Detect faults before they become system-level problems
In electronics manufacturing, what matters is not only whether an assembly “works” but also when and how clearly a fault is detected. In-circuit testing (ICT) closes a critical gap between optical inspection and functional testing by checking assembled PCBs at the net and component level before they operate in the system under real operating conditions.
This article explains what can be achieved with ICT, which design and manufacturing requirements are critical, where its limits lie, and how ICT can support process stability, repeatable testing, and manageable fault analysis in the MedTech environment.
- Why ICT is especially relevant in medical technology
- What is in-circuit testing (ICT)?
- Technical fundamentals: How ICT works
- What ICT typically detects and what it does not
- Requirements: Test access, DFT, and test strategy
- Typical fault patterns and countermeasures
- Cost efficiency: When is ICT worthwhile?
- Compliance, validation, and traceability in the MedTech context
- Summary and next step
1. Why ICT is especially relevant in medical technology
In regulated environments, an electrical fault quickly becomes more than a simple defect. The later it is detected, the more complex fault isolation becomes and the more effort is required for analysis, documentation, and approval processes.
If a fault becomes visible only during functional testing, the root cause can often no longer be clearly isolated at the component or net level. If the fault is detected even later, the effort required for structured root cause analysis, documentation, and additional testing or requalification increases.
As part of ICT, fault detection is intentionally shifted to a stage where defects can still be localized with technical precision. This keeps a component or net fault clearly identifiable as a manufacturing defect instead of allowing it to escalate into a system-level problem that is difficult to isolate.
2. What is in-circuit testing (ICT)?
In-circuit testing is an electrical test method for printed circuit board assemblies (PCBAs). Using defined test access points, nets and components are contacted directly on the assembly to verify basic electrical properties (resistance, capacitance, inductance) and detect typical manufacturing or assembly faults early on.
ICT is not a “one-size-fits-all” test. The test concept, test access, measurement methods, and coverage depend heavily on topology, component density, and layout/test points as well as product requirements.
3. Technical fundamentals: How ICT works
At its core, ICT consists of three elements:
- Assembly interface
The assembly is typically contacted using a fixture or adapter concept (e.g., a bed-of-nails fixture). Stable contact conditions, accurate alignment, and reproducible contact resistance at the contact points are critical. - Measurement and test logic
The test system compares measured values against defined limits. Typical measurements include continuity and insulation tests (opens/shorts) as well as in-circuit measurements of electrical parameters. - Test program and reference data
Reliable ICT requires a consistent data set (e.g., netlists, design data, and assembly data) as well as a test program matched to the assembly. Depending on the system and design, programming or scan mechanisms (e.g., boundary scan/JTAG) can also be integrated if supported by the design.
Important: ICT is not primarily a system test but rather a test focused on the net and component level for the clear identification of manufacturing faults.
4. What ICT typically detects and what it does not
Typical test scope (depending on the test concept and design access):
- Open and short-circuit testing at the net level
- In-circuit measurements of passive components (e.g., resistance, capacitance)
- Plausibility and parameter checks in defined circuit areas (cluster tests) to the extent that meaningful isolation within the circuit is possible
- Tests for assembly faults (e.g., missing or incorrect components) depending on test access and measurement logic
- Optional: programming or additional methods (e.g., boundary scan) if included in the design
What ICT typically does not replace:
- Functional testing under real operating conditions (interaction between hardware and software, system limits, dynamic behavior)
- End-of-line tests specifically designed to verify system parameters under load or during interaction
In practice, ICT is therefore usually just one element within a multi-stage test strategy rather than the sole measure of quality.
5. Requirements: Test access, DFT, and test strategy
Because ICT depends heavily on whether an assembly is designed to be testable, design for test (DFT) is critical and should be addressed early in the project:
- Test access/test points: quantity, placement, mechanical robustness, accessibility
- Measurability within the circuit: Parallel paths, protection networks, pull-ups, or active components can distort measurements or make them impossible
- Fixture concept: contacting, contact pressure, alignment, maintainability
- Test coverage: ICT becomes more effective when critical nets and relevant circuit areas are reliably covered
As density increases and physical access becomes more limited (fine pitch, miniaturization), a well-defined test concept becomes increasingly important and is often supplemented by alternative or additional test methods.
