Seok-Hwan Huh

A novel high-speed shear test for lead-free flip chip packages

Despite the importance of lead-free solders in modern environmentally friendly packaging, few studies have been conducted on their mechanical reliability at the wafer level. In the present study, high-speed die shear tests were conducted to investigate the effects of strain rate on the shearing resistance and fracture mode of Sn-3wt%Ag-0.5wt%Cu solder joints on electroless Ni-P/immersion Au surface finish pads. The results indicated that the solder joints underwent ductile and mixed ductile-brittle fracture at low (<855 s−1) and high (>25,385 s−1) strain rates, respectively. Thus, the overall shear stress-strain curve can be divided into three areas according to Hollomon’s law, starting from low strain rates: area I, 100% ductile fracture of the solder itself; area II, mixed ductile-brittle fracture resulting in a ductile-brittle transition region; and area III, 100% brittle fracture at the interface between the intermetallic compound and the Ni-P layer.

Corrosion behavior of electroless nickel/immersion gold plating by interfacial morphology

AbstractPad discoloration is caused by Ni corrosion during electroless nickel immersion gold (ENIG) treatment, and here it was investigated by SEM, XPS and cross-sectional EDS analysis. Interestingly, we found that the corrosion occurred at two different sites. For relatively thinner Ni layers, the Ni corrosion occurred at the nodule boundary, whereas thicker Ni deposits caused pit corrosions. The electroless Ni had an amorphous structure and had isotropic surface energy. In other words, the domain boundary energy between two Ni nodules did not change during Ni growth. However, the intersection angle of the two surfaces gradually increases during film growth, and the cusp stress between the two nodules also decreases gradually during Ni growth. Hence, the corrosion mode changed from nodule boundary corrosion to pit corrosion. Promoting Ni nucleation as well as increasing the Ni thickness is expected to suppress the pad discoloration by reducing the nodule boundary corrosion.

Evaluation of the peel strength in Cu/epoxy thin film using a novel interfacial cutting method

– The purpose of this paper is to evaluate the relationship between the Cu trace and epoxy resin and to check the validity of surface and interfacial cutting analysis system (SAICAS) by comparing its results to those of the 90° peel test. , – In this study, the effects of surface morphology on the adhesion strength were studied for a Cu/epoxy resin system using a SAICAS. In order to evaluate the peel strength of the sample, the curing degree and surface morphology of the epoxy resin were varied in the Cu/epoxy resin system. , – The results indicated that the peel strength is strongly affected by the curing degree and the surface morphology of the epoxy layer. As the pre-cure time increased, the interactions between the epoxy resin and permanganate during the adhesion promotion process decreased, which decreased the surface roughness (Ra) of the resin. Therefore, the surface roughness of the epoxy resin decreased with increasing pre-cure time. The curing degree was calculated with the FTIR absorption peak (910 cm−1) of the epoxy groups. The high curing degree for the epoxy resin results in a coral-like morphology that provides a better anchoring effect for the Cu trace and a higher interfacial strength. , – It is necessary to study the further adhesion strength, i.e. the friction energy, the plastic deformation energy, and the interfacial fracture energy, in micro- and nanoscale areas using SAICAS owing to insufficient data regarding the effects of size and electroplating materials. , – From findings, it is found that measuring the peel strength using SAICAS is particularly useful because it makes the assessment of the peel strength in the Cu/epoxy resin system of electronic packages possible.

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.

Chlorine effect on ion migration for PCBs under temperature-humidity bias test

By the trends of electronic package to be more integrative, the fine Cu trace pitch of organic PCB is required to be a robust design. In this study, the short circuit failure mechanism of PCB with a Cl element under the Temperature humidity bias test (/85%RH/3.5V) was examined by micro-structural study. A focused ion beam (FIB) and an electron probe micro analysis (EPMA) were used to polish the cross sections to reveal details of the microstructure of the failure mode. It is found that were formed and grown on Cu trace during the /3hrs and that was decomposed into Cu dendrite and gas during the /85%RH/3.5V. It is suggested that Cu dendrites formed on Cu trace lead to a short circuit failure between a pair of Cu traces.

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...

Effect of Microstructural Evolution on Electrical Properties of the Copper Electrodeposits for ULSI

Copper electrodeposits annealed at 80 °C were investigated by electrical resistance measurement, X-ray diffraction and electron backscattered diffraction analyses. The decrease of electrical resistivity had a linear relationship with the re-crystallized area. Interestingly, the texture coefficient of (200) orientation increased as the re-crystallization occurred. Such appearance of (200) texture during annealing seemed to be related to the residual strain in the copper electrodeposits. It is possible to evaluate the progress of grain growth by measuring the electrical resistivity or texture coefficient in copper electrodeposits. †(Received July 23, 2013)