A method for bonding an LED assembly (71) or other electronic package (31) to a substrate PCB containing a heat-sink (52), which utilizes layers of reactive multilayer foil (51) disposed between contacts (32, 34) of the electronic package 31 and the associated contact pads (55) on the supporting substrate PCB. By initiating an exothermic reaction in the reactive multilayer foil (51), together with an application of pressure, sufficient heat is generated between the contacts (32, 34) and the associated contact pads (55) to melt adjacent bonding material (54) to obtain good electrically and thermally conductive bonds between the contacts 32, 34 and contact pads (55) without thermally damaging the electronic package (31), heat-sensitive components (35) associated with the electronic package (31), or other the supporting substrate PCB.