PULSE EEWeb.comIssue 55

July 17, 2012

Parviz Ghaffaripour Akros Silicon

Electrical Engineering Community

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TABLE O

F CO

NTEN

TSTABLE OF CONTENTS

Parviz Ghaffaripour 4AKROS SILICON

Featured Products 10

Illogical Logic - Part 4: Counters BY PAUL CLARKE WITH EBM-PAPST

BY VLADIMIR KRAZ WITH ONFILTER, INC.

RTZ - Return to Zero Comic

Interview with Parviz Ghaffaripour - President, CEO and Director

A look into how a soldering tip gets voltage from high frequency signals.

The last installmant of the Illogical Logic series shows how to build a counter with a 7-segment display.

12

16Reducing EOS Exposure of Components During Soldering

23

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How did you become interested electronics and engineering? I was very interested in mathematics and science in junior high and high school, so studying engineering seemed to be the logical choice in college. I went to UC Berkeley and got my bachelor’s degree in Electrical Engineering. Later on, I continued my education to receive my MSEE from Santa Clara University and Executive MBAs

from Stanford and Western Ontario.

I started my career as a professional analog IC design engineer at Exar Corporation. I’m old enough to know how to design circuits by relying on paper and pencil rather than computers. What I always liked about analog IC design was anticipating the results of several parameters before making a decision, which I see as analogous to playing chess.

I spent the next 21 years at Exar Corp, National Semiconductor and Maxim Integrated Products. When I joined Maxim the late Jack Gifford, whom I regard as a legend in our industry, offered me the amazing opportunity to choose what I wanted to work on. There I helped start several different product lines including LED display drivers, supervisory system functions (including thermal monitoring and power management devices),

AKROS SILICON

ParvizGhaffaripour

President, CEOand Director

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and high-speed interconnects for infotainment in automotive applications.

I left Maxim to follow my dream of starting my own company in the power management area. I met the board of directors of Akros Silicon while I was pitching my own company. Akros, which was founded in 2005, had developed a unique isolation technology called GreenEdgeTM and faced the challenge of utilizing and proliferating this proven technology into many product types and creating revenue. Given my background, I immediately realized I wanted to join the company.

Have you had any noteworthy engineering experiences, and is there any advice you could give to the EE community based on your experience?With 28 years in the industry working with five companies, I’ve worked on many different projects. The noteworthy products that come to mind that I designed or co-designed are the ignition controller for Magnavox (Honda) motorcycles, the first 3v RS232, the first LVDS driver and receiver products, and the Boomer audio power amplifier. And now, of course, with Akros I am working with a very unique technology that revolutionizes the whole concept of energy management

From my experience I believe it’s very important for designers to think outside of the frame, or the box, we’re put in. For example, an IC designer is typically given a set of specifications that narrowly define a specific part and is then asked to

design to those specifications. This “bag of chips” approach might have been adequate in early days, but today this design methodology leads to what I believe is a difficulty in the industry. Today’s system boards incorporate many component ICs that were not designed to work together but were designed by different people, at different times, and in different technologies.

In contrast, it’s beneficial to consider the needs of the overall system and to be able to explain in layman terms how a specific part will be used and how it will benefit the end design. Each of us should try to step outside of our comfort zone and dabble in other areas; IC designers should be able to take the system designers’ point of view and system designers should understand IC design, and so forth. This is the approach we take at Akros.

Could you tell us more about GreenEdge?The concept behind our GreenEdge isolation technology is based on approaching energy management differently from the way power management is approached. Traditionally, power management has been identified with voltage or current conversion, and almost every analog IC design company provides products for this arena. And now in the last five years, several overseas companies have joined the power management business with the goal of providing similar solutions but at much lower prices. Meanwhile, in recent years the “green” movement has made energy management more of a priority. Akros recognized this important shift back in 2005 and

began to focus on how to increase the energy efficiency of systems.

