| 摘要: | 探討Sn-Ag-Cu無鉛銲料與Au/Ni基板表面處理層(surface finish)之間的反應是非常複雜的。因為其中包含了（1）不同的銲錫球球徑760、500、300微米（2）搭配著不同孔徑的銲墊600、425、250微米（3）銲墊上方不同厚度的Au表面處理層0、0.6、3微米（4）不同的銲錫球組成Sn-3Ag-xCu，X= 0.3 ~ 0.7（5）兩種迴銲時間，共五大類的變因。 本研究的結果顯示，工業界慣用的銲料與基板在銲接過程中，銲料所具有的Cu濃度，依然是左右界面反應的重要角色。即使微量改變銲料的Cu濃度，將會使界面上呈現不同的介金屬種類與生長型態。當Cu濃度由0.3 wt.%逐漸增加至0.7 wt.%，迴銲後界面生成物與型態將由單一的Ni3Sn4相，轉變為Ni3Sn4與Cu6Sn5共存，再轉變為單一的Cu6Sn5相。Cu些微改變，界面反應截然不同。 銲墊上Au/Ni表面處理層的Au厚度也對銲接反應有重要的影響。當Au表面處理層厚度為3 微米時，造成Sn-3Ag-0.4Cu反應界面，產生大量Cu6Sn5相介金屬剝離情形，此現象於三種不同大小的銲錫球與銲墊搭配均會發生，且不論反應時間為90或300秒。由此可見，過厚的Au層將會造成介金屬脫離界面，並間接使得銲點可靠度發生問題。 值得一提的是，即使銲墊上方Au層厚度薄如0.6微米，也會使得直徑300微米的銲錫球，於90秒迴銲後，界面處介金屬中產生許多清晰可見的孔洞。這些孔洞被銲料所填滿，並隨著反應時間增長而變大。相信只要施以足夠的反應時間，孔洞上方的介金屬層也會完全脫離界面而進入銲料內部。 上述結果顯示，介金屬剝離的現象會隨著Au層厚度的增加而趨於嚴重。且隨著銲點縮小，即便Au層厚度保持不變，也會使得銲料中具有相對較高的Au濃度，Au濃度越高越容易致使介金屬剝離。因此由本實驗結果可以得知，為了確保銲點的品質，對於銲料組成的選擇，以及Au表面處理層厚度的控制應該要非常謹慎。為了避免此介金屬剝離現象的發生，銲接反應時應注意（1）盡量使用Au層厚度較薄的表面處理層，（2）盡量選用Cu濃度較高的銲料，避開剝離反應發生的區間，（3）以最短但容許範圍內的迴銲時間進行迴銲。 The soldering reactions between the Au/Ni surface finish and several Sn-3Ag-xCu (x= 0.3, 0.4, 0.5, 0.6, and 0.7 wt. %) solders were investigated. The varied volume of the solder balls with 760, 500 and 300 µm diameter were used on the 0, 0.6 and 3 µm thick Au lay having a circular area with 600, 425 and 250 µm. It was found that interfacial reactions were controlled by a number of factors, including the concentration of Au and Cu, the reflow time, and paired the solder volume and pad area. With increasing Cu concentration, the reaction product at the interface switched from Ni3Sn4-based to Cu6Sn5-based + Ni3Sn4-based, then to Cu6Sn5-based. In addition, the Au thickness was found to have a strong influence on the microstructures of the reaction products. After Sn-3Ag-0.4Cu solder ball reflowed on a 3 µm Au layer at 235°C for 90 sec, a Cu6Sn5-based layer had departed from the solder/pad interface and moved towards the solder joint. In addition, a layer of solder located between detached Cu6Sn5-based and adhered Ni3Sn4-based layer. Similar phenomenon occurred on smaller size of solder as 500 and 300 µm. It deserved to be mentioned that even 0.6 µm-thick Au layer can cause a series voids formed between (Ni, Cu)3Sn4 and (Cu, Ni, Au)6Sn5 layers at the interface. Due to production of Au concentration had been raised over an unsafe level. These voids indeed weaken the Sn-3Ag-0.4Cu solder joints and lead serious reliability problem further. As the device size shrinks, precise control of solder composition and thickness of surface finish should be more critical. |
