O. van der Sluis

Moisture diffusion model verification of packaging materials

The use of the non-hermetic material for electronic packaging does raise a potential concern, i.e. moisture induced interfacial delamination and pop corning during reflow. Therefore, it is very important we can correctly model the moisture absorption property. In this study, moisture absorption and desorption properties of three kinds of package materials were investigated. Moisture absorption equilibrium weight gain and diffusion coefficient at different temperature and different humidity are characterized. Moisture absorption processes are simulated using a 3D model at conditions according to the moisture sensitivity test levels. Finally moisture absorption is verified by our research carrier.

Characterization of moisture properties of polymers for IC packaging

In this paper we determined the water uptake of a die attach and a molding compound. The two types of polymer which were selected are a die attach filled with silver particles and an epoxy molding compound filled with silica particles. The water absorption is carried out in an adjustable thermal and humidity chamber, SGA-100, at different temperatures and humidity levels. Moisture absorption equilibrium of test data were obtained by experiment. The moisture absorption equilibrium prediction equation was modeled by using the extrapolated experimental data. Diffusion coefficients at different temperature were obtained from the moisture absorption experiments.

A new method to measure the moisture expansion in plastic packaging materials

Moisture induced failure in plastic encapsulated packages is one most important failure mechanisms in microelectronics. This failure is driven by the mismatch between different material properties, such as CTE, CME (Coefficient of Moisture induced Expansion) caused by moisture absorption in plastic packaging materials. Therefore, it is important to know moisture effects on mechanical properties of plastic packaging materials, especially CME. Moisture induced expansion can be calculated using ε = β · c, here ε is the strain, β is the CME and C is the moisture concentration. Traditionally using the combined TGA (Thermal Gravimetric Analyzer)/TMA (Thermal Mechanical Analyzer) technique, the CME of plastic packaging materials is characterized. TGA is used to measure the weight change and TMA is used to measure the length change. By combining both the TMA and TGA measurements, the CME can be determined. This method is often used in industry and it is observed that the CME value is often over estimated. In order to get precise CME values a high precision DMA (Dynamic Mechanical Analyzer) is used to measure the length change of a sample while a humidity generator is used to regulate the relative humidity. Therefore, temperature and relative humidity are controlled in the DMA chamber and can be used to measure the length change under different relative humidity conditions. CME values measured by the DMA plus humidity method are much lower than that of the TGA/TMA method. In order to find out which method is more reliable, a third experiment was done. A bi-material sample is created to verify our measured CME value. TDM equipment (oven + camera system to detect vertical displacement of the sample) is used to measure the warpage of the bi-material sample. Using our measured CME value, finite element model simulation result shows that the hygro-mechanical warpage of the model fits well with TDM test result.

Characterization and Modeling of Moisture Absorption of Underfill for IC Packaging

Underfill is a highly particle filled epoxy polymer used in flip chip to fill the gap between the leadframe and die or between die and die. In order to be able to flow in the thin gap, the silica filler particle must have a diameter below 10 mum. This epoxy underfill material mechanically couples the chip and substrate and decreases the stress in the solder joints, therefore enhancing solder fatigue life. Good adhesion between the epoxy underfill and the surface of solder ball, silicon chip, and substrate is necessary to minimize stress in a package. Use of the non-hermetic material does raise a potential concern, i.e. moisture induced interfacial delamination and moisture expansion may cause failure. In this study, moisture absorption and desorption properties were investigated, such as moisture absorption equilibrium weight gain and diffusion coefficients at different temperature and different humidity are tested and characterized, moisture absorption and desorption kinetics are tested and fitted.

Moisture effects on a system in package carrier

Moisture induced failures in the plastic encapsulated packages are one most important failure mechanisms in microelectronics. These failures are driven by the mismatch between different material properties, such as CTE, CME (Coefficient of Moisture induced Expansion) and degradation of interface strength caused by moisture absorption of polymer materials. Therefore, it is critical to know how much moisture exists in packaging materials, the moisture distribution in the package and hygro-mechanical effects on the package. In this paper moisture diffusion, moisture distribution and hygro-mechanical effects are simulated at the following conditions: 85°C/85%RH, 60°C/60%RH and 85 °C/dry, 60 °C/dry using 2D SiP(System in Package) finite element model.