At Akros we asked a very basic question: What does energy management mean? We’ve all seen the advertisements telling us to unplug our TVs and computers because even though they’re turned off, they still consume power when connected to, say, AC power or to a high-voltage power source. Estimates are that consumers spend something like $28 billion dollars in energy waste from our PCs being connected to power while not in use. That translates to 30% of energy that is generated being wasted.

This knowledge led us to ask a more difficult question: Why is this happening? The obvious answer was lack of access to the primary side of the system.

I can explain it this way: a system has both a primary and a secondary side. The high-voltage, or primary, side is usually connected to either an AC voltage or a high-voltage DC. The low-voltage, or secondary, side is the one that consumers come in contact with. Safety purposes and regulations require that the secondary side is separated, or isolated, from the primary side of the system. Most of the activities in the power management arena have been focused on this secondary side.

This system-level view spurred us to come up with a solution that not only handles the requirements of the secondary side, but also creates a “bridge” to the high-voltage primary side. In this way, GreenEdge provides an isolation

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barrier between the primary and secondary side of the system and also serves as a communication path between the two sides. This results in physical isolation for safety reasons, but it also enables system designers to communicate across the isolation barrier so they can monitor either side and make decisions based on the environmental parameters, thereby creating a digital communication path and isolation barrier at the same time.

Now that we had the concept crystallized, it opened up the door to a lot of other possibilities. It meant that we could integrate anything that is around a system. For example, the products that we have introduced in the isolated DC to DC converter area, whether Power over Ethernet (PoE) or isolated DC-to-DC, can replace the functionality of up to nine ICs, several opto-couplers, and many other control functions.

This solution also allows us to eliminate many redundancies in the system, making the solution smaller and lower cost. It also provides energy management features, which means being able to manage power based on the system’s environmental parameters. Take an IP phone for example. Typically, a phone is only used about 20% of the time, yet it consumes power the other 80% of the time when it’s not in use. Using the GreenEdge for motion sensor or input monitoring, the phone can be put into different stages of standby or shutdown, saving energy when it’s not in use, and then it can be quickly turned back on when it is.

Where has the technology been implemented?GreenEdge can be used in many different applications. It can be

Our answer to energy management is to

give system designers access to both the

high-voltage primary side and the low-voltage secondary

side with our GreenEdge technology.

By providing a communication

path for each side to communicate, system designers can now make the

right decisions.

used to create energy management solutions for isolated interface applications where isolation is required for active performance and safety reasons. It also can be used in the area of battery management and in alternative energy applications, such as solar cells and so forth. So this technology provides a

basis for different technologies and applications. Initially, we have chosen two main areas: PoE and general purpose, isolated DC-DC converters. For PoE, the main drivers for applications are IP telephony, security cameras, wireless access points, IP terminals and security systems, to name a few. The isolated DC-DC converters expand horizontally across many applications and many different equipment types, including medical, industrial, telecom, and datacom applications. Today, we have shipped many products and have many tier-1 customers who have designed in our devices. We started getting revenue in late 2009, and since then it’s been growing rapidly.

How do Akros’ solutions help manufacturers of electronic equipment create more efficient and advanced products at reduced costs?System designers know how to design systems that conserve energy. The problem has been the practicality of their designs. In other words, designers have to incorporate many extra, individual IC components and circuitries that can cause the end solution to be too large or expensive. When coming up with GreenEdge technology, the most important factor was to provide a solution that was practical. As a result, GreenEdge allows designers to incorporate energy management features into their system designs in a simple, cost-effective way. The GreenEdge products are not only pin-compatible but also PCB-layout compatible. With this family of products, we offer a solution that can fulfill a variety of needs by

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customizing the feature set. So now system designers can use basically one design to address the needs of nearly all of their products.

