in circuit test concepts part 2 analog in circuit michael j smith michael j smith@teradyne com l.
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In-Circuit Test Concepts Part 2 Analog In-circuit Michael J Smith Michael.J.Smith@Teradyne.com. 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

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the series
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
agenda in circuit analog measurement
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
what is in circuit test
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.
defect spectrum
Defect Spectrum

ICT finds defects!

But it does not normally find potential defects

in solder quality!

analog test program flow
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
initial routines
Initial Routines
  • Capacitor Discharge
    • 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.
shorts tests
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
alternative shorts tests
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

ohms law
Ohms Law
  • 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

real life circuits
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
use of the virtual ground
Use of the Virtual Ground
  • All the paths are connected together and a virtual earth is created
kelvin resistor test
Kelvin Resistor Test
  • Relays and fixture resistance can effect low-value resistor measurements and therefore we use a “Kelvin” test ( <20 Ω).
electrical impedance or simply impedance
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,
diode test
Diode Test
  • Looks for the characteristic knee voltage ( Typ 0.65V)
  • Also use the dynamic resistance as a secondary test
zener diode test
Zener Diode Test
  • Looks for the switch voltage.
transistor test
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)

other tests
Other Tests
  • Transformers
    • AC gains
  • Relay
    • Switch Test
  • Etc.
applying power
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
op amp test
Op-Amp Test
  • A number of preset test are normally available
    • This is a simple AC gains test
op amp test30
Op-Amp Test
  • A number of preset test are normally available
    • This is a simple switch to rail test
powered analog
Powered Analog
  • Frequency generator
  • Plus generator
other analog tests
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.
why analog digital opens test
Why Analog Digital Opens Test?
  • Increasing use of complex connectors and sockets
  • Lack of digital vectors
what is analog digital opens
What is Analog Digital Opens?
  • Capacitance Coupling Technique
  • Software replaced by fixture hardware
types of analog open techniques
Opens Xpress

Passive Probe

Low Cost

Easy of Manufacture

FrameScan & FX Probe

Active Probe

High Signal Integrity

5 Ω

2 Vac

@ 3.0 KHz

-0.6 Vdc

200 Ω

DUT

-

Signal

Detector

2 V

VBIAS

+

Conductor

Vcc

Gnd

Carrier

RCM

PCB

Component under Test

Standard Nail

Types of Analog Open Techniques
active analog opens

Gain

Filter

Opens

Sensor

Scanner

MuxBoard

Device-

Under-Test

ActiveBufferassembly

ProbePlate

DUT

ICLead

Printed

Circuit

Board

Guard

AC

Source

AC

Detector

ICA

Active Analog Opens
the sequels
The Sequels!
  • Part 1 – In-Circuit Test Overview
    • http://atd-teradyne.01o.com/ajtk/servlet/JJ?H=13q7oj&R=665215672/resource/type/web_recordings.html.
  • 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