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12 SMT007 MAGAZINE I MAY 2018 capable of delivering high throughput without introducing production defects and/or insidious thermal damage to the internal struc- ture of a PCB and components. To this end, the alloy shall possess "agile" wetting ability and a compatible melting (liqui - dus) temperature. In this regard, wetting ability controls not only inter- facial metallurgical interaction but also the rate of interaction that needs to be in sync with the inherent char - acteristics of the reflow process. With these baselines in mind, a viable alloy should possess an adequate thermal fatigue resistance to withstand the increasingly adverse and harsh conditions in micro- electronics and electronic applications while providing a moderate melting temper - ature (170°C–215°C, more desirably 175°C–213°C) suitable for sound manufac- turability without causing undue thermal damages. This was the genesis of designing quaternary alloys, as stated in many of my professional development courses, workshops, webinars and publications since the late 1980s, including the U.S. Patent 6,176,947 (1999). SMT Prospects & Perspectives by Dr. Jennie S. Hwang, CEO, H-TECHNOLOGIES GROUP To link science and technology with commer- cial applications, Part 4 of this series continues to address two pivotal questions: Why SAC is not able to be a univer- sal interconnecting material for electronic circuits, and why a quaternary alloy system offers a more wholesome approach (note: a quaternary system referred herein does not include SAC incorporated with one or more doping elements). The baseline for designing a viable solder joint material for applica - tions in advanced electronic circuit boards that require increasingly higher function- alities and higher power in a small form factor is to deliver reliable physical properties and mechanical perfor- mance that are not lower than 63Sn37Pb alloy. Another baseline characteristic is to provide an alloy that can adapt to the established electronics manu - facturing infrastructure including production flow, process parameters and compatibility with the thermal stability of a PCB and a variety of components. One of the critical process parame - ters is the required minimum peak temperature in the reflow process that enables mass production The Role of Bismuth (Bi) in Electronics, Part 4

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