Papers about soldering
by Dr. Ning-Cheng Lee , Iris Artaki, James Slattery, John R. Sovinsky, Paul T. Vianco
Environmental and toxicity concerns related to the use of lead have initiated the search for acceptable, alternate joining materials for electronics assembly. This paper describes a novel
lead-free solder designed as a "drop in" replacement for common tin/lead eutectic solder. The physical and mechanical properties of this solder are discussed in detail with comparison to tin/lead eutectic solder. The performance of this solder when used for electronics assembly is discussed and compared to other common solders. Fatigue testing results are reported for thermal cycling electronics assemblies soldered with this lead-free composition. The paper concludes with a discussion on indium metal availability, supply and price.
pb-free, surface mount, SMT, solder paste, reflow, electronic, lead-free, soldering, solder
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Paul A. Jaeger, Dr. Ning-Cheng Lee
As one of the major approaches to address the CFC issue, no-clean solder paste has received rapidly increasing attention. Although currently the industry seems to accept full residue paste as a temporary solution, the low residue no-clean paste technology using inert or reactive atmosphere advances immensely to meet the challenge. Presently consensus has not been established yet regarding how low a residue level could be achieved and how inert the atmospheres needs to be. In this study, a semi-empirical model is proposed to predict the soldering performance of low residue solder pastes under various levels of inert reflow atmosphere. The model predicts that the soldering performance would improve rapidly then gradually level off with decreasing oxygen content. The soldering performance vs oxygen content curves are superimposable, with the lower residue one leveling off at lower oxygen level. In general, the experimental data match this model fairly well. However, the data also indicate that, although inert atmosphere improves soldering performance, the optimum condition for bond strength performance seems to demand the presence of some oxygen. This unexpected behavior suggests that a very tight low oxygen level control may not be required. The mechanism responsible for this phenomenon can be attributed to oxidation-induced resin crosslinking. This slows down the flux drying rate as well as hinders the permeation of oxygen through the flux layer.
lead-free, pb-free, nitrogen, flux, reflow, soldering, low-residue, no-clean, solder paste, solder
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee , Dr. Benlih Huang, William Manning, Dr. Yan Liu
Voiding is attributed to the flux outgassing within the solder joints when the solder is at molten state. The effect of reflow profile on voiding at microvia for lead-free soldering is strongly dependent on the flux chemistry. In general, wetting is more important than
melting outgasing behavior, and can be enhanced by employing a higher melting energy, including both higher peak temperature and longer dwell time. Use of a high soaking energy can help drying out volatiles hence reduce the melting outgasing and result in low
voiding, but may also increase oxidation for pastes with poor oxidation resistance and cause a high voiding. Testing oxidation resistance of solder paste beforehand will promise a more accurate selection of soaking energy.
pb-free, soldering, BGA, CSP, void, voiding, SMT, solder, lead-free, microvia, profile, reflow
[Permanent Link to this Paper ]
Posted on 2 Mar 2010
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Tombstoning of SnAgCu is affected by the solder composition. At vapor phase soldering, both wetting force and wetting time at a temperature well above the melting point have no correlation with the tombstoning behavior. Since tombstoning is caused by unbalanced wetting force, the results suggest that the tombstoning maybe dictated by the wetting at the onset of paste melting stage. A maximal tombstoning rate is observed at 95.5Sn3.5Ag1Cu. The tombstoning rate decreases with increasing deviation in Ag content from this composition. DSC study indicates that this is mainly due to the increasing presence of pasty phase in the solders, which is expected to result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlates with a higher tombstoning rate. SnAgCu composition with a Ag content lower than 3.5%, such as 2.5Ag, is more favorable in terms of reducing tombstoning rate with minimal risk of forming AgSn intermetallic platelet.
