9 research outputs found
1/f Noise in conductive adhesive bonds under mechanical stress as a sensitive and fast diagnostic tool for reliability assessment
No full textClassical lifetime predictions of conductive adhesive bonds require time consuming thermal cycling measurements. Therefore, faster lifetime test are needed with more detailed information about degradation mechanisms. This paper reports on the low frequency noise of such contacts. Our results show that the evolution of l/f noise in contacts is a fast and non-destructive diagnostic tool for reliability testing. The l/f noise of the contact resistance can be interpreted within an existing contact noise model in terms of a multispot contact behaviour. In comparison to classical reliability tests, l/f noise measurements reveal more detailed information about reduction in the real electrical contact area and are much faster and are non-destructive
The use of impedance spectroscopy, SEM and SAM imaging for early detection of failure in SMT assemblies
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The Use Impedance Spectroscopy, SEM and SAM Imaging for Early Detection of Failure in SMT Assemblies
No full textInternational audienc
The use of impedance spectroscopy, SEM and SAM imaging for early detection of failure in SMT assemblies
No full text1/f Noise as a diagnostic tool to investigate the quality of isotropic conductive adhesive bonds
No full textReliability assessment of conductive adhesive bonds by thermo-cycling up to 830 cycles is time consuming, and does not give much information about the details of the onset of degradation. There is a need for faster tests giving more details about degradation. In this paper, low frequency noise of such contacts is investigated. 1/f Noise stems from conductance fluctuations. The observed voltage noise is enhanced due to current crowding in the electrical contacts on a microscopic scale. In this research contact bonds were made and compared of isotropic conductive adhesives from three suppliers. The 1/f noise of the contact resistance can be interpreted in terms of a multispot contact behavior. We investigated the relative noise C versus contact resistance R in two ways: (1) after an increasing number of thermo-cycles; (2) after increasing mechanical stress. The results often show an increase in relative noise of three orders of magnitude for poor quality polymer bonds. A maximum increase of one order of magnitude is observed for the best quality conductive adhesive. The contact resistance increases by a factor 1.7 and not more than 1.14 for the poor and best quality bonds, respectively. From the analysis based on a noise model for multispot contact, the onset of delamination can be characterized as a reduction in electrical contact area Ae. The relative noise is proportional to Ae-5/2. The surprising result is that samples submitted to a mechanical stress show pictures similar to thermocycled samples. Thermo-cycling with less than 200 cycles leads to less noise, an increase in electrical contact area, and hence a contact improvement. This behavior is understood. Noise analysis under mechanical stress on nondegraded or slightly cycled bonds is a fast diagnostic tool for reliability characterization. The degree of delamination is expressed quantitatively by the D-factor D=Aemax /Aemin¿(Cmax/Cmin)2/5
Growth undercooling in multi-crystalline pure silicon and in silicon containing light impurities (C and O)
No full textInternational audienceUndercooling during the solidification of silicon is an essential parameter that plays a major role in grain nucleation and growth. In this study, the undercooling of the solid-liquid interface during growth of multi-crystalline silicon samples is measured for two types of silicon: pure, and containing light elements (carbon and oxygen) to assess and compare their impact on crystal growth. The solid-liquid interface undercooling is measured using in situ and real time X-ray synchrotron imaging during solidification. As a subsequent step, ex situ Electron Backscattered Diffraction (EBSD) is performed to obtain information about the crystalline structure, the grain orientation and the grain boundary character. Two main conclusions arise: (i) the undercooling of the global solid-liquid front increases linearly with the growth rate which indicates uniform attachment, i.e. all atoms are equivalent, (ii) the same trend is observed for pure silicon and silicon containing carbon and oxygen. Indeed, the growth law obtained is comparable in both cases, which suggests that the solutal effect is negligible as concern the undercooling in the case of a contamination with carbon (C) and oxygen (O). However, there is a clear effect of the impurity presence on the crystalline structure and grain boundary type distribution. Many grains nucleate during growth in samples containing C and O, which suggests the presence of precipitates on which grain nucleation is favored
X-ray Based in Situ Investigation of Silicon Growth Mechanism Dynamics - Application to Grain and Defect Formation
No full textInternational audienceTo control the final grain structure and the density of structural crystalline defects in silicon (Si) ingots is still a main issue for Si used in photovoltaic solar cells. It concerns both innovative and conventional fabrication processes. Due to the dynamic essence of the phenomena and to the coupling of mechanisms at dierent scales, the post-mortem study of the solidified ingots gives limited results. In the past years, we developed an original system named GaTSBI for Growth at high Temperature observed by Synchrotron Beam Imaging, to investigate in situ the mechanisms involved during solidification. X-ray radiography and X-ray Bragg diraction imaging (topography) are combined and implemented together with the running of a high temperature (up to 2073 K) solidification furnace. The experiments are conducted at the European Synchrotron Radiation Facility (ESRF). Both imaging techniques provide in situ and real time information during growth on the morphology and kinetics of the solid/liquid (S/L) interface, as well as on the deformation of the crystal structure and on the dynamics of structural defects including dislocations. Essential features of twinning, grain nucleation, competition, strain building, and dislocations during Si solidification are characterized and allow a deeper understanding of the fundamental mechanisms of its growth
