Technical Library | 2013-02-07 17:01:46.0
Silicone contamination is known to have a negative impact on assembly processes such as soldering, adhesive bonding, coating, and wire bonding. In particular, silicone is known to cause de-wetting of materials from surfaces and can result in adhesive failures. There are many sources for silicone contamination with common sources being mold releases or lubricants on manufacturing tools, offgassing during cure of silicone paste adhesives, and residue from pressure sensitive tape. This effort addresses silicone contamination by quantifying adhesive effects under known silicone contaminations. The first step in this effort identified an FT-IR spectroscopic detection limit for surface silicone utilizing the area under the 1263 cm-1 (Si-CH3) absorbance peak as a function of concentration (µg/cm2). The next step was to pre-contaminate surfaces with known concentrations of silicone oil and assess the effects on surface wetting and adhesion. This information will be used to establish guidelines for silicone contamination in different manufacturing areas within Harris Corporation... First published in the 2012 IPC APEX EXPO technical conference proceedings.
Technical Library | 2020-10-14 14:33:36.0
Epoxy based adhesives are prevalent interface materials for all levels of electronic packaging. One reason for their widespread success is their ability to accept fillers. Fillers allow the adhesive formulator to tailor the electrical and thermal properties of a given epoxy. Silver flake allow the adhesive to be both electrically conductive and thermally conductive. For potting applications, heat sinking, and general encapsulation where high electrical isolation is required, aluminum oxide has been the filler of choice. Today, advanced Boron Nitride filled epoxies challenge alternative thermal interface materials like silicones, greases, tapes, or pads. The paper discusses key attributes for designing and formulating advanced thermally conductive epoxies. Comparisons to other common fillers used in packaging are made. The filler size, shape and distribution, as well as concentration in the resin, will determine the adhesive viscosity and rheology. Correlation's between Thermal Resistance calculations and adhesive viscosity are made. Examples are shown that determination of thermal conductivity values in "bulk" form, do not translate into actual package thermal resistance. Four commercially available thermally conductive adhesives were obtained for the study. Adhesives were screened by shear strength measurements, Thermal Cycling ( -55 °C to 125 °C ) Resistance, and damp heat ( 85 °C / 85 %RH ) resistance. The results indicate that low modulus Boron Nitride filled epoxies are superior in formulation and design. Careful selection of stress relief agents, filler morphology, and concentration levels are critical choices the skilled formulator must make. The advantages and limitations of each are discussed and demonstrated.
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