February 21, 2007 introduction failure analysis of bga devices can be both expensive and daunting. Voids are largely caused by the amount of outgassing flux that gets entrapped in the solder during reflow 2. Typical, leadfree solder, such as sac305, has a thermal conductivity of about 60. In this paper, various types of voids found in solder joints will be described. Some solder pastes are prone to generate higher voiding than others. Effect of voids on thermomechanical reliability of solder joints.
A solution shown on a us design web site 6 suggests defining a solder mask area around the via hole. Voids are defined as cavities formed in the solder joint. Solder voiding solder paste, solder flux fct solder. Occurrence of voiding dropped from 76% to 39% and 23%, respectively, for partial and full via filling. In small solder joints, voids can significantly reduce their current carrying capacity. For example, acidflux solders that are commonly used in plumbing should never be used on electronics. How does surface finish affect solder paste performance. Solder voiding within surface mount technology smtnet. Only voids in the solder joint crack propagation path reduced the solder joint thermal cycle life. Voids are related to flux thats entrapped in the joint, as well as paste oxidation. Analysis of voiding levels under qfn package central.
Many stress tests were conducted over the years and they have all supported each other in the results and conclusions. Voids in solder joints voids in solder joints smta. Jennifer nguyen, david geiger, and dongkai shangguan, ph. Regular cleaning of the tip before use is one of the best ways to prolong tip life and make soldering easier. Thus even with vacuum reflow, the debate remains regarding the effect of voiding on solder joint reliability. The biggest cumulated area of void scanned has an apparent diameter of 48.
The basic soldering guide photo gallery s oldering is a delicate manual skill which only comes with practice. Understanding voids in flip chip interconnects ieee electronics. To be published in the proceedings of smta international, september 17 21, 2016, rosemont, il. Xray images of large voids in lts legs 41 chee chee solder paste mid solder joint location 100% bi mixing in balls. Jan 21, 20 taking a close look at voids in bga solder balls researchers are questioning the impact of voids in bga solder balls.
So as this is a variable it needs to be eliminated in the experiment. Aspandiar, voids in solder joints, smta journal, v19, issue 4, 2006 pinhole microvoids. Struk2 nasa glenn research center, cleveland, oh, 445 and anthony rotella3 case western reserve university, cleveland, oh, 44106. Although there are other options available such as alloys containing bismuth or indium and other elements, tinsilvercopper solders, also known as. Most of the voids come from out gassing of the chemicals in the flux. Let it flow keep heating the solder and allow it to flow into the joint. Solder voiding in ball grid array bga solder joints has been well characterized and documented in ipca610 and ipc. However, with some methods showing that voiding can be. Leadfree smt soldering defects how to prevent them tinsilvercopper alloys are the primary choice for leadfree smt assembly. Aspandiar, smta northwest chapter meeting 2005 ieee components, packaging and manufacturing technology, scv chapter 9242015. Voids reduce the thermal conductivity of the solder joints. The main objective of this study was to study the effect of voids on the reliability of bgacsp solder joints. Mechanism of void formation in reflow voids from solder paste flux clean tin oxide sno2 flux substratepcb void substratepcb void acid b acid c halide acid a shenmao. With the electronics manufacturing industry moving to lead free soldering and with ball grid array bga packages becoming thinner and having finer ball pitches, there is an increase in the incidences of a smt nonwet type of defect known as headandpillow hnp.
Voiding control at qfn assembly surfacemount technology. Have good ventilation when soldering, and try not to breathe in the fumes. The effect of voids on the reliability of a solder joint depends on size, frequency and location 1. Even the leadfree solders may contain other harmful components. Void free soldering with a new vaporphase with vacuum technology a. Voids can cause solder transfer between neighboring solder joints during the reflow soldering process. First and foremost, solder paste contributes to voiding. Voids in solder joints are largely a function of differential pressure between vapor pressure of the gases inside of the. Crystallographically faceted void formation in the matrix of. Crystallographically faceted void formation in the matrix. The effect of voiding in solder interconnections formed. A model study of profiling for voiding control at leadfree. The effect of vacuum reflow processing on solder joint.
