Comparative Study of Wire Bond Degradation Under Power and Mechanical Cycling Tests
Translated title
Sammenligningsstudie af nedbrydningen af wire bonds ved power og mekanisk cycling test
Author
Buhrkal-Donau, Steffen
Term
4. term
Education
Publication year
2018
Abstract
IGBT power modules demand high reliability, prompting accelerated tests to clarify wire bond failures. This project evaluates whether pure mechanical high-frequency loading (MC) can serve as a faster alternative to active temperature cycling (ATC) by comparing wire bond degradation under the two regimes. Modules were cycled using ATC or MC and then examined via micro-sectioning and optical microscopy to track crack initiation and propagation; selected samples were electro-etched to reveal the Al wire grain structure and assessed under polarized light. The study observed atypical crack paths in ATC samples, where cracks propagated beneath the metallization–wire interface—likely reflecting poor bond quality—whereas MC samples showed cracking predominantly within the wire material, consistent with expectations. Crack propagation rates appeared broadly similar at low to moderate cycling, albeit with considerable scatter for both methods, while discrepancies in bond fracturing rates near estimated end-of-life were noted for MC wires. Grain analysis showed no strengthening fine-grained refinement zone for ATC wires but a more pronounced zone and generally smaller grains for MC wires, suggesting reconstruction of the wire’s grain structure under MC. Overall, MC may mirror early degradation trends, but atypical crack paths, sensitivity to bond quality, and end-of-life differences indicate that further investigation is needed before MC can replace ATC.
IGBT-baserede effektmoduler kræver høj pålidelighed, og derfor bruges accelererede tests til at forstå wire bond-fejl. Dette projekt undersøger, om ren mekanisk højfrekvent belastning (MC) kan fungere som et hurtigere alternativ til aktiv termisk cycling (ATC) ved at sammenligne, hvordan wire bonds degraderer i de to tests. Moduler cykles enten med ATC eller MC og analyseres ved mikrosektionssnit og optisk mikroskopi for at kortlægge revnedannelse og -udbredelse; udvalgte prøver elektro-ætses for at frembringe kornstrukturen i Al-wiren og vurderes i polariseret lys. Observationerne viser atypiske revneforløb i ATC-prøver, hvor revner breder sig under interfacet mellem metalisering og wire, sandsynligvis på grund af dårlig bondkvalitet, mens MC-prøver primært revner i wirematerialet som forventet. Revneudbredelseshastighederne synes overordnet sammenlignelige ved lav til moderat cykling, om end med stor spredning for begge metoder, mens der ses uoverensstemmelser i brudraten nær estimeret end-of-life for MC-wires. Kornanalyse indikerer fravær af en forstærkende fin-kornet reaktionszone ved ATC, men en mere udtalt zone og generelt mindre korn ved MC, hvilket kan pege på rekonstruktion af kornstrukturen under MC. Resultaterne antyder, at MC kan spejle tidlige degraderingstendenser, men atypiske revneforløb, indflydelse af bondkvalitet og afvigelser nær levetidens slutning kræver yderligere undersøgelser, før MC kan erstatte ATC.
[This apstract has been generated with the help of AI directly from the project full text]