Fast qualification using thermal shock combined with moisture absorption

Time to market is becoming one of the most important factors because of the fierce market competition. However, traditional reliability and interface toughness characterization tests take very long time. For example, moisture sensitivity level assessment (MSL1) will take 168 hours pre conditioning at 85°C/85%RH and tradition thermal cycling takes even longer time. The long preconditioning times are chosen to ensure that also the thicker sections of a package are completely saturated. Thinner package, however, are already saturated after one to two days. In this study, we therefore investigated whether it would be possible to speed up the qualification process by shortening the preconditioning time. We focus in particular on the interface toughness. From our four point bending test and analysis, it is found that temperature has great effects on the interface toughness and moisture also has small effects on the interface toughness. In order to do the fast qualification test, thermal shock cycling tests combined with moisture absorption are performed. Experiments show that moisture can speed up the delamination.

Effect of aging of packaging materials on die surface cracking of a SiP carrier

Generally, the viscoelastic properties of packaging materials used in the simulation models are obtained from the materials after postcuring. However these properties were observed to change during humidity conditioning and the thermal cycling. Two kinds of packaging materials are tested, one is molding compound and another is underfill. All samples are cured according to the curing procedure, postcured at 180degC. Before the test, first the samples are pre-dried at 125degC for 24 hours and then preconditioned at 60degC/60%RH for 40 hours. Secondly, one reflow at 260degC. Finally, all samples are subjected to thermal cycling. Thermal cycling temperature range is from -65degC to 150degC and every cycle is finished in 30 minutes. For the DMA test, a TA Instrument Q800 is used. Test results show the glass modulus, rubber modulus and glass transition temperature increase with the number of thermal cycles. This change in materials after humidity and thermal treatment is here referred to as aging. The finite element software Marc is used to simulate the internal change of stress and displacement. The simulation result shows that the total warpage has increased a little at the corner of passive die, which is where the critical cracks and crazes were found in our qualification tests. And the Von Mises stresses increase after thermal cycling.

Characterization and Modeling of Thin Film Interface Strength Considering Mode Mixity

Interfacial delamination is a common cause of failure in microelectronic packages. Characterization and prediction of interface behavior in manufacturing, testing and application conditions is demanded in order to reduce development times and costs of IC packages. In the design processes of microelectronics, possible interface delamination is evaluated by the critical energy release rate to detach the materials. This critical energy release rate can be obtained experimentally using various approaches. However, its measurement is complicated due to the fact that adhesion strength is not only temperature and moisture dependent but also stress state (mode mixity [1]) dependent. This paper describes our efforts on interface characterization as a function of mode dependency. A new test setup is designed and built. It allows transferring two separated loads on a single specimen. The test methodology that is developed in this paper is also able to evaluate the interfacial fracture toughness as function of temperature and moisture. The crack length, necessary for calculation of the energy release rate is measured by means of an optical microscope. Finite element simulation is used to interpret the experimental results and thus to establish the critical energy release rates and mode mixities.

The mechanical influence of the porosity and nano-scale pore size effect of the SiOC(H) dielectric film

We propose a molecular modeling method which is capable of modeling the mechanical impact of the porosity and pore size to the amorphous silicon-based low-dielectric (low-k) material. Due to the electronic requirement of advanced electronic devices, low-k materials are in demand for the IC backend structure. However, due to the amorphous nature and porosity of this material, it exhibits low mechanical stiffness and low interfacial strength, as well as inducing numerous reliablity issues. The mechanical impact of the nano- scaled pore, including the porosity ratio and pore size, is simulated using molecular dynamics on the mechanical stiffness and interfacial strength. A fitting function is formulated based on the continuum homogenour theory and atomic interaction in nano-scale. The simulation results are fitted into analytical equation based on the homogenous theory.

The chemical-mechanical relationship of the SiOC(H) dielectric film

We propose an atomic simulation techniques to understand the chemical-mechanical relationship of amorphous/porous silica based low-dielectric (low-k) material (SiOC(H)). The mechanical stiffness of the low- k material is a critical issue for the reliability performance of the IC backend structures. Due to the amorphous nature of the low-k material which has till now unknown molecular structure, a novel algorithm is required to generate the molecular structure. The molecular dynamics (MD) method is used as the simulation tool. Moreover, to understand the variation of the mechanical stiffness and density by the chemical configuration, sensitivity analyses have been performed. A fitting equation based on homogenization theory is established to represent the MD simulation results. The trends which are indicated by the simulation results exhibit good agreements with experiments from literature. Moreover, the simulation results indicate that the slight variation of the chemical configuration can induce significant change of the mechanical stiffness (over 80%) but not the density.