11 Finding power to ground plane shorts How VPS* helps find ground plane shorts (*Vector plane stimulus) PolarInstruments.com

22 Finding power to ground plane shorts Overview Toneohm help locate shorts - After ATE or flying probe test has isolated a faulty net. Short circuit and bus fault location - Simple trace to trace or - Multilayer plane / trace or plane / plane

33 Finding power to ground plane shorts Tools for post ATE faultfinding How do you deal with an ATE printout that lists 50 components on one node all short to 50 components on another? E.G. a Vcc +5V short to Gnd? Or a Trace to plane short?

44 Finding power to ground plane shorts For simple track shorts Milliohm measurement For bus leakage non invasive track current measurement... –Contact –Or non contact 

55 Finding power to ground plane shorts Plane to plane shorts... Present a new set of challenges The short (or bus fault) has to be located in two dimensions So what how can a VPS equipped Toneohm help?

66 Finding power to ground plane shorts Are plane shorts worth repairing? Surprisingly most plane shorts occur during assembly.... –Without a 950 they can be difficult to find they are assumed to be “internal” However 90% are assembly related and Easy to repair

77 Finding power to ground plane shorts Why not throw away boards with plane shorts? From a quality standpoint it is important to know why the plane short has occurred... –Is it a thermal cause? –a layout problem? –a latent defect with the PCB?

88 Finding power to ground plane shorts How? – The next slides tell you how VPS works

99 Finding power to ground plane shorts First imagine a track to ground short Ground Plane

10 Finding power to ground plane shorts VPS also works for plane to plane shorts Ground Plane Track

11 Finding power to ground plane shorts The unknown short circuit is a position  Ground Plane Track  Short

12 Finding power to ground plane shorts VPS Injects a current across the plane Ground Plane Track  Short I+ I-

13 Finding power to ground plane shorts This sets up a potential gradient across the PCB Ground Plane Track  Short I+ I

14 Finding power to ground plane shorts Measure voltage between short and plane position. The track simply acts as an extension of the meter lead Ground Plane Track  Short I+ I V1

15 Finding power to ground plane shorts The short is somewhere along the line where V=0. Ground Plane Track  Short I+ I V1

16 Finding power to ground plane shorts This has isolated the short in one dimension. Inject the current at right angles to locate the second dimension.

17 Finding power to ground plane shorts By injecting at right angles.. Ground Plane Track  Short I+ I V2

18 Finding power to ground plane shorts Now find where V2 = 0 Ground Plane Track  Short I+ I V2

19 Finding power to ground plane shorts Ground Plane Track  Short I+ I V The short is located where V1 + V2 = 0

20 Finding power to ground plane shorts By looking at the polarity of V1 and V2 the 950 can display directional arrows on the front panel that guide you to the area of the short Ground Plane Track I+ I V Short 

21 Finding power to ground plane shorts The 950 Plane shorts mode uses this VPS technique to help you rapidly locate plane to plane shorts, A 950 gives a continuous display of short direction while you probe and the current injection is switched automatically Ground Plane Track I+ I V Short 

22 Finding power to ground plane shorts Your Toneohms pay for your investment very quickly

23 Finding power to ground plane shorts Toneohm short and bus fault locators USA / Canada - Polar Instruments Inc (800) Richard Smith UK Polar Instruments (UK) Ltd Paul Norrington Asia / Pacific Polar (Singapore) Amit Bhardwaj R.O.W. - Polar Instruments Ltd Tel: Martyn Gaudion all offices:  Polar Instruments 2001 All trademarks recognized