A simulation of air bearing surface materials with copper substrate for corrosion investigation
Corrosion defect is one of the important defects found in hard disk drive manufacturing. Fail to detect this defect might lead to fatal hard disk drive failure. In general, corrosion defect was found after the end of process. The fundamental methodology used to measure corrosion defect in head magnetic process of hard disk drive manufacturing is Electrochemical impedance spectroscopy (EIS). This method applies a low frequency voltage to a chemical cell in order to measure corrosion rate which is defined as a reaction of material in aqueous solution. The data obtained from EIS measurement method are complex and thus hard to analyze. Furthermore, EIS method is destructive materials measurement and the obtained results cannot well predict corrosion behavior of the system. However, head magnetic materials/slider is a stack of three materials in layers i.e. soft magnetic layer, diamond like carbon (DLC) layer, and photoresist layer respectively. These three stack layer of slider can be replaced by R-C equivalent circuit. Nyquist plot and Bode plot are used to observe the frequency response of the equivalent circuit. This observation can help in prediction of corrosion behavior before starting of mass fabrication or transferring to new materials. This work shows that the results obtained from an equivalent R-C circuit model of copper substrate coated with photoresist and the one obtained from EIS method are comparable. It should be noted that the parameters of R-C equivalent circuits are modified for corrosion behavior studying according to two different types of photoresists.
Conformal photoresist coating for critical dimension improvement
3D surface topography of read / write head fabrication is difficult for lithography process. Photoresist deposition by using the conventional spin coating method is troubled. Spray coating is a replacement technique that eliminates the problem by producing micro-resist droplets that adhere firmly to the deposition location; thus, spray coating with optimal parameters from designed experiment is a suitable method for photoresist deposition on structures with high aspect ratio. By using proper nitrogen flow rate to spread out AZ4999 resist to be micro-droplet in the same time with proper traveling nozzle speed, the photoresist turbulence will perform good resist coverage over all surfaces. From design of experiment show the optimum condition for conformal deposition is 0.8 Bar at 117mm/s for nitrogen pressure and nozzle speed, respectively. Photoresist thickness was dropped at 30um far away from groove or edge of the head.
Complexation of poly(vinylidene fluoride):LiPF6 solid polymer electrolyte with enhanced ion conduction in ‘wet’ form
Abstract Poly(vinylidene fluoride) (PVDF):LiPF 6 complex membranes as ‘solid’ and ‘wet’ polymer electrolytes are evaluated. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies show a decrease in crystalline size and crystallinity of the polymer PVDF with increasing LiPF 6 concentration. Although PVDF is not an ionomer, acid–base complexation between the PVDF polymer at fluorine sites and the Li ions of the LiPF 6 salt is evident from X-ray photoelectron spectroscopy (XPS) spectra. Such interaction is responsible for the reduction in both PVDF crystallinity and sol particle size during solid film formation. As evident from scanning electron micrographs, smaller spherical domains in the dry film are found with increasing lithium salt. Impedance (ac) measurements suggested the ionic conductivity of PVDF:LiPH 6 film increases with increasing lithium salt. By comparison, PVDF:LiPH 6 solid polymer electrolyte (SPE) wetted with Ethylene carbonate/propylene carbonate (EC/PC) shows less dependence of conductivity on salt concentration with a shallow maximum at about 15 wt.% salt. The average value is comparable with that of the solvent-free film at 20 wt.% LiPF 6 . This result suggests the existence of dual conduction mechanisms in ‘wet’ SPE via the amorphous PVDF matrix and the EC/PC solution trapped in the swollen region of the PVDF porous network.