Method for producing an electronic device that is sealed in relation to fluids and solids

Abstract

The invention relates to a method (1000) for producing a sealed device (1), comprising the following steps: • producing (1001) a housing (2) defining an open cavity (20) delimited by a free edge (40), one of the inner surfaces (31, 32, 34, 35) of the housing (2) having a groove (41) extending from the free edge (40) to an inner surface (33) of the lower plate (13) of the housing (2), the inner surface (33) having a series of projecting elements (45); • positioning (1002) an electronic board (50) inside the open housing (2), the electronic board (50) bearing against the series of projecting elements (45); • pouring (1003), via the groove (41) of the housing (2), a raw material into the cavity (20) of the housing (2) in order to form an assembly; • depressurizing (1005) the assembly for a duration T; and • polymerizing (1006) the raw material for a duration T'.

Description

DESCRIPTION TITLE: METHOD FOR MAKING AN ELECTRONIC DEVICE THAT IS WATERPROOF AGAINST FLUIDS AND SOLIDS Scope of the invention

[0001] The present invention relates to the field of "drive over" fixed electronic systems measuring the characteristics of a tire passing over said electronic system, in particular the characteristics of the tread. Technological background

[0002] In the field of electronic devices installed on roads in outdoor environments, their design must withstand significant climatic variations throughout the year. This varies depending on the geographical location of the electronic devices—oceanic, mountainous, or continental—and their altitude—sea level, medium altitude, or high altitude. Furthermore, the mechanical stresses borne by the electronic devices are varied and often very high, especially when the electronic device is intended for transport vehicles, particularly freight vehicles or public transport vehicles.

[0003] Consequently, standard encapsulation solutions for electronic circuit boards, where sealing is ensured by a gasket, age poorly under the wide climatic variations and high mechanical stresses. Indeed, after a period of use, cracks appear in the protective casing of the electronic device, allowing access to the electrical or electronic components of the board by fluids and solid particles, which eventually corrode them before they permanently lose their functionality.

[0004] The object of the following invention is to propose an economical technical solution to solve this problem in order to increase the lifespan of electronic devices by improving the fluid and solid sealing of the electronic board of electronic devices. Description of the invention

[0005] The invention relates to a method for making a fluid- and solid-proof electronic device comprising the following steps: • To produce a unidirectional U-shaped housing, closed at each axial end by a stop plate, defining an internal cavity delimited by the internal surfaces of the two stop plates, an internal surface of a lower plate and the internal surfaces of two side plates, the internal cavity being open, the opening of which is delimited by a free edge of the housing, at least one of the internal surfaces of the side plates and / or stop plates having at least one groove extending from the edge of the housing to the internal surface of the lower plate; each internal surface of the side plates or the internal surface of the lower plate having at least one series of protruding elements arranged along the axial direction, preferably said housing having an orifice passing through one of the housing plates, • Position an electronic board inside the open case, the electronic board comprising at least one printed circuit board, at least one electronic component positioned on the printed circuit board, at least one sensor and the electronic board resting on at least one series of protruding elements of the case, preferably the electronic board being connected to at least one communication cable extending from the electronic board to the outside of the case through the opening of the case; • Pour a raw material into the internal cavity of the housing containing the electronic board to create an assembly until the electronic board is fully encapsulated. The pouring should be carried out through at least one groove in the housing. The material should have a hardness between a Shore D hardness of no more than 36 and a Shore 000 hardness of at least 35, and be fluid-tight at a temperature of 25°C in its cured state. • Place the assembly in a vacuum chamber. • Depressurize the assembly to a depressurization pressure PI for a duration T, and • Polymerize the raw material for a duration T' in order to obtain an encapsulation system for the electronic board.

[0006] The term "fluid-tight" here means that the encapsulation material can withstand a pressure of 10 bars, i.e., a column of water 100 meters high.

