In the fields of medical imaging and wearable devices, product safety and reliability are non-negotiable red lines. As a reliability and compliance engineer, I deeply understand the stringent requirements imposed by standards such as IEC 60601 (Safety of Medical Electrical Equipment) and ISO 10993 (Biological Evaluation of Medical Devices) on PCB design and manufacturing. In this context, Flying Probe Test is not only an advanced electrical testing technology but also a core validation method that runs through the entire product development lifecycle to ensure compliance. It provides unparalleled flexibility and precision for high-density, high-complexity medical PCBs, making it a critical component in addressing regulatory challenges.
IEC 60601 Core Clauses and the Validation Role of Flying Probe Test
The IEC 60601 standard is the "constitution" for medical electrical equipment, with its core focus on protecting patients, operators, and the equipment itself from hazards such as electric shock, mechanical risks, and radiation. At the PCB level, the standard emphasizes leakage current, clearance, and creepage. Any minor manufacturing defect, such as solder bridges, open circuits, or non-compliant spacing, can lead to catastrophic consequences.
Flying Probe Test plays the role of a "guardian" here. Unlike traditional In-Circuit Test (ICT), flying probe testing does not require expensive custom fixtures. Instead, it uses programmable-controlled probes to directly contact test points, component pins, and vias on the PCB. This enables it to:
- Accurately Measure Isolation Parameters: Precisely detect the isolation between high-voltage circuits and low-voltage signal circuits, ensuring creepage and clearance meet design specifications and preventing excessive leakage current.
- Early Detection of Potential Shorts/Opens: Identify any connectivity issues that may arise during production, either before component placement (Bare Board Test) or after, eliminating electrical safety hazards at the source.
- Validate Complex Designs: For compact medical devices using HDI PCB technology, flying probe testing can easily access tiny test points, achieving comprehensive coverage that traditional methods struggle to accomplish.
At HILPCB, we integrate Flying Probe Test into our quality control system to ensure every medical PCB delivered strictly complies with the safety requirements of IEC 60601.
ISO 10993 Biocompatibility: From Material Selection to the Protection of Conformal Coating
For wearable devices that come into direct or indirect contact with the human body, the ISO 10993 standard imposes strict biocompatibility requirements. This means that substrate materials, solder mask inks, and final surface finishes must not contain any substances that could cause allergic or toxic reactions.
While Flying Probe Test does not directly evaluate chemical composition, it plays an indirect yet crucial role in ensuring the final product's biocompatibility. Many medical devices employ Conformal Coating processes to form a dense protective film on the PCB surface, completely isolating the circuitry from external environments (e.g., sweat, bodily fluids). This coating serves as the last line of defense for achieving biocompatibility.
If a PCB fails rigorous electrical testing before Conformal Coating is applied, subsequent coating could mask these potential defects, making repairs extremely difficult or even leading to complete scrapping. Therefore, performing a comprehensive Flying Probe Test before coating is a critical step to ensure flawless electrical functionality, laying a solid foundation for subsequent biocompatibility treatments.
Key ISO 10993 Compliance Reminders
- Material Traceability: Ensure complete supply chain records and biocompatibility reports for all materials in contact with the human body (including substrates, inks, and coatings).
- Process Control: Strictly control processes such as cleaning and coating to avoid cross-contamination. For example, the thickness uniformity of Conformal coating directly affects its isolation performance.
- Change Management: Any changes to materials or processes must undergo re-evaluation for biocompatibility and be documented (CAPA).
- Final Validation: The integrity of electrical functionality is a prerequisite for biosafety. Thorough testing before coating is an indispensable step.
Reliability Verification and Testing Strategies for NPI EVT/DVT/PVT Phases
During each phase of New Product Introduction (NPI)—Engineering Verification Testing (EVT), Design Verification Testing (DVT), and Production Verification Testing (PVT)—testing strategies must balance speed, cost, and coverage. In the early stages of NPI EVT/DVT/PVT, when designs undergo frequent iterations and production volumes are low, the advantages of Flying probe test become particularly evident.
