CN1188439A - 焊料、用焊接法贴装的电子元件及电路板 - Google Patents

焊料、用焊接法贴装的电子元件及电路板 Download PDF

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CN1188439A
CN1188439A CN96194876A CN96194876A CN1188439A CN 1188439 A CN1188439 A CN 1188439A CN 96194876 A CN96194876 A CN 96194876A CN 96194876 A CN96194876 A CN 96194876A CN 1188439 A CN1188439 A CN 1188439A
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indium
solder
scolder
electronic component
fusing
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CN1080616C (zh
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山口敦史
末次宪一郎
福岛哲夫
古泽彰男
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Panasonic Holdings Corp
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    • B23K35/00Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
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    • B23K35/22Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24Selection of soldering or welding materials proper
    • B23K35/26Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L23/00Details of semiconductor or other solid state devices
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    • H05K3/3457Solder materials or compositions; Methods of application thereof
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    • H05K3/3457Solder materials or compositions; Methods of application thereof
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    • BPERFORMING OPERATIONS; TRANSPORTING
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    • B23KSOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
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    • B23K35/0244Powders, particles or spheres; Preforms made therefrom
    • B23K35/025Pastes, creams, slurries
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
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    • H05K2203/04Soldering or other types of metallurgic bonding
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    • H05K3/34Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
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    • H05K3/3421Leaded components
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Abstract

通过改善浸润性增加粘接强度和使焊料逐渐熔化,可减少局部芯片脱离的发生。提供高性能和高可靠性的焊接材料、电子元件和电路板。用金属元素铟(In)或铋(Bi)涂敷焊料芯表面、电子元件的引线框架表面和电极表面、以及电路板的铜(Cu)焊区表面。

Description

焊料、用焊接法贴装的电子元件及电路板
本发明涉及焊接焊料、用焊接法贴装的电子元件及电路板。
近年来,随着电子元件间距变小和变窄,电路板上表面贴装的密度正不断地增大。例如,如图14所示,由于在宽度为1.0mm、长度为0.5mm的1005型芯片(EIAJ标准)为代表的电子部件的小型化和引线线间距为0.3mm的QFP(方形扁平封装)为代表的窄间距化,加速了表面贴装的高密度。因而,要求高性能和高可靠性的贴装用焊接材料。
在使用由锡和铅合金(Sn-Pb)构成的焊接材料时,由于含铅而存在在环保方面的问题。特别是,当使用含铅焊料的电子装置置于或暴露于酸雨时,有毒的铅大量析出,引起了环境问题。因此,要求用不含铅的新的焊料(无铅焊料)代替常规的含铅焊料。
下面说明常规焊料例。
图15示出现有技术焊料粉的示意性剖示图。焊料粉21与助焊剂混合,制成焊膏,用于表面贴装技术中。焊膏的金属组分是锡(Sn)和铅(Pb)共晶合金。例如,63Sn-37Pb(组分比按重量百分比)的熔点为183℃。
下面说明现有技术电子电子元件电极例。图14示出现有技术的表面贴装电子元件。如图14所示,电子元件电极22的表面镀敷锡(Sn)或焊料(90Sn-10Pb)。
现有技术电路板上的焊区是无表面镀敷的铜(Cu),或表面镀敷金(An)或焊料(90Sn-10Pb)的铜。
用焊接法粘接电路板上的焊区与电子元件的电极或引线框架。
可是,由于在焊区与焊料之间生成了易脆的Cu/Sn合金的金属间化合物,以上常规结构可引起焊料浸润不良;在Cu焊盘与焊料之间、或在电子元件的电极或引线框架与焊料之间引起未充分扩散的层。
其中,焊料浸润性指焊料熔化时焊料的扩散能力。
此外,由于Cu焊区与焊料的线性膨胀系数差引起的锡(Sn)须晶(Whisker)和破裂,造成电路短路,从而,现有技术的焊接部分没有足够的可靠性。
再者,高密度的电路已经使电子元件不断地小型化,这在熔点下和未充分浸润点会使焊料突然熔化,使芯片局部脱离。
其中,芯片的局部脱离指电子元件3贴装在电路板4上之后在焊料上的一部分升高,如图5所示。电子元件的这种不恰当的安装使导电性不良。特别是,如上述1005芯片那样的小电子元件常常出现芯片局部脱离。这已使电子电路进一步高密谋化困难。
本发明通过改善浸润性而提高粘接强度,通过确保焊料逐渐熔化还可防止局部芯片脱离。因而,本发明提供具有更好性能和更高可靠性的焊料、电子元件和电路板。
图1是本发明第一实施例的表面敷有铟(In)的焊料粉的剖面图。
图2A-2E示出本发明第一实施例的焊料粉熔化过程。
图3是贴装了电子元件的电路板。
图4A-4C示出本发明第一实施例的焊料粉,铟合金焊料和常规Sn-Pb焊料的熔化状态。
图5展示芯片的局部脱离。
图6是焊料粘接强度测试器。
图7说明焊料的浸润性。
图8展示浸润状态。
图9是比较本发明敷铟焊料与铟(In)合金焊料的粘接强度的曲线图。
图10是比较本发明敷铟焊料与铟合金焊料的浸润性的曲线图。
图11是按本发明实施例的焊丝。
图12是按本发明实施例的已涂敷了引线框架表面和电极表面的电子元件。
图13A和13B是按本发明实施例的已涂敷了铜(Cu)焊区表面的电路板。