[0007] The technical problem is solved using this process, since the electronic board encapsulation system makes the board impermeable to fluids and solids once the encapsulation material has cured. In fact, the raw material is poured directly into the closed casing containing the electronic board. First, no mechanical manipulation of this encapsulation system is required for its placement inside the electronic device's casing, thus ensuring its physical integrity since it is manufactured directly at the point of use. Furthermore, this encapsulation system is protected by the electronic device's casing, which is just as rigid as the encapsulation system itself, particularly against external physicochemical attacks.Furthermore, the contact created between the internal surfaces of the housing and the encapsulation system provides either additional rigidity or a level of damping to the electronic device, enabling it to better withstand high external thermomechanical stresses while sealing the electronic device between the protective housing and the encapsulation system. Moreover, increasing this contact surface between the electronic board's encapsulation system and the housing helps to locally reduce stresses or deformations acting on structural elements of the electronic device.Furthermore, the contact created between the internal surfaces of the housing and the encapsulation system provides additional protection to the electronic device, enabling it to better withstand high external thermomechanical stresses while sealing the electronic device between the protective housing and the encapsulation system. Moreover, the damping characteristics of the electronic board's encapsulation system allow for the local reduction of stresses or deformations acting on structural elements of the electronic device.

[0008] In particular, the mechanical stresses and deformations suffered by the electronic board are reduced by increasing the application surface of the stresses or deformations on the electronic board, which diffuses and minimizes the mechanical stresses and deformations.

[0009] Furthermore, the process includes a degassing operation of the assembly consisting of the electronic board and the encapsulation system. Indeed, during the pouring of the raw material, air or fluid bubbles can become trapped on the electronic board or the internal surfaces of the casing. The assembly depressurization step increases the size of these trapped bubbles. This increase in size increases the likelihood that these bubbles will find a path through the raw material, which is in a fluid state, to escape from the assembly. During the subsequent pressurization phase, the bubble will have partially or completely escaped from the assembly or will be smaller than before the depressurization phase and will therefore have shifted position within the assembly.Thus, the depressurization step homogenizes the encapsulation system by reducing or eliminating potential air bubbles in the assembly. This depressurization is achieved by placing the electronic device housing, equipped with the assembly, in a vacuum chamber. The pouring of the raw material can take place after the device is placed in the vacuum chamber and the chamber has been depressurized to the target pressure.

[0010] To allow time for bubbles to move within the raw material, the depressurization step must last for a duration T that depends on the dimensions of the assembly and the geometry of the circuit board. The entire circuit board must be covered with the raw material to ensure complete encapsulation.

[0011] Once the assembly is homogeneous, meaning that most of the gas bubbles have been released (which, through condensation, can generate water droplets that may damage the electronic components or printed circuit boards), the assembly must be solidified by curing the raw material. Depending on the nature of the raw material, this curing can be carried out with or without crosslinking agents and according to standard elastomer crosslinking techniques. The temperature and pressure limits that the components of the electronic board can withstand must be respected. This results in an electronic device that is leak-proof and solid-proof because, firstly, an intimate mechanical contact is formed between the casing and the crosslinking system without fluid bubbles, due to the pouring of the raw material directly into the electronic device's casing.On the other hand, the electronic circuit board is embedded in the encapsulation system, which is homogenized by the depressurization process. As a result, the electrical and electronic components are no longer in contact with fluids, particularly water and air. Furthermore, the consistency of the crosslinked material ensures that it will not crack, even if a solid comes into contact with its free surface. In addition, the crosslinked material is chosen to be impermeable to water or any other fluids potentially present during use, thus ensuring fluid sealing. In the case of a soft crosslinked structure, the gel will deform to mechanically balance the solid attempting to enter the gel without causing the gel surface to tear. In the case of a rigid solid, a gap must be left between the free surface of the crosslinked material and the surface bearing against the free edge of the housing.For example, prior to placing an electronic device on the floor with the opening of the casing facing the floor, it would be advisable to clean the floor surface where the electronic device is to be placed of solids with a characteristic dimension greater than the thickness of the void so that the solids do not come into contact with the free surface of the encapsulation system of the electronic casing.

[0012] Preferably, the depressurization step is carried out by n depressurization cycles, preferably of a duration of T / 2n, between which the assembly returns to a nominal pressure PO, preferably for a duration T / 2n.

[0013] If the depressurization step occurs in several cycles, it is possible to expel a larger quantity of fluid, such as water or air. This is because depressurization leads to an increase in the volume of the fluid bubbles, which facilitates the search for a path through the raw material for the fluid to escape. When the assembly is repressurized, the remaining fluid bubbles shrink in volume, but there is no guarantee that the position of the newly pressurized bubble will be exactly the same as it was during the previous pressurization cycle. This geographical displacement of the bubbles within the raw material then allows for the discovery of alternative fluid escape paths during the next depressurization step. Necessarily, the nominal pressure PO during the pressurization cycle is higher than the depressurization pressure PI.

