Method for testing an electronic assembly, and electronic assembly having a device for testing

Abstract

The invention relates to a method for quality testing and to an electronic assembly (10) which is designed to carry out the method. The electronic assembly (10) is, in particular, an interconnect device. According to the invention, at least one component (50, 60) of the interconnect device (10) is examined by means of an electrical characterisation process, wherein the examined component (50, 60) is excited by means of ultrasonic waves (110) such that, as a result, changes are brought about in the signal of the electrical characterisation process, which signal changes are evaluated by means of a signal analysis (210) in order to draw conclusions about material changes to the component (50, 60) therefrom.

Description

[0001]202208201 Foreign version 1 Description Method for testing an electronic assembly and electronic assembly with testing device The invention relates to a method for testing an electronic assembly and to an electronic assembly with a device for carrying out such a method. During the manufacture of electronic assemblies, in particular after the assembly of circuit carriers for electronic assemblies, a quality control of the electronic assembly for manufacturing defects must be carried out. Regularly occurring manufacturing defects are defects. Such defects include, in particular, large-area cavities in solder joints, circuit board warping, inadequate solder joint contact, delamination of conductor materials in circuit boards, flux residues, chip twists and defective laser-welded connections of metallic load connections.It is known to examine electronic assemblies, particularly populated circuit boards, for potential defects using optical imaging and / or electrical testing. However, optical quality control using automated imaging is not yet sufficiently reliable with regard to some defects. In particular, circuit board warpage is difficult to detect using optical imaging. Large-area cavities, delamination of conductor materials in circuit boards, and defective laser welds of metallic load connections cannot yet be detected optically and electrically with sufficient reliability. However, quality control remains necessary even during operation of electronic assemblies, particularly power electronic assemblies, since operational or aging-related defects can occur.Power electronic systems, such as power modules, age primarily due to operational temperature cycles. Power electronic systems and their power switching modules, such as IGBT modules, subject to high thermal stress, are subject to noticeable aging during normal operation within their specified operating limits. IGBT modules are used, for example, in power electronic converters. This aging is primarily caused by a high number of load cycles of operational heating and cooling, which lead to the gradual destruction of chip solder layers beneath the semiconductor chips and to the fatigue of bond wires and chip metallizations that conduct current to the switching and rectifying chips.Typical failure mechanisms include bond lift-off, i.e., the lifting or even cracking of the bond wire, heel cracking, and solder fatigue of chip and system solder, which includes the underlying solder of the ceramic carrier. One problem, among others, is that the time of failure depends so strongly and in such a complex way on past loads that even advanced prediction models are highly inaccurate. In addition, aging also occurs in the chip periphery due to temperature fluctuations. For example, the circuit carrier (DCB, AMB) can be destroyed due to the different expansion coefficients (ceramic / copper) above a conch fracture, and the overlying driver control can also be destroyed, especially in future integrated power modules. Model-based estimation methods, for example, are currently used, but these are highly inaccurate.Another option is impedance spectroscopy, which determines the thermal impedance of the module structure. Here, an electronic switch is used as both a heating element and a sensor. This measurement can only be performed when the system is not in operation. Another approach is distortion measurement using electrical excitation, which occurs at interfaces and transitions. These measurements are also performed during operation using high-frequency signals. The results require interpretation because the signals are very small. In difficult-to-access or continuously operating applications where converter failure must be avoided at all costs, e.g., offshore wind converters or traction applications, there are currently various solutions for organizationally preventing unexpected shutdowns as far as possible.Spontaneous outages can be countered through redundancy of the power electronics or through maintenance measures, such as preventative replacement of power modules. Advanced thermal models based on previous, accelerated lifetime tests can be used to determine the expected and already used lifetime. However, due to the high complexity of the interdependencies, these calculations are still subject to very large errors. Some power module manufacturers offer IGBT power switching modules with small measuring diodes integrated into their IGBTs as temperature sensors. The increasing temperature increase of the IGBT at a given operating current can then be used indirectly to determine (solder) aging. However, this is associated with a loss of chip area and higher chip costs.Against this background of the prior art, it is therefore an object of the invention to provide an improved method for testing an electronic assembly and an electronic assembly with a device for carrying out this improved method. In particular, the method according to the invention for testing an electronic assembly should enable simple, cost-effective and reliable testing of the electronic assembly. 