Although it’s getting late, there is still time to meet the RoHS deadline of 1 July 2006. Nonetheless, it’s a huge challenge that starts with finding out what compliance actually means. That’s still taxing the legislators charged with transposing the legislation—with the British, French and Germans arguing over interpretation—so what chance has a production engineer got?
Robert Hills, project manager for Christchurch-based Tait Radio Communication, understands the enigma of RoHS better than most. He’s been at it since the company gave him the job of eliminating lead-free solder back in May 2003 and is happy to share his experience.
According to Hills, information was harder to come by back then. “We didn’t know what the true scope of the WEEE and RoHS directive was when the program kicked off,” he says, “All we had were drafts of EU2002/96/EC and EU2002/95/EC. Nothing had been signed off.
“Fortunately, in the long run, the directives didn’t change although interpretations have.”
While much of the small print has been shaken out since Hills began Tait’s compliance program, he still advises engineers against simply typing “RoHS” into Google and taking the results as gospel.
“There’s a lot of Internet material that’s old, outdated – and not peer reviewed,” says Hills. “People need to be aware the knowledge base is evolving rapidly and as such, there is a lot of the old information that is quite dangerous.”
Hills advises due diligence on the source and accuracy of information before making hasty decisions. One document he particularly suggests looking at is the EU’s WEEE/RoHS FAQ document published in Aug 2005 (“It’s not legally binding but it’s well worth reading,” says Hills.)
Trawling through even the latest documentation can make meeting the Directive seem like a Herculean task, so the best approach, advises Hills, is to target effort at the highest risks to non-compliance first. For electronics manufacturing companies that often means changing to a lead-free solder and ensuring their supply chain is purged of non-compliant components.
“Before we started our project we ran a risk review assessment,” he explains. “We weighed up about 200 risks, to find those that were critical.
“If you break down your workflow and run a risk assessment you’ll probably find three to five [major risks]. Concentrate your efforts on these - don’t try to work on thousands.”
Soldering without lead
One of the major risks identified was undertaking lead-free process testing on a small scale—by purchasing equipment for the trial—and then migrating to full production.
“We concluded if we did the former we would have two process development iterations to manage [qualifying both small scale and production scale],” explains Hills. “So we decided to test only in a live production environment using existing equipment only.”
Underpinning this were test vehicles for accelerated life testing based upon assessing the known failure mechanisms.
Tait managed to accelerate its compliance program by visiting fellow NZ company Fisher & Paykel which had started even earlier. (“They reduced our workload for the assessment by about 3-5 months,” says Hills). Conversations with the white goods firm helped Hills’ team to quickly narrow down prospective alternative solder alloys.
The change to lead-free solder was also eased by formulating a strategy based on work done by Dr Ron Lasky and Tim Jensen of US solder manufacturer Indium.
“We designed our solder paste selection and qualification based on Lasky’s and Jensen’s previous work and extended a number of test cases for our use.”
“We had started our testing with a reflow profile peak of 260oC but rapidly closed that down to an operational range of 230 to 245oC,” explains Hills.
Tait has replaced one reflow oven, and is looking to change another, because of the higher temperature and tighter process control required for lead-free. The process super heat has been reduced to 15oC compared to 35oC for tin/lead solder. Some older ovens struggle to meet this criteria.
“We have also had to train staff how to detect which alloy is being used,” Hills notes. “If you accidentally substitute a leaded for a non-leaded alloy or vice versa, it’s a big problem. And it’s not just about the compliance issue, what we are also worried about is process failure.” This is important for Tait, because the company intends to run production lines using tin/lead solder for high reliability infrastructure equipment not under the WEEE and RoHS directives.
Although the introduction of lead-free has progressed well, Hills does highlight some ongoing challenges, notably changing PCBs to meet compliance requirements and data for solder joint reliability modelling.
“PCBs have been a major headache,” he says. “As we raised the reflow time and temperature profiles bow and twist increased, so we had to revisit our PCB designs.
“We have excluded more than one fabricator from supplying production quantities because of risks of variability within their processes, for example due to variations in barrel quality.
“We are still struggling to find technical data for reliability modelling, in particular fatigue ductility resistance for SAC [tin/silver/copper] alloys. The fatigue ductility constants for the SAC alloys are a big unknown.”
SAC alloys are based on high tin content. The US trade association, the IPC, has recently released a report recommending SAC 305 (96.5/3.0/0.5 percent tin/silver/copper) as the alloy of choice for lead-free applications.
Controlling the supply chain
Controlling what goes on in your factory is one thing, controlling compliant component deliveries is quite another. Hills is still grappling with this challenge.
“We haven’t yet been able to resolve all the supply issues,” he admits, “but we are getting there. For example, for electronics COTS [Commercially Off The Shelf] items, it is likely we will achieve better that 99.5 percent compliance [by the deadline]. When we started in 2003, only 15 percent of components were compliant. However for electro mechanical items this is significantly lower.
“The main concern is OEM equipment, for example, routers, duplexers, cabinets and computers. We don’t have direct control over these units. For items used in fixed infrastructure it’s likely they won’t come under the WEEE & RoHS directives, however at this stage we are not fully informed as to the extent of the scope of the directives.”
If you speak to suppliers, they will tell you component manufacturers have varying approaches to lead-free part numbering.
Internally, Tait’s approach is still to be finally decided, but for now, Hills is balancing risk against unnecessary work.
“If we change an item from lead to lead-free and it’s a COTS item that isn’t process sensitive we will not change the part number. We rely on stock control [FIFO] to purge the non-compliant item over time.
“If the item is process dependent—a BGA for example—it will come under engineering change control together with a part number change and synchronised process change order control.
“The third rule concerns designed items. If we make a change that is not process dependent then I advocate leaving it to the design engineer to justify if they need to make a part number change strictly on a case-by-case basis, for example if the change in process alters the colour.
“The exception is PCBs which will have part number changes because this is critical from a process perspective.”
Next steps
“Our understanding at the moment is that compliance is self regulating,” explains Hills. “In other words, if you sell product on the market, the [EU] deems it’s compliant. But this is an assumption and requires clarification.”
The risk is that somewhere, deep inside a product is a single, non-compliant component that has made it through even the most carefully controlled supply chain. Tait is taking a pragmatic approach. “We are taking a view similar to the aircraft industry,” explains Hills. “We make our designed items—including all the materials and processes under Tait’s control—compliant and rely upon approved suppliers doing the same.”
However, the company will also undertake due diligence to ascertain the compliance level of its raw material supply chain.
“We have modified our inventory master database so that we’ve got information captured about the compliance status of our raw material,” says Hills. “That way we can bore down from the assembly level and identify any items that are non-compliant.
According to Hills, engineers should be aware that there are manufacturers of raw material items that don’t have the capability or motivation to ascertain if their product is compliant. “Generally, these are small manufacturers traditionally supplying into non-EU markets” he notes.
This is one area where your supplier can help — some suppliers now offer services where they will advise which manufacturers provide compliant alternatives. However, there will always be instances where custom components remain non-compliant because it isn’t economic for the manufacturer to change. The long-term solution is to design out these devices.
While Hills advises due diligence he does believe common sense will eventually prevail.
“Personally, I can’t see border control opening up a product and boring down to the microscopic level of an 0201 resistor to make an assessment that the item is non-compliant – however they will demand compliance certificates.”