In circuit testing (ICT) is traditionally used on mature products, especially in subcontract manufacturing. It uses a bed-of-nails test fixture to access multiple test points on the PCB’s bottom side. With sufficient access points, ICT can transmit test signals into and out of PCBs at high speed to perform evaluation of components and circuits.
A bed of nails tester is a traditional electronic test fixture. It has numerous pins inserted into holes, which are aligned using tooling pins to make contact with test points on a printed circuit board and are also connected to a measuring unit by wires. These devices contain an array of small, spring-loaded pogo pins making contact with one node in the circuitry of the device under test (DUT).
By pressing the DUT down against the bed of nails, a reliable contact can be made quickly with hundreds and in some cases thousands of individual test points within the DUT’s circuitry. Devices that have been tested on a bed of nails tester may show a small mark or a dimple which comes from the sharp tips of pogo pins used in the fixture.
It takes a few weeks to create the ICT fixture and do its programming. A fixture can either be vacuum or press-down. Vacuum fixtures give better signal reading versus the press-down type. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. The bed of nails or in-circuit tester such as 3070 from Agilent is the most common and popular in the contract manufacturing environment.
- Although a costly fixture is required, ICT covers 100% testing so that all power and ground shorts are detected.
- ICT testing does power up testing and eliminates customer debug needs to almost ZERO.
- ICT does not take a very long time to perform, for example if flying probe takes 20 minutes or so, ICT for the same time might take a minute or so.
- Checks and detects shorts, opens, missing components, wrong value components, wrong polarities, defective components and current leakages in the circuitry.
- Highly reliable and comprehensive test catching all manufacturing defects, design faults, and flaws.
- Testing platform is available in Windows as well as UNIX, thus making it slightly universal for most testing needs.
- Test development interface and operating environment is based on standards for an open system with fast integration into an OEM customer’s existing processes.
ICT is the most tedious, cumbersome, and expensive type of testing. Creating an ICT fixture can cost from $10,000 to $50,000 and 4-6 weeks of fixture build time. However, ICT is ideal for mature products requiring high volume production. It runs the power signal to check voltage levels and resistance measurements at different nodes of the board. ICT is excellent at detecting parametric failures, design related faults and component failures.