Abstract
Due to environmental concerns and regulatory initiatives, electronics manufacturers are replacing the tin/lead solder commonly used on printed wire boards (PWBs) with alternative solders. To determine the potential waste management impacts of the alternative solders versus the tin/lead solder, two leaching tests on PWBs manufactured with five alternative types of solder were performed: the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP). These tests are commonly used in the US regulatory community to assess pollutant leachability in different disposal scenarios. The article discusses the application and limitations of these tests. The five types of solders investigated were 63Sn/37Pb, 99.3Sn/0.7Cu, 95.5Sn/4Ag/0.5 Cu, 96Sn/2.5Ag/1Bi/0.5Cu, and 42Sn/1Ag/57Bi. The leaching tests were conducted on four PWB sections, each with a unique configuration and solder density. The largest lead concentrations were observed from the PWBs containing Sn/Pb solder, with concentrations exceeding the hazardous waste toxicity characteristic (TC) in TCLP leachates. Silver, the other regulated element used in the solders, was rarely detected, with none of the samples exceeding the TC limit for silver. High copper concentrations were observed and were determined to result from the PWB itself, not from the copper-containing solders.
Highlights
In these days of advanced integrated circuitry, it is easy to overlook the intricacies of an apparently simple component such as a capacitor
The crystalline oxide is a poorer dielectric and the breakdown voltage is reduced. This effect is virtually unknown in wet tantalum units operated within their rated capability since the sintering operation greatly reduces the level of surface impurity of the anode
The wear-out mechanism of wet tantalum units is the loss of water vapour leading to open-circuit, at rated temperatures, long life times are achieved
Summary
In these days of advanced integrated circuitry, it is easy to overlook the intricacies of an apparently simple component such as a capacitor. The wet tantalum device is used primarily in the military, avionic and professional equipment industry where its high reliability and long working life are essential. The anode is manufactured by pressing high purity tantalum powder and sintering into a porous slug. The tantalum pentoxide dielectric is formed over the total slug surface by anodic oxidation, normally at constant current and elevated temperature, in a suitable aqueous or partially aqueous electrolyte. In both instances a high capacitance is required at the electrolyte to case interface in order that the capacitance of the overall device is controlled essentially by the anode film. Silver is chosen as a case material because of its good chemical resistance to conventional working electrolytes and its suitability for drawing into a can and forming a good spun seal. Tantalum has the advantage of resisting electrochemical dissolution in the working electrolyte as is discussed in this paper
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