pb-free, tombstoning, solder, soldering, solder paste, flux, lead-free, surface mount
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Effect of solder alloy composition and properties on tombstoning of SnAgCu has been investigated. Both wetting force and wetting time at a temperature will above the melting point have no correlation with the tombstoning behavior observed at vapor phase soldering. Since tombstoning is caused by unbalanced wetting force, this unbalanced wetting force may occur at the onset of melting DSC study indicates that the tombstoning rate decreases with increasing pasty temperature range and increasing mass fraction of solid in solder at onset of melting. This slower wetting in turn results in a more balanced wetting force and accordingly reduces the tombstoning. The mass fraction of solid may be the more essential factor. Surface tension also plays a role, with lower surface tension correlates with a higher tombstoning rate. Tombstoning of SnAgCu can be regulated by the solder composition. A maximal tombstoning rate is observed a 95.5Sn3.5Ag1Cu. The tombstoning rate decreases with increasing deviation in Ag content from this composition, particularly toward the end of lower Ag content. SnAgCu composition with a Ag content lower than 3.5%, such as 2.5Ag, is more favorable in terms of reducing tombstoning rate with minimal risk of forming Ag3SN intermetallic platelet.
tombstoning, solder, soldering, solder paste, flux, lead-free, surface mount, pb-free
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Andy C. Mackie PhD
In my twenty years in the electronics manufacturing industry, I have heard a lot of claims made about the use of nitrogen in inerted soldering processes: many of them completely wrong.
In this paper, we will talk about reflow in an enclosed oven, although many of these discussions may pertain to wave soldering and even vacuum soldering.
electronics manufacturing, reflow, soldering
[Permanent Link to this Paper ]
Posted on 24 Jan 2011
by Dr. Arnab Dasgupta, Dr. Benlih Huang, Dr. Ning-Cheng Lee
For SnAgCu solder, the voiding rate at microvia was studied with the use of simulated microvia, and was the lowest with 95.5Sn3.8Ag0.7Cu and 95.5Sn3.5Ag1Cu, and increased with further decrease in Ag content. Results indicated that voiding at microvia was governed by via filling and exclusion of fluxes. The voiding rate decreased with decreasing surface tension and increasing wetting force which in turn was dictated by the solder wetting or spreading. Both low surface tension and high solder wetting prevented the flux from being entrapped within microvia. A fast wetting speed might also facilitate reducing voiding. However, this factor was considered not as important as the final solder coverage area.
pb-free, reflow, surface mount, microvia, voiding, void, lead-free, soldering, solder
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee , Dr. Mikolaj E. Jozefowicz
The IPC-SF-818 Surface Insulation Resistance (SIR) test data taken with the use of a variety of
halide-free no clean fluxes are analyzed against Bellcore TR-NWT-000078 Electromigration (EM) test data. Neither test results show correlation with bulk flux resistivity, flux water extract resistivity, flux residue moisture pickup, and flux corrosivity without bias. However, in the case of rosin fluxes, the insulation resistance behavior in both SIR and EM tests is a function of pH value of fluxes. This phenomenon is more profound in SIR test. In the case of low residue no clean fluxes, only SIR test displays such a pH dependent relationship. Data suggest that the 50 volts bias voltage used in SIR test may be responsible for this, and can be explained with a high-bias-voltage-induced electrolysis mechanism which is further promoted by a high pH environment. This failure mechanism is absent in EM test which utilizes 10 volts bias voltage, and probably will not occur at normal 5 volts application condition. Overall, the SIR test seems to be more stringent while the EM test appears to be more realistic.
lead-free, pb-free, no-clean, surface insulation resistance, EM, flux, soldering, solder, electromigration, SIR
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Posted on 1 Jan 2009
by Dr. Anu Maria, K. P. Rangan, Rajkumar B. Raj, Dr. Ning-Cheng Lee , Dr. Xiaohua Bao
Rheology of a solder paste has a significant effect on its stencil printing, tack, and slump performance. This paper describes a series of tests designed to investigate the rheological properties of a suite of solder pastes and fluxes, and the correlation with the solder paste performance prior to reflow. Data indicate that 1) print defect is proportional to the compliance (J1 and J2) and inversely proportional to the elastic properties (G’/G’’ and Recovery) and meta-rigidity (Yield Stress); 2) slump resistance is proportional to elastic properties (Recovery), solid characteristics (Stress [G’=G’’]), and rigidity ( êG* ê); 3) high elastic properties (Recovery), low compliance (J1 and J2), and low solid characteristics (Stress [G’=G’’]) are required in order to achieve high tack value. Good correlation between fluxes and solder pastes are observed for Yield Stress and Recovery only, suggesting those two properties are primarily dictated by fluxes.
