回流焊峰值温度对混装BGA焊点的影响研究

针对当前大量使用有铅焊料焊接无铅BGA的实际现状,通过调控有铅制程回流曲线的峰值温度,研究其对混装BGA焊点坍塌高度、空洞率及微观组织的影响。结果表明,峰值温度从210℃提升至225℃,无铅BGA焊球能够全部充分坍塌且高度保持一致;峰值温度为210℃时,混合焊点内的空洞率最低,随着峰值温度的升高,空洞尺寸和空洞率均有所增加;峰值温度为215℃时的微观组织最细小且尺寸分布最均匀,继续提升峰值温度,微观组织尺寸会随之增大。因此使用有铅焊料焊接无铅BGA的最佳峰值温度为215℃,与有铅制程保持一致。     

焊接温度曲线对混装BG A塌落和空洞的影响

采用有铅焊膏焊接无铅BG A 是当前高可靠电子产品组装中应对BG A 器件无铅化的手段之一。混合焊接时焊接温度曲线是影响BG A 焊接质量和焊点性能的关键因素。研究不同焊接温度曲线条件下无铅BG A 的塌落高度和焊点中空洞状况。研究结果表明,采用有铅焊膏焊接SnA gCuBG A ,但焊接峰值温度为215℃和220℃时,BG A 未完全塌落,继续提高峰值温度到225℃,BG A 塌落高度与有铅焊膏焊接有铅BG A 的塌落高度接近;继续升高峰值温度,无铅BG A 的塌落高度变化不大。当焊接峰值温度从215℃提高到230℃,混装焊点中的空洞逐渐减少;焊接峰值温度继续提高,焊点中空洞反而增加。     

用真空再流焊实现BGA的无铅无空洞焊接

BGA焊接后常常会在焊点中形成很多的空洞,特别是对于BGA的无铅焊接,由于焊接温度高,氧化严重,以及焊料的特殊性能决定了BGA的无铅焊接更容易形成空洞.空洞的产生不仅影响焊点的导热、导电性能,也会影响焊点的强度,从而对BGA工作的长期可靠性产生影响.分析了空洞产生的机理,以及用真空再流焊接实现BGA无铅、无空洞焊接的原理和工艺过程.指出真空再流焊接工艺在解决BGA的无铅、无空洞化焊接问题上确实是一项行之有效的方法.     

控制BGA组装过程中的焊点空洞

前言BGA 焊点内的空洞将会影响其机械性能,使焊点强度、韧性、蠕变和疲寿命降低,还会使焊点过热,降低可靠性。空洞与回流焊时焊膏所带助焊剂的气化,特别是可焊性有直接的关系。1 试验1.1 溶剂沸点四种膏状助焊剂 B1、B2、B3、B4,其溶剂沸点分别为276℃、231℃、171℃和137℃,其他组分都相同。为了减少溶剂化学特性的差异并且使它们的差异只表现在沸点不同上,所有     

热疲劳载荷作用下不同成分BGA焊点可靠性

针对微电子组装中常见的BGA封装形式,对比采用3种不同成分的BGA焊球和焊膏组合(锡铅共晶焊球和锡铅共晶焊膏Sn63Pb37、Sn3Ag0.5Cu焊球和锡铅共晶焊膏以及Sn3Ag0.5Cu焊球和Sn3Ag0.5Cu焊膏)焊接得到的BGA焊接界面。经过不同周期的热疲劳试验后,在金相显微镜和电子背散射衍射下观察,发现Sn3Ag0.5Cu焊球和锡铅共晶焊膏混装形成的BGA焊点中黑色的富锡相均匀弥散分布在焊球内,在热循环载荷作用下极难形成再结晶,抗热疲劳性能最好。     

热疲劳载荷作用下不同成分BGA互连焊点可靠性研究

本文针对微电子组装中常见的BGA 封装形式,对比采用三种不同成分的BGA焊球和焊膏组合（锡铅共晶焊球和锡铅共晶焊膏、Sn3Ag0.5Cu 焊球和锡铅共晶焊膏、以及Sn3Ag0.5Cu焊球和Sn3Ag0.5Cu焊膏）焊接得到的BGA 互连点,经过不同周期的热疲劳试验后,在金相显微镜和电子背散射衍射下观察,发现Sn3Ag0.5Cu焊球和锡铅共晶焊膏混装形成的BGA焊点中黑色的富锡相均匀弥散分布在焊球内,在热循环载荷作用下极难形成再结晶,抗热疲劳性能最好。     