Once we designed the GreenEdge isolation technology and provided solutions for isolated applications, we turned our attention to other as-pects of the system in the second-ary side. Our GreenEdge product is a pretty complicated system-on-a-chip (SoC), incorporating many innovative circuit blocks. One of the blocks inside is called power management unit, or PMU. Many companies in our industry have re-ferred to blocks similar to our PMU as SoCs. So you can see, in rela-tive comparison from a functionality point of view, we offer much more sophisticated products, which are also easy to use.

So, we took the PMU block that serves the same function as GreenEdge for the non-isolated application and generated an energy management solution that is programmable and flexible for the secondary side. We dubbed it Energy$ense™ since it is cost effective. It is also a sensible energy management solution that accommodates a variety of combinations for power management architectures such as buck, boost, LED drive, and it adds converter channels as needed.

For an example of how it is used, take a set-top box application. One of the functions in any set-top box or media player is video encoding. To save energy, you want to enable video encoding functions only when necessary because these functions consume so much power. Actually, it’s only rarely that the video encoding function must be

turned on. Energy$ense products enable the system designer to turn off the power to the video encoding function when it isn’t needed, and as soon as it’s needed, to instantly turn it back on, which saves a lot of energy. Another feature of Energy$ense is programmability in

With GreenEdge technology, Akros has developed a

differentiated and pragmatic solution that addresses the

actual needs of system designers. It’s an

invention that comes once in a lifetime.

terms of sequencing, or how to start up the different ICs. By providing this programmability and flexibility, a designer can provide a better solution for the devices that are using different CPUs. In today’s systems, for instance, several CPU manufacturers require special sequencing and startup for their power supplies. Now, with typical solutions, you have to use different circuitries for each one of these CPUs. But the Energy$ense solution allows our ICs to work with different CPUs through the programmability feature. In this way, the system

designer basically uses one design that works with several different CPUs.

What direction do you see your business heading in the next few years?We provide programmability through the I2C in order to customize our solution for different system designs. This enables the system designer to create a solution for today while adapting it for future designs, even if the future design is different in terms of the system architecture or the CPU selections. For example, there are now different international standards for energy efficiency, including Euro 6, which did not exist a few years ago.

Our GreenEdge solution is flex-ible enough to put the system into different levels of standby and, through the programmability fea-ture, it meets different international standards. Additionally, we can set up various output voltages, we can do voltage margining on output volt-ages, we can monitor input power profiles and we can accommodate several sequencing scenarios. All of these features give system de-signers the confidence knowing they can use our system today and adopt it for later designs as well.

The GreenEdge solution is changing the industry paradigm. Many of our colleagues answer system designers’ need for energy management by providing higher-efficiency power converters. After much hard work they may gain a few more percentages of efficiency and call it an energy management solution. We, on the other hand, look at efficiency as just one aspect

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of energy management. In order to provide an energy management solution, we offer key features that system designers can use to monitor their design.

In our view, energy management is providing a solution that encompasses five aspects. The first is being able to do real-time energy monitoring; meaning, for example, being able to measure how much power the device actually uses so it can instantly make the right decision. By having the ability to do health monitoring of the system, the customer can reduce diagnostics and service calls. The second, of course, is providing high-efficiency converters. The third is providing the flexibility for the system designer to do different functions, which we call digital power control, such as being able to reduce or increase the backlight depending on when you need it, or to adjust output voltages customized to the CPU mode. The fourth is providing fast-transient response, which is the ability to react quickly to the environment and to turn power supplies on and off accordingly, or leave one on while turning the other off. And, finally, the fifth aspect is providing a solution with low EMI emissions and that reduces radiation and filtering.

What challenges do you foresee in the industry and where is Akros headed?The industry challenge, I believe, is for other companies to think about how they’re going to provide solutions for energy management. There are many IC companies providing single function ICs or components for power management applications, but, as we discussed, these components do not necessarily “talk” to each other. Therefore today’s system designers have the onerous job of providing a system using disconnected components to address energy management issues, which is not very practical. System designers are looking for easy, effective solutions. This means that IC companies must rethink their strategies and start providing more integrated and more intelligent products.

