Post-reflow residue results following pH-neutral cleaner application: a study of 40 leaded and Pb-free solders compares alkaline to newer cleaning technologies.

Author:Wack, Harald
Position:SMT CLEANING
 
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PH-neutral product technologies that are fully compatible with anodized aluminum parts, sensitive metals and other challenging substrates are now available. Despite the absence of alkalinity, pH-neutral chemistries can still complete the job of defluxing agents. Their unique physical properties also come into play as users strive for minimal equipment wear-and-tear, which had not been the case in the past. Equipment replacements are costly and can add significantly to the overall process cost. Safety is also improved if operators can completely avoid working with caustic materials.

The performance of today's pH-neutral, aqueous cleaning agents hinges on previously unknown reaction pathways, which in turn permit the complete removal of any alkalinity in the product. While prior cleaning pathways relied heavily on solubilization and saponification, novel pathways include but are not limited to dipole mechanisms (FIGURE 1). The latter introduces the benefits of:

[FIGURE 1 OMITTED]

* High reactivity, especially for cleaning under low-standoff components.

* Highest level of material compatibility known to date.

* Low operating concentrations of 5 to 15%.

* Easy disposal; i.e., no permits or costs due to the neutralization of alkaline products.

* Operator safety.

* Reduced shipping costs due to noncorrosive nature.

For predominantly competitive reasons, experimental data on pH-neutral cleaners remained unpublished in 2009. Research presented in here focuses on internal qualification experiments leading up to the product's market introduction. Various customer studies completed in 2009 will be presented shortly.

Test Parameters

This study was initiated in 2005 to evaluate new product technologies developed in response to challenges presented by use of standard alkaline cleaning products for defluxing processes. One of the often-cited drawbacks of alkaline materials is their effect on sensitive metals, which include anodized and bare aluminum, copper, different metal alloys, plastics, materials of construction, inks and others. To mitigate but not eliminate any potential surface reaction, chemical companies generally add corrosion inhibitors to alkaline products. These additives, however, pose limitations, as they are chemically altered during regular production conditions, thereby introducing an unwanted variation in effectiveness.

Furthermore, alkalinity introduces a pH-level that requires water treatment in most municipalities. PH-levels above 7...

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