Lead-Free Electronics Assembly for the Real World: Joint Failures, Lead Contamination and Other Important Considerations

摘要

A tremendous a nount of interest exists in lead-free soldering. Much of this is derived from a fear of Jegislation and marketing activities. This has spurred a great deal of committee and consortia activity, some of which has been valuable to the industry. One of the mest pressing questions in lead-free soldering pertair s to the lead-contamination of lead-free solders and its effects. As the above evidence demonstrates, lead-free alloys can suffer decreased reliability when contaminated with lead. To avoid problems related to this, the most prudent course of action is to reduc e the lead-free transition period to as short as possible. In other words, when a company implements a lead-free solder alloy, it should also implement lead free component terminations and circuit board costings. If these above guidelines are not followed, the reliability of the solder joint is risked. Several problems related to processing and reliability are associated with Sn/Cu alloys. In addition, difficulties arise when using two alloys to assemble a circuit board; dual inventories, policing the use of two alloys, inventory costs and the cost of potential liability if a product failure occurs are arguments in favor of utilizing a single lead-free alloy for all soldering operations. As pointed out earlier, silver is the cost element in the Sn/Ag/Cu alloys. Since there are no advantage s in terms of processing, reliability, or availability for the high-silver alloys as compared to the low-silver alloys, it is only logical to utilize the less expensive of these for use in all soldering applications. In fact, the low-silver alloys eliminate the potential for silver phase change problems with high-silver alloy - and offer improved wetting and a slightly lower melting temperature. Most importantly, the low-silver Sn/Ag/Cu alloys provides users with the advantages of the Sn/Ag/Cu family of alloys, are less cost-prohibitive and therefore may be utilized in all solder operations, and thus eliminate the problems associated with Sn/Cu alloys and a dual-alloy process.