Teck-Yong Tou

Investigation of mechanical shock testing of lead-free SAC solder joints in fine pitch BGA package

Abstract The lead-free Sn–Ag–Cu (SAC 305/405) solder that replaced the tin–lead eutectic solder tends to be more brittle in nature due to high stiffness and excessive solder interfacial reactions. This leads to higher occurrences of solder joints failure during surface mount assembly and handling operations as a result of PCB bending, shock impact and drop. In this work, mechanical tests simulating the shock impact were conducted on lead-free SAC of different weight percentages. These SAC materials were prepared for use in the solder joints of fine pitch ball grid array (BGA) components which were mounted onto the motherboard. After the mechanical shock tests, strain measurements were performed on the BGA components to gauge the solder joint integrity, which was shown to be related with the formation of intermetallics in the bulk and at the interface of the SAC solder. The ball pull tests were conducted to determine both the bulk and interfacial strength and the solder joint fracture, which was classified as either mode 1, 2 or 3. A correlation was made between the silver (Ag) and copper (Cu) weight percentages with the metallurgical reactions.

Effects of substrate temperature on electrical and structural properties of copper thin films

This paper addresses the effects of substrate temperature on electrical and structural properties of dc magnetron sputter-deposited copper (Cu) thin films on p-type silicon. Copper films of 80 and 500 nm were deposited from Cu target in argon ambient gas pressure of 3.6 mTorr at different substrate temperatures ranging from room temperature to 250 °C. The electrical and structural properties of the Cu films were investigated by four-point probe and atomic force microscopy. Results from our experiment show that the increase in substrate temperature generally promotes the grain growth of the Cu films of both thicknesses. The RMS roughness as well as the lateral feature size increase with the substrate temperature, which is associated with the increase in the grain size. On the other hand, the resistivity for 80 nm Cu film decreases to less than 5 μΩ-cm at the substrate temperature of 100 °C, and further increase in the substrate temperature has not significantly decreased the film resistivity. For the 500 nm Cu films, the increase in the grain size with the substrate temperature does not conform to the film resistivity for these Cu films, which show no significant change over the substrate temperature range. Possible mechanisms of substrate-temperature-dependent microstructure formation of these Cu films are discussed in this paper, which explain the interrelationship of grain growth and film resistivity with elevated substrate temperature.

Red-green-blue laser emissions from dye-doped poly(vinyl alcohol) films.

A microscope slide acting as a passive waveguide was coated by three separate poly(vinyl alcohol) films that were doped with Coumarin 460, Disodium Fluorescein, and Rhodamine 640 perchlorate. On collinear pumping by a nitrogen laser, these dyes furnished primary red-green-blue laser emissions that were collected and waveguided by the microscope slide but exited from both ends. Frosting the waveguide exit introduced light scattering at the glass-air interface and spatially overlaid the red-green-blue laser emissions that emerged as a uniform white-light beam.

Laser Emissions from Disodium Fluorescein-Doped Poly(Vinyl Alcohol) Films

Superradiant-mode laser emissions were obtained from disodium fluorescein (DF)-doped poly(vinyl alcohol) (PVA) films which had been dip-coated on a microscope glass slide. When the film was transversely pumped using a nitrogen laser, superradiant emission was trapped and propagated in the supporting glass slide which acted as a waveguide. The trapped light underwent multiple internal reflections before it exited at both ends of the slide, producing a lasing effect. The laser beam profile varied with the edge condition of the glass slide; a circular beam was obtained with a frosted edge. An output conversion efficiency of 22% was obtained for a fresh sample while its lasing output energy at a localized excitation position, or operating lifetime, decreased at a rate of 0.015% per shot of nitrogen laser. Despite the decrease in output energy, the laser peak wavelength of DF was largely unchanged.

Space and time-resolved optical emission spectroscopy in TEA-CO/sub 2/ laser ablation of polymers and graphite

The luminous plumes from the TEA-CO/sub 2/ laser ablation of polymethylmethacrylate, polyimide, polyethylene terepthalate, and graphite in helium were characterized by using gated optical emission spectroscopy that measured the spatial-temporal distribution of singly ionized carbon species, and also by streak photography that examined the dynamics of the propagation of the luminous plumes. The plume splitting was implicated by the fast and slow components of plume species in curve-fitting their spatial-temporal distribution with the shifted Maxwell-Boltzmann distribution function. The best-fit velocities of the fast components were confirmed by the streak photographs.