- EVT/DVT Phase: With designs not yet finalized, creating expensive test fixtures (e.g., Fixture design (ICT/FCT)) is neither economical nor practical. Flying probe test requires no fixtures, offers flexible program adjustments, and can quickly adapt to design changes, helping engineers rapidly verify circuit connectivity and component parameters to accelerate iteration cycles.
- PVT Phase: During small-batch trial production, flying probe testing remains an ideal choice for verifying production process stability. It can be combined with early DFM/DFT/DFA review outcomes to ensure testability is effectively implemented in actual production.
Throughout the entire NPI EVT/DVT/PVT process, HILPCB's rapid prototyping services, combined with flying probe testing capabilities, significantly shorten development cycles for medical device clients.
DFM/DFT/DFA Review: Ensuring Testability and Compliance from the Source
A design that cannot be effectively tested has no basis for reliability. This is why conducting a comprehensive DFM/DFT/DFA review (Design for Manufacturability/Testability/Assembly) at the project's outset is critical. The goal of DFT (Design for Testability) is to ensure every critical node on the PCB can be tested efficiently. During the DFM/DFT/DFA review phase, we work closely with clients to optimize test point layout, size, and spacing, ensuring seamless compatibility with Flying probe test or ICT testing in mass production. A well-planned DFT strategy can:
- Maximize test coverage and eliminate blind spots.
- Reduce test development time and lower testing costs.
- Facilitate automated testing and improve production efficiency.
Neglecting early-stage DFM/DFT/DFA review often leads to testing difficulties, low yield rates, or even redesigns—an unacceptable outcome in the highly regulated, long-cycle medical industry.
DFM/DFT/DFA Implementation Process
- Initial Review: Analyze client design files (e.g., Gerber, BOM) for manufacturability.
- Test Point Planning: Identify critical test nodes based on schematics and netlists, ensuring probe accessibility.
- Rule Check: Use automated tools to verify test point spacing/size compliance with **Flying probe test** equipment capabilities.
- Reporting & Recommendations: Generate detailed review reports with optimization suggestions (e.g., adding test points or adjusting component layout).
- Design Iteration: Collaborate with clients to finalize modifications meeting all manufacturing and testing requirements.
Production Control & Traceability: Low-void BGA Reflow & Cleanroom Environment
Medical PCB reliability hinges not only on design and testing but also on stringent production controls. For devices with complex packages like BGA, solder joint quality directly impacts product lifespan and performance. The Low-void BGA reflow process—optimizing temperature profiles and using vacuum reflow ovens—minimizes internal voids, enhancing mechanical strength and thermal conductivity.
These internal welding qualities are ultimately validated through electrical testing. Low-void BGA reflow reduces risks of open/short circuits caused by poor soldering, thereby improving Flying probe test first-pass rates. Additionally, all production activities—from component storage to SMT Assembly—are conducted in ISO 13485-compliant cleanrooms, with a robust Device History Record (DHR) system ensuring full traceability for every PCB.
Evolution of Testing Methods: From Fixture Design (ICT/FCT) to Flying Probe Test Flexibility
In the field of PCB testing, ICT (In-Circuit Test) and FCT (Functional Test) are two mainstream methods, which typically rely on expensive and time-consuming customized Fixture design (ICT/FCT). This model is suitable for high-volume, design-stable consumer electronics, but its limitations are becoming increasingly apparent in the medical device sector.
The emergence of Flying probe test has provided a superior solution for medical PCB testing. The table below clearly illustrates its differences from traditional ICT:
| Feature | Flying probe test | ICT (Bed-of-nails test) |
|---|---|---|
| Upfront investment (NRE) | Very low, no custom fixture required | High, requires expensive Fixture design (ICT/FCT) |
| Applicable stage | Prototype, small batch, NPI EVT/DVT/PVT | Mass production |