[0014] Advantageously, depressurization or pressurization is done gradually.

[0015] It is possible to apply pressurization and depressurization pressures in stepped increments. However, the applicant has observed that a gradual pressurization or depressurization using a progressive time evolution between the nominal pressure PO and the depressurization pressure PI allows for gradual changes in bubble volume, making it easier to find leakage paths through the raw material, which is more effective for degassing the raw material.

[0016] Most advantageously, the depressurization stage comprises 3 to 10 cycles, preferably 5 cycles.

[0017] The applicant observed that increasing the number of cycles during the depressurization stage was beneficial for effectively removing the fluid trapped within the raw material. Depending on the dimensions of the electronic device and the geometry of the circuit board, the efficiency of this degassing is achieved more or less quickly. In standard electronic devices of a drive-over system for a passenger vehicle or freight vehicle, five cycles appear to be the most effective for sufficient fluid degassing from the raw material relative to the cycle time of the operation, thus optimizing the cost of the depressurization process.

[0018] According to a preferred embodiment, the depressurization step is carried out with a maximum pressure variation of between 0.1 and 0.9 bars, preferably 0.8 bars.

[0019] The greater the pressure variation, the more the volume of the fluid bubbles changes between extreme pressures, thus allowing the fluid to find a path of escape from the raw material. In simple applications, the nominal pressure P is atmospheric pressure. The targeted pressure range allows this level of vacuum to be created using a standard vacuum chamber. When the vacuum is too high, bubble formation occurs in certain raw materials, such as silicones. This physical phenomenon, called foaming, becomes problematic for the homogenization of the raw material before curing. This foaming of the raw material must be avoided. Therefore, the targeted range allows both the prevention of foaming of raw materials and the ensuring a sufficient variation in bubble volume to optimize the escape of unwanted fluids within the assembly in a reasonable timeframe.

[0020] Preferably, the duration T of the depressurization step is between 1 second and 120 seconds, preferably between 30 seconds and 50 seconds.

[0021] Depending on the dimensions of the open housing and the geometry of the electronic board, this duration ensures sufficient degassing of the fluids within the assembly. For standard housing geometries used in drive-over systems for passenger vehicles or large vehicles transporting goods or people, a duration of 30 to 50 seconds appears satisfactory for efficient fluid degassing within the assembly, thus optimizing the manufacturing cost of the depressurization operation.

[0022] According to a first specific embodiment, during the operation of pouring the raw material into the open casing, a void is left between the free surface of the raw material at the end of the filling and a flat surface resting on the free edge of the casing.

[0023] In the event of foaming of the raw material during the depressurization stage, or a change in the pouring conditions leading to an increase in the volume of raw material poured, this vacuum prevents any overflow of the raw material outside the open casing. Generally, especially with silicone-type raw materials, overflow of raw material from the open casing leads to contamination of the casing's exterior, particularly at the free edge, which can render the casing unsuitable for future use.

[0024] Preferably, the duration T' of the polymerization step is between 1 hour and 48 hours, preferably 24 hours.

[0025] Depending on the dimensions of the open enclosure, the geometry of the circuit board, and the nature of the raw material, the polymerization time of the raw material must be set within the specified range. For standard enclosure geometries used in drive-over systems for passenger vehicles or large vehicles for transporting goods or people, a polymerization time of 24 hours appears to be efficient for setting the assembly geometry and positioning the circuit board within the assembly. Polymerization occurs when the encapsulation system is poured into the open enclosure. Therefore, the exposure of the raw material to ambient air is limited to the moment the enclosure is opened.

[0026] Preferably, when the material in the crosslinked state has a hardness between Shore 000 of at least 35 and Shore A of at most 90, the process includes a step of closing the case using a closing plate fixed to the free edge of the case.

[0027] If the circuit board's encapsulation system is less rigid than the open casing, solids can come into contact with it. Although the soft structure of the encapsulation system limits potential damage, depending on the sharpness of the solids, cracks may appear in the encapsulation system. Sealing the open casing with the closure plate prevents cracks from forming in the encapsulation system, which are potential pathways for contamination of the device's circuit board, leading to a reduced lifespan of the circuit board.

[0028] Preferably, the fixing of the closing plate is ensured by an adhesive agent placed between the free edge of the case and the closing plate.

[0029] Here, the enclosure's obstruction is sufficient to ensure the sealing function, particularly the seal against solids. Therefore, the system for attaching the cover plate to the enclosure does not perform any specific mechanical function. Thus, an adhesive agent is sufficient, provided it is chemically compatible with the materials of the protective enclosure and the cover plate.

