Suk-Jin Ham

Ultrathin nanoclay films with tunable thickness as barrier layers in organic light emitting devices

A novel concept where the inorganic ultrathin nanoclay (organo-treated montmorillonite) film is incorporated into the organic light-emitting diodes (OLEDs) as a buffer layer is exploited to enhance the performance and the stability of the devices. To precisely control the thickness of organoclay films within ∼1 nm scale, which can be a critical length in OLEDs research, we employ the charge-controlled deposition technique wherein the molecular interactions between nanoclay sheets and charged polymeric surface (mixture of poly(3,4-ethylenedioxythiophene) and poly(styrenesulfonate)) are elaborately manipulated. As a result, significantly improved device performance is observed for the case with the 5 nm thick clay films as compared to those without buffer layer, wherein the reduced turn-on voltage and the suppression of luminous efficiency (Cd A−1) decay over time can be obtained. Eventually, device lifetime of the OLEDs is greatly enhanced and the brightness is maintained while minimizing the occurrence of dark spots. This substantial improvement in environmental stability of the device can be attributed to the role of the ultrathin nanoclay film which prevents the active polymer layer from directly contacting the indium contaminated and strongly acidic PEDOT:PSS bottom layer. In addition, it also works as a barrier film against the oxygen and moisture.

In situ measurement of gas diffusion properties of polymeric seals used in MEMS packages by optical gas leak testing

Abstract. A novel inverse approach is proposed for in situ measure-ment of gas diffusion properties of polymeric seals used in microelectro-mechanical systems MEMS packages. The cavity pressure evolution ofa polymer-sealed MEMS package subjected to a constant bombing pres-sure is documented as a function of time using classical interferometry,and the diffusion properties of the polymeric seal are subsequently de-termined from the measured pressure history. A comprehensive numeri-cal procedure for the inverse analysis is established considering threediffusion regimes that characterize the leak behavior through a polymericseal. The method is implemented to determine the helium diffusivity andsolubility of a polymeric seal.

Effects of the Electroless Ni-P Thickness and Assembly Process on Solder Ball Joint Reliability

The ability of electronic packages and assemblies to resist solder joint failure is becoming a growing concern. This paper reports on a study of high speed shear energy of Sn-4.0wt%Ag-0.5wt%Cu (SAC405) solder with different electroless Ni-P thickness, with HNO3 vapors status, and with various pre-conditions. A high speed shear testing of solder joints was conducted to find a relationship between the thickness of Ni-P deposit and the brittle fracture in electroless Ni-P deposit/SAC405 solder interconnection. A focused ion beam (FIB) was used to polish the cross sections to reveal details of the microstructure of the fractured pad surface with and without HNO3 vapor treatment. A scanning electron microscopy (SEM) and an energy dispersive x-ray analysis (EDS) confirmed that there were three intermetallic compound (IMC) layers at the SAC405 solder joint interface: (Ni,Cu)3Sn4 layer, (Ni,Cu)2SnP layer, and (Ni,Sn)3P layer. The high speed shear energy of SAC405 solder joint with 3µm Ni-P deposit was found to be lower in pre-condition level#2, compared to that of 6µm Ni-P deposit. Results of focused ion beam and energy dispersive x-ray analysis of the fractured pad surfaces support the suggestion that the brittle fracture of 3µm Ni-P deposit is the result of Ni corrosion in the pre-condition level#2 and the HNO3 vapor treatment.

Comprehensive Quantification of Sorption Characteristics in Polymer Material of Thin Film Form

In this paper, the standard procedures for measuring moisture sorption properties of thin film form of polymer materials such as polyethylene terephthalate (PET) using thermo-gravimetry method and permeation method to characterize the moisture diffusion in polymer is presented. Analytical solution of moisture diffusion and FEA implementation using thermal-moisture analogy for comparison with measurements are presented, in which temperature dependent material properties are characterized. The measurement of permeability is used for validation of moisture diffusion characteristics. Nonlinear behavior of moisture diffusion dependent on concentration is investigated using a specimen having diffusion on half side and diffusivity constants are obtained by solving non-Fickian model and minimizing errors of least square with measurement. Application of characterizing moisture sorption properties to moisture effect on the interfacial layer in multi-layered printed circuit board (PCB) and estimation of relative humidity (RH) through permeation of moisture in hermetic sealing of crystal resonator are presented in this paper: i) The discrepancy of moisture concentration at the interlayer in multi-layered PCB was estimated as loading condition varies. ii) Moisture content through sealant based on temperature dependent permeability was estimated using mixture of ideal gases and vapor pressure.Copyright

Fine Leak Batch Testing of Multiple MEMS Packages

An analysis method for fine leak batch testing is developed for effective hermeticity inspection of metal-sealed MEMS packages in a mass production environment. It employs a forward-stepwise regression analysis based on a physical gas flow model to infer the information of leaky packages from batch test data. The proposed method can determine accurately the number of leaky packages and the true leak rate of each leaky package when the number of leaky packages in a batch is less than 5. A top-down hierarchical batch test is proposed as a reliable and effective test scheme by addressing this limitation of the developed analysis scheme.

Characterization of the surface morphology of electroless NiP deposited on conductive Cu film

Purpose – This study aims to elucidate the reaction mechanism of electroless NiP deposits on conductive but non-catalytic Cu films on the basis of their nucleation and growth without Pd catalyst and to measure the deposition rate and activation energy of electroless NiP deposits on the non-catalytic Cu film at various deposition times (60, 120, 240 and 480 s) and temperatures (70, 80 and 90°C) at pH 4.6. Design/methodology/approach – Specimens with and without Pd catalyst on Cu film were prepared as follows: the Pd catalyst was deposited on half of the Cu film using a deposition protector, and the specimen containing the Pd catalyst deposited on half of its area was immersed in electroless NiP solution. The growth of NiP on the Cu films with and without the Pd catalyst was observed. Findings – The number of Pd nanoparticles increased with Pd activation time; the nucleation of Pd dominated over growth at 60 s. Lattice images show that the d-spacing of Ni nanoparticles doped with less than 10 at% P increase...

Forward-stepwise regression analysis for fine leak batch testing of wafer-level hermetic MEMS packages

An advanced regression scheme is proposed to analyze fine leak batch testing data of multiple MEMS packages. The scheme employs the forward-stepwise regression method to infer the information of leaky packages from a batch test data. The analysis predicts the number of leaky packages and the true leak rate of each leaky package in a progressive manner. The scheme is implemented successfully using an actual batch test data obtained from wafer-level hermetic MEMS packages. An error analysis is followed to define the applicable domain of the scheme. Advanced formulations are also suggested to extend the applicable domain.