Solidification begins at around 219°C with the growth of primary tin (Sn) dendrites which continue to grow as the solder cools to 217°C when the remaining liquid, enriched in silver (Ag) and copper (Cu), solidifies as a eutectic. Pools of molten solder can be isolated within the network of primary tin dendrites so that when they solidify the reduction in volume has to be accommodated as a void. Voids formed in this way have an irregular shape that reflects the shape of the solidification front that formed them and, because they occupy interdendritic spaces, a high aspect ratio. If these shrinkage voids intersect the surface they can appear as a crack-like contraction cavity or shrink hole.