Quick assessment methodology for reliability of solder joints in ball grid array (BGA) assembly—Part I: Creep constitutive relation and fatigue model

In this study, a new unified creep constitutive relation and a modified energy-based fatigue model have been established respectively to describe the creep flow and predict the fatigue life of Sn−Pb solders. It is found that the relation successfully elucidates the creep mechanism related to current constitutive relations. The model can be used to describe the temperature and frequency dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part II to develop the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly. The project supported by the National Natural Science Foundation of China (59705008)     

Hydrogen bonding incis-2,3-epoxycyclooctanol

Hydrogen bonding and the electron-withdrawing or electron-donating characteristics of substituent groups that are neighboring to epoxide groups can affect the reactivity of the epoxide ring. The crystal structure ofcis-2,3-epoxycyclooctanol has been determined as a saturated eight-membered ring compound in which a hydroxyl group is attached to the C(1) atom that is adjacent to a 2,3-fused epoxy ring. The findings are that the longer epoxide C-O bond (and hence the one expected to be more readily broken) is the one farther from the hydroxyl group [1.462(1) å versus 1.447(1) å] and that the optimal hydrogen bonding is to an adjacent molecule radier than within the molecule. The shortest C-C bond is that of the epoxide group; the bond adjacent to it (on the side farther from the hydroxyl group) is the next shortest.     

X-Ray crystal analysis of the substrates of aconitase: XI. Manganous citrate decahydrate

The crystal structure of hydrated manganese citrate, [Mn(H₂O)₆] [Mn C₆H₅O₇(H₂O)]₂2H₂O has been determined. The crystals are monoclinic, space group P2₁/n cell dimensions a = 20.575 ± 0.005, b = 6.755 ± 0.002, c = 9.230 ± 0.002 Å, β = 96.74 ± 0.01°. The structure is isomorphous with that of the magnesium salt for which the structure has been determined⁴. There are two [Mn(H₂O)₆]²⁺ ions, four [Mn C₆H₅O₇(H₂O)] ions and four water molecules per unit cell. Each citrate ion forms a tridentate chelate to one manganese ion. A correlation of Mn²⁺ ? H distances for manganese citrate, found in this crystallographic study, was made with those determined by NMR studies in solutions in the absence and presence of the enzyme aconitase, and indicated that the assumption that citrate chelates to enzyme-bound manganese ion fits all the available data.