Voids in solder joints are representing one of the main problems especially for power. This embedded solder flux helps the solder flow and bond to the parts being soldered, but this type of solder isnt ideal for all jobs. Detailed industry investigations have shown that voids have little effect on solder joint integrity unless they fall into specific locationgeometry configurations. Torch soldering is widely used in the plumbing trade for soldering copper tubing to copper fittings. Types of solder for the right application lifewire. Siminski1, and tim bao2 1air products and chemicals, allentown, pa 181951501, usa 2air products and chemicals, shanghai 201203, china email.
Also the effect of void location, frequency, and the size of the void on the reliability of solder joints was investigated. An opposing school of thought was that voids act as crack arrestors, which improve solder joint life. Accurately capturing systemlevel failure of solder joints. The effect of vacuum reflow processing on solder joint voiding. Partial filling produced almost equivalent results with 64% reduced solder void size. This paper gives a preliminary report on observations of voids which tend to be associated with, and adjacent to, intermetallic compounds in the solder bulk and nearsubstrate. Ipc solder products value council, the effect of voiding in solder interconnections formed from leadfree solder. Power dissipation for a surface mount device the power dissipation for a surface mount device is a function of the draincollector pad size. Voiding criteria in bgacsp component solder joints ipc blog. Wilcox 3 ibm corporation 1rochester, mn, 2poughkeepsie, ny, 3endicott, ny abstract solder voiding in ball grid array bga solder joints has been well characterized and documented in ipca610 and ipc. Solder joint voids were observed in the solder joint, not at the. Recently, voids in solder joints has been a hot topic of discussion within the electronics manufacturing industry. Leadfree soldering for space applications leadfree.
Boards using solder pastes selected in phase 1 drop shock testing under appropriate test conditions select two ductile and two jrp pastes from shock test results to evaluate under temperature cycling pop soc tv tests completed shock results published at 2018 smtai. The effect of voiding in solder interconnections formed from. The causes are starting to surface by mark currie, the electronics group of henkel while there are conflicting opinions on the effect of voiding in leadfree solder joints in relation to how much is too much and whether or not voiding causes any longterm. However, sweatman et al showed that vacuum reflow by itself does not ensure a void free solder joint 18. Figure 1 illustrates aspandiar s solder joint void classifications. Remember that your ability to solder effectively will determine directly how well the prototype or product functions during its lifespan. Addressing the issues around solder joint voids in surface.
Vent channels resulted in additional open areas that reduced solder joint continuity. System level solder joint reliability using sherlock 9 strains on the board and in bga solder joints are evaluated for each boundary condition small variation in peak board strain is observed between boundary conditions mount points in proximity of bga component can significantly increase strain in solder. Figure 4a is the linear profile used in the experiment, and figure 4b shows the voids. Effect of voids on thermomechanical reliability of solder. However, it cant eliminate voids completely due to the surface finish wetting issues. The root cause of voids in bga solder joints is well understood by the electronics industry with a number of papers published on the topic 1, 2, 3.
Reduction of voids in solder joints an alternative to. There are many different types of voids in solder joints, and these can impact the solder joints reliability depending on the type, area or volume content and location of voids in a solder. No clean sn63pb37 solder paste works well with most surface finishes no clean sac305 solder paste is a good leadfree option enig and hasl 6337 work well with most solder pastes immersion tin and immersion silver did not perform as well as the other surface finishes osp and leadfree hasl showed a wide range of performance. David bernard dage precision industries fremont, ca. Both design and process were studied for minimizing and controlling the voiding. Obviously, this trend depends on the total void ratio that has to be treated in an additional design of experiments.
