Daisuke Echizenya

Effect of surface damage on strength of silicon wafer for solar cells

Recently, solar power generation using crystalline silicon wafers has been rapidly growing. It is well known that the mechanical properties of silicon wafers are affected by defects caused by slicing processes of the wafers. However the effect of the defects on the mechanical properties, especially, strength of the crystalline silicon wafers has not been clarified yet. In this paper, to clarify the effect of the defects during slicing process, bending tests are conducted using defects specimens. The specimens are given a defect by indentations referred to the slicing process of wafers. The two indentation loads are chosen to reveal the effect of the defects size on the bending strength. The bending strength is evaluated using based on fracture mechanics. The residual stress and the initial crack affect the bending strength; therefore, the residual stress and Raman spectrometry of the specimens are measured before the bending tests. Fracture surfaces are also observed by Transmission Electron Microscope (TEM). The experiments show that the bending strength depends on the defects size and that there are numerous cracks on the wafer surface caused by the slicing process. Finally, it is found that the minimizing of the mechanical surface defects on wafers gives the high reliability for photovoltaic modules and the increase in the wafer strength. Furthermore the residual stress and Raman spectrometry show that the difference of surface damage mode caused by the slicing processing method.

Precise lens-assembly techniques based on adhesive bonding and hammering for compact 100GbE TOSA

Two precise lens-assembly techniques based on the adhesive bonding and hammering are proposed. These techniques allow us to realize a compact 100GbE TOSA 15.1 × 6.5 × 5.6 mm which is suitable for the QSFP28 form factor. The measured DC output powers are more than +4.0 dBm which fully achieve the target value of+1.0 dBm with the large margin.

Biaxial Ratchetting Deformation of Solders Considering Halt Conditions

Recently, Halt (Highly accelerated limit test) is widely employed for evaluation of reliability of electronic products. Halt condition is quite severe. The tested products are subjected to mechanical impacts, thermal shock, and vibration at same time. However, there has not been a reasonable and accurate evaluation method for Halt yet. To construct an accurate evaluation method of Halt, basic deformation mechanism of parts of the electronic products should be clarified from both experimental and theoretical points of view. In this paper, focusing on solder joints of circuit boards of electronic products, ratchetting deformation, especially, biaxial ratchetting deformation of solder joints is revealed from both experimentally and theoretically. The authors have already conducted biaxial ratchetting test combining axial and torsional cyclic loading using a tubular specimen of Type 304 stainless steel. However, as for solders, it is difficult to make tubular specimen. Since size of the solder joints is micron, a small size joint specimen of copper tube and solder is employed in this paper. First, to confirm the quality of the joint specimen such as boundary between copper and solder, both the tensile and cyclic loading tests are conducted at several temperatures using Sn-3Ag-0.5Cu. The basic characteristic of tensile and fatigue failure is obtained from these tests. After the confirmation of the accuracy of the joint specimen, biaxial ratchetting tests are conducted superposing the tensile load on cyclic torsion. The biaxial ratchetting tests are conducted using a biaxial loading testing machine developed for the joint specimens of solder and copper.