lead-free, pb-free, viscosity, flux, tack, slump, print, rheology, solder paste, soldering, solder
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
Package-on-package (PoP) is a packaging that rapidly prevails in mobile devices of the electronic industry, due to its flexibility in combining memory and processor into one component with a reasonably low profile. However, similar to BGA, the solder joints of assembled PoP are prone to cracking upon dropping onto the floor, thus needing reinforcement by underfilling. The underfilling process needs an underfill material plus additional dispensing equipment, dispensing and flowing steps, and subsequent time-consuming curing. Furthermore, underfilled PoP suffers solder extrusion upon rework, particularly when reworking at the opposite side of the board right underneath the PoP. Epoxy flux is a new material developed to address the issues described above; it is a liquid epoxy with fluxing power, and it is compatible with solder paste. Applied by a dipping process, epoxy flux can be used at the mounting of bottom package and top package. First, the bottom package is dipped in a film of epoxy flux, and then placed onto the footprint pad on a PCB with or without solder paste. Then, the top package is dipped in epoxy flux and placed on top of the bottom package. The PCB with a stacked PoP is subsequently reflowed in the oven together with other surface mount components placed on printed solder paste. Epoxy flux combines soldering and reinforcement into one single process. With a controlled pick up flux volume, a venting channel is formed, allowing outgassing at reflow. The low stress characteristics of epoxy flux prevents the formation of solder extrusion. Overall, epoxy flux provides a low cost and high reliability solution for PoP assembly.
Reliability, soldering, assembly, PoP, package-on-package, epoxy flux
[Permanent Link to this Paper ]
Posted on 14 Oct 2011
by Dr. Ning-Cheng Lee
In general,
new lead-free solder alloys with the following characteristics are desired in order to enable the continuation of miniaturization trend: (1) alloy with a reduced melting temperature, (2) alloy with a better solder spread, (3) alloy with a slower wetting speed at melting temperature, (4) a softer alloy, or alloy with a reduced voiding tendency or greater ductility, (5) alloy with a refined grain size, (6) alloy with low tendency to form large IMC plate, (7) alloy with a higher resistance toward corrosion and electrochemical migration, (8) alloy with a greater oxidation resistance. On the other hand, no-clean fluxes with the following features are needed: (1) reduced volatile, (2) halide-free, (3) greater fluxing
capacity, (4) higher residue resistivity, (5) more resistant to oxidation and charring, (6) more efficient oxidation barrier, (7) lower activation temperature, (8) slower wetting speed when solder begins to melt, (9) less spattering, (10) higher probe penetratability, (11) capability of inducing nucleation of solder upon cooling, and (12) greater resistance against slump.
SAC, solder joint, soldering, flux, solder alloy, lead-free
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee
This paper reviews the status of
lead-free solder developmental works. Some of the solder systems, Bi-Sn, Bi-Sn-Fe, In-Sn, Sn, Sn-Ag, Sn-Ag-Zn, Sn-Ag-Zn-Cu, Sn-Bi-Ag, Sn-Cu, Sn-Cu-Ag, Sn-In-Ag, Sn-Sb, Sn-Zn and Sn-Zn-In are discussed in more details, while the others are briefly commented on. In general, compared with eutectic Sn-Pb solder, all the lead-free solder alternatives investigated more or less exhibit some shortcomings, such as price, physical, metallurgical, or mechanical properties. Relatively, Sn-In-containing systems are more promising in terms of solder mechanical properties and soldering performance, although the price of In may be a concern. Eutectic Sn-Ag solder doped with Zn, Cu, or Sb exhibits good mechanical strength and creep resistance, due to refined microstructure. The Bi-Sn systems doped with other elements may have a niche in the low temperature soldering field. Eutectic Sn-Cu has a good potential due to its good fatigue resistance. Eutectic Sn-Zn system modified with In and/or Ag may be promising in mechanical properties. Finding a lead-free alternative for high temperature solders presents the biggest challenge to the industry.
