Trend Plots for Different Mold-Thick Selection on Warpage Design of MUF FCCSP with 4L ETS

Abstract

Embedded trace substrate (ETS) plays a major role in future growth of microelectronic industry, such as reduction of line and space (L/S). This is due to the low cost and reliability of plastic packages, includes not be attacked trace width during micro etching process of copper foil remove, pre-treatments of prepreg (PP) limitation and metal finished, as well as to the excellent compatibility of plastic package designs with mass production techniques. With more feasibility for copper pillar bond and higher performance for electrical conduction, ETS has high flexibility and asymmetric thickness of copper foil and solder mask enough to satisfy several serious concerns in the rapid evolution of plastic packaging technology, and one of the most critical of them is evaluated residual warpage of electronic packaging. To enhance and compare the modeling accuracy in warpage behavior, not only temperature-dependent properties but also post mold cure (PMC) temperature and associated cure shrinkage (residual strain; chemical shrinkage) for molding compound; real out of plane dimension for ETS structure; one-equivalent stress-free temperature and curing temperature for MUF all aligned at 175oC were studied for non-processing model. In this paper, we present stress conservation law of linear elasticity which have been discovered. The newly discovered conservation law is expressed solely in terms of the Hook's law, and it is genuine, non-trivial conservation law that is intrinsically different from the strain conservation law previously known. As a result, to validate the temperature-dependent warpage with a high accuracy, we found that the residual strain, process model, and stress conservation law should be considered in numerical analysis, besides applying the precise material properties. Contrarily, the effect of reality and tolerance for ETS structure dimensions are not significant, thus sometime these can be overlooked to apply mean values. For simplification of real trace patents, the properties of copper trace / foil layers with different coverage ratio can be considered by mixture rule of property. Finally, package structure with laminated-based ETS and temperature-dependent material properties were utilized in finite element-based modeling, meanwhile verified well with measured data of shadow Moire for temperature-dependent warpage. In particular, the mold-thick exerts great influence on warpage. More compound volume has been understood as the decrease in convex warpage at the time of cooling. However, compare to evaluation of different compound types, more compound volume by increasing mold-thick cannot be sufficiently explained which is dominant for warpage improvement. Thus, we have developed an comparison method for warpage improvement by trend plot, where these points described in trend plot is based on modulus-CTEeff (effective coefficient of thermal expansion) plane are derived by DMA (dynamic mechanical analysis) and TMA (thermo-mechanical analyzer) raw data of these compound types, and the results presented that selection by different compound types has 100% effective more than designed by different mold-thick of 0.29 and 0.46 mm. In this study, the non-incremental solution based on stress conservation law for evaluation of thermally induced warpage through FEA (Finite element analysis) was developed to predict the following three types of plastic packages: compound type A with 0.365mm mold-thick, compound type B with 0.4mm mold-thick and compound type B with 0.29 mm mold-thick. Furthermore, the trend plots of different thickness of mold-cap and type of compound were presented to compare which was dominant. In the comparison of compound type A with 0.375 mm mold-thick and compound type B with 0.46 mm mold-thick, the conclusion shown that package warpage at 25oC and 260oC all caused mainly by the mold-thick and secondly by the compound type. Continuously, in the case of compound type B with 0.29 mm mold-thick presented that the ultra-thin mold-cap for could full fit warpage specification below 100um while the die thickness is the same.