Qualification of no-clean solver pasted for telecommunication applications

The paper reports the results obtained by a test program started in the last quarter of 1990. As first step, chemical and physical evaluation of eight different kinds of commercial no-clean solder pastes was performed. This step included solder ball, tackiness, spread and slump, wetting and printability tests. Three products were selected and submitted to tests in order to qualify their application in the telecommunication field; they were compared to the standard freon and water cleaning solder pastes, at present used in our manufacturing plants. Temperature-humidity-bias tests were performed on ad hoc designed printed circuit boards. They were reflowed in a production infra-red oven and then loaded into an environmental chamber in order to control the behaviour of surface insulation resistance between interdigitated tracks. One type of solder paste was also reflowed in an inert atmosphere infra-red oven at different oxygen contents: its influence on the surface insulation resistance was evaluated. It was found that acceptable reliability is obtained with standard air atmosphere oven. Finally, two no clean solder pastes were introduced in one manufacturing line: the results of the first run are given and compared with the water cleaning process yields.