202208201 Foreign version 4 This object of the invention is achieved by a method for testing an electronic assembly with the features specified in claim 1 and by an electronic assembly with a device for carrying out such a testing method with the features specified in claim 11. Preferred developments of the invention are specified in the associated subclaims, the following description and the drawing.The inventive method for quality testing an electronic assembly, in particular a power electronic assembly, comprises the examination of at least one component of the electronic assembly using an electrical characterization method in which the examined component is excited by ultrasonic waves in such a way that changes in the signal of the electrical characterization method are thereby caused. The ultrasound-induced changes in the electrical signal are evaluated using signal analysis. This indicates material changes in the component. The inventive method therefore implements condition monitoring on which a remaining service life can be determined. Unplanned failures are avoided and predictive maintenance is enabled.Furthermore, there is the advantage of being able to offer a commercial solution for the condition monitoring of entire power modules in converters, which can be used for service life prediction. The errors that can be advantageously detected by the specified quality control are, in particular, defects such as material defects, which can occur after production, particularly due to aging. Damage is caused in particular by excessively high component temperatures and particularly by temperature changes, and this can be detected very reliably using the described method. Accordingly, the method according to the invention is also very well suited for component or assembly testing after production; it is also advantageously used for aging prediction and failure risk assessment based on the results of a post-production test.A particularly advantageous aspect of the method is its applicability during operation of the electronic component or electronic assembly. Testing that can be carried out during operation, and also repeatedly, offers particular advantages for deriving aging predictions or failure risk assessments. An electronic assembly is understood to mean, in particular, a power electronic assembly, e.g., a power module. An electronic assembly comprises at least one component, in particular a semiconductor component, e.g., a power switch. The structure of an electronic assembly therefore comprises different layers and generally different materials, which are also produced and joined using different manufacturing processes. Material changes can include damage, delaminations, cracks, and general material aging.Typical power electronics components include: bipolar power transistors such as switching power supplies and DC / DC converters, power MOSFETs, IGBTs, especially switching power supplies, motor controllers and converters, as well as thyristors, especially power converters, semiconductor relays, pulse current sources, thyristor controls, GTO thyristors, which are high-power power converters, triacs, especially dimmers or semiconductor relays, as well as diodes for rectification and freewheeling diodes, such as Schottky diodes or silicon diodes, and finally, power capacitors. Applications of power electronics can include, for example, switching power supplies, frequency converters, high-frequency generators, DC / DC converters, phase-angle controllers, high-voltage DC transmission, inverters, or semiconductor relays.A further advantage of the method according to the invention is, for example, that the measurement is not only possible during operation and repeatedly during operation, but even continuous measurement of aging is enabled. This allows the condition of an entire module assembly to be measured continuously during operation, and necessary measures can be derived from this. This solution is commercially applicable for the condition monitoring of entire power modules in converters. The specified quality testing method is robust with regard to service life prediction. The method enables improved, non-destructive, more reliable detection of aging-related damage or delamination on a power electronic assembly as well as on individual components of this assembly, in particular power modules of power electronic devices, which can be carried out during component operation.The inventive method for quality testing a power electronic assembly has the further advantage that the assembly and components of the assembly can be examined for manufacturing defects after assembly, even