Underfill Inspection and Testing in Surface Mount Technology: A Review of Diagnostic and Analytic Methods

The underfill process is essential for the reliability of flip-chip and electronic assemblies, particularly for BGA and CSP components on printed circuit boards (PCBs). Quality control and defect diagnosis pose significant challenges due to the complexity of these assemblies and the diversity of materials used. This study systematically evaluates seven methods for assessing underfill at the board level, analyzing their applicability, advantages, and disadvantages. It emphasizes both qualitative and quantitative approaches to verify underfill effects and assess chemical compatibility among materials. The findings indicate that no single method is universally suitable for underfill assessment; instead, a combination of techniques is recommended based on specific inspection requirements, production stages, and available resources. The limitations of each method highlight the need for further research and the development of non-destructive techniques for a comprehensive evaluation of underfill quality. Ultimately, these insights can aid in selecting appropriate methods for underfill control throughout various application phases.