Glass transition temperature of nanoparticle-enhanced and environmentally stressed conductive adhesive materials for electronics assembly

Pavel Mach,David Bušek,Attila Geczy,Radek Polanský

doi:10.1007/s10854-019-00784-5

Abstract

In our paper, the characterization of glass transition temperature (Tg) was performed for one- and two-component electrically conductive adhesive used in electronic joining technologies. Both adhesives were of the epoxy type with the silver filler. Dynamic mechanical analysis (DMA) was used to measure the Tg. The adhesives were modified with nanoparticles, namely, carbon nanotubes (concentration of 0.5 and 0.8% by weight) and silver nanoballs (2.5% by weight). The values of Tg were determined from the plot of the Tg δ parameter. Two types of environmental stresses were used for climatic aging: 125 °C/56% RH and 85 °C/85% RH. The aging of the samples at 125 °C and 56% RH caused increase Tg for all formulations. The cause of these changes is additional curing of adhesive. Aging in the combined climate 85 °C/85% RH caused a shift in Tg toward lower values for formulations based on the one-component adhesive modified by CNT and toward higher values for all other formulations. The major cause of the decrease in Tg was that CNT inhered the curing reactions and banned them from completion. In cases where Tg grew, glue hardening take place. DMA was performed to examine Tg of the samples. The DMA measurements were carried out up to 200 °C. Repeated DMA measurement confirmed that this measurement caused additional hardening and increase Tg for all samples. The results will contribute to the use of conductive adhesives with better quality and reliability in electronics manufacturing.

Highlights

Conductive adhesives have significant advantages over conventional solders, in given cases
It was found that modification of a one-component adhesive with Carbon nanotubes (CNT) did not change the Tg, whereas the modification using nAg produced a small decrease in this temperature
The increase of Tg was very high for individual formulations based on the one-component adhesive, where it was between 40 and 80% and for two-component adhesive between 70 and 180%

Summary

Introduction

Conductive adhesives have significant advantages over conventional solders, in given cases. Adhesive joints are more flexible and creep resistant, and the curing temperature of ECAs is lower than the soldering temperatures. Adhesives with isotropic electrical conductivity (ICAs) are often used for surface mounting components sensitive to heat, die attachment and small passive chip attachment. Adhesives with anisotropic electrical conductivity (ACAs) are used for interconnections in LCD displays, flexible electronics [1], surface mount technology of chip-scale packages, flip-chip and ball grid array technology. Using ACAs foils (ACFs) for mounting fine-pitch and ultrafine-pitch packages is more advantageous than soldering because there is no danger of creating short formations between adjacent terminations [2]. The detailed classification of adhesives used in assembling electronic circuits is carried out in [3]

Methods

Results

Conclusion