BGA Void气泡问题分析

1、Sources of VoidsSources of VoidsN2(g)Chamber2Pressure=P2P1P2LN2N2(g)Chamber1Pressure=P1Molten solder在锡球生产过程中,会使用两个压力不同的Chamber,上方镕解槽C的压力大于下方冷却槽,并借着压力差使镕融的锡从Chamber 1被挤压到Chamber 2滴落,并在Chamber 2冷却成形在溶融的锡中,所有的气泡都会因为浮力而悬浮在镕融的表面上,所以在溶融液中是没有气泡的镕融且未含气泡的锡在冷却阶段随着时间变成球形锡球生产的方式Sources of VoidsPackage sideFluxP

2、ackage sidePackage sidePackage sidePackage sideBoard sidePasteBoard sideBoard sidePackage sideBubblePackage side芯片植球的过程芯片Mount在主板上的过程有机会消散掉三明治结构让气泡无法散去Sources of Voids Shrinkage the interior of a solder joint is the last part of the joint to solidify so you expect it to have a void. Moisture and con

3、taminates supply gases that can be trapped. Flux in the paste degrades and becomes gaseous during ramp-up in the reflow oven. On a BGA the gases are tightly sandwiched between two surfaces and the voids that occur typically rise to the top of the solder joint. A high ramp rate can cause more voiding

4、 by not allowing time for void migration out of the joint (ramp rate example, 75 vs. 60C/minute) Paste flux to attach PBGAs tends to produce fewer voids than with solder paste. Too much flux added during the rework process can cause voids. Proper oven profile and clean parts can reduce solder voids锡

5、球内的气泡通常导因于锡球陷缩,湿气与锡膏挥发物-陷缩:通常,锡球的内部是在整个焊点的固化过程中最后冷却凝固的部份,可以预期这样的现象会导致陷缩孔产生-湿气跟污染物在挥发时被锡球捕捉而形成锡球内气孔-锡膏内的助焊剂在回焊炉升温的过程中因为降解而呈现汽化的状态.而在BGA中,挥发的气体将被紧包在像三明治一样的两层PCB板间,而产生的气泡也通常会上升到锡球的上方.通常一个比较快速的升温曲线会使锡球内产生更多的气泡,因为没有足够的时间让气泡可以移动到锡球表面消散掉-PBGA所使用的助焊膏比锡球用的助焊剂较不易产生气泡-在维修过程中所加入的过多助焊剂会导致锡球产生气泡-合适的炉温及干净的零件会降低锡球产

6、生气泡Sources of Voids: Especially for ImAg BoardGalvanic Corrosion:电镀锈蚀腐蚀当两种不同的金属直接接触并曝露在水或含融盐的水等电解质中，会产生电镀锈蚀腐蚀。电流会在两种金属之间流动，类似电池的化学反应因而产生。两种金属之间的电位差越大，氧化的速度越快；反之，电位差越小，氧化的速度越慢。而铜与银之间的电位差使得铜箔表面出现陷穴Sources of Voids: Especially for ImAg BoardImmersion AgCu caveFluxIMCIMCIMC铜箔中的陷穴,导致了气泡的生成IPC-7095B对锡球的描述

7、Type A: Void(s) within the ball (package level) as received.Type B: Void(s) at the ball/package substrate interface as received.Type C: Void(s) within the ball after board level assembly process.Type D: Void(s) at the ball/package substrate interface after board level assembly process.Type E: Void(s

8、) at the ball/board substrate interface after board level assembly process.Voids classification in IPC-7095BMacrovoidsare the most widely occurring voids in solder joints. These are caused by volatile compounds that evolve during the soldering processes. These macrovoids generally do not affect the

9、solder joint reliability unless they are present at interfacial regions in the solder joints where cracks typically propagate.Macrovoids 是最常在锡球中广泛出现的Void,导因是挥发性的成分在焊接过程中释出的气体.这类的Void并不会影响锡球的可靠度,除非是在出现在交界面上的Void,因为这类的Void通常会使裂痕增长Planar Microvoidsare a series of small voids, in relatively the same pla

