Avoiding ESD Damage in Design and Production

Transcription

1 in Design and Production Frits J.K. Buesink, Senior Researcher EMC

2 in Design and Production overview How to pick up charge? What s the damage? Measures to prevent ESD damage in production Measures to prevent ESD damage by design the threat mechanisms Current boundaries cable protection input protection Testing

3 Static Discharge Accidents do happen usually you do not see the effects immediately

4 Air Human Skin Glass Wool Tribo Electric Series if two materials touch, charge is transferred. Aluminium Cotton Steel Gold Polyester - Silicon - Teflon

5 Electric Fields exert Forces on Other Objects equal charges repel, opposite charges attract each other Adhesive Tape demo Mutual repulsion and: attraction to neutral or negatively charged objects

6 What to do if plastics cannot be avoided? discharge with an ioniser or keep your distance to charged objects How to fight? 1. a flame With ionised air! 2. an ioniser Risky alternative: Keep at least 30 cm distance to (necessary) plastics if there is no ioniser!

7 Electric charging by induction Wool direct contact not necessary! Teflon 1. Charging of an insulator Printed Circuit Board Insulated PCB on charged surface

8 Electric charging by induction direct contact not necessary! Touch or Ground PCB: negative charge disappears (spark) (PCB possibly damaged) Q PCB VPCB (C PCB decreases) CPCB Lift PCB: voltage increases! More Sparks fly!

9 The Danger: Large Discharge Current, Fast Rise Time direct damage to components or via inductive coupling into circuit loops Human Body is a conductor 15 kv 200 pf 100 ns 200 kw 1 k charged person Capacitance in soles or floor covering 100 pf 100 pf

10 in Design and Production overview How to pick up charge? What s the damage? Measures to prevent ESD damage in production Measures to prevent ESD damage by design the threat mechanisms Current boundaries cable protection input protection Testing

11 Destruction mechanisms ultimately, all damage is caused by current Gate oxide puncture: high voltage Trace evaporates: large current break down: 20 V gate oxide [insulator] N P N

12 The person can be charged or the component or both essential for an ESD event is the difference in charge voltage charged thing 1 k charged person 100 pf 100 pf

13 in Design and Production overview How to pick up charge? What s the damage? Measures to prevent ESD damage in production Measures to prevent ESD damage by design the threat mechanisms Current boundaries cable protection input protection Testing

14 Part, handler and assembly: same potential! when in proximity, there can be no voltage difference! Employee (M/F) ESD sensitive part these three objects must be continuously interconnected during handling! Electronics in in cabinet or: ESD-bag

15 If there is charge? Get rid of it! but not too fast! fast enough too slow through resistance [ ] insulating static dissipative acceptable desired safe for component k conductive safe for people discharge time [s] (at 50% humidity) Standard: IEC 61340

16 ESD Protected Area (EPA) everything conductive and interconnected ESD Coat grounded through cuff Employee (M/F) possibly: wrist strap Work Surface ESD Sensitive Part Equipment cabinet (usually not not in in this thisarea) Shoe Floor EPA Earth

17 Prevent charging of persons and furniture standard: IEC specifies through-resistances

18 ESD shoes should contact the ESD floor. we are actually only interested in the maximum charge voltage ESD STM Presently Future : <100 V : <20 V and lower!

19 ESD Protected Workstation employee, work surface and electronics cabinet mutually interconnected Employee (M/F) (Wrist Strap) ESD Sensitive Part Electronics in in equipment or: ESD-bag Work Surface Equipment Cabinet Marking Approved Workbench ESD Workstation Earth

20 in Design and Production overview How to pick up charge? What s the damage? Measures to prevent ESD damage in production Measures to prevent ESD damage by design the threat mechanisms Current boundaries cable protection input protection Testing

21 Better be prepared if your design is planned here! keep electronics protected in harsh environments

22 the ESD Threat ESD pulse from IEC immunity standard 20 Contact discharge current IEC Current [A] I( i) t( i) time [sec] The ESD contact discharge current waveform (IEC )

23 Time to frequency domain conversion two characteristic frequencies appear related to pulse duration and rise time A 90% 50% 10% h amplitude F 1 F 2 ~ 1 f F knee r 1 ~ f 2 1 h log (frequency) 1 r 1 2 r

24 ESD pulse can be decomposed into two trapezoids this allows an estimate of the ESD current frequency spectrum 20 Building blocks contact discharge pulse Fast pulse: r =0.7 ns; h =10 ns IS( i) 15 Slow pulse: r =10 ns; h =60 ns current [A] IF( i) I( i) 10 5 To convert the ESD pulse to to frequencies, it it can be split into two trapezoids t( i) time [s] Short and long pulse added in the time domain

25 Spectra of slow and fast pulse can be added the resulting spectrum is used for shielding analyses current contribution Iesd( i) IesdS( i) IesdF( i) ESD current spectrum Sum Fast pulse Slow pulse f( i) frequency Total current