无铅焊膏中松香含量对焊点剪切强度的影响

对不同松香含量的助焊剂进行了润湿力性能测试和黏度测试。用这些助焊剂配制成焊膏,并对焊后的焊点进行了剪切试验,以此来测定不同的松香含量下焊点的剪切强度。结果表明:焊膏的黏度随着松香含量的增加而增加,而其润湿力逐渐降低。当松香的质量分数为42.69%时,焊点的剪切强度可达48.36MPa,焊膏焊接性能良好,焊点饱满光亮。     

有铅焊料与无铅BGA混合焊点显微组织性能研究

随着近年来电子产品无铅化的发展,越来越多的有铅器件被无铅器件替代,其中SnAgCu合金成为BGA器件锡球的主要成分.然而在无铅焊点的可靠性未被认可之前的过渡时期,有铅焊膏和无铅器件混合焊接的情况就不可避免,尤其是在高可靠电子产品领域.因此混合焊接工艺和焊点的性能成为高可靠性电子产品组装和焊点寿命分析中的研究重点.总结了近年来对有铅焊料和无铅BGA混合焊接的一些相关研究,主要涉及混合焊接温度、混合焊点的显微组织、界面处金属间化合物、焊点力学性能、可靠性以及焊点失效机制等方面.     

枕头效应的测试与预防

在PCB上组装BGA或CSP时,产生的枕头效应(HIP)令电子制造业很苦恼.枕头效应是由于在再流焊接过程中元件或板子翘曲所引起的,且氧化作用会使枕头效应更为严重.行业急需用于评估可能产生HIP的方法.除了介绍染色法外,还介绍了另外两种简单的方法小滴焊膏法(Tiny Dot Paste)和焊膏上焊球法(Ball Onto Paste).小滴焊膏法重点评估焊膏的抗氧化能力.焊膏上焊球法评估抗氧化性和助焊剂组合能力.这两种方法均是快速、简易和高度仿真的方法,而后者在实际工艺仿真过程中效果更好一些.     

BGA元器件受热模型分析与SMT工艺控制

不同BGA封装结构的元器件在回流焊过程中,由于其焊球的受热路径和热阻不同,导致焊球受热不均匀、PCB变形甚至引起IC芯片的"虚接触",严重影响BGA元器件的焊接质量.通过对BGA封装元器件受热模型,热阻的分析,提出了不同BGA封装结构的元器件回流焊温度设置和控制要点:PBGA元器件峰值温度在235～245℃时焊接时间1...     

Effect of Selected Process Parameters on Durability and Defects in Surface-Mount Assemblies for Portable Electronics

This paper presents a systematic approach to study the effect of manufacturing variables on the creation of defects and the effect of those defects on the durability of lead-free (Pb-free) solder joints. An experiment was designed to systematically vary the printing and reflow process variables in order to fabricate error-seeded test assemblies. The error-seeded samples were then inspected visually and with X-ray, to identify different types of defects, especially voids, and then test for electrical performance. The specimens were subjected to an accelerated thermal cycling test to characterize the durability of these error-seeded specimens and to study the effect of each manufacturing variable on the durability of the solder joints. The response variables for the design of experiments are thermal cycling durability of the solder joints and void area percentage in ball grid array (BGA) solder joints. Pretest microstructural analysis showed that specimens produced under inadequate reflow profiles suffered from insufficient wetting and insufficient intermetallic formation. Statistical analysis of the response variables shows that waiting time, heating ramp, peak temperature, and cooling rate have nonlinear effects on thermal cycling durability. Two variables in particular [peak temperature and waiting time (the time waited after the solder paste barrel was opened and before print)] appear to have optimum values within the ranges investigated. Statistical analysis of void percentage area for all design of experiment (DOE) runs show that higher stencil thickness results in higher void percentage and that void percentage increases as time above melt and peak temperature increases.     

