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Corrosion Issues in Solder Joint Design and Service

Description: Corrosion is an important consideration in the design of a solder joint. It must be addressed with respect to the service environment or, as in the case of soldered conduit, as the nature of the medium being transported within piping or tubing. Galvanic-assisted corrosion is of particular concern, given the fact that solder joints are comprised of different metals or alloy compositions that are in contact with one-another. The (thermodynamic) potential for corrosion to take place in a particular environment requires the availability of the galvanic series for those conditions and which includes the metals or alloys in question. However, the corrosion kinetics, which actually determine the rate of material loss under the specified service conditions, are only available through laboratory evaluations or field data that are found in the existing literature or must be obtained by in-house testing.
Date: November 24, 1999
Partner: UNT Libraries Government Documents Department

High temperature solder alloys for underhood applications. Progress report

Description: Under a cooperative research and development agreement with General Motors Corporation, lead-free solder systems including the flux, metallization, and solder are being developed for high temperature, underhood applications. Six tin-rich solders, five silver-rich metallizations, and four fluxes were screened using an experimental matrix whereby every combination was used to make sessile drops via hot plate or Heller oven processing. The contact angle, sessile drop appearance, and in some instances the microstructure was evaluated to determine combinations that would yield contact angles of less than 30{degrees}, well-formed sessile drops, and fine, uniform microstructures. Four solders, one metallization, and one flux were selected and will be used for further aging and mechanical property studies.
Date: February 1, 1995
Creator: Drewien, C.A.; Yost, F.G.; Sackinger, S.; Kern, J. & Weiser, M.W.
Partner: UNT Libraries Government Documents Department

Creep Properties of Pb-Free Solder Joints

Description: Describes the creep behavior of three Sn-rich solders that have become candidates for use in Pb-free solder joints: Sn-3.5Ag, Sn-3Ag-0.5Cu and Sn-0.7Cu. The three solders show the same general behavior when tested in thin joints between Cu and Ni/Au metallized pads at temperatures between 60 and 130 C. Their steady-state creep rates are separated into two regimes with different stress exponents(n). The low-stress exponents range from {approx}3-6, while the high-stress exponents are anomalously high (7-12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95 to 60 C. The anomalous creep behavior of the solders appears to be due to the dominant Sn constituent. Joints of pure Sn have stress exponents, n, that change with stress and temperature almost exactly like those of the Sn-rich solder joints. Research on creep in bulk samples of pure Sn suggests that the anomalous temperature dependence of the stress exponent may show a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating Sn-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.
Date: April 1, 2002
Creator: Song, H. G.; Morris, J. W., Jr. & Hua, F.
Partner: UNT Libraries Government Documents Department

The Resistance and Strength of Soft Solder Splices between Conductors in MICE Coils

Description: Two of the three types of MICE magnets will have splices within their coils. The MICE coupling coils may have as many as fifteen one-meter long splices within them. Each of the MICE focusing coils may have a couple of 0.25-meter long conductor splices. Equations for the calculation of resistance of soldered lap splices of various types are presented. This paper presents resistance measurements of soldered lap splices of various lengths. Measured splice resistance is shown for one-meter long splices as a function of the fabrication method. Another important consideration is the strength of the splices. The measured breaking stress of splices of various lengths is presented in this paper. Tin-lead solders and tin-silver solders were used for the splices that were tested. From the data given in this report, the authors recommend that the use of lead free solders be avoided for low temperature coils.
Date: August 3, 2010
Creator: Wu, Hong; Pan, Heng; Green, Michael A; Dietderich, Dan; Gartner, T. E.; Higley, Hugh C et al.
Partner: UNT Libraries Government Documents Department

Appendix to the report from the low-residue soldering task force: Phase 2 results