And, of course, all of these solutions must be cost-competitive. For instance, a typical scenario in last few years is for a company to design in a DSP and then add a lot of other analog components to it. Everything including the kitchen sink is thrown into the design since it’s a big engine that does everything. But, unfortunately, this is not a practical solution.

Solutions must be practical, cost effective, and flexible enough to be customized for the system in mind. This is the challenge that I see our industry is facing and I believe the Akros approach is changing the playing field.

Our answer to energy management is to give system designers access to both the high-voltage primary side and the low-voltage secondary side with our GreenEdge technology. By providing a communication path for each side to communicate, system designers can now make the right decisions.

In terms of where Akros is headed, we are beginning to apply this technology to other market segments and have many more in mind. With GreenEdge technology, Akros has developed a differentiated and pragmatic solution that addresses the actual needs of system designers. It’s an invention that comes once in a lifetime. ■

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Illogical Logic

Paul ClarkeElectronics DesignEngineer

For the last part of my Illogical Logic series, I would like to show how we can take what we have looked at so far and use it in one small project: to build a counter with a 7-segment display.

This circuit loops back the inverted Q output back to the D input. This means that every time the clock signal rises the output flips.

Figure 1

Let’s start with counters, as this will be the heart of the design. Last time, we looked at the D-type Flip Flop, which drives the gears inside a counter. There is a standard use of the D-Type to half a clock frequency.

Figure 2

A counter simply works by feeding the Q output into the next D-Type’s Clock input. Because this is running at half the frequency, it counts in 2s. Add another and it would count in 4s then another to get 8s, 16s, 32s etc. This quickly becomes a binary counter.

Decoder

CLK a

b

c

d

Q3

Q2

Q1

Q0R e f g CLK

Q

Q

D

- ebm-papst

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This can be simplified to the following:

This is easy, but if we want to drive a 7-segment display,

you can do by going back and looking at the Karnaugh Maps and using one per seven segment. That’s a lot of work to show here, so I’ll leave you to do that!

However, you should end up with a circuit like the one below with the counter input at the top.

Figure 3

Figure 4

then we need an output that runs from 0 to 9, not 0 to 15 (or F in Hexadecimal). Thankfully, the reset pins of the D-types are connected together and allowed access to. Remember back to our J-K flip-flops; they had a Set and Reset input. In this case, this is the Reset connection.

What we need is to reset the counter when it gets to 10. This has the binary value of 1010 and I think it should be clear that we only need an AND gate to react to this output on Q1 and Q3. In fact, because the Reset input is a inverted input, we really need a NAND gate as follows. I should also note that this is an asynchronous input so the reset is instantaneous in resetting back to zero.

4-bit Counter with Reset

What we need now is a bit of logic—well actually a lot of logic—that will drive each segment of the displayed only when needed based on the output of the counter. This

To add more digits, you would link the 4th bit of the counter to the input of the next and repeat all the decoder logic etc. As you can see, this is a lot of work and I personally remember how much effort this all took to design and build.

Hopefully, over these last four posts you learned a little about low level logic. Nowadays, these circuits are buried inside FPGAs, or dedicated ICs doing the job for you. Designs like this one are now easy to find on chips, however if you find a need to design something a little

Figure 5

CLK

Q

Q

D Q

Q

D Q

Q

D Q

Q

D

CLK

+5V

Q3

Q2

Q1

Q0R

a

b

c

d

0 1 1 1

e f g

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special then you know where to start. For the rest of us, just remember how much is being done for us now to make life easy, and maybe give these devices a bit more respect.

About the Author

Digital Electronics Engineer with strong software skills in assembly and C for embedded systems. At ebm-papst I’m developing embedded electronics for thermal management control solutions for the air movement industry. These controllers monitor environmental inputs like Temperature, Humidity and Pressure and then control the speed of our fans based on various profiles.