Growth prediction of tin/copper intermetallics formed between 63/37 Sn/Pb and OSP coated copper solder pads for a flip chip application

This study quantifies the effect of temperature and time on the growth of Cu-Sn intermetallics, specifically for flip chip/ball grid array packaging technology. The activation energy and the growth rates were determined for solid state diffusion, after the initial assembly reflow(s). Three different types of solder joints were investigated. 1) BGA 63/37 solder joints which were formed by a standard convection oven attach of 30 mil (760 /spl mu/m)diameter solder spheres to OSP protected, Cu plated ball pads of an organic flip chip substrate. The ball pads are solder mask defined and of 0.635 mm nominal diameter. 2) Flip chip bump pad solder joint consisting of 63/37 eutectic solder bumped die attached to a nonsolder mask defined, OSP protected, Cu plated pad of the flip chip substrate. The flip chip bumps on the die are created by screen printing solder paste on the die pads and subsequent reflow attach, by a standard convection oven to the die under bump metallurgy (UBM). The nominal die UBM pad diameter is 0.085 mm. 3) Solder joint formed on a coupon which involved the reflow of the balls randomly placed on a Cu plated layer with no solder mask coating. The investigation was performed by first establishing the intermetallic growth rate at six different temperatures, ranging from 85/spl deg/C to 150/spl deg/C. The relationship between intermetallic growth and time was shown to essentially follow the common parabolic diffusion relationship to temperature especially above 100/spl deg/C. The activation energy (E/sub a/) and the growth constant (k/sub 0/) were then calculated from this data. The results showed that the E. for the total intermetallic thickness was essentially similar for the three solder joint configurations of the ball, bump and the coupon described above. E. varied from 0.31 eV to 0.32 eV, while the k/sub 0/ varied from 18.0 /spl mu/m/s/sup 1/2 / to 24.2 /spl mu/m/s/sup 1/2 /.     

有铅焊料焊接无铅BGA回流参数探索

航天电子产品尚未允许采用无铅焊接,而航天电子产品中采用的进口元器件多为无铅器件,因此需要对有铅焊料焊接无铅元器件进行研究。通过对无铅焊球和有铅焊料的焊接特性分析,设计数种回流参数,进行回流焊接试验,并对试验结果进行焊接分析,得出回流峰值温度为228℃~232℃,液相线(217℃)以上时间为50s~60s的回流曲线能较好完成有铅焊料对无铅BGA的焊接。     

Reliability Investigation of Mixed BGA Assemblies

The effect of different reflow profiles on the reliability of lead-free (LF) Sn-3.0 Ag-0.5 Cu (wt.%) (SAC 305) ball grid array (BGA) devices assembled with a SnPb eutectic paste was investigated. The memory modules in a back-to-back configuration were reflowed on standard graphic cards finished with immersion silver (IAg) or hot air solder leveling (HASL) coatings. The reflow peak temperatures ranged from 209$^circ$C to 227$^circ$C, while the time above liquidus (TAL) varied from 45 to 80 s. Depending on the reflow conditions, the solder interconnects displayed varied degrees of SnPb and LF solders intermixing. It was established that in order to receive a homogeneous solder alloy, the reflow peak temperature had to be in the 218$^circ$C–222$^circ$C range. The reliability of solder interconnects of memory modules was assessed by subjecting the cards to 1500 cycles of accelerated thermal-cycling with a profile from 0$^circ$C to 100$^circ$C. It was found that the control SnPb/SnPb assemblies displayed superior reliability to that of the mixed assemblies. Regardless of the degree of homogeneity of the BGA balls, the predominant failure mode of the mixed solder joints was interfacial cracking through a Pb-rich phase near the intermetallic layer. In contrast, only partial cracks propagating diagonally through the bulk solder were present on the control boards. It was concluded that a combination of state of stress and segregation of the Pb-rich phase at the interface was responsible for the shortened thermal–mechanical fatigue life of the mixed solder interconnects.     