in optically inaccessible areas. Impedance spectroscopy is preferably used as the electrical characterization method. In an advantageous embodiment of the method, at least one component of the power electronic assembly is examined by measuring at least one impedance spectrum of the component and its change as a result of ultrasonic excitation. The impedance spectra are compared using signal analysis, with any changes detected indicating damage or delamination in the component.In particular, signal analysis interacts functionally with the measurement: The measurement of the frequency-dependent impedance is carried out for comparison once with and once without additional ultrasonic excitation. The difference signals are evaluated. During electrical distortion measurement, nonlinear electrical, thermal, and mechanical properties of high-frequency transmission in power electronic systems lead to the generation of high-frequency signals that deviate significantly from the original frequency. Frequency signals are generated that correspond to a multiple of the original frequency or, when multiple frequencies are input, to a difference or sum frequency. In an advantageous embodiment of the method, the ultrasonic waves are generated by means of electrical excitation.For example, an ultrasonic signal is coupled into the component or assembly to be characterized using electrical excitation. At the interfaces of the connecting layers (solder, bond, etc.), electrical distortions then occur due to nonlinear effects based on local temperatures, mechanical delamination, and electrical contact resistance. In a further advantageous embodiment of the method according to the invention, the ultrasonic signal components are modulated onto the intermodulated electrical signal. The term "electrical signal" refers to the output signal of the electrical characterization method. This offers the particular advantage that defects in the tested structure are initially amplified and thus more easily detectable.Advantageously, in one embodiment of the method according to the invention, a signal analysis is carried out by means of which thermo-mechanical components and mechanical components of wear are separated. This is possible because the ultrasonic signal primarily amplifies the mechanical signals that provide indications of defects. 202208201 Foreign Version 8 In a further advantageous embodiment of the method according to the invention, an electronic assembly having a planar structure is examined, and the ultrasonic waves are generated by means of an ultrasonic generator that is placed directly on the planar AVT. AVT is understood to mean a planar structure in packaging and connection technology. The use of an ultrasonic generator in the method that is directly integrated into the planar structure, in particular as a piezoelectric layer, is particularly preferred.In one of these described embodiments, for example, the ultrasonic waves are coupled into the power electronics assembly as a near-surface wave. Alternatively or additionally, in a further advantageous embodiment of the method according to the invention, the ultrasonic waves can be generated as a bulk wave within the electronic assembly. In particular, the ultrasonic waves are generated for this purpose at several positions on the power electronics assembly. For this purpose, there are in particular several ultrasonic generators in a planar structure. In a further preferred embodiment of the method, the electronic assembly is subjected to ultrasonic vibrations continuously, once, or at discrete times. The electronic assembly according to the invention, in particular a power electronics assembly, in particular a circuit carrier, is designed to carry out an inventive method as described above.For this purpose, the assembly comprises at least one ultrasound source configured and arranged to cause the electronic assembly to vibrate ultrasonically, a measuring device configured to perform electrical characterization, in particular a frequency-dependent impedance measurement, and an evaluation device configured to use the detected electrical signal change to determine whether there is a defect in the electronic assembly. The assembly is, in particular, a power electronic assembly, in particular a circuit carrier, i.e., at least one component of the assembly is a power switch.A spectrum analyzer or lock-in amplifier, for example, can serve as a measuring device designed to perform a frequency-dependent impedance measurement. In an advantageous embodiment of the invention, the electronic assembly according to the invention has a planar structure and comprises an ultrasound generator which is placed directly on the planar AVT. For the near-surface ultrasound signal irradiation, a piezo actuator or a sonotrode, for example, can be used. In an alternative advantageous embodiment of the invention, the electronic assembly according to the invention has a planar structure and comprises an ultrasound generator which is integrated into the planar structure, in particular as a piezoelectric layer. Silicon carbide semiconductors or silicon carbide MOS (metal oxide semiconductors) or gallium nitride are preferably used as the ultrasound generator.In a further advantageous embodiment of the invention, the electronic assembly according to the invention alternatively or additionally has an ultrasonic generator which is integrated into a component of the power electronic assembly which has piezoelectric properties, in particular as a piezoelectric layer. This means that at least one ultrasonic generator is included which, in a further function, represents a component of the power electronic assembly, which component comprises a piezoelectric layer. 