(1. 哈爾濱工業(yè)大學(xué) 現(xiàn)代焊接生產(chǎn)技術(shù)國家重點(diǎn)實驗室，哈爾濱 150001;
2. 哈爾濱理工大學(xué) 材料科學(xué)與工程學(xué)院, 哈爾濱 150080;
3. 日東電子發(fā)展有限公司 無鉛焊接研發(fā)中心， 深圳 518103)
摘 要: 對波峰焊常用的Sn-Bi-Ag-Cu無鉛釬料進(jìn)行了通孔波峰焊焊點(diǎn)剝離現(xiàn)象的模擬實驗。分析表明， 凝固延遲及鉍元素偏析導(dǎo)致焊盤拐角附近釬料區(qū)在結(jié)晶后期殘存液相最終成為縮孔的聚集區(qū)， 結(jié)晶后期該區(qū)的低塑性使收縮應(yīng)變?nèi)菀壮^材料的塑性而發(fā)生開裂， 且發(fā)生機(jī)制與結(jié)晶裂紋發(fā)生的機(jī)制相同，強(qiáng)偏析元素鉍的存在導(dǎo)致剝離概率極高。 通孔拐角附近是應(yīng)力應(yīng)變的集中區(qū)， 沿界面至焊盤外緣， 應(yīng)力應(yīng)變逐漸降低。 Sn-Bi-Ag-Cu系釬料焊點(diǎn)剝離的發(fā)生機(jī)制是由于Bi元素在焊盤/釬料界面富集使拐角附近釬料的液相線溫度降低， 結(jié)晶后期該區(qū)因固液共存而成為相對低塑性區(qū)， 在應(yīng)力作用下開裂并向焊盤外緣擴(kuò)展。
關(guān)鍵字: Sn-Bi-Ag-Cu釬料； 無鉛波峰焊； 焊點(diǎn)剝離； 偏析； 結(jié)晶裂紋
solder joint in lead-free wave soldering
（ 1. State Key Laboratory of Advanced Welding Production Technology,
Harbin Institute of Technology, Harbin 150001, China;
2. School of Materials Science and Engineering,
Harbin University of Science and Technology, Harbin 150080, China;
3. Sun East Electronic Development Co. Ltd., Shenzhen 518103, China）
Abstract: The mechanism of fillet-lifting for the Sn-Bi-Ag-Cu solder was studied, which is one of the mainly used lead-free solder in wave-soldering. The analysis results show that the segregation of Bi becomes more remarkable at the corner of the solder body/PCB pad. The local irregularity of Bi delays the solidification of the solder at the above area, and thus the residual liquid solder at that place becomes the aggregation area of shrinkage void during the following crystallization. The shrinkage strain exceeds the low plasticity of the Bi segregation solder in the later crystallization, then the crack is similar to that of the crystal crack. The presence of strong segregation element Bi exacerbates the probability of lift-off, which could be reduced by the rapidly cooling only in a limited extent. The stress-strain concentration is detected at the corner of Cu pad, the lower stress for the outer of Cu pad. Based on the above two leading reasons for fillet-lifting, the stress-strain concentration at the corner of Cu pad and the solidification delay, the mechanisms of fillet-lifting for Sn-Bi-Ag-Cu through-hole lead-free solder joint were given. Near the interface region of solder and Cu-pad, the liquidus of solder is lowered by the enriched Bi element, and the low plasticized zone produces at this region due to the existence of residual liquid phase. With the stress-strain concentration, the cracks produces near the corner of Cu pad and then propagated to its outer.
Key words: Sn-Bi-Ag-Cu solder; lead free wave soldering; fillet lifting; segregation; crystalline crack
