Premature Cleaning Equipment Selection
Chemistry cleaning trials should be conducted prior to equipment selection.
With the recent pressure to implement more cost-effective (i.e., lower cost) processes, a number of companies have purchased concentration monitoring or other equipment prior to selecting the actual cleaning agent. In the majority of cases, this approach has led to cleaning processes that did not provide satisfactory or expected results. Once implemented, real production conditions reveal process problems the customer did not foresee during the evaluation period. As a result, the engineer realizes they made a premature decision, and tries to rectify it. What complicates the situation (in most cases) is the fact that the budget has been spent based on information available at the time.
But what should an engineer do once they discover that the process foams or monitoring equipment does not work with all fluxes? Further, what if the overall cost-effectiveness falls short of what was promised? In the short term, most will try to make the selected cleaning agent work as it has been qualified and supported. It’s difficult to go to a supervisor and ask for forgiveness once the equipment already has been purchased.
We frequently witness this or similar dilemmas, often enough in fact to alert unsuspecting customers and help them avoid such mistakes.
A related scenario of what we have taken to calling premature equipment purchase relates to cleaning with DI water, which is reaching its limits of cleaning ability. The majority of the North American SIA cleaning processes still use DI water for defluxing organic acid residues. This worked well in the past; however, recent studies suggest that water alone cannot completely remove water-soluble Pb-free flux residues. The equipment, however, was not purchased with a chemical isolation section at the time, which means it relied on cascading DI water from back to front. This means the equipment cannot be used with a chemical product, unless the user is prepared to face the (enormous) chemistry bill of dragged-out product.
Learning from both lessons, we conclude the following: Talking to a chemical service provider will help avoid either scenario. We also recommend testing under production conditions (i.e., for 30 days) prior to making final decisions. While testing new inline equipment under production conditions typically is not feasible, it might however be possible for peripheral capital equipment.
A checklist of key aspects to include during process selection is below. They include, but are not limited to:
Selecting the cleaning agent. Cleaning products vary greatly in performance and price. Some carry a low price tag, but might not be sufficient for the application.
Ensure a 100% match between the chemistry and contaminants. If that is not given, even the best mechanical assistance won’t help clean the residues.
Process parameters. During equipment selection, pay particular attention to the exposure time variable.
Equipment requirements. Cleaning equipment and peripheral tools do vary and need to be examined in detail to fit the requirements.
Process recommendations. Talk to peers who have implemented similar cleaning processes and have gathered similar data during their own process evaluations.
It is important to keep in mind that the balance between residues and their chemical counterpart is very complex. Traditional surfactants are known to be quickly exhausted and have a limited process window. Their main drawbacks become obvious when cleaning under production conditions. Products are available that can lift off contamination without a chemical reaction, and thus do not deplete easily. This provides a much larger cleaning process window and fewer process hiccups.
Over the years, many suppliers have invited customers to their facilities to provide an “entire” process solution. The offered support ranges from equipment selection, analytical help, and other process support services. Clearly this strategy is intended not only to help the customer save on travel by minimizing vendor visits, but also allows vendors to minimize the customer’s exposure to competitive products.
Customers today are diligent in determining the most cost-effective solution, but at the same time are restricted by reduced travel budgets. That said, some vendors offer complete cleaning process qualification, including automated concentration monitoring and vapor recovery solutions, allowing engineers to study their applications in depth.
Harald Wack, Ph.D., is president of Zestron (zestron.com); h.wack@zestronusa.com.