图14是现有技术的表面贴装电子元件。
图15是现有技术的焊料粉的示意性剖面图。
为解决上述问题,用金属元素铟(In)或铋(Bi)涂敷现有技术的焊料、电子元件的引线框架表面和电极表面、和电路板的铜(Cu)焊区,可实现本发明的上述目的。
下面说明上述涂敷铟(In)或铋(Bi)的理由。
仅添加铟(In)或铋(Bi)就可降低熔化的焊料的表面张力。这将改善焊料的浸润性和增加粘接强度。
此外,涂敷能够使焊料逐渐熔化,防止芯片局部脱离。
如上所述,用上述金属元素之一涂敷焊料、电子元件和电路板,本发明可改善粘接强度。
抑制局部脱离的发生也使电子元件组件具有高可靠性。
下面,参照附图说明本发明的焊料、电子元件和电路板。
第一实施例
图1示出了本发明第一实施例焊膏中的焊料粉的剖面示意图。在焊料主体1的表面上设置铟覆盖膜2。其中,焊料主体1是常规焊料。在该实施例中,用锡和铅合金作焊料主体1。可是,它也可以是如Sn-Ag-Zn-Bi系列、Sn-Ag-Zn-In系列、Sn-Ag-Bi-Cu系列焊料等无铅焊料,任何含锡焊料。
在该实施例中,用镀敷法在焊料材料表面上敷铟,当然也可用蒸镀和扩散法作为焊料表面覆盖铟的方法,虽然本实例中用了镀,但也可用蒸镀或涂敷。
下面,说明本实施例焊料粉的熔化过程。图2A-2E示出本实施例的焊料粉熔化过程。图2A示出焊料熔化前的状态,图2E示出焊料熔化后的焊料粉状态。本实施例中的焊料粉按图2A、2B、2C、2D和2E所示的顺序熔化。图3示出贴装了如晶体管和电容器等电子元件的电路板。将电子元件3和4放置于电路板5上,用焊料8(焊膏)固定引线框架6和电极7。
用图2和3作为焊接电路板和电子元件的例子详细说明焊料的熔化。
将电子元件3和4装在电路板5上之后,用焊接法将电子元件3和4的电极7和引线框架6粘接到电路板5上的电极(焊区)9上。其中,焊料按下述顺序熔化。
首先,当加热焊料时,在焊料主体1与铟(In)2之间的边界表面10开始熔化,产生焊料主体中的锡(Sn)与铟(In)2的共晶合金,Sn和In熔解并沿图2B中箭头所示方向扩散。然后,当加热温度达到In和Sn的共晶合金的熔化点温度(118℃)时,已熔化和扩散的共晶合金11如图2C所示析出。熔化和扩散层(在焊料主体1与In2之间的边界表面)10逐渐移出In2的周边,共晶合金11开始从In2的周边析出,浸润电子元件3和4的电极7和引线框架6以及焊区9。
锡的熔点为232℃,铅的熔点为328℃,铟的熔点为156℃,本发明的焊料粉的熔点是118℃。铟是低熔点金属,具有降低焊料熔点的作用。因此,低熔点的铟(In)2和锡(Sn)的合金首先开始浸润电子元件的电极6和引线框架7以及电路板的电极(本实施例中为铜(Cu)焊),随后焊料主体1开始熔化。铟(In)2和焊料主体1逐步熔化引起逐渐浸润,从而减少出现局部芯片脱离。
为示意性地展示焊粉如何熔化,图2中的边界表面10均匀地扩开,但边界表面10实际上是非均匀地熔化的。低熔点金属从铟(In)2周边的一部分开始熔化,并逐渐扩散开。
参照图4A至4C和图5说明如何减少芯片的局部脱离。图4A至4C示出在本发明第一实施例中敷有铟的焊料粉、由含铟的铟合金构成的焊料和常规Sn-Pb焊料的熔解状态。
如图4C所示,在不含铟(In)2的焊料(Sn-Pb)熔化时,它从固相突然改变为液相,这意味着它的相位转变范围非常窄。通常,为用焊接法在电路板上贴装电子元件,首先按预定图形将焊膏印刷在电路板上,以电子元件的电极或引线框架与印刷焊膏接触的方式,将电子元件安放在电路板上,并在回流炉中加热电路板,熔化焊料进行粘接。其中,在回流炉内部的温度不均匀,使电子元件3的电极7a和7b的温度不均匀。这可能使电子元件3的电极7a的焊料熔化,另一电极7b的焊料不熔化。如上所述,由于在不含铟(In)2的焊料熔化时从固相突然转变为液相,因而受电极7a的焊料的表面张力吸引,另一电极7b升高。
因此,没有铟(In)2的焊料由于上述焊料凝固可能引起局部脱离。
