New Approaches for CDM TestingAlternative approaches to CDM ESD evaluation are gaining prominence, among which capacitively coupled TLP (CCTLP) offers numerous advantages over the standardized field-induced CDM setup. Testing accuracy depends on transferring charging voltage levels to peak current levels. The effective capacitance (Ceff) serves as an indicator of stress severity, and FEM simulations can provide accurate Ceff values. However, considering the impact of device dimensions, volume is introduced as a preferred parameter for estimating stress current levels. By leveraging the relationship between volume and current established using metal coin modules, reasonable estimations can be obtained. These approaches facilitate the use of alternative CDM testing methods and provide a practical solution for CDM target translation.
New Approaches for CDM Testing
It is now well known that testing for CDM Electrostatic Discharge [ESD]
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
" href="https://incompliancemag.com/terms/electrostatic-discharge/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">ESD evaluation is becoming a bigger challenge. Previously (In Compliance Magazine, March 2021), capacitively coupled TLP (CCTLP) was described as an alternate approach. It offers many advantages compared to the standardized field-induced CDM setup according to the JS002 standard [1]. Testing of a package, bare die, or wafer is enabled with high reproducibility. The failure correlation between CDM and CCTLP has been investigated based on peak current stress levels and not by a charging voltage level [2]. If testing with an alternative CDM method as CCTLP is done to reproduce JS002, the CDM charging voltage must be transferred into peak current levels.
Device and Tester Capacitance
The ability of a a component or circuit to store an electric charge.
A measure for the severity of the CDM stress is the effective Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance Ceff of a device [3]. Ceff characterizes the amount of exchanged charge between DUT and test setup at a specific stress level (e.g., VCDM) in a specific testing environment.
Products can be categorized with respect to Ceff in an FICDM setup because of the direct relation to the peak current for a given test voltage, as described in [4].
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During a CDM stress, different Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance values play a role according to the three-capacitances model, as shown in Figure 1.
The three Capacitance
The ability of a a component or circuit to store an electric charge.
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance CDUT is defined as the Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance from the device to the field plane. The static Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance value for CDUT is extracted from a Finite Element Method [FEM]
A technique for finding approximate solutions to boundary value problems for differential equations.
" href="https://incompliancemag.com/terms/finite-element-method/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">Finite Element Method (Finite Element Method [FEM]
A technique for finding approximate solutions to boundary value problems for differential equations.
" href="https://incompliancemag.com/terms/finite-element-method/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">FEM) simulation according to the three-capacitances model shown in Figure 1. Differences between Ceff and CDUT capacitances either extracted from FEM-simulation or calculated as parallel plate Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance Cplate (A is the area of the DUT, and d is the thickness of the FR4 dielectric layer) are demonstrated based on the metallic circular coin modules (height 1.27 mm, diameters see Table 1).
P1
P2
JS
P4
JL
P5
P6
P7
P8
2.29
4.49
8.89
18.03
25.37
36.05
43.04
51.02
62.52
Table 1: Coin diameter in mm, height of coin: 1.27 mm
The Finite Element Method [FEM]
A technique for finding approximate solutions to boundary value problems for differential equations.
" href="https://incompliancemag.com/terms/finite-element-method/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">FEM simulation of CDUT does not coincide with the simple plate Capacitor
A passive electronic component that consists of two conductive plates separated by an insulating dielectric.
" href="https://incompliancemag.com/terms/capacitor/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitor formula since fringing effects are also considered, especially for small devices. CDUT also shows a linear dependency on the area-capacitance relation. In contrast, Ceff values show saturation with increasing area or volume of a DUT. As a result, not only the area of the bottom surface contributes to the Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance but also the sidewalls and, therefore, the volume.
Impact of Device Dimensions
To calculate the CDM discharge current from the volume, the device area is considered as the maximum edge length a x b, including the pins and mold compound (Figure 3). For a bare die product that does not go into a final package, the area is calculated from the edge length of the silicon accordingly.
