Predicting non-Fickian moisture diffusion in EMCs for application in micro-electronic devices

This study made an attempt to predict the temperature-dependent moisture diffusion of an epoxy molding compound with 3 different diffusion models: Fickian, dual stage and Langmuir diffusion. The Langmuir model provided the best prediction of the moisture diffusion when simulating the input experiments. Beyond the temperature range of the input experiments, the Langmuir model was still able to provide a fair prediction. Hence, the Langmuir model also provides better predictions for the moisture distribution in general. This allows for building on existing prediction models and enabling simulations of reliability tests like UHST.     

Dual stage modeling of moisture absorption and desorption in epoxy mold compounds

A dual stage diffusion model is developed in this paper for both absorption and desorption processes. Both stages in moisture absorption and desorption, i.e., Fickian and non-Fickian process, are described mathematically using a combination of Fickian terms. Absorption and desorption tests are also conducted on six distinct commercial epoxy mold compounds (EMCs) used in electronic packaging. For absorption, the samples are subjected to 85 °C/85% relative humidity and 60 °C/85% relative humidity soaking, respectively. Desorption conditions are above glass transition temperature at 140 °C and 160 °C. The dual stage models generate reasonable results for the diffusive properties and display outstanding experimental fits. All six compounds show strong non-Fickian diffusion behaviors, which are further verified by the experiments with different thicknesses. For absorption, while Fickian diffusion is dominant in the beginning of process, non-Fickian mechanism plays a large role with time increasing. Saturated moisture concentration associated with Fickian-stage diffusion appears to be independent of temperature under the tested conditions. For desorption, higher temperature leads to less percentage of the permanent residual moisture content in most compounds. At 160 °C, 90% of the initial moisture for all samples is diffused out within 24 h, following an approximate modified Fickian diffusion process. The dual stage model developed in this paper provides a mathematical formulation for modeling anomalous moisture diffusion behavior using commercial finite element analysis software.     

Moisture ingress into organic laminates

The electronic industry's most common laminates (FR-4, HTFR-4, PI, CE, and BT) were investigated for their equilibrium levels of moisture and diffusion rates and monitored for their moisture content as a function of electrical capacitance. Isothermal sorption tests were performed on the laminates to find the equilibrium moisture content in each laminate at various environmental conditions. The moisture content of each laminate was evaluated as a function of electrical capacitance via a capacitance monitoring plate attached to each laminate. A model was developed to assess the equilibrium content as a function of both temperature and humidity. Data from the sorption-time experiments was used to evaluate a diffusion coefficient for each laminate. The Fickian model was used to facilitate the evaluation. The results of the laminate moisture content analyses were subsequently applied to a printed wiring board (PWB) with a capacitor plate on each of its laminates. The capacitance method of moisture measurement in PWB shows slower moisture ingress than the theoretical moisture diffusion based on laminate experiments     

全光纤微型土壤水分含量传感器

基于掺杂光纤光热转换效应和光纤光栅测温原理研发了一种全光纤微型土壤水分含量传感器。利用1480 nm泵浦激光对埋设在土壤中的掺钴光纤加热，同时利用刻写在掺钴光纤上的布拉格光栅测定其温度变化，根据加热过程中温度特征值与含水率之间存在的线性关系实现土壤水分含量的原位测量。为了验证该方法的可行性和传感器准确度，搭建了土壤水分含量测试平台并进行实验，实验表明温度特征值与土壤含水率之间存在线性关系；且研发的全光纤微型土壤水分含量传感器所测土壤含水率与烘干法有较好的一致性，最大误差?1.41%，明显优于电导率法。这种新型的土壤水分含量测量方法具有微型化、低功耗的特点。     

Thickness-dependent non-Fickian moisture absorption in epoxy molding compounds

The objective of this research is to characterize the relationship between the moisture uptake behavior and the thickness in epoxy-based molding compounds (EMCs). Experimental results from the literature were adopted for this purpose. A thickness-dependent moisture uptake model was proposed to describe the moisture uptake behavior. In order to apply the model, a methodology to develop the fictitious Fickian curve was suggested. Subsequently, the relationships between the non-Fickian parameters and the thickness were correlated and compared. Results showed that the apparent diffusivity of the fictitious curve was sensitive to the environmental conditions but not the thickness. In addition, when combining all data, it was found that each normalized non-Fickian parameter could be described by a single equation with respect to the normalized thickness. Based on the thickness-dependent model, the moisture concentration across the thickness was further characterized. In conclusion, the model proposed in this study allows the prediction of moisture uptake behavior at various thicknesses of EMCs. This could greatly reduce the time and cost of extensive experimental works.     

