Humidity detection by impedance measurement between two lanes

Description

[0001] The invention relates to the field of humidity detection on electronic boards. BACKGROUND OF THE INVENTION

[0002] There are a number of causes that can lead to excessively high humidity levels on an electronic circuit board.

[0003] One such cause is as follows. In the case of a coated or overmolded circuit board, if the resin is not properly degassed (a necessary process to eliminate all air bubbles before polymerization), the bubbles can become trapped near the board's electronic components. Temperature fluctuations can then cause condensation, leading to a significant risk of short circuits and corrosion.

[0004] It is known that a humidity sensor is used to assess the humidity level on a map. A capacitive sensor integrated into a surface-mount package (SMD) is frequently used for this purpose. Composant Monté en Surface ) to measure humidity.

[0005] This type of sensor presents the following problem. The sensor's performance is limited when soldered onto an electronic board covered with resin (such as a flexible resin) or varnish, because the resin or varnish obstructs the sensor and reduces the reliability of the measurements.

[0006] Furthermore, the power consumption of this type of sensor is relatively high, which can be a drawback for certain applications. In fluid meters, for example (water, gas, etc.), the electronic functions are generally powered by a battery, and it is therefore crucial to minimize the power consumption of these functions.

[0007] US 45 98 333 and US 88 23 535 disclose moisture detection devices on a printed circuit board based on a current measurement between two conductive traces printed on the circuit. SUBJECT OF THE INVENTION

[0008] The invention aims to improve the efficiency of moisture detection on or in a printed circuit board, while reducing the electrical consumption required by this detection. SUMMARY OF THE INVENTION

[0009] To achieve this goal, a humidity monitoring device on a printed circuit board is proposed, according to claim 1.

[0010] The monitoring device is capable of detecting the presence of moisture on the printed circuit board, even when it is covered with resin or varnish.

[0011] The monitoring device is extremely simple to build and very inexpensive, since conductive traces printed on the circuit board act as sensors. The monitoring device's power consumption is very low.

[0012] We also propose a monitoring device as previously described, in which the test voltage is a DC voltage.

[0013] We also propose a monitoring device as previously described, in which the first portion of track and the second portion of track are covered with a protective coating intended to prevent a main material, with which the first conductive track and the second conductive track are made, from corroding.

[0014] In addition, a monitoring device as previously described is proposed, with the protective coating being gold-nickel.

[0015] We also propose a monitoring device as previously described, in which the first conductive track and the second conductive track form two loop-shaped electrodes.

[0016] We also propose a monitoring device as previously described, in which the first conductive track and the second conductive track form two interdigitated electrodes.

[0017] Furthermore, a monitoring system as previously described is proposed, in which: The first conductive track is connected to at least one first castellation formed in one thickness of the printed circuit board, and the second conductive track is connected to at least one second castellation formed in the thickness of the printed circuit board. the test voltage being applied to the first conductive track and the target voltage being measured on the second conductive track.

[0018] We also propose a monitoring device as previously described, in which the first conducting track has two first sections connected to each other, perpendicular to each other and each connecting two first castellaments to each other, and the second conducting track has two second sections connected to each other, perpendicular to each other and each connecting two second castellaments to each other.

[0019] We also propose a monitoring device as previously described, in which the first conductive track and the second conductive track are located on the same layer of the printed circuit board.

[0020] We also propose a monitoring device as previously described, in which said layer is an internal layer of the printed circuit board.

[0021] We further propose a monitoring device as previously described, comprising a first conductive track and a second conductive track located on a first layer of the printed circuit, and another first conductive track and another second conductive track located on a second layer of the printed circuit, the first conductive tracks being connected to each other by at least one first through via and the second conductive tracks being connected to each other by at least one second through via.

[0022] We also propose a monitoring device as previously described, comprising several first conductive tracks connected in series and several second conductive tracks connected in series.

[0023] We also propose a monitoring device as previously described, comprising several first conductive tracks connected in parallel and several second conductive tracks connected in parallel.

[0024] We also propose a monitoring device as previously described, in which the first conductive track and / or the second conductive track are also used to carry signals used for another function, the detection of the excessively high humidity level being carried out by the monitoring device when said other function is inactive.

[0025] We also propose a monitoring device as previously described, in which electrical components are mounted on the printed circuit board, these electrical components including a component most sensitive to humidity, the most sensitive component being positioned in an area surrounded by the first conductive track and the second conductive track.

[0026] We also propose a monitoring device as previously described, comprising an analog comparator and a voltage source, the target voltage being compared by the analog comparator with a reference voltage produced by the voltage source, the predetermined threshold thus being an analog threshold.

