In the wire bonding process of microelectronic packaging,heat affect zone(HAZ)is an important factor governing the loop profile of bonding.The height of loop is affected by the length of the HAZ.Factors governing the HAZ were studied.To investigate this relationship,experiments were done for various sizes of wire and free air ball(FAB).Electric flame-off(EFO)current, EFO time,EFO gap and recrystallization were also studied.The results show that as the size of FAB becomes larger,the length of HAZ increases.With the increase of EFO current and time,the length of HAZ becomes longer.When FAB forms at the same parameter the length of HAZ becomes shorter with the high temperature of recrystallization. In the wire bonding process of microelectronic packaging, heat affect zone (HAZ) is an important factor governing the loop profile of bonding. Height of loop is affected by the length of the HAZ. Factors governing the HAZ were studied. To investigate this relationship , experiments were done for various sizes of wire and free air ball (FAB). Electric flame-off (EFO) current, EFO time, EFO gap and recrystallization were also studied.The results show that as the size of FAB becomes larger, the length of HAZ increases.With the increase of EFO current and time, the length of HAZ becomes longer. WF Forms at the same parameter the length of HAZ becomes shorter with the high temperature of recrystallization.