202208201 Foreign version 10 Examples and embodiments of the present invention will be described by way of example with reference to Figures 1 and 2 of the attached drawings: Figure 1 schematically shows a flow diagram of the measurement signal evaluation of the method according to the invention, Figure 2 schematically shows an assembly with corresponding devices for carrying out the method according to the invention.In the method according to the invention for testing an electronic assembly 10, the electronic assembly 10 is subjected to ultrasonic vibrations 110. Ultrasonic vibrations 110 typically extend over a frequency range of 10 to 300 kHz. At the same time, the electronic assembly 10 is examined using an electrical characterization method, in particular impedance spectroscopy. The impedance spectrum Z altered by ultrasonic vibrations 110 is preferably used in the method according to the invention. us [Ω] of the electronic assembly 10, or only of an electronic connection 80, 90, or of a component 50, 60 is recorded and used to determine a defect. For the evaluation 210, the changed impedance spectrum Z us [Ω] with the impedance spectrum without ultrasonic excitation Z o[Ω], as shown schematically in the flow diagram of Fig. 1. This measurement signal evaluation preferably takes place in an evaluation unit 210, which is designed to record and evaluate the electrical measurement signals. By means of the specified method, electronic assemblies 10 can advantageously be tested for defects, such as in particular for local flaws 95, which cannot be detected using optical or electronic methods as are known from the prior art. In the method according to the invention, the electronic assembly 10 is preferably subjected to ultrasonic vibrations 110 once. For this purpose, the electronic assembly 10 is expediently excited by means of a time-limited ultrasonic wave train 11 and thus set into vibration. Alternatively and likewise preferably, the electronic assembly 10 can be subjected to ultrasonic vibrations repeatedly at discrete points in time.For example, several temporally localized ultrasonic wave trains are used for this purpose. In this way, even decaying ultrasonic vibrations 110 of the electronic assembly 10 can be evaluated. In particular, information about local attenuation and natural resonances can be obtained from decaying ultrasonic vibrations 110. Alternatively or additionally, the electronic assembly 10 can also be continuously subjected to ultrasonic vibrations 110. In particular, changes in the resonance frequencies of natural vibrations of the electronic assembly 10 or parts of the electronic assembly 50, 60, 80, 90 can be used to infer the presence of defects and / or the location 95 of such defects. In the method according to the invention, the electronic assembly 10 is preferably subjected to ultrasonic vibrations 110 in several regions 120 of the electronic assembly 10.Thus, subjecting the electronic assembly 10 to ultrasonic vibrations 110 in several areas of the electronic assembly 10 can provide information about the spatial localization of defects 95. Furthermore, it can advantageously be ensured that all relevant natural vibrations of the electronic assembly 10 are excited if the electronic assembly 10 is subjected to ultrasonic vibrations 110 in more than just a single area. The reliability of the method according to the invention is consequently further increased in this development. In particular, faulty connections 80, 90 of different materials result in a changed vibration behavior of the electronic assembly 10 during ultrasonic vibrations 110. In particular, a large-area soldered connection 80, 90 of components 50, 60 or laser welding of load connections exhibit a changed vibration behavior in the event of defects.Even and especially defective metallizations 40 of circuit carriers 20 or warping 202208201 foreign version 12 of circuit carriers 20 can be easily detected using the method according to the invention. Consequently, the method according to the invention enables particularly reliable testing of electronic assemblies 10. For example, the electronic assembly 10 is a circuit carrier, or the electronic assembly has a circuit carrier 20. An electronic assembly 10 is frequently composed of various components 50, 60 or parts and accordingly of various materials, in particular materials of assembly and connection technology, in which materials defects in the form of cavities, cracks, or partial detachments of the connection regularly occur.In this way, especially in this important case of the electronic assemblies 10 comprising circuit carriers 20, a test for defects can be carried out reliably and efficiently. Fig. 2 shows a schematic diagram of an electronic assembly 10 which is arranged and designed to carry