Experimental and Numerical Characterization of Non-Fickian Moisture Diffusion in Electronic Packages

This study investigates moisture diffusion characteristics of electronic packaging materials exhibiting Fickian and non-Fickian behaviors. The experimental investigation involves moisture absorption and desorption tests of homogenous underfill materials and inhomogeneous organic substrates representing Fickian and non-Fickian solids, respectively. In absorption tests, samples are dried out in an oven prior to testing in a humid environmental chamber. In desorption tests, samples are saturated in an environmental chamber under a specified temperature and relative humidity prior to the moisture desorption inside an oven. Samples in both tests are removed from the test environments and weighed frequently to obtain moisture weight change data. Using the test measurements of several different Fickian and non-Fickian materials, diffusivity/moisture concentration relationships are constructed. These relationships are implemented into a customized finite element simulation tool under the ANSYS platform. This tool is validated by using the experimental measurements on multimaterial samples prepared from underfill and substrates.      

The impact of moisture in mold compound preforms on the warpage of PBGA packages

The moisture in the mold compound preforms influenced the resultant mechanical properties as well as the warpage of IC packages after the molding and post mold curing (PMC) process. Moisture will diffuse into the mold compound preforms (compound pallet) after thawing from cold room and exposing to clean room condition before molding process. The moisture will cause the package to swell, and combine with thermal stress, and finally result in the warpage of molded package after molding process. The main objective of this paper is to address the impact of moisture in the compound preforms on the warpage of the PBGA packages and explain the change in mechanical properties under different moisture conditions, e.g., the variations of the flexural modulus, T_g, and CTE with respect to moisture level. The compound preforms exposure to a clean room condition were simulated by a series of experiments. The warpage of PBGA packages were measured by the moiré test. The moisture control during the IC manufacturing process was highlighted in terms of the mechanical properties variation and warpage measurement due to the moisture effects on the mold compound preforms.     

Comprehensive treatment of moisture induced failure-recent advances

This paper describes a comprehensive treatment of moisture induced failure in integrated circuit (IC) packaging with emphasis on recent advances. This includes advanced technique for modeling moisture diffusion under dynamic boundary conditions such as experienced by packages during solder reflow, autoclave, and temperature-humidity cycling; advanced characterization technique for moisture sorption and diffusion properties of packaging materials including effect of edge diffusion on transverse diffusivity, anisotropic diffusivity in organic laminates, impact of non-Fickian sorption; advanced techniques for modeling vapor pressure during solder reflow; advanced techniques for modeling dynamic delamination propagation during solder reflow; interfacial fracture strength as a function of temperature and moisture; as well as plastic analysis of popcorn cracking.     

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.     

Diffusion of moisture through optical fiber coatings

The strength of polymer-coated fused silica optical fiber is dependent on the ambient moisture because of stress corrosion. The diffusion rate of water vapor through the polymer coating can be estimated by monitoring the strength as a function of time after suddenly changing the ambient humidity. Not only is this technique a new way of sensing humidity, but it also allows estimation of the time needed for the coated fiber to equilibrate with its environment. A comparison has been made between the diffusion coefficients measured in this way and by monitoring the weight of free-standing polymer films as a function of time. Fickian diffusion has been assumed and is justified by the good agreement between the experiment and theory. The diffusion of water vapor both into and out of various polymers was investigated     

中药水分检测系统的传感系统和采样装置设计

在中药生产过程中,中药水分含量测定是十分重要的环节,现阶段的中药水分测量需要专业人员在一定的环境内测量,操作复杂、耗时较长,从而会延误中药生产时间和降低测量精度,故本研究中设计了一种中药水分检测系统,对检测系统中的传感系统和采样装置进行了设计。传感系统采用近红外(Near Infrared,NIR)光谱技术,该技术具有快速、无损、准确的特点,可以满足测定中药水分含量的要求。采样系统设计为六自由度机械手臂,灵活方便,满足生产要求。     

一种微带谐振式含水量测量传感器设计

设计了一种用于土壤含水量测量的微带谐振环式传感器。利用仿真软件对所设计传感器进行了仿真分析,并完成了谐振环的制作及实验测量。仿真与测量结果表明,这种谐振环式含水量传感器可用于测量土壤含水量,相较传统的电容传感方法、时域反射仪传感方法等,其在测量准确性上具有优势,且体积小巧,易于安装使用。     

Modeling nonlinear moisture diffusion in inhomogeneous media

While moisture diffusion in microelectronic device and packaging has been studied for decades, the problems involving complex nonlinear moisture diffusion in multi-material assembly have not been fully studied. This paper has developed a general nonlinear diffusion model by adopting water activity, a continuous state variable, as the field variable. The generalized solubility is introduced, which is temperature- and water activity-dependent. The effective diffusivity is defined and derived in terms of generalized solubility and water activity. By comparing the water activity-based model with the existing various normalized models, the present theory can unify and generalize the current approaches. More importantly, the present model can solve both linear and nonlinear moisture diffusion in inhomogeneous material system without normalization. The commercial finite element software has been applied to solve the nonlinear generalized moisture diffusion problem using the analogy of water activity and temperature. A source code of user-defined subroutines in ABAQUS has been provided in the Appendix of the paper. The mathematical formulation and the numerical implementation method presented in this paper can be applied to any nonlinear sorption or diffusion problems in inhomogeneous material system.     

