Cure processes optimization

Curing of Polyimlde Resin. Thermoset processing involves a large number of simultaneous and interacting phenomena, notably transient and coupled heat and mass transfer. This makes an empirical approach to process optimization difficult. For instance, it is often difficult to ascertain the time at which pressure should be applied to consolidate the laminate. If the pressure is applied too early, the low resin viscosity will lead to excessive bleed and flash. But if the pressure is applied too late, the diluent vapor pressure will be too high or the resin molecular mobility too low to prevent void formation. This example will outline the utility of our finite element code in providing an analytical model for these cure processes. 

The analysis of epoxy resins has been a particular challenge for the polymer chemist because of the complexity of the repeating units. The multitude of comonomers, the number and type of initiators, the variety of possible polymerization reactions, the insoluble nature of the product and the susceptibility of the network to hydrolysis and other types of chemical attack. Consequently there has been little knowledge of the structural basis of the physical, chemical and ultimate mechanical properties of the epoxy resins. However, it is essential that knowledge of the structures and curing processes be obtained in order to optimize the performance of the epoxy resins. 

In order to optimize each embedding material property, complete cure of the material is essential. Various analytical methods are used to determine the complete cure of each material. Differential scanning calorimetry, Fourier transform-infrared (ftir), and micro dielectrometry provide quantitative curing processing of each material. Their methods are described below. 

Polymer properties are very often dependent on the polymer preparation. So, a good monitoring of the polymerization process is the key step to obtaining good and reproducible materials. The extent of the polymerization can be controlled in different ways. IR is the most usual [27,30] but is not very accurate and requires the extraction of samples to analyze. Recently, an in situ monitoring of PMR-15 processing has been provided by means of frequency-dependent dielectric measurements [33,34]. This non-destructive technique allows the characterization of all the steps of the curing process and thus they can be optimized. 

Optimization of the cure cycle is inextricably linked to the design of processes for specific applications. Typically, this involves a clear understanding of the influence of temperature and time used to cure the thermosets. This is key to predicting resin flow and the degree of cure. Consequently, much attention has been placed on the curing process/morphology/ structure relationship of thermosets. " ... 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

There is a strong necessity to define formulations components processes conditions for nanostructured materials filled by metallic additives. Another task is optimization of components, nanocomposites and diluents combination and, in what follows, curing processes with determined temperature mode. The result of these arrangements will be materials with layerwise homogeneous metal particles/nanocomposites distribution formulation in ligand shell. 

The proposed synergetic model allows to estimate temperature boundaries of curing process reahzation and to select its optimal temperature regime. For this let us estimate system adaptabihty measure by curing temperature j as follows... 

It may be seen that hybrid numerical methods based on FE and CV concepts are able to provide necessary process analysis capability including the process optimization. Phenomena such as resin injection, resin flow, state and degree of cure as function of different process variables can be simulated. 

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