Analysis the PCBA Faults and Defect Resolution Measures

The printed circuit board assembly (PCBA) forms the backbone of all electronic devices, from home appliances to aerospace systems. As products become more complex, driven by rising capabilities and shrinking component sizes, PCBA reliability stands increasingly critical. Even minute flaws can disable functionality or severely hamper performance.

Proactively identifying and resolving assembly defects before products ship prevents field failures and lowers warranty costs. This requires a rigorous quality program encompassing design analysis, process controls, inspection, testing and continuous improvement. Partnering with expert PCBA manufacturers leverages their knowledge, best practices and analytical capabilities.

This paper provides an overview of common PCBA failure mechanisms ranging from design shortcomings and manufacturing defects to handling damage and environmental factors. Analysis of root causes enables implementing preventative measures and inspection methods to enhance PCBA quality and reliability.

PCBA Defect Origins and Effects

Key defect categories

1. Design flaws – Insufficient spacing – Inadequate protection – Electromagnetic compatibility issues
2. Manufacturing defects
   Solder bridging – Plating voids
   Poor adhereance – Contamination
3. Usage damage – Electrostatic discharge – Thermal stresses – Mechanical fracture
4. Environmental – Oxidation – Moisture – Dust/debris

Design flaws manifest as functionality or reliability problems in the field. Manufacturing defects reduce yields and field survival rates. Usage damage accumulates over time from various stress factors leading to eventual failure. Environmental exposure also degrades materials and connections.

Across categories, the effects

• Signal loss or distortion
• Intermittent operation
• Thermal runaway
• Short circuits
• Open circuits
• Unit failure

Well-designed analysis programs catch the PCBA fault and defects early while easier and less costly to correct. This prevents failures or recalls down the line which prove exponentially more expensive. We now examine frequent defect types in further detail including root causes and solutions.

PCBA Design Deficiency Analysis

Several recurring design flaws predispose PCBAs to failure from the outset if not addressed. Rigorous design analysis performed by PCBA production partners identifies risks early when revisions cost less in time and materials versus late stage changes.

Insufficient Clearances

Board layouts must allow adequate spacing between adjacent conductors and components based on voltage levels, process capabilities and environmental conditions. Typical clearance guidelines fall around 10-15 mils between printed conductors. Higher voltages, automated assembly and test probing, or harsh operating environments demand extra margin.

Violating clearance rules risks:

• Bridge shorts from solder, coatings or debris
• Electrostatic arcs during operation
• Test probe or repair damage
• Signal coupling/interference

Remedies involve adjusting component placement and routing paths to open clearances before release to production. Simple design rule checks performed by PCBA designers screen for violations, as do thermal simulations assessing heat buildup between parts.

Inadequate Shielding

Electronic devices produce electromagnetic interference (EMI) emissions which can disrupt nearby sensitive components, circuits, or external equipment functionality. Certain high frequency circuits also require shielding from external interference.

Key problems from unshielded designs are:

• Signal loss/distortion
• Equipment malfunctions
• EMI regulatory failures

Shielding remedies include:

• Enclosing circuitry in conductive housings
• Using ground plane layers in multilayer PCBs
• Adding EMI gaskets around enclosures
• Employing shielded cables

Electromagnetic Compatibility Issues

Related to shielding, electromagnetic compatibility (EMC) means electronics operate properly without emitting or receiving disruptive radiated noise per acceptable emissions limits. EMC problems arise from:

• Inadequate filtering
• Poor grounding
• Leakage via cables
• Insufficient chassis isolation
• High frequency digital logic

Effects manifest as:

• Signal distortion
• False sensor readings
• Control malfunctions
• Units shutting down
• Equipment damage

Fixes require improvements like:

• Extra filtering components
• Adding radio frequency chokes
• Enhanced grounding topologies
• Ferrite beads on cables
• Metal chassis bonding
• Lower noise digital logic families

Rigorous EMC testing by PCBA partners verifies acceptable radiated and conducted emissions before product release.

PCBA Manufacturing Defect Analysis

Defects introduced during PCB fabrication and PCBA production also contribute to functionality or reliability issues. Robust process controls minimize manufacturing defects while inspection methods catch remaining flaws.

