Ask the Experts
October 19, 2018
Class 3 Cleaning Requirements
We recently received our first contract to assemble Class 3 circuit board assemblies. Are there any changes we need to make in our cleaning operations to switch from Class 2 to Class 3?
Expert Panel Responses
It is unclear as to whatspecification you are working under. There is no general specificationfor "Class 3" cleanliness. Apparently, there is aspecification accompanying your contract that will dictate exactly whatconforms to "Class 3" cleanliness in your particularapplication. Refer to that specification for the exactrequirements. Undoubtedly, it will require a verification step, soexpect either a particle count per MIL STD 1246 or similar spec, or some typeof solvent rinse of the surface with a GC / FTIR scan of the rinsing agentassociated with the part. Unless it requires 100% verification (ason many NASA and black DoD programs), once you have proven the process youshould be able to maintain QC by sampling.
Rick Perkins is a chemical engineer with more than 33 years of Materials & Processes experience. He has worked with Honeywell Aerospace in high-reliability manufacturing, as well as with several oil-field manufacturing companies. He also has a good understanding of environmental, health, and safety regulations.
IPCTM650 describes cleanliness testing methods and required results.Unfortunately, the cleanliness results outlined in both military and IPCstandards were written so long ago, they are, in practical terms, obsolete.
IPC allows up to 10 ug NaCl equivalent /in2. Thisnumber is far too high. Due to the nature of ROSE testers (the industry'sapproved cleanliness testing method), contamination is detected then averagedover the entire assembly's surface area. Because actual contamination is notequally distributed, actual contamination levels are concentrated in some areasof the assembly and less concentrated in others. Because of this, one must alsoconsider other factors in determining an allowable contamination level. Onemust consider the density and diversity of component population, standoffheight, flux application method, the device's intended environment, and fluxtype. Most importantly, one must consider the cost of failure. There may bediffering costs for failure between a class 2 device and a class 3 device. Themore critical the reliability, the lower the allowable contamination level.While industry standards allow 10 ug NaClequivalent /in2, I would initiate an internal requirement of 2 ug NaClequivalent /in2, particularly for class 3 devices.
Mr. Konrad has been in the electronic assembly equipment industry since 1985. He is founder and CEO of Aqueous Technologies Corporation, a manufacturer of automatic de-fluxing equipment, chemicals, and cleanliness testing systems.
The answer is "it depends."Whether or not you need to make any changes to cleaning operations dependsentirely on the requirements that your customer sets forth. If your customer isasking you to work to J-STD-001, for example, they would specify any cleaningrequirements according to Section 8 of that document. You'd want to review therequirements and the test methods and compare to your existing process. Thiswould tell you whether your existing process is capable of meeting the desiredlevel of cleanliness. In the event that your customer has failed tocommunicate cleanliness requirements, a discussion with the customer issuggested to avoid any potential for misunderstanding.
Also recognize thatthere may be a need for documentation of cleaning results for Class 3 products.You may need to be able to demonstrate that cleanliness was tested on theproduct, and have records of the results. Again, open communication with thecustomer is essential to ensure you are meeting their needs with regard to testmethods, contamination limits, testing frequency and reporting.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Yes,there are certain spec changes, for example amount of rosin based residues leftbehind on the board surface differs from Class 2 to Class 3 assemblies. Wewould highly recommend reviewing the:
- IPCJ-STD-001-E, Requirements for Soldered Electrical and Electronic Assemblies; Section 8 - Cleaning Process Requirements and additional industryspecific made addendums
- IPC A 610-E Acceptability of ElectronicAssemblies, Section 10.6 - Cleanliness.
Application Technology Manager
Mr. Tosun has published numerous technical articles. As an active member of the SMTA and IPC organizations, Mr. Tosun has presented a variety of papers and studies on topics such as "Lead-Free Cleaning" and "Climatic Reliability".
It is really comes down to your company having datashowing you can meet and control your process to the limits called out in IPCclass 3 requirements. If you have not recently certified your cleaningprocess meets the JSTD-001 class 3 requirements of surface insulationresistance(SIR) and Ion Chromatography (IC) you should consider thiscourse. These are complex and time consuming test and only need to be performed initially and when significant process changes are made. You should select an appropriate test assemble with similar component types anduse your flux, soldering process, and cleaning material sets when performingthese tests.
Resistance of solvent extract (ROSE) testing isrecommended to control the cleaning process on a ongoing basis once the IC andSIR testing passes. The important thing with ROSE testing is not theabsolute value (assuming you pass) as much as the cleanliness data trend dayto day.
There are not many inspection differences related tocleaning between class 2 and 3 in the IPC JSTD-001 assembly requirements andthe 610 inspection requirements. You may want to send a lead inspectorfor re-certification to IPC 610 if they are not certified.
Austin American Technology
Founder and President of AAT. Steve holds numerous patents and has authored numerous research papers and articles in cleaning and soldering. Steve is a founding member of the Central Texas Electronics Association and is a past Director of IMAPS. Steve is active on several IPC cleaning committees.