銅箔在液態Sn-0.3Ag-0.7Cu銲料中的固溶研究

Dissolution of copper foil contact with liquid Sn-0.3Ag-0.7Cu solder

簡信方(Hsin-fang Chien)

指導教授 ： 李天錫

國立中央大學/工學院/機械工程研究所碩士在職專班/碩士(2014年)

摘要

自2010歐洲RoHS 2.0法規正式生效，完全限制可販售的電子產品中的鉛含量。絕大多數電子印刷電路板與組裝業者，為了符合產品無鉛化法規的規範，陸續的升級自我的相關生產設備與製程能力，以符合法令與市場的要求。
在已揭露的無鉛化製程的相關議題中，無鉛焊料的選用具有相當重大的影響力，其不只關係著後續的熱組裝製程中的設備、元件材料的選用，更是關係著產品的可靠度與生命週期。由於錫- 3.0wt％銀- 0.5wt％ 銅銲料具有優異的焊接與機械性質，被絕大多數的相關研究機構與協會推薦為無鉛製程的最佳選擇，因此被廣泛地在基板組裝業界中使用，嚴然成為業界的標準無鉛銲料。
再者，因為鉛元素的含量被嚴格限制，傳統的錫鉛噴錫板(HASL)也被禁止使用，印刷電路板業者需另外找尋可行的替代方案。其中有機保護膜(OSP)的表面處理因為具備有低廉的生產設備投資與製造成本、製程良率高與銲點的可靠度高等優勢，已經成為目前產業界的主流選擇。唯因其銲墊為純銅，不似化鎳金板(ENIG)或無鉛噴錫板(LF HASL)銲墊表面有其他元素保護著，特別是鎳元素；當錫-銀-銅銲料與PCB進行銲接時，會將銲墊的銅箔溶解進入銲料中，進而縮小銲墊的厚度甚至將銲墊溶化殆盡。
在搜尋有關銅墊溶解的研究時發現，絕大多數研究或以實驗目的，或只針對表面黏著技術(SMT)相關議題而進行探討，實驗條件大多在有限的銲錫狀態下進行，因為銲料中的銅濃度會隨著銅墊的溶解而增加，因而減緩了溶解的速率甚至達到了平衡點而停止溶解。
但在貫通孔零件的波峰銲接製程中，由於印刷電路板貫穿孔的銅墊直接在大量且高溫的液態錫槽中浸泡、沖刷，電路板上的銅墊溶解是目前業界所面臨的重大問題。因為在高階設備的基板組裝製程中，為了產品的穩定性與需要提供大功率以驅動附屬的設備，需要使用大量的貫穿孔元件與波峰銲製程來因應，在貫穿孔元件經過波峰銲的銲接過程中，銅墊將直接與巨量的錫-銀-銅銲料接觸並且溶入銲錫液中。故本研究將在選定的液態銲料(錫-0.3wt%銀-0.7wt%銅)中，利用銅箔為測試載體，依據錫湯溫度、錫湯流速和浸錫時間對銅載體進行溶解，以模擬實際生產的狀況來進行相關的研究與探討。

關鍵字

錫銀銅 ； 無鉛銲料 ； 銅溶解

並列摘要

Since 2010 the European RoHS 2.0 regulations come into effective and restricted to selling electronic products with limited lead content. The vast printed circuit boards and electronic assembly manufacturers, In order to meet product specifications of RoHS lead-free regulations, they have to upgrade own equipment and process capabilities to comply the requirements of the laws & the market.
In the exposed lead-free process relevant issues, the selection of lead-free solder has a very significant influence, which is not only related to the equipments of thermal assembly process and the choice of component materials. It is related to the product's reliability and life cycle also. As the Sn-3.0wt%Ag-0.5wt% Cu solder alloy with excellent wetting and mechanical properties, Which as the best choice for lead-free process of recommendation by major research institutions and associations, and widely used in the industry in printed circuit board assembly process, that become the mainstream lead- free solder alloy of the industry.
Furthermore, due to the lead content as the strictly limited element of RoHS compliance, the traditional tin-lead HASL board has been restricted too. PCB industry needs to find another solutions to instead tin-lead HASL board . The organic surface protective (OSP) board has become the mainstream product due to low production equipment investment and manufacturing costs, good process yield rate and higher reliability of solder joints. But it is unlike gold plate (ENIG) or lead-free HASL (LF HASL) board, which with nickel protect copper surface to prevent Cu dissolute into solder and less copper dissolution affect in PCBA process.
In the search of copper dissolution studies, we found the most studies are for experimental purposes, or just focus on Surface Mount Technology (SMT) relevant issues, under limited solder alloy conditions. The dissolution rate will decrease as the copper solute into solder and increasing the concentration of copper, even to stop the dissolution reaction of the equilibrium point.
Due to the PCB copper is contacting to mass liquid solder directly, and caused the copper pad dissolution of through-hole components area during the wave solder process, That is the major concern of the current PCBA industry. In order to provide and stabilize the power to drive those attached devices, the amount of through hole components are necessary for high end Enterprise products. During the soldering process of through hole components, the huge melting solder alloy will contact with copper foil directly, and dissolve it into the solder. This study will based on selected solder alloy Sn-0.3Ag-0.5Cu, and using copper foils as the test vehicle, varying the solder’s temperature、immersion time and solder flow rate, to simulate actual production condition and calculate the copper dissolution, to carry out the relationship of copper dissolution v.s process parameter and further discussion.

並列關鍵字

SAC ； lead-free ； dissolution

參考文獻

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