Sn-XAg-0.5Cu無鉛釬料熔化特性、潤(rùn)濕性及力學(xué)性能研究

衛(wèi)國(guó)強(qiáng),萬忠華,趙四勇,張宇鵬,劉鳳美

(1華南理工大學(xué)機(jī)械與汽車工程學(xué)院,廣州510640;2廣州有色金屬研究院焊接材料研究所,廣州510651)

Sn-XAg-0.5Cu無鉛釬料熔化特性、潤(rùn)濕性及力學(xué)性能研究

衛(wèi)國(guó)強(qiáng)1,萬忠華1,趙四勇2,張宇鵬2,劉鳳美2

(1華南理工大學(xué)機(jī)械與汽車工程學(xué)院,廣州510640;2廣州有色金屬研究院焊接材料研究所,廣州510651)

應(yīng)用差示掃描量熱(DSC)法、潤(rùn)濕平衡分析技術(shù)和拉伸試驗(yàn),研究了Sn-XAg-0.5Cu(X=0.1～3.0)無鉛釬料合金的熔化特性、潤(rùn)濕性能及力學(xué)性能。實(shí)驗(yàn)結(jié)果表明:所有釬料合金的開始熔化溫度均為217.3℃;隨合金中Ag含量增加,熔化溫度區(qū)間變窄。釬料的潤(rùn)濕鋪展面積和潤(rùn)濕力隨Ag含量的增加而先顯著增加,而后趨于穩(wěn)定;對(duì)潤(rùn)濕鋪展面積和潤(rùn)濕力(或潤(rùn)濕時(shí)間)產(chǎn)生顯著影響的閾值A(chǔ)g含量為1.0%(質(zhì)量分?jǐn)?shù),下同)。Ag含量在0.5%～3.0%時(shí),隨著Ag含量的增加,釬料的斷后伸長(zhǎng)率逐漸下降,而抗拉強(qiáng)度和0.2%屈服強(qiáng)度均逐漸增加。

Sn-XAg-Cu無鉛釬料;熔化特性;潤(rùn)濕性;力學(xué)性能

Sn-(3.0～3.9)Ag-(0.5～0.7)Cu(質(zhì)量分?jǐn)?shù)/%,下同)無鉛釬料由于具有較低的共晶溫度(固相線溫度:Ts=217℃)、較好的綜合力學(xué)性能和良好的潤(rùn)濕性現(xiàn)已在微電子工業(yè)中得到廣泛應(yīng)用[1-3]。但是,該Sn-Ag-Cu系釬料合金在凝固過程中β-Sn存在較大的過冷度,會(huì)形成粗大的板條狀A(yù)g3Sn初晶(冷卻速度越慢,Ag3Sn粗化越嚴(yán)重),同時(shí)在隨后的服役過程中,板條狀A(yù)g3Sn會(huì)進(jìn)一步粗化,導(dǎo)致釬料合金抗沖擊及抗跌落(高應(yīng)變速率條件)性能明顯降低;另一方面,高的Ag含量使初生β-Sn含量降低,共晶相含量增加,同樣導(dǎo)致更多的粗大的板條狀A(yù)g3Sn存在,致使釬料合金強(qiáng)度指標(biāo)增加,塑性指標(biāo)降低,從而降低焊點(diǎn)可靠性[4-6]。此外,由于Ag含量高,明顯增加了釬料的材料成本。

