Continuity testing in semiconductor ATE: Fundamentals and test methods

Continuity is the first and most basic test performed on a device (chip). It checks the electrical connections between the device under test (DUT) and the automatic test equipment (ATE). Its purpose is to confirm that:

No device pin is shorted to another pin.
No device pin is accidentally shorted to power or ground.
No open circuit exists inside of the device.
Each device pin has a complete electrical path to the correct test resource inside the ATE.
The connection between the device and the tester is neither open nor incorrectly connected.

This test is usually performed at the beginning of the test flow. Detecting opens or shorts early confirms that the device is properly connected to the tester and that the test hardware is functioning correctly. A short can also damage the device, especially if it connects a pin to an incorrect voltage, power, or ground. If an open or short is not detected, it can cause incorrect measurements, false test failures, or unreliable results in later tests.

Figure 1 The block diagram shows the required electrical connectivity from the DUT to the corresponding ATE resource through the socket, DIB, and connectors. Source: Author

Before going deeper into continuity testing, it’s important to understand the ESD protection circuit connected to the device pins.

ESD, or electrostatic discharge, is a sudden flow of electrical charge that can damage the internal circuits of a device. To protect the device, many pins include ESD protection diodes. These diodes help direct excessive current away from the sensitive internal circuitry.

A typical input/output pin may have two ESD protection diodes:

One diode connects the I/O pin to the positive supply voltage, V_DD.
The other diode connects the I/O pin to ground, V_SS or GND.

Depending on the design, some pins may have only one protection diode connected to either V_DD or GND. Other types of pins, such as power, ground, or special-purpose pins, may use a different protection structure. These ESD diodes are important during continuity testing because they provide a known electrical path between the device pin and the supply or ground pins.

The ATE applies a small voltage or current to the pin and measures the response. The measured response is then compared with the expected behavior of the protection circuit.

This allows the tester to determine whether:

The pin is properly connected to the tester.
The device is correctly installed in the socket.
An open connection exists in the path.
A pin is shorted to another pin, V_DD, or GND.
The device may be damaged or incorrectly connected.

Therefore, continuity testing does not only check a direct wire connection. It also uses the expected electrical behavior of the device’s ESD protection circuit to verify that the pin and its connection path are functioning correctly.

Figure 2 Here is an illustration of the ESD diode connections for a typical I/O pin. Source: Author

Let us now understand the continuity test using a device pin with two protection diodes, as shown in Figure 2. This test first checks whether the protection diode connected to V_DD is functioning correctly (neither open nor shorted), as shown in Figure 3.

Figure 3 The test shows the electrical path of the current between the “resource inside of the ATE” to the V_DD diode. Source: Author

The following steps are used to perform the test:

Ground all pins except the one under test.
Using a parametric measurement unit (PMU), force a small positive current into the pin, typically +100 µA to +500 µA.
Apply a +3-V voltage clamp at the same time. This acts as a safety limit, preventing the voltage from climbing too high if the diode isn’t conducting properly (for instance, in an open-circuit condition).
While forcing this current, use the PMU to measure the resulting voltage at the pin.

Based on the measured voltage, the test result will fall into one of the following categories.

This method is generally used to test signal pins, such as input and output pins. It’s not normally used for power pins, such as V_DD or V_SS.

Next, we check whether the protection diode connected to GND is functioning correctly, as shown in Figure 4.

Figure 4 The image shows the electrical path of the current between the “resource inside of the ATE” to the GND diode. Source: Author

We can check the protection diode by following the steps below:

With pins still grounded, force a small negative current into the pin, typically between -100 µA to -500 µA. This forward-biases the GND diode.
Apply a – 3 V voltage clamp to prevent the voltage from dropping too far.
While forcing this current, use the PMU to measure the resulting voltage at the pin.

Based on the measured voltage, the test result will fall into one of the following categories.

The same procedure is repeated sequentially for each applicable device pin until the continuity check is complete. It’s important to note that power pins, such as VDD and GND, are not typically tested using this method. These pins require a different testing approach, which will be discussed separately in a future article.

Keep in mind that each device has its own characteristics, so you may need to experiment to find the test method that works best for your device.

In the upcoming articles, we will build on the fundamentals covered here and take a more practical look at continuity testing. Topics will include:

Writing a continuity test method in C++: A step-by-step look at how a continuity test can be implemented in an ATE test program.
Reviewing a real continuity test data log: Understanding how to read the test results and interpret pass and fail conditions.
Debugging continuity test failures: A practical approach to identifying the possible causes of continuity failures and the steps used to troubleshoot them.

Usman Khan is an analog/mixed-signal test engineer.

Continuity testing in semiconductor ATE: Fundamentals and test methods

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