[0030] Advantageously, the adhesive agent is a double-sided adhesive tape which is attached in a first step to the edge of the case.

[0031] Very advantageously, before the depressurization stage, one side of the double-sided adhesive tape is fixed to a part of the free edge of the casing, leaving the protective film on the second side of the adhesive tape.

[0032] In the event of foaming of the raw encapsulation material during the depressurization step, the presence of the adhesive tape protects the free edge surface of the package from any chemical attack by the raw material. Therefore, removing the second side of the tape allows the closure plate to be attached even if the encapsulation material has foamed during the process, thus reducing the need for discarding the electronic devices produced. Thus, the double-sided adhesive tape serves to protect the package surface during the depressurization step and to secure the closure plate once the protective backing of the second adhesive side of the tape is removed.

[0033] Optionally, the process includes, before the step of positioning the electronic board inside the open case, a step of placing at least one fastening element between at least two elements of the electronic board.

[0034] Advantageously, at least one of the fixing elements is an adhesive.

[0035] To optimize the process cycle time, it is preferable to assemble the electronic board outside the open enclosure. To ensure optimal positioning of the electronic board within the enclosure, taking into account the manufacturing tolerances of both the individual board components and the open enclosure itself, adhesive bonding of the components provides sufficient freedom of movement. This avoids forcing the board into the enclosure while still securing the components together. This bonding is further reinforced by the board's encapsulation system. More rigid fixings, such as bolts or solder joints, can excessively constrain the board's geometry and thus hinder its placement within the enclosure.The alternative is to perform certain assemblies between the elements of the card within the open case itself, which is costly in cycle time but also difficult due to the dimensions of the mainly unidirectional case. Brief description of the drawings

[0036] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and made with reference to the accompanying figures in which the same reference numbers designate identical parts throughout and in which: • Fig. 1 presents a synoptic diagram of the process according to the invention. • Fig. 2 shows an example of a protective case for an electronic device. • Fig. 3 shows an example of an electronic board intended to be incorporated into the protective housing. • Fig. 4 shows a view of an assembly of a protective housing equipped with its electronic board before the casting stage. • Fig. 5 shows an example of the electronic device encapsulation system following the crosslinking step of the raw material cast in the protective housing. • Fig. 6 shows a cross-sectional view of an example of an electronic device including a closure plate to make the electronic device watertight against solids. Detailed description of the implementation methods

[0037] Fig. 1 illustrates the synoptic diagram of the process for manufacturing 1000 of an electronic device that is sealed against fluids and solids.

[0038] The first step 1001 consists of creating a protective case to house the electronic board of the device and in which the encapsulation system of the electronic board will be formed.

[0039] The second step, 1002, consists of positioning the electronic board within the protective housing to avoid pre-stressing the board and to ensure its correct alignment with the housing's external surfaces. Indeed, in certain configurations of the electronic device, its functionality requires precise geometric alignment of the board's sensors with the outer surface of the protective housing, similar to determining the remaining tread depth of a tire. Preferably, the electronic board, once positioned in the protective housing, is pre-assembled with all its components, which improves the process cycle time because this assembly can be performed outside the flow.However, it is perfectly possible to position part of the circuit board within the protective enclosure and to secure certain components of the circuit board directly within the enclosure. The circuit board assembly step is described in step 1008 of Figure 1. The double arrow between step 1002 and step 1008 illustrates the various assembly paths mentioned.

[0040] Once the entire circuit board is installed in the protective housing, the process moves to step 1003, which involves pouring raw material into the internal cavity of the housing containing the circuit board. The assembly of the circuit board and the open protective housing then constitutes a single assembly. Part of the internal cavity of the open housing is filled by grooves on the internal surfaces of the side plates and / or the end plates of the protective housing, extending from the free edge of the open housing to the internal surface of the bottom plate of the housing.

[0041] The pouring of the raw material in its liquid state is done simply by gravity. Filling the internal cavity ensures complete encapsulation of the assembly's circuit board by the raw material. A gap may remain between the free surface of the raw material and the flat surface of the housing, delimited by the free edge of the housing. Performing this pouring within the internal cavity of the housing creates an intimate contact surface between the raw material and the internal surfaces of the housing and the circuit board. This intimate contact ensures adhesion of the material to the solid components across almost the entire surface of the protective housing and the circuit board, thus increasing the rigidity of the electronic device and minimizing the stresses exerted locally on the circuit board during external loads on the electronic device during its use.

