Indium Thermal Interface Material Assembly Manufacturability and Reliability

摘要

Bonding silicon to an external copper lid with a solder requires extensive process development. This includes siliconrnmetallization development, metallization of the lid cavity, extensive assembly process development to ensure good control inrnthermal interface material (TIM) bond line thickness (BLT), minimal voids at the interface, and the metallic bonding meeting allrnrelevant reliability tests. Among many reliability tests performed to ensure product field life, high-temperature storage (HTS)rntest is critical. Therefore, a comprehensive HTS test was conducted to study its impact on thermal performance, inter-metallicrncompound (IMC) formation and growth, voids, and stability of BLT.rnTwo indium-TIM attachment methods were studied: pre-attached indium approach and indium pre-form approach.rnPre-attach refers to pre-attaching indium-TIM on a lid cavity prior to assembling lid/indium with the microprocessor package.rnIndium pre-form refers to bonding indium pre-form to lid and silicon concurrently. HTS was conducted on thermal test vehiclesrn(TTVs) built with indium to measure thermal resistance at each read point of HTS. Research found no significant change ofrnthermal resistance up to 1,000 hrs of HTS at 125℃. C-SAM was used to monitor structural changes in indium such as voidrnsize. There is no significant change in voids after 1,000 hrs of HTS.rnSEM and TEM were used to study IMC formation at each HTS read point. Two types of IMC were identified: AuIn2rnand In27Ni10. This research found that IMC thickness at the indium/silicon interface is very stable and does not increase withrnHTS time. However, significant IMC thickness increase is observed at the lid/indium interface. This observation can bernexplained by the nickel layer thickness used in the lid cavity and silicon backside. However, the increase of IMC at thernlid/indium interface does not result in any thermal degradation or reliability degradation. This study concludes that indium-rnTIM is stable under HTS test.