Three-point Bending Test Method Experimental Study for Package Strength and Crack Prediction through Finite Element Analysis

In recent years with the thinner, smaller, higher-density stack trend for package (PKG) design, the package crack risk becomes higher and higher in the assembly process and reliability tests. Therefore, it is crucial to establish an effective method to measure and predict package strength. The three-point bending (3PB) test is widely used to evaluate package strength. However, detailed parameters of the 3PB test vary among different manufacturers, making it difficult to compare data. Here, the main impact factors and mechanisms were evaluated to demonstrate the impact of 3PB test parameters on data. Additionally, a package strength prediction method was established using ANSYS software and Python based on epoxy mold compound (EMC) fracture. Results showed that the placement direction determined how the package crack and internal chips cracked before EMC instead of simultaneous fracture when the indenter was parallel to the package`s long side. Both crack force and strain were changed by more than 20% when one of the indenter sizes, span, or pretreatment was altered greatly. The effect of speed and strain gage type on the test results was less than 10%. Furthermore, 3PB finite element models were set up, in which boundary setting was solder ball side towards up, short side parallel to indenter, phi 0.6mm indenter size, and 12mm span without pretreatment. The crack force of a typical same-die structure package was predicted through iterations, starting with an initial load value of 100Nton and increments of 5Nton. It was observed that EMC and chips broke simultaneously under the setting test conditions, with the EMC fracture threshold of 130MPa adopted as the criterion for terminating iterations. The highest prediction accuracy of package 3PB strength was 92%, which assists in package crack risk management and provides guidance for future structured design.