solder, soldering, lead-free, electronic, tin, lead, pb-free
[Permanent Link to this Paper ]
Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee
In this article, the interconnect infrastructure for SMT, BGA, and
flip chip are reviewed, with particular emphasis on the bonding technology. Interconnection technologies are the vital part of electronic packaging. Obviously, interconnections of SMT industry, from components to boards to board-level assembly methods, are the most mature and well established technology. BGA, on the other hand, intelligently utilizes the knowledge of SMT interconnections and re-engineers the design through combining the strength of various interconnect technologies and successfully comes up with a great family of versatile packages. Flip chip interconnects, while also trying to incorporate existing technology, place a good deal of emphasis on the polymeric systems, and very much develop a new arena of interconnect concepts and processes. The impact of flip chip interconnect progress is expected to ripple through the rest of electronic industries in the near future.
SMT, BGA, Flip Chip, CSP, Interconnection, surface mount, ball grid array, Packaging, assembly, soldering, pb-free, lead-free
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Mike Bixenman D.B.A., Steve Stach, Dr. Ning-Cheng Lee
Ionic Cleanliness testing machines are designed to determine the total ionic content extractable from the printed wiring board for purposes of process control. The conductivity of the extract solution is measured and the results are expressed as sodium chloride equivalence per unit area. The problem with this method is two fold: 1.) Many of today’s low residue flux and lead-free flux residues are not soluble in the extract solution. 2.) Contamination of concern is with site specific components, from which contamination does not correlate to the area of concern. The purpose of this study is to research low residue and lead-free flux structures, identify solvent compositions that will dissolve these residue types, and offer options for performing both bulk and site specific ionic cleanliness testing methods.
lead-free, Cleaning, flux residue, flux, soldering, solder, solder paste, SMT
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
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Lead-Free Flux Technology and Influence on Cleaning
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Lead-free flux technology for electronic industry is mainly driven by high soldering temperature, high alloy surface tension, miniaturization, air soldering due to low cost consideration, and environmental concern. Accordingly, the flux features desired included high thermal stability, high resistance against burn-off, high oxidation resistance, high oxygen barrier capability, low surface tension, high fluxing capacity, slow wetting, low moisture pickup, high hot viscosity, and halogen-free. For each of the feature listed above, corresponding desired chemical structures can be deduced, and the impact of those structure on flux residue cleanability can be speculated. Overall, lead-free flux technology results in a greater difficulty in cleaning. Cleaner with a better matching solvency for the residue as well as a higher cleaning temperature or agitation are needed. Alkaline and polar cleaner are often needed to deal with the larger quantity of fluxing products. Reactive cleaner is also desired to address the side reaction products such as crosslinked residue.
lead-free, flux, flux residue, solder, soldering, cleaner, Cleaning, SMT
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
Lead-free soldering for electronic industry is a segment of global trend toward lead-free environment. Although initiated in U.S. in early 1990's, it advanced much more rapidly in Japan and Europe. This differentiation in Pb-free progress triggered great concerns of users of Pb-containing solders about maintaining business opportunity, therefore further expedites the advancement of Pb-free soldering programs. The favored Pb-free solder alternatives vary from region to region. However, in general, high tin alloys are preferred, including Sn/Ag, Sn/Cu, Sn/Ag/Cu, Sn/Ag/Bi, and various versions of those alloys with small amount of additions of other elements, such as Sb. Sn/Ag/Bi systems are used in some Japanese products already. However, Sn/Ag/Cu systems are more tolerant toward Pb contamination than Bi-containing systems, therefore are more compatible with existing infrastructure for the transition stage. Pb-free surface finishes for PCBs include OSP, immersion Ag, immersion Au/electroless Ni, HASL Sn/Cu, Sn/Bi, electroless Pd/electroless Ni, electroless Pd/Cu, and Sn. The challenge for components is greater than for solder materials or PCBs. Although some Pb-free surface finishes for components exist, such as Sn, Pd/Ni, Au, Ag, Ni/Pd, Ni/Au, Ag/Pt, Ag/Pd, Pt/Pd/Ag, Ni/Au/Cu, Pd, and Ni, the performance remains to be verified. In addition, options for higher melting temperature solder is still not available for high temperature applications, including first level interconnect within the components. Thermal damage can be a concern for both PCBs and components.
