Testing Glossary
Terminology reference for PCB testing and bed-of-nails fixtures. Clear definitions for test engineering terms, fixture components, and testing methodologies.
B
- Bed-of-Nails Fixture
- A test fixture that uses an array of spring-loaded probes (pins) arranged to make contact with test points on a PCB. Named for its appearance resembling a bed of nails. Used for in-circuit testing (ICT) and functional testing of assembled PCBAs.
- Related:Test Fixture,Spring-Loaded Probe,Test Point
C
- Contact Resistance
- The electrical resistance at the interface between a test probe and the test point on a PCB. Lower contact resistance improves measurement accuracy. Affected by probe force, tip condition, and surface contamination.
- Related:Spring-Loaded Probe,Test Point
D
- DUT
- Device Under Test. The PCB assembly being tested. Also sometimes called UUT (Unit Under Test).
- Related:PCBA,Test Fixture
F
- First Article Inspection (FAI)
- The process of verifying the first production unit of a new design meets specifications. Often includes comprehensive testing with a bed-of-nails fixture to validate manufacturing quality before full production.
- Related:ICT,Test Coverage
- Flying Probe
- A test method using movable probes that travel to test points sequentially, rather than a fixed array of probes. Slower than bed-of-nails testing but requires no custom fixture, making it suitable for prototypes and low-volume production.
- Related:Bed-of-Nails Fixture,ICT
- Functional Test
- Testing that verifies a PCBA operates correctly as a complete system under conditions simulating actual use. Often performed after ICT to verify the assembled product works as designed.
- Related:ICT,Test Coverage
G
- Guide Pin
- Precision alignment pins used to ensure accurate positioning of the PCB in a test fixture. Engage with tooling holes in the PCB to achieve repeatable probe-to-pad alignment.
- Related:Test Fixture,Tooling Hole
I
- ICT
- In-Circuit Test. A testing method that verifies individual component values and connections on a PCBA by probing test points. Detects shorts, opens, wrong components, and component failures. Typically performed using bed-of-nails fixtures.
- Related:Bed-of-Nails Fixture,Test Coverage,Test Point
J
- JTAG
- Joint Test Action Group. Refers to the IEEE 1149.1 standard for boundary scan testing. Provides a way to test interconnects and program devices through a standard 4-5 wire interface.
- Related:Boundary Scan
K
- Keyed Connector
- A connector designed to prevent incorrect insertion. Test fixtures often include keyed connectors to ensure proper orientation of interface cables and prevent damage.
L
- Lift-Off Plate
- A mechanism in a test fixture that raises the PCB off the probe field after testing, ensuring clean probe separation and preventing damage to the board or probes.
- Related:Test Fixture
P
- PCBA
- Printed Circuit Board Assembly. A PCB with all components soldered in place, ready for testing or integration into a larger system.
- Related:DUT,SMT
- Probe Force
- The amount of force a spring-loaded probe exerts on the test point. Higher force generally means better contact but can damage delicate pads. Typical forces range from 85g to 225g depending on probe type.
- Related:Spring-Loaded Probe,Contact Resistance
S
- Signal Interface
- The method by which test equipment connects to a fixture. Options include pogo blocks, zero-insertion-force connectors, and various standard connectors. The interface must match the test equipment being used.
- Related:Test Fixture,Pogo Block
- SMT
- Surface Mount Technology. A method where components are mounted directly onto the surface of a PCB rather than through holes. Most modern PCBAs use primarily SMT components, which require appropriate probe tip geometry for testing.
- Related:PCBA,Test Point
- Spring-Loaded Probe
- A test probe with an internal spring that provides consistent contact force against a test point. Also called a pogo pin. Various tip styles are available for different pad types and sizes.
- Related:Bed-of-Nails Fixture,Probe Force
T
- Test Coverage
- The percentage of a PCBA's components and connections that can be verified through testing. Higher coverage means more potential defects can be detected. Bed-of-nails testing can achieve high coverage when sufficient test points are available.
- Related:ICT,Test Point
- Test Fixture
- A mechanical device that holds a PCB and provides electrical connections for testing. Bed-of-nails fixtures are the most common type for high-volume testing, providing simultaneous access to many test points.
- Related:Bed-of-Nails Fixture,DUT
- Test Point
- A designated location on a PCB designed for probe contact during testing. Usually a bare pad or via accessible from one or both sides of the board. Proper test point placement is critical for effective ICT.
- Related:ICT,Spring-Loaded Probe
- Tooling Hole
- A non-plated hole in a PCB used for mechanical alignment in fixtures and during manufacturing. Typically located at board corners. Test fixtures use guide pins that engage these holes for precise positioning.
- Related:Guide Pin,Test Fixture
V
- Vacuum Hold-Down
- A method of securing a PCB in a test fixture using vacuum pressure. Provides consistent force across the board and can be quickly engaged and released. Common in high-volume production testing.
- Related:Test Fixture
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