Reliability of SMD interconnections on flexible low-temperature substrates with inkjet-printed conductors

Abstract

This work dealt with potential reliability issues in inkjet-printed electronics. The aim was to increase our understanding of how failures occur in hybrid electronic structures that utilize inkjet printing. A future goal in this field will be to enable expansion of this product area from low-life-expectancy and -performance products to high-life-expectancy and -performance products.In this work the reliability of isotropically conductive adhesive interconnections between 0402- and 0805-sized ceramic resistors and three types of flexible substrates was investigated. The use of low-temperature ink material (curing temperature 150°C) allows new, inexpensive substrates to be introduced into the process. In addition, the interconnection reliability of a more complex low-temperature cofired ceramic module attached to a flexible substrate with ball grid array interconnections was investigated.Reliability testing was carried out in a thermal cycling test chamber in a 0–100°C temperature range. Daisy-chain resistances of the samples were monitored with a datalogger during the cycling. Besides optical inspections, the interconnections were analyzed with X-ray microscopy. Also scanning acoustic microscopy was used to observe crack propagation. Finally, scanning electron microscopy was used to detect failure mechanisms.The two main failure mechanisms of the chip resistor components were loss of adhesion at the ICA/component terminal cladding interface and cracking of matte tin cladding of the component. For the tested LTCCs it was noted that breakdowns of interconnections occurred because of fractures on the module side of the interconnection—in most cases in the solder/intermetallic compound interface—and not because of ICA fractures or ink delamination on the substrate side.