Near-field probes play an important role in the development of assemblies. They are successfully used in both high-frequency technology and EMC technology to evaluate simulation values, identify sources of interference and carry out real-time monitoring.
Near-field probes have the following properties:
- Low feedback on the measuring system due to contactless measurement
- Versatile application options thanks to optimized tip design
- Even structures that are difficult to reach can be examined
- Broad frequency spectrum
- Measurements in the frequency and time domain
These characteristics enable good integration of the near-field probes into the development process of assemblies. Near-field analysis can be used to measure various effects caused by the influence of electric or magnetic fields on the assembly, for example. As the magnetic field and electric field are measured separately, their effects can be assessed individually. Field distributions, including the distribution of currents and voltages, can be derived from this. This is why the probes manufactured by Langer EMV-Technik are designed in such a way that magnetic field probes, for example, are shielded against the penetration of electric fields.
Different spatial resolution of measured values
Depending on the size of the near-field probes, measurement volumes can be measured with a higher or lower resolution. This allows the field distribution of entire assemblies as well as the smallest circuits to be measured and displayed graphically. The near-field microprobes of the ICR series are suitable for the field distribution of circuits. These probes are characterized by a high spatial resolution of approx. 70 -250 μm. With this resolution, field distributions of integrated circuits can be recorded and evaluated. Fig. 1 and 2, for example, show the field distribution of the processor chip of a Raspberry Pi at different spectral frequencies. The field distributions result from the internal switching processes of the IC. These activities reflect the processes and functions of the circuit and depend, for example, on the technology of the IC and the software or firmware. In comparison, the field distribution of the memory circuit of the Raspberry Pi shows the diversity of the structure. Fig. 3 and 4 show the activity of the IC distributed over the entire chip surface. It is generated by the function of the IC distributed over the chip. Due to the possibilities of fault diagnosis and optimization of integrated circuit components, these near-field investigations can be used both in development and for troubleshooting in finished devices. Due to the high spatial resolution and the wide frequency range, these measurements are suitable for investigating safety-critical functions of integrated circuits. In so-called side-channel attacks, circuits are exposed to specific signals in the time domain and the reaction of the circuit is investigated at various positions using field strength increases. The near-field probes can be used to measure the reactions of the circuits and interference signals can be injected using pulsed field generators, also from Langer EMV-Technik. The spatial resolution of the injected pulsed fields is in the range of approx. 200-300 μm.
Fig. 1: Field decoupling, measured with ICR HH150-27 at 25 MHz
Fig. 2: Field decoupling, measured with ICR HH150-27 at 163.7 MHz
Fig. 3: Field decoupling, measured at memory IC with ICR HH150-27 at 18 MHz
Fig. 4: Field decoupling, measured on memory IC with ICR HH150-27 at 24 MHzESD suppression of stacked boards
The sensitivity of electronic assemblies to electrostatic discharge (ESD) has increased in recent years. This is due to the further development of IC technology. The structural widths of the silicon have been significantly reduced. This results in higher switching speeds and, by reducing the supply voltages, lower switching thresholds of the ICs. This increases sensitivity to ESD interference in particular. Fault isolation and interference suppression for ESD-sensitive assemblies is usually carried out using an ESD generator (ESD gun). The ESD gun is a very coarse tool, which acts on the assembly over a large area. For this reason, localized exposure of individual components is generally not possible. The identification of specific weak points is therefore time-consuming. The ESD gun is used to inject an ESD current pulse into the metal component(Fig. 5).
The current pulse flows out into the environment via connectors and network cables. This creates a voltage difference between the two circuit boards. This voltage difference generates an electric field that acts on the assembly of the lower module and can affect the IC (2) and the quartz (3). Furthermore, the magnetic field of the ESD current pulse can cause a coupling to the useful signals of the IC (2) in the connector and also cause a fault in the IC. Other components (4), (5) and the LAN socket (6) could also be affected. The Troublestar TS-23 interference generator from Langer EMV-Technik, which will soon be available, is used to isolate the fault locations(Fig. 6 and 7).
Fig. 5: Exposure of an electronic device to an ESD gun
Fig. 6: Localization of the fault locations with the TS-23 interference generator
The differential outputs of the Troublestar can be used to generate an ESD voltage difference between the two assemblies of the device under test. This ESD voltage difference can essentially only disturb the connector (1), the IC (2) and the quartz (3). This allows the fault locations to be narrowed down to these areas. To narrow down the fault location further, the individual components must be selectively subjected to the differential voltage from the Troublestar TS-23. A copper foil is bonded to the IC (2) (signal processor) or the oscillating quartz (3) (to couple interference pulses from the Troublestar). One differential output of the Troublestar is connected to the copper foil (solder connection). The other differential output is connected to the ground of the circuit board (soldered connection). The DF 10 differential coupler is used for this connection(Fig. 7). This arrangement enables local coupling of electric field into the IC without significantly affecting other areas. This allows the ESD sensitivity of the IC to be tested. If the oscillating quartz is exposed in a similar way, the same effect occurs. If the metal housing is connected to earth as standard, the coupled interference voltage pulses are short-circuited. A strong magnetic field is created around the relevant pin of the quartz crystal, which can influence the other pins of the quartz crystal. It is also possible for the oscillating quartz crystal to be disturbed. This method can be used to identify ESD-sensitive components. As a countermeasure, the two assemblies can also be adequately connected to earth. Appropriate countermeasures can be implemented and tested for their effect with the Troublestar TS-23.
Fig. 7: Localization of the fault location by selectively applying the differential voltage of the Troublestar to the individual assemblies