Our controls also interface with other systems over RS232/485 or TCP/IP as well as a host of other user or control interfaces.

As an engineer I’m responsible for the entire development cycle, from working with customers on requirement specifications though to circuit and PCB design, developing the software, release of drawings and supporting our production. In the past I have worked in range of industries developing scientific equipment, retail weighing systems, street lighting ballasts, motor sport. A full list of my job roles can be found on LinkedIn. ■

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Vladimir KrazPresident, OnFILTER, Inc.

EOS Exposureof Components inSoldering Process

Soldering irons, solder extractors and other equipment that comes in direct electrical contact with sensitive components can inject significant energy into these devices. Specifically, metal-to-metal contact between the tip of the soldering iron and pins of the components is a gateway for high current that can cause significant device damage.

Where would a soldering iron tip get voltage? After all, it is supposed to be grounded, just like the PCB with the components, so theoretically there should be no difference in voltage and thus no harmful currents between the tip of the iron and the devices. This, however, may be true only for DC or for very low frequencies such as power mains (50/60Hz). For high frequency signals, it may be very different.

Transient Signals as a Source of EOSAssuming the tip of the iron is properly grounded, the voltage on it can arrive mainly via ground connection and to some degree via capacitive coupling between the heating element and the tip.

Ground by itself is not a generator of any signal. However, grounding wires connect the entire factory and once some stray electrical signal enters grounding network, this signal can reach quite far.

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Main source of voltage on ground is transient signals leaked from power lines. Transient signals can come from a number of sources, such as switched power supplies, thyristor control, servo motors, equipment commutation and so on [1]. These signals can reach significant magnitude. Figure 1 shows transient signal on power line caused by turning on ubiquitous heat gun. As seen, the peak signal reaches 13.3V and this is not the highest magnitude found in manufacturing environment where plenty of high-current equipment is operating.

By virtue of neutral and ground being eventually connected together at some point and because of leakage currents (parasitic currents between power lines and ground) present in almost all equipment and, to a much higher degree, in manufacturing equipment, these transient signals are also present on ground. Current leakage at high frequencies is significantly higher than often-specified leakage at power line frequencies. This is due to much-reduced impedance of parasitic capacitance coupling at higher frequencies. With the complexity of grounding network and increased leakage at high frequencies in the soldering iron itself, there is a strong possibility of current spikes between grounded iron tip and grounded PC board with components.

What is Acceptable and Safe?There are a number of standards and recommendations limiting signal on the tip of a soldering iron. ESD Association’ STM13.1-2000 [2] sets current limit at 10mA and voltage limit at 20mV. While the test set-up in this

document implies mains (50/60Hz) signal, there is no stated limit of properties of the signal. It should be noted that the current limit in this document is about 15 years old (it takes at least three years to finalize and to release a document within the standards organizations); the current limits now should be substantially lower to reflect higher sensitivity of today’s components.

Now-obsolete MIL-STD-2000 [3] and its associated military standards specify no more than 2mV RMS voltage on the tip. RMS values may be very misleading for transient signals. 2mV RMS may translate into quite high peak voltage of transient signal – the voltage spikes can be very narrow, i.e. have very short duty cycle – please refer to Figure 2 to see the difference between peak and RMS values of a transient signal, also from turning on the same heat gun on a workbench where the time base was spread to the degree where typical multimeter can measure it. 761mV peak translates into only 15.8mV RMS signal – a 48 times ratio in this case. For this type of waveform, a 2mV RMS signal would translate into 96mV peak signal. Obviously, RMS value is not the best way to specify signal on the tip of the iron. A common multimeter often used for this purpose provides measurements of either RMS value or close to average – good for 50/60Hz, but unusable for transient high frequency signals.