Solder Bridging

Solder forms both the mechanical and electrical connections between component terminations and circuit board pads. Occasionally solder can spread where undesired, contacting neighboring pads or traces. Triggers consist of:

• Excessive solder application
• High density component packing
• Component misalignment
• Non-wetting finishes

Solder bridges produce short circuits with effects like:

• Units fail testing
• Components overheat
• Damage from excessive current

Remediation involves:

• Improved process training
• Tweaked placement programs
• Additional ventilation
• Higher temperature materials

Inspection using X-ray imaging or automated optical scanning reveals hidden or difficult to spot bridges allowing rework before shipment.

Plating Voids

Plated through holes (PTHs) electrically connect layers in multilayer boards. Electrolytic copper plating lines the holes for conductivity but gaps or voids in coverage can develop interrupting current flow between layers. Voids stem from:

• Poor hole roughening
• Drilling debris
• Contaminated solutions
• High speeds inducing bubbles

Efforts to minimize plating voids encompass:

• Tighter drilling parameters
• Better hole cleaning procedures
• Filtered plating solutions
• Lower current densities
• X-ray monitoring

Small voids get caught during electrical testing while X-ray inspection also screens for larger hidden voids.

Contamination

Airborne particulates, oils, solvent residues, or metallics adhering to PCBs during handling or processing impairs quality, reliability and aesthetics. Common contamination types consist of:

• Fingerprint oils
• Solder flux residue
• Metal or fiber shards
• Cleaning solution carryover
• Dust/lint

Problems manifest via:

• Reduced surface insulation
• Visible stains or debris
• Poor solder flow
• Dendrite growth

Solutions include:

• Operator gloves/finger cots
• Dedicated cleaning stations -Filtered air/enclosures
• Purified chemicals
• Package sealing after finish

Routine inspection combined with process audits by PCBA experts safeguards against latent contamination issues.

Usage and Handling Damage of PCBA

Internal or external stress factors applied over time degrade PCBA integrity leading to eventual failures. Careful handling and protection aids resilience.

Electrostatic Discharge

Built up static electricity frequently discharges through sensitive PCBA components when handled, causing instant or latent damage. Failure modes consist of:

• Gate oxide breakdown
• Metallization fusing
• Parametric shifts

Anti-static approaches involve:

• Conductive/dissipative work surfaces
• Grounding straps
• Low humidity environments
• Anti-static packaging

Shielding, grounding and ESD immunity also help strengthen product design robustness.

Thermal Stress

Repeated temperature fluctuations induce expansion/contraction cycling generating mechanical stresses over time. This accelerates solder fatigue, wire bond heel cracks, substrate fracturing, dielectric breakdowns, and more depending on materials used and interfaces involved.

Reliability stands enhanced through:

• Graded CTE bonds
• Interposers/buffer layers
• Underfill epoxies
• Low modulus encapsulants
• Thick copper PCBs

Shock/Vibration

Electronics face abundant vibration and shock exposures from dropping, transportation, operating environments or internal forces which apply cyclic mechanical stresses. Fatigue cracks then emerge at vulernable junctions and interfaces risking intermittency or failures. Package-level enhancements aid resilience:

• Vibration isolation mounts
• Potting compounds
• Avoiding heavy connectors
• Supporting large components
• Conformal coatings

Environmental Degradation Factors

Long duration exposure to temperature, humidity, chemicals or radiation degrades PCBA materials, finishes and connections. This accelerates time-to-failure.

Oxidation

Copper traces, pad finishes and metallic terminations naturally oxidize when exposed to oxygen, moisture and contaminants. Non-noble surface metals readily form oxide barriers impeding solderability and conductivity causing issues like:

• Intermittent contacts
• Solder opens
• Increased resistivity

Common remedies involve:

• Sealed moisture barriers
• Electroplated gold over nickel
• Immersion silver, tin or solder finishes
• Organic solderability preservatives

Moisture Absorption

Prolonged humidity exposure allows moisture permeation into polymer insulators and epoxies leading to swelling, mechanical weakening, loss tangents and enhanced conductor corrosion rates. This means:

• Electrical shorts
• Leakage currents
• Material fractures
• Dendritic growths

Protection methods encompass:

• Hermetic seals
• Conformal barriers
• Low moisture permeation polymers
• Hydrophobic coatings

Particulate Contaminants

Airborne dust and debris settle and accumulate on PCBA surfaces under certain environments combining with humidity to create leakage paths, corrosion sites and insulation breakdowns over time:

• Electrochemical migration
• Conductive anodic filaments
• Surface insulation resistance drops

Reliability stands improved by:

• Enclosures
• Periodic cleaning
• Conformal coatings
• Keepout zones

PCB Failure Analysis Test Types

PCBs are crucial in the realm of electronic information products, serving as the primary carriers for various components and the conduit for circuit signal transmission. The quality and reliability of PCBs are pivotal, directly influencing the overall performance of electronic equipment. Despite technological advancements, PCB production and application are still prone to failures due to cost constraints and technical challenges.