6. Typical fault patterns and countermeasures
Effective fault control in practice consists of three steps: detecting faults, isolating faults, and validating rework. Typical ICT-related risks and measures:
Typical risks and countermeasures
| Defect/fault pattern | Cause | Prevention/countermeasure | Test/verification method |
| Unstable contacting/false fails | Wear or contamination of contacts, alignment issues, unsuitable test pad geometry | Fixture maintenance and cleaning procedures, robust test pad definitions, alignment features | Contact checks within the test program, retesting and verification |
| Opens | Soldering faults, open connections, trace or via defects, assembly faults | Process control, DFM/DFT review, upstream optical inspection as a complementary measure | Continuity test, retest after repair |
| Shorts | Solder bridges, stencil printing issues, component misalignment, particles | Process window, inspection strategy, handling and cleaning procedures | Insulation testing supplemented by additional inspection if required |
| Incorrect component values/incorrect material | Material or feeder faults, variant or assembly data errors | Material management, verification processes, testable design of measurement points | In-circuit parameter testing |
| Low test coverage | Insufficient test access, high density, DFT not considered | Early DFT reviews, complementary test methods, clearly defined coverage goals | Coverage reports and fault statistics throughout series production |
7. Cost efficiency: When is ICT worthwhile?
An ICT system consisting of a base unit and bed-of-nails adapter typically provides economic value when:
- designs are stable and manufactured repeatedly
- fast testing and clear diagnostic times are important
- Early fault detection reduces downstream testing and analysis effort as well as associated costs
In practice, the main drivers of cost and effort are often:
- Effort required to create the fixture (including modifications for design revisions)
- Maintenance of the test program and data consistency
- Maintenance and qualification of the contacting system to ensure reproducible test results
For smaller production volumes or frequent design changes, the use of flying probe testing (e.g., fixtureless testing or other inspection methods) may be a suitable alternative depending on production volume, cycle time requirements, and test coverage objectives. One advantage of flying probe testing is its flexibility. If changes are made to the assembly, the test can be adapted simply by updating the test software. No additional investment in a bed-of-nails adapter is required.
Against this background, EPnP follows both strategies by using flying probe systems as well as ICT systems with customer-specific bed-of-nails adapters.
8. Compliance, validation, and traceability in the MedTech context
In medical technology, the view of testing is often broader: the question is not only whether the assembly passes the test but also whether the test process is reproducible, traceable, and integrated into the overall process.
For ICT, this typically means:
- Clearly defined test characteristics and limit values
- Reproducible contacting and stable test conditions
- Documented test results with traceability to series and batch structures
- Manageable handling of changes (design revisions, variants, process changes)
In this environment, ICT can help generate test data early in the process and identify fault patterns at a level where they can still be isolated most effectively from a technical standpoint. This supports process stability over long product lifecycles provided that the test concept and DFT are aligned early on.
9. Summary
In medical technology applications, ICT is especially valuable when faults need to be detected as early and clearly as possible at the component or net level before they become difficult to isolate during system testing or later analyses.
The key is not “more testing at any cost” but rather the right test concept: sufficient test access, clearly defined coverage goals, reproducible contacting, and clean integration into a multi-stage test strategy.
If you would like to evaluate whether and how in-circuit testing makes sense for your assembly, the best time is during the design and industrialization phase. A brief DFT and test concept review before layout freeze helps define achievable test coverage and keeps fault analysis manageable during series production.
If you would like to validate your ICT concept at an early stage, you can schedule a brief coordination meeting directly using the appointment form on this page. During this discussion, we will clarify which test access points and coverage objectives are appropriate for your assembly and how ICT can be seamlessly integrated into your overall test strategy.