[0027] We also propose a detection method, implemented in a monitoring device as previously described, comprising the following steps: apply a test voltage on one of the first conductive track and second conductive track, the other of the first conductive track and second conductive track being connected to a constant or controlled voltage reference; compare a target voltage, representative of an impedance between the first conductive track and the second conductive track, with a predetermined threshold, said impedance being reduced in the presence of moisture; detect an excessive moisture level on or in the printed circuit board, between the first conductive track and the second conductive track, based on a result of said comparison.

[0028] We also propose a computer program comprising instructions which lead the test device of the monitoring device as previously described to execute the steps of the detection process as previously described.

[0029] In addition, a computer-readable recording medium is proposed, on which the computer program as previously described is recorded.

[0030] The invention will be better understood in light of the following description of particular, non-limiting embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Reference will be made to the attached drawings, among which: [ Fig. 1 ] there figure 1 is a cross-sectional view of a portion of a printed circuit board according to a first embodiment, along a plane perpendicular to said printed circuit board; [ Fig. 2 ] there figure 2 represents the first conductive track and the second conductive track forming loop-shaped electrodes, as well as a test device according to a first embodiment; [ Fig. 3 ] there figure 3 represents the first track and the second track forming interdigitated electrodes; [ Fig. 4 ] there figure 4 represents the first conductive track and the second conductive track forming electrodes in a castellar configuration; [ Fig. 5 ] there figure 5 represents the first conductive track and the second conductive track forming loop-shaped electrodes, as well as a test device according to a second embodiment; [ Fig. 6 ] there figure 6 represents the first conductive track and the second conductive track forming loop-shaped electrodes, as well as a test device according to a third embodiment; [ Fig. 7 ] there figure 7 represents the first conductive track and the second conductive track forming loop-shaped electrodes, as well as a test device according to a fourth embodiment; [ Fig. 8 ] there figure 8 represents the steps in a detection process; [ Fig. 9 ] there figure 9 is a cross-sectional view of a portion of a printed circuit according to a second embodiment, along a plane perpendicular to said printed circuit. DETAILED DESCRIPTION OF THE INVENTION

[0032] With reference to figures 1 And 2 , a water meter 1 includes an electronic board 2 comprising a printed circuit board 3 on which electronic components are mounted.

[0033] Electronic components include components performing one or more various functions implemented in a water meter: metrology functions (measuring water consumption), communication (transmitting consumption measurements, interfacing with the user), monitoring (detecting leaks, meter malfunctions, attempted fraud), powering the electronic board components, etc.

[0034] The water meter 1 includes a monitoring device 5 for the humidity level prevailing on the printed circuit board 3.

[0035] The monitoring device 5 includes a first conductive track 6a (of copper for example) and a second conductive track 6b (of copper for example) printed here on the same layer (top layer) of the printed circuit 3. The first track 6a and the second track 6b are not connected to each other.

[0036] The first track 6a and the second track 6b form two electrodes, each in the shape of a loop. The first electrode thus forms a first loop and the second electrode forms a second loop. Each loop has the shape of a rectangle with rounded corners.

[0037] The first track 6a and the second track 6b are arranged so that the second track 6b surrounds the first track 6a.

[0038] The first track 6a is therefore located inside the second loop formed by the second track 6b.

[0039] The first 6a run and the second 6b run have the same shape, but the dimensions of the second 6a run are slightly smaller than those of the first 6b run. The second 6b run parallel to the first 6a run along their entire length.

[0040] The first track 6a and the second track 6b are very close: each point of the first track 6a is located at a distance from a nearest point of the second track 6b, which is between 1% and 10% of a larger dimension of the shape of the first electrode and / or the second electrode.

[0041] Here, the largest dimension of the first electrode is the length L1, and the largest dimension of the second electrode is the length L2.

[0042] Printed circuit board 1 is coated with solder varnish 7 over a large part of its outer layers (upper and lower).

[0043] The first track 6a includes (at least) a first portion of track 8a, which is not covered with solder mask, and the second track 6b includes (at least) a second portion of track 8b, which is not covered with solder mask.

[0044] Here, the first track 6a includes three first portions of track 8a not covered with solder mask and the second track 6b includes three second portions of track 8b not covered with solder mask.

[0045] For the first track 6a, the first portions of track 8a are located on a first side (length) of the first loop, on a second side (width) of the first loop, and on a third side (length) of the first loop.

[0046] Similarly, for the second track 6b, the second sections of track 8b are located on a first side (length) of the second loop, on a second side (width) of the second loop, and on a third side (length) of the second loop.

