本研究所使用的 C194 合金成分為: Cu-2.35 wt.% Fe-0.07 wt.% P-0.12 wt.% Zn，C194 合金為目前常做為導線架使用之銅合金，其多用於 100 pins 以下之引腳數，其優點有高強度、高電導率、細晶結構、高抗腐蝕性、優秀的銲接性、高抗軟化性等。雖然 C194 被廣泛應用，但並未有在 C194 上電鍍鎳和無鉛銲錫進行界面反應之研究。因此，本研究目的在探討其液/固界面反應，以判斷在 C194 上鍍鎳的最佳厚度。
本實驗使用 Sn 作為銲料，Sn 銲料為最常使用的基礎銲料，其優點在於適用較高溫環境、優良的可銲性、良好的濕潤性以及極低的成本等。本研究中，在 C194/Sn 界面電鍍一層 Ni，電鍍 Ni 層的目的在於可作為 C194/Sn 界面的擴散阻障層，因 Ni 和 Cu 交互擴散不會形成介金屬相 (intermetallic compound, IMC)，且 Ni 和銲料的反應速率相較於 Cu 和銲料的反應速率較低，能減緩銲點之間的界面反應。因此，本研究探討了 Sn 銲料與三種不同厚度的 Ni (1、3 和 5 µm) 電鍍在 C194 合金基材之間的界面反應，並判斷何種厚度的 Ni 層有最好的最佳厚度。在 240、255 和 270 °C 迴銲溫度下，使用液體/固體反應耦合，迴銲時間範圍設定在 30 到 480 秒。樣品製備完畢後使用掃描式電子顯微鏡並搭配能量散射光譜儀來觀察並探討不同迴銲條件下 IMC 的種類、形態和組成。此外，基於不同迴銲條件下 IMC 的厚度，更深入探討了反應機制和生長速率常數。
研究結果顯示，若 Ni 未因迴銲形成 IMC 消耗完畢，則界面形成的 IMC 為 (Ni, Cu)3Sn4 相。迴銲溫度為 240 °C，迴銲時間到 360 秒 ，則電鍍 1 µm Ni 層的樣品其 Ni 層會因和 Sn 迴銲形成介金屬相而消耗完畢，在界面處形成 (Cu, Ni)6Sn5 相，若迴銲溫度上升為 255 °C，則在迴銲時間 60 秒電鍍 1 µm Ni 層的樣品就發現 Ni 層和 Sn 迴銲形成介金屬相而消耗完畢，在界面處形成 (Cu, Ni)6Sn5 相，而迴銲溫度上升至 270 °C，電鍍 1、3 µm Ni 層的樣品，迴銲時間分別為 30、480 秒，發現 Ni 層和 Sn 迴銲形成介金屬相而消耗完畢，在界面處形成 (Cu, Ni)6Sn5 相。經由結果發現，當迴銲溫度相同，樣品電鍍越厚的 Ni，形成 (Cu, Ni)6Sn5 相的時間會越晚。在 240、255、270 °C下，若 Ni 層在迴銲中未消耗完畢，則形成的 IMC 為 (Ni, Cu)3Sn4 相。隨著迴銲時間和溫度增加， IMC 厚度也會上升，且 (Ni, Cu)3Sn4 相上升的幅度比 (Cu, Ni)6Sn5 相更低。本研究中，除了 240 °C Sn/Ni(1 μm)/C194 迴銲時間 240 - 480 秒外，其餘不同迴銲條件的介金屬相厚度與迴銲時間之平方根皆呈線性關係，探討 IMC 成長機制可發現為擴散反應控制。在電性的分析中可以發現，若該樣品形成的 IMC 為 (Cu, Ni)6Sn5 相，相較於形成 (Ni, Cu)3Sn4 相的樣品，基材到銲料之間的電阻值較高。而若樣品形成的 IMC 都為同一種 IMC，當迴銲時間增加或迴銲溫度上升，IMC 的厚度上升，從基材到銲料之間的電阻值也會上升。若形成的 IMC 都為(Ni, Cu)3Sn4 相，當迴銲時間和迴銲溫度皆相同，電鍍越薄 Ni 層的樣品其電阻值較高。

The composition of the C194 alloy used in this study is Cu-2.35 wt.% Fe-0.07 wt.% P-0.12 wt.% Zn. C194 alloy is commonly used as a copper alloy for lead frames, particularly for pins numbering less than 100. Its advantages include high strength, high electrical conductivity, fine grain structure, high corrosion resistance, excellent solderability, and high softening resistance. Although C194 is widely used, there has been no research on the interfacial reactions of nickel electroplating and lead-free soldering on C194. Therefore, the purpose of this study is to explore the liquid/solid interfacial reactions to determine the optimal thickness of nickel electroplating on C194.