[0042] Next, the assembly with the fluid cavity filling is placed in a vacuum chamber during step 1004. It is quite possible, as illustrated by the dotted arrows, to carry out step 1004 of placing the assembly in the vacuum chamber before step 1003 of pouring the raw material into the internal cavity of the housing, which avoids potentially handling and / or moving the assembly with the presence of the liquid material within the internal cavity of the housing.

[0043] To ensure the homogeneity of the electronic board's encapsulation system, and in particular the absence of air or water within the encapsulation material, the assembly must be degassed after the internal cavity of the package has been filled with the raw material. This degassing, performed during step 1005, consists of depressurizing the assembly, which, in the liquid material, will cause a change in the characteristic dimensions of the gas bubbles. During depressurization, the gas bubbles will increase in size, while during pressurization or return to nominal pressure, their size will decrease. These gas bubbles become trapped within the assembly, primarily due to solid components obstructing the bubble evacuation pathways, mainly in the direction of gravity.Increasing the size of the bubbles often allows the gas to find a leak path through the liquid that was inaccessible to smaller bubbles obstructed by solids. The complete leakage of the gas ensures the disappearance of the initial bubble upon return to nominal pressure. If the gas leak is partial during depressurization, returning to nominal pressure leads to a decrease in bubble size due to the gas leak, which is accompanied by a shift in the location of the gas bubble relative to the solid elements of the assembly. Therefore, repeating the pressurization / depressurization cycles leads to the complete disappearance of gas bubbles in the encapsulation system. Consequently, in a preferred embodiment, the depressurization step is performed by repeating n depressurization cycles.Indeed, these bubbles eventually escape from the encapsulation system through the free surface created at the end of the internal cavity filling during step 1003 of the casting process. These gas bubbles are detrimental to the durability of the electronic device if these bubbles, containing water molecules, come into contact with electrical or electronic components on the circuit board. To prevent the risk of "foaming" of the raw material during the depressurization step 1004, for example, with silicone-based gels, it is preferable to place a protective layer on the free edge of the protective housing, such as double-sided tape, with the protective film facing away from the housing. The foaming of the raw material during depressurization leads to a rapid increase in the volume of the raw material, which will naturally escape through the opening of the protective housing.In addition to this protection, it is possible to leave a gap at the end of the pouring step 1003 between the free surface of the raw material and a dummy surface resting on the free edge of the protective casing. This allows the onset of foaming to be addressed by modifying the pressure or temperature conditions during the depressurization step 1004 without triggering an uncontrolled foaming phenomenon.

[0044] Once the liquid material is homogenized, meaning that almost all gas bubbles have been eliminated, the encapsulating material is solidified during polymerization step 1006. This polymerization is gentle to avoid thermomechanical stress on the assembly, particularly the electronic board. Preferably, this polymerization of the raw material is carried out under ambient temperature and pressure conditions over a long period. It is also possible to accelerate the polymerization time by adding accelerations to the chemical crosslinking reaction or by modifying the pressure and temperature conditions, while taking care to respect the maximum stresses that can be tolerated by the components of the electronic board and the protective housing material.

[0045] Finally, the last optional step 1007 consists of sealing the opening of the electronic device's open casing with a closure plate. This prevents solids from penetrating the protective casing, even without a gap between the free edge of the casing and the free surface of the encapsulation system. For cross-linked materials in the encapsulation system with low rigidity, this also prevents significant deformation upon contact with sharp objects, which could initiate cracks in the encapsulation system and lead to malfunctions of the electronic board over time.In a specific embodiment, the closure plate is attached to the protective housing using an adhesive, for example, double-sided tape, to hold the closure plate in position relative to the housing. This adhesive can be applied in a closed loop around the free edge of the protective housing to provide, for example, an additional fluid seal.