[0047] Each first section of track 8a is associated with a second section of track 8b. The first section of track 8a extends over the first segment of the first track 6a. The second section of track 8b extends over the second segment of the second track 6b.

[0048] The first and second segments run parallel to each other on the printed circuit board 3, are substantially parallel (that is to say they extend substantially in the same direction without electrical contact), have substantially the same length (possibly with a small difference, on the order of mm for example), and have their ends substantially aligned along X axes perpendicular to said segments (possibly with a small difference, on the order of mm for example).

[0049] The first sections of track 8a and the second sections of track 8b are defined in areas in which the first track 6a and the second track 6b have dimensions that are perfectly controlled in manufacturing.

[0050] Each first segment of track 8a is therefore defined on the first segment of the first track 6a. The first segment of track 8a is defined along the entire length and an internal portion of the width of the first segment. Similarly, each second segment of track 8b is defined on the second segment of the second track 6b. The second segment of track 8b is defined along the entire length and an internal portion of the width of the second segment.

[0051] By "internal," we mean on the side of a plan P (visible on the figure 1 ) perpendicular to the printed circuit 1, located between the first portion of track 8a and the second portion of track 8b associated and parallel to them; the first portion of track 8a and the second portion of track 8b are therefore arranged opposite each other and symmetrically with respect to plane P.

[0052] Surface 9 of printed circuit 1 located between each first portion of track 8a and the associated second portion of track 8b is also not covered with solder mask.

[0053] However, the entire surface of each of the first section of runway 8a and second section of runway 8b is covered here by a protective coating 11, which is preferably made of gold-nickel.

[0054] The coating is intended to prevent a main material, from which the first track 6a and the second track 6b are made, from corroding.

[0055] The lateral edges of each of the first sections of runway 8a and second sections of runway 8b are also covered with this protective coating 11.

[0056] It is also noted that here, the entire printed circuit board 1 is covered with a resin 12 (which therefore also covers the first and second portions of track 8a, 8b, not covered with solder varnish).

[0057] The monitoring device 5 further includes a test device 15.

[0058] Here, the test device 15 includes electronic components that are mounted on the printed circuit board 1 (but they could be positioned on another board).

[0059] Test device 15: • applies a test voltage Vt on the first track 6a (possibly via one or more components), the second track 6b being connected to a constant or controlled voltage reference; • compares a target voltage Vc, representative of an impedance between the first track 6a and the second track 6b, with a predetermined threshold, said impedance being reduced in the presence of humidity; • detects an excessively high level of humidity on or in the printed circuit board 1, between the first track 6a and the second track 6b, based on a result of said comparison.

[0060] The constant or controlled voltage reference, to which the second track is connected, is here an electrical ground 23. The second track is connected to this electrical ground 23 via passive components (17, 18, 19) described below.

[0061] The test voltage Vt is a DC voltage, and the impedance is a DC current impedance. The impedance between the first track 6a and the second track 6b depends on current leakage due to the presence of moisture.

[0062] The test device 15 here includes a microcontroller 16, a resistor 17, an inductor 18 and a capacitor 19.

[0063] The microcontroller 16 incorporates an analog-to-digital converter (ADC) 20a. The test device 15 also includes one or more memories 20b, connected to or integrated into the microcontroller 16. At least one of these memories 20b forms a computer-readable recording medium, on which is recorded at least one computer program comprising instructions which lead the microcontroller 16 to execute at least some of the steps of the detection process which will be described below.

[0064] The microcontroller 16 has an output 21 (CTRL output), and an input 22 which is connected to its CAN 20a.

[0065] Output 21 is connected directly to the first track 6a. Input 22 is connected to the second track 6b via resistor 17, inductor 18, and capacitor 19. Inductor 18 could itself be replaced by a resistor.

[0066] Resistor 17 has a terminal 17a connected to input 22 and a terminal 17b connected to electrical ground 23 of electronic board 2.

[0067] Resistor 17 exhibits good robustness to humidity and has a high resistance value, for example equal to 10 MΩ.

[0068] Capacitor 19 also has a terminal 19a connected to input 22 and a terminal 19b connected to electrical ground 23.

[0069] Capacitor 19 and resistor 17 are therefore connected in parallel.

[0070] Capacitor 19 is optional. Capacitor 19 is, for example, a ceramic capacitor, which offers good resistance to humidity. Capacitor 19 has, for example, a capacitance value of 100 nF.

[0071] The inductance (or resistor) 18 has a terminal 18a connected to the input 22, to the terminal 17a of the resistor 17 and to the terminal 19a of the capacitor 19, and a terminal 18b connected to the second track 6b.