Description: The LRSTF report for Phase I of its evaluation of low-residue soldering was issued in June 1995. This Appendix summarizes the results of follow-on testing performed in Phase II and compares electrical test results for both phases. Deliberate decisions were made by the LRSTF in Phase I to challenge the design guideline limits in MILSTD-275, Printed Wiring for Electronic Equipment The LRSTF considered this approach to produce a ``worst case`` design and provide useful information about the robustness of LR soldering processes. As such, good design practices were sometimes deliberately violated in designing the LRSTF board. This approach created some anomalies for both LR boards and RMA/cleaned controls. Phase II testing verified that problems that affected both RMA/cleaned and LR boards in Phase I were design related.
Date: December 1, 1995
Creator: Iman, R.L.; Anderson, D.J. & Huffman, D.D.
Partner: UNT Libraries Government Documents Department

The influence of microstructure on the mechanical properties of solder

Description: Solder joints in microelectronics devices consist of low-melting solder compositions that wet and join metal contacts and are, ordinarily, used at high homologous temperatures in the as-solidified condition. Differences in solidification rate and substrate interactions have the consequence that even solder joints of similar compositions exhibit a wide range of microstructures. The variation in microstructure causes a variation in properties; in particular, the high-temperature creep properties that govern much of the mechanical behavior of the solder may differ significantly from joint to joint. The present paper reviews the varieties of microstructure that are found in common solder joints, and describes some of the ways in which microstructural changes affect mechanical properties and joint reliability.
Date: June 1, 1996
Creator: Morris, J.W. Jr. & Reynolds, H.L.
Partner: UNT Libraries Government Documents Department

Modeling non-isothermal intermetallic layer growth in the 63Sn-37Pb/Cu system

Description: A model describing diffusion-controlled growth of multiple intermetallic layers and the displacement of the interfaces between layers was developed and implemented in a 1-D computer code based on method-of-lines. The code was applied to analysis of intermetallic layer growth in isothermal solder aging experiments performed with 100 Sn/Cu and 63Sn-37Pb/Cu solder-substrate systems. Analyses indicated that intermetallic layer growth was consistent with a bulk diffusion mechanism involving Cu and/or Sn. In this work, nonisothermal solder-aging experiments were done with the 63Sn- 37Pb/Cu system using two temperature histories (4 cycles/day between 223-443 K, and 72 cycles/day between 223-443 K). Isothermal experiments were also done at 443 K. Thickness of Cu{sub 3}Sn and Cu{sub 6}Sn{sub 5} intermetallic layers were determined vs time for each temperature history. An updated version of the model and code were used to predict the intermetallic layer growth. Arrhenius expressions for diffusion coefficients in both Cu3Sn and Cu6Sn5 layers were determined. Agreement between prediction and experiment was generally good. In some cases, predicted layer growth was less than experiment, but within error. This paper describes the nonisothermal experiments and a comparison of predicted and observed layer growth vs time.
Date: December 31, 1996
Creator: Vianco, P.T.; Hopkins, P.L.; Erickson, K.L.; Frear, D.R. & Davidson, R.
Partner: UNT Libraries Government Documents Department

A note on the transition from coupled plasticity and damage to decohesion in the evolution of solder failure

Description: A key issue of solder joint reliability is joint failure due to thermomechanical fatigue (TMF). TMF is caused by different coefficients of thermal expansion (CTEs) of the materials in an electronic package, combined with changes in the ambient temperature. Different CTEs result in cyclical strain in the assembly, and this strain is concentrated almost entirely in the solder because it is the most deformable portion of the package. Since solder alloy is at a significant fraction of its melting point even at room temperature, the cyclical strain enhances mass diffusion and causes dramatic changes in the alloy microstructure over time. As the microstructure changes and becomes coarser, the solder alloy weakens and eventually microcracks nucleate and grow in the joint, leading to component failure. the failure of solder joints is difficult to detect due to the inert nature of the electrical system. If the system is not on for extended periods then failures can not be observed. Therefore it is important to develop an advanced predictive capability which allows scientists and engineers to predict solder degradation and identify reliability problems in aging electronics early.
Date: April 25, 2000
Partner: UNT Libraries Government Documents Department

