Advanced Packaging – Defects, Failures & Analysis (Lecture Notes Vocabulary)

Vocabulary flashcards summarizing key terms, defects, mechanisms, materials, reliability issues, and analytical tools discussed in the lecture on advanced packaging defects and failure analysis.

Advanced packaging

Modern semiconductor assembly techniques that integrate multiple dies or components in compact, high-performance structures (e.g., 3D stacks, fan-out, SiP).

Plastic-encapsulated microelectronic package

A microchip assembly where the die is sealed in a molded plastic compound for mechanical and environmental protection.

Fractured die

Cracking or breaking of the semiconductor chip, often caused by bonding force, dicing, die-attach stresses, or overstress events.

Passivation

Protective dielectric layer on a die that shields underlying circuitry from contamination, moisture, and mechanical damage.

Delamination

Loss of adhesion at an interface (e.g., die/passivation, encapsulant/lead-frame), creating gaps that jeopardize reliability.

Paddle shift

Deformation and displacement of the die paddle caused by unbalanced encapsulant flow during molding.

Lead-frame

Metal frame that supports the die and provides lead terminals for external connections in many plastic packages.

Encapsulant

Polymeric molding compound (usually epoxy-based) that surrounds and protects the assembled device.

Popcorning

Moisture-induced package cracking during rapid solder reflow when trapped water vaporizes explosively.

Overstress failure

Instantaneous, catastrophic failure caused by a load that exceeds the material or design limit (e.g., ESD strike, mechanical shock).

Wearout failure

Gradual failure resulting from cumulative damage over time, such as fatigue, corrosion, or electromigration.

Mechanical load

External or internal forces (shock, vibration, filler shrinkage, inertial forces) acting on the package structure.

Thermal load

Temperature-related stresses arising from processing steps (die-attach cure, solder reflow) or environmental heating/cooling.

Coefficient of Thermal Expansion (CTE)

Rate at which a material expands per degree of temperature rise; mismatch between materials drives thermo-mechanical stress.

Electrical overstress (EOS)

Condition where applied voltage or current exceeds device limits, potentially causing junction damage or metallization burnout.

Electrostatic discharge (ESD)

Sudden transfer of static charge that can destroy thin oxide layers or metal lines in semiconductor devices.

Electromigration

Atom migration in conductors driven by high current density, leading to voids and open circuits, especially in solder bumps.

Chemical load

Exposure to corrosive or reactive environments (humidity, salts, chemicals) that interact with package materials.

Moisture ingression

Absorption and diffusion of water molecules through plastic encapsulant into internal interfaces and the die surface.

Depolymerization (Reversion)

Breakdown of cured polymer chains under prolonged heat/humidity, reducing encapsulant mechanical strength.

3D integration

Stacking of multiple active silicon layers or dies, interconnected vertically to enhance performance and footprint.

Through-Silicon Via (TSV)

Vertical electrical interconnect etched and filled through a silicon wafer to link stacked layers in 3D ICs.

Copper pumping

CTE-induced extrusion of Cu in TSVs or bumps, generating stress and protrusions that can crack surrounding silicon.

Micro-bump

Very small solder bump (10–30 µm tall) forming fine-pitch connections between stacked dies or interposers.

Underfill

Epoxy adhesive filled between chip and substrate after solder reflow to share mechanical load and enhance reliability.

C4 bump

High-lead or lead-free solder ball used in controlled-collapse chip connection (flip-chip) assemblies.

Ball Grid Array (BGA)

Package style using an array of solder balls on the underside for board mounting.

Embrittlement

Loss of ductility in solder joints (often due to intermetallic growth) that promotes cracking under stress.

Flux residue

Chemical remnants from soldering flux that may trap moisture or cause corrosion if not cleaned before underfill.

Warpage

Out-of-plane bending of the package or board due to thermal or cure-induced stresses.

Die cracking

Fracture within the silicon die generated by encapsulation stress, thinning, handling, or thermal mismatch.

Void (encapsulant)

Trapped air pocket in molding compound or underfill that weakens the structure and acts as a moisture path.

Non-uniform encapsulation

Non-homogeneous filler distribution or thickness variations in molded or potted compounds, leading to local stress concentrations.

Failure analysis (FA)

Systematic investigation to verify, locate, and determine root cause of device failures to guide corrective actions.

Non-destructive testing (NDT)

Examination methods that do not damage the sample, e.g., X-ray, SAM, optical microscopy.

Scanning Acoustic Microscopy (SAM)

Ultrasonic imaging technique that detects internal delamination, cracks, and voids by acoustic reflections.

Focused Ion Beam (FIB)

Instrument that mills and images micro-regions with a gallium ion beam, enabling cross-sections for FA.

Residual Gas Analysis (RGA)

Mass-spectrometry method to identify and quantify gases released from a sealed package or during outgassing.

Energy Dispersive X-ray Spectroscopy (EDS)

SEM-based elemental analysis technique that measures characteristic X-rays emitted from the sample.

Scanning Electron Microscopy (SEM)

High-resolution imaging using focused electron beam to observe surface topology and fracture features.

Lock-In Thermography (LIT)

Infrared technique that modulates electrical stimuli and detects synchronized heat signatures to locate faults.

Root cause analysis (RCA)

Process of identifying the fundamental reason for a defect so that it can be permanently eliminated.

Fishbone diagram (Ishikawa)

Cause-and-effect chart that categorizes potential causes (e.g., 6Ms) contributing to a specific problem.

5 Whys

Iterative questioning technique that drills down through successive ‘why’ queries to uncover the root cause.

8D approach

Eight-discipline problem-solving methodology that uses team actions, containment, RCA, corrective and preventive measures.

Interim containment action

Temporary measure that isolates customers from the problem while long-term corrective action is developed.

Permanent corrective action (PCA)

Verified fix implemented to remove the root cause and prevent recurrence of the failure.

Preventive action

Steps taken to modify processes or systems so that similar problems cannot occur in the future.

Cause-effect chain

Sequence linking a root cause through intermediate events to the observed failure mode.

Contributing factors

Material, design, environmental, or process attributes that participate in creating a defect or failure.

6Ms

Fishbone categories: Machine, Method, Material, Measurement, Man (people), Mother Nature (environment).

Hot chemical shrinkage

Volume reduction of epoxy mold compound during high-temperature curing, a driver for warpage and stress.

Capillary underfill

Underfill applied by capillary action after flip-chip reflow, filling the gap between die and substrate.

Electromigration voiding

Formation of voids in solder or metal lines due to atom transport under high current density.

Thermal cycling

Repeated temperature excursions that induce expansion-contraction fatigue in solder joints and interfaces.

Fatigue crack propagation

Incremental crack growth under cyclic loading leading to eventual fracture.

Creep

Time-dependent plastic deformation under constant stress, accelerated at elevated temperatures.

Popcorning effect

Moisture-driven delamination or cracking during rapid heating, similar to popcorn bursting.

Die-attach

Process of bonding the silicon die to a substrate or paddle using adhesive or solder.

Molding compound

Epoxy-based resin filled with silica or other fillers, used to encapsulate and protect the device.