There are three core technology groups employed to protect sensitive integrated circuits from the affects of electrostatic discharge (ESD) these include the silicon diode, the metal oxide varistor and the polymeric suppressor. With respect to component configuration, we also note that either individual surface mount designs are employed or array packages. For the design engineer, selecting the right component and configuration for the end-product at hand requires an analysis of the expected transient, the volumetric efficiency requirements, the interface where the transient will enter the system and budgetary considerations. This MarketEYE installment takes a granular look at choosing the right electronic component for protection against the unique and ubiquitous phenomena known as ESD.
ESD Suppression Versus Other Forms of Overvoltage Protection
There are two distinct markets for overvoltage protection components in both power and telecommunications markets, and there are internationally recognized regulations governing each of these two markets.
The first market is for overvoltage protection components used to guard against the damaging effects of transients that result from electrostatic discharge; and the second market is for overvoltage protection components used to guard against transients imposed on power, coax and twisted pair lines resulting from lightning, or in the case of power lines, transients imposed on the line as a result of line or load switching.
The ultimate difference between the two markets is the type of transients resulting from electrostatic discharge as opposed to a lightning strike; each of which is equally damaging, and which is measured with respect to the waveform it produces on the respective lines.
For ESD protection, the primary components used are multilayered chip varistors, zener and avalanche diodes; and polymeric ESD suppressors. Generally speaking, those companies supplying these products successfully note that their components comply with specific regulations.
For lightning and load switch protection we note that leaded varistors, thyristors, and gas discharge tubes are employed, and once again, those companies who are successful at supplying these components generally note that their products meet a select group of specifications. The primary difference between the performance criteria associated with the varying specifications is the transient rise time and the required clamping voltages; however, in the case of ESD protection the additional variable is the volumetric efficiency requirements of the finished components. Electronic portability, by nature, is a ripe breeding ground for electrostatic discharge.
IEC 61000 4-2 SPECIFICATIONS
The majority of vendors who compete in the expanding market for ESD suppression components qualify and market them based upon their ability to comply with the International Electrotechnical Commission’s (IEC) 61000 4-2: Electrostatic Discharge Immunity Test.
The IEC 61000-4-4 test directly addresses electrostatic discharge which results from the build up of electrical charge and the dissipation of that charge through contact and separation of two non-conductive materials. This IEC standard also includes the “Human Body Model” because human contact with I/O ports, switches, keyboards, capacitive touchscreens and equipment housing is a primary cause of one of the most damaging causes of ESD. IEC 61000-4-2 specifies the ESD current waveform and the rise time is defined as 0.7 to 1ns, with a second peak at 30ns and a total duration of only 60ns. The total energy contained within the pulse is approximately a few hundred microjoules. This is a fast rise time with a lot of energy. The components on the market that can “clamp” this type of energy include the metal oxide varistor, the TVS silicon diode and the polymeric ESD suppressor. Competition between these three technologies is understandably intense due to the large number of interfaces requiring protection on a global basis.
COMPETITION AMONG ESD SUPPRESSION TECHNOLOGIES
Demand for Individual multilayered chip varistors and multilayered varistor arrays, have grown substantially because of their preferred use in wireless handsets for IEC 61000-4-2 compliance, especially in Korea and China. Chip varistors are also used in automotive electronic subassemblies to protect engine control units and other sensitive subassemblies against the affects of transients. The same applies to TVS diodes, which are either zener diodes or silicon avalanche diodes, and also available in a volumetrically efficient surface mount package (many different molded case variations exist) but the purpose is to create an ultra-small package design for use in port circuitry in modern electronics. Polymeric ESD suppression components are very similar in construction case sizes to MLVs and are available in ultra-small package sizes in accordance to EIA specifications.
Varistors compete against TVS (transient voltage surge) diodes directly, but have made inroads in wireless communications devices and automotive electronic subassemblies because of their volumetric efficiency (small case size parts, which are important for handset use), and because of their robust nature in harsh automotive environments. Although some varistors are used in the personal computer markets in Taiwan and China, we note that semiconductor devices such as zener diodes and avalanche TVS diodes are used in larger volumes for IEC-61000 4-2 compliance. Additional competition comes from the relatively new surge polymer materials, which have better performance when compared to both varistors and TVS diodes with respect to lower capacitance and are preferred in interfaces where the quality of the transmission is paramount, such as in Data ports utilizing such high-speed protocols as USB 2.0, IEEE1394, HDMI and DVI can benefit from polymeric ESD suppression- because they ensure ESD protection while ensuring signal integrity is maintained.
KEY MARKET DRIVERS BEHIND ESD SUPPRESSION COMPONENTS
The following is a list of some key market drivers that Paumanok Publications, Inc. has identified as reasons for the rapidly increasing demand for components that can comply with IEC 61000 4-2 specifications.
Volumetric Efficiency and IEC-61000 Compliance in ESD Suppression Components
The key market driver in ESD suppression component markets is the combination of the components ability to comply with IEC-61000 specifications with respect to rise times and clamping voltages, and to do so in an ultra-small case size for maximum volumetric efficiency.
