一种BGA器件的低温组装工艺方法

介绍了BGA焊接的一般方法,分析了BGA空洞产生的原因;针对高可靠应用场合需求,详细描述了一种可有效减少空洞发生的BGA低温焊接方法,并对采用这种方法焊接的BGA的焊点可靠性进行了分析.     

国外工艺文献导读

BGA柔性植球技术；通过选择最佳的炉温曲线减少电力消耗；关于底部填充在倒装芯片应用中空洞缺陷的影响因素；堆叠封装工艺的开发和可靠性评价；无铅BGA／有铅焊锡膏混装焊点的典型失效问题；SnAgCuBi和SnAgCuBiSb焊点性能研究。     

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。     

BGA焊点空洞对信号传输性能的影响

焊点空洞问题是影响BGA焊点质量和可靠性的重要因素之一.基于三维电磁场仿真软件HFSS对单个焊点空洞建模,分别研究了BGA焊点中不同位置、大小和数目的空洞对焊点传输性能的影响.研究结果表明,焊点内部空洞比表面处空洞对信号传输性能的影响更大;在焊点表面上的空洞,位于焊点中部的空洞比接近上下焊盘的空洞对信号传输性能的影响大;随着焊点中空洞体积增大或空洞数目的增加,焊点的回波损耗增大.     

BGA空洞形成的机理及对焊点可靠性的影响

BGA空洞是BGA组装过程常见的工艺缺陷,系统介绍了BGA空洞形成的机理与主要影响因素,讨论了BGA空洞的接受标准及其对焊点可靠性的影响,提出了消除及减少空洞缺陷的主要措施.     

BGA焊点空洞问题分析

BGA器件已经广泛应用于各个领域,首先对BGA器件进行了简介,在给出其焊点质量检验合格判据后,针对BGA组装过程中常见现象空洞,分析了空洞产生的机理,并进一步说明空洞对焊点可靠性的影响。最后根据空洞产生机理提出了一些措施以减少和改善空洞。     

BGA封装器件焊点缺陷X-射线检测法

讨论了BGA器件焊接的特点,并对BGA器件焊接过程中产生的缺陷进行了阐述,采用X-射线检测仪检测了BGA封装器件安装焊点的几种常见缺陷,分析、阐述了其图像与相应缺陷的关系,结果表明X-射线检测方法能够准确地检测出BGA封装器件安装中的各种焊点缺陷,并能够自动计算BGA封装器件安装焊点的空洞率,对空洞缺陷的快速检测和预防具有实际意义.     

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.     

BGA焊点可靠性工艺研究

伴随高密度电子组装技术的发展,BGA(Ball Grid Array)成为高密度、高性能、多功能及高I/O数封装的最佳选择。文章分析了影响BGA焊点可靠性的关键因素,特别提出了减少焊点空洞缺陷和提高剪切强度的主要措施,并通过试验优化出各工艺参数。结果表明:运用优化的工艺参数制作的BGA焊点,焊接空洞以及芯片剪切强度有了明显改善,其中对BGA焊接样品进行150℃、1000h的高温贮存后,焊点的剪切强度完全满足GJB548B-2005的要求。     

BGA无铅焊点零空洞缺陷控制研究

在无铅BGA封装工艺过程中,通过不同组分的BGA焊球合金与焊膏合金组合焊接、焊膏助焊剂活性剂不同配比及其不同再流焊接条件等实验,对焊料合金和助焊剂配比、再流焊接峰值温度、再流保温时间等参数变化,以降低BGA焊点空洞缺陷进行了研究。结果表明选用相同或相似的BGA焊球和焊膏合金组合焊接、选用活性强的焊膏、选择焊接保温时间较长均有助于降低BGA焊点空洞缺陷产生的几率和空洞面积,BGA焊点最佳再流焊接峰值温度为240℃,当峰值温度设置为250℃时,BGA焊点产生空洞缺陷几率会比240℃高出25%～30%。     

有铅和无铅BGA混装工艺研究

分析比对了有铅和无铅两种焊料的不同温度特性。针对军工产品经常面对的有铅和无铅BGA同时组装在一块印制板上的情况,提出了有铅和无铅BGA混合组装的工艺难点。通过工艺试验列举了混合组装中各个环节所应注意的要点,强调要加强过程控制。最后利用各种可靠性试验和分析证明了混合组装焊点的可靠性。     

High Cycle Cyclic Torsion Fatigue of PBGA Pb-Free Solder Joints

In this study, a comprehensive experimental and numerical approach was used to investigate high cycle cyclic torsion fatigue behavior of lead-free solder joints in a plastic ball grid array (PBGA) package. The test vehicle was a commercial laptop motherboard. The motherboard was subjected to torsional loading and life tests were conducted. Using finite element analysis (FEA), the test assembly was simulated as a global model and the BGA component was simulated as a local model. Strains measured on the motherboard surface near by the BGA were used to calibrate the FEA models. By combining the life test results and FEA simulations, a high cycle fatigue model for the lead-free solder joints was generated based on the Coffin-Manson strain-range fatigue damage model. This model can now be used to predict the cycles to failure of BGA interconnects for new electronic product design under cyclic torsion loading.     

