A heatsink fin is a compromise frozen in metal. Every fin adds surface area for convection, but every fin also chokes airflow, adds mass, and must carry heat away from its root before the air can take it. How that fin is manufactured decides which compromise is even possible. The dominant processes, each with its own geometric ceiling: - Extrusion: 6063-T5 aluminium billet forced through a steel die. Cheap and fast, but die tongue strength limits the fin height-to-gap aspect ratio to roughly 6:1 to 10:1 in common practice. - Bonded fin: individual fins pressed or epoxied into a grooved base. Breaks the extrusion limit, reaching aspect ratios near 40:1, at the cost of a thermal interface at every root. - Skived fin: a sharp blade slices thin layers from a solid copper or aluminium block and curls each one upright. Fin and base are one continuous piece of metal, so there is zero joint resistance. Fins well under 0.3 mm thick are routine. - Forged fin: cold forging pushes aluminium or c...