BEST PRACTICES FOR SYSTEM LEVEL ESD TESTING OF SEMICONDUCTOR COMPONENTS. Kathleen Muhonen CSICS October 2013

Transcription

1 BEST PRACTICES FOR SYSTEM LEVEL ESD TESTING OF SEMICONDUCTOR COMPONENTS Kathleen Muhonen CSICS October 2013

2 Motivation OEM s are asking IC manufacturers to test their components to the IEC standard. IEC is for system level testing not component testing. There is no guidance on how to test a component according to the IEC system level test. Despite attempts to give guidance, this test has a lot of variability in the test result. Waveform Variations Gun Repeatability Test Set-Up

3 Waveform Ip 0.9 Ip Current I 30 t=0 is the 10% point of the rising edge I Ip 0 30ns 60ns tr Time This waveform is used in IEC and the Human Metal Model preferred test method.

4 Waveform Parameters Table 1. General Waveform Parameters Output voltage contact mode 1 At least 1 kv to 8 kv, nominal Tolerance of output voltage ± 5% Polarity of output voltage Discharge mode of operation Positive and negative Single discharges Table 2. Human Pulse Parameters Metal Model Pulse Parameters Human Metal Model Pulse Value Unit 10 to 90% Pulse Rise-time 0.8 ± 25% ns First peak current of the discharge (Ip) Current at 30 ns from initial 10% point Current at 60 ns from initial 10% point 3.75 ± 15% A / kv 2 ± 30% A / kv 1 ± 30% A / kv

5 Test Setup A for HMM ESD Pulse Source Ground clamps insuring that test board is securely grounded to Ground Plane Discharge Points Ground Cable A A = 0.5 meters minimum A Test or circuit board Ground Plane Note: In IEC the gun ground cable is connected to the floor ground plane, not the table top ground plane.

6 Waveform Verification Pellegrini Target

7 Waveform Verification Pellegrini Target

8 Waveform Verification Pellegrini Target High Power Attenuator ATT Gun Tip V scope V corr 48 Ω 50 Ω 2 Ω V pulse Scope R in =50 Ω Target V corr V scope 10 ATT 20 =

9 50 Ω V corr Waveform Verification Peligrini Target V pulse V corr V scope 10 I gun 48 Ω Vcorr I corr = I corr 2 Ω I pulse 50 V pulse I ( 50 + I gun ATT 20 = = corr Vpulse Vcorr Icorr 98 V I gun = I pulse + Icorr = + = V corr 98 Vcorr = + = = 20 Vcorr Vpulse I gun V scope 10 ATT 20 = ATT corr 48) ATT = attenuation in db that is in front of scope input

10 Test Setup Powered Board Note: This is the IEC set-up where there is capacitance between the DUT and table top metal. There is another capacitance between the table and the floor ground. The gun is connected to the floor ground.

11 Example of Test Fixture Board for an RF Part For an RF part it is important to terminate other ports in 50 ohms (system impedance) to eliminate reflections that would not be present in the system (cell phone for example).

12 Example of Test Fixture Board for an RF Part Whatever path is turned on for the powered on test that path should have attenuation before the termination. Otherwise the termination will eventually fail from the high voltage and current stresses. This example the receive path of a switch may be turned on. Zap the antenna port and attenuate the receive output before it hits the termination.

13 Peligrini Target Data: 2kV Current (A) Gun 1 Gun E-08 2.E-08 7.E-08 1.E-07 2.E-07 Time (sec)

14 Peligrini Target Data: Peak, 30 and 60 ns Current Gun Current (A) Gun 1 - Peak Gun1-30ns Gun 1-60ns Gun 2 - Peak Gun 2-30ns Gun 2-60ns IEC Voltage (V)

15 Waveforms in Test Fixture Board, 2kV 6 5 Current (A) Gun 1 Gun E E E E E E-07 Time (sec)

16 Current Comparison: Pulses Through TFB Gun Current (A) Peak - Gun1 30ns - Gun1 60ns - Gun1 Peak - Gun2 30ns - Gun2 60ns - Gun IEC Voltage (V)

17 Motivation: Impact of Test Bench Parameters Inconsistent test results at different locations. Multiple test set-ups. Purpose: Find factors that significantly perturb test results. Follow-on DOE s based on these results. Assumptions Cannot use these results to predict IEC performance on other parts. Step stressing and results are RELATIVE absolute numbers are not to be used to make conclusions. Goal to see what perturbs results, goal is not to get the part to pass the spec.

18 Selected Factors for Investigation Wire line length: 1 vs12 (from battery pack to part) Supply line decoupling: 10nF vs1µf Test Point: 90 o pogo pin vs contact microstrip Gun Type: Teseq vs Mini Zap IEC vs HMM test setup IEC: gun ground connected to ground on the floor HMM: gun ground connected to table top 1kΩ resistor in the control lines only: with and without Grounding: through switch box and at metal holder 4 parts following standard procedure and Teseq gun 4 parts following standard procedure and Keytek gun 3 parts to be handled with the DOE but not ESD tested

19 Used a Screening Design of Experiments (DOE) 18 different combinations of the factors. Four individual parts were tested for each combination. Total of 72 parts used in this experiment All parts from same date code All parts RF tested before and after zapping Step stress used to determine failure (i.e. If part survived a voltage stress it could be used for the next higher voltage) One-Way Analysis using Statistical Software to determine what factors effected the failure point of the part.

20 One-way Analysis Resistance of the control lines is a significant factor Microstrip point of entry is not consistent like the pogo pin All other factors need a follow-on experiment to resolve.

21 Factors that stood out Resistance: no resistance in line decreased failure voltage Standard: HMM decreased failure level Standard-gun: Gun type + test type influenced failure level Gun-wire length: Gun type + wire length influenced failure level

22 Summary and Conclusions Adding resistance is a significant factor Concluded use of resistance should reside on the eval board (not the battery harness). Evaluation boards should mimic the system environment. Using the micro strip as a contact point may look advantageous this is misleading. The gun tip can slip when contacting the small microstrip line. Therefore the pulse may not be delivered to the part. Second order interactions may need further investigation Based on a lot of other experiments the gun is a source of large variability. Although they are in spec, they all produce different results on components.

23 Round Robin for HMM Round Robin testing used to see if a test method is repeatable and reliable. 8 different labs participated. Each lab received 4 replicates of 4 different kinds of parts. - Transient Surge Protection Device (TSPD) - TVS 2 kinds (Transient Voltage Suppressor) - RF Switch Each part was tested with the HMM document and the failure level was recorded. Some initial settings were agreed upon - Start voltage, step voltage and how to determine failure

24 Statistics Variability of Failure Voltages TSPD TVS #1

25 Statistics Variability of Failure Voltages TVS #2 RF Switch

26 Variance Sources Lab to Lab! TSPD TVS #1

27 Variance Sources Both lab to lab and interlab TVS #2 Switch

28 Summary HMM is a test procedure to give guidance to testing components to a system level standard. - Unfortunately its variability is just as high as the IEC test set-up. - Recommended to do what the customer requests. All examples here show that this test a high variation in failure voltage. - Not a useful test for system level ESD robustness. - No indication it predicts field failures. Best guidance is to document everything: - Type of equipment, test bench set-up and step by step procedure. - Helps the customer understand how the results can differ from site to site.