本實驗為了簡化碲化鉍系熱電材料之元素種類來評估熱電模組中銲點的可靠度，選用純碲做為基材，將Ni-P及Ni-P/Co-P擴散阻障層以無電鍍製程鍍在基材上，與銲料接合後觀察界面反應。Ni為常用於電子構裝中作為擴散阻障層之材料。Sn/Ni-P/Te擴散偶中界面主要生成Ni3Sn4、Ni2SnP 、Ni3P及NiTe介金屬化合物，NiTe介金屬化合物生成所需活化能為70.9 kJ/mol。Sn/Ni-P和Ni-P/Te界面皆生成Ni3P，Ni3P層中生成大量的柱狀孔洞。Ni-P/Te界面的孔洞數量大於Sn/Ni-P界面，因為Ni-P/Te界面Ni不平衡之交互擴散通量較大所造成的結果。為了改抑制Ni-P/Te界面的柱狀孔洞，本實驗將Co-P鍍在Ni-P/Te的中間觀察Sn/Ni-P/Co-P/Te擴散偶之界面反應。Sn/Ni-P/Co-P/Te擴散偶在本實驗之退火條件下，Co-P/Te界面沒有生成Co-Te化合物。180℃退火240小時後在Co-P/Te界面生成極薄的Ni-Te化合物，目前尚無法確認Ni是經由何種擴散路徑穿過Co-P層擴散到Co-P/Te界面與Te反應生成Ni-Te化合物。比較NiTe及CoTe2在450K下的自由能發現，NiTe比CoTe2來的穩定。Co-P/Te界面並沒有觀察到Ni3P及孔洞的生成，代表Co可以有效抑制Ni3P、Ni-Te化合物及孔洞的生成，改善附著及銲接品質。To simplify the element of bismuth telluride thermoelectric materials, the experiments reported in this study used Te as the substrate to evaluate the capability of Ni as a diffusion barrier. Ni-P or Ni-P/Co-P was coated on Te by electroless plating and then jointed to observe interfacial reaction with Sn solder. Ni has been widely used as a diffusion barrier between Sn-based solder and chip in electronic industry. Ni3Sn4, Ni3P, and NiTe are the major compound layers formed at the Sn/Ni-P /Te interfaces. The apparent activation energy of NiTe in a Ni-P/ Te system is 70.9 kJ/ mol. The Ni3P layers formed both at the Ni/Sn and Ni/Te interfaces, with columnar voids embedded in Ni3P. The number of columnar voids at the Ni/Te interface is greater than that at the Ni/Sn interface. The larger Ni flux caused a greater unbalance interdiffusion and induced more voids formed at the Ni/Te side. To inhibit the flux of Ni toward the Te side, a layer of Co was selected as the diffusion barrier. The Co-P was electroless plated between the Ni and Te substrate. In Sn/Ni-P/Co-P/Te couple, Co-Te IMC was not found between Co-P and the Te interface at all annealing temperatures. A very thin Ni-Te IMC layer formed between Co-P and Te at 180℃ for 240 h. At 450 K, the formation Gibbs free energy of NiTe and was -1.78 kJ/mol and lower than that of CoTe2 was -0.86 kJ/mol, suggesting that the formation of Ni-Te IMC was energetically favorable. At all annealing temperature, Ni3P and columnar voids did not appear at the Ni-P/Co-P/Te interface. These results prove that Co is an effective diffusion barrier suppressing the growth of Ni3P and thereby preventing voiding problems. Finally, the Co-P barrier enhanced the quality of the solder joint because it suppressed the formation of Ni-Te IMC and large voids.
