POLLEN FLORA OF PAKISTAN – LXVIII
Pollen morphology 20 species of the family Alliaceae from Pakistan has been examined by light and scanning electron microscope. Pollen grains are usually bilateral, hetropolar mostly boat shaped, sexine thicker tor thinner than nexine. Tectal surface is mostly rugulate foveolate or subpsilate rarely reticulate. On the basis of apertural types 3 distinct pollen types are recognized, viz., Allium fedtschenkoanum –type, Allium grifthianum-type and Allium roylei-type.
Pollen morphology of Callicarpa L. (Lamiaceae) from China and its systematic implications
Pollen morphology of 36 species and 9 varieties of Callicarpa L. (Lamiaceae) from China was investigated through scanning electron microscopy. Pollen grains of the genus are monads, radiosymmetric and tricolpate, mainly medium in size, spheroidal (rarely subprolate, prolate or suboblate) in equatorial view and (sub) circular or rounded triangular in polar view. The edge of colpus is thin, perforate or thickened but imperforate and the colpus membrane of the investigated taxa is usually uneven (sunken or raised), with finely/coarsely granular or irregular striation. Four different ornamentation types are delimited on the basis of exine sculpturing: (1) coarsely reticulate; (2) microreticulate; (3) rugosely reticulate and (4) rugulate reticulate. The results do not support the traditional infrageneric classification of Callicarpa which is based on stamen characters. However, pollen characters provide evidence to support Callicarpa as the sister to the Australian subfamily Prostantheroideae, a relationship previously suggested by molecular phylogenetic analyses.
Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review
Ultrathin silicon wafer technology is reviewed in terms of the semiconductor applications, critical challenges, and wafer pre-assembly and assembly process technologies and their underlying mechanisms. Mechanical backgrinding has been the standard process for wafer thinning in the semiconductor industry owing to its low cost and productivity. As the thickness requirement of wafers is reduced to below 100 μm, many challenges are being faced due to wafer/die bow, mechanical strength, wafer handling, total thickness variation (TTV), dicing, and packaging assembly. Various ultrathin wafer processing and assembly technologies have been developed to address these challenges. These include wafer carrier systems to handle ultrathin wafers; backgrinding subsurface damage and surface roughness reduction, and post-grinding treatment to increase wafer/die strength; improved wafer carrier flatness and backgrinding auto-TTV control to improve TTV; wafer dicing technologies to reduce die sidewall damage to increase die strength; and assembly methods for die pick-up, die transfer, die attachment, and wire bonding. Where applicable, current process issues and limitations, and future work needed are highlighted.