Measurements of Time Delays in Superradiant Laser Emssions from Binary Dye Mixtures

The concentration dependence of the time delays, in the range of 80–800 ps, between two-color superradiant laser emissions from three enthanol solutions of the binary dye mixtures, C460/DF, DF/R640, and C460/R640, which were excited using a 1 ns transversely excited atmospheric (TEA) N2 laser was measured by a fast streak camera. While these time delays confirmed that radiative laser energy transfer as the predominant mechanism for multicolor laser emission from a single dye-mixture solution, these emissions were not usually obtained simultaneously, even when a broadband optical resonator was used.

Analysis of Atomic Force Microscopy Images of Crystal Originated “Particles” on Silicon Wafers Treated with NH4OH:H2O2:H2O Solution

Crystal-originated particle (COP) side-wall angles and rates of change in width were measured after treatment in an SC-1 solution by atomic force microscopy (AFM) to determine the shape, size and type of the particles on a polished (100) Si wafer surface. The etched silicon tips maximum measurable slope angles were used to determine whether a COP originated from either the upper or the lower portion of an octahedral void. If the COP side-wall angle is equal to the maximum measurable slope angle of around 72°, the COP originated from the upper portion of the void. The lower portion of an octahedral void corresponds to a side-wall angle of 55°. This was confirmed through the study of COP width changes in NH4OH:H2O2:H2O (SC-1) solution. The COP width depends on the rates of change in width and the shape of its void. The rates of change of width of the COP which originated from the lower portion of the void was found to be 0.8 nm/min whereas that of the COP which originated from the upper portion of the void was 2.5 nm/min. It is also shown that a perceived single-type COP could very well be the upper part of a twin-type COP, which reveals its form of a much larger geometry only after the wafers are dipped repeatedly in the SC-1 solution.

Influence of process parameters on the substrate heating in direct current plasma magnetron sputtering deposition process

Purpose – The purpose of this paper is to address the influence of deposition process parameters. The substrate heating mechanisms are also discussed.Design/methodology/approach – Deposition duration, sputtering power, working gas pressure, and substrate heater temperature on substrate heating in the direct current (DC) magnetron sputtering deposition process were investigated.Findings – Results from the experiments show that, in DC magnetron sputtering deposition process, substrate heating is largely influenced by the process parameters and conditions.Originality/value – This paper usefully demonstrates that substrate heating effects can be minimized by adjusting and selecting the proper sputtering process parameters; the production cost can be reduced by employing a higher sputtering power, lower working gas pressure and shorter deposition duration.

Detection of Kite-Shaped COPs in Nitrogen-Doped Czochralski-Grown Silicon Wafers

Surface analyses by atomic force microscopy and field-emission scanning electron microscopy have revealed new shape of truncated voids, commonly known as crystal-originated-particles (COPs), that appear as kite-shaped pits with two (111) planes and two non-(111) planes in twin and triplet clusters, when viewed from the surface plane of nitrogen-doped Czochralski (CZ)-grown silicon (100) wafers. Also, the detection of higher number density but smaller size for these COPs indicates that the presence of nitrogen during CZ-growth of silicon crystals has strong influence on the size and density of COPs

Zinc Oxide Thin Films Fabricated with Direct Current Magnetron Sputtering Deposition Technique

Zinc oxide (ZnO) is a very promising material for emerging large area electronic applications including thin‐film sensors, transistors and solar cells. We fabricated ZnO thin films by employing direct current (DC) magnetron sputtering deposition technique. ZnO films with different thicknesses ranging from 100 nm to 1020 nm were deposited on silicon (Si) substrate. The deposition pressure was varied from 12 mTorr to 25 mTorr. The influences of the film thickness and the deposition pressure on structural properties of the ZnO films were investigated using Mahr surface profilometer and atomic force microscopy (AFM). The experimental results reveal that the film thickness and the deposition pressure play significant role in the structural formation of the deposited ZnO thin films. ZnO films deposited on Si substrates are promising for variety of thin‐film sensor applications.