There are several tests that may be used in PCB failure testing to find the flaws in the Electronic device. When the PCB failure analyst understands the flaws and knows how to avoid them, the business can expand both its production method and the assemblies it manufactures.

1. Visual Inspection: This involves a thorough examination of PCBs using simple instruments like stereo microscopes, metallographic microscopes, or magnifying glasses. It focuses on identifying physical evidence of failure, such as pollution, corrosion, and circuit irregularities. This method is particularly effective in pinpointing failure locations and understanding failure modes.
2. X-ray Fluoroscopy: Utilized for examining internal and through-hole defects unobservable through visual inspection. This method leverages material density variations to inspect solder joint defects and through-hole anomalies in BGA or CSP devices. With advancements, X-ray fluoroscopy is evolving into more sophisticated three-dimensional and even five-dimensional imaging technologies, although the latter remains rare in industrial applications due to high costs.
3. Slice Analysis: This destructive technique involves sampling, embedding, slicing, polishing, corroding, and observing PCB cross-sections. While providing extensive microstructure information, it requires skilled technicians and extensive preparation time.
4. Scanning Acoustic Microscope: Primarily used for analyzing electronic packaging and assemblies, this method employs high-frequency ultrasonic reflections to detect material discontinuities, revealing defects such as cracks, delamination, inclusions, and voids. Its non-destructive nature makes it advantageous for inspecting multilayer, high-density PCBs.
5. Microscopic Infrared Analysis: This technique combines infrared spectroscopy with microscopy, identifying organic contaminants that affect solderability. It is critical in analyzing organic pollutants on welded surfaces and joints, contributing to understanding corrosion or solderability issues.
6. Scanning Electron Microscope (SEM) Analysis: SEM is a powerful tool for observing fine structures or surface features at high magnifications. It’s instrumental in examining pad surface morphology, solder joint metallurgy, intermetallic measurement, and tin whisker analysis. However, it requires conductive samples, and non-conductors need gold or carbon coating.
7. X-ray Energy Spectrum Analysis: Typically coupled with SEM, this method analyzes chemical compositions by detecting characteristic X-rays emitted from sample surfaces under high-energy electron bombardment. It’s primarily used for component analysis on pad surfaces and detecting contamination leading to poor solderability.
8. Photoelectron Spectroscopy (XPS) Analysis: XPS identifies chemical states of surface atoms through kinetic energy measurement of electrons dislodged by X-ray irradiation. It’s crucial for analyzing pad coating quality, contamination, and oxidation levels to pinpoint causes of poor solderability.
9. Thermal Analysis Differential Scanning Calorimetry: This technique measures the power difference relationship with temperature (or time) between a substance and a reference under controlled temperature changes. In PCB analysis, it is mainly used to measure the solidification degree and glass transition temperature of polymer materials on the PCB.
10. Thermomechanical Analyzer (TMA): TMA measures deformation properties of materials under heat or mechanical force. It’s essential for determining two critical PCB parameters: linear expansion coefficient and glass transition temperature. High expansion coefficients in PCB substrates often lead to metallized hole failure post-solder assembly.

Conclusion

This overview of PCBA defect origins, effects, analysis and solutions emphasized the necessity of preventative quality practices spanning design, production and field deployment stages in averting functionality or reliability issues.

No production process proves completely flawless. However, understanding manufacturing defect mechanisms allows targeting root causes for permanent elimination versus mere temporary containment.

Quality-focused PCBA partners offer knowledge and analytical skills complementing internal expertise early during development when remediation proves simplest and most affordable prior to high volume manufacturing commitments. Investments here prevent far greater costs over product lifetimes via sustainable defect reductions and continuous advancement.