為提高焊點(diǎn)抗沖擊能力及綜合力學(xué)性能,降低釬焊材料成本,眾多學(xué)者對(duì)降低Sn-Ag-Cu共晶無鉛釬料合金Ag含量對(duì)熔化溫度、力學(xué)性能及界面和焊點(diǎn)內(nèi)的組織演變進(jìn)行了研究[7-10],同時(shí)通過添加第四合金組元來進(jìn)一步提高該系無鉛釬料合金的性能[11-13]。D.W.Suh等人對(duì)低Ag的Sn-Ag-Cu釬料合金在高應(yīng)變速率條件下的斷裂性能進(jìn)行了研究[14],K.S.Lin等人就Ag含量對(duì)Sn-Ag-Cu釬料合金焊后時(shí)效處理對(duì)焊點(diǎn)界面強(qiáng)度的影響進(jìn)行了研究[16]。但至今為止,Ag含量對(duì)Sn-Ag-Cu無鉛釬料合金性能影響的系統(tǒng)研究還不多?；阝F料熔化溫度、力學(xué)性能和潤(rùn)濕性能是評(píng)價(jià)無鉛釬焊材料性能的重要指標(biāo),同時(shí)為后期開發(fā)四元低Ag含量的Sn-Ag-Cu無鉛釬料合金提供理論基礎(chǔ),本工作就Ag(0.1%～3.0%)含量對(duì)Sn-Ag-Cu無鉛釬料合金熔化特性、潤(rùn)濕性能及力學(xué)性能的影響進(jìn)行了系統(tǒng)的研究。

1 實(shí)驗(yàn)材料和方法

1.1 實(shí)驗(yàn)材料

所用的原材料為 Sn-10Cu中間合金、純 Sn(99.95%)和純Ag(99.95%),釬料合金配方為Sn-(X=0.1,0.3,0.5,0.8,1.0,1.5,2.0,2.5,3.0)Ag-0.5Cu,將稱好的樣品在坩堝中進(jìn)行熔煉,熔化溫度為400℃,熔煉過程中充分?jǐn)嚢枋钩煞志鶆?然后保溫30min,最后在鋼模中進(jìn)行澆注。

1.2 熔化特性測(cè)試

采用差示掃描量熱分析儀(DSC型號(hào):STA-409-PC)測(cè)試釬料合金的熔化特性,實(shí)驗(yàn)前采用標(biāo)準(zhǔn)純 In對(duì)儀器進(jìn)行溫度校正,試樣約為20mg,加熱速率為5℃/min,溫度范圍為 35～300℃,實(shí)驗(yàn)采用 ADAMIS7軟件來記錄各釬料熱流隨溫度的變化規(guī)律。

1.3 潤(rùn)濕平衡實(shí)驗(yàn)

采用可焊性測(cè)試儀(型號(hào):SA T-5100)進(jìn)行潤(rùn)濕平衡試驗(yàn),標(biāo)準(zhǔn)試樣為純銅無鍍層試片,規(guī)格為30mm×5mm×0.3mm,釬料浴溫度為250℃(精度:±1℃),浸入深度為2mm,浸入速度為5mm/s,浸入時(shí)間為10s,助焊劑為 EF8000(Alpha Metal)。

1.4 潤(rùn)濕鋪展實(shí)驗(yàn)

用分析天平(精度:±0.1mg)分別稱取各種釬料200mg,然后把釬料放置在溫度為250℃的油浴中,使其變成球狀釬料,自然冷卻后,用超聲波對(duì)釬料球進(jìn)行清洗待用。鋪展實(shí)驗(yàn)的銅基板采用20mm×20mm×2mm的紫銅板(純度為99.95%),實(shí)驗(yàn)前用400#砂紙打磨銅板,然后將打磨好的銅板放入稀HCl(5%)中清洗,再用去離子水沖洗,最后用無水乙醇清洗。潤(rùn)濕鋪展實(shí)驗(yàn)熱源為錫浴爐,實(shí)驗(yàn)溫度為260℃,保溫時(shí)間40s,助焊劑為 EF8000(Alpha Metal),采用數(shù)字式求積儀(QCJ-2A)測(cè)量釬料合金的鋪展面積。

1.5 室溫拉伸力學(xué)性能實(shí)驗(yàn)

將澆注好的棒料加工成標(biāo)準(zhǔn)拉伸試樣,然后在100℃恒溫爐中保溫1h,以除去殘余應(yīng)力,隨爐冷至室溫。拉伸試驗(yàn)參照 IPC J STD-004標(biāo)準(zhǔn),拉伸速度為20.00mm/min。