[0072] Inductor (or resistor) 18 is optional. Inductor (or resistor) 18 is, for example, a multilayer inductor, which offers good resistance to humidity. Inductor 18 has, for example, an inductance value of 22 nH.

[0073] To perform the moisture detection, the microcontroller 16 biases the first electrode by applying the test voltage Vt to the first track 6a, which here is a DC voltage equal to 3.3 V (which is also the supply voltage Vcc of the microcontroller 16).

[0074] The ADC 20a then digitizes the target voltage Vc present at the input 22 of the microcontroller 16, which depends on the impedance between the first track 6a and the second track 6b. The target voltage Vc is measured at a measurement point connected to the second track 6b via the inductor (or resistor) 18, the resistor 17, and the capacitor 19.

[0075] The higher the target voltage Vc, the higher the impedance, and therefore the higher the humidity level.

[0076] The microcontroller 16 therefore compares the target voltage Vc with a predetermined threshold and detects an excessively high humidity level on the printed circuit board 1, between the first track 6a and the second track 6b, based on the result of this comparison. The microcontroller 16 detects an excessively high humidity level if the target voltage Vc is greater (here, strictly) than the predetermined threshold.

[0077] The predetermined threshold is, for example, equal to 200mV.

[0078] The detected moisture may be present either on the surface of the printed circuit board 1 between the two tracks 6a, 6b, in the resin 12, or in the thickness of the printed circuit board 3 (i.e. in the insulating material of the printed circuit board).

[0079] Note that the absence of masking varnish on the first portion of track 8a and the second portion of track 8b allows for better capture of leakage currents.

[0080] In the presence of humidity, leakage currents of around 10 nA are measurable.

[0081] With reference to the figure 3 In an alternative embodiment, the first track 6a and the second track 6b form two interdigitated electrodes.

[0082] Interdigitated electrodes are a specific electrode configuration widely used in electrochemical devices, such as gas sensors, pH sensors, glucose sensors, and so on. An interdigitated electrode consists of a series of parallel metallic electrodes arranged alternately and interconnected at distinct electrical regions. The interdigitated structure allows for an increased length (and surface area) of the active electrode.

[0083] The first 6a route here includes a first base 25a and three first fingers 26a perpendicular to the first base 25a. The second 6b route here includes a second base 25b and three second fingers 26b perpendicular to the second base 25b.

[0084] The first fingers 26a and the second fingers 26b are arranged alternately while being parallel to each other.

[0085] Each first finger 26a includes at least a first portion of track 8a which is not covered with solder mask, and each second finger 26b includes at least a second portion of track 8b which is not covered with solder mask.

[0086] Here, the first finger 26a.1 comprises a single first portion of track 8a, whereas the first finger 26a.2 and the first finger 26a.3 each comprise two first portions of track 8a.

[0087] Similarly, the second finger 26b.3 comprises a single second portion of track 8b, whereas the second finger 26b.1 and the second finger 26b.2 each comprise two second portions of track 8a.

[0088] The first sections of track 8a and the second sections of track 8b are similar to those previously described.

[0089] The test voltage Vt is applied to a central point of the first base 25a (at one end of the first central finger), possibly via one or more components, and the target voltage Vc is measured at a free end of the second bottom finger 26b (in the figure), possibly via one or more components.

[0090] With reference to the figure 4 In an alternative embodiment, the first track 6a and the second track 6b form electrodes arranged in a castellation configuration.

[0091] Castellation is an electrode configuration used in semiconductor devices such as CMOS technology chips (for Complementary Metal-Oxide-Semiconductor ) or image sensors. It consists of a series of superimposed metallic layers with step-like or crenellated openings, creating a stepped structure. This configuration allows for vertical connections between different layers of integrated circuits, thus facilitating the integration and interconnection of components.

[0092] The first track 6a is connected to at least one first castellation, formed in a thickness of the printed circuit board 3.

[0093] The second track 6b is connected to at least one second castellation, formed in the thickness of the printed circuit board.

[0094] The test voltage is applied to the first conductive track and the target voltage is measured on the second conductive track.

[0095] The first track, 6a, comprises a first section, 24a, which connects the first two towers, 35a and 36a, and a first section, 24a, which connects the first two towers, 27a and 28a. The first two sections, 24a, are connected and are perpendicular to each other. The second track, 6b, comprises a second section, 24b, which connects the second towers, 35b and 36b, and a second section, 24b, which connects the second towers, 27b and 28b. The two second sections, 24b, are connected and are perpendicular to each other.