另一方面,如图4A所示,涂敷铟(In)2的焊料在铟(In)和锡(Sn)之间的边界表面10上产生In和Sn的共晶合金,和逐渐地绕In的周边扩散开。当熔化时,熔化的共晶合金11开始从焊料的一部分析出,浸润电子元件的焊盘9和电极7。这时,In的一部分2仍然未熔化,但此后逐渐熔化和扩散。更具体地说,铟(In)2和锡(Sn)的熔化和扩散,以及熔解和扩散的共晶合金的熔化继续,同时熔化的铟(In)2和锡(Sn)的共晶合金析出。当固相和液相焊料共存时,逐渐产生熔化的铟(In)2和锡(Sn)共晶合金使转变时间延长。这导致固相与液相之间的转变变慢,焊料完全变为固相需要一定时间。这允许电子元件另一电极7b的焊料在料料凝固产生焊料表面张力之前熔化,从而焊接电子元件而无局部芯片分离。因此可明显地减少局部脱离的产生。
但是,由于下列原因,用本发明可以减少局部芯片脱离,但由含铟(In)的铟合金构成的焊料不能减少局部芯片脱离。
如图4B所示,由铟(In)合金构成的焊料立即产生熔化的Sn和In的化合物。这避免如图2所示本发明那样的首先是铟(In)2和锡(Sn)的共晶合金、然后是焊料主体1的逐步熔化。因而焊料的熔化不能逐渐进行。因此,当固相和液相焊料共存时,由铟(In)合金制成的焊料不能产生足够的转变时间,于是导致局部芯片脱离。特别是,如1005芯片等小电子元件高概率地发生局部脱离。
如上所述,本发明用铟(In)涂敷焊料表面,能够使铟(In)2和锡(Sn)共晶合金、然后是焊料主体逐步地熔化。这允许逐渐浸润,因而能减小出现局部芯片脱离。
铟(In)2还能减小熔化焊料的表面张力,改善电路板上铜(Cu)焊区的浸润性,从而增加粘接强度。
而且,与其它金属相比,铟(In)与铜(Cu)更可能相互扩散。这导致在边界表面上产生与铜(Cu)的足够的扩散层,从而如在本实施例中那样,能够增加电子元件的电极焊接到铜(Cu)焊区上时的粘接强度。铟(In)也是比铜(Cu)软的金属和焊接材料。这能使铟(In)当作缓冲剂,吸收由铜(Cu)和焊接材料的线性膨胀系数差引起的任何畸变,抑制产生断裂和减小焊接材料中的内部应力,并且抑制产生锡(Sn)须晶。
因此,本发明用铟(In)涂敷焊料主体表面,能够改善焊料浸润性,减少局部芯片脱离的产生。
下面参照实施数据详细说明本发明的焊料。
本实施例中,为测量焊料粘接强度,进行如图6所示的粘接强度测试。
将已贴装了电子元件的电路板按45°角固定在台面12上。电子元件的一个电极用钩13钩住,向上拉。该电子元件是引线间距为0.5mm的QFP。进行二十次拉力试验,每次测量电子元件的电极被拉脱时的抗拉强度,计算平均值F。
下面,为测量浸润性,进行如图7所示的浸润性试验。
这是称作扩散率比(Spreadability ratio)方法的方法。熔化一定量的焊料并散布于加热的基板14上,按照扩散焊料的最大高度h和按球形的相同体积的焊料的直径D之比的下列公式计算扩散率:
扩散率S=(D-h)/D×100
图8示出浸润状态。如图所示,扩散焊料的最大高度h小些较好。
表1示出常规焊料、本发明焊料和铟(In)合金焊料的浸润性和粘接强度的比较。
表1
扩散率S(%) 粘接强度F(Kg)
本发明的焊膏 91.0 1.15
常规焊膏 89.7 1.05
铟(In)合金焊膏 90.0 1.07
从表1可知,本发明焊料的浸润性和粘接强度比常规焊膏和铟合金焊膏的浸润性和粘接强度好。
图9和10示出本发明敷有铟的焊料与铟合金焊料的粘接强度和浸润性的比较。由图可知,本发明敷有铟的焊料的粘接强度和浸润性好于含铟的铟合金焊料的粘接强度和浸润性。
表2示出常规焊料、铟(In)合金焊料和本发明焊料的局部芯片脱离数的比较。我们在10,000个单独的1005芯片中计数了局部脱离的数量,并计算了发生率百分比。
表2
局部脱离数 发生率(%)
本发明焊膏 53 0.53
常规焊膏 150 1.50
铟(In)合金焊膏 98 0.98
由表2可知,使用本发明焊料的局部芯片脱离数低于使用常规焊料和铟合金焊料的局部芯片脱离数。
锡和铅焊料用于第一实施例中,但使用无铅焊料也可实现浸润性和粘接强度的相同改善和局部芯片脱离数的相同减少。
还可用铋(Bi)代替铟(In)。但用铋(Bi)不能防止须晶产生。
第二实施例
图11示出本发明实施例的焊料丝。用焊料主体16涂敷助焊剂15,用铟(In)17涂敷焊料主体16。
表3示出了如上构形的焊料丝的实验数据。表3是常规焊料和本发明焊料的粘接强度的比较。为测量粘接强度,进行与第一实施例中所述相同的粘接强度试验。
表3
本发明的焊料丝 粘接强度F    (Kg)
本发明的焊料丝 1.19
常规焊料丝 1.05
