FADOS VI Curve Tracer vs In-Circuit Testing (ICT)…

Two Approaches to Board-Level Testing

In-Circuit Testing (ICT) and VI curve tracing are both used to detect faults on populated PCBs, but they work on fundamentally different principles and serve different operational contexts. Understanding where each approach excels, and where it falls short, is essential for choosing the right test strategy.

In-Circuit Testing (ICT): The Production Standard

ICT systems use a bed-of-nails fixture to simultaneously contact hundreds or thousands of test points on a board. The system then measures individual component values (resistance, capacitance, inductance), tests semiconductor junctions, verifies connectivity, and checks for shorts and opens.

ICT Strengths

Component-level measurement: ICT measures actual component values, not just signatures. A 10 kohm resistor is verified as 10 kohm within tolerance.
High throughput: With all probes making contact simultaneously, a complete test can execute in seconds.
Standardized pass/fail criteria: Component value tolerance bands are defined by the design, making pass/fail determination objective and repeatable.
Boundary scan integration: Modern ICT systems integrate JTAG boundary scan for testing interconnects to BGA and fine-pitch devices.

ICT Limitations

Fixture cost: A bed-of-nails fixture for a modern board costs Rs 5–20 lakh, depending on complexity. This cost is justified only for high-volume production runs.
Fixture lead time: Custom fixture fabrication takes 4–8 weeks.
Test point access: The board must be designed with ICT test points, accessible pads connected to each node. Many modern designs, especially HDI boards, lack adequate test point coverage.
Equipment cost: ICT systems (Keysight, Teradyne, SPEA) cost Rs 50 lakh to several crore, placing them beyond the reach of small and medium repair operations.
Design change rigidity: When the board design changes, the fixture must be modified or rebuilt.

VI Curve Tracing (FADOS): The Flexible Alternative

The FADOS 9F1 and FADOS 7F1 VI curve tracers apply a controlled AC stimulus to test points and measure the resulting voltage-current relationship. Instead of measuring individual component values, VI tracing captures the aggregate impedance signature of each circuit node and compares it against a known-good reference.

VI Tracing Strengths

No fixture required for manual testing: A technician with probes can test any board immediately, no fixture design, no lead time.
Equipment cost: A FADOS 9F1 with software costs a fraction of an ICT system, making it accessible to repair shops, depot maintenance facilities, and small EMS operations.
Design-agnostic: VI tracing works on any board regardless of whether it was designed with test points. Probe any accessible pad or via.
Repair diagnostics: VI tracing excels at fault localization, identifying which specific component or area has failed, whereas ICT is primarily designed for go/no-go production screening.
Legacy board support: VI tracing can test boards for which no schematics, netlists, or design data exist. A golden reference board is sufficient.
Scalable automation: The FADOS MUX adds 96-channel automated testing when throughput demands increase, at a fraction of ICT fixture cost.

VI Tracing Limitations

Relative measurement: VI tracing compares signatures, not absolute values. Without a reference, you are interpreting signatures based on experience.
Lower throughput than ICT: Even with the MUX, FADOS scans 96 channels sequentially, not simultaneously. Per-board test time is measured in tens of seconds, not single seconds.
Sensitivity to board state: Discharged capacitors, residual charge, and board temperature can affect signatures. Consistent test conditions are important.

Head-to-Head Comparison

Criterion	ICT	FADOS VI Tracing
Equipment cost	Rs 50 lakh–5 crore	Rs 3–8 lakh (9F1 + MUX)
Fixture cost per board	Rs 5–20 lakh	Rs 20,000–1 lakh (MUX fixture)
Fixture lead time	4–8 weeks	1–2 weeks (simple pogo fixture)
Test coverage	Component-level values + connectivity	Node-level impedance comparison
Throughput	5–15 seconds per board	30–90 seconds per board (MUX)
Schematic required?	Yes (for fixture design)	No (golden board sufficient)
Repair diagnostics	Limited (identifies failed node)	Strong (localizes specific fault)
Legacy board support	Requires design data	Works with reference board only
Best for	High-volume production (>10,000/year)	Repair, low-mid volume, mixed boards

When to Use Each Approach

Choose ICT When:

Production volumes exceed 10,000 boards per year of the same design
Board design includes adequate ICT test point access
Component-level measurement is required by quality standards (automotive, aerospace)
Test time per board must be under 15 seconds

Choose FADOS VI Tracing When:

You repair or refurbish boards from multiple designs
Production volumes are low to medium (under 10,000/year per design)
Board designs lack dedicated ICT test points
Budget for test equipment is under Rs 10 lakh
You need to support legacy boards without design documentation
Fault localization and root cause analysis are primary goals

Use Both When:

Large EMS operations often deploy ICT for production screening and FADOS for failure analysis. Boards that fail ICT go to a diagnostic bench where a FADOS 9F1 localizes the fault for rework. The two approaches are complementary, not competing.

Why Buy FADOS from GSAS

GSAS Micro Systems is India’s authorized CBT Electronic partner and ODM assembler. We can help you evaluate whether VI curve tracing, ICT, or a combined approach best fits your production and repair requirements.

Contact our engineers at offices in Bengaluru, Hyderabad, Chennai, Pune, Mumbai, and Delhi NCR for a consultation and live demonstration.