電子封裝銀合金線之電遷移與退火晶粒結構研究

Abstract

經由抽線和退火製程的改善，可以產生大量退火雙晶的銀金鈀線，在600℃時效180分鐘，退火雙晶銀金鈀線幾乎保持相同晶粒大小，擁有很高的熱穩定性，晶粒含雙晶比例更可達到65%，遠高於傳統的銀金鈀線材以及純金線、純銅線。此高退火雙晶比例使其在高溫處理後仍擁有良好的抗拉強度、降服強度、延展性，均高於傳統銀金鈀線，且不會降低其導電率。 此新穎的退火雙晶銀金鈀線，線徑17.5μm可承受0.3A電流達61小時，遠高於傳統銀金鈀線材的25小時，達兩倍以上壽命。此結果可歸因於退火雙晶強化，及線材通電時，產生之特殊階梯狀結構和表面再建構形貌導致。此表面再建構由電子風力驅動所造成的主滑移及垂直方向的次滑移，造成了原子堆積並產生hillock。而此線材通電不同時間後，破壞強度及延展性均高於傳統銀金鈀線。這些優越的性質，使退火雙晶銀金鈀線極具潛力取代現有的4N金線以及傳統銀金鈀線，作為打線接合的封裝銲線。 而若降低金或鈀的比例，除了可降低電阻外，更可以提高通電測試的壽命，不含金的銀鈀線材，通電壽命超越銀金鈀線材，這是由於銀本身具良好導電導熱性，提高了通電時的散熱效果，降低焦耳熱及溫度，進而阻止電遷移現象發生。雖然純銅具有更好的導電導熱性，然而即使是較耐腐蝕的銅鍍鈀線，其抗氧化力仍然極差，在室溫通電會產生氧化現象，使局部電流密度大增而提早斷裂。 然而降低金或鈀的比例，也會影響熱穩定性，使其晶粒在高溫時會略微增大。但除非使用純銀，不然即使在600℃時效120分鐘，其晶粒仍然不會成長到接近線徑。由於擁有高抗電遷移性和優於現有線材的熱穩定性，銀鈀線材亦是極具潛力的封裝銲線。

The Ag-8Au-3Pd wire can achieve enrichment of annealing twins by improvement of drawing and annealing processes. It remains almost the same grain size during aging at 600℃ for 180 minutes, thus possesses high thermal stability. Besides, the twinned-grain percentage of this wire reachs 65%, more than conventional Ag-8Au-3Pd wire, gold wire and copper wire. After high temperature storage, this wire still has higher tensile strength, yield stress, elongation than conventional Ag-8Au-3Pd wire, keeping high electrical conductivity meantime. This innovative annealing-twinned Ag-8Au-3Pd wire with diameter of 17.5 μm can sustain 0.3A for 61 hours, which is much higher than conventional Ag-8Au-3Pd wire’s 25hours, reaching more than twice the life. This result can be attributed to the annealing twins’ strengthening effect, the stepwise structure and reconstruction during curren stressing. The reconstruction is produced by primary slip and perpendicular secondary slip, the two directional slips result atom pile up and generate hillock. Theis annealing-twinned Ag-8Au-3Pd wire possesses higher tensile strength and elongation than conventional Ag-8Au-3Pd wire with different current stressing time. Since these superior properties, this annealing-twinned Ag-8Au-3Pd wire has potential to replace the existing gold and conventional Ag-8Au-3Pd bonding wire. The conducitivity and lifetime during current stressing can be increasd by reducing the addition of Au or Pd. The AgPd wire having much higher lifetime than annealing-twinned Ag-8Au-3Pd because silver possess high electrical and thermal conductivity, lower the Joule heating and temperature during current stressing, retarding the electromigration. Although pure copper has higher electrical and thermal conductivity than silver alloy, the most anti-corrosive CuPd wire oxidate during current stressing at room temperature, leading to a higher local current density and breaking at early stage, having a lowest lifetime. However, reducing the addition of Au or Pd also decreases the thermal stability of wire, leading to a larger grain size after high temperatre storage. However, the silver bonding wires’ grain sizes are still smaller than wire diameter after aging at 600℃ for 120 minutes, except pure silver wire. Owing to high resistance to electromigration and better thermal stability, the Ag low Pd wire also has potential to replace existing bonding wires.