Electronic assembly and method for producing an electronic assembly

Abstract

The invention relates to an electronic assembly (10) comprising a housing (3) and a printed circuit board (1), which has a heat-generating electrical load (2), wherein, in the region of the electrical load, a cooling section (4) is formed which protrudes from the housing (3) in a direction of the load (2) and at least sections of which are contacted with a gap filler material (5), such that heat can be conducted away from the electrical load (2) to the housing (3) and direct electrical insulation is formed between the power IC (2) and the housing (3).

Description

[0001] Electronic assembly and method for manufacturing an electronic assembly

[0002] The present invention relates to an electronic assembly comprising a housing and a printed circuit board, which includes a heat-generating electrical component. The invention further relates to a method for manufacturing an electronic assembly.

[0003] In electrical and electronic assemblies, many components generate waste heat during operation. This heat must be dissipated to ensure reliable operation and a long service life. The components requiring heat dissipation can include current-carrying conductors such as busbars or busbars, individual electronic components mounted directly on a circuit board, or even entire assemblies. In the case of current-carrying components, electrical insulation between the components is often necessary in addition to thermal insulation. Therefore, the thermal interface material (TIM) must possess good electrical insulation properties in addition to its thermal conductivity. Particularly in high-voltage applications, maintaining sufficient clearance and creepage distances is crucial to prevent arcing from current-carrying components to surrounding components.This places special demands on the selection of the TIM and the design of the interfaces.

[0004] The use of thermal interface materials (e.g., gap pads or gap fillers) for heat dissipation and electrical insulation is state of the art. Numerous suppliers offer these products, differing in shape, materials, and material properties. Gap pads are generally mounted on flat surfaces. Paste-like gap filler material is also typically applied to flat surfaces. This process sometimes compensates for unevenness, such as unfinished casting surfaces or manufacturing tolerances. Furthermore, the material can be dispensed into recesses or holes, causing it to rise during assembly due to displacement, similar to a potting compound. This often provides additional mechanical fixation for tall or heavy components.

[0005] All known solutions described in the prior art involve either the manual or automated assembly of a separate component, often a purchased part with external value creation, or the combination of assembly and dispensing of gap filler material. The combination of purchased part, assembly, and potentially a dispensing process results in significant costs, particularly due to the high labor commitment required for assembly and the many sequential process steps, which necessitate investment in equipment.

[0006] Furthermore, the use of elastomers or solids, such as gap pads or pre-formed elastomer components, generally leads to exceeding the maximum permissible strain rates when applied to printed circuit boards. This results in deflection of the board due to the contact forces of the elastomer component.

[0007] German patent DE 102022102408A1 discloses a device for heat dissipation in electronic assemblies that uses thermal interface materials (TIMs) to ensure efficient thermal connection and electrical insulation. Specifically, DE 102022102408A1 describes the use of a paste-like gap filler material dispensed into recesses or around components to achieve optimal distribution and fixation during assembly. DE 102022102408A1 requires a combination of assembling separate components and dispensing gap filler material, resulting in significant costs due to high labor demands and numerous sequential process steps. Furthermore, the use of different materials (e.g., heat shrink tubing and gap filler material) to meet creepage distance requirements leads to transition points where gaps can form.This can impair electrical insulation and reduce the reliability of the assembly. Furthermore, mounting elastomer or solid components on printed circuit boards can lead to exceeding the maximum permissible strain rates. This causes the board to deflect due to the contact forces of the component. The present invention aims to solve these problems by providing an efficient and cost-effective method for heat dissipation and electrical insulation in electrical and electronic assemblies.

[0008] This task is solved by an electronic assembly with a housing and a printed circuit board, which has a heat-generating electrical consumer, wherein a cooling section protruding from the housing towards the consumer is formed in the area of ​​the electrical consumer, on which at least section a gap-filler material is in contact, so that heat can be dissipated from the electrical consumer to the housing and a direct electrical insulation is formed between the power IC and the housing.

[0009] This electronic assembly offers the advantage of efficient heat dissipation from the electrical load to the housing, thereby reducing the load temperature and extending the assembly's lifespan. Simultaneously, the gap-filler material ensures direct electrical insulation between the power IC and the housing, enhancing the assembly's safety and reliability. Furthermore, the unique arrangement allows for a compact and space-saving design, which is beneficial for modern electronic applications.