In this process a bath of molten solder is kept at the desired temperature to provide adequate heat and solder to the work to produce a solder joint. Overcoming the challenges of the qfn package, by karl seelig and kevin pigeon 4. Solder joint voiding is a phenomenon that causes empty spaces or voids to occur within the joint. By jasbir bath, ipc principal engineer over the last few years, there have been many discussions on the affect of voiding on bgacsp solder joint reliability.
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. A low and homogeneous thermal resistance of solder joints is demanded for a quick and uniform. Strain and energy density in solder joints is evaluated for the three boundary conditions shear strain is proportionally larger than axial strain for all three boundary conditions energy density ratio decrease compared to strain ratio for bc2 and increases for bc3. Based on many researches on kirkendall void through a variety of. Bottom terminated component btc assembly has rapidly increased in. Crystallographically faceted void cfv formation in leadfree solder joints has been observed after solidification and during subsequent solidstate aging. Imaging and analysis of void defects in solder joints formed in reduced gravity using highresolution computed tomography john w. A model study of profiling for voiding control at lead. The average data of three samples for each solder paste was derived. To reduce voids change the chemicals in the formulations that create the out gassing. Easton1 national center for space exploration research, cleveland, oh, 445 peter m. As simulated with a compactness of 80% in the studied part of the solder volume, this size of voids would produce a variation of 10 mpa. Fa results to be published at 2019 pan pacific conference.
Characterization of mixed alloy sacbisn bga solder joints inemi. Solder paste consists of solder alloy, flux and rheology modifiers. How to reduce voiding in components with large pads. A large number of voids will reduce the soldering joints reliability. Design and assembly of bgas and voiding requirements. Imaging and analysis of voiddefects in solder joints formed. System level solder joint reliability using sherlock 9 strains on the board and in bga solder joints are evaluated for each boundary condition small variation in peak board strain is observed between boundary conditions mount points in proximity of bga component can significantly increase strain in solder joints. The main classifications of solder voiding within bga and pth soldering applications have been identified by aspandiar 1 as the following. The solder alloy is in the form of spherical particles of defined size, which depends on the printing needs and required printing result. Inclusion macrovoids voids containing byproducts that result from fluxing. Nepp tro leadfree soldering for space applications leadfree solder body of knowledge kurt kessel itb, inc.
The impact of voiding on the solder joint integrity of ball grid arrays bgaschip scale packages csps can be a topic of lengthy and energetic discussion. Controlling voiding mechanisms in the reflow soldering process. How to reduce voiding in components with large pads 98788 r0. The main interest stems from the impact that these voids have on the long term reliability of solder joints. It should melt and flow smoothly onto both the pin and the pad. Voids in solder joints are largely a function of differential pressure between vapor. Solder paste voids can be form during reflow due to solder dewetting. Prior to starting any further discussion on voids, it is important to distinguish the various types of voids. Effect of voids on thermal fatigue reliability of lead. The voids in the solder joint with two different reflow profiles being used. Ibm restrictions on solder voids have in the past also been vague, in that for nonbga solder joints the solder voiding shall be less than 25% of the solder joint 8. Assembly challenges of bottom terminated components.
The sethuraman investigation demonstrated that the solder void location, rather than the solder void size, is the primary mechanism by which voids can reduce solder joint integrity. A cavity within a solder joint that exposes device or substrate metallization. Illustrations of voidassisted cracking at the pcb side above and package side below of the solder joints. Inclusion macrovoids voids containing byproducts that result from fluxing reactions inherent to the solder reflow melting process. Some voids result from very specific choices of solder alloys or. Solder joint voiding often occurs on bgas and larger pads. Effect of voids on the reliability of bgacsp solder joints. If the solder does not flow, heat the joint for another second or two and try again. Complex comparison of flux influence on voids formation inside the solder joints five different flux types, two flux quantities one common reflow profile for lead and leadfree paste proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence.