out a method according to the invention for testing the electronic assembly 10. The electronic assembly 10 comprises, for example, an ultrasound source 120 which is set up and arranged to replace the electronic assembly 10 in ultrasonic vibrations 110. In addition, the electronic assembly 10 comprises a device 200 for carrying out an impedance measurement or electrical contacts for connecting a device 200 for carrying out an impedance measurement. An evaluation device 210, which is not shown in Fig.2, since it does not necessarily have to be structurally connected to the assembly 10, by means of the ultrasonic wave-influenced impedance spectroscopy Z. us[Ω] for a defect 95 of the electronic assembly 10. The method for testing an electronic assembly in the form of a power module 10 is preferably carried out. The power module 10 has a circuit carrier in the form of a printed circuit board 20, which is designed as a flat part with a flat side 30. On the flat side 30 there is a copper metallization in the form of a surface-bonded copper layer 40. Semiconductor components 50, 60 and a load connection 70 are connected to the copper layer 40. The semiconductor components 50, 60 are connected to the copper metallization 40 by means of solder layers 80, 90. The load connection 70 is welded to the copper metallization 40 by means of a laser weld 100.Defects in the form of cavities, such as shrink holes or delaminations, occur in the solder layers 80, 90, by means of which the semiconductor components 50, 60 are connected to the copper metallization 40, as well as in the laser welding 100, by means of which the load connection 70 is connected to the copper metallization 40. To test the power module 10 for these defects, the power module 10 is subjected to ultrasonic vibrations 110. For this purpose, ultrasonic sources 120 are provided which radiate ultrasonic waves 130 in a direction 140 perpendicular to the flat side 30 onto a side of the circuit board 20 facing away from the flat side 30. The ultrasonic sources 120 are arranged at mutually distant ends of the flat side 30 of the circuit board 20, viewed in the planar extension directions of the flat side 30. The power module 10 is thus subjected to ultrasonic vibrations 110 in several areas.Aging in the power module becomes noticeable through a changed vibration behavior of the bond wires 70 and soldered chips 50, 60, since these connections 80, 90 become loose due to delamination. The vibration load from the ultrasound 110 attacks such delaminations, amplifies the signals, and in particular generates additional signals when delaminations occur and grow. For example, in the case of cracks, the US components can be modulated onto the electrical signal. The thermal and mechanical components can be separated using signal analysis 210. This can be used particularly advantageously with planar packaging and connection technology (AVT), since a US transmitter 1250 can easily couple into the planar structure. The US transmitter 120 is then located on the planar AVT and can couple the ultrasonic waves 110 into the planar structure.The ultrasonic transmitter 120 comprises piezoelectric layers, which can also be integrated into planar assembly and connection technology. It should be noted here that the ultrasound 110 can be coupled both as a near-surface wave and generated as a bulk wave in the component to be examined. A power component 50, 60 can particularly advantageously function as the ultrasonic transmitter 120 and receiver, since SiC and GaN semiconductors in particular possess piezoelectric properties. In this case, the ultrasonic transmitters 120 are also integrated into the power module 10. Through appropriate electrical excitation, the component 50, 60 can emit ultrasonic signals 110 and detect returning signals. The additional mechanical stimulation using ultrasound 110 can be achieved particularly easily with planar assemblies. This allows delaminations and cracks to be better detected.Advantageously, compared to previous testing methods, such as RF reflectometry, the proposed method is wired and operates at significantly lower frequencies. Piezo actuators for ultrasound stimulation 120 can be integrated directly into the planar assembly, or the power components 50, 60 themselves can perform this function. A further advantage is the high measurement accuracy, possibly with spatial resolution, depending on the number and distribution of the ultrasound generators 120 and sensors used. Furthermore, the proposed measurement technology is relatively cost-effective, and the proposed method enables early detection of the extent and type of thermomechanical aging. List of reference symbols: 110 Ultrasonic vibrations 202208201 Foreign version 15 120 Ultrasonic source, e.g.electrically excitable piezoelectric layer 130 ultrasonic waves 140 direction of the ultrasonic waves 10 electronic assembly, power module 20 circuit board 30 flat side 40 copper layer 50 semiconductor component 60 semiconductor component 70 bond wires, solder connections 80 solder layer 90 solder layer 95 local defect 100 laser welding Z. us [Ω] Impedance during ultrasonic excitation Z o [Ω] Impedance without ultrasonic excitation 200 Receiver unit, measuring unit for impedance 210 Evaluation unit