[0046] Fig. 2 shows a perspective view of an example of a protective housing (2) for the electronic device. This housing (2), unidirectional along a principal direction Y, has a U-shaped cross-section. This creates an opening providing access to an internal cavity 20 that will house the future electronic circuit board of the electronic device. The opening is delimited by a free edge 40 on the perimeter of the protective housing 2. The protective housing 2 consists of a lower plate 13 whose normal is directed along the Z direction and two parallel side plates 13 and 14, whose normal is directed along the X direction. The lower plate 13 and the side plates 14 and 15 together form the U-shaped cross-section. The axial ends of the protective housing 2 are blocked by stop plates 11 and 12, whose normal is primarily directed along the Y direction, which axially delimit the axial dimension of the protective housing 2.Here, the plates are made from a monolithic block using a molding process. It is entirely possible for the plates to be manufactured individually and then assembled using fastening techniques adapted to the material(s) of the protective housing 2 and commonly used in the state of the art. Finally, an opening 3 passing through one of the plates of the protective housing 2, here the stop plate 11, allows the passage of a communication wire between the electronic circuit board of the electronic device and the outside of the protective housing 2. This communication wire allows, for example, the power supply to the electronic circuit board and / or the transmission of information between the outside of the housing 2 and the electronic circuit board to give instructions to the electronic circuit board and / or retrieve data from the electronic circuit board, such as the outputs of the electronic circuit board's sensors.An alternative would be a source to power the electronic device electrically such as a battery and / or a radio frequency communication system to provide power to the electronic device by radio frequency waves or to receive and transmit data to and / or from outside the electronic device.

[0047] The plates 11, 12, 13, 14 and 15 each having an internal surface 31, 33 and 35 internal to the protective housing 2. These internal surfaces 31, 33 and 35 delimit the internal cavity 20 of the protective housing 2.

[0048] In the specific case of this casing, the internal surfaces 35 of the side plates 14 and 15 have grooves 41 along the entire length of the protective casing 2. These grooves 41 open onto the free edge 40 of the protective casing 2 and extend to the internal surface 33 of the lower plate. These grooves allow the raw material of the encapsulation system to pass through during the casting stage. Similarly, these grooves also serve as escape routes for gas bubbles during the depressurization stage, particularly since they extend to the bottom of the internal cavity 20 of the protective casing 2, which acts as a reservoir for the raw material at the end of the casting stage. It would have been possible to place such grooves on the internal surfaces 31 of the stop plates, but this is not the case in this example.

[0049] Finally, a series of protruding elements 45 are positioned on the inner surface 33 of the lower plate 13. These elements 45 are positioned to accommodate the electronic circuit board. They ensure a common distance between certain elements of the electronic circuit board and the outer surface of the lower plate 13, which is intended to be in contact with the objects to be measured. Consequently, these elements 45 ensure isostatic alignment of the electronic circuit board with the protective housing 2. Furthermore, the large number of these elements 45 allows for a better distribution of thermomechanical stresses on the electronic circuit board during operation of the electronic device, thus improving the durability of the electronic circuit board and, therefore, that of the electronic device.Although the example of this housing 2 does not illustrate it here, these elements 45 could also have been arranged on the internal surfaces 35 of the side plates 14 and 15 while having the same functionality. This protective housing 50 is the final result of step 1001 of the process shown in Figure 1.

[0050] Fig. 3 shows an example of an electronic circuit board 50 designed to be inserted into an internal cavity of a protective housing like the one illustrated in Figure 1. This electronic circuit board comprises a first printed circuit board 60 equipped with measuring sensors 71. In this example, the measuring sensors 71 are Hall effect sensors for measuring the variation of the magnetic field. However, they could just as easily have been force sensors measuring the forces applied to the electronic circuit board. Each sensor 71 is associated with a static magnetic field source 80 in the form of a ring-shaped magnet with an axial magnetic field, meaning that the magnetic poles are positioned along the axis of revolution of the ring. In this case, the magnetic poles are oriented along the Z direction.These static magnetic field sources could have been constructed using solenoids whose axis of revolution is directed along the Z-axis and powered by a DC current source. This configuration requires a DC current source attached to the electronic board 50.

[0051] Here, the electronic board 50 includes a second printed circuit board 61 containing electronic components 70 such as a microprocessor, memory, and a current transformer. This second printed circuit board 61 is the brain of the electronic board 50. It is wired to the first printed circuit board 60 to receive signals from the measurement sensors 71. The printed circuit board enables the wired transmission of this data and its routing to the memory for storage. The transmitted data is then processed to obtain a result that will be transmitted outside the board via wired or radio frequency communication. In this specific case, the electronic board is powered via a communication cable, which is not shown in the figure.In the electronic board 50 shown in Figure 3, the static magnetic field sources 80 are attached to the first printed circuit board 60 using an adhesive that allows for degrees of freedom in the dimensions of the electronic board 50, thus facilitating its insertion into the protective housing. In contrast, the measurement sensors 71 are precisely fixed to the electronic board 50, specifically their altitude along the Z direction. Here, the ring-shaped magnets 80 are contact points with the protruding elements of the protective housing. The electronic board 50 is primarily unidirectional along the Y direction. This electronic board 50 is the final result of step 1008 of the process shown in Figure 1.