Voids in solder joints are representing one of the main problems especially for power electronics. Request pdf on oct 10, 2002, doseop kim and others published effect of voids on thermal fatigue reliability of lead free solder joint find, read and cite all the research you need on researchgate. They may not cause defects, which may prompt a revision of standards that set defect levels for voids. In most cases you wont need to add any more solder to the connection. Thermal pad voiding control at qfn assembly is a major challenge due to the large coverage area, large number of via, and low standoff. Voids in solder joints, by raiyo f, aspandiar, intel corp 2. Flux effect on void quantity and size in soldered joints. Taking a close look at voids in bga solder balls ipc. David hillman, dave adams, tim pearson, brad williams, brittany petrick, and ross wilcoxon. Voidfree soldering with a new vaporphase with vacuum. Low temperature solder process and reliability ltspr project team. Their type and mutual ratio has influence on solder paste deposition properties, e. Oct 25, 2012 the challenge that has faced the industry is what data is available to support the greater than 25% voiding defect classification and how early will a failure occur when a bga or csp component solder joint has a void greater than 25% versus a solder joint which does not. With the correct pad geometry, the packages will self align when subjected to a solder reflow process.
No solder paste fill results in increased voids propensity. One school of industry thought held that a void in a solder joint would be a stress riser that initiated cracks, leading to solder joint failure. Nov, 2019 you can find solder with one or more rosin flux cores that run through the center of the solder wire. 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. Indium corporations suite of solder pastes offers formulations designed to deliver lowvoiding, plus enhanced benefits such as improved responsetopause, stability, hip minimization, reliable incircuit testing, and enhanced sir performance. Voids in solder disrupt the flow of heat transfer, reducing efficiency. Four ways to reduce voiding in bgacsp packages to substrate. Solder joint reliability of snagcu bga component attached with eutectic pbsn solder paste, fay hua, raiyo aspandiar, tim tothman, cameron anderson, greg clemons, mimi klier, intel corp, materials. The high number of io is also what makes the failure analysis task so complex. Fluxless soldering in activated hydrogen atmosphere.
Solder void size compared to conformal plating was reduced by 74% with full via fill. The voids impact becomes more severe if it is near one of the bonding interfaces. Voids in solder joints voids in solder joints raiyo aspandiar intel corporation raiyo. Its important that solder wet or cling to the surface of the ironwithout solder in between the tip and.
This defect is hard to detect after smt assembly and most likely will fail at the customer. How to prevent solder joint voiding and cold solder defects. Characterization of mixed alloy sacbisn bga solder joints. How to prevent solder joint voiding and cold solder. Newer solder pastes have been formulated with the specific goal of minimizing voiding. There have been concerns raised in the industry, and it was highly recommended in ipc 7095 that solder maskdefined lands are undesirable because they impact reliability adversely. While a significant level of voiding can be tolerated in solder joints where electrical conductivity is the main requirement. For example, there are two common approaches for designing lands for bga solder maskdefined and non solder mask, or copper, defined. How to reduce voiding in components with large pads introduction. The void content is expressed as area percentage of solder dome. Figure 1 shows a comprehensive summary by aspandiar 6 describing the types of voids.
Aspandiar and others published voids in solder joints find, read and cite all the research you need on researchgate. Imaging and analysis of voiddefects in solder joints. Apply the solder touch the end of the solder to the joint so that it contacts both the solder pad and the component lead or pin. The results are in agreement with previous studies on tinlead assemblies that demonstrated. The first three categories macro voids, imc micro voids, and shrinkage. Such voids have not previously been reported in the literature. Vacuum reflow processing on solder joint voiding heller industries. Voids can be differentiated with respect to how they are formed, where they reside in the solder joint and how they affect the reliability of the solder joint. Keith sweatman, takatoshi nishimura, kenichiro sugimoto, akira kita. Reduction of voids in solder joints an alternative to vacuum soldering.
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