2 結(jié)果與討論

2.1 Ag含量對(duì)熔化特性的影響

圖1為Sn-XAg-0.5Cu釬料合金在加熱階段吸熱峰處的DSC曲線,從圖 1可以看出,當(dāng) Ag含量在0.1%～3.0%范圍內(nèi)時(shí),所有釬料合金的起始熔化溫度(Ton)均約為217℃(平均:217.3℃),說明 Sn-0.5Cu加少量的Ag,就可使釬料合金的起始熔化溫度降為三元共晶反應(yīng)溫度。圖2為Ag含量對(duì)峰值熔化溫度(Tp1,Tp2)和熔程(ΔT=Tp2-Ton)的影響,從圖2可以看出,隨Ag含量的增加,Tp1逐漸向高溫方向漂移,說明參與三元共晶反應(yīng)的相分?jǐn)?shù)逐漸增加,而Tp2隨Ag含量的增加,逐漸移向低溫端,從而使Sn-XAg-0.5Cu釬料合金熔程減小。

圖1 Sn-XAg-0.5Cu的吸熱DSC曲線 (a)X=0.1,0.3,0.5,0.8;(b)X=1.0,1.5,2.0,3.0Fig.1 Endothermic DSC profiles from Sn-XAg-0.5Cu solder alloys(a)X=0.1,0.3,0.5,0.8;(b)X=1.0,1.5,2.0,3.0

圖2 Ag含量對(duì)峰值溫度和熔程的影響Fig.2 Effect of Ag content on peak temperatures and melting ranges

從以上分析可知,在Sn-0.5Cu合金中加少量的Ag就可降低釬料合金的固相線溫度,但Ag含量較少時(shí),參與三元共晶反應(yīng)的相分?jǐn)?shù)較少,同時(shí)釬料合金的熔程相對(duì)較大。

2.2 Ag含量對(duì)潤(rùn)濕性能的影響

圖3為Sn-XAg-0.5Cu釬料合金鋪展面積隨Ag含量變化曲線,當(dāng) Ag含量在0.1%～1.0%時(shí),隨著Ag含量的增加,釬料的鋪展面積迅速增加,當(dāng)Ag含量大于1.0%時(shí),隨Ag含量的增加,釬料的鋪展面積變化不大。圖4為Sn-XAg-0.5Cu釬料合金潤(rùn)濕力(包括最大潤(rùn)濕力Fmax和最終力Fend)隨Ag含量變化曲線,圖5為Sn-XAg-0.5Cu釬料合金潤(rùn)濕時(shí)間(包括交零時(shí)間T0和最大潤(rùn)濕時(shí)間T)隨Ag含量變化曲線,當(dāng)Ag含量大約在0.1%～1.0%時(shí),隨Ag含量的增加,釬料合金的潤(rùn)濕力顯著增加,潤(rùn)濕時(shí)間顯著減少,隨著Ag含量的進(jìn)一步增加(從1.0%～3.0%),潤(rùn)濕力和潤(rùn)濕時(shí)間幾乎不變,說明Ag含量在0.1%～1.0%范圍內(nèi)增加時(shí),Sn-XAg-0.5Cu釬料合金的潤(rùn)濕性能得到顯著改善。

圖3 Ag含量對(duì)Sn-XAg-0.5Cu釬料鋪展面積的影響Fig.3 Effect of Ag content on spreading area of Sn-XAg-0.5Cu solder alloys

從以上實(shí)驗(yàn)數(shù)據(jù)分析可以看出,在低Ag范圍(0.1%～1.0%),隨Ag含量的增加,潤(rùn)濕力、潤(rùn)濕時(shí)間和鋪展面積都顯著增加,潤(rùn)濕時(shí)間顯著減少。如再繼續(xù)增加Ag含量,則對(duì)釬料合金的潤(rùn)濕特性影響不大。