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Statistical analysis of CDM testing data shows the relevance of device area and volume for predicting stress current levels in a CDM test since the height h of the device has a non-neglectable influence on the discharge current. A database with over 15 million CDM waveforms has been used to evaluate the relation between area, volume, peak current, and the effective Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance Ceff. The area and volume of about 10000 different device types can be derived from the package dimensions included in the database. For each device type, only the waveforms are evaluated, showing the maximum positive peak current Ipeak out of several CDM discharges for a positive charging voltage level of 500 V. According to the measurement results, the peak current reduces with the increasing height of the device.
This can be shown using the set of nine cylindrical solid metal coins P1 to P8 with different diameters and volumes (see Table 1)[5]. The coin reference for the peak current still gives a reasonable orientation for the maximum peak current. Figure 4 shows the dependency of the effective Capacitance
The ability of a a component or circuit to store an electric charge.
" href="https://incompliancemag.com/terms/capacitance/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">capacitance Ceff on the volume. For very flat packages, the limit of the coins is exceeded but still givesa meaningful value. The coin with the smallest volume and, therefore, lowest Ceff reaches the lowest peak current and vice versa. For devices, this means that their Ceff with the according current can be related to the current of the coins. As shown, the device height is becoming relevant for the estimation of the stress current level, therefore, the volume is introduced as the preferred parameter. Thus, the volume value can be used to estimate the expectable peak current with respect to the coin values as shown in Figure 5.
Conclusion
A practical solution is presented for the problem, how CDM targets can be translated to current test levels. CDM current test levels are important as they allow using alternative CDM testing methods, such as CCTLP. The first testing proposal is a simple approach, representing the worst case: Increase the CCTLP testing voltage until the peak current value is reached at the product pin given in Figure 5.
To avoid over-testing, these levels can be lowered based on the second proposal if details of the electrical properties on-package and on-chip are known. Ceff values can be predicted by Finite Element Method [FEM]
A technique for finding approximate solutions to boundary value problems for differential equations.
" href="https://incompliancemag.com/terms/finite-element-method/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">FEM simulation even before devices are available.
The full paper was published in [6].
References
American National Standards Institute [ANSI]
A private non-profit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.
" href="https://incompliancemag.com/terms/american-national-standards-institute/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">ANSI/JEDEC/ESDA, “Joint Standard for Electrostatic Discharge [ESD]
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
K. Esmark, R. Gaertner, S. Seidl, F. zur Nieden, H. Wolf and H. Gieser, “Using CC-TLP to get a CDM robustness value,” 2015 37th Electrical Overstress/Electrostatic Discharge [ESD]
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
" href="https://incompliancemag.com/terms/electrostatic-discharge/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">ESD), Anaheim, CA, USA, 2007, pp. 5A.1‑1‑5A.1-10.
N. Jack, B. Carn and J. Morris, “Toward Standardization of Low Impedance Contact CDM,” 2019 41st Annual EOS/Electrostatic Discharge [ESD]
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
" href="https://incompliancemag.com/terms/electrostatic-discharge/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">ESD), Riverside, CA, USA, 2019, pp. 1-7.
T. J. Maloney and N. Jack, “CDM Tester Properties as Deduced From Waveforms,” in Institute of Electrical and Electronics Engineers [IEEE]
A professional association that is dedicated to advancing technological innovation and excellence.
" href="https://incompliancemag.com/terms/institute-of-electrical-and-electronics-engineers/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">IEEE Transactions on Device and Materials Reliability, vol. 14, no. 3, pp. 792-800, Sept. 2014, doi: 10.1109/TDMR.2014.2316177
L. Zeitlhoefler, T. Lutz, F. Zur Nieden, K. Esmark and R. Gaertner, “Voltage to Current Correlation for CDM Testing,” 2023 45th Annual EOS/Electrostatic Discharge [ESD]
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
Sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.
" href="https://incompliancemag.com/terms/electrostatic-discharge/" data-mobile-support="0" data-gt-translate-attributes='[{"attribute":"data-cmtooltip", "format":"html"}]' tabindex="0" role="link">ESD), Riverside, CA, USA, 2023, pp. 1-11, doi: 10.23919/EOS/ESD58195.2023.10287735
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