[0096] The second castellation 35b is positioned at the first edge 30 of the printed circuit board 3 between the first castellation 35a and the first castellation 27a (in the middle). Similarly, the second castellation 36b is positioned at the first edge 31 (opposite the first edge) of the printed circuit board 3 between the first castellation 36a and the first castellation 28a (in the middle).

[0097] The second castellation 27b is positioned in the middle of a third edge 32 (perpendicular to the first edge 30 and the second edge 31), and the second castellation 28b is positioned in the middle of a fourth edge 33 (opposite the third edge 32). The first sections 24a form essentially diagonals of the printed circuit board 3.

[0098] The test voltage Vt is applied to the first 35a castellation (and therefore to the first track), possibly via one or more components, and the target voltage Vc is measured on the second 35b castellation (and therefore to the second track), possibly via one or more components.

[0099] The castellations are formed within the thickness of the printed circuit board 3.

[0100] The castellancies are formed, for example, by first creating through vias (or PTH for Plated Through Hole ) in the printed circuit board 3, then by cutting (by milling for example) the printed circuit board 3 so as to leave half of each via passing through the edge edge of the printed circuit board.

[0101] We now describe, with reference to the figure 5 , a second embodiment of the test device 15.

[0102] Output 21 of microcontroller 16 is directly connected to the first track 6a.

[0103] Input 22 of microcontroller 16 (which is connected to CAN 20a) is connected to the second track 6b via resistor 17, inductor (or resistor) 18 and capacitor 19.

[0104] The inductance (or resistor) 18 has a terminal 18a connected to the input 22 and a terminal 18b connected to the second track 6b.

[0105] The capacitor 19 has a terminal 19a connected to the input 22 and to the terminal 18a of the inductor (or resistor) 18, and a terminal 19b connected to ground 23 (GND), to the supply (Vcc) or to any other voltage reference of the electronic board 2.

[0106] Resistor 17 has a terminal 17a connected to input 22, to terminal 18a of inductance (or resistor) 18 and to terminal 19a of capacitor 19, and a terminal 17b connected to the Vcc supply.

[0107] Capacitor 19 and resistor 17 are therefore connected in parallel.

[0108] The device is activated this time by bringing the first track 6a to electrical ground (the CTRL signal of the microcontroller 16, which activates the measurement, is active to ground).

[0109] The test voltage is therefore this time the Vcc voltage.

[0110] The target voltage Vc is measured at a measurement point Pm connected to the second track 6b by the inductor 18.

[0111] The microcontroller 16 detects a humidity level that is too high if the target voltage Vc is less than (here less than or equal to) the predetermined threshold.

[0112] Again, capacitor 19 and inductance (or resistance) 18 are optional.

[0113] We therefore reversed the electrical measurement by referencing it to the power supply rather than to ground.

[0114] We now describe, with reference to the figure 6 , a third embodiment of the test device 15.

[0115] This time, output 21 of microcontroller 16 is connected to the first trace 6a via resistor 17 and inductor 18, which are connected in series. Terminal 17a of resistor 17 is connected to output 21. Terminal 17b of resistor 17 is connected to terminal 18a of inductor 18. Terminal 18b of inductor 18 is connected to the first trace 6a.

[0116] Input 22 of microcontroller 16 (which is connected to CAN 20a) is connected to a measurement point Pm located between terminal 17b of resistor 17 and terminal 18a of inductor 18.

[0117] Terminal 19a of the capacitor is connected to input 22 and to measurement point Pm. Terminal 19b of capacitor 19 is connected to electrical ground 23.

[0118] The second track 6b is connected to electrical ground 23.

[0119] The target voltage Vc is therefore measured at a measurement point Pm connected to the second track 6b by the inductance 18.

[0120] The microcontroller 16 detects a humidity level that is too high if the target voltage Vc is less than (here less than or equal to) the predetermined threshold.

[0121] Again, capacitor 19 and inductance (or resistance) 18 are optional.

[0122] We now describe, with reference to the figure 7 , a fourth embodiment of the test device 15.

[0123] Detection by the CAN is replaced by detection by a comparator with a threshold of 40. The comparator is an analog comparator.

[0124] The test device 15 this time includes a voltage source 41 (generating a reference voltage Vref, equal here to 1.2V) and the comparator 40.

[0125] Output 21 of microcontroller 16 is connected to the first trace 6a via resistor 17 and inductor 18, which are therefore connected in series. Terminal 17a of resistor 17 is connected to output 21. Terminal 17b of resistor 17 is connected to terminal 18a of inductor 18. Terminal 18b of inductor 18 is connected to the first trace 6a.

