Authored By:
Dr. Mike Bixenman
Kyzen Corporation, Nashville, TN USA
Julie Fields
Technical Devices Company, Torrance, CA USA
Eric Camden
Foresite, Kokomo, IN USA
Summary
The functional reliability of electronic circuits determines the overall reliability of the product in which the final products are used. Market forces including more functionality in smaller components, no-clean lead-free solder technologies, competitive forces and automated assembly create process challenges. Cleanliness under the bottom terminations must be maintained in harsh environments. Residues under components can attract moisture and lead to leakage currents and the potential for electrochemical migration.
Removing flux residues from under bottom terminations is extremely challenging. As components decrease in size, the Z-axis gap height also reduces. When the Z-axis gap is less than 3 mils (75um), the capillary and wetting action of flux during reflow underfills the bottom termination component with flux residue. To clean, the cleaning fluid and mechanical action must reach, wet and dissolve the soil in order to create a flow channel. Once a flow channel is created, the soils under the terminations are effectively cleaned.
The purpose of this research study is to evaluate innovative spray and soak methods for removing low residue flux residues and thoroughly rinsing under Bottom Termination and Leadless Components. Targeted spray nozzles deliver the cleaning agent to the soil. Following this interaction with an agitated soak allows the flux residues to dissolve. Targeted spray nozzles rapidly move the dissolved residues and fully clean residues under terminations. This designed experiment will study process parameters in order to draw inferences from the data findings.
Conclusions
The new equipment technology is a novel technology for cleaning under the body of Bottom Termination Components. The data finds that the new equipment technology is effective at cleaning both flux residues and ionic contamination under the body of the component. Placing a light layer of cleaning and rinsing fluids over the surface of the printed circuit board creates desirable properties. One of those properties comes from the soaking action of the cleaning agent onto the residue. The soaking action softens the flux residue and when bombarded with spray impingement rapidly displaces the flux residue. Cleaning agent pooled onto the surface of the board lowers surface tension, which helps penetration under tightly gapped components.
Another key benefit of the new equipment technology is reduced need for coherent spray jets. Coherent spray jets deliver the cleaning agent at higher pressures onto the printed circuit board. The pressurized spray jets provide strong deflective forces for penetrating and moving the cleaning agent under the component. A tradeoff of coherent jets is the ability to undercut labels, remove part marking and potentially affect other material compatibility effects. With the new technology, fan sprays are used, which provides less impact to the board. As a result, material compatibility effects may be less.
Rinsing is another area of concern when cleaning under the body of Bottom Termination Components. The new equipment technology can improve rinsing. The cleaning agent is attracted to water. With a layer of water covering the surface of the board within the rinse section, removal of the cleaning agent under Bottom Termination Components can be improved. Since rinse sections are relatively short on inline cleaning machines, the addition of the flooded technology can be highly beneficial to assuring that residual cleaning agent is rinsed from under the component.
Initially Published in the IPC Proceedings
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