[0010] consumer

[0011] For the purposes of this patent application, a consumer is an electrical component or circuit that absorbs electrical energy and converts it into another form of energy and / or performs a specific electrical function. A consumer can comprise a variety of electrical and electronic components that generate heat when operated.

[0012] Preferably, the load comprises power electronic components, such as power ICs, which are used in power supply and control circuits. These components are known for their ability to handle large amounts of electrical energy, resulting in significant heat generation that must be efficiently dissipated. In the context of inverters for powering electrical machines, various load configurations are conceivable. A preferred load could be a power transistor or an IGBT (Insulated Gate Bipolar Transistor), which are used in inverters to control and modulate the current flow. These components are crucial for converting direct current (DC) to alternating current (AC), which is used to control electrical machines, such as electric motors.

[0013] Another advantageous consumer in this context could be a microcontroller or a special control IC that monitors and adjusts the operating parameters of the inverter circuit. These components also generate heat and benefit from effective cooling, such as that provided by the electronic assembly according to the invention.

[0014] A consumer may be selected, in particular, from a group comprising power ICs, power transistors, IGBTs (Insulated Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), diodes, thyristors, transformers, resistors, capacitors, inductors, relays, stepper motors, electric motors, heating elements, semiconductor relays, rectifier bridges, voltage regulators, DC-DC converters, inverter ICs, microcontrollers, control ICs, sensors, actuators, and other power electronic components. It is also conceivable, in principle, to consider electrically conductive components, such as busbars, as electrical consumers within the meaning of this application.

[0015] Housing

[0016] For the purposes of this patent application, a housing is a structure that serves to mechanically protect electronic components and circuits and / or to provide electrical insulation and / or to dissipate heat. A housing encompasses the electronic assembly, at least partially, and can assume various shapes and sizes, depending on the specific requirements of the application. Preferably, the housing is made of materials that possess good thermal conductivity, such as aluminum, copper, or thermally conductive plastics. These materials enable efficient heat dissipation from the heat-generating components to the environment, which increases the thermal stability and reliability of the electronic assembly.

[0017] An enclosure can be fully enclosed to completely protect the electronic components from external influences such as dust, moisture, electromagnetic interference (EMI), and mechanical damage. Alternatively, an enclosure can be open or partially open if improved airflow and cooling are required. Preferably, the enclosure can also incorporate additional cooling structures, such as fins or louvers, which increase the surface area and improve heat dissipation to the environment. These structures can be an integral part of the enclosure or attached as separate heat sinks.

[0018] Cooling section

[0019] For the purposes of this patent application, a cooling section is a specially designed part of the housing that serves to efficiently dissipate heat from a heat-generating electrical consumer and transfer it to the environment or other cooling components.

[0020] Preferably, the cooling section is made of materials with high thermal conductivity, such as aluminum, copper, or thermally conductive plastics. These materials enable rapid and efficient heat dissipation from the electrical component to the housing and then to the environment or additional cooling structures. The cooling section can have a frustoconical shape, which advantageously provides a large contact area for heat transfer while ensuring mechanical stability. This shape also facilitates the easy application of the paste-like gap filler material, as the material can be applied from bottom to top without slipping. Alternatively, the cooling section can be designed as a rib, fin, or pin to increase the surface area and improve heat dissipation. These structures can be an integral part of the housing or added as separate elements to further optimize cooling performance.It is particularly preferred if the cooling section is monolithic with the housing.

[0021] Preferably, the cooling section can also be coated or surface-treated to improve heat transfer properties. A coating with thermally conductive adhesive or an anodized surface can increase heat dissipation efficiency while also improving corrosion resistance.

[0022] Furthermore, it is preferred that the cooling section be incorporated into the housing by forming. However, it would also be possible to machine the cooling section by subtraction.

[0023] Gap filler material

[0024] For the purposes of this patent application, a gap filler material is a thermally conductive material that is inserted into gaps or spaces between a heat-generating electrical component and a cooling section to enable efficient heat transfer while simultaneously ensuring electrical insulation. The gap filler material serves to minimize thermal resistance and maximize the cooling performance of the electronic assembly.