[0126] Output 21 of microcontroller 16 is also connected to a power supply port 40a of comparator 40 (which is therefore powered by the test voltage Vt.

[0127] The voltage source 41 is connected between the negative input 40b of the comparator 40 and the electrical ground 23, so that the reference voltage Vref is applied to this negative input 40b.

[0128] Terminal 19a of capacitor 19 is connected to the positive input 40c of comparator 40. Terminal 19b of capacitor is connected to ground 23.

[0129] The positive input 40c of comparator 40 is connected to a measurement point Pm located between resistance 17 and inductance 18 (and therefore to terminal 17b of resistance 17, to terminal 18a of inductance 18 and to terminal 19a of capacitor 19).

[0130] The comparator 40 therefore compares the target voltage Vc with a reference voltage Vref produced by the reference source 41. When the target voltage Vc is lower than the reference voltage Vref, the microcontroller 16 detects a level of humidity that is too high.

[0131] The predetermined threshold, with which the target voltage is compared, is therefore here an analog threshold.

[0132] We now describe, with reference to the figure 8 , a detection process, which is implemented here by the microcontroller 16. The process is repeated periodically.

[0133] The microcontroller 16 starts the test software: step E1.

[0134] The microcontroller 16 waits for a waiting time. The waiting time has a predetermined duration (equal to, for example, 500 s), or a random duration drawn at random (and possibly between a minimum bound, equal to, for example, 1 s, and a maximum bound, equal to, for example, 1000 s): step E2.

[0135] The microcontroller 16 applies the test voltage to the first track 6a and thus biases the monitoring device 5: step E3.

[0136] The microcontroller 16 waits for a certain duration for the target voltage Vc to stabilize (10 ms typically), then measures the target voltage Vc: step E4.

[0137] The microcontroller then depolarizes the monitoring device 5: step E5.

[0138] The microcontroller 16 compares the target voltage Vc with the predetermined threshold Sp (200 mV for example): step E6. Note that this predetermined threshold Sp can be configured. The threshold value could, for example, be chosen according to the desired detection sensitivity.

[0139] We are considering the case where the test device 15 used is that of the figure 2 .

[0140] If the target voltage Vc is less than (here less than or equal to) the predetermined threshold, the process returns to step E2.

[0141] If the target voltage is higher (here strictly) than the predetermined threshold, the microcontroller 16 detects a humidity level that is too high: step E7.

[0142] If the test device used is that of the figure 5 , 6 Or 7 The excessively high humidity level is detected when the target voltage is below the predetermined threshold.

[0143] The microcontroller generates an alarm (or continues to generate one if an alarm has already been generated) that alerts to a potential risk to product reliability. The microcontroller 16 keeps track of the number of alarms already generated, optionally associating each alarm with a timestamp.

[0144] This alarm, with or without its additional information, can be displayed on the screen of product 1 or sent to the user and / or the network manager and / or the fluid distributor if the meter is equipped with a communication module (LoRa, NB-IoT, W-Mbus, etc.).

[0145] This alarm allows the user and / or the network manager and / or the fluid distributor to take preventive measures to ensure the durability and proper functioning of the meter.

[0146] The process returns to step E2.

[0147] Many variations are possible.

[0148] The printed circuit board can include several first traces connected in series, and several second traces connected in series. Each set of a first trace and its associated second trace is positioned in a separate area of ​​the printed circuit board. Excessive humidity is detected when leakage currents are present in multiple areas simultaneously.

[0149] Similarly, the printed circuit board can include several first tracks connected in parallel, and several second tracks connected in parallel.

[0150] The first track 6a and second track 6b can run along the edges of the printed circuit board 3.

[0151] The first and second tracks can be printed on the same layer of the printed circuit board (which can be an inner layer), or on two different layers. This allows for precise measurement of the printed circuit board's moisture content within its thickness between the two layers. This configuration is not part of the invention.

[0152] With reference to the figure 9 It is also possible to have several first tracks on separate layers and several second tracks on separate layers.

[0153] Here, we have two first tracks 6a.1, 6a.2 connected by at least one first via through 50a, the first track 6a.1 being located on a top layer and the first track 6a.2 on an inner layer of the printed circuit 3. We also have a second track 6b.1 and a second track 6b.2 connected by at least one second via through 50b.

[0154] We also have a first track 6a.3 and a second track 6b.3 on the lower layer.

[0155] In the event that the electrical board contains one or more components that are more sensitive to humidity than others, this or these components can be positioned in an area surrounded by the first track 6a and the second track 6b.

