It is reported that DELO has developed a new method to improve the process performance of fan-out wafer-level packaging (FOWLP). Feasibility studies have shown that using UV-curable molding materials instead of traditional heat-curing materials can significantly reduce warpage and die shift. In addition, the method speeds up the curing time and effectively reduces energy consumption.
Warpage and chip drift are common problems in fan-out wafer-level packaging. As a cost-effective way to package semiconductors, FOWLP integrates multiple chips on a single carrier. Despite advances in fan-out packaging at the wafer and panel levels, these issues persist in traditional compression molding processes.
One of the causes of warpage is that during the cooling phase of the molding process, liquid compression molding compounds (LCMs) can deform due to chemical shrinkage. Another reason is the difference in coefficient of thermal expansion (CTE) between silicon chips, mold materials, and substrates. Similarly, chip drift can also occur during high-temperature and high-pressure molding, as paste-molded materials with high fill loads need to be molded at higher temperatures and pressures. Temporarily bonded chips can cause the adhesive to soften at high temperatures, weakening the immobilization effect on the chip, while the high pressure of the molding material can also exert thrust on the chip.
Figure: DELO develops a new UV-curable encapsulation material
To solve these problems, DELO conducted a feasibility study using a model system in which the analog chip was adhered to a carrier substrate. After the substrate is coated with a temporary adhesive, the chip is placed on the carrier. It is then molded using a low-viscosity DELO material and cured by UV light to remove the carrier. Typically, this type of application requires the use of highly viscosity, heat-curing molding materials.
DELO compares the warpage performance of thermal-curable and UV-curable encapsulants. The results show that significant warpage occurs when the conventional molding material is heat-cured and then cooled. As a result, switching to UV curing can be done at room temperature without the need for heat treatment, significantly reducing warpage caused by CTE mismatch between the mold material and the carrier.
Another advantage of UV-curable materials is the reduced filler content, which reduces viscosity and Young's modulus. In testing, one of DELO's model adhesive systems achieved a viscosity of 35,000 mPa · and a Young's modulus of 1 GPa. This significantly reduces the risk of die drift, as there is no need for high temperatures or pressures to disperse the molding material. In contrast, conventional compounds have viscosities of about 800,000 mPa · and Young's modulus in the double-digit range.
Overall, this study demonstrates that UV-cured, large-area molding materials are effective in reducing warpage and die shift in chip-first fan-out wafer-level packaging. Although there are significant CTE differences between materials, the process is highly adaptable because it does not involve temperature changes. In addition, UV curing reduces curing time and energy consumption.
DELO will be presenting this research and other adhesive solutions for advanced packaging at the SEMICON Europa trade fair in Munich from November 12 to 15, 2024.
