Publication date: 08 December 2011
Today we hear a lot about cleanliness and the need for circuit card assemblies (CCA) to meet a cleanliness specification or standard. Unfortunately, there is no industry specification or guideline that outlines what microgram per square inch of Anions (Chloride, Fluoride, Nitrite, Sulfate, Bromide, Nitrate and Phosphate), Weak Organic Acids (Acetate, Formate, MSA, Adipic and Succinic) and Cations (Lithium, Sodium, Ammonium and Potassium) are needed. Does it matter if the CCA was manufactured using a No-Clean Flux? What about a CCA that was manufactured using either an RMA Flux or a Water-Soluble Flux that has been cleaned or washed?
For years, the Omegameter was used to determine or test for cleanliness using IPC -6012C-2010 Specification 3.9.1. The acceptable threshold was 1.56 micrograms per centimeter squared of sodium chloride equivalent, or 10 micrograms per square inch. This test only works for rosin-based fluxes that are soluble. As no-clean and water-soluble fluxes were introduced to the manufacturing market, companies had to define the cleanliness in their procurement documents or assembly specifications and address each flux type as well as anion, weak organic acid and cation individually. This opened the door for individual interpretation of what is important and what that level should be defined as. STI’s Analytical Lab has taken input from the large OEMs and has taken test data to create a recommended acceptance level for washed and no-clean flux chemistries that is achievable and can be monitored through IC testing.
STI’s recommended cleanliness levels are data supported and achievable with mainstream flux chemistries. The landscape of fluxes is ever changing and new chemistries are being introduced each year that requires one to stay diligent in their process materials and manufacturing processes to ensure cleanliness that meets their customers’ expectations. One must have the ability to match a cleaning chemistry to a flux type to ensure that one meets all the recommended guidelines or customer guidelines. It is better to know what your cleanliness level is and should be than to have returned product for corrosion from your customer. There have been rumblings and rumors that someday we will see industry guidelines but the truth and challenge lies in the fact that what is critical to some may not be as critical to others. Therefore, a consensus and collaboration effort for a cleanliness standard is still at some ambiguous point in our future. High reliability, deep space, aerospace and medical always will demand ultra clean hardware whereas industrial and consumer want it to work for its warranty period.
So do you know your cleanliness level and how to define it? Below are good reference points as well as a solid place to start. Just in the last four months four customers asked inquired about cleanliness levels. Some have been because of corrosion on hardware and others wanting to be able to answer customers’ internal questions. Be prepared and decide what is required for your situation. Again, the following are good guidelines and are conservative, safe recommendations that are achievable. Additionally, these are what STI uses in its manufacturing lab as a guide for cleanliness.
For more information or with any questions, contact Mark McMeen, VP of Engineering, at STI Electronics Inc., 261 Palmer Rd., Madison, AL 35758; 256-705-5515; E-mail: mmcmeen@stielectronicsinc.com; Web site: www.stielectronicsinc.com.
