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Page 50


www.us- tech.com Cleaning Chemicals: Qualification Versus Production By Haley Reid, Senior R&D Chemist, and Chelsea Jewell, Application Lab Manager, KYZEN


to ensure the best product is chosen for the process. The goal of any qual- ification is to determine the cleaning chemical’s ability to remove flux ma- terials, prove compatibility with all assembly materials present and be operator friendly. Generally, when evaluating


D


aqueous cleaning materials, it be- comes a balancing act of physical properties, such as cleaning charac- teristics, metal compatibility, and pH. Typically, there are three combi- nations of these physical properties that are often considered. First, a traditional alkaline cleaner with lim- ited metal compatibility, but excel- lent cleaning properties. Second, a balanced alkaline cleaner with out- standing metal compatibility and cleaning properties, but a pH be- tween 8 to 11. Third, a neutral clean- er with good metal compatibility and cleaning with a pH between 6 to 8.


Evaluating Cleaning Processes When all factors are considered


for an electronic assembly cleaning qualification process, a balanced alka- line cleaner and a neutral cleaner are the most commonly evaluated prod- ucts. The two cleaning chemicals have similar attributes that make them ap- pear to be successful candidates for the process, with the neutral based


etermining a cleaning process for an electronic assembly often involves a qualification


cleaner often perceived to be superior due to its neutral pH range. Both a balanced alkaline clean-


er and a pH neutral cleaner claim to remove flux residues and protect any sensitive component washed in the solution. During the initial trial, both chemicals are found to achieve the cleanliness goal, but otherwise not


time used during the trial. After qualification, the process


is ramped up to a production level and the real-world application be- gins. In a perfect scenario, the quali- fication results would match the real-world results with cleaning and compatibility staying consistent after hundreds of boards and hundreds of


Experimental Procedure In order to determine if there is a


method that can predict long-term outcomes of a cleaning chemical with- out putting it into production, a series of different tests were conducted. The tests compared a balanced alkaline cleaner to a neutral cleaner. The be- ginning pH of each solution was 9.59 for the balanced alkaline cleaner and 7.45 for the neutral cleaner. As a control, 16.9 fl oz (500 ml)


SEM image taken after cleaning in 3 percent flux-loaded


balanced alkaline cleaner (left). SEM image taken after cleaning in 3 percent neutral cleaner bath (right).


affect the assembly. Because qualifi- cations can consume a large amount of resources, testing is often abbrevi- ated to short runs with smaller batches. Based on the results of this trial


in which a limited number of assem- blies and a minimal amount of flux is introduced to the process, a chemical is selected. The chemical is then qualified for the process with the op- timized parameters such as, concen- tration, temperature and exposure


hours of run time. In reality, the cleaning process


proves to be very dynamic. Changes seen while running a production line are very seldom comparable to a qual- ification process. A few differences that are seen in production lines in- clude chemical drag out, evaporative losses and flux loading. Over time the unaccounted-for differences from qualification to real-world production can turn into problems large enough for production line shut down.


of each solution was heated to 149°F (65°C) in a stirred beaker. Control parts with aluminum pads were sub- merged in solution for one hour, as well as an aluminum coupon for a rinse test. After one hour, the parts were removed from the solution, rinsed with room temperature deion- ized water for two minutes, and then dried with compressed air. In order to prevent non-measured soil addi- tions, samples chosen for this evalu- ation had been previously cleaned. A no-clean flux commonly found


in the industry was added to each so- lution. Solutions were flux loaded to 3 percent, which is a normal level for an aged bath that has been running full production. The flux was reflowed in aluminum pans to ensure that it mim- icked a fully activated flux removed from production boards. After the two solutions were flux loaded both were heated to


Continued on next page


September, 2019


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