Materials for Advanced Packaging by Daniel Lu & C.P. Wong

Materials for Advanced Packaging by Daniel Lu & C.P. Wong

Author:Daniel Lu & C.P. Wong
Language: eng
Format: epub
Publisher: Springer US, Boston, MA


2.4 Conductive Fillers

2.4.1 Solid Metal Particles

Conductive fillers are used to provide the adhesive with electrical conductivity. The simplest fillers are metal particles such as gold, silver, nickel, indium, copper, chromium and lead-free solders (SnBi) [6, 7, 9–11]. The particles are usually spherical and range 3–15 μm in size for ACA applications [12]. Needles or whiskers are also quoted in some patents [6].

2.4.2 Non-metal Particles with Metal Coating

Some ACA systems employ non-conductive particles with a thin metal coat. The core material is either plastic or glass with a metal coating consisting of gold, silver, nickel, aluminum or chromium. The basic particle shape of these systems is also spherical. Plastic-cored particles deform when compressed between opposing contact surfaces, thus provide a large contact area. Polystyrene (PS) is often selected as the core material because the coefficient of thermal expansion of metal-coated PS beads is very close thermoset adhesives. The combination of epoxy resin and metal-plated PS beads results in a large improvement in thermal stability [7]. In addition, glass can also be selected as the core material. Glass-cored particles coated with metal lead to a controlled bond-line thickness because the glass core is not deformable. Since the conductive particle size is known, the conductivity of the joint can be predicted.



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