Surface mount technology-a study of safety considerations: silver migration and adhesive flammability

This original work was sponsored by the Electronics Industries Association (EIA). The purpose of this work was to determine if products employing surface mount technology (SMT) would be required by UL to undergo additional end-product silver migration and flammability testing of printed wiring boards (PWB) having surface mount devices (SMD). This work was conducted to 1) assess the effect of a nickel plating over a SMD silver electrode on inhibiting silver migration, and, 2) assess the effect that surface mount adhesives have on the flammability characteristics of PWBs. This work represents original application of silver migration and flammability testing for evaluating SMD silver electrodes and surface mount adhesives. Silver migration tests were conducted on SMDs having silver electrodes with and without a nickel plating. Tests were conducted at five different voltages and spacings using two different types of laminated PWB materials. The results showed that a nickel plating over a SMD silver electrode has an inhibitory affect on the migration of silver. The vertical burning test for classifying materials was conducted in accordance with the Standard For Safety, Tests For Flammability of Plastic Materials, UL 94, Third Edition, on surface mount adhesives to acquire data on the effect that adhesives have on the flammability classification of a PWB. The vertical burning test was conducted on 16 different adhesives separately applied to a CEM-1 industrial laminate material. The results of this work showed that the flammability classification of PWBs are not adversely affected by surface mount adhesives. As a result of this original work, UL does not require additional end-product based testing of PWBs employing SMDs, such as those used in the radio and TV industries. This outcome results in a long-term cost-effective benefit to industry.<
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