Performance and Reliability Requirements of Soldering Fluxes

Karl Seelig and Timothy O'Neill
AIM
Cranston, RI, USA

Soldering flux chemistries have been in a constant state of evolution since the beginning of electronics assembly. For example, early fluxes were high solid rosin based materials that were cleaned in CFC solvents. The elimination of these solvents drove the development of water washable fluxes and ultimately no clean fluxes.

As miniaturization and proliferation of electronics accelerates, the assembly processes and material requirements are evolving rapidly. These changes are driving flux chemistry manufacturers to develop fluxes for the new processes, new materials and new equipment to meet the performance, design and reliability challenges for new and as yet unimagined electronics applications. Some examples of this are selective soldering fluxes, PoP fluxes and 'jettable' solder pastes.

Miniaturization and ruggedization are becoming more of a concern as electronics find their way into virtually every aspect of our lives. Fluxes need to be more process capable than ever, yet be even more reliable under harsher conditions. Additionally, the specifications may have to be amended to accommodate the competing attributes of residue reliability characteristics versus process capability.

This paper will outline the evolution of flux chemistry and detail the challenges in developing flux chemistries to address current and future application requirements.

In summary, the rapid evolution of the industry is driving innovation like never before. Three simple types of flux have ballooned into hundreds of fluxes for applications and processes that would have seemed inconceivable just twenty years ago. Flux developers are forced to create more aggressive materials, with a wider process window and better reliability; and to do it with fewer, less effective materials.