Claims

202208201 Foreign version 16 Claims 1. A method for quality testing of an electronic assembly (10), in which at least one component of the electronic assembly (10) is examined by means of an electrical characterization method, wherein the examined component is excited by means of ultrasonic waves (130) such that changes in the signal of the electrical characterization method are caused, which are evaluated by means of a signal analysis (210) and which indicate material changes in the component.

2. The method according to claim 1, wherein the electrical characterization method is impedance spectroscopy and wherein the impedance spectra are compared by means of the signal analysis (210), wherein detected changes in the impedance spectrum indicate damage or delamination in the component. 3.A method according to claim 2, wherein a frequency-dependent impedance measurement is performed and wherein the signal analysis functionally interacts with the measurement, such that the measurement of the frequency-dependent impedance is carried out comparatively, once with and once without additional ultrasound excitation, and the difference signals are evaluated.

4. A method according to claim 1, 2 or 3, wherein the ultrasound waves (130) are generated by means of electrical excitation.

5. A method according to any one of the preceding claims, wherein the ultrasound signal components are modulated onto the intermodulated electrical signal.

6. A method according to any one of the preceding claims, wherein a signal analysis is performed by means of which ther-. 202208201 Foreign version 17 Mo-mechanical components and mechanical components of the wear are separated.

7. Method according to any one of the preceding claims, wherein the electronic assembly (10) has a planar structure, and wherein the ultrasonic waves (130) are generated by means of an ultrasonic generator (120) which is placed directly on the planar AVT.

8. Method according to claim 7 above, wherein the ultrasonic generator (120) is integrated into the planar structure, in particular as a piezoelectric layer.

9. Method according to any one of claims 7 or 8 above, wherein the ultrasonic waves (130) are coupled into the electronic assembly (10) as a near-surface wave.

10. Method according to any one of the preceding claims, wherein the ultrasonic waves (130) are generated as a volume wave within the electronic assembly (10). 11.A method according to one of the preceding claims, wherein the electronic assembly (10) is continuously or once or at discrete times subjected to ultrasonic vibrations (110).

12. Electronic assembly (10), in particular a switching carrier, which is configured to carry out a method according to one of the preceding claims, comprising at least one ultrasonic source (120) which is configured and arranged to subject the power electronic assembly (10) to ultrasonic vibrations (110), comprising a measuring device (200) which is configured to perform an electrical characterization, in particular a frequency-dependent impedance measurement, comprising an evaluation device (210) which is configured to use the detected electrical 202208201 Foreign version 18 Signal change to indicate a defect in the electronic assembly (10).

13. Electronic assembly (10) according to claim 12, which has a planar structure and includes an ultrasonic generator which is directly mounted on the planar AVT.

14. Electronic assembly (10) according to one of the preceding claims 12 or 13, which has a planar structure and includes an ultrasonic generator which is integrated into the planar structure, in particular as a piezoelectric layer.

15. Electronic assembly (10) according to one of the preceding claims 12 to 14, which includes an ultrasonic generator which is integrated into a component of the electronic assembly (10) which has piezoelectric properties, in particular as a piezoelectric layer.

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