Porosity in collapsible Ball Grid Array solder joints

Description: Ball Grid Array (BGA) technology has taken off in recent years due to the increased need for high interconnect density. Opposite to all the advantages BGA packages offer, porosity in collapsible BGA solder joints is often a major concern in the reliability of such packages. The effect of pores on the strength of collapsible BGA solder-joints was studied by manufacturing samples with different degrees of porosity and testing them under a shear load. It was found that the shear strength of the solder joints decreased in a linear fashion with increasing porosity. Failure occurred by internal necking of the interpore matrix. It was confirmed that entrapment of flux residues leads to porosity by manufacturing fluxless samples in a specially made furnace, and comparing them with samples assembled using flux. Also, contamination of Au electrodeposits (in substrate metallization) was determined to cause significant porosity. It was found that hard-Au (Co hardened Au) electrodeposits produce high degrees of porosity even in the absence of flux. Finally, increasing the time the solder spends in the molten state was proven to successfully decrease porosity.
Date: May 1, 1998
Creator: Gonzalez, C.A.
Partner: UNT Libraries Government Documents Department

Development of a hybrid microcircuit test vehicle for surface mount applications

Description: The technology drivers of the electronics industry continue to be systems miniaturization and reliability, in addition to addressing a variety of important environmental concerns. Surface mount technology (SMT) has evolved in response to these issues. Prototype hybrid test vehicles have been developed at Sandia National Laboratories to evaluate three lead-free solders for Au-Pt-Pd thick film soldering. The alloys are based on the Sn-Ag, Sn-Ag-Bi and Sn-Ag-Bi-Au systems. Populated test vehicles with surface mount devices were designed and fabricated to evaluate actual solder joints. Pastes were screen printed on the test substrates and reflowed with the components in place. The test components consist of a variety of dummy chip capacitors and leadless ceramic chip carriers (LCC`s). The development of the reflow profiles will be discussed. Comprehensive defect analysis will also be presented.
Date: August 1, 1997
Creator: Hernandez, C.L.; Hosking, F.M. & Vianco, P.T.
Partner: UNT Libraries Government Documents Department

Effect of firing conditions on thick film microstructure and solder joint strength for low-temperature, co-fired ceramic substrates

Description: Low-temperature, co-fired ceramics (LTCC) are the substrate material-of-choice for a growing number of multi-chip module (MCM) applications. Unlike the longer-standing hybrid microcircuit technology based upon alumina substrates, the manufacturability and reliability of thick film solder joints on LTCC substrates have not been widely studied. An investigation was undertaken to fully characterize solder joints on these substrates. A surface mount test vehicle with Daisy chain electrical connections was designed and built with Dupont{trademark} 951 tape. The Dupont{trademark} 4569 thick film ink (Au76-Pt21-Pd3 wt.%) was used to establish the surface conductor pattern. The conductor pattern was fired onto the LTCC substrate in a matrix of processing conditions that included: (1) double versus triple prints, (2) dielectric window versus no window, and (3) three firing temperatures (800 C, 875 C and 950 C). Sn63-Pb37 solder paste with an RMA flux was screen printed onto the circuit boards. The appropriate packages, which included five sizes of chip capacitors and four sizes of leadless ceramic chip carriers, were placed on the circuit boards. The test vehicles were oven reflowed under a N{sub 2} atmosphere. Nonsoldered pads were removed from the test vehicles and the porosity of their thick film layers was measured using quantitative image analysis in both the transverse and short transverse directions. A significant dependence on firing temperature was recorded for porosity. The double printed substrates without a dielectric window revealed a thick film porosity of 31.2% at 800 C, 26.2% at 875 C and 20.4% at 950 C. In contrast, the thick film porosity of the triple printed substrates with a dielectric window is 24.1% at 800 C, 23.2% at 875 C and 17.6% at 950 C. These observations were compared with the shear strength of the as-fabricated chip capacitor solder joints to determine the effect of firing conditions on solder joint ...
Date: January 4, 2000
Creator: Hernandez, C.L.; Vianco, P.T. & Rejent, J.A.
Partner: UNT Libraries Government Documents Department