[0025] Preferably, the gap filler material consists of a paste-like or gel-like substance that allows for easy application and uniform distribution within the gap. Silicone-based materials are advantageous because they offer good thermal conductivity and excellent dielectric properties. These materials can be further enriched with fillers, such as ceramic particles, to increase thermal conductivity even more. A paste-like consistency enables precise application and ensures that the material adheres completely, even to complex geometries or irregular surfaces. This improves the thermal connection between the electrical component and the cooling section. The advantage of a paste-like gap filler material therefore lies, among other things, in...The advantage is that the functions of heat dissipation and electrical insulation can be ensured even with pasty gap filler material via a 3D geometry, and that one does not have to resort to molded parts, which are usually quite complex and expensive to manufacture and then generate preload forces due to the elastomer properties.

[0026] Preferably, the gap filler material can also be supplied in the form of pads or films that can be cut to size and inserted into the gaps. These more dimensionally stable forms—compared to the pasty material—offer ease of handling and can be readily integrated into automated manufacturing processes. Pads and films can also be enriched with thermally conductive fillers to maximize thermal efficiency.

[0027] Advantageous embodiments of the invention

[0028] According to an advantageous embodiment of the invention, the gap filler material can be made on a silicone basis and preferably contains at least one filler, preferably a ceramic filler.

[0029] This combination of features offers the advantages that the silicone-based gap filler material ensures high thermal conductivity and excellent electrical insulation. The use of a ceramic filler further increases thermal conductivity, resulting in even more efficient cooling of the electrical component. In addition, the silicone material offers good flexibility, which absorbs mechanical stresses and thus protects the structural integrity of the assembly. However, it would also be possible, in principle, to use an acrylate-based gap filler material.

[0030] According to a further preferred embodiment of the invention, it can also be provided that the cooling section protruding from the housing has a frustoconical contour, the top surface of which points towards the electrical consumer.

[0031] This combination of features offers the advantages that the frustoconical cooling section provides an enlarged surface area, which improves heat dissipation to the housing. The specific contour of the cooling section maximizes the contact area with the gap filler material, thereby improving thermal conductivity. This geometry also contributes to the stability of the assembly by distributing mechanical loads evenly. A frustoconical cooling section has also proven particularly advantageous with regard to the dispensing and processing of a pasty gap filler material.

[0032] Furthermore, according to another advantageous embodiment of the invention, the frustoconical cooling section may have a half-opening angle β between 20° and 30°. This half-opening angle β between 20° and 30° of the frustoconical cooling section offers the advantage of an optimal balance between increasing the heat dissipation area and minimizing the required material. This specific angle range improves heat transfer efficiency and contributes to the mechanical stability of the cooling section. A frustoconical cooling section with this half-opening angle has also proven particularly advantageous with regard to the metering and processing of a pasty gap filler material.

[0033] According to a further particularly preferred embodiment of the invention, the gap filler material can be provided in essentially complete contact with the protruding cooling section, thereby providing a maximum thermal contact area and significantly improving heat dissipation efficiency. This minimizes thermal resistance and optimizes the cooling performance of the system, thus promoting the thermal stability and longevity of the electronic components.

[0034] Furthermore, the invention can also be further developed such that the gap filler material is paste-like. The use of a paste-like gap filler material (5) offers the advantage of simple and precise application, thereby minimizing air inclusions and ensuring a uniform distribution of the material. This property improves heat transfer and ensures that the cooling performance remains constant, thus increasing the thermal efficiency of the assembly. In addition, the frustoconical contour offers the advantage in this context that the paste-like gap filler material can be applied more easily. Due to the conical shape, the material can be applied from bottom to top in the direction of gravity, which is particularly advantageous in automated manufacturing processes.When applying the paste-like material, a nozzle can be guided along the contour of the cooling section, with the wider base and tapered shape holding the material in place. This prevents the material from slipping or being spread unevenly during application. The application process begins at the lower, wider base of the cooling section and proceeds upwards, applying the material evenly across the surface. Gravity and the viscous nature of the paste-like material keep it in position, forming a uniform layer. This ensures that the cooling section is completely and evenly covered with the gap filler material, guaranteeing optimal heat dissipation and electrical insulation.The simplified application of the gap filler material contributes to the efficiency and precision of the manufacturing process, reduces potential sources of error, and increases the quality of the finished assembly.

