| 摘要: | 電子元件上有數以千計的銲點，通常元件中最易失效的部位就在於銲點。事實上，若其中有一銲點失效，都易造成整個元件的故障。因此提高銲點的可靠性及壽命是電子業界相當重要的一個課題，故本研究也將朝這方面去執行。 擴散阻障層在銲點底層金屬（Under Bump Metallurgy, UBM）中扮演了一個相當重要的角色。目的在於避免銲料與導電基材發生反應，而導致元件失效。目前最常使用且具低消耗速率的阻障層材料為Ni。由於Ni易氧化，故還需鍍一抗氧化層（Au層）。但Au層也會引發Au會進入銲料中，生成易脆之介金屬(Au1-xNix)Sn4，而影響銲點的可靠性。因此，本論文將著重於提高銲點墊層的使用壽命，期望尋找一相較於Ni基材具有更低消耗速率之阻障層材料。由於作為一良好的擴散阻障層須具備有低的消耗速率以及良好的潤濕性質。故本研究將針對此兩項性質進行測試。 本研究藉由Ni、Co、Pt墊層與液態錫進行固/液反應，以模擬銲接時的反應。實驗結果顯示，Pt墊層的消耗速率在任何溫度及時間下均較Ni、Co墊層慢，其順序為Pt<Ni<Co。且Pt墊層之消耗厚度約為Ni墊層的1/3 ? 1/2左右。另外，界面觀察時，發現Pt/Sn系統所生成之介金屬PtSn4厚度反而比Ni/Sn系統所生成之介金屬Ni3Sn4厚。這是因為1莫耳的Pt需消耗4莫耳Sn才能生成1莫耳的PtSn4，而1莫耳Ni僅消耗4/3莫耳Sn即可生成Ni3Sn4。因此，造成所觀察到PtSn4之厚度會稍厚於Ni3Sn4。 由於擴散阻障層需具備良好之潤濕效果，因此也針對Pt基材作潤濕性測試，並且以Ni墊層當作對照組加以比較。由實驗結果中得知，不管是使用松香類助銲劑或水溶性助銲劑，Pt基材之潤濕性均較Ni基材差一些，但Pt基材之潤濕效果仍屬於許可範圍內。 由兩部分的實驗結果中顯示，Pt墊層之消耗速率僅約為Ni墊層之1/3 ? 1/2。且知Pt墊層屬於貴金屬，因此它亦具有抗氧化的作用，故使用一Pt墊層即可取代原先的Au/Ni兩層表面處理層，亦可簡化製程上的步驟。另外，雖然Pt基材之潤濕性不及Ni基材，但其潤濕性仍屬於許可範圍內。因此，由本研究結果中顯示，Pt墊層是一極具潛力之銲點墊層材料。 Solder joints are the most friable links in microelectronic devices. In fact, a failure in solder joints is the easiest root which would take the responsibility for malfunction in electronic products. Therefore, to improve the reliability of solder joints is one of the most important tasks for electronic industry. In microelectronic, optoelectronic, and MEMS packaging, the contact pads for solder usually use the Au/Ni bi-layers, such as UBM（Under Bump Metallurgy）and surface finish. The Ni layer needs to be plated an oxidation protection layer, such as Au. However Au will get into the solder and form many Au-bearing intermetallic particles, e.g.（Au1-xNix）Sn4. In addition, the Ni layer is easily to be consumed that causes the solder reacting with the conducting layer fast and results the failure of the devices as the consequence. This paper emphasized on the improvement of solder joints, whereas we probed the solder reacting with the diffusion barrier layer and measured the consumption degree of the diffusion barrier layer at different temperatures and time. In this paper, it was mentioned that the Ni, Co and Pt pads reacted with liquid tin. The results could be obtained that the consumption rate of Pt pad was slower at different temperatures and time. The order of the consumption rate was Pt<Ni<Co, then the consumption thickness of Pt pad was about 1/3 ? 1/2 of Ni pad. Moreover, it was discovered that the thickness of PtSn4 is thicker than the thickess of Ni3Sn4, because one mole of Pt required to consume four mole of Sn, and then produced one mole of PtSn4. Nevertheless one mole of Ni only consumed 4/3 mole of Sn, and then produced one mole of Ni3Sn4. As a result, it caused the thickness of PtSn4 is thicker than the thickess of Ni3Sn4. The diffusion barrier layer was considered that required better wetting. We did a wetting test for the platinum and compared with the nickel. The results showed that the wettability of the platinum was worse than the nickel, however we used RMA or water-soluble flux. But the wetting time of the platinum still is lower 5sec. Finally, we summarized the results into two parts. Firstly, it was obtained that the thickness of consumption was about 1/3 ? 1/2 of Ni pad for Pt pad. Secondly, the platinum was a noble metal which could be also considered to serve as the oxidation protection layer. Furthermore, the wettability of the platinum had an acceptable range and the wetting time was reduced when using water-soluble flux. In other words, a single Pt layer could be utilized to replace both the oxidation protection layer and diffusion barrier layer. Hence these results showed that the Pt pad had a potential to be applied for solder joints. |
