Study on FEM Numerical Simulation and Strain Monitoring of Tunnel Secondary Lining

Safety of secondary lining is of utmost importance to tunnel engineering quality as the main load-bearing structure and the last waterproof line of rock tunnel under type III. The comparative study of strain state results from FEM numerical simulation and on-site monitoring in Yunnan Tianxin Tunnel was conducted to obtain the stress regularity of tunnel lining. The results showed that except vault, the strain states of secondary lining obtained by numerical simulation and on-site monitoring were consistent. The strain value of on-site monitoring was approximately 60%~70% to the simulation value. And the strain value of right side was greater than the value of the corresponding location on the left side. It’s noticed that high strain were found in tunnel haunch and arch springing. Great attention should be paid to arch springing for the largest strain value. The strain monitoring value of vault (309.83με~327.23με) has been detected larger than simulation value (209.37με), which matches well the crack phenomenon of vault. Therefore it’s significant to focus on the long-term monitoring of vault. The defects of single on-site monitoring method such as poor predictability were made up effectively by comparative study. The results achieved can be recommended for similar projects.

Simulation and Experiment of Molded Underfill Voids

The molded underfill (MUF) has become one of the trends in the IC packaging industry due to its simplification of assembly process steps and the saving of the cost. However, for the fine pitch flip chip bumping array, the void generation is one serious issue causing the short of the electrical connections and the cracking of the bumps. In this paper, the main focus is to predict the void generation and to compare with the experimental data. The early stage FEM numerical simulation not only can predict the risk of voids but also provide the best economic approach without the need to spend trial and error budget. A multiple segments substrate strip, with totally 64 packages populated on it, is used in the experiment. The manufacturing process parameters are programmed and recorded for comparison. The filling, packing, and curing of molding compound are carefully chosen in order to compare their effects. After the assembly process, each package is scanned with C-SAM inspection to check if the voids appear. For FEM numerical simulation, only one segment of the substrate strip, with totally 16 packages, is modeled to save computational resources and time. However, all the bumps, on each of the package, are modeled in order to check how the flow field is affected by the packages. In conclusion, we have obtained good match of experimental vs. simulation data. The prediction of voiding location is very close to each other.