<p>With the progressive implementation of hybrid bonding, TCB (Thermal Compression Bonding) is evolving into a pragmatic workhorse and critical bridge technology for advanced heterogeneous integration. To further improve yield of TCB processing, underfill materials are advancing towards unlocking their potential in heat dissipation. While enhancing thermal conductivity, it is compulsory to simultaneously preserve other requirements such as electrical resistance, dielectric properties, and rheology, thus limiting the range of component materials for formulation. These considerations can be further condensed into a complex problem of composite material science with three incompatible factors: higher heat dissipation, minimum dielectricity and optimum rheology. This investigation gathers insights from prior studies, reviewing the research progress with industrial potential. Based on the needs of high-density packaging, evaluation and comparisons of various fillers is conducted. It is assessed that the hybridized addition of silica nanoparticles offers limited improvement in thermal conductivity, while the dielectric performance of aluminum oxide/nitride is inadequate, carbon-based nanomaterials face challenges such as “agglomeration,” “percolation,” and “modulus mismatch,” leading to suboptimal performance, silver nanowires demonstrate potential in characterization, but their gap-filling performance requires further investigation. In contrast, boron nitride exhibits performances comparable to silica while possessing superior thermal conductivity and, through appropriate surface modification, can overcome the flaw of “agglomeration”, making it a promising filler candidate for the development of high-performance products.</p>