Characterizing Coupled Mass Transport Flux in Microbump Assemblies
Characterizing coupled electromigration, thermomigration, and stressmigration flux in microbumps demands decoupled thermal-electric testing to prevent voiding.
Lock in Thermography
Meaning
Modulation of thermal energy through an external frequency source allows lock in thermography to detect non-visible defects in solid materials. The technique functions by applying periodic heat pulses to a test subject while a detector captures infrared emission patterns in sync with the reference frequency. This synchronisation extracts periodic temperature signals from background noise, enabling the identification of sub-surface features like delamination or voids.
Frequency Analysis
Signal processing occurs through the comparison of the detected infrared data against the reference waveform applied to the object. A phase shift between the input heat and the output emission reveals differences in thermal diffusivity across the test area. Variations in these phase angles highlight material discontinuities that remain invisible during standard static thermal imaging.
Narrowing the bandwidth of detection to the modulation frequency provides the high signal to noise ratio required to resolve these small amplitude thermal differences.
Defect Resolution
Quantitative analysis of the captured data provides information regarding the depth and size of internal structures. Deeper defects shift the phase of the thermal wave significantly due to the time taken for heat to traverse the material thickness and return to the surface. Higher modulation frequencies provide better lateral resolution for shallow features, whereas lower frequencies permit penetration into thicker components.
Practitioners evaluate these phase images to map the geometric extent of internal bonding issues or material inclusions without damaging the part.
Jurisdictional Compliance
Industrial safety standards in Chinese manufacturing oversight mandate the application of verified non-destructive testing for critical components. The State Administration for Market Regulation requires that any method used for product certification aligns with established thermal wave parameters to ensure public safety. Local enforcement agencies perform audits to confirm that the equipment matches the sensitivity requirements defined in the relevant national GB standards for technical inspection.
Failure to adhere to these prescribed calibration cycles results in the invalidation of quality control logs during official site investigations. Operators retain the responsibility to maintain current records of all phase measurement data for submission upon request from the quality bureau.