METHOD FOR CONTROLLING A DEVICE BY ESTIMATING THE WEAR OF ONE OF ITS ASSEMBLIES AND ASSOCIATED SYSTEM

Abstract

The invention relates to a method for monitoring an aircraft electronic device, the electronic device having a first assembly formed by joining at least one electronic component with a first support using first solder joints. The method comprises the following steps: - providing a wear indicator for the first assembly, the wear indicator comprising a second assembly formed by joining at least one reference electronic component with a second support using second solder joints, said at least one reference electronic component having a lifetime shorter than the lifetime of each of the electronic components in the first assembly; - detecting a risk of failure of the electronic device by checking the condition of the reference electronic component, the risk of failure being identified when the condition of the reference electronic component demonstrates the presence of a defect in at least one of the second solder joints.Figure for the abridged version: no figure.

Description

Title of the invention: Method for controlling a device by estimating the wear of one of its assemblies and associated system technical field

[0001] The present invention relates to the general field of aircraft electronic devices, in particular equipped printed circuit boards (ICBs).

[0002] In particular, the invention aims to estimate the service life of the assemblies of an aircraft CIE, in order to be able to schedule the repair of the assemblies of a CIE before the occurrence of a failure or to be able to schedule the replacement of the CIE before such a failure. PREVIOUS STATE OF THE ART

[0003] In the context of the present invention, we are interested in electronic devices obtained by assembling electronic components (such as, for example, integrated circuits, resistors, capacitors, connectors, etc.) with a substrate. Preferably, the substrate is a printed circuit board and the electronic device is then an equipped printed circuit board (ECB) (also called an "electronic board").

[0004] These assemblies are made using an assembly material, called solder, which consists of a metal alloy chosen so that its remelting temperature (generally between 180°C and 240°C) is suitable for the electronic components to be assembled on the substrate, in order not to damage them. This assembly material provides both mechanical retention of the electronic component on the substrate and electrical contact between these two elements. An electronic component 2 assembled on a substrate 3 using solder 4, the whole forming an electronic device 1, is shown in [Fig. 1]. The substrate 3 is here a printed circuit board comprising a substrate 4 and pads or conductive tracks 5.

[0005] In certain specific environments, particularly in harsh aeronautical environments (nacelles, engine, landing gear, wheels, etc.), the supports 3 of the electronic devices 1 are subjected to significant temperature and vibration cycles, which cause the assembly material to age prematurely, resulting in cracking of the solder joints 6 and a break in electrical contact, ultimately leading to failure of the device 1. Figure 2 shows an example of a crack-type defect 7 in a solder joint 6.

[0006] This aging phenomenon of the assembly material is directly related to the type of electronic component (geometric configuration, material, etc.) assembled to the substrate, but also to the volume of solder used to make the bond electrical, as well as the method of soldering. It is also known that, for the same soldering method, there is a hierarchy among electronic components with respect to this phenomenon, the aging phenomenon occurring more rapidly on some components than on others.

[0007] In the case of CIEs, it is estimated that approximately 48% of failures are related to soldering. It would therefore be advantageous to be able to estimate the aging of the assemblies of a CIE-type electronic device used in an aircraft, in order to anticipate their failure with a view to planning their repair, thus keeping the electronic device in service, or to plan the replacement of the CIE. Description of the invention

[0008] To achieve this, the invention proposes a method for controlling an electronic device having a first assembly formed by assembling at least one electronic component with a first support using first solder joints, the method comprising the following steps: - the provision of a wear indicator for the first assembly, the wear indicator comprising a second assembly formed by assembling at least one test electronic component with a second support using second solder joints, said at least one test electronic component having a lifespan shorter than the lifespan of each of the electronic components of the first assembly; - the detection of a risk of failure of the electronic device by checking the condition of the indicator electronic component, the risk of failure being identified when the condition of the indicator electronic component demonstrates the presence of a defect in at least one of the second solder joints.

[0009] In other words, with the method according to the invention, it is detected when maintenance of the electronic device will become necessary by detecting the presence of a defect in at least one of the second solder joints of the wear indicator.

[0010] Time To Failure (TTF) is a well-known term in the field of electronics. This lifespan is often expressed in hours and indicates the expected lifespan of a component. The term "potential lifespan" is also encountered, which indicates the expected lifespan of a component expressed as a relative percentage.

