在導電漿料製作技術中，導電金屬粉末是關鍵。對於導電漿料而言，導電粉末大多以金、銀等貴重金屬粉末為主，還有其它價格相對低的銅、鎳或鋁金屬粉末…等為輔，其中以銀導電漿料之應用最為廣泛。近幾年來由於貴重金屬價格的飆升，使得導電漿料成本增加，因此以低成本之導電金屬粉末代替貴金屬製作電子漿料已成為未來發展的趨勢，在此前提下提出了本研究論文。
本論文探討利用伽凡尼置換反應製備銀包銅粉末並製作成低燒結溫度低導電率之研究，藉由表面生成之奈米銀做為金屬銅粉接觸的黏著劑，以降低金屬銅粉接觸電阻。在低溫300℃以內及無還原氣氛下燒結，並於金屬銅粉氧化前將表面奈米銀燒結為熔融態使其包覆於金屬銅粉，不但可防止金屬銅粉之氧化及填補孔隙，亦可使導電率大幅提升及提高燒結後的緻密性。對於提升銅膏的導電率及降低燒結溫度都有極大的幫助。
綜合以上特性，若利用化學置換反應把銀析出長在銅顆粒上，就能使以銀包銅粉製備之導電膏具有以下優點：1.整體的導電率上升、2.內部的銅不被氧化、3.成本比原本只使用銀來的低、4.抗電遷移性佳、5.銅被奈米銀包覆住後，就能夠在低溫空氣下燒結而不被氧化。
銅膏導電率會隨著燒結溫度升高而增加；另一方面，低溫燒結銅膏則因含部份「不導電樹酯」導致其導電率大幅降低如表1。
本研究計畫在於提升目前低溫燒結銅膏的導電率，且克服以往製程僅限制於氮氣下燒結的困難，期望得到在低溫空氣下燒結處理之「超低溫、高導電率、低應力印刷式銅電極」。
本實驗分別測試四種硝酸銀與金屬銅粉銅粉莫耳比例：a. 0.0058 : 0.0786、b. 0.0117 : 0.0786、c. 0.0176 : 0.0786、d. 0.0235 : 0.0786，當硝酸銀與金屬銅粉莫耳數比為 0.0235 : 0.0786 時，奈米銀包覆率達到最高，形成明顯且包覆率 >90% 的奈米銀包覆結構。本實驗使用兩種溶劑，包括去離子水以及乙二醇，其中，去離子水當溶劑時置換反應會過快，無法產生均勻之奈米銀包覆金屬銅粉表面，而有機溶劑乙二醇能使置換反應速度趨於平緩，且具有分散劑效果，固有無添加分散劑，對本實驗銀包銅粉並無太大影響；整個實驗所需的反應最佳時間約為90分鐘，這時間能讓銀顆粒有足夠反應還原出來，並且在金屬銅粉的表面形成奈米銀結構。另外由表面成份分析及SEM結果可知，經由銀離子與銅離子置換反應後，其表面之奈米銀包覆比例約為 > 90% 以上，形成完整的奈米銀結構包覆銅粒子，並將包覆率最好之比例的奈米銀包金屬銅粉調成銀包銅膏，印於氧化鋁基板進行燒結，最佳實驗條件下所獲得的片電阻值為5.7x10-3 Ω/□及電阻率為5.468x10-5 Ω·cm，與相對於市售它牌低溫燒結銀膏，本實驗成功以低溫、低成本、低應力印刷之製程，獲得高導電率之銀包銅膏。

In technology of manufacturing the electrically conductive paste, the electrically conductive metallic powder is the key. For the electrically conductive paste, in addition to gold and silver powder that is often applied as the electrically conductive powder, other metallic powder with lower price like copper, nickel, or aluminum powder play a secondary role. Among those metals, silver is applied most extensively. In recent years, since the price of the precious metals soars, the cost of the electrically conductive pastes raises as well. Therefore, it has become a trend to replace the electrical paste made of the precious metals by the low-cost electrically conductive metallic powder in the future.
This paper discusses utilization of Gal Tiffany displacement reaction to make and prepare silver-coated copper powder, which is then made as metallic powder with low sintering temperature and low electrically conductivity rate. The nano-silver on the surface is employed as the adhesive to contact the metallic copper powder, so that the contact resistance value can be reduced. Then, the copper powder is sintered under 300℃ in no reducing atmosphere, while the nano-silver on the surface is sintered until it is in the melting status to cover the copper powder before it oxidize. Such methods can prevent oxidation of the copper powder, have the copper powder fill the gaps and holes, extensively raise the electrically conductivity rate, and significantly decrease the sintering temperature.
To sum up, by exerting the chemical substitution reaction to separate out the silver for growing on the copper particles, the conductive paste made by covering the copper powder with silver is characterized with the following advantages: 1. the overall conductivity raises; 2. the copper inside will not oxidize; 3. the cost is lower than the silver's; 4. good electromigration resistance; 5. after copper is covered by the nano-silver, it can be sintered under low temperature without getting oxidized.
The copper paste's conductivity will increase as the sintering temperature raises. On the other side, the conductivity of the copper paste sintered with low temperature reduces remarkably due to partial 「Non-conductive resin」, as shown in Table 1.
This research aims to raise the conductivity of the copper paste sintered with low temperature, as well as overcoming the difficulty of overcoming the restriction of making copper paste merely in nitrogen. It is thus expected to obtain "super low temperature, high conductivity, and low stress print-based copper electrode" sintered in air at low temperature.
In our experiment, we tested the mole ratio of four kinds of silver nitrate and metallic copper powder, respectively: a. 0.0058 : 0.0786, b. 0.0117 : 0.0786, c. 0.0176 : 0.0786, d. 0.0235 : 0.0786. When the mole ratio of silver nitrate and the metallic copper powder is 0.0235 : 0.0786, nano-silver's coverage rate achieves the highest; that is, the nano-silver covering structure is formed with the coverage rate more than 90%. In this experiment, two solution are used, including deionized water and EG. The former reacts too fast upon changing the solution, unable to produce an even nano-silver covered metallic copper powder surface. In contrast, the latter can slow down the displacement reaction rate, and it is characterized with the effect of dispersant without adding any dispersant, so that it is not very influential on the silver covered copper powder in our experiment. The best reaction time of the whole experiment is around 90 minutes, which is sufficient enough for the silver particles to reduction reaction, and form the nano-silver structure on the surface of the metallic copper powder. In addition, from the analysis of the surface content and SEM results, it is learned that following the displacement reaction of silver ion and copper ion, the nano-silver coverage proportion reaches more than 90%. In other words, the copper particles are covered by the complete nano-silver structure. Then, the nano-silver covered copper powder with the optimal coverage rate is mixed as the silver-covered copper paste, printed on the oxidized aluminum for sintering. Under the optimal experimental conditions, the sheet resistance value 5.7x10-3Ω/□ and the resistance rate 5.468x10-5Ω·cm are obtained. Contrary to other silver paste sintered with low temperature in the market, our experiment successfully obtains the silver-covered copper paste with high conductivity through low-temperature, low-cost, and low-stress printing process.

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