What is the ICT test?
In-Circuit Test will ensure 100% quality pass, When design your board, Pls request electronic engineers to pre-design ICT, We will use diagram to make ICT fixture, and 100% testing before shipping
Introduction
ICT stands for In-Circuit Test. It is an electronic testing method used to verify the quality and integrity of circuit board assemblies. ICT testing detects defects like shorts, opens, missing components, wrong values, misplaced parts, and improper solder joints.
This article provides a comprehensive overview of ICT covering test basics, fixture types, program development, test coverage analysis, optimizing fault diagnosis, considerations for combining with functional test, and selecting ICT solutions suited for production volumes.
What is ICT Testing?
In-circuit testing refers to testing a populated printed circuit board to verify:
- Electrical connections between components per the design netlist
- Presence of correct component values at specified locations
- Absence of manufacturing defects like shorts or opens
- Overall assembly quality and workmanship
ICT leverages mechanical “bed-of-nails” test fixtures that make temporary electrical contact with test nodes across the board being tested. The connected tester then energizes various circuit paths and checks that corresponding nodes are properly excited.
Deviation from expected node levels pinpoints defects in assembly such as wrong components, missing parts, poor solder joints, short circuits or open circuits. By energizing multiple circuit nets, ICT can rapidly validate board assembly quality prior to functional testing.
Why Perform ICT Testing?
Below are some key benefits provided by ICT testing:
- Detects manufacturing defects – Such as missing components, wrong polarity, opens, shorts etc.
- Verifies component presence – Confirms BOM is assembled correctly.
- Catches workmanship issues – Like poor solder joints, wrong placement etc.
- Accelerates fault finding – Quickly diagnoses if board failures are due to manufacturing or design issues.
- 100% pre-functional testing – Increases chances of passing final functional testing.
- Improves process control – Statistical tracking of failure rates highlights production issues.
- Reduces rework costs – Problems identified early are cheaper to rework than post-functional test diagnosis.
- Works for powered off state – Can test boards before powering up which is safer.
ICT provides an efficient and cost-effective means of validating board assembly quality prior to functional test. It weeds out manufacturing issues ahead of time.
ICT Test Basics
Below are some key concepts related to in-circuit testing:
ICT Testing Principle
Test Fixtures
The fixture makes temporary electrical contact with test nodes on the board being tested. Popular styles include:
- Bed of Nails – Consists of an array of spring-loaded “nails” or “pins” that contact test points. Very common fixture type.
- Flying Probe -Uses movable probes that get positioned dynamically over desired test nodes. Eliminates need for custom fixture.
- Pogo Pin – Uses an array of spring-loaded pins. Combines high probe density with probe cleaning for longevity.
Node Access
To energize and measure circuits, test probes must make contact with nodes like:
- Testpads – Added specifically for ICT contact
- Vias – Access inner layer nodes
- Component leads – Contact leads protruding through board
- Traces – Probe can land directly on exposed track pads
Test Program
A specialized software program tailor-made for each PCB design. It contains vectors describing stimulus and measurements for each test node. Determines pass/fail based on measuring circuit nodal responses.
Fault Diagnosis
Using the test program, failures get pinpointed to specific components, nets, or nodes. For example, a short between two pins implies a defective component. Out of tolerance measurements imply wrong value components. Open circuits indicate poor solder joints.
Proper fault diagnosis allows targeted and rapid rework.
ICT Test Fixture Types
There are three common fixture types used in ICT. Each has particular pros and cons:
Bed of Nails
Consists of an array of spring-loaded “nails” or “pins” that make electrical contact with test points on the board. Very common fixture type.
Pros – Low cost, high density probing, fast fixture build
Cons – Pin damage over time requiring maintenance
Flying Probe
Uses movable probes mounted on XY arms. Probes get positioned dynamically over desired test nodes selected by the program.
Pros – No need for custom fixture, flexible, easy changeovers
Cons – Slower testing than bed of nails, higher machine cost
Pogo Pin Fixtures
Use an array of spring-loaded pins that can compress and spring back when contacting boards. Provides both high density and reliability.
Pros – Reliable, high cycle life, fine pitch capability
Cons – Higher fixture cost than traditional nails
Fixtures must be matched to PCB design and production volume. Low volume prototyping benefits from flying probe flexibility while higher throughput production favors bed of nail or pogo pin fixtures.
ICT Test Program Development
To perform testing, unique test programs need to be developed matched to the circuit design of each PCB variant:
CAD Data
PCB CAD data provides key inputs like netlist, testpoint locations, and board dimensions needed to develop the test program.
Fixture Modeling
For bed of nail fixtures, fixture plates are designed with probes precisely aligned to contact test nodes on the PCB.
Node Access Analysis
Determines optimal points to access key nets – identifying testpads, component pins, vias etc. balanced with minimizing probe count.
Test Vectors
Test vectors define the electrical stimulus patterns that should be applied to nets and the expected responses to verify at corresponding test nodes for fault detection.
Diagnostic Routines
Algorithms that analyze measurement deviations and map them to specific fault conditions like open, short, misplaced part, wrong value etc.