pb-free, alloy, soldering, sn, Pb, solder, lead-free, lead
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
Lead-free soldering , originally started as an environmental issue, is evolving rapidly into a business survival tool for the worldwide electronic industry. Promising lead-free solder alternatives for surface mount assembly applications include eutectic Sn/Ag, eutectic Sn/Cu, Sn95/Sb5, eutectic Sn/Bi, Sn/Ag/Cu, Sn/Ag/Cu/X, Sn/Bi/Ag/X, Sn/Zn/X, and Sn/In/Ag/(X). However, for wafer level area array solder bump interconnects, most of those options fall short in terms of fatigue resistance. Sn/In/Ag/(X) appears to be superior when compared with Sn63/Pb37, as demonstrated by Sn/In/Ag/Cu. For applications involving high lead solders, no solder alternatives have been developed yet. While the industry is advancing toward being finer, smaller, lighter, and faster, wafer level packages using area array solder interconnects is suffering from the soft error due to alpha emission from the lead in the solders. Although lead-free solder alternatives for eutectic Sn/Pb are virtually free from alpha emission, the continuous dependence on the use of high-lead solders for C4 applications indicates that the challenge of alpha emission from lead-containing solders will persist regardless of the lead-free move of the industry. This challenge is getting tougher with the rapid advancement of IC design toward further miniaturization. Low alpha lead can be obtained from cold lead ore, old lead, and laser isotope separation process, with the latter having potential as a long term solution. The price of those low alpha lead is very expensive when compared with the regular lead. Due to the increase in I/O density, requirement on alpha emission level may soon move from LC2 to LC3 level. The supply of low alpha lead for wafer level interconnects does not seem to be an issue.
lead-free, solder, soldering, wafer level interconnect, Flip Chip, CSP, BGA, alpha emission, low alpha solders, soft error, indium, pb-free
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Tombstoning has plagued the surface mount assembly industry for decades. While the problem seemed under control, it has begun creeping in again due to the miniaturization of discretes such as 0402S and 0201S. This article studies tombstoning behavior on a series of SN AG CU Lead-Free Solders and attempts to find a way to control the problem.
lead-free, pb-free, tombstoning, solder, solder paste, SMT, solder alloy, pasty range, soldering, reflow
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
No-clean soldering process is the cheapest available process alternatives in the post-CFC era. In order to enjoy the benefit of no-clean process, care should be taken to assure the cleanliness of products before and after assembly. In addition, the no- clean soldering materials have to be properly formulated in order to deliver the high reliability and adequate flux residue appearance. Due to the elimination of cleaning process, issues such as solder beading, solder balling, probe testability, wire bondability, compatibility with polymeric coatings or wave soldering fluxes have to be addressed. No-clean fluxes typically utilize hydrophobic chemicals and often are in line with RMA flux chemistries. Nitrogen is required if a low residue level is desired for reflow process. Some conventional testing methods may not be adequate for evaluating no-clean soldering materials. Concurrent trends of shifting toward finer pitch, higher reliability, lower residue, and air reflow processes pose a great challenge for no-clean soldering process.
lead-free, pb-free, paste, flux, soldering, solder, no-clean
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
The reflow profile is engineered to optimize the soldering performance based on defect mechanisms analysis. In general, a slow ramp-up rate is desired in order to minimize hot slump, bridging, tombstoning, skewing, wicking, opens, solder beading, solder balling, and components cracking. A minimized soaking zone reduces voiding, poor wetting, solder balling, and opens. Use of low peak temperature lessens charring, delamination, intermetallics, leaching, dewetting, and voiding. A rapid cooling rate helps reducing intermetallics, charring, leaching, dewetting, and grain size. However, a slow cooling rate reduces solder or pad detachment. The optimized profile favors that the temperature ramps up slowly until reaching about 180°C. The temperature is then gradually raised further up to 186°C within about 30 seconds, then raised rapidly until reaching about 220°C. After that, the temperature is brought down with a rapid cooling rate. The conventional profile was developed due to the limitation of past reflow technologies. Implementation of the optimized profile requires the support of a heating-efficient reflow technology with a controllable heating rate. Vapor phase reflow can provide a rapid heating, but has difficulty to control the heating rate. Infrared reflow can regulate the heating rate, but is sensitive to variation in parts features. Emergence of the forced air convection reflow provides controllable heating rate. In addition, it is not sensitive to variation in parts
features, thus allows the realization of the optimized profile.
