With the explosive growth of generative AI, large language models (LLMs), and high-performance computing (HPC), the complexity of AI chips has reached unprecedented heights. Advanced technologies such as HBM3/HBM3e high-bandwidth memory, 2.5D/3D packaging like CoWoS and InFO, and the widespread adoption of Chiplet architectures have placed extreme demands on the underlying interconnect IC substrates and PCBs. In such tiny and densely packed spaces, even the slightest manufacturing defect can lead to the failure of an entire expensive module. Therefore, precise electrical testing at every critical node of manufacturing and assembly is essential, and Flying Probe Test is the core technology addressing this challenge.
Unlike traditional In-Circuit Test (ICT), Flying Probe Test eliminates the need for expensive custom fixtures by using high-speed movable probes to directly contact test points, pads, and vias on the PCB, enabling the detection of electrical performance such as opens, shorts, resistance, and capacitance. This flexibility makes it the ideal choice for high-density, high-value, and rapidly iterating products like AI substrates. This article delves into the critical role of Flying Probe Test in the entire process of AI chip interconnects and substrate PCB manufacturing, as well as how it ensures precision from prototyping to mass production. Discover how Highleap PCB Factory (HILPCB) leverages cutting-edge testing technology to help you optimize the design and manufacturing of AI interconnect substrates.
What is Flying Probe Test, and Why is It Critical for AI Substrates?
Flying Probe Test is an automated test equipment (ATE) that uses 2 to 8 independently movable probes (flying probes) to contact test points on a circuit board. The test program is generated directly from CAD data (e.g., Gerber files), and the machine precisely controls the probes to move to specified locations for measurements based on the program instructions. This "fixture-less" characteristic is its core advantage.
For AI substrates, this advantage manifests in the following aspects:
- Adaptability to High Density and Complex Designs: AI substrates feature trace widths/spacing at the micron level, with极小 BGA pad pitches. Traditional bed-of-nails fixtures are difficult to manufacture and costly. Flying probes can accurately contact pads as small as 0.1mm or even smaller, perfectly meeting the testing needs of high-density interconnects (HDI) and IC substrates.
- Cost-Effectiveness for Prototyping and Low-Volume Production: During the New Product Introduction (NPI EVT/DVT/PVT) phase, designs undergo frequent changes. If bed-of-nails testing is used, each design modification requires reworking expensive fixtures, increasing costs and slowing down the R&D cycle. Flying Probe Test eliminates the need for fixtures, requiring only test program updates, significantly improving flexibility and reducing testing costs in the NPI phase.
- Exceptional Defect Detection Capability: Flying probe testing not only detects basic opens and shorts but also identifies potential connection issues like cold solder joints or micro-cracks through precise four-wire Kelvin measurements. This is critical for ensuring the quality of high-speed signal paths, such as HBM channels.
- Rapid Program Generation: From CAD data to executable test programs, the process typically takes only a few hours, enabling Flying Probe Test to quickly respond to design iterations, making it a key enabler of agile development workflows.
How Does Flying Probe Test Ensure High-Speed Signal Integrity for AI Chips?
The performance of AI chips directly depends on data transmission speed and stability. Whether it’s the thousands of I/O channels connecting to HBM3e memory or high-speed serial links communicating via PCIe 6.0/CXL, stringent signal integrity (SI) requirements must be met. Any flaws on the substrate, such as impedance mismatches, crosstalk, or signal attenuation, can lead to data errors or even system crashes.
Flying Probe Test ensures high-speed signal integrity through the following methods:
- Impedance Control Verification: Although flying probe testing does not directly measure high-frequency impedance, it can accurately verify whether physical parameters such as trace width and distance to reference planes-which constitute transmission lines-conform to the design. By detecting minute variations in trace resistance, it can indirectly determine whether manufacturing deviations causing impedance drift exist.
- Micro-Short/Micro-Open Detection: Between micron-level traces fabricated on advanced materials like ABF, there may be tiny shorts that are difficult to detect with the naked eye or AOI (Automated Optical Inspection). Similarly, micro-opens (poor connections) may exist at the bottom of laser-drilled microvias. Flying probe test can detect these defects with extremely high precision, preventing flawed high-speed PCBs from proceeding to the next stage.
- Via and Connection Reliability Check: AI substrates typically consist of dozens of layers, with complex stack-up structures containing numerous buried/blind vias and back-drilled holes. Flying probe testing can verify the reliable conductivity of these intricate Z-axis interconnects, ensuring every path from chip pads to bottom-layer BGAs remains unobstructed.