Program Simulation
The test program is simulated on virtual board models prior to testing live boards. Debugging and performance optimization done during simulation.
Fixture Validation
The test fixtures are verified on known good boards to validate contact reliability prior to starting production testing.
Developing optimized test programs is key to maximizing test coverage and fault diagnosis capabilities.
Maximizing Test Coverage
Some key strategies help maximize the detection of assembly defects using ICT:
- Include testpoints on designs upfront to access nets – recommended at least 4-6 testpoints per side.
- Identify critical nets used by multiple components that provide the best test coverage.
- Verify access to nets for low resistance, capacitance, and inductance measurements.
- For program development, focus on highest risk component types like BGAs.
- Divide tests into functional blocks matching board layout to simplify diagnostics.
- Optimize node access to balance dense probing against fixture cost and debugging.
- Ensure testvectors detect both catastrophic and out-of-tolerance issues.
- Validate coverage by fault insertion on known good boards.
- Set pass/fail limits based on statistical prediction of error rates.
Thorough test coverage analysis during development reduces escapes into functional testing.
Optimizing Fault Diagnosis
Some key aspects aid quick and accurate fault diagnosis during ICT testing failures:
- Dedicated Test Nets – Add testnets on the board design just for ICT diagnosis. Forces faults to known nets.
- Topology Mapping – Database mapping components to testpins enabling rapid fault localization.
- Rules Engine – Maps failure signatures to known fault conditions and rework actions.
- Debug Features – Program controls like node toggling, subset testing help isolate issues.
- Traceability – Track components by serial numbers through production and test data.
- Data Analytics – Statistical tools identify high failure rate components.
- Operator Guidance – Simple instructions, graphics, trained operators speed rework.
Proper fault diagnosis prevents wasting time chasing ghosts and enables targeted rework lowering the cost of repairs.
Functional Testing vs ICT
While functional test validates overall board operation, ICT focuses on assembly workmanship and component correctness.
ICT Pros
- Catches manufacturing defects functional testing can miss
- Executes at powered off state – Safer
- Much faster fault isolation to specific components
- 100% pre-functional testing improves yields
Functional Test Pros
- Confirms board operates correctly under power
- Detects issues missed by ICT – Bad solder joints can still conduct
- Validates performance – Clock speeds, voltages, timing, temperatures
- Tests functionality – exercizes circuits in operation
Introducing ICT testing prior to functional test improves quality and debug efficiency. ICT diagnoses manufacturing issues while functional testing confirms proper functionality. The two methodologies complement each other.
Key ICT Equipment Considerations
Below are key considerations when selecting ICT systems:
Throughput
- Tests per hour rating
- Ability to handle small or large boards
- Multi-site testers for parallel testing
Expandability
- Spare fixture sites for future board variants
- Probe capacity for dense fixtures
- Easy programming integration for new boards
Fixturing Approach
- Bed of nails, flying probe, or hybrid fixture strategy
Software
- Flexible program development tools
- Intuitive diagnostics and repair instructions
- Statistical process control and analysis
Hardware
- Pin electronics design – Matrix, multiplexer, instruments
- Test probe technologies – Nails, pogo pins, MEMS
- DUT power management for live current tests
Integration
- Interfaces with handling systems like loaders/unloaders
- Data exchange with manufacturing execution systems
- Combination with functional testers
Evaluating technical factors ensure the system matches both current and future testing needs.
Conclusion
In-circuit testing is a efficient way to validate component assembly and soldering quality before functional testing. Investing in test coverage analysis, fault diagnosis, fixturing, and equipment optimized for the product mix enables finding issues early. This prevents time wasted troubleshooting bad boards escaping to system test. However, ICT requires upfront effort to develop fixtures and programs tailored to PCB designs. Combining in-circuit testing with follow-on functional test provides a robust validation approach covering both manufacturing quality and operational correctness. As volumes scale, purpose-built ICT systems with fast fault diagnosis maximize quality and rework efficiency. With today’s complex PCBs, finding ways to thoroughly test assemblies before powering boards up improves overall yields.
FAQ
What types of defects can be detected with ICT testing?
ICT testing can detect wrong components, missing parts, reversed polarities, shorts, open circuits, poor solder joints, wrong component values, misplaced components, and counterfeit parts among other assembly defects.
What level of test coverage can be expected from ICT?
Typical ICT test coverage ranges from 60% to 90% depending on board complexity. Critical factors are accessibility of test nodes, fixture density, and test program development time invested.
How long does it take to develop an ICT test fixture and program for a new PCB?
For a medium complexity board, test program development can range from 1 to 4 weeks. Developing custom bed of nails fixtures adds 4 to 6 weeks depending on node density. Flying probe avoids custom fixturing.
What are some key differences between ICT and functional board testing?
Key differences are that ICT focuses on manufacturing defects, does not require powered up state, provides rapid fault isolation, and is much faster but may miss certain faults detected during system operation by functional testing.
When should ICT vs flying probe fixturing be used?
ICT bed of nails fixtures provide fastest throughput and are preferred for high volume production while flying probes are flexible and better suited for prototypes or low volumes due to no fixed fixturing requirement.