lead-free, pb-free, SMT, vapor phase, infrared, convection, soldering, solder paste, flux, defect, profile, reflow
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee , Dr. Benlih Huang
The prospects of 10 major lead-free solder alloys for being widely used for reflow soldering are studied in this work. Compatibility of those alloys with a variety of representative flux chemistries is considered essential, and is determined for performance in handling- ability, including shelf life and tack time, and soldering capability, including solder balling, wetting, and solder joint appearance. Results indicate that the control 63Sn37Pb is still the most compatible alloy, rated 27.1 in compatibility out of a full scale 30 when using warm profile. The primary factor which distinguishes 63Sn37Pb from the rest alloys is the soldering performance, particularly the wetting and solder appearance. As to the solder balling, although 63Sn37Pb is also the best, it is fairly close to the best lead-free systems. Among the lead-free options, both SnAgBi alloys studied here, 91.7Sn3.5Ag4.8Bi and 90.5Sn7.5Bi2Ag, turn out to be on the top of lead-free systems, rated 22.9 and 22.8, respectively. This is mainly attributed to the better wetting and solder balling performance. Shelf life and tack time of the SnAgBi systems are also fairly good, while the solder appearance is at best considered average. The six alloys, 99.3Sn0.7Cu, 95.5Sn3.8Ag0.7Cu, 93.6Sn4.7Ag1.7Cu, 96.2Sn2.5Ag0.8Cu0.5Sb, 58Bi42Sn, and 95Sn5Sb, show fairly comparable performance to each other, with compatibility ranging from 19.3 to 20.3. In general, the whole group displays a quite noticeably poorer wetting than SnAgBi systems. 58Bi42Sn exhibits a fairly poor solder balling performance, but an outstanding solder appearance among lead-free systems. 96.2Sn2.5Ag0.8Cu0.5Sb shows a relatively poor performance in both wetting and solder appearance among these six alloys. 96.5Sn3.5Ag, rated 17.1 in compatibility, is ranked below the other alloys described above, mainly due to poor performance in solder balling, and particularly the poor wetting. 89Sn8Zn3Bi, rated only 2.2 in compatibility, falls far short in every category when compared with all other alloy systems. Obviously, this is attributable to the very reactive nature of zinc, which results in excessive oxidation of metal and excessive reaction with fluxes, and consequently a definitely unacceptable performance for solder paste applications. High-tin-content lead-free alloys seem to display a thicker IMC layer than eutectic SnPb when reflowed.
pb-free, tack time, shelf life, solder appearance, solder balling, wetting, flux, paste, reflow, soldering, solder, lead-free
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Ning-Cheng Lee
Reflow soldering of solder paste is the primary interconnection method used in SMT assembly process. The major issues which plague the reflow soldering performance include, but not limited to, bottom-side-component-holding, bridging, dewetting, low-residue, opening, solder balling, solder beading, solder-fillet-lifting, tombstoning, defective balling for BGA, and voiding. The mechanisms, causes, and cures for each issue are briefly discussed in this article.
lead-free, soldering, solder paste, SMT, bridging, dewetting, opening, solder balling, solder beading, solder-fillet-lifting, tombstoning, balling for BGA, voiding, pb-free, reflow
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Dr. Yan Liu, Pamela Fiacco, Derrick Herron, Dr. Ning-Cheng Lee
Consideration and selection of dip transfer fluxes and solder pastes for PoP assembly are described, based on process considerations. The crucial properties vital for successful dip transfer include homogeneity, open time on the flux/paste bed, volume and consistency of the dip transferred material, open time after the dip transfer before reflow, and solder joint formation. For each property, one or more practical, recommended test methods are described. Overall, this work should provide the assembly house with an easy way to select a flux or solder paste adequate for dip transfer of PoP assembly applications.