[0035] In a further preferred embodiment of the invention, the electrical load can also be a power electronic component, in particular a power IC. This offers the advantage that the assembly can be used in demanding environments where efficient heat dissipation and reliable electrical insulation are crucial.

[0036] It can also be advantageous to further develop the invention such that the creepage distance between the power IC and the housing along the outer surface of the gap filler material does not fall below a minimum length of 4 mm, preferably 5 mm. The minimum creepage distance of 4 mm, preferably 5 mm, along the outer surface of the gap filler material offers the advantage of reliably preventing electrical flashovers. This increases the electrical safety of the assembly and reduces the risk of short circuits and failures, further improving the reliability and service life of the electronic assembly. The object of the invention can also be achieved by a method for manufacturing an electronic assembly comprising the following steps:

[0037] • Providing a printed circuit board with a heat-generating electrical load on it,

[0038] • Providing an enclosure with a cooling section protruding from the enclosure towards the consumer,

[0039] • Three-dimensional application of a paste-like gap filler material around the cooling section, so that the cooling section is at least partially, preferably completely, enclosed with the gap filler material,

[0040] • Joining the circuit board to the housing so that the cooling section protruding from the housing towards the electrical consumer is positioned in the area of ​​the electrical consumer and

[0041] • Distributing the gap filler material in a gap between the cooling section and the electrical load, so that heat can be dissipated from the electrical load to the housing and direct electrical insulation is formed between the load and the housing.

[0042] The process for manufacturing the electronic assembly offers the advantage that the individual steps are clearly structured and coordinated to ensure efficient and precise assembly. The three-dimensional application of the paste-like gap filler material enables a uniform distribution of the material, resulting in optimal heat dissipation and electrical insulation. This methodical approach improves production quality and efficiency.

[0043] Finally, the invention can also be advantageously implemented such that the three-dimensional application of the paste-like gap filler material is carried out using an automatic dispensing system. The automatic dispensing system for the three-dimensional application of the paste-like gap filler material offers the advantage of high precision and repeatability in material application. This reduces human error, accelerates the manufacturing process, and ensures consistent quality of the manufactured assemblies. This automation contributes to lower production costs and increased efficiency, resulting in economic benefits for the production of the electronic assembly.

[0044] The invention will now be explained in more detail with reference to figures, without limiting the general concept of the invention.

[0045] It shows:

[0046] Figure 1 shows an electronic assembly without gap filler material in a perspective sectional view.

[0047] Figure 2 shows a schematic sectional view of the electronic assembly with a gap filler material in a sectional representation.

[0048] Figure 3 shows a housing with a cooling section and gap filler material before joining it to the printed circuit board in a sectional view.

[0049] Figure 4 shows four different manufacturing states of the housing with the cooling section during the application of the gap filler material with a nozzle, each in a perspective view.

[0050] Figure 1 shows an electronic assembly 10 with a housing 3 and a printed circuit board 1, which includes a heat-generating electrical load 2. In the embodiment shown, the load is a power IC. In the area of ​​the electrical load 2, a cooling section 4, projecting from the housing 3 towards the load 2, is monolithically formed with the housing 3. The air gap between the load 2 and the cooling section 4 of the housing 3 is clearly visible. According to the invention, this air gap is bridged by a gap-filler material 5, which will be explained in more detail below with reference to Figure 2. A gap-filler material 5 is in contact with the cooling section 4, at least partially, so that heat can be dissipated from the electrical load 2 to the housing 3 and direct electrical insulation is formed between the power IC 2 and the housing 3.The pasty gap filler material 5 is silicone-based and preferably contains at least one filler, preferably a ceramic filler.

[0051] Figure 2 also clearly shows that the cooling section 4 projecting from the housing 3 has a frustoconical contour, the top surface 8 of which points towards the electrical load 2. In the embodiment shown, the frustoconical cooling section 4 has a half-opening angle β between 20° and 30°.

[0052] The creepage distance 6 between the power IC 2 and the housing 3 along the outer surface 7 of the gap filler material 5 has a minimum length of 4 mm, preferably 5 mm.