[0052] Fig. 4 shows the assembly resulting from step 1002 of the process described in Figure 1. This corresponds to the positioning of the electronic board 50, illustrated in Figure 3, within the protective housing 2 shown in Figure 2. The assembly thus formed is ready for step 1003, which involves pouring the raw material into the internal cavity of the protective housing in which the electronic board 50 is positioned. This is therefore the shape of the electronic device 1 that will be obtained at the end of the various steps of the process shown in Figure 1.

[0053] Fig. 5 shows the encapsulation system 100 of the electronic card 50 obtained at the end of steps referenced 1005 and 1006 of the process shown in figure 1.

[0054] Here, the electronic board 50 is completely encased in an encapsulation material. The encapsulation system is manufactured within the internal cavity of the protective housing. Consequently, the surfaces 31', 32', 33', 34', and 35' shown here are each part of the internal surfaces of the protective housing plates. They therefore conform to the geometry of the housing. This figure does not depict the internal surfaces of the plates for clarity. This representation also does not show the communication cable connected to the electronic board 50 and passing through the through-hole in the stop plate of the protective housing shown in Figure 1, for example. Figure 5 illustrates the encapsulation system material 100 in a cross-linked state, that is, at the end of step 1006 of the process shown in Figure 1.Prior to the crosslinking of the material, degassing of bubbles was carried out within the raw material during step 1005 of the process shown in Figure 1. As a result, since the raw material was homogenized, the crosslinked material of the encapsulation system 100 is also inherently homogenized. Because the casting and crosslinking of the encapsulation system 100 material took place within the internal cavity of the protective housing, no handling of this encapsulation system 100 (gripping, movement) was performed, thus limiting local deformations and making it more durable.There is not necessarily complete desuperposition between the surfaces 31', 32', 33', 34' and 35' of the encapsulation system 100 and the internal surfaces of the plates of the open protective housing if a void space has been generated at the end of the filling by the raw material of the internal cavity of the open housing (final state of the step referenced 1003 of the process shown in Figure 1) to avoid any overflow of the raw material outside the housing during the depressurization step referenced 1005 in the process shown in Figure 1.

[0055] Figure 6 shows the optional step, referenced as 1007, of the process shown in Figure 1, which consists of blocking the opening of the initially open protective housing 2 by means of a closing plate 16. Previously, the electronic board 50 was placed in the internal cavity of the housing 2 to form an assembly. An encapsulation system for the electronic board 50 was then fabricated by pouring a raw liquid material into the internal cavity of the assembly, followed by cross-linking the material to give it fluid-tight properties and surface hardness. This closing plate 16 rests here on the free edge of the open case 2. In this specific case, the fixing system between the closing plate 16 and the open case 2 is a double-sided adhesive tape 21 placed on the two longest sides of the free edge of the case 2. In a first step, one side is fixed to the case 2.Preferably, this first step takes place before the depressurization step referenced 1005 in the process shown in Figure 1. This prevents chemical damage to the free edge of the casing 2 from the raw material of the encapsulation system during the depressurization step should foaming occur. The protective backing of the adhesive tape is then removed just before the closure plate 16 is presented during step referenced 1007 in the process shown in Figure 1.