PoP, package-on-package, flux, solder paste, dip transfer, soldering, SMT
[Permanent Link to this Paper ]
Posted on 24 Jan 2011
by Dr. Benlih Huang, Dr. Ning-Cheng Lee
Several unique solder paste systems have been developed and tested for 63Sn/37Pb solder bumping for wafer, CSP, and BGA with the low cost print-detach-reflow process. The results indicate that the bump height achieved is very adequate and consistent for all three area array package systems. Microstructure of solder bumps appears normal. The yield is also very high for both before reflow and after reflow condition, and is dictated by printing performance. With the unique high slump resistance exhibited by those newly developed pastes, the paste transfer efficiency at printing stage becomes the most critical performance for this process. The transfer efficiency increases with increasing area ratio, increasing taper angle, decreasing pitch, decreasing stencil thickness, decreasing challenge, with adoption of square aperture design, and is not sensitive to aspect ratio of aperture to solder particle size. The paste systems appear to have more potential for depositing a larger amount of paste per unit pitch, as evidenced by the linear relation between expected paste volume and the deposited paste volume. Increasing metal content helps improving bumping performance. The bottleneck of increasing bumping performance for wafer applications appears to be developing a stencil manufacturing technology capable of providing an aperture pattern with spacing considerably smaller than the stencil thickness. Slow print speed is also essential for adequate printing. A non-shiny non-smooth stencil surface is considered beneficial for aiding paste rolling. The flux residue of those pastes is cleanable with solvents.
solder, soldering, area array package, Flip Chip, BGA, CSP, sphere, Bumping, paste, flux, fluxless, pb-free, lead-free
[Permanent Link to this Paper ]
Posted on 1 Jan 2009
by Amanda Hartnett , Dr. Ronald C. Lasky , Timothy Jensen
Chinese version of Soldering Challenges in a Halogen-Free PCB Assembly Process
halogen-free, halide-free, solder, soldering, graping, flux, head-in-pillow, hole-fill, CHINESE LANGUAGE
[Permanent Link to this Paper ]
Posted on 13 May 2011
by Timothy Jensen , Dr. Ronald C. Lasky , Amanda Hartnett
Flame retardants have played an important role in the safety of many products. It is safe to say that thousands of lives have been saved by flame retardants. Flame retardants are used in products as varied as children's pajamas to electronics assemblies. Some of the more successful flame retardants are halogenated compounds. Halogenated materials are found in polyvinyl chloride (PVC), brominated flame retardants (BFRs), chlorinated flame retardants (CFRs), as well as in fluxes used in the electronics assembly industry. Product does not contain any halogenated compounds. However, that is not exactly how the term is used for soldering fluxes. A flux that is classified as
halide-free by the IPC/J-STD-004 is actually only free of ionic halides.
hole-fill, head-in-pillow, flux, graping, soldering, solder, halide-free, halogen-free
[Permanent Link to this Paper ]
Posted on 10 Mar 2010
by Dr. Ning-Cheng Lee , William Casey
Soldering is the primary interconnection technology for area array packages. Methods for solder bumping for area array packages can be categorized as follows: (1) build-up process, (2) liquid solder transfer, (3) solid solder transfer, and (4) solder paste bumping. The first group includes both evaporation and electroplating processes, while the second group includes meniscus bumping and solder jetting. The third group includes wire bumping, sphere welding, decal solder transfer, tacky dot solder transfer, integrated preform, and pick and-place solder transfer processes, with the last one (pick & place solder transfer) being the current prevailing option. Solder paste bumping exhibits great potential to reduce bumping costs dramatically, and includes the print-detach-reflow, print- reflow-detach, and dispense approaches. For an area array package attachment process, depending on the type of packaging, either flux, fluxless soldering or solder paste printing may be used as the attachment medium. Although area array packaging generally offers a robust process, attention should be paid to reduce defects such as delamination, misalignment, elongated joint, voiding, bridging, opens, cracking, poor wetting and various attachment interactions.
