▁a ▁natural ▁path way ▁for ▁the ▁rejected ▁heat . ▁The ▁substr ate ▁might ▁also ▁be ▁a ▁mult il ayer ▁substr ate ▁like ▁a ▁printed ▁w iring ▁board ▁( P W B ) ▁designed ▁to ▁provide ▁a ▁high - dens ity ▁inter connect . ▁ ▁In ▁this ▁case , ▁the ▁thermal ▁conduct ivity ▁of ▁the ▁P W B ▁may ▁be ▁relatively ▁poor , ▁so ▁adding ▁thermal ▁v ias ▁( e . g . ▁metal ▁pl ugs ) ▁can ▁provide ▁excellent ▁path ways ▁for ▁the ▁rejected ▁heat . ▁ ▁App lications ▁Th erm al ▁b umps ▁can ▁be ▁used ▁in ▁a ▁number ▁of ▁different ▁ways ▁to ▁provide ▁chip ▁cool ing ▁and ▁power ▁generation . ▁ ▁General ▁cool ing ▁Th erm al ▁b umps ▁can ▁be ▁even ly ▁distributed ▁across ▁the ▁surface ▁of ▁a ▁chip ▁to ▁provide ▁a ▁uniform ▁cool ing ▁effect . ▁ ▁In ▁this ▁case , ▁the ▁thermal ▁b umps ▁may ▁be ▁inter sp ers ed ▁with ▁standard ▁b umps ▁that ▁are ▁used ▁for ▁signal , ▁power ▁and ▁ground . ▁ ▁This ▁allows ▁the ▁thermal ▁b umps ▁to ▁be ▁placed ▁directly ▁under ▁the ▁active ▁circuit ry ▁of ▁the ▁chip ▁for ▁maximum ▁effect iveness . ▁The ▁number ▁and ▁density ▁of ▁thermal ▁b umps ▁are ▁based ▁on ▁the ▁heat ▁load ▁from ▁the ▁chip . ▁ ▁Each ▁P / N ▁couple ▁can ▁provide ▁a ▁specific ▁heat ▁p ump ing ▁( Q ) ▁at ▁a ▁specific ▁temperature ▁differential ▁( Δ T ) ▁at ▁a ▁given ▁electric ▁current . ▁ ▁Tem per ature ▁sens ors ▁on ▁the ▁chip ▁(