Cohesive zone modeling and experimental verification. Since the voids in solder joints cant be eliminated then think differently to define how many voids or its size can be acceptable at a certain ratio. Understanding the reliability of solder joints used in. Design and material parameter effects on bga solderjoint. The crack area as percentage of total solder joint area is plotted in figure 2. Mitigate bga and qfn failures using redesigns, underfills. In these cases the shear strength of the solder is exceeded, resulting in fracture of the joint. Crack at the bga package and solder ball junction figure 2. Thermomechanical reliability of leadfree solder joints in surface.
Sacbisn bga solder joints part ii of report on inemi project on process development of bisnbased low temperature solder pastes raiyo aspandiar. Solder joint cracks caused by overloading are often the result of an accident or harsh treatment. Through many kinds of failure analysis method, the failure analysis conclusion is that bga solder joints crack is due to the solder joints. It has been possible for radio waves and messages to. Bga solder void correlation to viainpad, via fill, surface finish, and. Ball grid array bga and quad flatpack nolead qfn are among the most prevalent packages for integrated circuits ics. Cracks typically appear in the packagepcb boundary. Intel has defined selected solder joints as noncriticaltofunction nctf when. Reliability analysis of snpb and snagcu solder joints in. Statistical degradation modeling is the current method for predicting solder joint faults in programmed, operating fpgas.
Watch a video that shows robotic bga component deballing. Longterm reliability of flexible bga solder joints under. Taeho kang, ara lee, jaewoo jeong, and dongok kwak 2015 evaluation about solder imc crack of fine pitch bga package. Example of a cu6sn5 imc needle in the bulk microstructure of a sac alloy bga solder joint. Furthermore, dissolution of substrate metals during process reflow can lead to shifts in phase composition, additional primary phases, and volumetric contraction artifacts.
Meanwhile, most of the vippo solder joints reconnected just after becoming molten solder. From that point of view, this paper presented a novel fatigue crack propagation model for ball grid array package solder joint thermal fatigue life. This paper introduces the solder joints of bga on pcb top side appearing crack phenomenon after the bottom side passed wave soldering, the reason for solder joints crack is that partial solder joints are dewetting on the component side imc pad. Double reflowinduced brittle interfacial failures in pb. Nsmd had significantly less cracking as predicted by fem but nsmd failures occurred sooner different failure mode. Many stress tests were conducted over the years and they have all supported each other in the results and conclusions. In our case, we found the bga solder joint crack is not the same root cause as mentioned above. With the continued shrinking of electronic components, it has become more difficult to analyze defects in the materials. The trouble with bga solder joints the increasing density of modern assemblies always imposes new requirements on the packaging technology of the used chips. Mixing two different solder powders also causes this. The bga solder joint lifted cleanly along with the nisn intermetallic compound layer off of. This paper describes and characterizes electrically intermittent, brittle interfacial solder joint failures in a pbfree ball grid array bga subjected to two reflow cycles.
Voiding criteria in bgacsp component solder joints ipc blog. The collapse of the bga during reflow may not be even without compensation of one or more of the parameters. The challenge is that bgas and qfns present a greater risk than their leaded counterparts for solder joint failure. Sj bist conference paper pdf available in ieee aerospace conference proceedings april 2008 with 1,264 reads how we measure reads. These solder joint failures occur because bgas and qfns are susceptible to. Research on micro crack induced during the process of assembling. Package pad type nsmd smd package substrate trace crack nsmd. Alloys that undergo solidification over a wide range of temperatures generally exhibit a difference in the contraction behavior of the ensuing solid and liquid phases. The specific type of solder used in this experiment is.
Ball grid array bga solder joint intermittency detection. Reliability issues of leadfree solder joints in electronic. Evaluation about solderimc crack of fine pitch bga. In the extreme case, the solder joint may crack and result in an electrically open circuit. This could be due to either weak flux activity or excessive solder powder oxidation. It is important throughout the life of the product that the solder remains crack and fracture free. Addressing the issues around solder joint voids in surface mount products 1. Experiment results fc bga test data with preload has been reported in 2. Realtime xray 3d inspection of bga ic and pcb part 2. Visual bga inspection on all of the bga joints is not possible as one cannot see each of the solder joints through direct visual observation. It was interesting to find that serious crack defects appeared at the mixed bga solder joints.
Bga inspection ball grid array inspection is necessary to detect and isolate process defects between a chip and circuit board. Especially bga housings are in the centre of attention. Pdf solidification shrinkage defects in electronic solders. Early experience with messagepassing on the shrimp multicomputer.
Dye and pry bga inspection dye and pry dye and pry technique, which relies on a liquid dye that penetrates existing micro cracks or under open solder balls is a destructive test method for the revealing of defects on the solder ball to pad interface see figure below. Able to view for bga solder joint cracks able to inspect between components with gaps as tight as 35 mils and component height gaps as small as 2 mils. How to detect solder joint faults in operating fpgas in. Solder is important in the mechanical and electronic functionality of the component. The concentration of phosphorous at the surface was measured as 28 wt% based on eds spectra. Fine pitch bga solder joint split in smt process ieee. Addressing the issues around solder joint voids in surface. Crosssectioning and scanning electron microscopy sem is a destructive method. Solder joint fatigue life prediction methodology by measuring the crack growth rate of actual solder joints, darveaux 20 was able to establish four crack. The main reason is that the solder joints at the four most corners of the bga package bear relatively large stress, which is likely to cause cracks. As solder mask define soldering is used, soldering can only cover the surface with side neglected, which leads intensity of soldering connection worse than copper define soldering. Ability to view multiple bga rows or jleads to view solder joint profiles able to detect the presence of nonmetallic contamination such as flux. Cracks in a real solder joint are difficult to identify using an xray system.
