1、a,1,Sources of Voids,a,2,Sources of Voids,錫球生產(chǎn)的方式,a,3,Sources of Voids,芯片植球的過程,芯片Mount在主板上的過程,有機(jī)會消散掉,三明治結(jié)構(gòu)讓氣泡無法散去,a,4,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 contaminates supply gases that can

2、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 by not allowing time for void m

3、igration 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 錫球內(nèi)的氣泡通常導(dǎo)因于錫球陷縮,濕氣與錫膏揮發(fā)物 陷縮:通常,錫

4、球的內(nèi)部是在整個焊點(diǎn)的固化過程中最后冷卻凝固的部份,可以預(yù)期這樣的現(xiàn)象會導(dǎo)致陷縮孔產(chǎn)生 濕氣跟污染物在揮發(fā)時被錫球捕捉而形成錫球內(nèi)氣孔 錫膏內(nèi)的助焊劑在回焊爐升溫的過程中因?yàn)榻到舛尸F(xiàn)汽化的狀態(tài).而在BGA中,揮發(fā)的氣體將被緊包在像三明治一樣的兩層PCB板間,而產(chǎn)生的氣泡也通常會上升到錫球的上方.通常一個比較快速的升溫曲線會使錫球內(nèi)產(chǎn)生更多的氣泡,因?yàn)闆]有足夠的時間讓氣泡可以移動到錫球表面消散掉 PBGA所使用的助焊膏比錫球用的助焊劑較不易產(chǎn)生氣泡 在維修過程中所加入的過多助焊劑會導(dǎo)致錫球產(chǎn)生氣泡 合適的爐溫及干凈的零件會降低錫球產(chǎn)生氣泡,a,5,Sources of Voids: Espec

5、ially for ImAg Board,Galvanic Corrosion:電鍍銹蝕腐蝕,當(dāng)兩種不同的金屬直接接觸并曝露在水或含融鹽的水等電解質(zhì)中，會產(chǎn)生電鍍銹蝕腐蝕。電流會在兩種金屬之間流動，類似電池的化學(xué)反應(yīng)因而產(chǎn)生。兩種金屬之間的電位差越大，氧化的速度越快；反之，電位差越小，氧化的速度越慢。而銅與銀之間的電位差使得銅箔表面出現(xiàn)陷穴,a,6,Sources of Voids: Especially for ImAg Board,Immersion Ag,Cu cave,Flux,IMC,IMC,IMC,銅箔中的陷穴,導(dǎo)致了氣泡的生成,a,7,IPC-7095B對錫球的描述,a,8,Ty

6、pe 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

7、(s) at the ball/board substrate interface after board level assembly process.,Voids classification in IPC-7095B,a,9,Macrovoidsare 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 aff

8、ect the solder joint reliability unless they are present at interfacial regions in the solder joints where cracks typically propagate. Macrovoids 是最常在錫球中廣泛出現(xiàn)的Void,導(dǎo)因是揮發(fā)性的成分在焊接過程中釋出的氣體.這類的Void并不會影響錫球的可靠度,除非是在出現(xiàn)在交界面上的Void,因?yàn)檫@類的Void通常會使裂痕增長 Planar Microvoidsare a series of small voids, in relatively th

9、e same plane, 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氣泡,且通常座落在PCB面與Solder之間.這通

10、常來自于化銀板表面處理上的銅的孔洞.雖然不會影響初期的產(chǎn)品質(zhì)量但是卻會對solder的壽命產(chǎn)生影響(化銀板容易有微氣泡) 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 Voi

11、ds導(dǎo)因于固化過程的收縮,常出現(xiàn)于Sn-Ag-Cu等無鉛錫球上.這些Void不會出現(xiàn)在錫球跟PCB的接面上,且不會損害錫球的可靠度,Voids classification in IPC-7095B,a,10,Microvia 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 relia

12、bility. Microvia Voids是因?yàn)閷⑽⒚た椎脑O(shè)計應(yīng)用在PCB板上所造成的.大型的微盲孔,如果位置是在芯片高應(yīng)力區(qū)的錫球中,將會沖擊到錫球的可靠度 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 a

13、fter aging at high temperatures 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 with

14、in the IMC during drop or mechanical shock to the solder joint. IMC Microvoids通常發(fā)生在含錫量高的錫球中的IMC層內(nèi)錫球與銅之間,包括Sn-Ag-Cu跟錫/鉛類的錫球.這類IMC中的Microvoids不會在焊接過程中立刻出現(xiàn),但是會因?yàn)楦邷乩匣蚴歉邷匮h(huán)而出現(xiàn).真正的根源仍在調(diào)查中,但是Kirkendall微孔形成機(jī)制可能在其中扮演了一部分的角色.這些Void會影響錫球的可靠度,舉個特別的例子來說,這些Void會在IMC層中成為摔落或沖擊測試時粒子破裂的起始點(diǎn). Pinhole Voidsare caused b

15、y pinholes in the copper lands of the PCB. With sufficient quantity, they can affect solder joint reliability Pinhole Voids是因?yàn)镻CB板銅面上的針狀凸點(diǎn)或凹陷造成.如果數(shù)量夠多的話,會影響到錫球的可靠度,Voids classification in IPC-7095B,a,11,When there is more than one void per solder ball, the dimensions of the voids will be added to ca

16、lculate the total voiding in that solder ball. 如果錫球中的氣泡多于一個,則氣泡尺寸的計算必須根據(jù)所有氣泡的尺寸來加總,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 a

17、t the interface between the ball-and-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

18、 path to accelerate the cracking condition.,相對于對Void本體及Void在錫球中的大小, Void的Location才是比較需要在意的.目前并沒有證據(jù)或是經(jīng)驗(yàn)值可以指出在錫球內(nèi)的氣泡會導(dǎo)致失效發(fā)生.但是生成在芯片封裝底層跟錫球間與錫球跟PCB板之間的Voids比較可能使得錫球破裂.這是因?yàn)榱押?如果有的話)通常會出現(xiàn)在接口層或是氣泡上,亦或是由氣泡提供了一個可以使破裂情況加速的途徑,a,12,Intel JG Fab B Socket H X-section,Shrinkage Voids,a,13,Intel JG Fab B Socket H X-section + PCH D&P,Planar Microvoids,a,14,Comparison between Different Suppliers: Fab A,Ellington BTHC9350000E,在Fab A,不同的Vendor所呈現(xiàn)的氣泡模式中,即可發(fā)現(xiàn)BTC與E&E不同,但也都出現(xiàn)在最具威脅性的IMC層上,a,15,Comparison between Different Suppliers: Fab B,在Fab B時, E&E的氣泡有了大幅度的改善,但是BTC的問題反而更加突顯了出來,a,16,Comparison between Dif