Determining the Bath Life of a Cleaning Chemistry
By Tim Noble
With the development of newer chemistries, in order to meet the needs of the complexity of solder fluxes and soils that we find on our assemblies in today's industries, we are coming across some chemistries that are promoting long term bath lifes, almost implying that bath lifes are infinite.
I personally do not find any chemistry to be infinite considering that as we clean, soils are loading in our wash solution and similiar to washing dishes, the longer you wash with the same water, the more loaded with soils (dirty) the wash solution becomes. At some point you need to believe that if the soils outnumber the cleaning composition of the chemistry the effectiveness of the cleaning chemistry will be compromised.
So that brings us to how do we determine bath life of a chemistry? I refer to an article by Tim Wright, which can be found on our website (http://www.jdnoble.com/) which discusses the proper method for Non-Volatile Residue (NVR) testing. In a nutshell, this covers collecting samples from your wash solution tank at various intervals (0, 25, 50, 75, 100, etc.) and evaporating all the fluids, which will leave any solids in the collection cup. This will show you how much soil is collecting in your wash solution tank.
Tim Wright Article:
Taking this a further step, if you perform Ionic Contamination testing (i.e. Aqueous Technologies Zero-Ion Tester) on your circuit assemblies at the same intervals, you should be able to determine at how many wash cycles of a bath, that you witness degradation of your wash performance. This will help you to identifiy how frequently you will need to change out the chemistry solution in your wash solution tank.