1. In-Circuit Test Concepts Part 2 Analog In-circuit Michael J Smith Michael.J.Smith@Teradyne.com

2. The Series Part 1 – In-Circuit Test Overview
What and Why In-Circuit Test?
The Defect Spectrum
In-circuit Test System Architecture
Part 2 - In-Circuit Analog Measurement
Shorts and Opens Testing
2,3,4,6 Wire Measurement
R,C,L, Diode, Zener, Transistor Measurement
Powered Analog Testing
Analog Digital Opens Testing
Part 3 - In-Circuit Digital Testing
Digital Vectors
Backdriving
Inhibits and Disables
Bus Testing
Boundary Scan
ISP and FLASH programming
Part 4 - In-Circuit Program Development Process

3. Agenda: In-Circuit Analog Measurement
Introduction
Analog Test Flow
Startup Procedures
Shorts Testing
Resistor Measurement
2,3,4,6 Wire Measurement
C,L, Diode, Zener, Transistor Measurement
Powered Analog Testing
Analog Digital Opens Testing

4. What is In-Circuit Test?
Uses a “Bed of Nails” to access as many electrical nodes on the Unit Under Test (UUT) as possible.
Voltage and current source(s) and measure(s) are used to test analog devices, one device at as time, using guarding techniques to negate the effects of other devices.
A technique called backdriving, using voltage overdriving, is used to test digital devices in isolation with digital vectors by voltage forcing techniques.

5. Defect Spectrum ICT finds defects!
But it does not normally find potential defects
in solder quality!

6. Analog Test Program Flow
Capacitor Discharge
Contact Test
Shorts Test
Analog Test – Un-powered
Resistor
Capacitor
Inductor
Diode
Transistors
Analog Digital Opens
Power Board
Power Up Tests
Op-Amps.
Un Power Board

7. Initial Routines Capacitor Discharge Contact Test
Checks for voltages on large capacitors and then removes potential
Can effect measurement
Normal method is to discharge through a resistor to ground and measure the voltage,
Contact Test
Lifts the potential of the board ( VCC and GND ) and checks to see if all contacting nails reflect the raised potential.

8. Shorts Tests Shorts Test Check for shorts between all points
Normal shorts test is to test one node against all other nodes
Number of tests = Number of nodes -1

9. Alternative Shorts Tests
Fast Shorts Test use a binary search method
Number of tests = only log2 (N) tests
Faster Shorts Testing by Anthony Suto, Teradyne Inc

10. I = V/R V=IR R = V/I Ohms Law I = V/R
states that, in an electrical circuit, the current passing through a conductor between two points is proportional to the potential difference (i.e. voltage drop or voltage) across the two points, and inversely proportional to the resistance between them. In mathematical terms, this is written as:
I = V/R
I = V/R
V=IR
R = V/I

11. How is Ohm’s Law applied?

12. 8-Wire Scanner Relay – Connected for a resister test

13. Real Life Circuits Only a few measurements are per 2-terminal
Series, Pull-ups, Pull-downs and Terminators etc.
Minimize Voltage!
Most other circuits and networks of resistors

14. Use of the Virtual Ground
All the paths are connected together and a virtual earth is created

15. 3- and 4-Terminal Guarded Measurement

16. 4-Terminal Guarded Resistor Test

17. 4-Terminal Guarded Resistor Test – Ex 2

18. Kelvin Resistor Test
Relays and fixture resistance can effect low-value resistor measurements and therefore we use a “Kelvin” test ( <20 Ω).

19. 6-Terminal Resistor Test

20. Electrical Impedance, or Simply Impedance
A term coined by Oliver Heaviside in July of 1886 to describe a measure of opposition to a sinusoidal alternating current.
Electrical impedance extends the concept of resistance to AC circuits, describing not only the relative magnitudes of the voltage and current, but also the relative phases.
In general, impedance is a complex quantity ; the polar form conveniently captures both magnitude and phase characterstics,

21. 4-Wire Guarded Capacitor Test

22. 4-Wire Guarded Inductor Test

23. Diode Test Looks for the characteristic knee voltage ( Typ 0.65V)
Also use the dynamic resistance as a secondary test

24. Zener Diode Test
Looks for the switch voltage.

25. Transistor Test
Transistor NPN and PNP tests are normal gain measurements.
Set the current source to a nominal predetermined value (IE1).
Measure the current in the base circuit (IB1).
Slightly increase the current source to a new known value (IE2).
Measure the new current in the base circuit (IB2).
Use the values in the following formula to calculate the gain.
GAIN = (IE2-IE1) - (IB2-IB1)/(IB2-IB1)

26. Other Tests
Transformers
AC gains
Relay
Switch Test
Etc.

27. Powered Analog Tests

28. Applying Power
Power needs to applied correctly ie emulate the system supply
Right order, timing and slew rate
Limited Current
Verify Stable
Verify Voltage Levels

29. Op-Amp Test A number of preset test are normally available
This is a simple AC gains test

30. Op-Amp Test A number of preset test are normally available
This is a simple switch to rail test

31. Powered Analog
Frequency generator
Plus generator

32. Other Analog Tests Custom Test – Needs language support
V,I,
Frequency
V and I measured over time for complex waveform
Hybrid Tests – Synchronized Analog and Digital
D to A
A to D
Complex circuits.

33. Analog Digital Opens Testing

34. Why Analog Digital Opens Test?
Increasing use of complex connectors and sockets
Lack of digital vectors

35. What is Analog Digital Opens?
Capacitance Coupling Technique
Software replaced by fixture hardware

36. Types of Analog Open Techniques
Opens Xpress
Passive Probe
Low Cost
Easy of Manufacture
FrameScan & FX Probe
Active Probe
High Signal Integrity
Component under Test
PCB
RCM
Carrier
Conductor
Standard Nail
Signal
Detector
2 Vac
@ 3.0 KHz
-0.6 Vdc
Vcc
Gnd
DUT
VBIAS + -
2 V
200 Ω
5 Ω

37. Active Buffer assembly
Active Analog Opens
Active Buffer assembly
Device-
Under-Test AC
Source
Printed
Circuit
Board
Opens
Sensor
IC Lead
Filter
Scanner
Detector
Probe Plate
Gain
Mux Board
ICA
Guard
DUT

38. In-Circuit Test Concepts Part 2 Analog In-circuit Michael J Smith Michael.J.Smith@Teradyne.com

39. The Sequels! Part 1 – In-Circuit Test Overview
Part 3 - In-Circuit Digital Testing
Digital Vectors
Backdriving
Inhibits and Disables
Bus Testing
Boundary Scan
ISP and FLASH Programming
Part 4 - In-Circuit Program Development Process