[0011] In the context of the present invention, a test electronic component is a component composed of at least two electrical contacts connected to each other, allowing the passage of an electric current, and which is passive, that is to say, it obeys the generalized Ohm's law. It can therefore be any standard package used to integrate an electronic component and which is passive.

[0012] According to one embodiment of the invention, the verification of the condition of the test electronic component during the step of detecting a risk of failure of the electronic device consists of a verification selected from the group comprising: - a physical check of the condition of the test electronic component and / or the second solder joints; for example, an operator can check, by manipulating it with a pair of pliers for example, whether the component moves or not; - an acoustic check of the condition of the reference electronic component and / or the second solder joints; for example, an acoustic microscopy device can be used; - a visual check of the condition of the test electronic component and / or the second solder joints; for example, an operator can check if an electronic component is still in its place or check, using binoculars, if there are cracks in the solder joints (according to the standardized techniques IPC-A-610); - an electrical check of the condition of the electronic indicator component and / or the second solder joints.

[0013] Advantageously, when supplying a wear indicator, the wear indicator includes a detection unit for detecting a defect in at least one of the second solder joints by an electrical control of a functional state of the electronic indicator component.

[0014] The invention also proposes an electronic system, comprising: - an electronic device to be controlled having a first assembly formed by assembling at least one electronic component with a first support using first solder joints; - a wear indicator of the first assembly comprising a second assembly formed by assembling at least one electronic indicator component with a second support, using second solder joints; in which said at least one electronic component has a lifespan shorter than the lifespan of each of the electronic components in the first set.

[0015] According to one feature of the invention, the wear indicator further comprises a detection unit configured to detect a defect in at least one of the second solder joints by electrically monitoring the functional state of the electronic indicator component. The functional state is then representative of an electrical connection of the indicator component via the second solder joints.

[0016] Advantageously, the detection unit is selected from a unit for measuring the impedance of the test electronic component, a unit for measuring and / or detecting electrical continuity in the test electronic component when it is powered.

[0017] Some preferred but not limiting aspects of this method and electronic system are as follows: - the first and second supports are the same support, preferably a printed circuit board; - the second set includes at least two electronic indicator components having two different lifespans; - said at least one electronic control component is a passive electronic component chosen from a resistor, an inductor or a capacitor or a component chosen from a BGA package (for "Bail Grid Array" in English, i.e. matrix of balls), an LGA package (for "Land Grid Array" in English, i.e. matrix of pellets) or a TSOP package (for "Thin Small Outline Package" in English).

[0018] The invention also relates to a turbomachine, characterized in that it comprises an electronic system according to the invention.

[0019] Finally, the invention relates to a method for maintaining an electronic device for an aircraft, which comprises: - control of an electronic device for an aircraft by implementing the control method according to the invention; and - a reformation of the first and second brazes when a risk of failure is identified.

[0020] The reformation (or repair) of the solder joints can for example be obtained by passing the electronic device through a baking oven, in order to pass the solder alloys back into a remelted state and thus reform the solder joints. Brief description of the drawings

[0021] Other advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings, among which:

[0022] [Fig.1], already described, is a cross-sectional view of an electronic device 1, comprising a support 3 on which an electronic component 2 is assembled using solder 6;

[0023] [Fig.2], already described, represents an enlargement of a solder joint 6, allowing an electronic component 2 to be assembled with a support 3, this solder joint having a defect 7 (in this case, a crack);

[0024] [Fig.3] schematically represents an electronic system according to the invention;

[0025] [Fig.4] represents, according to a cross-sectional view, an example of an electronic device 1 according to the invention;

[0026] [Fig. 5] represents, in cross-section, an example of a wear indicator 9 according to the invention;

[0027] [Fig.6] schematically represents, from a top view, an example of implementation of an electronic system according to the invention.

[0028] Detailed description of particular embodiments

[0029] Fig. 3 schematically represents, in the form of boxes, an electronic system 8 according to the invention, comprising an electronic device 1 to be controlled and a wear indicator 9 (the wear indicator comprising a detection unit 18).

[0030] An example of an electronic device 1 in cross-sectional view is shown in [Fig. 4]. It comprises several electronic components 12 and a first support 13, the electronic components 12 being assembled onto the first support 13 using first solder joints 14. There are then several assemblies, which form a first assembly 10.

