As the carrier of various components and the hub for circuit signal transmission, PCB has become the most important and critical part of electronic information products. Its quality and reliability determine the quality and reliability of the entire equipment. However, due to cost and technical reasons, a large number of failures occur during PCB manufacturing and application.
As the carrier of various components and the hub for circuit signal transmission, PCB has become the most important and critical part of electronic information products. Its quality and reliability determine the quality and reliability of the entire equipment. However, due to cost and technical reasons, a large number of failures occur during PCB manufacturing and application.
To address these failures, common failure analysis technologies are required to ensure the quality and reliability of PCBs during production. This article summarizes nine key PCB failure analysis techniques, including visual inspection, X‑ray inspection, cross‑section analysis, thermal analysis, X‑ray photoelectron spectroscopy (XPS), micro‑infrared analysis, scanning electron microscopy (SEM), and energy‑dispersive X‑ray spectroscopy (EDS).
Due to the structural characteristics and typical failure modes of PCBs, cross‑section analysis is destructive—samples cannot be recovered after testing. SEM and EDS may also partially damage samples due to sample preparation requirements. Additional tests such as thermal stress, electrical performance, solderability, and dimensional measurement may be used for failure location and verification but are not detailed here.
1. Visual Inspection
Visual inspection uses visual observation or simple instruments (stereo microscope, metallographic microscope, magnifier) to examine the PCB appearance, locate failure sites, and identify physical evidence.
Its main purposes are
failure positioning and preliminary judgment of failure modes.
Key inspection items include contamination, corrosion, delamination, circuit routing, and failure patterns (batch vs. random, regional concentration).
For failures found after PCBA assembly, inspect for influences from assembly processes and materials.
2. X‑ray Inspection
X‑ray inspection is used for internal defects invisible to the naked eye, such as plated through‑holes (PTHs) and inner‑layer anomalies. It images based on differences in X‑ray absorption or transmission caused by material thickness and density.
It is widely used to inspect
solder joint defects, PTH integrity, and hidden solder joints in high‑density BGA/CSP packages.
Industrial X‑ray systems now reach sub‑micron resolution, evolving from 2D to 3D imaging. 5D systems exist for packaging inspection but are costly and rarely used in industry.
3. Cross‑Section Analysis (Metallographic Sectioning)
Cross‑section analysis is a process involving sampling, mounting, sectioning, grinding, polishing, etching, and observation to obtain PCB cross‑sectional structures.
It provides rich microstructural information about PCB quality (vias, plating, etc.) and supports quality improvement.
This method is
destructive; samples are irreparably damaged. It requires skilled technicians and strict preparation per
IPC‑TM‑650 2.1.1 and
IPC‑MS‑810.
4. Scanning Acoustic Microscopy (SAM)
C‑mode SAM is widely used in electronic packaging and assembly analysis. It uses high‑frequency ultrasound reflections at material interfaces to image discontinuities in amplitude, phase, and polarity while scanning X‑Y planes along the Z‑axis.
SAM detects internal defects in components, materials, PCBs, and PCBAs, including
cracks, delamination, inclusions, and voids.
With sufficient frequency range, it can inspect internal solder joint defects.
SAM is especially valuable for
non‑destructive testing of high‑density multilayer PCBs, particularly for popcorning and delamination caused by moisture absorption during high‑temperature lead‑free reflow.
5. Micro‑Infrared Analysis
Micro‑infrared analysis combines infrared spectroscopy with microscopy. It identifies organic compounds based on characteristic infrared absorption and uses coaxial visible/infrared optics to locate trace organic contaminants.
Conventional IR spectroscopy requires large samples, but micro‑IR enables analysis of minute contamination that causes poor solderability on PCB pads or leads.
Main applications: analyzing organic contaminants on solder surfaces, identifying causes of corrosion and poor solderability.
6. Scanning Electron Microscopy (SEM)
SEM is a powerful electron imaging system for failure analysis. A focused high‑energy electron beam scans the sample surface, emitting secondary electrons and backscattered electrons to form high‑magnification images.
- Secondary electrons (5–10 nm deep) show surface morphology.
- Backscattered electrons (100–1000 nm deep) indicate elemental distribution based on atomic number.
In PCB and solder joint analysis, SEM is used for:
- Pad surface morphology
- Solder joint microstructure
- Intermetallic compound (IMC) measurement
- Solderability plating analysis
- Tin whisker inspection
SEM requires conductive samples; non‑conductors need gold or carbon coating. It offers much greater depth of field than optical microscopes.
7. Energy‑Dispersive X‑ray Spectroscopy (EDS)
Most SEM systems are equipped with EDS. High‑energy electron beams excite characteristic X‑rays from sample surfaces, enabling
elemental composition analysis.
EDS supports
point, line, and area analysis to map elemental distribution.
In PCB analysis, EDS identifies pad surface composition and contaminants on poorly solderable pads and leads.
Quantitative accuracy is limited; elements below 0.1 wt% are difficult to detect.
SEM+EDS is widely used because it provides
morphology + composition simultaneously.
8. X‑ray Photoelectron Spectroscopy (XPS)
XPS irradiates samples with X‑rays to emit photoelectrons, measuring binding energy as a “fingerprint” for elements.
It performs
qualitative and quantitative analysis of the
shallow surface (nanometer scale) and determines chemical valence states and bonding environments.
XPS analyzes
insulating samples non‑destructively with higher sensitivity than EDS. Argon ion sputtering enables depth profiling.
In PCB analysis, XPS evaluates plating quality, surface contamination, and oxidation to identify root causes of poor solderability.
9. Thermal Analysis
9.1 Differential Scanning Calorimetry (DSC)
DSC measures the power difference between a sample and a reference under controlled temperature ramping.
In PCB analysis, DSC measures
curing degree and
glass transition temperature (Tg) of polymer materials—two critical parameters for process reliability.
9.2 Thermomechanical Analysis (TMA)
TMA measures dimensional changes under thermal and mechanical load.
In PCB analysis, TMA determines:
- Coefficient of thermal expansion (CTE)
- Glass transition temperature (Tg)
Excessively high CTE frequently causes PTH cracking after soldering and assembly.
Conclusion
With the trend toward high‑density PCBs and environmental requirements for lead‑free and halogen‑free materials, more failures occur, including poor wetting, delamination, popcorning, and CAF. Understanding failure mechanisms through these analysis techniques supports quality control and prevents recurring issues.
About Maxipcb
Maxipcb enables advanced electronic innovation. We deliver one-stop solutions including circuit design, simulation, testing, PCB fabrication, component sourcing and SMT&PCBA assembly, to boost R&D efficiency, speed up mass production and control full-cycle risks. We serve global sectors like communication, industrial automation, aerospace, automotive and semiconductor, jointly forging a safer, connected intelligent future.