Ball-grid-array solder joint model for assembly-level impact reliability prediction

It has been well established that lead-free solder underperforms conventional leaded solder in reliability under dynamic impact. Common failures observed on ball-grid-array (BGA) solder balls on chip under board level impact include bulk solder ductile failure, intermetallic (IMC) layer crack and pad-lift. In this work, a finite element modeling approach was proposed to model bulk solder ductile failure and intermetallic layer crack. The use of beam elements and connector elements to represent the bulk solders and board/component side intermetallic layers, respectively, offers the advantage of simplicity over the use of continuum elements and cohesive elements for solder joints. This approach enables the modeling of assembly level impact with significantly less computational resources. The model was verified by comparing its prediction of BGA solder reliability against actual test results in a dynamic four-point bend test. The physical tests consist of ball impact at varying heights on a board with a mounted chip, and the subsequent analysis of the failure modes of the BGA solder joints. Simulation results were in good agreement with test results. The study shows that it is feasible to model BGA solder joint ductile failure and intermetallic layer crack under impact with simple elements with reasonable accuracy.     

Random vibration reliability of BGA lead-free solder joint

Solder joint fatigue failure under vibration loading has been a great concern in microelectronic industry. High-cycle fatigue failure of lead-free solder joints has not been adequately addressed, especially under random vibration loading. This study aims to understand the lead-free solder joint behavior of BGA packages under different random vibration loadings. At first, non-contact TV Laser holography technology was adopted to conduct experimental modal analysis of the test vehicle (printed circuit board assembly) in order to understand its dynamic characteristics. Then, its first order natural frequency was used as the center frequency and narrow-band random vibration fatigue tests with different kinds of acceleration power spectral density (PSD) amplitudes were respectively carried out. Electrical continuity through each BGA package is monitored during the vibration event in order to detect the failure of package-to-board interconnects. The typical dynamic voltage histories of failed solder joints were obtained simultaneously. Thirdly, failed solder joints were cross-sectioned and metallurgical analysis was applied to investigate the failure mechanisms of BGA lead-free solder joints under random vibration loading. The results show that the failure mechanisms of BGA lead-free solder joint vary as the acceleration PSD amplitude increases. Solder joint failure locations are changed from the solder bump body of the PCB side to the solder ball neck, finally to the Ni/intermetallic compound (IMC) interface of the package side. The corresponding failure modes are also converted from ductile fracture to brittle fracture with the increase of vibration intensity.     

SAC105焊锡膏的开发与评价

采用低银化焊料合金是无铅化电子组装提高性价比的发展趋势。开发了采用SAC105低银焊料合金的SUPER105系列焊锡膏,抗氧化、表面绝缘电阻、印刷性能、BGA空洞率、焊点推力等测试结果表明,SUPER105焊锡膏完全适用于消费类电子产品组装。     

Investigation of mechanical shock testing of lead-free SAC solder joints in fine pitch BGA package

The lead-free Sn-Ag-Cu (SAC 305/405) solder that replaced the tin-lead eutectic solder tends to be more brittle in nature due to high stiffness and excessive solder interfacial reactions. This leads to higher occurrences of solder joints failure during surface mount assembly and handling operations as a result of PCB bending, shock impact and drop. In this work, mechanical tests simulating the shock impact were conducted on lead-free SAC of different weight percentages. These SAC materials were prepared for use in the solder joints of fine pitch ball grid array (BGA) components which were mounted onto the motherboard. After the mechanical shock tests, strain measurements were performed on the BGA components to gauge the solder joint integrity, which was shown to be related with the formation of intermetallics in the bulk and at the interface of the SAC solder. The ball pull tests were conducted to determine both the bulk and interfacial strength and the solder joint fracture, which was classified as either mode 1, 2 or 3. A correlation was made between the silver (Ag) and copper (Cu) weight percentages with the metallurgical reactions.     

BGA的无铅返修工艺

无铅焊料的应用,对电子组装工艺提出了新的要求,特别是对BGA的无铅返修提出了新的挑战。从符合RoHS标准的BGA封装入手,介绍了BGA封装技术的”无铅化”改进。然后,结合BGA的无铅返修工艺流程,详细阐述了各步骤的具体操作方法及关键工艺点,并对如何正确设定无铅返修温度曲线进行了重点分析。最后,对比锡铅返修工艺总结了无铅返修工艺的特点。     

Solder Ball Attachment Assessment of Reballed Plastic Ball Grid Array Packages

The ban of lead in consumer-based electronics by many countries has resulted in a dramatic reduction in the availability of electronic components with tin-lead terminations. With the uncertainty associated with lead-free reliability and the issues associated with mixing lead-free solder with tin-lead solder, medical, defense, and aerospace equipment manufacturers are examining and in some cases implementing reprocessing practices to convert lead-free terminations to tin-lead. For area array packages, the practice is referred to as reballing. While reballing has been used for part reclamation, very little information is available on the reliability of reballed parts. This paper presents lead-free ball grid array (BGA) packages subjected to two ball removal and two ball reattachment techniques. Solder attach strength was used as a metric to examine the reballing process. Both the ball shear test and the cold bump pull (CBP) test were used to test solder strength. The impact of isothermal aging was also examined. The solder strength of reballed BGAs remained at the same level when different reballing methods were used and under different aging conditions. The lead-free non-reballed BGAs had higher solder strength and wider strength distribution than reballed tin-lead BGAs. The pull strength increased as the pull speed increased in the CBP test.