This cross-sectional view of a Flip-Chip BGA provides valuable insights into a better understanding of the relative die size. The red rectangular object represents the actual silicon die and as the arrows indicate this is the source of the heat. As electrical signals are processed through the millions of transistors within the die, heat is generated. This heat is dissipated down through the solder balls into the PCB and upwards through the heat spreader (yellow object), through the thermal interface material (gray spotted layer), and into the heat sink (black horizontal and vertical object). Eventually this heat is transferred into the ambient air surrounding the heat sink. Typically the heat flow is split with 10-20% being dissipated into the PCB and 80-90% dissipated up through the heat sink. The relatively small heat sourced area of the die (usually only 20-25% of the package area) places a demand for high thermal conductivity of the TIM. The higher conductivity TIMs such as phase-change or thermal grease do not offer any adhesive properties, and therefore they necessitate the use of additional mechanical attachment.