Technique for Measuring Hybrid Electronic Component Reliability

Description: Materials compatibility studies of aged, engineered materials and hardware are critical to understanding and predicting component reliability, particularly for systems with extended stockpile life requirements. Nondestructive testing capabilities for component reliability would significantly enhance lifetime predictions. For example, if the detection of crack propagation through a solder joint can be demonstrated, this technique could be used to develop baseline information to statistically determine solder joint lifelengths. This report will investigate high frequency signal response techniques for nondestructively evaluating the electrical behavior of thick film hybrid transmission lines.
Date: January 1, 1999
Creator: Green, C.C.; Hernandez, C.L.; Hosking, F.M.; Robinson, D.; Rutherford, B. & Uribe, F.
Partner: UNT Libraries Government Documents Department

Fermilab Failure Analysis of TeV I (TIE) Array Soldier Joints

Description: Failure of TIE array loop assembly solder joints within Stochastic Cooling Tanks during system operation resulted in the loop base plate dropping into the beam region. This caused a non-operational condition to exist within the system. In order to understand the failure mechanism, several loop assemblies were submitted to Midwest Materials and Engineering Consultants for complete metallurgical evaluation and failure analysis. Because of the similarity between the loop assembly material construction and the TIE resistor assemblies, several resistor assemblies were also evaluated.
Date: September 2, 1987
Creator: Runge-Marchese, Jude M.; Daehn, Ralph C. & /Fermilab
Partner: UNT Libraries Government Documents Department

Microstructure and Performance of Kovar/Alumina Joints Made with Silver-Copper Base Active Metal Braze Alloys

Description: Poor hermeticity performance was observed for Al{sub 2}O{sub 3}-Al{sub 2}O{sub 3} ceramic-ceramic joints having a Kovar{trademark} alloy interlayer. The active Ag-Cu-Ti filler metal was used to braze the substrates together. The Ti active element was scavenged from the filler metal by the formation of a (Fe, Ni, Co){sub x}Ti phase (x= 2-3) that prevented development of a continuous Ti{sub x}O{sub y} layer at the filler metal/Al{sub 2}O{sub 3} interface. Altering the process parameters did not circumvent the scavenging of Ti. Molybdenum barrier layers 1000, 2500, or 5000 {angstrom} thick on the Kovar{trademark} surfaces successfully allowed Ti{sub x}O{sub y} formation at the filler metal/Al{sub 2}O{sub 3} interface and hermetic joints. The problems with the Ag-Cu-Ti filler metal for Kovar{trademark}/Al{sub 2}O{sub 3} braze joints led to the evaluation of a Ag-Cu-Zr filler metal. The Zr (active element) in Ag-Cu-Zr filler metal was not susceptible to the scavenging problem.
Date: December 15, 1999
Partner: UNT Libraries Government Documents Department

Environmental evaluation of Surface Mounted Devices (SMD)

Description: We evaluated the comparative reliability of solder interconnections used for Leadless Chip Carriers (LCCs), Meaded, and flat-pack hybrid microcircuits mounted on FR-4 glass epoxy printed wiring boards (PWBs). The board assemblies, with solder attached microcircuits, were repeatedly thermal cycled from - 65 to +125{degrees}C. We recognize that this temperature range far exceeds most testing of assemblies. The purposes of these tests were to evaluate worst-case conditions and to obtain comparative information. Identical PWB assemblies, using these three component types, were subjected to both thermal shock testing (1 cycle every 42 minutes) and temperature cycle testing (1 cycle every 3 hours). The double testing evaluated the differences in stress application and evaluated the potential of replacing slow transition, expensive temperature cycle testing (which has been an industry standard for years) with the much more rapid thermal shock testing.
Date: June 1, 1997
Creator: Barr, V.C. & Andrade, A.D.
Partner: UNT Libraries Government Documents Department

