Tin cleans up in electronics

 作者:浦劂肚     |      日期:2019-03-08 06:01:01
By Jeff Hecht FOR several years, the electronics industry has been seeking a nontoxic replacement for traditional solder, which contains 63 per cent tin and 37 per cent lead. Now a new electroplating process, developed by Electroplating Chemicals and Services, a subsidiary of Lucent Technologies in Staten Island, New York, looks set to solve the problem. The technique allows pure tin to replace lead-alloy solder when coating chip contacts on electronic circuit boards or applying a protective layer of solder to their conductive copper tracks. Lucent says that the development marks a major step toward eliminating toxic lead from electronics factories. Last year, Japanese electronics firms promised to make their consumer electronics products free from lead by 2000, and proposed European legislation could insist on lead-free solders in cars by 2002. However, lead-free solders have yet to match the stability and the circa 183 °C melting point of popular lead-alloy solders. Pure tin contact platings usually suffer from the growth of fine “whiskers” as the 0.1 micrometre grains of the metal film recrystallise—and the conductive filaments short out circuit boards. So Yun Zhang of Lucent’s Bell Labs in Murray Hill, New Jersey, has developed the new electroplating process using a set of water-soluble organic chemicals that grows larger tin crystal grains—5 micrometres—that do not form the whiskers. While the new process could replace 30 per cent of lead-based solders, it cannot replace the lead-based solders used in other stages of electronics manufacture, says David Bergman, vice-president of technical programmes at IPC, an electronics packaging consortium in Northbrook, Illinois. The pure tin cannot be used for the “assembly” solders that account for 70 per cent of electronics solder because they are applied in molten form, rather than electroplated,