No abstract

Absorption and desorption tests were conducted on five distinct commercial epoxy mold compounds (EMCs) used in electronic packaging. For absorption, the samples were subjected to 85°C /85% relative humidity and 60°C /85% relative humidity soaking. Desorption conditions were above glass transition temperature at 140°C and 160°C. A dual stage model is developed in this paper for both absorption and desorption processes. Both stages in moisture absorption and desorption, i.e., Fickian diffusion and relaxation process, are described mathematically using a combination of Fickian terms. The models generated reasonable results for the diffusive properties and displayed outstanding experimental fits. All five compounds have shown strong non-Fickian diffusion behaviors, which were further demonstrated by experiments with different thicknesses. For absorption, results show Fickian diffusion is significantly faster than non-Fickian diffusion. Saturated moisture concentration associated with Fickian-stage diffusion is independent of temperature if it is below glass transition temperature. Sample thickness played a major role in diffusive behavior in the second stage where non-Fickian diffusion occurs. For desorption, higher temperature corresponds to less percentage of the permanent residual moisture content. At 160°C, 90% of the initial moisture for all samples could be diffused out within 24 hours, following a modified Fickian diffusion process. The dual stage model developed in this paper provides a foundation for modeling anomalous moisture diffusion behavior using commercial finite elemental method software.

No abstract

Polymer transfer films are thought to reduce friction and wear during sliding. In such cases, a continuous, uniform transfer film is thought to yield better wear performance. However, several polymers, including the thermoplastic polyetheretherketone (PEEK), do not always display this behavior. Recent works analyzing transfer film quality of PEEK resulted in no clear correlation to wear. Currently, the mechanisms for PEEK transfer film development are unknown, but there is evidence suggesting roughness orientation relative to sliding and frictional heating play key roles. In this work, the development of PEEK transfer film is explored in relation to multidirectional versus linear sliding, roughness orientation and temperature rise. Three distinct wear paths were chosen for wear tests. The transfer film of the square wear paths was analyzed using white light profilometry and imaging software to obtain the volume and area coverage by the film. The temperature rise during sliding of the bulk polymer pin was recorded with infrared camera radiometry for linear reciprocating tests. Scratch tests and chemical etching were conducted on the polymer pin surface to evaluate any directional bias or crystallinity orientation induced by sliding. It was found that wear debris and polymer chain orientation play no noticeable role in PEEK's transfer film formation. The transfer film gradient increased with frictional heating, and transfer film color changed under certain conditions. This color changed also correlated to reduced wear. This study also confirms that transfer film development is strongly dependent on roughness orientation, and its effects are examined.

No abstract

Modern power electronics has the increased demands in current density and high temperature reliability. However, these performance factors are limited due to the die attach materials used to affix power dies microchips to electric circuitry. Although several die attach materials and methods exist, nanosilver sintering technology has received much attention in attaching power dies due to its superior high temperature reliability. This paper investigated the sintering properties of nanosilver film in double side sintered power packages. X-ray diffraction (XRD) results revealed that the size of nanosilver particles increased after pressure-free sintering. Comparing with the pressure-free sintered nanosilver particles, the 5 MPa sintered particles showed a higher density. When increasing sinte ring pressure from 5 to 30 MPa, the shear strength of the sintered package increased from 8.71 MPa to 86.26 MPa. When sintering at pressures below 20 MPa, the fracture areas are mainly located between the sintered Ag layer and the surface metallization layer on the fast recovery diode (FRD) die. The fracture occurs through the FRD die and the metallization layer on bottom Mo substrate when sintering at 30 MPa. Index Terms-power electronics, nanosilver sintering, shear strength, fracture I. INTRODUCTION HE rapid development of wide-band gap semiconductors have facilitated power electronics becoming key components in hybrid electric vehicles, traction, wind turbine and high-voltage power transmission systems due to their

No abstract