Microstructurally based finite element simulation of solder joint behavior

Description: The most commonly used solder for electrical interconnects in electronic packages is the near eutectic 60Sn-40Pb alloy. This alloy has a number of processing advantages (suitable melting point of 183C and good wetting behavior). However, under conditions of cyclic strain and temperature (thermomechanical fatigue) the microstructure of this alloy undergoes a heterogeneous coarsening and failure process that makes the prediction of solder joint lifetime complex. A finite element simulation methodology to predict solder joint mechanical behavior, that includes microstructural evolution, has been developed. The mechanical constitutive behavior was incorporated into the time dependent internal state variable viscoplastic model through experimental creep tests. The microstructural evolution is incorporated through a series of mathematical relations that describe mass flow in a temperature/strain environment. The model has been found to simulate observed thermomechanical fatigue behavior in solder joints.
Date: January 1, 1996
Creator: Frear, D.R.; Burchett, S.N.; Neilsen, M.K. & Stephens, J.J.
Partner: UNT Libraries Government Documents Department

Environmentally compatible solder materials for thick film hybrid assemblies

Description: New soldering materials and processes have been developed over the last several years to address a variety of environmental issues. One of the primary efforts by the electronics industry has involved the development of alternative solders to replace the traditional lead-containing alloys. Sandia National Laboratories is developing such alternative solder materials for printed circuit board and hybrid microcircuit (HMC) applications. This paper describes the work associated with low residue, lead-free soldering of thick film HMC`s. The response of the different materials to wetting, aging, and mechanical test conditions was investigated. Hybrid test vehicles were designed and fabricated with a variety of chip capacitors and leadless ceramic chip carriers to conduct thermal, electrical continuity, and mechanical evaluations of prototype joints. Microstructural development along the solder and thick film interface, after isothermal solid state aging over a range of elevated temperatures and times, was quantified using microanalytical techniques. Flux residues on soldered samples were stressed (temperature-humidity aged) to identify potential corrosion problems. Mechanical tests also supported the development of a solder joint lifetime prediction model. Progress of this effort is summarized.
Date: February 1, 1997
Creator: Hosking, F.M.; Vianco, P.T.; Rejent, J.A. & Hernandez, C.L.
Partner: UNT Libraries Government Documents Department

Solder joint aging characteristics from the MC2918 firing set of a B61 accelerated aging unit (AAU)

Description: The B61 accelerated aging unit (AAU) provided a unique opportunity to document the effects of a controlled, long-term thermal cycling environment on the aging of materials used in the device. This experiment was of particular interest to solder technologists because thermal cycling environments are a predominant source of solder joint failures in electronic assemblies. Observations of through hole solder joints in the MC2918 Firing Set from the B61 AAU did not reveal signs of catastrophic failure. Quantitative analyses of the microstructural metrics of intermetallic compound layer thickness and Pb-rich phase particle distributions indicated solder joint aging that was commensurate with the accelerated aging environment. The effects of stress-enhanced coarsening of the Pb-rich phase were also documented.
Date: October 1, 1997
Creator: Vianco, P.T. & Rejent, J.A.
Partner: UNT Libraries Government Documents Department