IPC-TM-650 section 2.5.33.2 allows for 2V peak voltage on the tip of the soldering iron, which is extremely high; section 2.5.33.3 of the same document allows maximum of 1µA of current measurable with a multimeter, not a scope thus providing RMS or average value.

Figure 1: Transient Signal on Power Line Caused by Turning on Heat Gun

Figure 2: RMS and Peak Values of a Transient Signal Typical on Power Lines

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In dissent with the above IPC standards, IPC-A-610-E [4], the most fundamental document controlling quality of PCB assembly, provides the following instructions:

3.1.1 EOS/ESD Prevention – Electrical Overstress (EOS)

…Before handling or processing sensitive components, tools and equipment need to be carefully tested to ensure that they do not generate damaging energy, including spike voltages. Current research indicates that voltages and spikes less than 0.5 volt are acceptable. However, an increasing number of extremely sensitive components require that soldering irons, solder extractors, test instruments and other equipment must never generate spikes greater than 0.3 volt.

IPC-7711 [5] which provides directions for rework of the electronic circuits mimics IPC-A-610-E.

What Measurements are ImportantLet’s examine the properties of the EOS signal caused by conducted EMI. As a rule, conducted emission signals are high-energy signals, i.e. having low output impedance and capable of delivering high currents. The reason for this is that creation of disturbances on low-impedance power line requires power and only truly low-impedance sources of noise can deliver. Even fairly low voltage transient signals on power lines can be quite dangerous because of their current capability.

Current is a better measure of EOS safety of sensitive devices since it is the current that causes actual damage (with very few exceptions). In addition, due to complex impedances the current capability of some devices and boards may be limited at high frequencies; therefore voltage measurements alone may not be a definitive indication of current injection into the circuit.

Another factor in favor of current measurements vs. voltage is that strong transient signals on power lines and ground can easily inject corresponding signals into oscilloscope probe cables via radiated emission thus distorting voltage measurement results. Injection of radiated signal into current probe is significantly less than into a voltage probe due to a number of factors, including lower impedance of the current probe arrangement. We will focus on measurements of current.

A typical setup of a workbench is seen in Figure 3. A grounded metal plate is used in lieu of a PCB as the worst-case scenario. Current is measured using Tektronix’ CT1 current probe [6] with bandwidth of 1GHz. This probe has conversion factor of 5mV/ma, meaning that 1mA of current would be seen as 5mV on the oscilloscope.

There are many sources of noise in manufacturing environment. Some of them are random, such as transients from turning on and off a typical heat gun or other piece of equipment. Others are periodic, synchronized with the waveform of voltage on the mains (50 or 60 Hz). Periodic transient signals are caused by a variety of equipment, including heaters, brightness control for vision systems and countless more. For the

Figure 3: Test Setup for Measuring EOS Exposure

Figure 4: Transient on Power Line from Periodic Signal and Resulting Current from the Tip

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purposes of repeatability of the data we will focus on periodic signals. An easily-reproducible noise from a common light dimmer connected to a 60W light bulb was used in tests described below.

Figure 4 depicts such transient signal on power lines and corresponding current between the tip of the soldering iron and the component in the setup of Fig. 3. As seen, the peak current from the tip (19.12mA) is significantly higher than allowed by ESDA STM13.1-2000. It should be noted that typical transient signals on power lines in the industrial settings are often significantly higher than the ones shown in Figure 4 – see earlier Figure 1.

Data from previously-published sources corroborate the above data. Raytheon in its paper [7] presented at the ESD Symposium in 2005 show transient currents at the tip of soldering iron reaching 1000mA.

How Does the Noise Get on the Tip of the Soldering IronAlthough the tip of most professional-grade soldering irons is grounded quite sufficiently for DC and very low frequencies, at high frequencies the situation is quite different. Figure 5 shows how the soldering iron and a workbench look like at high frequencies. Several factors are at play (in no particular order of significance):

• Noise on power lines induces corresponding noise on ground via capacitive and inductive coupling as well as

via leakage currents.