Any mismatch in coefficient of thermal expansion cte between the bga package and the pcb will cause stress on the solder joint. To understand the solder joint reliability, a daisychain structure was designed and built to evaluate the microstructure and thermal mechanical stress on the solder joint. It has been shown that voids are stress relievers within the solder joint, implying that they provide the solder joints with some stress relief and they dont promote the propagation of cracks within the joints. At the solder joint level, the damage is seen as a crack at the packagepcb boundary, although there are other possible points of failure in the solder joint network. Outline this document includes figures and tables for solder joint acceptability criteria on a variety of component types. Whenever this much voiding forms in a single bga, it is an indication of a poor solder joint formation. Kimb ajet propulsion laboratory, california institute of technology, pasadena, ca 91109, usa bboeing defense and space group, seattle, washington, usa received 20 april 1998. The effect of ramp rate on temperature cycle fatigue in. One common way to do this analysis is through a bga solder joint section. The chip is soldered to the motherboard with many small solder balls bga and one ore more solder joints crack with time due to the thermal cycle which creates thermal stress contraction and. Unfortunately, the voids in the solder joint are difficult to avoid completely during the soldering process, especially the bga, qfn, lga kind of package need a large volume of solder. Current engineering approaches for solder joint reliability assessment include the methodologies of the life prediction, computer modeling, and accelerated testing of solder joints.
Transient solder separation of bga solder joint during second reflow cycle steven perng and weidong xie cisco systems, inc. Thermal fatigue lifetime prediction of bga solder joint via a novel. Transient solder separation of bga solder joint during. By jasbir bath, ipc principal engineer over the last few years, there have been many discussions on the affect of voiding on bga csp solder joint reliability. A crack was observed in the reaction layer following exposure to a vibration environment. Confessions of a pcb designer on solder mask medium. One of the challenges in an experimental study of solder joint reliability is to determine when cracks occur in a solder joint or when a solder joint fails. This bga definitely has too much voiding and needs to be corrected. The effect of ramp rate on temperature cycle fatigue in solder joints fig. Typical xray image of completely reflowed solder balls under bga. In this article, well do a bit of a primer on this process and how it works in practice. The brittle fracture cracks are located at the interface between the nisn intermetallic and the phosphorus rich electroless ni layer 2, 3, and the package corner solder joints are generally most susceptible.
Pcbcart has rich experience in assembling bga chip onto circuit boards. Ball grid array reliability assessment for aerospace applications r. Bi region of solder joint pcb land crack cracking in the solder and along the solder imc interface crack 9 bga solder joint example. A crack can cause the partial separation of the solder ball from either the bga package or the pcb. For example, when using too much force to mount a soldered assembly in position in an enclosure, or when dropping a mobile phone. Reballing toshiba satellite laptop with homemade bga. Ipca610 and jstd001 standards state that greater than 25% of voiding in any ball in the xray image area is classified as a defect according to electronic product classifications. How to detect solder joint faults in operating fpgas in real time ee.
Regarding the solder joint crack, most of cases are caused by external force, such as assembly operation, board testing operation, or unmatched mechanical parts assembly. Visual bga inspection consists of the bga rework technician use a microscope or pure visual inspection in order to see the outer row and sometimes even the start of the second row into the center of the device. Micro crack induced by process stress becomes one of the critical factors which affect yield and long term reliability of bga solder joints. Finite element based solder joint fatigue life predictions. Challenges in manufacturing reliable leadfree and rohs. Ipc7095c design and assembly process implementation. One solderjoint in the thermal array t19 an smd pad was 90% cracked distribution of cracking more balanced between perimeter rows and thermal array than for pure smd designs. Solder ball materials were meshed in ansys using the visco107 elements, whereas all other package materials were meshed using solid45 elements. Four corners of bga had better be designed to be smd solder mask define because the enlarging of bga base and the presence of solder mask cover around pad will dramatically improve crack resistance of pad. Challenges in manufacturing reliable leadfree and rohscompliant components july 2010 altera corporation altera pbfree solutions altera s pbfree solutions are motivated by the requirements being imposed on the semiconductor and electronics industry to reduce or eliminate the use of lead. Study on failure mechanism of bga solder joints crack. To understand the solder joint reliability, a daisychain structure was designed and built to evaluate the microstructure and thermal mechanical stress on the solder joint under thermal cycling 65c to 150c. This precision process is highly reliable when preparing bga. The optimization work was designed to solve the above problem and the reliability of the bga solder joints after the optimization was evaluated.
Author links open overlay panel amir nourani saeed. Example of a cu3sn interfacial imc of a sac alloy bga solder joint on osp board. Characterization of mixed alloy sacbisn bga solder joints. However, the terminals of those components escape from. Solder joint reliability of pbfree snagcu ball grid.