Claims

DEMANDS 1. Method for making (1000) an electronic device (1) that is leak-proof against fluids and solids, comprising the following steps: - To fabricate (1001) a unidirectional U-shaped housing (2), closed at each axial end by a stop plate (11, 12), defining an internal cavity (20) delimited by the internal surfaces (31, 32) of the two stop plates (11, 12), an internal surface (33) of a lower plate (13) and the internal surfaces (34, 35) of two side plates (14, 15), the internal cavity (20) being open, the opening of which is delimited by a free edge (40) of the housing (2), at least one of the internal surfaces (31, 32, 34, 35) of the side plates (14, 15) and / or the stop plates (11, 12) having at least one groove (41) extending from the free edge (40) of the housing (2) to the internal surface (33) of the lower plate (13);each internal surface (34, 35) of the side plates (14, 15) or the internal surface (33) of the lower plate (13) having at least one series of protruding elements (45) arranged along the axial direction, preferably said housing (2) having an orifice (3) passing through one of the plates (11, 12, 13, 14, 15) of the housing (2); - Position (1002) an electronic card (50) inside the open housing (2), the electronic card (50) comprising at least one printed circuit board (60, 61), at least one electronic component (70) positioned on the printed circuit board (60, 61), at least one sensor (71) and the electronic card (50) resting on at least one series of protruding elements (45) of the housing (2), preferably the electronic card (50) being connected to at least one communication cable extending from the electronic card (50) to the outside of the housing (2) through the opening (3) of the housing (2);- To pour (1003) a raw material into the internal cavity (20) of the housing (2) comprising the electronic board (50) in order to constitute an assembly up to the total encapsulation of the electronic board (50), the pouring being carried out through at least one groove (41) of the housing (2) and the material having a hardness between a Shore D hardness of no more than 36 and a Shore 000 hardness of at least 35 and being hermetic to fluids at a temperature of 25° Celsius in the crosslinked state; - Place (1004) the assembly in a vacuum chamber; - Depressurize (1005) the assembly between a depressurization pressure PI and a nominal pressure PO for a duration T; and - Polymerize (1006) the raw material for a duration T' in order to obtain a crosslinked material.

2. Method of making (1000) an electronic device (1) sealed against fluids and solids according to claim 1 in which the depressurization step (1005) is carried out by n depressurization cycles, preferably of a duration of T / 2n, between which the assembly returns to a nominal pressure PO, preferably for a duration T / 2n.

3. Method of making (1000) an electronic device (1) sealed against fluids and solids according to claim 2 in which the depressurization or pressurization during the depressurization step (1005) is done gradually.

4. Method of making (1000) an electronic device (1) sealed against fluids and solids according to any one of claims 2 to 3 wherein the depressurization step (1005) comprises 3 to 10 cycles, preferably 5 cycles.

5. Method of making (1000) an electronic device (1) sealed against fluids and solids according to any one of claims 2 to 4 wherein the depressurization step (1005) is carried out with a maximum pressure variation of between 0.1 and 0.9 bars, preferably 0.8 bars.

6. Method of making (1000) an electronic device (1) that is fluid and solid sealed according to any one of claims 1 to 5 wherein the duration T of the depressurization step (1005) is between 1 second and 120 seconds, preferably between 30 seconds and 50 seconds.

7. Method of making (1000) an electronic device (1) that is fluid and solid sealed according to any one of claims 1 to 6 wherein during the operation of pouring (1003) the raw material into the open housing (2), a void is left between the free surface of the raw material at the end of the filling and a flat surface bearing against the free edge (40) of the housing (2).

8. Method of making (1000) an electronic device (1) that is fluid and solid sealed according to any one of claims 1 to 7 wherein the duration T' of the polymerization step (1006) is between 1 hour and 48 hours, preferably 24 hours.

9. Method of making (1000) an electronic device (1) sealed against fluids and solids according to any one of claims 1 to 8 wherein when the material in the crosslinked state has a hardness between Shore 000 of at least 35 and Shore A of at most 90, the method (1000) includes a step of closing (1007) the housing (2) using a closing plate (16) fixed on the free edge (40) of the housing (2).

10. Method of making (1000) an electronic device (1) sealed against fluids and solids according to claim 9 in which the fixing of the closure plate (16) is ensured by an adhesive agent disposed between the free edge (40) of the housing (2) and the closure plate (16).

11. Method of making (1000) an electronic device (1) sealed against fluids and solids according to claim 10 in which the sticking agent is a double-sided adhesive tape (21) which is fixed in a first step on the free edge (40) of the housing (2).

12. Method of making (1000) an electronic device (1) sealed against fluids and solids according to any one of claims 10 in which, before the depressurization step (1005), a first side of the double-sided adhesive tape (21) is fixed to a part of the free edge (40) of the housing (2) leaving the protective film on the second side of the adhesive tape.

13. Method of making (1000) an electronic device (1) sealed against fluids and solids according to any one of claims 1 to 12 in which the method (1000) comprises, before the step of pouring (1003) the raw material into the housing, a step of placing (1008) at least one fixing element between at least two elements of the electronic board (2).

14. Method of making (1000) an electronic device (1) sealed against fluids and solids according to claim 13 wherein at least one fixing element is an adhesive.

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