Comparison of PCB Electrical Testing Technologies
| Feature | Flying Probe Test | In-Circuit Test (ICT) | AOI / AXI |
|---|---|---|---|
| Testing Principle | Electrical contact measurement | Electrical contact measurement | Optical/X-ray imaging | NRE Cost | Very Low (No Fixture) | High (Custom Fixture Required) | Low |
| Applicable Stage | Prototype, Low Volume (NPI) | Mass Production | All Stages |
| Test Speed | Slower (Point-by-Point Testing) | Very Fast (Parallel Testing) | Fast |
| Defect Coverage | Open Circuits, Short Circuits, Component Values | Open Circuits, Short Circuits, Component Values, Functionality | Visual Defects, Soldering Quality |
| Design Change Flexibility | Extremely High | Low (Fixture Rebuild Required) | High |
How Does Flying Probe Test Accelerate Product Iteration During NPI Phase?
New Product Introduction (NPI EVT/DVT/PVT) is a critical period that determines the success or failure of an AI chip project. During this phase, engineers need to rapidly validate design assumptions, evaluate new material performance, and optimize manufacturing processes. The flexibility of flying probe test makes it an indispensable tool in the NPI workflow.
When the design team releases a new Gerber version, test engineers can generate new flying probe test programs within hours and test the first batch of samples. Test reports can precisely pinpoint every failed network and its coordinates, providing immediate, actionable data feedback to design and manufacturing teams. This rapid "design-manufacture-test" closed-loop enables teams to:
- Quickly Validate Stackup Design: In complex CoWoS or EMIB substrate designs, verifying the interconnections of RDL layers, power/ground layers, and signal layers is crucial.
- Assess New Material Risks: When using novel low-loss materials (e.g., ABF), their manufacturing process window may be narrow. Flying probe testing helps identify material-related potential issues early.
- Optimize DFM (Design for Manufacturability): By analyzing test failure data, systematic design or process issues can be identified, guiding engineers to optimize before mass production, thereby significantly improving final product yield.
As an experienced PCB/substrate manufacturer, HILPCB offers rapid prototyping services and utilizes advanced flying probe test equipment to ensure your design receives fast and accurate validation during NPI EVT/DVT/PVT phases.
How Does Flying Probe Test Collaborate with Traceability/MES Systems?
In high-reliability applications like AI and data centers, traceability is a mandatory requirement. Customers need to know that every shipped IC substrate has undergone rigorous testing, with all data recorded and traceable. This is where Traceability/MES (Manufacturing Execution System) comes into play.
Flying probe test equipment can seamlessly integrate with a factory's Traceability/MES system. Before testing, each PCB's unique serial number is scanned. During testing, all measurement data-including each network's test results, any detected defects, and their coordinates-are automatically recorded and linked to that serial number.
This collaboration delivers significant value:
- Full Lifecycle Traceability: From bare board manufacturing to final assembly and field application, if any issues arise, the complete production and test history can be immediately traced via the serial number to quickly identify root causes.
- Process Control & Optimization: By statistically analyzing (SPC) the vast amount of test data accumulated in the Traceability/MES system, manufacturing process stability can be monitored, yield fluctuation trends identified, and preventive measures taken.
- Quality Compliance Proof: Providing customers with detailed test reports and data proves compliance with stringent quality standards (e.g., IPC-A-600), which is key to winning trust from high-end clients.
Key Value of AI Carrier Board Flying Probe Testing
- No Fixture Cost: Perfectly aligns with rapid iteration in NPI EVT/DVT/PVT processes, significantly reducing R&D expenses.
- High-Precision Detection: Capable of identifying micron-level open/short circuits, ensuring electrical performance of HDI and RDL structures.
- Data-Driven Decisions: Provides accurate data for Traceability/MES systems, enabling full-process quality control and optimization.
- Design Validation Accelerator: Delivers fast, accurate feedback, shortening design-validation cycles and accelerating time-to-market.
Beyond Electrical Testing: How to Ensure Physical Reliability of AI Modules?
A successful AI module requires not only flawless electrical performance but also long-term physical reliability in harsh operating environments. Electrical testing (e.g., Flying probe test) is the first checkpoint. Once passed, a series of protective processes are needed.
Conformal Coating: A thin polymer film applied to the PCBA surface effectively protects circuits from moisture, dust, chemicals, and extreme temperatures. For AI modules deployed in edge computing or industrial environments, conformal coating is a critical process to enhance environmental adaptability and lifespan.
