The Evolution of RoHS Technology

Lead has been extensively used before in engineering and construction fields, but now, the same material is known to pose a serious environmental hazard.

Lead poisoning can have an acute detrimental impact on how the human central nervous system functions and this can be specifically serious if children are exposed to it.

Lead and its Hazards

During the 1970s/1980s, lead was slowly removed from people’s lives when scientific studies performed during the 1960s discovered that this element was extracted from paints, gasoline, and other household products, while additional legislative measures made sure that it is gradually removed from the majority of other high-risk areas.

The Restriction of Hazardous Substances Directive 2002/95/EC (RoHS) was enacted to ensure that metallic lead is eliminated from electronic components and also other hazardous constituents like cadmium and mercury, and substitute them with alternative materials that would bring down the overall ecological impact.

The legislation became effective in 2006, but by then, most of the suppliers had taken the initiative and adhered to it. There are two prominent exemptions to the RoHS directive, where no practical substitute could be found during its implementation.

Thick-film resistors were one of the areas where an exemption was permitted to be applied, and even now, lead oxide compounds are allowed to be utilized in their glass elements. Since lead oxide compounds are relatively more stable, they do not pose a major immediate threat; however, there would still be a potential risk when these devices are dumped in landfill and the dangerous heavy metal compounds are allowed to seep into the groundwater.

Many smart devices contain thick-film resistors. Since more of these devices are being directed to landfill each year, there is renewed pressure to explore the options available to narrow down the scope of the current exemptions and make regulatory guidelines more rigorous.

Periodical Review of RoHS Exemptions

OEMs should be aware that existing RoHS exemptions in place are conditional to periodical review because a component that was earlier cleared for use and specified into electronics designs may no longer be within the exemption area. Evidently, this would have serious and costly repercussions for an OEM that fails to be sufficiently prepared, and this is fueling interest in preemptive action against such a situation.

The next review of the pertinent RoHS exemption—7(c)-I “Electrical & Electronic Components Containing Lead in a Glass or Ceramic Material”—has been planned for 2021, and it is believed that at the time of this review, the incorporation of lead oxides in thick-film resistors will be subject to significant scrutiny.

In case changes are made to RoHS exemption, OEMs should be able to access compliant components as these can make their devices future-proof. As a result, they will not have to be concerned about assigning engineering resources and valuable time to make corrections further down the line, especially when there is a looming deadline.

Getting the lead out with the help of Welch Allyn

Getting the lead out with the help of Welch Allyn

It is not that simple to develop glass for thick-film materials without lead oxides, and until now, those materials that have been created have had related performance penalties. Already, commodity resistors with lead-free glass are available that could be utilized in certain less-challenging cases. Conversely, these resistors are still not close to achieving the benchmarks required to tackle higher-end applications.

New Generation of Green Thick-Film Resistors

This limitation is set to change with the advent of a new range of fully green thick-film resistors. Building on the work performed by TT Electronics and its supply partners during the 18-month period, the green thick-film resistors make sure that long-term RoHS compliance eliminates the dependence on exemptions. The inconvenience of OEMs having to undertake ensuing system redesign work is also reduced.

Features and Advantages of Green High-Voltage Chip Resistors

The Green High-Voltage Chip (GHVC) resistors, which cover resistance values ranging from 25 to 100 MΩ, are provided in standard EIA 2512, 2010, and 1206 formats and include power ratings of 1.0, 0.5, and 0.3 W, respectively.

The GHVC resistors support a working temperature range of −55 °C to 125 °C, with each of these rugged components providing around 3000 V Limiting Element Voltage (LEV) and being sufficiently resilient to tolerate around 7 kV peak voltage for a 1.2/50 µs surge.

The −1.5 ppm/V voltage coefficient and ±100 ppm/°C temperature coefficient make sure that the accuracy of the resistors’ operational parameters is continuously maintained. In addition to this, the resistors have anti-sulfur terminations that have passed ASTM-B-809 tests. This means they can be used in the aggressive sulfurous environments that may result from use in chemical and mining processing tasks.

Green High-Voltage Chip (GHVC) resistors

Green High-Voltage Chip (GHVC) resistors

The wide array of compact resistors has been improved for deployment in the contemporary, densely packed electronic circuitry, enabling the device to maintain increased voltage levels without having to use numerous components. This not only saves the board space but also keeps a check on the overall cost of materials.

The resistors are targeted for use in either circuit protection or high-voltage sensing functions in premium devices such as clinical, medical, industrial automation, hybrid electric vehicles (HEVs), and home healthcare applications.

The future-proofing aspect, though important in all forms of electronic design, will be particularly useful in a medical context because the use of GHVC components will prevent expensive redesigns and also lengthy requalification processes.


The migration to a fully lead-free strategy has prevented a substantial increase in production costs, and this can be attributed to the use of next-generation materials and a novel fabrication process, but without the significant financial burden of upgrading equipment.

As a result, the price points have effectively remained the same as with products comprising lead oxides. The initial anticipation is for GHVC pricing to average about 20% higher, although this will come down post-launch as economies of scale begin to kick in and volume demands increase.

OEMs that are operating in an already erratic business landscape should do everything in their power to protect the investment they have made in their system designs and reduce the financial risks of having to make changes or perform time-intensive re-spins.

The sourcing of components that pre-empt additional limitations to RoHS, and any redefining of the exempt area, can have an important role to play in realizing this objective. Although the RoHS exemption for lead oxide in glass has stayed constant for a number of years, it would not be wise for OEMs to believe that it is fully immutable—with a potential chance of greater limitations.

Technological developments in the materials used in passive components have currently reached a phase where the probability of fully lead-free supply is tangible, without having to witness unit cost increases or make performance compromises.

This information has been sourced, reviewed and adapted from materials provided by TT Electronics plc.

For more information on this source, please visit TT Electronics plc.


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