lead-free, pb-free, solder, soldering, area array package, Flip Chip, BGA, CSP, sphere, Bumping, paste, flux, fluxless
[Permanent Link to this Paper ]
Posted on 10 Mar 2010
by Dr. Ning-Cheng Lee , Dr. Yan Liu, Pamela Fiacco
Head-in-pillow (HIP) is ailing the electronic industry when assembling BGAs or CSPs onto PCBs. It is caused by warpage of components or boards at reflow process, and is aggravated by oxidation. Methods for assessing the potential for occurrence of HIP are highly desired by the industry. Besides using BGA rework station followed by tedious dye and pry treatment, two other simpler methods are introduced in this work, Tiny Dot Paste method and Ball Onto Paste method. The Tiny Dot Paste method is stressed on the assessment of oxidation barrier capability of solder paste, while Ball Onto Paste method assesses combined capability of oxidation resistance and excessive fluxing capacity. Both methods are quick, easy, and close simulation, with the latter being better in real process simulation. Prevention of HIP can be accomplished by (1) designing packages without warpage, (2) printing more paste, (3) dipping solder paste or flux, (4) using inert reflow atmosphere, (5) reducing reflow temperature, (6) placing heat shield on BGA or CSP, (7) avoiding using water soluble solder paste for BGA bumped with no-clean process, (8) using solder bumps or solder powder with oxidation resistant alloy, (9) using fluxes with high oxidation barrier capability and high fluxing capacity. Among all options listed above, using solder paste with high oxidation barrier capability and high fluxing capacity is considered the most easily implemented approaches.
head-in-pillow, solder, soldering, reflow, SMT, solder paste, BGA, CSP
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Posted on 24 Jan 2011
by Chris Nash
In this article, I will present a basic overview of soldering for those who are new to the world of soldering and for those who could use a refresher. I will discuss the definition of soldering, the basics of metallurgy, how to choose the proper alloy, the purpose of a flux, soldering temperatures, and typical heating sources for soldering operations.
soldering, metallurgy, flux, Solder Basics
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Posted on 10 Mar 2010
by Wanda B. O’Hara, Dr. Ning-Cheng Lee
Voiding in BGA assembly using Sn63 solder bumps is primarily introduced at board-level assembly stage. On the pretinned PCBs, voiding of BGA joints increases with increasing solvent volatility, increasing metal content, and increasing reflow temperature, and with decreasing powder size. This can be explained by a viscosity dictated flux-exclusion-rate model. In this model, a higher viscosity in fluxing medium at reflow temperature could hinder the exclusion of flux from the interior of molten solder, hence increase the chance of outgassing due to the increasing amount of entrapped flux, and consequently result in a higher voiding in BGA assembly. Flux activity and reflow atmosphere appear to have negligible effect on voiding when the solderability of the immobile metallization is not a concern. Increase in void content is accompanied by an increase in fraction of large voids. This suggests that, similar to voiding phenomena in SMT process, factors causing voiding in BGA will have an even greater impact on the joint reliability than what shown by the total-void-volume analysis results.
void, BGA, viscosity, volatility, flux-exclusion-rate, soldering, pb-free, lead-free
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Posted on 1 Jan 2009
by Wanda B. Hance, Dr. Ning-Cheng Lee
The mechanisms for void formation are investigated for applications involving solder paste in SMT. Generally the voids are caused by the outgassing of entrapped flux in the sandwiched solder during reflow. The voiding is mainly dictated by the solderability of metallization, and increases with decreasing solderability of metallization, decreasing flux activity, increasing metal load of powder, and increasing coverage area under the lead of the joint. Decrease in the solder powder particle size shows only a slightly negative effect toward voiding. The data indicate that voiding is also a function of the timing between the coalescing of solder powder and the elimination of immobile metallization oxide. The sooner the paste coalescing occurs, the worse the voiding will be. Increase in voiding usually is accompanied by an increasing fraction of large voids, suggesting factors causing voiding will have an even greater impact on the joint reliability than what shown by the total-void-volume analysis results. Preliminary data show that certain predry treatment and flux solvent with higher boiling point appear to cause increased voiding.
lead-free, pb-free, solderability, reflow, solder joint, SMT, voiding, void, flux, solder paste, soldering, solder
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Posted on 1 Jan 2009