[0156] The components most sensitive to humidity include, for example, an ASIC, a quartz crystal, etc.

[0157] During the design of the electronic board, the first step is to identify the component(s) most sensitive to humidity. Then, the first and second traces are designed to surround the area where this component(s) are located. "Most sensitive to humidity" refers, for example, to components that exhibit the highest failure rate at a given humidity level.

[0158] The first track and / or the second track are not necessarily dedicated to moisture detection.

[0159] The first track and / or the second track can also be used to carry any electrical signals (communication, control, power supply, etc.) used for any other function.

[0160] The detection of excessively high humidity levels is performed when the other function is inactive.

[0161] The invention has the following advantages.

[0162] Humidity detection is effective even in the presence of resin. Unlike traditional humidity sensors (especially those integrated into an SMD package), the monitoring device works effectively even when the printed circuit board is resin-coated or varnished, thus offering a more reliable solution for detecting humidity on electronic boards.

[0163] The monitoring device has low power consumption. It consumes significantly less current than traditional capacitive methods, which is particularly advantageous for low-power applications (e.g., battery-powered fluid meters).

[0164] Humidity detection can be activated on demand; but it is also possible to leave the function active constantly because the current leakage is very low (and therefore the consumption of the device is very low).

[0165] The monitoring device is very simple and low-cost. It uses simple electrodes and DC (direct current) impedance measurements to detect humidity, making it less complex and less expensive than traditional SMD sensors.

[0166] These electrodes offer excellent adaptability. The shape of the electrodes used in this DC impedance-based humidity monitoring device can be easily adapted to specifically target areas of the printed circuit board at increased risk of moisture. This adaptability allows for more precise detection and improved integrity assessment of critical areas of the circuit board.

[0167] The electrodes can be installed on one side, on both sides of the printed circuit board and possibly inside in an inner layer.

[0168] The location and surface area of ​​the electrodes can vary; the electrodes can be placed in the most exposed or least exposed areas.

[0169] The measurement of leakage current can be complemented by filters (capacitor, inductor, common mode transformer) in order to reduce external disturbances.

[0170] The open mask allows for moisture measurement very close to the electrical conductors. Protection of the copper conductors with a coating (such as gold-nickel) is recommended to prevent oxidation, but is not essential for the measurement function.

[0171] The monitoring device can be used on different types of electronic boards, materials and printed circuit board configurations, thus providing a versatile solution for detecting moisture in various electronic applications.

[0172] The monitoring device is very sensitive. It is capable of detecting current leaks on the order of 10 nA in the presence of high humidity / condensation, offering high sensitivity for detecting humidity on electronic boards.

[0173] The monitoring device is less sensitive to electromagnetic interference and disturbances than traditional SMD sensors, making it more robust and reliable in complex electronic environments.

[0174] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0175] As we have seen, the test device applies a test voltage to one of the first and second conductive tracks, while the other of the first and second conductive tracks is connected to a constant or controlled voltage reference. The second track can thus be connected to ground, possibly via one or more components, but the constant or controlled voltage reference is not necessarily the 0V present on ground. It could be, for example, a voltage obtained from a supply voltage, or produced by a voltage source.

[0176] The monitoring device is not necessarily implemented in a fluid meter, or even in a meter, but can be integrated into any type of electrical equipment.

[0177] The processing component of the test device, in which the detection process is implemented, is not necessarily a microcontroller. Another component could be considered, for example a "general-purpose" processor, a processor specialized in signal processing (or DSP, for Digital Signal Processor ), or a programmable logic circuit such as an FPGA (for Field Programmable Gate Arrays ) or an ASIC (for Application Specific Integrated Circuit ).

[0178] The processing component of the test device is not necessarily dedicated to humidity monitoring; it could be used for other functions (e.g., metrology).

[0179] The comparator used could be a different comparator, for example a Schmitt trigger.

Claims

1. Device (5) for monitoring humidity on a printed circuit (3) covered with solder mask over a large part of its external layers, comprising: - a first conductive track (6a) and a second conductive track (6b) printed on the printed circuit, and not connected to one another, the first conductive track (6a) comprising a first track portion (8a) which is not covered with solder mask (7), the rest of the first conductive track being covered with solder mask, and the second conductive track (6b) comprising a second track portion (8b) which is not covered with solder mask, the rest of the second conductive track being covered with solder mask, the first track portion extending over a first segment of the first conductive track, and the second track portion extending over a second segment of the second conductive track, the first track portion being defined over the entire length and on an internal part of the width of the first segment, the second track portion being defined over the entire length and on an internal part of the width of the second segment, the first track portion and the second track portion being therefore disposed facing one another, the first segment and the second segment going along over the printed circuit, being substantially parallel and being substantially of the same length ; - a test device (15) arranged to: ∘ apply a test voltage (Vt) on one of the first conductive track and second conductive track, the other of the first conductive track and second conductive track being connected to a constant or controlled voltage reference (23); ∘ compare a target voltage (Vc), representative of an impedance between the first conductive track and the second conductive track, with a predetermined threshold (Sp), said impedance being reduced in the presence of humidity; ∘ detect a humidity level which is too high on or in the printed circuit, between the first conductive track and the second conductive track, according to a result of said comparison.

