Defluxing with ultrasonics

With the increased use of no-clean flux technology and reduced requirements for cleaning/defluxing PWAs, some manufacturing sites have found that replacing in-line cleaning with batch cleaning systems is advantageous and economical. Defluxing is accomplished through the sustained action of chemical, thermal and mechanical energy. With many batch cleaners, the spray systems and racking configurations preclude application of sufficient levels of mechanical energy to clean and rinse small spaces. As many as five years ago, more than half of the PWA batch cleaners covered in a Circuits Assembly survey had some ultrasonic capability, and 10 percent of the units listed used only ultrasonics for mechanical energy.1

Packaging technology is continuing to be driven to more densely populated assemblies and device packages with smaller clearances. With some devices, underfill materials are needed for CTE (coefficient of thermal expansion) accommodation. While some underfill materials are compatible with flux residues, or even compounded with fluxes, the application and bonding of many current...