[0053] With reference to Figures 2-4, a method for manufacturing the electronic assembly 10 is explained in more detail below. First, a printed circuit board 1 is provided, with a heat-generating electrical load 2 located on it, as well as a housing 3 with a cooling section 4 projecting from the housing 3 towards the load 2. Then, the paste-like gap-filler material 5 is applied three-dimensionally around the cooling section 4, so that the cooling section 4 is at least partially, and preferably completely, enclosed by the gap-filler material 5. This state is shown, for example, as a sectional view in Figure 3 or also in Figure d of Figure 4.

[0054] Then the circuit board 1 is joined with the housing 3, so that in the area of ​​the electrical consumer 2 the cooling section 4 protruding from the housing 3 towards the consumer 2 is positioned and the gap filler material 5 is distributed in a gap between the cooling section 4 and the electrical consumer 2, so that heat can be dissipated from the electrical consumer 2 to the housing 3 and direct electrical insulation is formed between the consumer 2 and the housing 3, as can be seen in Figure 2.

[0055] The three-dimensional application of the paste-like gap filler material 5 is carried out using a nozzle 9 of an automatic dosing system.

[0056] To dissipate heat from the consumer 2 to the housing 3, a pasty gap filler material 5 is used, consisting of a silicone-based material enriched with ceramic fillers. This special material combines excellent thermal conductivity with high electrical insulation, which is essential for the safe and efficient operation of the electronic assembly.

[0057] The gap filler material 5 is applied three-dimensionally around the truncated cone-shaped cooling section 4, which is specifically provided on the housing 3, using the automated metering system or nozzle 9. This metering system enables precise control of the material quantity and distribution, ensuring that the cooling section 4 is completely and uniformly encased in the gap filler material 5, as can be clearly seen in Figure 4. The cooling section 4 is designed to provide an optimal contact surface for heat transfer while simultaneously ensuring mechanical stability.

[0058] During the joining process, the circuit board 1, on which the consumer 2 is mounted, is connected to the housing 3. The gap filler material 5 spreads into the available gap between the consumer 2 and the cooling section 4. The paste-like material flows into all gaps and conforms to the surface contours of the consumer 2 and the cooling section 4. This ensures that any tolerances or irregularities are compensated for, resulting in a homogeneous and seamless thermal connection.

[0059] The function of the gap filler material 5 extends beyond mere heat dissipation. It forms direct electrical insulation between the load 2 and the housing 3. This insulating layer prevents electrical short circuits and protects the electronic components from potential damage caused by electrical arcing. The material exhibits high dielectric strength, which contributes to increased electrical safety of the entire assembly.

[0060] To achieve the creepage distance requirements, which have a minimum length of 4.9 mm, the gap filler material 5 is metered laterally around the cooling section 4. This targeted and continuous metering creates an electrically insulating layer without any breaks or interfaces. This continuous layer ensures that the electrical creepage distance requirements are fully met, which is particularly important for compliance with electrical safety standards.

[0061] Another advantage of using gap filler material 5 is that it helps prevent deflection of the circuit board 1. During the joining process, the pasty material is displaced and distributed without significant forces, thus minimizing mechanical stresses and loads on the circuit board 1. This contributes to the mechanical stability of the assembly and prevents potential damage or deformation of the circuit board 1 that could impair the function and reliability of the electronic components.

[0062] Figure 4 further illustrates the manufacturing process. This figure a shows the "bare" cooling section 4, which is an integral part of the housing 3. The cooling section 4 protrudes from the housing 3 and is specifically designed to dissipate heat from the power IC 2. In this initial state, the cooling section 4 is not yet coated with the gap filler material 5. The cooling section 4 has a frustoconical contour, which provides an optimal contact area for heat transfer and is mechanically stable. This basic shape of the cooling section ensures that a uniform and complete coating with the gap filler material 5 can be achieved in the subsequent process steps.

[0063] Figure b illustrates the beginning of the dosing process of the gap filler material.

[0064] 5. An automated dispensing system with a nozzle 9 begins applying the pasty gap filler material 5 at the bottom of the cooling section 4. This is a silicone-based material enriched with ceramic fillers to ensure both high thermal conductivity and electrical insulation. The dispensing head with nozzle 9 is precisely positioned to apply a uniform amount of material to the base of the cooling section 4. This step is crucial for creating a solid foundation for the subsequent vertical dispensing.

