Nano-particle enhanced encapsulants for improved humidity resistance

Abstract

Polymer materials - mainly epoxy resins - are widely used in microelectronics packaging. They are established in printed circuit board manufacturing, for adhesives as die attach glues or for encapsulants as molding compounds, glob tops or underfill materials. Low cost and mass production capabilities are the main advantages of these materials. But like all polymers they can not provide a hermetical sealing due to their permeability properties. The susceptibility to water diffusion through the polymer and along the interfaces is a drawback for polymer materials in general. Water inside a microelectronic package might lead to softening of the material and to a decreasing adhesive strength and resulting delaminations close to solder bumps or wire bonds reducing package reliability by decreasing the package structural integrity. During package reflow, the incorporated humidity might lead to popcorning, i.e. abrupt evaporation of humidity during reflow soldering, is one major problem during plastic package assembly. The introduction of high temperature lead- free soldering processes has even increased this issue. Therefore, plastic packaging materials with enhanced humidity resistance would increase package reliability during assembly and lifetime without cost increase and with no changes in processing. The incorporation of nano-particles into plastic packaging materials is discussed as one potential solution for improved humidity resistance as it is a rather low effort approach to material modification opposed to chemical modification of the matrix. To evaluate the potential of such additives concerning moisture resistance the effect of nano-particles mixed with a microelectronic grade epoxy resin is studied. From the large variety of fillers available this work mainly focuses on three different types: nano-sized silica, modified bentonite and zeolites. Working principles of these particles range from large surface impact of nano-particles, barrier functionality due to - stacked layer formation and molecular catcher function. Formulations with different particle concentrations and surface modifications are characterized regarding their influence on humidity diffusion, absorption and desorption behavior as well as their influence on other material properties as reaction kinetics, viscosity and thermo- mechanical properties. Additionally the combination of nano- and standard micro-particles needed for thermo-mechanical adjustment of the polymer properties is studied. Experimental work is accompanied by simulations, in order to provide further qualitative understanding on effects of particle form, size and surface properties. In summary this paper describes the potential of different nano-particles as additives for plastic packaging materials for enhanced humidity resistance/barrier enhancement within microelectronic packages. This topic is gaining increased importance when considering the trend towards system in package, where a multitude of components is encapsulated to form one SiP that incorporates a large number of...

Improving the water resistance of epoxy-anhydride matrices by the incorporation of bentonite

“…With this propose, a promising alternative is based in adding fillers to traditional polymer matrices to develop composite materials with enhanced mechanical, thermal, and barrier properties. Clay mineral results are very attractive because of its high aspect ratio, high intercalation chemistry that allows increasing clay‐polymer compatibility and low cost …”

Trends and Challenges

“…Many studies have investigated nano-fi lled encapsulants [35][36][37][38][39][40][41]. Nano-particles can be added as fi llers to improve the properties of the encapsulant material.…”

“…8.20(a) [41]. The substance montmorillonite (named after the location of occurrence at Montmorillon, France) is a hydrated sodium calcium aluminum magnesium silicate hydroxide with the chemical formula (Na,Ca) 0.33 (Al,Mg) 2 (Si 4 O 10 )(OH) 2 ⋅ nH2O.…”

“…Various methods and devices are available for deagglomeration including ultrasound, rotor stator mixer, piston homogenizers, and gear pumps, among which ultrasound have been found to be more effective [41]. Effective dispersing and deagglomeration are often required when the nano-particle powder is wetted.…”

“…20 Nano-fi llers explored for improving encapsulant properties: (a) bentonites, (b) silica particles, and (c) zeolites[41].…”