Cleaning High-power Electronics A closed-loop SOlvent-Based Approach

BY STEVE STACH, Austin America; HARALD WACK, Ph.D., NAVEEN RAVINDRAN, Zestron America; and JOACHIM BECHT, Ph.D, Zestron Europe

Flux residues must be be removed from flip chip components prior to subsequent processes to prevent malfunctions in high-power electronics. Solvent-based applications have reappeared on the scene, requiring a green process solution. One single-solvent based process may do the trick.

To prevent malfunctions in high-power electronics, flux residues must be removed from flip chip components prior to subsequent processes. As a result, integrating a suitable cleaning application into the manufacturing process of flip chip components is often required. Solvent-based applications have re-emerged, and with that an overall process solution is necessary. Previous solvent-based processes required ozone-depleting chemicals or flammable/combustible solvents requiring multiple rinsing steps and long drying cycles. However, recent advancements, including a novel single solvent-based process, set out to eliminate all aforementioned shortcomings.

One cleaning process was developed to replace vapor degreasing applications. Its principle relies on a single solvent system of sufficient polarity to give a bulk resistivity range of 1 to 100 MΩ-cm. This automated, self-monitoring closed-loop wash, rinse, and dry process uses spray-under immersion dynamics to enhance the performance of the cleaning agent. The cleaning process can also be assisted with ultrasonic energy if required. Unique to this process, the solvent, or solvent blend, is renewed by passing the flux-bearing solvent across special ion exchange resins selected for organic solvent compatibility. The regeneration operates on the same principle as DI water resins.

The process activates spray-under immersion cleaning jets and continuously monitors the resistivity of the solution. The cleaning cycle continues until the resistivity slope nears zero, indicating complete removal of the flux residues. The cleaning solvent automatically re-routes to the resin bed, which removes flux contaminants from the solution until bulk resistivity returns to high resistivity. The solution is then drained and the parts are dried automatically with clean, dry air or nitrogen. This water-free, self-monitored process provides fast residue-free drying for high-power cleaning applications. In addition, a small footprint, sealed tank meeting new VOC requirements, and low chemical and power consumption make it a very ”green“ process.

The solvent system designed for use with this series of test was specifically formulated to dissolve a large variety of residues, provide low surface tension, flash point above 100


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