In this experiment, Sn was used as the solder. Sn solder is the most commonly used base solder due to its suitability for higher temperature environments, excellent solderability, good wettability, and very low cost. In this study, a layer of Ni was electroplated on the C194/Sn interface. The purpose of electroplating the Ni layer is to act as a diffusion barrier at the C194/Sn interface since Ni and Cu do not form intermetallic compounds (IMCs) through mutual diffusion. Additionally, the reaction rate between Ni and the solder is slower compared to that between Cu and the solder, which can slow down the interfacial reaction between the solder joints. Therefore, this study investigates the interfacial reactions between Sn solder and three different thicknesses of Ni (1, 3, and 5 µm) electroplated on C194 alloy substrates to determine the optimal thickness of the Ni layer.
Reflow temperatures of 240, 255, and 270 °C were used with liquid/solid reaction couples, and reflow times ranged from 30 to 480 seconds. After sample preparation, a scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS) was used to observe and analyze the types, morphologies, and compositions of IMCs formed under different reflow conditions. Additionally, based on the thickness of the IMCs under different reflow conditions, the reaction mechanism and growth rate constants were further investigated.
The results show that if the Ni layer is not completely consumed by forming IMCs during reflow, the IMC formed at the interface is (Ni, Cu)3Sn4. At a reflow temperature of 240°C, the Ni layer of the sample with 1 µm Ni is completely consumed by forming IMCs after reflowing for 360 seconds, forming (Cu, Ni)6Sn5 at the interface. If the reflow temperature is increased to 255°C, the Ni layer of the sample with 1 µm Ni is consumed after 60 seconds, forming (Cu, Ni)6Sn5 at the interface. When the reflow temperature is further increased to 270°C, the Ni layers of the samples with 1 µm and 3 µm Ni are consumed after 30 and 480 seconds, respectively, forming (Cu, Ni)6Sn5 at the interface. The results indicate that at the same reflow temperature, the thicker the electroplated Ni, the later the formation of (Cu, Ni)6Sn5. At 240, 255, and 270 °C, if the Ni layer is not completely consumed during reflow, the formed IMC is (Ni, Cu)3Sn4. As reflow time and temperature increase, the thickness of the IMC also increases, with the increase in (Ni, Cu)3Sn4 thickness being lower than that of (Cu, Ni)6Sn5.
In this study, except for the 240°C Sn/Ni (1 μm)/C194 reflow for 240 - 480 seconds, the thickness of the IMCs under different reflow conditions showed a linear relationship with the square root of the reflow time, indicating that the reaction mechanism is diffusion-controlled. In the electrical analysis, it was found that samples with (Cu, Ni)6Sn5 IMC had higher resistance between the substrate and the solder compared to those with (Ni, Cu)3Sn4 IMC. Furthermore, if the IMCs formed are of the same type, an increase in reflow time or temperature results in a thicker IMC, leading to higher resistance between the substrate and the solder. If the formed IMCs are (Ni, Cu)3Sn4, samples with thinner electroplated Ni layers have higher resistance under the same reflow time and temperature.

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