IEC 61000-4-2 ESD test in display down configurationfor cell phones

During the IEC 61000-4-2 test the DUT is placed on a 0.5 mm insulating sheet, which is on the horizontal coupling plane (HCP). For discharge points on the back side of the phone this leads to a situation in which the display is facing the HCP. The phone or tablet forms a capacitance between 50 pF and 300 pF to the HCP. The capacitance value depends on the size of the phone, its screen flatness, and the flatness of the insulator which may deteriorate over time. The discharges to the phone lead to a large displacement current flowing through the display. This current has multiple paths to the body of the phone: via the touch electronics, via the display electronics, and directly to the body of the phone. As these currents can reach 30 A (at 8 kV contact mode) they can lead to upset and damage of both the display and the touch layers. This paper provides analysis of the display down test situation in order to show reproducibility problems. The effect of the capacitance variation is shown by the measurement and the PSPICE model. Full-wave model was used to help understand how much of the total current flows through the body of the phone. The Lichtenberg dust figure method was used to show the contribution of the corona discharge.