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In contrast to the military market, the general commercial electronics industry woke up on the morning of July 1, 2006 with little or no anxiety about the European Union’s Restriction of Hazardous Substances (RoHS) directive. The major semiconductor vendors took little time to shift over to RoHS compliance. They had no issues to face like that of the military market: such as long-term reliability or mixing leaded and lead-free components in the same system. That’s because in the biggest chip markets like consumer electronics, boards and even end-user devices are now always disposed of rather than repaired.
Ironically, the defense industry, while one of the industries that’s exempt from the RoHS initiative, was (and is) much more affected by it than other industries. Makers of board-level products for the military are far from off the hook, because in this age of COTS most companies craft board designs targeted for both military and non-military markets. Even companies purely in the military market can’t escape RoHS’s effects, because these days it would be extremely costly and inefficient not to use the chips and components designed for the commercial market. The only alternative would be boards populated with completely customized silicon—a strategy that is far too costly for all except the most niche military electronics. The sidebar “Coping with RoHS: A Contract Manufacturer’s Point of View” looks at one company’s experience dealing with RoHS.
Clearly military and aerospace markets face some unique requirements. Much higher reliability requirements, extremely long service lifetimes (decades) and extended temperature ranges top the list. Add to that the fact that the DoD is among the few segments that actually repairs embedded computer boards, rather than just disposing of them when a component goes bad. Meanwhile, lead-free components face solder issues and tin whisker failures that aren’t acceptable. The link between using pure tin solders and component lead finishes and the resulting occurrence of tin whiskers is well known and thoroughly documented. Figure 1 shows a tin whisker that has spontaneously grown between two pure tin IC pads, creating a short circuit. Fortunately strategies to deal with those issues are starting to mature.
In the year or so leading up to the July 1, 2006 RoHS deadline, the DoD and other major defense industry institutions had given little direction to the industry on what to do about the RoHS problem. That said, there were efforts underway by the Lead-Free Electronics in Aerospace Project Working Group (LEAP-WG) of the AIA. Formed in 2004, the group was tasked to develop and implement documents describing best practices and technical guidelines to enable the aerospace industry and the military to accommodate the global transition to lead-free electronics.
Coping with RoHS: A Contract Manufacturer’s Point of View
RoHS is an issue that any maker of electronic equipment or subsystem must wrestle with. COTS Journal recently sat down with a representative from Columbia Tech, a small U.S.-based turnkey contract manufacturer, about how they deal with RoHS and its impact on military design projects. Richard Schulman is VP quality and ITAR technology control officer at Columbia Tech.
COTS Journal: Although the defense industry is technically exempt from the European Union's RoHS directive, obviously any electronic system these days relies on the same pool of semiconductors that have mostly shifted over to lead-free. Many defense systems require leaded parts because they can't risk the problems of tin-based chips. What sort of challenges does this impose on you as provider of engineering and manufacturing services for military customers?
Richard Schulman: Certainly tin whiskers have been an industry concern. Coming from the semiconductor field, I know this all too well. The challenge the providers of engineering and manufacturing services face today is based on the bill of materials we are provided by the customer. Since we are not at liberty to digress from that BOM, when we attempt to procure those “older, leaded” devices on the BOM we are often times unsuccessful or only find these devices available from distributors. Where a distributor obtained the parts could be another mystery. Ultimately, all that might be available is the lead-free and not the required leaded device.
CJ: Explain the component obsolescence problems that you see caused by RoHS and how they can be managed for military customers.
RS: Because we’re not at liberty to stray from that customer BOM, all that might be available is the lead-free and not the called out leaded device. We’ve found that in some cases, the customer has made last time buys and can provide that leaded device to us. In other cases we've been successful at obtaining a waiver to substitute an equivalent leaded device. This route, however, takes time and is not always available. The procurement challenge of once plentiful leaded devices is not limited to the semiconductor industry. Interconnects, connectors as well as other active and passive devices can be difficult to find in their old leaded configuration. That said, the tin whisker issue is predominantly a semiconductor design/packaging issue. I'm sure Columbia Tech is not alone in strongly urging the DoD and the military to review their older designs for alternatives.
CJ: In the early days before the July 1, 2006 RoHS deadline, the DoD seemed very late to the game as far as providing a lot of leadership in explaining to the defense industry what they could do to deal with the looming problem of RoHS. Do you see much progress there since that time? In other words, are there useful DoD directives or protocols that you or your military customers follow to ensure that the use of lead-free IC packaging and solder material can either be avoided or that their problems can be mitigated?
RS: The DoD had plenty of time to deal with this looming issue. From my perspective they were late to provide guidelines. In my opinion lead-free is not going away and a solution needs to be found. If there is a DoD directive or protocol that addresses how to mitigate the issue, it hasn’t been well publicized.