由3可知,本发明焊料丝的粘接强度优于常规焊料丝的粘接强度。
与第一实施例相同,也降低了局部芯片脱离发生的百分率。
在第二实施例中,常规焊料被用作焊料主体。用无铅焊料也能获得相同效果。
第一和第二实施例中,焊料熔化后的合金组分中铟(In)的重量最好低于6重量%。限制铟(In)含量的原因是因为如图9和10所示,当铟含量为3重量%时铟的粘接强度和浸润性最大。当铟含量超过6重量%时,粘接强度和浸润性减小得低于无铟焊料的粘接强度和浸润性,这意味着添加铟无任何效果。
上述实施例中,以焊膏和焊料丝为例。但可以使用任何表面贴装的焊料。
上述实施例还使用涂有铟(In)的焊膏,并且,通过涂敷电子元件的引线框架表面或涂敷铜(Cn)焊区表面,也可获得相同效果。
下面说明电子元件和电路板的实施例。
第三实施例
图12A和12B示出本发明实施例中已涂敷引线框架表面和电极表面的电子元件。
电子元件的电极18和引线框架19的表面涂有铟(In)2。
用焊接法将该电子元件贴装在电路板上时,可获得与使用上述实施例的焊料相同的效果。并且,同时还使用本发明的焊料进行焊接,可获得更好的效果。
第四实施例
图13A和13B示出本发明实施例中其铜(Cu)焊区表面已涂有铟(In)的电路板。
电路板上的焊盘20涂有铟(In)。
当把电子元件贴装在电路板上并焊接时,可获得与使用上述实施例的焊料相同的效果。并且,同时还使用本发明的焊料进行焊接,则可获得更好的效果。
铟(In)的硬度为0.9HB(HB:布氏硬度),它比锡(5.3HB)、铅(33HB)和常规焊料软。当使用涂敷铟的电子元件和涂敷铟的电路板时,可以为无焊料接触,能够提供无焊料电路板。
如上所述,本发明用铟(In)涂敷焊接材料、电子元件的引线框架和电极、以及电路板的铜(Cu)焊区,能够降低熔化焊料的表面张力,增大粘接强度。
铟(In)和锡的共晶合金和焊料主体的逐渐熔化允许逐步浸润,因而可减少局部芯片脱离。
而且,与其它金属相比,铟(In)更可能与铜(Cn)相互扩散。这能够在与铜(Cn)的边界上产生足够的扩散层,从而粘接强度。铟(In)也比铜(Cn)和焊接材料软。这使得铟(In)可用作缓冲剂,吸引由铜(Cn)与焊接材料之间不同的线性膨胀系数产生的任何畸变,从而抑制焊接材料中的断裂和减小其内应力,并且,还能抑制锡(Sn)须晶产生。
因此,本发明能够改善焊料的浸润性,减少焊接部分产生的断裂和局部芯片脱离,从而确保电子元件组件的高可靠性。

Claims (14)

1.一种焊料粉,其特征为在其含锡的焊料主体表面敷有铟(In)或铋(Bi)。
2.一种焊料,其特征为在其含锡的焊料主体表面敷有铟(In)或铋(Bi)。
3.一种焊膏粉,其特征为在其含锡的焊料主体表面敷有铟(In)或铋(Bi)。
4.一种膏体焊料,为权利要求3中所述的焊膏粉与助焊剂的混合物。
5.一种焊料丝,其特征为绕助焊剂的外周面上覆盖含锡的焊料主体,在所述焊料主体的外周边覆盖铟(In)或铋(Bi)。
6.一种电子元件,其特征为引线框架表面或电极表面涂敷铟(In)或铋(Bi)。
7.一种电路板,其特征为铜焊区表面覆盖铟(In)或铋(Bi)。
8.如权利要求1所述的焊料粉,在焊料熔化后的合金组份中铟为6重量%或以下。
9.如权利要求2所述的焊料,在焊料熔化后的合金组份中铟为6重量%或以下。
10.如权利要求3所述的焊膏粉,在焊料熔化后的合金组份中铟为6重量%或以下。
11.如权利要求4所述的焊膏,在焊料熔化后的合金组份中铟为6重量%或以下。
12.如权利要求5所述的焊料丝,在焊料熔化后的合金组份中铟为6重量%或以下。
13.如权利要求6所述的电子元件,在焊料熔化后的合金组份中铟为6重量%或以下。
14.如权利要求7所述的电子元件,在焊料熔化后的合金组份中铟为6重量%或以下。
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CN1080616C (zh) 2002-03-13
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US5962133A (en) 1999-10-05
KR19990028259A (ko) 1999-04-15

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