Temperature cycling tests, and statistical analysis of the results, for various high‐density packages on printed‐circuit boards with Sn‐Cu hot‐air solder levelling, electroless nickel‐immersion gold, and organic solder preservative finishes are investigated in this study. Emphasis is placed on the determination of the life distribution and reliability of the lead‐free solder joints of these high‐density package assemblies while they are subjected to temperature cycling conditions. A data acquisition system, the relevant failure criterion, and the data extraction method will be presented and examined. The life test data are best fitted to the Weibull distribution. Also, the sample mean, population mean, sample characteristic life, true characteristic life, sample Weibull slope, and true Weibull slope for some of the high‐density packages are provided and discussed. Furthermore, the relationship between the reliability and the confidence limits for a life distribution is established. Finally, the confidence levels for comparing the quality (mean life) of lead‐free solder joints of high‐density packages are determined.
Failure analyses of the lead‐free and SnPb solder joints of high‐density packages such as the plastic ball grid array and the ceramic column grid array soldered on SnCu hot‐air solder levelling electroless nickel‐immersion gold or NiAu, and organic solderability preservative Entek printed circuit boards are presented. Emphasis is placed on determining the failure locations, failure modes, and intermetallic compound composition for these high‐density packages' solder joints after they have been through 7,500 cycles of temperature cycling. The present results will be compared with those obtained from temperature cycling and finite element analysis.
The high-intensity, high-resolution x-ray source at the European Synchrotron Radiation Facility (ESRF) has been used in x-ray diffraction (XRD) experiments to detect intermetallic compounds (IMCs) in lead-free solder bumps. The IMCs found in 95.5Sn3.8Ag0.7Cu solder bumps on Cu pads with electroplated-nickel immersion-gold (ENIG) surface finish are consistent with results based on traditional destructive methods. Moreover, after positive identification of the IMCs from the diffraction data, spatial distribution plots over the entire bump were obtained. These spatial distributions for selected intermetallic phases display the layer thickness and confirm the locations of the IMCs. For isothermally aged solder samples, results have shown that much thicker layers of IMCs have grown from the pad interface into the bulk of the solder. Additionally, the XRD technique has also been used in a temperature-resolved mode to observe the formation of IMCs, in situ, during the solidification of the solder joint. The results demonstrate that the XRD technique is very attractive as it allows for nondestructive investigations to be performed on expensive state-of-the-art electronic components, thereby allowing new, lead-free materials to be fully characterized.
The y-TiAI-based alloys are potentially very attractive low-density materials for use at elevated temperatures. In this article, a novel method of controlling the grain size of these alloys using mechanical alloying and hot isostatic pressing is presented. 390....-------------. (002) (100) (101) Figure 1. XRD trace of PBMed Ti-48AI-2Mn-2Nb after 50 hours showing the transformation to a-HCP titanium with standard peak positions and intensities (2-theta-scale).LJ 10f.lm Figure 2. BSE image of a SPEX-milled powder displaying modified (lighter surface regions) and retained (dendritic central region) microstructure after 12 hours of milling. 40 INTRODUCTIONTitanium aluminides based on the y-TiAI (LID structure) have been widely investigated for elevated-temperature applications due to their retention of good mechanical properties at elevated temperatures. 1 -3 However, these alloys, like most intermetallics, suffer from low ductility and fracture toughness at ambient temperatures; y-TiAI also suffers from greater-than-desirable oxidation at temperatures significantly lower than its melting temperature. The use of an alloying addition such as manganese for ductility and chromium and niobium for increased oxidation resistance can improve these properties. Modification of the microstructure may also increase the ductility and fracture toughness ofy-TiAI-based alloys. In this respect, nanocrystalline-equiaxed y grains and the fine lamellar y / a 2 microstructures are considered to be good candidates. 1 -3 The nanocrystalline material should also have superplastic-forming capabilities. 4 The mechanical alloying (MA) of elemental powders has been shown to be a versatile synthesis route capable of forming equilibrium and nonequilibrium phases. MA can also refine the microstructure and is capable of producing homogenous, nanocrystalline grains. Mechanical milling (MM) differs from MA in that prealloyed powders are used instead of elemental addition and, if appropriate measures are taken, oxygen and nitrogen pickup can be limited to acceptable levels. s Following milling, it is necessary to consolidate the powders; however, because of the far-from-equilibrium nature6-10 of the powder, care must be taken to avoid excessive-time temperature exposuresY At first, hot isostatic pressing (HIPing) appears to be an undesirable method of compacting far-from-equilibrium materials; however, several studies have been carried out on the HIPing of y-TiAI composition powders produced by MA/MM that have shown that nanograins can be retained with this process. 12-18 Thus, the excellent size-and shape-making capabilities ofHIPing 18 can be used in conjunction with this type of material.In this article, preliminary results on a novel method of controlling the microstructure in a milled and HIPed Ti-48AI-2Mn-2Nb prealloyed powder are presented. EXPERIMENTAL METHODSPrealloyed Ti-48AI-2Mn-2Nb powders supplied by the Interdisciplinary Research Center of Birmingham, United Kingdom, and GKSS of Germany were milled either in Fritsch Pulverisette P5 / 4...
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