10、ne, located at the interface between the PCB Lands and the solder. These are caused by copper caves under ImAg- surface-finish coated lands. They do not affect initial product quality, but can affect long term solder joint reliability.Planar Microvoids是位在同一平面的一系列小气泡,且通常座落在PCB面与Solder之间.这通常来自于化银板表面处理

11、上的铜的孔洞.虽然不会影响初期的产品质量但是却会对solder的寿命产生影响(化银板容易有微气泡)Shrinkage Voids are caused by the shrinkage during solidification, mostly for SAC and other lead-free solders. They do not generally appear near the solder-to-PCB land interface and do not impair the solder joint reliability.Shrinkage Voids导因于固化过程的收缩,

12、常出现于Sn-Ag-Cu等无铅锡球上.这些Void不会出现在锡球跟PCB的接面上,且不会损害锡球的可靠度Voids classification in IPC-7095BMicrovia Voidsare caused by the presence of microvias designed in the PCB lands. Large Microvia Voids, if located in solder joints in high stress areas of a package, can impact solder joint reliability.Microvia Void

13、s是因为将微盲孔的设计应用在PCB板上所造成的.大型的微盲孔,如果位置是在芯片高应力区的锡球中,将会冲击到锡球的可靠度IMC Microvoidsoccur within the Intermetallic Compound (IMC) formed between copper and high tin solders, including SAC and tin/lead solders. These IMC Microvoids do not form immediately after the soldering process, but after aging at high tem

14、peratures or during temperature cycling of the solder joints. The true root cause is still under investigation,but a Kirkendall voiding mechanism may play a part. These voids can affect solder joint reliability, particularly in instances when brittle fracture is initiated within the IMC during drop

15、or mechanical shock to the solderjoint.IMC Microvoids通常发生在含锡量高的锡球中的IMC层内锡球与铜之间,包括Sn-Ag-Cu跟锡/铅类的锡球.这类IMC中的Microvoids不会在焊接过程中立刻出现,但是会因为高温老化或是高温循环而出现.真正的根源仍在调查中,但是Kirkendall微孔形成机制可能在其中扮演了一部分的角色.这些Void会影响锡球的可靠度,举个特别的例子来说,这些Void会在IMC层中成为摔落或冲击测试时粒子破裂的起始点.Pinhole Voidsare caused by pinholes in the copper l

16、ands of the PCB. With sufficient quantity, they can affect solder joint reliabilityPinhole Voids是因为PCB板铜面上的针状凸点或凹陷造成.如果数量够多的话,会影响到锡球的可靠度Voids classification in IPC-7095BWhen there is more than one void per solder ball, the dimensions of the voids will be added to calculate the total voiding in that

17、solder ball.如果锡球中的气泡多于一个,则气泡尺寸的计算必须根据所有气泡的尺寸来加总In regard to voids and the percentage of voids within the ball, location of the voids is of greater concern. There is no evidence or empirical data that indicates that voids within the ball will cause failure. Voids at the interface between the ball-and

18、-package substrate as well as voids at the interface between the ball and the PCB will be more likely to contribute to solder joint cracking. This is because cracks (if they occur) will typically occur at the interface and the void or voids can provide (in time) a path to accelerate the cracking con

19、dition.相对于对Void本体及Void在锡球中的大小, Void的Location才是比较需要在意的.目前并没有证据或是经验值可以指出在锡球内的气泡会导致失效发生.但是生成在芯片封装底层跟锡球间与锡球跟PCB板之间的Voids比较可能使得锡球破裂.这是因为裂痕(如果有的话)通常会出现在接口层或是气泡上,亦或是由气泡提供了一个可以使破裂情况加速的途径Intel JG Fab B Socket H X-sectionShrinkage VoidsIntel JG Fab B Socket H X-section + PCH D&PComponent sidePCB sidePlanar MicrovoidsComparison between Different Suppliers: Fab AEllingtonBTHC9350000EE & EBTTM9370003DBTCBTJG9410002W在Fab A,不同的Vendor所呈现的气泡模式中,即可发现BTC与E&E不同,但也都出现在最具威胁性的IMC层上Comparison between Different Suppliers: Fab BE&EBTJG9460000TBTCBTJG9410005G在Fab B时, E&E的气