In Circuit Testing
In-circuit testing (ICT) is a type of white box testing that involves using an electrical probe to test a populated printed circuit board (PCB). This testing method focuses on checking for shorts, opens, resistance, capacitance, and other fundamental measurements to determine if the PCB assembly has been fabricated correctly. In-circuit testing can be conducted using a specialized test fixture commonly known as a “bed of nails” along with specific testing equipment. Alternatively, it can be performed without a fixture using a fixtureless in-circuit test setup.
The Equipments Used for In-circuit Testing:
- In-circuit tester: This is the core component of the in-circuit test system and is comprised of a matrix of. These drivers and sensors are responsible for setting up and performing measurements on the PCB. Typically, there are over 1000 of these driver sensor points, which are conveniently connected to a large connector on the system.
- Fixture: The connector on the in-circuit test system interfaces with the fixture, which is designed specifically for a particular board. The fixture acts as an interface between the board and the in-circuit tester. It takes the connections for the driver sensor points and routes them directly to the relevant points on the board using a “bed of nails” technique.
- Software: Software is developed for each board type that can be tested using the in-circuit tester. This software instructs the test system on what tests to perform, the specific points between which the tests should be conducted, and the pass/fail criteria for each test.
These three elements form the major components of an in-circuit test system. While the tester itself can be used for various boards, the fixture and software are specific to each board or assembly.
In-circuit test systems are typically expensive pieces of equipment and are commonly used in high-volume PCBA production lines. Due to the costs involved in generating the fixture and program, they are not viable for small production runs of less than 250 to 1000 items. A cost analysis should be conducted to ensure that the expense of creating the fixture and program is justified.
There are several types of In-Circuit Test (ICT) machines available, each serving specific purposes based on the manufacturing/test process, volume, and boards used. The main types of ICT machines include:
- Standard ICT machine: This is the most common type of ICT machine used. It can perform basic resistance/continuity measurements, as well as capacitance measurements and some device functionality testing.
- Flying probe tester: Instead of using a bed-of-nails access fixture, a flying probe tester utilizes a simple fixture to hold the board being tested. Contact is made using a few moving probes that can navigate the board and make contact where needed. This allows for flexibility and easy adaptation to board updates by making changes to the software program.
- Manufacturing defect analyzer (MDA): The MDA is primarily used for detecting manufacturing defects such as short circuits and open circuit connections. It performs basic resistance, continuity, and insulation testing on the board.
- Cableform tester: This type of tester is specifically designed for testing cables. It performs similar functions to an MDA but may also apply high voltages to test for insulation. The operation of a cable form tester is optimized for cable testing.
It’s important to select the appropriate type of ICT machine based on the specific requirements of the manufacturing process, volume of production, and the type of boards or cables being tested.