When it comes to PCB testing during manufacturing, two of the most common types of tests are flying probes and in-circuit. These two tests are similar in that they both create an electrical signal to test the board, but they have very different methods for creating this signal.

To understand both of these tests, it is helpful to first understand the basic concept of a PCB.

A printed circuit board (PCB) is a flat board with a non-conductive core that houses semiconductor chips, passive components, wiring, and sometimes other electronic components.

These boards are created using layers, or laminates, of material. The metal traces and pads found on the board represent the conductive and non-conductive materials of the board respectively.

To test a PCB, an electrical probe is passed over each pad individually to measure whether it will create the desired circuit.

There are two common methods for creating this probe signal, flying probe and in-circuit.

Flying probe tests

Flying probe tests are the original method for testing PCBs.

In this process, a probe is placed directly on each pad or pin of the board and a signal is sent through the probe and into the PCB.

Pros of flying probe tests

This form of testing is less costly than in-circuit.
Flying probe tests are quick, taking only minutes to complete.
More boards can be tested simultaneously with the flying probe.

Cons of flying probe tests

These tests only measure the conductivity of the traces on the surface of the board, not any internal connections.
Flying probe tests are often inaccurate due to damage caused by contact with the probe, such as scratches and scrapes.
The physical contact made with the probe can damage internal components on some PCBs.
Larger elements, such as connectors and chips, can be difficult to test with flying probe.

In-circuit tests

In-circuit tests allow for more in-depth testing than flying probe. To understand in-circuit testing, it is helpful to understand two concepts: how the probe signal is created and how this signal is sent to the PCB.

In-circuit testing requires two components to create a probe signal: a test generator and a driver, or sender. The test generator creates a signal between two leads for a specific amount of time, while the driver provides a route for this signal to follow. A ground reference point is created between the generator and sender by touching both probes at once. The probe connects this ground reference point to the desired connection on the board.

A control unit is used to send power from the generator to the driver, along with information about the specific signal being sent. All of this is done through an interface that allows for ease of use and quick connection. The driver then converts the signal into a form that can be read by the board, such as voltage or frequency.

Pros of in-circuit tests

In-circuit tests are more accurate than flying probe, as they test the connections within a PCB.
This form of testing is cost-effective, as multiple boards can be tested at once.
In-circuit tests are more accurate than flying probe, as they test the connections within a PCB.

Cons of in-circuit tests

These tests are highly destructive, as they require physical contact between the probe and board.
In-circuit tests are time-consuming and take an average of five minutes to complete.
Damage incurred during the in-circuit testing process can render the board unusable.

Verdict

The choice is completely up to the manufacturer and is dependent upon their specific needs.

Flying probe tests are a less expensive and faster alternative, but provide limited data about the PCB. In-circuit testing is more costly but provides a larger amount of data about the PCB.

Choose the best PCB manufacturing service to realize the full benefits of either testing method!