PCB in-circuit test: how do ATE machines measure resistors?

Hi folks,

does anybody know how ATE machine measures the value of a resistor placed on the target PCB?

I know that ATE machines, through a bed of nail, inject a certain voltage onto the test point.

Also, what happens if the resistor under measure is connected to other resistors?

thanks for any help, Enrico

Reply to
zigbee
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I don't know about all of them (obviously) but a general approach is to sample a known good board (better, sample several) and compare the values found on the unit under test to the expected values, +/- some allowed sample variation.

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Rich Webb     Norfolk, VA
Reply to
Rich Webb

Many years ago I programmed a incircuit tester. There was a solution like this: You have 3 resistors in a delta connection. The 3 nodes are numered 1, 2, 3 with its resistors R12, R13, R23. Connect a voltage between 1 an 2, connect the same voltage between 1 and 3. --> U23 = 0 --> I(R23) = 0. I(R12) = U/R12 I(R13) = U/R13

The current nail 1 = I(R12) + I(R13) The current nail 2 = I(R12) + I(R23) = I(R12) The current nail 3 = I(R13) + I(R23) = I(R13)

Hope this helps.

--
Freundliche Grüsse -- Regards
F. Seuhs
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Reply to
Friedrich Seuhs

3

ct

Hi, thanks for your answer.

First of all, I just discovered that PCB in-circuit test are carried out keeping the board UNPOWERED.

I also found on this Google book, a couple of schematics:

"Building a successful board-test strategy" by Stephen F. Scheiber

They usually use 3 signals:

  1. A voltage source (constant or sinusoidal)
  2. An inverting Op.Amp. that shows Virtual Earth
  3. Optionally a "Guard" GND that helps isolate the Part under test

As far as you know, is it possibile to distinguish 2 capacitance in parallel?

Enrico

Reply to
zigbee

That's exactly what I ment in my posting.

I would say: NO !!

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Freundliche Grüsse -- Regards
F. Seuhs
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Reply to
Friedrich Seuhs

er

ike

2,

If they're the same type and value, the answer is probably no. If they're of different types or values, you might be able to distinguish them by their different self-resonant frequencies or ESRs.

Mark Borgerson

Reply to
Mark Borgerson

Hi,

thanks for your answers.

I read many articles about in-circuit testing. The most important one is the following by Teradyne:

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Here are some important points:

1) It is impossible to distinguish 2 capacitors in parallel: the test will measure the sum of the two.

2) In-circuit tests are carried out on UNPOWERED targets. In words, ATE systems DON'T power up the boards during the test.

3) Probe signals have an amplitude of 0.2 Volt, in order not to power the IC's that are loaded on the board.

4) Some components can be tested by DC signals, others require AC signals (a sine wave at a certain frequency).

5) The polarity of Electrolytic Filter Capacitor is an issue. I'll post a thread as soon as discover how to test it

6) A good ATE system may cost from 30.000 to 50.000 USD

ciao, Enrico

Reply to
zigbee

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