Po-Yao Lin

Lidded FCCSP warpage evaluation: Process modeling and characterization of the effect of viscoelasticity and cured shrinkage for molded underfill

The viscoelastic behavior of the molded underfill (MUF) in fine pitch encapsulated electronic package has a significant impact on package warpage and SMT assembly reliability. To ensure high reliable solder joint yield, the warpage evolution during reflow is critical and should be optimized. This study presents an integrated process modeling approach with finite-element method to predict the package warpage based on the time-domain viscoelastic behavior of the MUF material and its chemical shrinkage properties. The predicted warpage not only shows good agreement with the experimental data characterized by shadow Moire, but also effectively evaluates the effect for different MUF type. The results indicate that warpage at high temperature is highly sensitive to the CTE/Modulus of MUF.

Warpage Modeling and Characterization of the Viscoelastic Relaxation for Cured Molding Process in Fan-Out Packages

The viscoelastic behavior of the molding compound in fine pitch encapsulated electronic packages has a significant impact on component warpage and SMT assembly reliability. This is particularly true for the thin or ultra-thin (such as fan-out) packages used in mobile handsets and tablets, where process-induced warpage behavior is exacerbated by a larger molding volume and higher density of Cu trace layout. To ensure good assembly process yield and long term reliability, warpage relaxation during wafer molding process should be specially addressed and optimized with the effects of cure-dependent and time-domain viscoelastic relaxation from the molding material. In this paper, warpage evolution over the entire compression molding curing process, including compression molding cure (CMC) and the subsequent post molding cure (PMC), are characterized. An integrated process modeling approach using finite element (FE) method incorporated with the cure-dependent viscoelastic constitutive models of the molding material is successfully developed. The curing kinetics and viscoelastic behavior in the time domain of the molding material are characterized with differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Not only are the predicted warpage results based on the integrated process modeling approach in agreement with the in-line warpage measurement data, but this paper also finds that curing process conditions such as cure time, cure temperature, and curing stages can be used to tailor the warpage behaviors. The optimized curing conditions effectively improve the in-line warpage to enhance process yield and throughput.

A novel integrated warpage prediction model based on characterization of viscoelasticity in time domain and chemical shrinkage for molded underfill

In order to efficiently optimize the structure and process of thin packages, it is crucial to accurately predict the warpage of thin packages during in-molding and post-mold curing (PMC) processes. In this paper, we describe an integrated modeling approach, which takes both viscoelastic and chemical shrinkage behaviors into account for molded underfill process. The time-domain viscoelastic properties and chemical shrinkage of molded underfill are included in the finite-element (FE) model. The simulation results are in good agreement with the measured 3D warpage contour and values by Shadow Moiré method. In contrast, the simulated constitutive behavior of molded underfill with only temperature-dependent elastic property exhibits poor agreement with the experimental results.