Flip-Chip Chip Scale Package (FCCSP) Process Characterization and Reliability of Coreless Thin Package with 7nm Si Technology

Advanced silicon nodes are continuously pushing the cutting edge of assembly technology with coreless thin packages used in mobile and electronic products to allow better power delivery, electrical performance, and higher routing capability. This results in a higher number of I/O and integration flexibilities. Furthermore, integration of a large die size in a smaller package with finer bump and ball pitches, increases the reliability risk. Also, typical mobile applications require stacking a memory die within the package without increasing the total package height. These combinations magnify the stress on back-end-of line (BEOL) stack and bump interconnection-especially on a thin coreless substrate which greatly influence extreme low-K dielectrics (ELK) fragility. This paper describes the qualification of the 7nm silicon (Si) BEOL stability on thin coreless embedded trace substrates (ETS) with a fine solder ball pitch and a high die to package aspect ratio. Coreless material is generally prone to warpage due to absence of the core that supports the package rigidity. Therefore, controlling and minimizing warpage at room and elevated temperature is crucial, as the stress propagates into the BEOL, resulting in a significant impact on the chip package interaction (CPI), especially for ELK structures. Simulation of thermal and mechanical stress in Finite Element Modeling (FEM) was completed to confirm warpage behavior. Shadow Moiré was documented under temperature loading and package coplanarity empirical data was collected.Within the development phase, package warpage was successfully reduced and coplanarity on thin coreless substrate was within specification. Significant improvement is attributed to mold compound mechanical properties. Multiple reliability tests in accordance with JEDEC standard were conducted including Moisture Level Sensitivity (MSL), Temperature Cycle (TC), Unbiased Highly Accelerated Stress Test (uHAST) and board level test Temperature Cycle on Board (TCoB) and Drop Test and additional CPI test Quick Temp Cycle (QTC) and Multiple Reflow (MR). Results confirmed the BEOL stack integrity and all related tests passed.