[0031] According to the invention, a second assembly 11 is used as a wear indicator 9 for the first assembly 10 of the electronic device 1. This second assembly is intended solely for this purpose and is formed by mounting, using a bonding material, at least one electronic indicator component 15 onto a second support 16. An example of a wear indicator 9 in cross-sectional view is shown in [Fig. 5]. It comprises an electronic indicator component 15 and a second support 16, which are assembled using second solder joints 17. This assembly forms a second assembly 11.

[0032] The first 13 and second 16 supports can be one and the same support 3, preferably a printed circuit board. Similarly, the first 14 and second 17 solder joints can be identical.

[0033] By using a single support, this simplifies the implementation of the method for controlling the electronic device according to the invention, since it is sufficient to implement one or more electronic indicator components, not electrically connected to the main electronic functions of the first assembly of the electronic device, to obtain the wear indicator.

[0034] The electronic indicator component 15 is chosen such that its assembly with the second support 16 ages more rapidly than the first assembly 10 of the device 1 (i.e., any of the assemblies of the device 1). Since the electronic indicator component(s) 15 of the wear indicator 9 are chosen with a shorter lifespan than the electronic component(s) 12 of the device 1, the second assembly 11 (i.e., the assembly(ies) of the wear indicator formed by assembling the electronic indicator component(s) with a second support) will age more rapidly than the first assembly (i.e., the assembly(ies) of the device formed by assembly of the electronic component(s) with the first support), which allows for an estimation of the relative wear state of the first assembly 10. Thus, the invention does not allow for the prediction of the lifespan of the first support 13 or the components 12 of the device 1, but it does allow for the prediction of the lifespan of the first assembly 10 (i.e., the assembly(ies) of the device 1), which makes it possible to define recommendations for the repair of the first assembly 10 of the device and to repair this first assembly 10 before it fails, which ultimately makes it possible to increase the lifespan and reliability of the device 1.

[0035] This capability is particularly relevant for an electronic device intended for use in an aircraft, the device being located in an area where the temperature, as well as the mechanical stresses, are significant. This is the case for devices located in aircraft or aircraft equipment, particularly in turbojet engines which are subjected to significant vibrational and thermal stresses.

[0036] According to the invention, the condition of the solder joints of the second assembly 11 formed by assembling at least one electronic test component 15 on a support 16 using solder joints 17 is checked. More particularly, the appearance of a defect, generally a crack, in the second assembly is detected, this defect having the effect of causing an electrical discontinuity in the second assembly.

[0037] This control can be a visual inspection, an electrical condition check (for example by installing a channel for measuring the electrical continuity of the second assembly), an acoustic check, a mechanical inspection (by applying a force), etc.

[0038] One of the advantages of monitoring the solder joints of this second assembly is that information on the remaining lifespan of the electronic device (i.e., its lifetime (if expressed in hours) or its potential lifetime (if expressed as a percentage)) is intrinsically contained in the solder material used to assemble the indicator electronic component(s), thus enabling monitoring of the cumulative damage throughout the lifetime of the second assembly. However, this requires careful selection of the indicator component(s) for the wear indicator so that they are appropriately sized for the first assembly of the electronic device.

[0039] The electronic component(s) 15 may be passive electronic components of the package type. An electronic component is said to be passive when it obeys the generalized Ohm's law; it may, for example, be a resistor, capacitor or inductor package.

[0040] The electronic indicator component(s) may also be selected from other package types, for example a BGA package. A continuous reading of Monitoring all the contacts in the BGA package allows us to estimate the wear of the first assembly of the electronic device. It's worth noting that a BGA package contains multiple solder joints, and it's known that solder joints located on the periphery are more prone to aging than those located in the center. Therefore, monitoring the electrical continuity of the peripheral solder joints provides an initial assessment of the assembly's aging, and tracking the progression of electrical breaks allows us to determine the level of damage.

[0041] By convention, passive components intended for surface mounting (also known by the acronym SMD) are defined according to their size. For example, a component called a 1206 resistor corresponds, for those skilled in the art, to a resistor of size 1206 in imperial code, which corresponds to a metric dimension of 3.2 mm x 1.6 mm.

