當對銅材，進行滾壓機械加工，一”表面滾壓層”會生成於其加工表面，這一薄薄的表面滾壓層性質、特性與銅塊材有顯著的不同。我們發現這一表面滾壓層會影響到銅材與焊料的溼潤性質，並且觀察到焊料在加工銅表面的溼潤性會隨著滾壓的進級率(material reduction percentage)改變。藉由溼潤性測試(wetting test)與背向式電子顯微觀察(back-scattered electron microscopy)，我們發現銅/焊料間界面反應性與溼潤性兩者之間存在對應的關係。並證實了，在高鉛銲料/銅的焊接系統下，界面反應是溼潤性的驅動力。然而，快速的反應會消耗焊料溼潤前緣的錫含量，此時因為錫含量的下降而降低溼潤的驅動力，進而抑制焊料的溼潤。同時，藉由X光繞射圖(X-ray diffraction)所得到的結構係數(texture coefficient)，我們了解到銅塊材經過滾壓後，在壓應力與剪應力的作用下，其優選方向會由原本(200)優選排列轉換至(220)優選方向，然而，在經過熱處理後會先恢復到隨機排列(random structure)方式，而在持續熱處理之後，最後恢復到(200)的優選方向。而我們也發現，銅塊材於(200)的優選方向具有較高的表面活性，進而導致了較高的反應性。最後，我們得到一個重要的結論:軟的銅塊材、高的進級率與多次的滾壓次數，會得到良好的濕潤性質。 Typically, a so-called surface rolling layer (SRL) would form on the Cu foil after mechanical process. This thin surface rolling layer has very different properties from the bulk Cu foil. We find that the thinner surface rolling layer by using the large cold-roll percentage, which affects the solder wettability on the rolled Cu. With wetting test results and BSE images, we can correlate the results of the reactivity with the solder wettability. And, we confirm that the reactivity is the driving force for wetting in high-Pb/Cu wetting solder system. The fast interfacial reaction depletes the Sn content in the wetting tip of the molten solder. As the Sn content in the wetting tip is insufficient, it is harmful for the wettability. From the XRD results and texture coefficient (TC), the preferred-orientation of the Cu raw material will transfer from (200) preferred-orientation to (220) preferred-orientation after rolling process. It is because of the compressive and the shear stress effects. Then, the Cu substrate reinstates to the random structure after annealing. Finally, the random structure will transform to the (200) preferred-orientation, as the Cu substrate is applied with a prolonged annealing. And we find that the (200) preferred-orientation has the highest surface reactivity. The higher TC of (200) will lead to the higher reactivity of the bulk Cu substrate. Finally, we conclude that: the softer Cu raw material, the higher MRP, and the higher rolling-times will lead to the better wettability.