[0065] Figure c of Figure 4 illustrates the progress of the dispensing process. The gap filler material 5 is continuously and uniformly dispensed upwards around the cooling section 4. The dispensing system with the nozzle 9 moves upwards from the base of the cooling section 4 in the direction of gravity, ensuring that the material is applied in a uniform layer. This three-dimensional dispensing guarantees that the cooling section 4 is completely and seamlessly covered with the gap filler material 5. The paste-like consistency of the material prevents it from slipping during application, resulting in a homogeneous coating. This uniform distribution is essential for optimal heat dissipation and electrical insulation in the subsequent use of the assembly.

[0066] Figure 4, section d, shows the final step in which the printed circuit board 1 with the mounted consumer 2 is connected to the housing 3. During the joining process, the gap filler material 5 spreads within the available gap between the consumer 2 and the cooling section 4. Any tolerances and unevenness are then compensated for by the gap filler material 5, resulting in a homogeneous and complete thermal connection. Simultaneously, the material provides direct electrical insulation between the consumer 2 and the housing 3, thus fulfilling the safety requirements. The use of the paste-like material prevents deflection of the printed circuit board 1, as the material is displaced during the joining process without significant force.

[0067] The invention is not limited to the embodiments illustrated in the figures. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Where the claims and the foregoing description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing any hierarchy.

[0068] List of reference signs

[0069] 1 circuit board

[0070] 2 consumers 3 housings

[0071] 4 Cooling section

[0072] 5 Gap Filler Material

[0073] 6 crawl distance

[0074] 7 Surface area 8 Cover area

[0075] 9 nozzle

[0076] 10 assembly

Claims

Claims 1. Electronic assembly (10) with a housing (3) and a printed circuit board (1) which has a heat-generating electrical consumer (2), characterized in that in the area of ​​the electrical consumer (2) a cooling section (4) is formed projecting from the housing (3) in the direction of the consumer (2), on which at least section a gap-filler material (5) is in contact, so that heat can be dissipated from the electrical consumer (2) to the housing (3) and a direct electrical insulation is formed between the power IC (2) and the housing (3).

2. Electronic assembly (10) according to claim 1, characterized in that the gap filler material (5) is silicone-based and preferably contains at least one filler, preferably a ceramic filler.

3. Electronic assembly (10) according to claim 1 or 2, characterized in that the cooling section (4) projecting from the housing (3) has a frustoconical contour, the top surface (8) of which points towards the electrical consumer (2).

4. Electronic assembly (10) according to claim 3, characterized in that the frustoconical cooling section (4) has a half opening angle β between 20°-30°.

5. Electronic assembly (10) according to one of the preceding claims, characterized in that the gap filler material (5) is substantially completely in contact with the protruding cooling section (4).

6. Electronic assembly (10) according to one of the preceding claims, characterized in that the gap filler material (5) is pasty.

7. Electronic assembly (10) according to one of the preceding claims, characterized in that the electrical consumer (2) is a power electronic component, in particular a power IC.

8. Electronic assembly (10) according to one of the preceding claims, characterized in that the creepage distance (6) between the power IC (2) and the housing (3) along the outer cladding surface (7) of the gap filler material (5) does not fall below a minimum length of 4 mm, preferably 5 mm.

9. Method for manufacturing an electronic assembly (10), comprising the steps: • Providing a printed circuit board (1) with a heat-generating electrical load (2) located on it, • Providing a housing (3) with a cooling section (4) extending from the housing (3) towards the consumer (2), • three-dimensional application of a paste-like gap filler material (5) around the cooling section (4) so ​​that the cooling section (4) is at least partially, preferably completely, enclosed with the gap filler material (5), • Assembling the circuit board (1 ) with the housing (3) so that the cooling section (4) protruding from the housing (3) towards the consumer (2) is positioned in the area of ​​the electrical consumer (2) and • Distributing the gap filler material (5) in a gap ( ) existing between the cooling section (4) and the electrical load (2), so that heat is transferred from the electrical load (2) to the Housing (3) is conductive and a direct electrical insulation is formed between the consumer (2) and the housing (3).

10. Method according to claim 9, characterized in that the three-dimensional application of the paste-like gap filler material (5) is carried out using an automatic dosing system.

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