[0042] Some examples of correspondence between the metric code and the imperial code are grouped in Table 1 below.

[0043] [Tables 1] Imperial Code Metric Code 01005 0402 0201 0603 0402 1005 0603 1608 0805 2012 1008 2520 1206 3216 1210 3225 1806 4516 1812 4532 2010 5025 2512 6332

[0044] For each type of passive component, there are predictive empirical models that indicate, based on knowledge of the usage (thermal environment, thermal cycling, vibrations, shocks, etc.) and for a given type of solder, the lifespan of an assembly formed by mounting the passive component on a given support and using that solder. For example, it is known that a solder made of Sn62Pb36Ag2 metal alloy on a 2512 resistor ages twice as fast. faster than the same localized solder joint on a 1210 resistor, which is the component most sensitive to aging after the 2512 resistor.

[0045] Thus, for an electronic device which is a CIE formed by assembling a resistor 1210 on a printed circuit board, if a resistor 2512 is placed as a wear indicator on this same printed circuit board and the condition of its solder joints is checked, for example by measuring the electrical continuity on the resistor 2512, it will be known, as soon as the electrical continuity is broken, that the assembly of the resistor 1210 is at its half life.

[0046] This principle can be applied to any type of electronic component and if the device includes several electronic components, it is necessary to know the relative lifespan of each component for the sizing of the component(s) used as indicators for the wear indicator.

[0047] A wear indicator according to the invention may include several indicator components with different lifespans. This makes it possible, for example, to detect phases at N% of the expected lifespan consumed of the first assembly of the device. For example, a passive component can be mounted to represent 30% of the expected lifespan consumed, another 50%, and another 90% of the first assembly of the device (in reality, this will represent the percentage of the expected lifespan consumed of the assembly of the weakest electronic component in the device). The indicator components at 30% and 50% allow for a prediction of the expected lifespan of the first assembly of the device. The indicator component at 90% will allow for scheduling the maintenance of the first assembly.

[0048] Ideally, in order to minimize the impact on the transfer of the test components, the alloy predominantly used for brazing the test components (the second brazing) will be used. All sorts of brazing materials can be used, such as, for example, Sn62Pb36Ag2 and SnQ6j5Ag3Cu0j5 alloys.

[0049] To illustrate the process according to the invention, we will take the case of a CIE made by assembling, on a machined printed circuit board serving as a support, components chosen from the five components below using, for soldering, a Sn63Pb37 metal alloy.

[0050] In order to choose the sizing of the test component(s), we start by determining which assembly is the weakest in the CIE by comparing their respective lifetimes.

[0051] The lifetime of these assemblies, which corresponds to resistance in thermal cycles over a temperature range from -55°C to +125°C and for brazing with an Sn63Pb37 alloy, is known and is presented in Table 2 below.

[0052] [Tables2] Component Thermal Cycle Withstand (-55 / +125°C) with Sn63Pb37 Alloy: Resistor "R12O6" 3246 cycles; Capacitor "Cl2O6" 4413 cycles; Inductor "il2O6" 8421 cycles; Resistor "R10O5" 4531 cycles; Capacitor "C0O8O5" 10428 cycles

[0053] The weakest assembly among these five components assembled on a support is that obtained with the resistance 1206. To choose the potential standards, passive components are therefore selected which, once assembled, have a thermal cycle resistance of less than 3246 cycles.

[0054] For example, the passive components below (Table 3) are chosen, which will serve as indicators of lifespan at 95%, 51% and 38% respectively.

[0055] The remaining life estimate of the "R1206" component is calculated by dividing the number of cycles of the control component by the number of cycles of the "R1206".

[0056] [Tables3] Reference component: Thermal cycle resistance (-55 / +125°C) with an Sn63Pb37 alloy. Estimated remaining service life of component "R1206" in %: Resistance "R1210 t" 3100 cycles 3100 / 3246 = 95% Resistance "RI812 t" 1680 cycles 1680 / 3246 = 51% Resistance "R2225 t" 1250 cycles 1250 / 3246 = 38%

[0057] Figure 6 schematically represents the electronic system 8 thus obtained. According to this embodiment, the electronic device and the wear indicator are mounted on the same support 3. The electronic device has a first assembly formed by mounting, on the support, eight electronic components 12, including three resistors R1206, two capacitors C1206, one inductor il206, one resistor R1005, and one capacitor C0805. The wear indicator has a second assembly formed by mounting, on the support, three indicator electronic components 15, namely one resistor R1210t, one resistor R1812t, and one resistor R2225t. The conductive traces electrically connecting the components are not shown.

