Lead And Lead-free Mixed Assembly Welding Technique Research

With the rapid development of electronics technology, lead-free component has been widely used .In spacecraft product, the problem of lead and lead-free mixed assembly appears inevitably. Because of the lead-free technology is not mature from theory to application , there is not conclusive and unified standard for the welding theory or soldering on the mechanism of different metallurgical forming or the reliability of the solders. How to cope with the development of new technology for electronic products has become imminent issue.This paper is based on the current electronic products'characteristics of the basic techniques In space model .In this paper the theory of how to finish the lead and lead-free mixed assembly for one time is describes, And analyses how to print the soldering paste, set the parameters of reflow soldering in order to find the method fitting the spacecraft products.By reference to international standards IPC, The relevant test is processed for the test samples assembled by the current techniques method through using solder accelerated life test methods. Through calculating and analysis the data, there have the indicators for welds life. A complete test can fully demonstrates that the current re-soldering technology has the ability of solving the reliability problems of lead and lead-free mixed assembly. The solder fatigue life can be met the reliability of the indicators of weapons systems for long-term storage.According to a series classify of test, there are all kinds of lead and lead-free mixed assembly techniques for electronic product, and have the concrete test data and preliminary target. The key problem of soldering is solved for the electronic products. This paper provides experiences and process parameters that proving the soldering techniques can meet the reliability of the requirements for lead-free component and lead solder mixed assembly.Through the study of lead and lead-free mixed assembly techniques on space models, the paper summarizes the reasonable and practicable process parameters:1) if using the lead free components of BGA, the soldering temperature of reflow soldering is 230℃~235℃,if the lead free components of BGA is not used, the soldering temperature of reflow soldering is 220℃.2) under the condition of the present products, the fatigue life for the solders assembled by this kind of methods is more than 1630h.This method brings many profits, such as improving the product quality , performance and reliability, and reducing production cost, solving the process of bottlenecks. The work and related method for the other types of components assembly and the welds have reference to the reliability of the test.