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May 30, 2023 - Updated April 29, 2015 - Originally Posted Can a Few Contaminated Joints Cause an Assembly to Fail RoHS Compliance?Can a few contaminated solder joints cause an entire assembly to fail RoHS compliance? Let's say I have 400 lead-free components on a board. All were processed with lead-free paste, but some of the joints were cross-contaminated with leaded solder during touch-up. All of the reworked component joints were tested with an XRF gun. Five joint locations failed. A few were in the yellow zone (around 950ppm), the remaining were in the acceptable range. If I could calculate that the combined solder weight that I added to this assembly was below 1000ppm of lead, would it pass? J.S. |
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The maximum ppm value for Lead is 0.1% by weight or 1000 ppm. If you calculated that the added Lead gives you a value below 1000 ppm then it is RoHS compliant.
Senior Manufacturing Engineer Northrop Grumman Edithel is a chemical engineer with 20 year experience in manufacturing & process development for electronic contract manufacturers in US as well as some major OEM's. Involved in SMT, Reflow, Wave and other assembly operations entailing conformal coating and robotics.
The answer to this question depends upon the RoHS definition of a homogeneous material. "Homogeneous material" means one material of uniform composition throughout or a material consisting of a combination of materials, that cannot be disjointed or separated into different materials; by mechanical actions such as unscrewing, cutting, crushing, grinding and abrasive processes. It is my understanding that the RoHS restriction applies to each solder joint separately. Theoretically each solder joint could be removed and tested individually. If the lead concentration of even one solder joint violates the limit, then the entire circuit assembly fails RoHS compliance.
Field Applications FCT Assembly Tony has worked in the electronics industry since 1994. He worked as a process engineer at a circuit board manufacturer for 5 years. Since 1999, Tony has worked for FCT Companies as a laboratory manager, facility manager, and most recently a field application engineer. He has extensive experience doing research and development, quality control, and technical service with products used to manufacture and assemble printed circuit boards. He holds B.S. and M.B.S. degrees in Chemistry.
From my understanding, the weight of the lead is based upon the weight of the solder on each individual component not the entire board. Unless the rules have changed, one component with leaded solder is enough to fail the lead free requirements of the Directives. If this was an acceptable alternative then we could add non metallic weights to the product so the lead weight is less than .1 % of the whole. Remember, dilution is not the cure for pollution. This is why the boards have to be identified and the people working on the boards have to be trained to use the proper material when conducting work on lead free boards. This also has to be documented on the material declaration sheets which highlight the leaded materials.
Vice President, Technical Director EPTAC Corporation At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
1000 ppm is only for unintentional contamination. If the joints were deliberately retouched with SnPb, the acceptable level is 0 ppm.
CEO & Managing Partner DfR Solutions Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.
If you regard all of the solder as one separable component of the assembly, I guess you could conclude that the assembly passes, since the level of Pb in that component is below the limit. The problem that could arise is that someone tests in the area that was repaired, and sees much higher concentrations. So there is some risk.One mitigation to look at is re-reworking the areas that have been contaminated. By wicking most of the contaminated solder off and re-soldering with the proper alloy, you could reduce the contamination by a factor of 10 or so. Also some words of caution on the XRF "gun" results. These guns "see" a very wide window, and they are averaging what they see within that window. The levels of Pb in some joints within the field of view will almost certainly be much higher than what you are reading.
Process Engineer Astronautics 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.
For better or worse it does not work that way. Every solder joint on a given assembly must be RoHS compliant in order for the whole assembly to be considered compliant.
Technical Support Engineer Indium Corporation Kay Parker is a Technical Support Engineer based at Indium Corporation's headquarters in Clinton, N.Y. In this role she provides guidance and recommendations to customers related to process steps, equipment, techniques, and materials. She is also responsible for servicing the company's existing accounts and retaining new business.
Yes, a few contaminated solder joints will cause you fail RoHS compliance. Lead contend for every solder joint on the board must be below 1000 ppm.
Director New Product Development Metallic Resources, Inc David Bao has more than fifteen years of experience in developing new solder paste, wave soldering fluxes and other SMT consumables. He currently serves as the Director of New Product Development at Metallic Resources Inc. He received a Ph.D. in Chemistry at Oklahoma State University.
Reader Comment
The standard specifies "Homogeneous material" but does not specify contiguous or non-contiguous.
Stephen Olan
If it is contiguous homogeneous material then each solder joint is separate. I think this is implied because each solder joint is "separable" since they are already separate. And tin/lead is not homogeneous with pure tin. But I do wish they had specified in the standard. J. S.; L. L. above said it best, "...dilution is not the solution..." to passing RoHS, otherwise any assembly could be made to pass by simply adding weight. If one tiny 0402 passive is not compliant, than the entire assembly is not. One can argue whether the solder is considered many small parts or one large part. If many small parts, it would not pass if you have a few contaminated solder joints. If one large part, you would pass because the total PPM of lead is under the limit. This however violates the intent of the directive. So in this case, the few contaminated solder joints will cause your entire assembly to fail RoHS.
Senior Project Engineer Electronic Controls Design Inc Paul been with Electronic Controls Design Inc. (ECD) in Milwaukie, Oregon for over 39 years as a Senior Project Engineer. He has seen and worked with the electronic manufacturing industry from many points of view, including: technician, engineer, manufacture, and customer. His focus has been the design and application of measurement tools used to improve manufacturing thermal processes and well as moisture sensitive component storage solutions.
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