[0058] By implementing resistors R1210t, R1812t and R2225t as test components and monitoring the electrical continuity of these resistors, it is possible to estimate the lifetime of the assembly formed with the 1206 resistor, which is the dimensioning point of the electronic device, with a consumption scale of 38%, 51% and 95%.

[0059] It should be noted that when maintenance is performed on the device, resulting in the reworking of all the solder joints on these components in order to increase the service life of the entire assembly, it is also necessary to perform the same repair on the wear indicator component(s) in order to "reset" the aging potential counter. In other words, when maintenance is performed on the aircraft electronic device to extend its service life by reworking the solder alloys, the electronic device is inspected using the inspection method according to the invention; and the first and second solder joints are reworked when a risk of failure is identified during the inspection.

Claims

Demands

1. Method for controlling an electronic device (1) for aircraft, said electronic device having a first assembly (10) formed by assembling at least one electronic component (2; 12) with a first support (3; 13) using first solder joints (6; 14), the method comprising the following steps: - providing a wear indicator (9) of the first assembly, the wear indicator comprising a second assembly (11) formed by assembling at least two test electronic components (2; 15) with a second support (3; 16) using second solder joints (6; 17), each test electronic component (2; 15) having a lifetime shorter than a lifetime of each of the electronic components (2; 12) of the first assembly (10), said at least two test electronic components having two different lifetimes;- the detection of a risk of failure of the electronic device (1) by checking the condition of each indicator electronic component (2; 15), the risk of failure being identified when the condition of at least one of the indicator electronic components demonstrates the presence of a defect (7) in at least one of the second solder joints (6; 17).

2. A method according to claim 1, wherein the verification of the condition of the electronic test components during the step of detecting a risk of defect of the electronic device consists of a verification selected from the group comprising: - a physical check of the condition of the electronic test components (2; 15) and / or the second solder joints (6; 17); - an acoustic check of the condition of the electronic test components and / or the second solder joints; - a visual check of the condition of the electronic test components and / or the second solder joints; - an electrical check of the condition of the electronic test components and / or the second solder joints.

3. A method according to claim 1 or claim 2, wherein, when supplying a wear indicator, the wear indicator comprises a detection unit (18) for detecting a defect (7) in at least one of the second brazes (6; 17) by a check electrical state of a functional state of the indicator electronic components (2; 15).

4. A method for maintaining an aircraft electronic device (1), comprising: - checking an aircraft electronic device (1) by implementing the checking method according to any one of claims 1 to 3; and - reforming the first and second solder joints when a risk of failure is identified.

5. Electronic system (8) for aircraft, comprising: - an electronic device (1) to be controlled having a first assembly (10) formed by assembling at least one electronic component (2; 12) with a first support (3; 13) using first solder joints (6; 14); - a wear indicator (9) of the first assembly (10) comprising a second assembly (11) formed by assembling at least two witness electronic components (2; 15) with a second support (3; 16), using second solder joints (6; 17); in which each witness electronic component (2; 15) has a lifetime shorter than a lifetime of each of the electronic components (2; 12) of the first assembly (10) and said at least two witness electronic components have two different lifetimes.

6. Electronic system according to claim 5, wherein the wear indicator (9) further comprises a detection unit (18) configured to detect a defect (7) in at least one of the second solder joints (6; 17) by an electrical control of a functional state of each electronic indicator component (2; 15).

7. Electronic system according to claim 6, wherein the detection unit (18) is selected from an impedance measurement unit of each test electronic component (2; 15), a measurement and / or detection unit of electrical continuity in each test electronic component (2; 15) when it is energized.

8. Electronic system according to any one of claims 5 to 7, wherein the first (13) and second (16) supports are the same support (3), preferably a printed circuit board.

9. Electronic system according to any one of claims 5 to 8, wherein each witness electronic component is a passive electronic component selected from a resistor, an inductor or a capacitor.

10. Turbomachine, characterized in that it comprises an electronic system according to any one of claims 5 to 9.

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