I/O Ports, Charging and Touchscreen Technology
Input and Output ports, charging docks and touchscreen technology in the wireless handset, tablet, notebook and desktop computer; and TV set markets worldwide are the market drivers behind demand for ESD suppression components. The combination of the number of I/O ports, the proliferation of touchscreen technology and the increased volume of portable electronic devices manufactured worldwide are the key driving force behind the volume of demand for ESD suppression components.
Customer Preference in ESD Suppression Components
With respect to multilayered varistors and surface mount TVS diodes, part of the competition among vendors is the customer’s preference. Some customers in wireless for example, prefer to use ceramic based components (Samsung Electronics would be an excellent example of this) instead of silicon based TVS diodes, while many others prefer to use silicon based devices- either SAD or Zener diode constructions. Vendors of both products compete on price, performance and volumetric efficiency, and it is important to note that the varistor has the smallest case size to date at 01005.
Both varistors and TVS diodes come in array packages, which is extremely important when protecting I/O ports in computers for example. The array package market in both silicon and varistor technologies is the fastest growth portion of the business.
Low Capacitance Solutions
In many instances where ports require ESD suppression but cannot risk signal distortion, lower capacitance component solutions are desired. In this instance the polymeric ESD suppressor is the preferred choice among design engineers, although it should be noted that the added protection at a lower capacitance value comes at a premium with respect to price.
Critical Ports and Interfaces Requiring ESD Suppression: 2015
The following chart summarizes the key port and interface applications by end-use product market that required ESD suppression components-
Summary of ESD Suppression Applications by Port/Interface and End-Use Market Segment: 2015
Source: Paumanok Publications, Inc.
Technology Roadmap for ESD Suppression Components: 2015-2020
Technology Roadmap For Multilayered chip Varistors and Arrays 2015-2020
Between 2011 and 2014 the area of technology development has been focused on the ultra-small 0201 and O1005 case size chip varistors for applications in wireless handsets and power amplifier modules consumed in wireless handsets. We do not see any smaller products coming on the market than the O1OO5 between 2015 and 2020. We make this statement based on the fact that case sizes smaller than O1OO5 have not been developed in other components as of yet. And since varistors usually follow developments in capacitors and thick film chip resistors, we would expect there to be a long time in development of ultra-small case size chips below the O1OO5 threshold. We would however, anticipate increases in operating voltage for the O1OO5 during this time period in attempt to match the operating voltage range of the 0201.
The recent developments in the O1OO5 case size chip varistor show the technical trends in maximum amperage handling by case size, with the O1OO5 able to handle up to 10 amps surge current. We anticipate that over the next five years that the peak handling current will be extended for the O1OO5 to 20 amps, while the peak handling for the 0201 and the 0402 will be extended to 30 amps.
The area of innovation has been in the development of the O1OO5 case size chip and its ability to handle up to 10 Volts maximum with respect to its clamping capabilities. We would expect that over the next five years that the maximum clamping voltage for the O1OO5 will increase accordingly and to match that of the 0201 at 35 to 40 volts.
The array technology in varistors is already impressive, although the relative high capacitance limits the competitive nature of the technology when compared to that of TVS diode arrays, therefore an ultra-low capacitance varistor array seems like a logical future development as well.
Technology Roadmap For TVS Diodes and Arrays 2015-2020
TVS diodes are good products with low comparative costs and excellent performance in volumetrically efficient packaging. The technology really excels in its array format, which has very low capacitance. The logical roadmap would be to develop, if possible, the 01005 case size chip to compete against the successful 01005 varistor chips now on the market, or to continue to push the envelope in the development of array technologies in SOT, SOD or related packages.
Technology Roadmap Polymeric ESD Suppressors: 2015-2020
The benefits of the polymeric ESD suppressor is its ultra-low capacitance, which really becomes important for protection of high- speed video lines where distortion of the signal integrity is unacceptable. We would expect this technology to increase its product offering to include the 0201 and the 01005 in the future and to expand into larger case sizes as well. There is also a need for an array package. Currently we note a 2-line protection device in a SOT23 package on the market, but we would expect this to expand into multiline protection in similar or larger packages in the future.
Summary and Conclusions
Three different technologies are employed for protection of sensitive electronic devices against the ravages of electrostatic discharge as outlined in IEC 61000 4-2 Electrostatic Discharge Immunity Test. These are metal oxide varistors, silicon diodes and polymeric ESD suppression components. The additional factor of note is that packaging is key and that each of these components is offered in extremely small and volumetrically efficient case sizes, or in some sort of array package that can protect multiple lines at different ports. Demand has increased for ESD protection in accordance with the number and type of ports and interfaces in portable electronic devices and their unique requirements with respect to added capacitance on certain lines that require pristine signal integrity. The future outlook for the technology suggests continued movements toward greater volumetric efficiency in both individual components and in array development. There is also a clear movement to lower the inherent capacitance of individual ESD suppression components over the next five years, as well as expected improvement in the maximum amperage handling capabilities of individual components and array packages, and an increase in operating voltages within individual case sizes and array packages as well.