetermined, or defined, minimum covering, wherein the potting compound container is, however, not completely filled with potting compound and wherein in the potting compound cover in an edge region, which borders a transition from the side wall to the potting compound cover, at least one gap is present, which extends at least over a convex edge region of the outer contour.
According to the invention, there is provided at least one convex edge region, preferably at all convex edge regions, of the potting compound container, at least one gap in the potting compound cover, in order to suppress capillary action and to prevent that the potting compound migrates on the potting compound cover. Such a convex edge region can be, for example, a corner or a rounding of the potting compound container. The arrangement of the one or more gaps is, in such case, as near as possible to the transition from the side wall to the cover of the potting compound container in an edge region of the potting compound cover.
An advantageous embodiment of the circuit board of the invention can provide that a breadth of the at least one gap is such that the at least one gap has a minimum gap breadth of at least 0.5 mm, preferably at least 1 mm, especially preferably at least 2 mm.
Another advantageous embodiment of the circuit board of the invention can provide that is a breadth of the at least one gap is such that the at least one gap has a maximum gap breadth of no more than 6 mm, preferably no more than 5 mm, especially preferably no more than 4 mm.
In turn, another advantageous embodiment of the circuit board of the invention can provide that a length of the at least one gap is such that the at least one gap extends at least over a convex edge region of the outer contour.
Another advantageous embodiment of the circuit board of the invention can provide that the potting compound container has in the potting compound cover a plurality of gaps located, in each case, in the edge region. Especially, the embodiment can provide that the number of gaps in the edge region of the potting compound cover is such that they extend essentially completely along the outer contour and are only interrupted by at least one land, preferably at least two lands, especially preferably at least three lands and/or that the at least one land has a minimum width of at least 0.5 mm, preferably of at least 1 mm, especially preferably at least 2 mm, separating gaps from one another.
Another advantageous embodiment of the circuit board of the invention can provide that the one or more gaps are formed by an injection molding method, a blanking method, a milling method or a laser cutting method.
Another advantageous embodiment of the circuit board of the invention can provide that the predetermined, or defined, minimum covering results from the standard, DIN EN60079-11, published June 2012, Explosive Atmospheres—Part 11: Equipment Protection by Intrinsic Safety “i” and/or amounts preferably to 1 mm.
The invention relates further to a field device of automation technology having at least one circuit board defined according to one of the above described forms of embodiment.
The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:
The potting compound container 2 is a plastic potting compound container 2 for placement over the electronic components. Potting compound container 2 includes a surrounding side wall 2c and a container cover 2d, which adjoins the side wall 2c. On a container cover 2d far side, the potting compound container is open, such that it can be set via the open side on the circuit board 1 over the electronic components to be potted.
In order to enable a filling of the potting compound container 2 after its placement on the circuit board 1, at least one filling opening 2a is provided in the potting compound container 2, via which the potting compound 3 can be fed in. To aid in this, at least one air escape opening 2b can be provided in the potting compound container 2.
Potting compound container 2 is filled with a potting compound 3, wherein the potting compound container is not completely filled with potting compound 3, but, instead, only to the extent that each electronic component under the potting compound container has at least a minimum covering dmin of potting compound. In such case, the minimum covering dmin is governed by the standard, DIN EN60079-11, published June 2012, Explosive Atmospheres—Part 11: Equipment Protection by Intrinsic Safety “i”. For example, the minimum covering can amount to 1 mm, such that all electronic components are covered by at least 1 mm thickness of potting compound.
As regards the breadth Bgap of the gaps, such is selected such that the minimum gap breadth is at least 0.5 mm, preferably at least 1 mm, especially preferably greater than or equal to 2 mm and/or the maximum gap breadth is not greater than 6 mm, preferably not greater than 5 mm, especially preferably not greater than 4 mm. As regards the length Lgap of the gaps, such is preferably selected in such a manner that the gaps 2e extend, in each case, at least over a convex edge region of the outer contour, such as, for example, a corner, of the potting compound container, such as shown in
The lands 2f serve, in such case, for mechanically stabilizing the cover 2d, such that the cover 2d offers, on the one hand, a certain protection against mechanical effects, and, on the other hand, the gap, e.g. the almost complete peripheral gap, prevents migration of the potting compound. Mechanical effects can arise, for example, during installation and/or replacement of the prefabricated circuit board in a field device.
The one or more gaps 2e can be formed, for example, directly during the manufacturing of the potting compound container 2, in that they are correspondingly provided for in an injection molding tool/die for the potting compound container 2. Alternatively, the gaps 2e can also be introduced into the potting compound container 2 after the molding of the potting compound container 2, for example, as a result of milling, blanking or by means of a laser.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 125 881.2 | Oct 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/076360 | 9/22/2022 | WO |
