RESUMEN
Composite laminates utilizing autoclave-grade carbon fiber-reinforced plastic (CFRP) prepreg were manufactured using a polymer nanoporous network (NPN) interlayer that generates capillary pressure in lieu of pressure from an autoclave. The polymer nanofiber NPN film is integrated into the interlaminar region and is shown to eliminate voids in a vacuum-bag-only (VBO) curing process. After a preliminary investigation of the effect of NPN thickness on the interlaminar region and performance, an 8 µm thick polymer NPN was selected for a scaled manufacturing demonstration. Combining the polymer NPN with "out-of-oven" (OoO) electrothermal heating of a carbon nanotube (CNT)-heated tool, a 0.6 × 0.6 m void-free plate is successfully manufactured. OoO cure enables an accelerated cure cycle, which reduces the cure time by 35% compared to the manufacturer-recommended cure cycle (MRCC). X-ray microcomputed tomography (µ-CT) reveals that the laminates are void-free and of identical quality to autoclave-cured specimens. An array of mechanical tests including tension, compression, open-hole compression (OHC), tension-bearing (bolt-bearing), and compression after impact, reveal that the accelerated NPN-cured composites were broadly equivalent, with some instances of improved properties, relative to the autoclave-cured parts, e.g., OHC strength increased by 5%. With reduced capital costs, energy consumption, and increased throughput, the facile polymer NPN-enabled out-of-autoclave (OoA) fabrication method is shown to be a practical and attractive alternative to conventional autoclave fabrication.
RESUMEN
Semiconductor packaging based on an epoxy molding compound (EMC) currently has several disadvantages including warpage, limited processing area, and variability that all negatively affect cost and production yield. We propose a facile EMC molding process method using a flash electro-thermal carbon fiber heating (FE-CH) device based on carbon fiber-based papers to manufacture an EMC molded to a copper substrate (EMC/Cu bi-layer package) via Joule heating, and using this device, a modified cure cycle that combines the conventional cure cycle (CCC) with rapid cooling was performed using FE-CH to reduce the curvature of the EMC/Cu bi-layer package. Compared to the conventional hot press process, which uses 3.17 MW of power, the FE-CH process only uses 32.87 kW, resulting in a power consumption reduction of over 100 times when following the CCC. Furthermore, the FE-CH-cured EMC/Cu bi-layer package exhibits mechanical properties equivalent to those of a hot press-cured specimen, including the degree of cure, elastic modulus, curvature, bonding temperature, residual strain, and peel strength. The modified cure cycle using the FE-CH results in a 31% reduction in residual strain, a 32% reduction in curvature, and a 47% increase in peel strength compared to the CCC, indicating that this new process method is very promising for reducing a semiconductor package's price by reducing the process cost and warpage.
RESUMEN
Semiconductor packaging continues to reduce in thickness following the overall thinning of electronic devices such as smartphones and tablets. As the package becomes thinner, the warpage of the semiconductor package becomes more important due to the reduced bending stiffness and driven by thermal residual stresses and thermal expansion mismatch during the epoxy molding compound (EMC) curing to create the package. To address this packaging reliability issue, in this study, we developed a modified cure cycle that adds a rapid cooling step to the conventional cure cycle (CCC) to enhance the reliability of the EMC molded to a copper substrate (EMC/Cu bi-layer package) by lowering the bonding temperature of the EMC/Cu bi-layer package. Modeling of the package via Timoshenko theory including effective cure shrinkage allowed the rapid cooling step to be quantified and confirmed via experiments. The modified cure cycle resulted in a 26% reduction in residual strain, a 27% reduction in curvature, and a 40% increase in peel strength compared to the CCC, suggesting that this is an effective new method for managing warping effects in such packaged structures.
RESUMEN
The energy losses and geometric constraints associated with conventional curing techniques of polymeric systems motivate the study of a highly scalable out-of-oven curing method using a nanostructured resistive heater comprised of aligned carbon nanotubes (A-CNT). The experimental results indicate that, when compared to conventional oven based techniques, the use of an "out-of-oven" A-CNT integrated heater leads to orders of magnitude reductions in the energy required to process polymeric layered structures such as composites. Integration of this technology into structural systems enables the in situ curing of large-scale polymeric systems at high efficiencies, while adding sensing and control capabilities.