What is an in-circuit tester?
An in-circuit tester is a computerized machine used to conduct an electrical performance test of a printed circuit board assembly (PCBA). The electrical performance test helps to identify the manufacturing defects, such as open, shorts, components missing, poor solder joints, and test for resistance, capacitance & inductance values ..., etc. The in-circuit tester (ICT) allows individual component testing on the assembled PCB (i.e., PCBA). In a PCB production line, The electrical performance test is performed before the function test of the PCBA to reduce the rework at the functional test section.
Figure 1: Inside view of in-circuit tester and a board under test
Typically, an in-circuit tester (ICT) consists of the computer, fixture, driver-sensors, multiplexing circuits, guarding, and software (see figure 1). The computer runs required software, drives, controls, and monitors the total ICT system. The fixture provides the physical contact between the ICT system and the PCB under test. The fixture has a "bed of nails" or spring-loaded test pins installed on the tester. Looking inside, the module interface pins on the tester are connected with the fixture interface pins. The fixture interface pins are wired to the probes (bed of nails) that provide the physical contact with the PCB under test.
The driver-sensor unit performs the measurements, and the guarding unit is used to improve the accuracy of measurements by removing the leakage path if any. Sometimes for a large PCB or complex board, the number of test points may increase beyond the capability of the ICT. When the number of test points increases, the allocation of pins for each test point is very costly. Hence, multiplexing circuits help the ICT system to allocate a pin for more than one test point of the PCB. But, at a time, only one multiplexed pin of the ICT tester can connect to a test point of the PCB. In this way, multiplexing limits the programming and fixture design.
How does in-circuit tester (ICT) work?
The fixture cover is opened, and the board that needs to test will be placed in the fixture (see figure 1). Then, the fixture cover will be closed. Now the in-circuit tester will start measurements, and the computer will display the progress of the test. The measured electrical data of the board under test is compared with the electrical data of a good quality reference board by the computer. The reference board electrical data has been already stored in the computer. After the test, the board status pass/fail (with the type of defect details, if any) will be displayed on the screen. If any defect is detected, then the board will be sent for a rework to fix the defect.
Key features of in-circuit tester:
- High-Accuracy Measurement and Testing
- Automatic storage reports and test data statistics
- Available with the self-diagnosis and remote assistance function
- Available in friendly UI and easy program development.
- Available in a small footprint
Key specs of in-circuit tester:
No of test points: Represents the number of testing that can be tested by the tester.
Frequency: Represents the frequency that can be supported by the tester.
Operating system: Represents the type of operating system that is supported by the tester.
Interface: Represents the type of interface that can be supported by the tester. For example, it can be Ethernet (LAN) interface.
PCB size: Represents the PCB size that can be handled by the in-circuit tester.