Computational continuum modeling of solder interconnects

Description: The most commonly used solder for electrical interconnections in electronic packages is the near eutectic 60Sn-40Pb alloy. This alloy has a number of processing advantages (suitable melting point of 183 C and good wetting behavior). However, under conditions of cyclic strain and temperature (thermomechanical fatigue), the microstructure of this alloy undergoes a heterogeneous coarsening and failure process that makes prediction of solder joint lifetime complex. A viscoplastic, microstructure dependent, constitutive model for solder which is currently in development was implemented into a finite element code. With this computational capability, the thermomechanical response of solder interconnects, including microstructural evolution, can be predicted. This capability was applied to predict the thermomechanical response of various leadless chip carrier solder interconnects to determine the effects of variations in geometry and loading. In this paper, the constitutive model will first be briefly discussed. The results of computational studies to determine the effect of geometry and loading variations on leadless chip carrier solder interconnects then will be presented.
Date: March 1, 1997
Creator: Burchett, S.N.; Neilsen, M.K.; Frear, D.R. & Stephens, J.J.
Partner: UNT Libraries Government Documents Department

Damage mechanics characterization on fatigue behavior of a solder joint material

Description: This paper presents the first part of a comprehensive mechanics approach capable of predicting the integrity and reliability of solder joint material under fatigue loading without viscoplastic damage considerations. A separate report will be made to present a comprehensive damage model describing life prediction of the solder material under thermomechanical fatigue loading. The method is based on a theory of damage mechanics which makes possible a macroscopic description of the successive material deterioration caused by the presence of microcracks/voids in engineering materials. A damage mechanics model based on the thermodynamic theory of irreversible processes with internal state variables is proposed and used to provide a unified approach in characterizing the cyclic behavior of a typical solder material. With the introduction of a damage effect tensor, the constitutive equations are derived to enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The fatigue evolution is subsequently developed based on the hypothesis that the overall damage is induced by the accumulation of fatigue and plastic damage. This damage mechanics approach offers a systematic and versatile means that is effective in modeling the entire process of material failure ranging from damage initiation and propagation leading eventually to macro-crack initiation and growth. As the model takes into account the load history effect and the interaction between plasticity damage and fatigue damage, with the aid of a modified general purpose finite element program, the method can readily be applied to estimate the fatigue life of solder joints under different loading conditions.
Date: August 1, 1998
Creator: Chow, C.L.; Yang, F. & Fang, H.E.
Partner: UNT Libraries Government Documents Department

A new active solder for joining electronic components

Description: Electronic components and micro-sensors utilize ceramic substrates, copper and aluminum interconnect and silicon. The joining of these combinations require pre-metallization such that solders with fluxes can wet such combinations of metals and ceramics. The paper will present a new solder alloy that can bond metals, ceramics and composites. The alloy directly wets and bonds in air without the use flux or premetallized layers. The paper will present typical processing steps and joint microstructures in copper, aluminum, aluminum oxide, aluminum nitride, and silicon joints.
Date: May 11, 2000
Partner: UNT Libraries Government Documents Department

Microstructural Coarsening during Thermomechanical Fatigue and Annealing of Micro Flip-Chip Solder Joints

Description: Microstructural evolution due to thermal effects was studied in micro solder joints (55 {+-} 5 {micro}m). The composition of the Sn/Pb solder studied was found to be hypereutectic with a tin content of 65--70 wt%.This was determined by Energy Dispersive X-ray analysis and confirmed with quantitative stereology. The quantitative stereological value of the surface-to-volume ratio was used to characterize and compare the coarsening during thermal cycling from 0--160 C to the coarsening during annealing at 160 C. The initial coarsening of the annealed samples was more rapid than the cycled samples, but tapered off as time to the one-half as expected. Because the substrates to which the solder was bonded have different thermal expansion coefficients, the cycled samples experienced a mechanical strain with thermal cycling. The low-strain cycled samples had a 2.8% strain imposed on the solder and failed by 1,000 cycles, despite undergoing less coarsening than the annealed samples. The high-strain cycled samples experienced a 28% strain and failed between 25 and 250 cycles. No failures were observed in the annealed samples. Failure mechanisms and processing issues unique to small, fine pitch joints are also discussed.
Date: December 1, 1998
Creator: Barney, Monica M.
Partner: UNT Libraries Government Documents Department