ALKALI METAL DERIVATIVES OF GROUP IV ORGANOMETALLICS: MECHANISTIC ASPECTS OF REACTIONS WITH HALIDES
Organometallic derivatives of the Group IV elements have been known and used as synthetic intermediates for a half century, but little has been done by way of systematic investigation of the scope, and limitations of their reactions. And only recently have investigators turned their attentions to the study of mechanistic aspects of these reactions. An overview of the field reveals many highly useful facts, but it is also strewn with some contradictory observations, along with many others that are difficult to fit into a coherent overall conceptual scheme. This scheme lies beyond the present horizon and will be revealed only after completion of systematic studies on the various parameters affecting the scope, limitations, and mechanisms of these reactions. Delineation of these, in turn, will provide reliable guides to their synthetic utility. This report deals with our present understanding of the mechanisms of Group IV organometalalkalis with organic halides, with reference to other reactions as appropriate, and with some of the questions concerning these reactions, whose answers lie beyond the horizon. Experimental observations which are relevant for understanding of mechanisms will be first summarized; mechanisms consistent with these will be reviewed; and questions remaining to be answered will be raised. Because of the nature of the presently known facts, those concerning silicon, germanium, tin, and lead alkalis will be intermingled, and valid trends within the series will be indicated.
Mise en evidence d'un mecanisme de substitution arynique pour la reaction d'halogenures aromatiques avec le tributylstannyllithium
Abstract Evidence for a benzyne mechanism is observed when tributylstannyllithium reacts with aromatic fluorides and chlorides, however with the corresponding bromides the reaction fails to proceed by this mechanism.
“ PARTIALLY-ACTIVATED ” FLUX RESIDUE IMPACTS ON ELECTRONIC ASSEMBLY RELIABILITIES
The reliabilities of the flux residue of electronic assemblies and semiconductor packages are attracting more and more attention with the adoption of no-clean fluxes by majority of the industry. In recent years, the concern of “partiallyactivated” flux residue and their influence on reliability have been significantly raised due to the miniaturization along with high density design trend, selective soldering process adoption, and the expanded use of pallets in wave soldering process. When flux residue becomes trapped under low stand-off devices, pallets or unsoldered areas (e.g. selective process), it may contain unevaporated solvent, “live” activators and metal complex intermediates with different chemical composition and concentration levels depending on the thermal profiles. These partially-activated residues can directly impact the corrosion, surface insulation and electrochemical migration of the final assembly. In this study, a few application tests were developed internally to understand this issue. Two traditional liquid flux and two newly developed fluxes were selected to build up the basic models. The preliminary results also provide a scientific approach to design highly reliable products with the goal to minimize the reliability risk for the complex PCB designs and assembly processes.