Aries CSP center probe socket DC Measurement Results prepared by Gert Hohenwarter 8/6/2004 GateWave Northern, Inc. 1 Table of Contents TABLE OF CONTENTS .......................................................................................................................................... 2 OBJECTIVE ......................................................................................................................................................... 3 METHODOLOGY.................................................................................................................................................. 3 Test procedures ................................................................................................................................................. 4 Setup ................................................................................................................................................................. 4 MEASUREMENTS ................................................................................................................................................. 6 Resistance ......................................................................................................................................................... 6 Current carrying capability............................................................................................................................... 7 Leakage current ................................................................................................................................................ 9 GateWave Northern, Inc. 2 Objective The objective of these measurements is to determine the DC performance of an Aries CSP center probe socket. Measurements are to determine parameters relevant to test applications. Among those are current carrying ability, contact resistance and leakage as a function of voltage. Methodology A four terminal (Kelvin) measurement setup is used that includes a computer controlled voltage source capable of delivering 10 A. The voltage developed across the contact is measured with a HP 3456A DMM and yields a V-I record. Contact resistance testing as a function of displacement is performed in a test fixture with a calibrated LDT linked to the data acquisition system and the same 4 terminal measurement setup as used for the V-I-curve determination. Leakage testing relies on acquisition of a large number of data points with subsequent averaging to reduce noise as much as possible. In this manner, pA leakage currents can be detected. GateWave Northern, Inc. 3 Test procedures During testing drive current is increased in binary steps up to a maximum of 2 A. The dwell time for each current step is 0.5 s for V/I curves. Setup For current handling tests, all contacts are grounded except for one. The CSP center probe socket is placed into the test setup between two metal plates. Au over Ni plating was applied to the surfaces of the brass plates. A four terminal (Kelvin) measurement setup is used that included a computer controlled current source capable of delivering 10 A. The voltage developed across the contact is recorded at separate terminals with an HP3456A digital voltmeter. Figure 1 CSP center probe socket test arrangement; the marked pin is driven Once the data are available, they are processed to reveal the resistance and power dissipation as a function of drive current. GateWave Northern, Inc. 4 For leakage measurements the shorting plate on the DUT side is removed and an excitation applied to the connection under test. The CSP center probe socket is held in a fixture consisting of insulating material similar to the one shown in Fig. 2: Figure 2 CSP center probe socket mounting plate example Leakage testing is performed via computer controlled voltage source and DMM. Voltage is increased in small steps and the associated current is recorded. From these values, resistance is computed. GateWave Northern, Inc. 5 Measurements Resistance The resistance as a function of deflection is an important quantity since it testifies to the minimum compression required to achieve a valid and stable electrical connection. The observed curve for the Aries CSP center probe socket is shown below: R [mOhms] Cres (z) 80 70 60 50 40 30 20 10 0 0 50 100 z [um] 150 GW N 504 Figure 3 Contact resistance as a function of displacement This measurement includes the contact resistance at the pads (Cres) and the dc resistance of the contact itself. For this graph, the value z=0 represents the maximum compression in operation, i.e. with the DUT fully inserted. GateWave Northern, Inc. 6 Current carrying capability The measured current – voltage relationship for the CSP center probe socket shows a linear slope: V and R as a function of drive current I 250 V[mV] / R [mOhms] 200 150 V R 100 50 0 0 0.5 1 1.5 I [A] 2 GW N 404 Figure 4 Voltage and resistance as a function of drive current There are no anomalies in this response. The slight resistance rise at the low end is due to inaccuracies in the 10A current source at extremely low current settings. GateWave Northern, Inc. 7 The accompanying power dissipation in the connection exceeds 100mW at currents above about 1.4A: P as a function of drive current I 250 P [mW] 200 150 100 50 0 0 0.5 1 1.5 I [A] 2 GW N 404 Figure 5 Power dissipation as a function of drive current GateWave Northern, Inc. 8 Leakage current Any conductive path between contacts can and will cause difficulties for accurate testing of devices with high input impedances. Thus, leakage current was measured as a function of excitation voltage between two adjacent connections: I [pA] Leakage current as a function of voltage 50 45 40 35 30 25 20 15 10 5 0 0 2 4 6 V 8 10 GW N 404 Figure 6 Leakage current as a function of drive voltage Leakage is very low and is at the system limits. When computing the corresponding resistance, very large values result: GateWave Northern, Inc. 9 Resistance as a function of voltage 10000 R [GOhm] 1000 100 10 1 0 2 4 6 V 8 10 GW N 404 Figure 7 Leakage resistance as a function of drive voltage The resistance values are well above 1000 GigaOhms for all excitation voltages. GateWave Northern, Inc. 10