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Why Switch From Pure DI-Water to Chemistry



Why Switch From Pure DI-Water to Chemistry
The purpose of this paper is to report a timely direct comparison between a pure DI-water process and a chemically assisted application.
Production Floor

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Authored By:


Harald Wack, Ph.D., Umut Tosun
ZESTRON America

Joachim Becht Ph.D., Helmut Schweigart, Ph.D.
ZESTRON Europe

Summary


It is noteworthy that while most cleaning processes in the North American and Asian markets rely on cleaning with DI-water only (for OA flux removal), recent market studies suggest that water is beginning to reach its cleaning limitation, favoring the use of chemistry assisted processes. Innovative cleaning solutions are already available to address this process limitation and, in some cases, are even more cost effective. The purpose of this DOE study is to report a timely direct comparison between a pure DI-water process and a chemically assisted application.

Conclusions


After entering the obtained data in the Minitab Software, the interaction among the factors in respect to the cleaning results was investigated. Figures 3 and 4 show the overall results. This lead to the following set of conclusions.

One of the initial observations is an improvement in cleaning with an increase in the wash temperature. Secondly, at lower wash temperatures, the tested cleaning agents 1 & 2 demonstrated superiority over the pure DI-water cleaning process when cleaning water-soluble flux residues.

When the role of the concentration levels of the two cleaning agents was examined, it was found that the cleaning results were not that different from each other at 3% concentration versus 5% concentration level. Out of 12 pastes five (5) were more responsive to an increase in wash temperature in terms of clean-ability, and not the cleaning agent concentration levels of 3% and 5%. Here the authors conclude that the removability for the remaining 7 pastes has a correlation with the exposure time of the flux residues to the tested cleaning agents, in other words longer wash exposure times would assist in removing the flux residues to achieve 100% cleanliness level. As expected, cleaning underneath low standoff components was more challenging (at least 25% or more) than cleaning around and top of the components.

As a conclusion of this study the use of cleaning agent 1 at a 3% concentration level, at 150 F wash temperature and 2.0 fpm belt speed would provide up to 111% better cleaning results (reaching 100% full cleanliness) underneath the low standoff components when compared to pure DI-water inline cleaning process!

The usage of chemistry in the long run seems to offer a number of previously unknown benefits. Despite the additional process cost of a cleaning agent, the "value added" benefits are sizable or should exceed the former.

They include but are not limited to better cleaning (i.e. lower ionic contamination), which in turn provides much higher product reliability. Recent studies have also demonstrated better bonding and coating after the introduction of chemistry assisted cleaning. To offset the added cost, users can operate at lower temperatures and with a wider process windows one clean not only OA but also RMA and no-clean fluxes. And that will become a requirement in the North American market as contract manufacturers are moving to lower volume, higher mix and a significantly more high reliability products.

At the end, the introduction of a chemistry assisted cleaning process, will increase your cleaning process window and permit the de-fluxing of all production boards in a single cleaning process.

Despite all the valid arguments encouraging the use of aqueous processes, the authors would like to caution interested users as well. Most equipments currently using strict DI-water are not properly equipped to use a closed looped chemistry. This means that they do not have a chemical isolation section included. The latter is an essential part not only to conserve chemistry but also to minimize foaming for example.

DI-water machines take advantage of cascading DI-water tanks from back to front. Employing a chemical product in the wash tank would lead to continuous dilution of the recommended application concentration by DI-water. Company's that are strategically planning their capital purchases are therefore well advised to incorporate the mechanical option to run aqueous chemistries. A slightly higher investment will provide significantly more process flexibility in years to come, and might lead to additional contracts.

Initially Published in the SMTA Proceedings

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