Potting/Encapsulation: This offers a higher level of physical protection. By completely encapsulating the entire board or specific areas with materials like epoxy or silicone, it provides superior moisture resistance, vibration damping, impact protection, and thermal management. For AI modules subjected to high mechanical stress or harsh environments, potting/encapsulation delivers ultimate protection.
These protective processes are typically performed after all electrical and functional testing, as they are irreversible. This further highlights the importance of preliminary Flying probe test-ensuring only 100% qualified boards proceed to these costly downstream processes.
What Are the Challenges of Flying Probe Test in Mixed Assembly Technology?
Modern AI computing boards often employ mixed assembly technologies. Core AI processors and HBM use advanced SMT processes, while high-current components like power connectors or I/O ports requiring mechanical strength may still rely on THT/through-hole soldering. This hybrid technology presents new challenges for Flying Probe Test. THT components are typically much taller than SMT components, requiring the test probes to intelligently plan their movement paths to avoid these tall obstacles. Additionally, test points may be distributed on both sides of the circuit board, demanding that the flying probe tester possesses dual-sided testing capabilities and can precisely flip and position the board.
Addressing these challenges requires:
- Advanced testing equipment: Flying probe testers with 3D path planning capabilities and high-precision optical positioning systems.
- Experienced engineers: Professionals capable of writing complex test programs, optimizing probe paths, and ensuring 100% test coverage without component collisions.
Highleap PCB Factory (HILPCB) not only excels in advanced SMT assembly but also maintains high-quality THT/through-hole soldering production lines. Equipped with advanced testing solutions capable of handling complex hybrid-technology boards, we provide customers with a truly one-stop service.
HILPCB AI Substrate and Interconnect Manufacturing Capabilities
| Parameter | Capability Range | Value for AI Applications |
|---|---|---|
| Layer Count | Up to 56 layers | Supports complex power/ground planes and high-speed signal routing |
| Minimum Line Width/Spacing | 25/25 µm (1/1 mil) | Meets high-density RDL interconnect requirements for HBM, Chiplet, etc. | Materials | ABF, Rogers, Megtron 6/7, High Tg FR-4 | Provides high-speed low-loss and high-reliability material options |
| Impedance Control Accuracy | ±5% | Ensures signal integrity for high-speed channels like PCIe 6.0/CXL |
| Testing Capabilities | 4-wire flying probe test, AXI, ICT, functional testing | Comprehensive quality assurance from bare boards to finished products |
How to Choose the Right AI Substrate Testing and Manufacturing Partner?
Selecting a partner for your AI project isn't just about choosing a supplier-it's about finding a technical ally who understands your challenges and grows with you. When evaluating potential partners, focus on the following aspects:
- Comprehensive Technical Capabilities: Does the partner possess both advanced IC substrate manufacturing and PCBA assembly expertise? Do they understand the entire process from THT/through-hole soldering to complex BGA balling?
- Quality Control System: Do they have complete testing equipment including Flying probe test and AXI (Automated X-ray Inspection)? Is their Traceability/MES system robust?
- Engineering Support: Can they provide professional DFM (Design for Manufacturability) suggestions to optimize designs, reduce costs, and improve yield?
- Flexibility and Services: Can they support rapid prototyping during NPI EVT/DVT/PVT phases and scale up to mass production? Do they offer value-added services like Conformal coating or Potting/encapsulation?
With over 10 years of experience in high-performance computing and AI, HILPCB has established a one-stop service system covering design support, advanced manufacturing, precision assembly, and comprehensive testing. We understand that for AI hardware, zero defects is the only acceptable standard.
Conclusion: Establishing the Cornerstone of AI Hardware Success with Flying Probe Test
In the precision-driven world of AI chip packaging and interconnects, every detail matters. The Flying probe test, as a critical quality safeguard, offers value far beyond simple "pass/fail" judgments. It serves as a powerful diagnostic tool, a catalyst for accelerating product iteration, and a data foundation for achieving full-process quality traceability. By leveraging Flying probe test early in manufacturing to identify and eliminate potential electrical defects, companies can effectively avoid discovering issues during costly chip mounting and system integration phases, thereby minimizing risks, reducing costs, and accelerating time-to-market.
Choosing a partner like HILPCB, with cutting-edge testing technology and profound manufacturing expertise, means laying the most solid foundation for your AI project's success. We are committed to ensuring every innovative idea is flawlessly realized through meticulous craftsmanship and rigorous testing.
Contact HILPCB today to begin your next-generation AI substrate and interconnect project.