热循环条件下空洞对PBGA焊点热疲劳寿命的影响

球栅阵列(ball grid array, BGA)封装器件的广泛应用使空洞对焊点可靠性的影响成为业界关注的焦点之一.采用非线性有限元分析方法和统一型粘塑性本构方程,以PBGA组装焊点为对象,建立了互连焊点热应变损伤的三维有限元模型,并基于修正的Coffin-Manson方程,分析了在热循环加裁条件下不同位置和大小的空洞对焊点疲劳寿命的影响.研究结果显示,位于原应力集中区的空洞将降低焊点疲劳寿命,基于应变失效机理,焊点裂纹易在该类空洞周围萌生和扩展;位于焊球中心和远离原应力集中区的空洞,在一定程度上可提高焊点的疲劳寿命.     

弯曲应力状况下微型BGA封装可靠性比较研究

微型球栅阵列（μBGA）是芯片规模封装（CSP）的一种形式,已发展成为最先进的表面贴装器件之一。在最新的IxBGA类型中使用低共晶锡．铅焊料球,而不是电镀镍金凸点。采用传统的表面贴装技术进行焊接,研讨μBGA的PCB装配及可靠性。弯曲循环试验（1000～1000με）,用不同的热因数（Qη）回流,研究μBGA、PBGA和CBGA封装的焊点疲劳失效问题。确定液相线上时间,测定温度,μBGA封装的疲劳寿命首先增大,接着随加热因数的增加而下降。当Q。接近500S·℃时,出现寿命最大值。最佳Qη范围在300-750s·℃之间,此范围如果装配是在氮气氛中回流,μBGA封装的寿命大于4500个循环。采用扫描电子显微镜（SEM）,来检查μBGA和PBGA封装在所有加热N数状况下焊点的失效。每个断裂接近并平行于PCB焊盘,在μBGA封装中裂纹总是出现在焊接点与PCB焊盘连接的尖角点,接着在Ni3Sn4金属间化合物（IMC）层和焊料之间延伸。CBGA封装可靠性试验中,失效为剥离现象,发生于陶瓷基体和金属化焊盘之间的界面处。     

Effect of reaction time on mechanical strength of the interface formed between the Sn-Zn(-Bi) solder and the Au/Ni/Cu bond pad

In this work, the shear strengths and the interfacial reactions of Sn-9Zn, Sn-8Zn-1Bi, and Sn-8Zn-3Bi (wt.%) solders with Au/Ni/Cu ball grid array (BGA) pad metallization were systematically investigated after extended reflows. Zn-containing Pb-free solder alloys were kept in molten condition (240°C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 min. to 60 min. to render the ultimate interfacial reaction and to observe the consecutive shear strength. After the shear test, fracture surfaces were investigated by scanning electron microscopy equipped with an energy dispersive x-ray spectrometer. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The solder ball shear load for all the solders during extended reflow increased with the increase of reflow time up to a certain stage and then decreased. It was found that the formation of thick Ni-Zn intermetallic compound (IMC) layers at the solder interface of the Au/electrolytic Ni/Cu bond pad with Sn-Zn(-Bi) alloys deteriorated the mechanical strength of the joints. It was also noticed that the Ni-Zn IMC layer was larger in the Sn-Zn solder system than that in the other two Bi-containing solder systems.     

Intermetallic compounds formed during the reflow of In-49Sn solder ball-grid array packages

The intermetallic compounds formed at the interfaces between In-49Sn solder balls and Au/Ni/Cu pads during the reflow of In-49Sn solder, ball-grid array (BGA) packages are investigated. Various temperature profiles with peak temperatures ranging from 140°C to 220°C and melting times ranging from 45 sec to 170 sec are plotted for the reflow processes. At peak temperatures below 170°C, a continuous double layer of intermetallics can be observed, showing a composition of Au(In,Ni)₂/Au(In,Ni). Through selective etching of the In-49Sn solders, the intermetallic layer is made up of irregular coarse grains. In contrast, a number of cubic-shaped AuIn₂ intermetallic compounds appear at the interfaces and migrate toward the upper domes of In-49Sn solder balls after reflow at peak temperatures above 200°C for longer melting times. The upward floating of the AuIn₂ cubes can be explained by a thermomigration effect caused by the temperature gradient present in the liquid solder ball. The intermetallic compounds formed under various reflow conditions in this study exhibit different types of morphology, yet the ball shear strengths of the solder joints in the In-49Sn BGA packages remain unaffected.