2. Monitoring device according to claim 1, wherein the test voltage (Vt) is a direct voltage.

3. Monitoring device according to any one of the preceding claims, wherein the first track portion and the second track portion are covered with a protective coating (11) intended to prevent a main material, with which the first conductive track and the second conductive track are manufactured, from corroding.

4. Monitoring device according to claim 4, the protective coating being made of gold-nickel.

5. Monitoring device according to any one of the preceding claims, wherein the first conductive track (6a) and the second conductive track (6b) form two loop-shaped electrodes.

6. Monitoring device according to any one of claims 1 to 4, wherein the first conductive track (6a) and the second conductive track (6b) form two interdigitated electrodes.

7. Monitoring device according to any one of claims 1 to 4, wherein: - the first conductive track (6a) is connected to at least one first castellation (25a, 26a, 27a, 28a) formed in a thickness of the printed circuit, and - the second conductive track (6b) is connected to at least one second castellation (25b, 26b, 27b, 28b) formed in the thickness of the printed circuit, the test voltage being applied on the first conductive track and the target voltage being measured on the second conductive track.

8. Monitoring device according to claim 7, wherein the first conductive track (6a) comprises two first sections (24a) connected to one another, perpendicular to one another and each connecting two first castellations (25a, 26a, 27a, 28a) to one another, and the second conductive track (6b) comprises two second sections (24b) connected to one another, perpendicular to one another and each connecting two second castellations (25b, 26b, 27b, 28b) to one another.

9. Monitoring device according to any one of the preceding claims, wherein the first conductive track and the second conductive track are located on one same layer of the printed circuit.

10. Monitoring device according to claim 9, wherein said layer is an internal layer of the printed circuit.

11. Monitoring device according to any one of the preceding claims, comprising a first conductive track (6a.1) and a second conductive track (6b.1) located on a first layer of the printed circuit, and another first conductive track (6a.2) and another second conductive track (6b.2) located on a second layer of the printed circuit, the first conductive tracks (6a.1, 6a.2) being connected to one another by at least one first through via (50a) and the second conductive tracks (6b.1, 6b.2) being connected to one another by at least one second through via (50b).

12. Monitoring device according to any one of the preceding claims, comprising several first conductive tracks connected in series and several second conductive tracks connected in series.

13. Monitoring device according to any one of the preceding claims, comprising several first conductive tracks connected in parallel and several second conductive tracks connected in parallel.

14. Monitoring device according to any one of the preceding claims, wherein the first conductive track and / or the second conductive track are arranged for transporting signals used for another function, the monitoring device being arranged to perform the detection of the humidity level which is too high when said other function is inactive.

15. Monitoring device according to any one of the preceding claims, wherein electrical components are mounted on the printed circuit, these electrical components comprising a component which is the most sensitive to humidity, the component which is the most sensitive to humidity being positioned in a zone surrounded by the first conductive track (6a) and the second conductive track (6b).

16. Monitoring device according to any one of the preceding claims, comprising an analogue comparator (40) and a voltage source (41), the target voltage being compared by the analogue comparator with a reference voltage (Vref) produced by the voltage source, the predetermined threshold thus being an analogue threshold.

17. Detection method, implemented in a monitoring device (5) according to any one of the preceding claims, comprising the steps of: - applying a test voltage (Vt) on one of the first conductive track and second conductive track, the other of the first conductive track and second conductive track being connected to a constant or controlled voltage reference (23); - comparing a target voltage (Vc), representative of an impedance between the first conductive track and the second conductive track, with a predetermined threshold (Sp), said impedance being reduced in the presence of humidity; - detecting a humidity level which is too high on or in the printed circuit, between the first conductive track and the second conductive track, according to a result of said comparison.

18. Computer program comprising instructions which cause the test device (15) of the monitoring device according to one of claims 1 to 16 to execute the steps of the detection method according to claim 17.

19. Recording medium which can be read by a computer, on which the computer program is recorded according to claim 18.