PCBA Testing Methods: What Each One Catches

Depending on the product: AOI after reflow, AXI/X-ray for hidden joints, ICT or flying probe for electrical checks, and FCT (functional test) to verify the product works as specified. Methods are complementary — the test plan is defined per product.

AOI (Automated Optical Inspection) uses cameras and algorithms to check visible features — component position, missing parts, offset, polarity, and solder joints. No: AOI mainly observes visible features and has limits on joints hidden under BGA, bottom-terminated devices, or internal structures, so some products need X-ray as a supplement.

AXI (Automated X-ray Inspection) inspects invisible areas — BGA joints, bottom-terminated devices, and some through-hole soldering. Specific coverage depends on the product and equipment.

SPI focuses on solder paste printing; AOI focuses on visible component and solder appearance; X-ray covers invisible joints and internal structure. The three are complementary.

ICT (In-Circuit Test) tests components, connections, and electrical parameters at circuit test points or nodes, catching assembly and some circuit-level anomalies. FCT (Functional Test) verifies the complete or near-complete PCBA against its functional requirements — I/O, power, communication, buttons, sensors, etc.

Flying probe testing uses movable probes contacting test points for electrical checks, without necessarily requiring a dedicated ICT fixture. It suits some low- to mid-volume products or products that change frequently.

A device that holds the PCBA and provides electrical, mechanical, or interface connections for testing, improving repeatability and efficiency.

A systematic check of the first unit(s) after production starts or after a change, confirming the manufacturing result meets design and process requirements. The specific definition follows the customer’s quality system.

Yield is the ratio of good units to units input; it can be tracked per process (first-pass rate, final yield). FPY (First Pass Yield) is the share of products passing a process on the first attempt with no rework — a key indicator of process stability.

DPMO (Defects Per Million Opportunities) standardizes quality performance for comparing processes of different complexity.

The ability to trace a product’s production history through serial numbers, batches, materials, equipment, programs, process parameters, and test data.

Tracing a defect to its true cause instead of only treating symptoms. Common methods: 5 Whys, fishbone/Ishikawa diagram, data stratification, and experimental verification.

CAPA (Corrective and Preventive Action) is the system for handling an occurred issue and reducing the probability of similar issues recurring.

ESD (Electrostatic Discharge) control reduces static risk to sensitive components and PCBAs through grounding, anti-static workstations, anti-static packaging, personnel protection, and environment management.

• IPC-A-610: acceptability standard for electronic assemblies — how to judge the appearance and acceptability of assembled products.
• J-STD-001: requirements for the soldering process, materials, and related work; it is typically used together with IPC-A-610.
• In short: J-STD-001 leans toward the soldering process and materials; IPC-A-610 leans toward assembly acceptability and inspection judgment. Projects follow the contract and applicable standard versions.

IPC product classes distinguish different product environments, performance, and reliability needs. Class 3 represents the stricter requirements for continuous high-performance, mission-critical, or demanding environments. Acceptance criteria follow the project documents and the applicable IPC revision.

RoHS is the regulation system restricting certain hazardous substances in electrical and electronic equipment. Whether a project needs RoHS, and which version and material requirements apply, follows the target market and customer requirements.

Lead-free assembly uses lead-free solder systems (e.g., tin-based lead-free alloys) meeting project requirements. Lead-free process affects soldering temperature windows, component thermal tolerance, reflow profiles, and some process controls.