Ion transport in encapsulants used in microcircuit packaging

Most semiconductor devices are encapsulated in epoxy molding compounds. These molding compounds contain ionic contaminants including chloride ions from epichlorohydrin used in the epoxidation of the resin and bromine ions incorporated into the resin as a flame retardant. Chloride ions are known to break down the protective oxide on the surface of aluminum metallization and accelerate corrosion. The encapsulant material is hydrophilic and will absorb moisture from the environment. When the absorbed moisture is combined with ions, there is an opportunity for electrolytic corrosion to occur on the metal surfaces of the device and package elements. However, the rate of corrosion in an encapsulated microcircuit may be expected to depend upon the rate of ion transport through the encapsulant. This paper evaluates two techniques for the measurement of ion diffusion in epoxy molding compounds used for microelectronic encapsulation. The data suggests that ion diffusion rates vary with molding compound formulation, the solution pH and the ion concentration. SEM-EDX analysis and TOF-SIMS analysis indicate that the mode of diffusion of ions in the encapsulants is primarily through the polymer resin matrix as opposed to diffusion at the interface of the resin and the filler particles. Calculated diffusion coefficients were slower than the literature values for moisture diffusion or the diffusion of gases. In fact, under basic conditions, the ions tend to diffuse through the molding compound almost as a front suggesting that the ions bind to the encapsulant and that the diffusion of ions in molding compounds can be modeled using a Type II non-Fickian model.     

Multiple resolution analysis of L-band brightness temperature forsoil moisture

Passive microwave Earth observing systems provide coarse resolution data. Heterogeneity in physical characteristics will typically be present within footprints, especially over land. How this affects the development and validation of methods of retrieving soil moisture has not been verified. In this study, aircraft-based 1.4 GHz microwave radiometer data were collected sit several altitudes over test sites where soil moisture was measured concurrently. The use of multiple flightlines at lower altitudes allowed the direct comparison of different spatial resolutions using independent samples over the same ground location. Results showed that the brightness temperature data from 1.4 GHz sensor in this study region provides the same mean values for an area regardless of the spatial resolution of the original data. The relationship between brightness temperature and soil moisture was similar at different resolutions. These results suggest that soil moisture retrieval methods developed using high resolution data can be extrapolated to satellite scales     

网络式温湿度监控系统研究

提出一种基于网络的温湿度监控系统方案,选取Scnsirion公司生产的数字温湿度传感器SHT75实现温湿度测量．测量精度可编程调节,控制湿度检测精度在±4％以内,温度检测精度在±0．4℃以内;采用模糊控制技术监控温度和湿度,减少了系统的状态切换;采用ASP．NET和AJAX及VML等技术相结合实现温湿度的网络监控,实现了Internet环境的远程监控与管理方案,以及传感器测量数据的异步传输,使系统的响应速度提高了20％,对于存在多个节点和测量频率较高的领域,这种方法更能显示其优势。     

Effect of organic/inorganic coating on moisture diffusion in a chip-on-board package with globtop

The moisture diffusion in globtop material for a chip-on-board (COB) package coated with SiN_x and silicone, respectively, or coated with SiN_x plus silicone were measured by embedding a humidity sensor in the globtop and recording the capacitive change in three different temperature/humidity environments. The experimental results were simulated by Fick’s diffusion law with finite-element method modeling. The moisture diffusion coefficients and activation energies were calculated to quantitatively compare the moisture-resistance effects of different coatings. For example, at 85°C/85% RH, the moisture diffusion coefficients for the uncoated reference, SiN_x-coated, silicone-coated, and silicone/SiN_x double-layered coated samples are 1E-5, 0.8E-5, 0.7E-5, and 0.2E-5 mm²/s, respectively. The experimental and simulation results show that double-layered coating with silicone/SiN_x has excellent moisture-resistance properties because it not only smoothes the steps on a printed circuit board (PCB) but also keeps the good moisture resistance of the inorganic films.     

Advancement in simulating moisture diffusion in electronic packages under dynamic thermal loading conditions

The normalization approach has been accepted as a routine to overcome the concentration discontinuity at multi-material interfaces in the moisture diffusion simulation by the finite element method. However, applying the normalization approach directly in the commercial finite element software under a dynamic thermal loading condition, such as reflow process, may lead to erroneous results. Special techniques are needed to obtain correct results. In this study, different approaches that can deal with the moisture diffusion under dynamic thermal loading conditions were reviewed and compared with case studies. Advantages and disadvantages of each approach were analyzed and discussed. Theoretical derivation was developed to show the direct concentration approach (DCA) violates the law of mass conservation. The effect of Fourier number on the accuracy of the DCA was also examined. The internal source approach was shown to be a universal method in modeling the moisture diffusion in a multi-material system under dynamic thermal loading conditions. The newest version of ANSYS also showed good performance in solving the diffusion problem under transient thermal loadings if a proper time step size was used.