2.3 Ag含量對(duì)室溫力學(xué)性能的影響

圖6為釬料合金抗拉強(qiáng)度、0.2%屈服強(qiáng)度和斷后伸長(zhǎng)率隨Ag含量的變化曲線。由圖6可以看出,在低Ag范圍(0.1%～0.5%),斷后伸長(zhǎng)率隨著Ag含量的增加先下降后上升,而抗拉強(qiáng)度和0.2%屈服強(qiáng)度正好與伸長(zhǎng)率呈相反的趨勢(shì),這種變化趨勢(shì)可能和顯微組織的變化有關(guān),有待進(jìn)一步研究。當(dāng)Ag含量在0.5%～3.0%范圍內(nèi)時(shí),各力學(xué)性能呈穩(wěn)定的變化趨勢(shì),即斷后伸長(zhǎng)率隨著Ag含量的增加而下降,抗拉強(qiáng)度和0.2%屈服強(qiáng)度隨著Ag含量的增加而逐漸增加。

3 結(jié)論

(1)所有釬料合金的固相線溫度(Ton)均約217.3℃。隨Ag含量的增加,三元共晶反應(yīng)相的數(shù)量增加,釬料合金的熔程(ΔT)減少。

(2)當(dāng)Ag含量在0.1%～1.0%時(shí),隨Ag含量的增加,潤(rùn)濕鋪展面積、潤(rùn)濕力顯著增加,潤(rùn)濕時(shí)間顯著減少,隨后再增加Ag含量,對(duì)潤(rùn)濕性沒有顯著影響。

(3)當(dāng)Ag含量在0.1%～0.5%時(shí),力學(xué)性能呈先下降后增加趨勢(shì);當(dāng)Ag含量在0.5%～3.0%時(shí),隨著Ag含量的增加,釬料的斷后伸長(zhǎng)率逐漸下降,而抗拉強(qiáng)度和0.2%屈服強(qiáng)度均逐漸增加。

圖6 Ag含量對(duì)Sn-XAg-0.5Cu釬料拉伸性能的影響Fig.6 Effect of Ag content on tensile properties for Sn-XAg-0.5Cu solders

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Investigations on Melting Property,Wettability and Mechanical Property of Sn-XAg-0.5Cu Lead-free Solder Alloys

WEI Guo-qiang1,WAN Zhong-hua1,ZHAO Si-yong2,ZHANG Yu-peng2,LIU Feng-mei2
(1 School of Mechanical and Automotive Engineering,South China University of Technology,Guangzhou 510640,China;2 Joining Materials Institute,Guangzhou Research Institute of Nonferrous Metals,Guangzhou 510651,China)

The melting property,wettability and mechanical property of Sn-XAg-0.5Cu(X=0.1-3.0)lead-free solder alloys were investigated by differential scanning calorimetry(DSC),wetting balance technique,sessile drop method and tensile test.The DSC revealed that the endothermic onset temperature on heating appeared at about 217.3℃for the all solder alloys.With increasing the Ag content of the solder alloys,the melting temperature ranges of the solders became narrow.It was also shown by the wetting balance and sessile drop experiments that the wettability remarkably increased with the Ag content increased,and then with Ag content farther increased,the wettability were kept constant approximately.The threshold value of the Ag content was 1.0%(mass fraction/%,the same below),which considerably effected on wetting-spreading areas and wetting forces(or wetting time).Meanwhile,when Ag content is between 0.5%and 3.0%,the specific elongation of solders decreased with the Ag content increased,while the tensile strength and 0.2%yield stresses increased,too.

Sn-XAg-Cu lead-free solder;melting property;wettability;mechanical property

TG454

A

1001-4381(2010)10-0053-04

國(guó)家自然科學(xué)基金(NSFC-廣東聯(lián)合)重點(diǎn)項(xiàng)目(U0734006);廣東省科技計(jì)劃項(xiàng)目(2008A080403008-06);廣州市天河區(qū)科技計(jì)劃項(xiàng)目(095G108)

2010-06-20;

2010-07-19

衛(wèi)國(guó)強(qiáng)(1960—),男,在職博士,副教授/高級(jí)工程師,主要從事釬焊、電子封裝及激光材料加工的研究工作,聯(lián)系地址:華南理工大學(xué)機(jī)械與汽車工程學(xué)院(510640),E-mail:gqwei@scut.edu.cn