• Switched power supplies (the ones that are used in soldering irons to convert 120/250V down to a typical 24V) can be transparent for high frequency signals due to a number of factors, parasitic capacitance being the dominant one. The noise from the mains thus can propagate to the low-voltage line of the iron’s heating element

• Switched power supply inside the soldering iron can be a source of noise by itself

• Iron’s heating element is capacitively coupled with the tip allowing propagation of high frequency signals

• Ground wires – from mains to the iron’s supply, from the iron’s supply to the iron itself and from the soldered object to the facility ground – have complex impedance, including resistance and inductance.

If the voltage on the tip is the same as the voltage on the PCB or on the soldered components, then there won’t be any current. At DC and 50/60Hz the grounding scheme of professional soldering irons typically works well. At high frequencies the voltage between the tip and the components is nearly impossible to equalize due the complex impedance of overall grounding wiring. This impedance causes, among other things, ground bounce [8] and phase shift, as well as resonance and ringing [9]. What sometimes aggravates the situation is that some factories opt for a separate “ESD Ground” – a different

Figure 5: Noise Propagation in the Soldering Iron

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grounding network which is eventually connected to a facility ground. The long wires in these two grounding networks leading to the soldering iron and to the workbenches greatly contribute to a voltage differential at high frequencies. Figure 6 shows the current from the tip of the iron in several situations with different distances between where the soldering iron is plugged in and grounding of the workbench/PCB. As seen, the difference in current reaches ~80%.

Soldering Iron PropertiesAre all soldering irons alike in generating and/or passing the noise down the tip? What about top-of-the line soldering irons? If there is a current from the tip of the soldering iron, does it mean that the iron itself is defective or unsuitable for work with sensitive components?

High-frequency currents from the tip of the professional-grade properly-installed iron are caused not by the iron itself, but by the reality of complex facility topology, wiring and operation of equipment. Soldering iron is just one component in soldering process and no matter how good it is, it cannot fundamentally solve the issues of facility by itself. In short, if you have a quality soldering iron, it is doing its job. It is a user’s task to provide safe EOS environment for the entire bench where the iron is only one of components.

Mitigating Effects of Transient Signals on Power Lines and GroundIf the sources of transient signals on power lines is known and can be removed without affecting production process, then the reduction of current from the tip of the soldering iron is relatively simple. However, too often the source is either unknown or cannot be removed. The only remaining options are grounding management and filtering out the transient signals on power lines and ground.

Grounding ManagementRe-routing of ground connection and separation of “noisy” ground from a clean one can help to reduce harmful currents. Techniques recommended and explained in this paper [4] help to alleviate some of the noise issues. Specifically, low impedance to facility ground and separation between “noisy” and “quiet” grounds

Figure 6: a) PCB is grounded ~1.5m from the iron b) PCB is grounded ~18” from the iron c) PCB is grounded next to the iron

Max(C1) 108.4mV

a

Min(C1) -26.0mV

5us/div

5us/div

5us/div

Max(C1) 57.2mV

b

Min(C1) -29.2mV

Max(C1) 22.3mV

c

Min(C1) -6.4mV

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Figure 7: Soldering Iron with Power Line EMI Filter (OnFILTER model APN515LG

and connecting soldering iron and the workbench to the “quiet” ground often result in lower level of transient signals.

As shown in Figure 6, grounding of the workbench and of the soldering iron as close as possible to each other can significantly reduce current exposure during soldering.

Grounding management alone, however, cannot satisfactory resolve noise issues since the source of EMI is not removed and the problematic signal still present in the soldering iron.

Filtering Out the NoiseUnless noise on power lines and ground is greatly reduces, there always will be a possibility of EOS

exposure during soldering. Two main scenarios are at play:

a)Noise is present both on ground and on power lines

b)Noise is present only on ground, but not strongly on power lines, i.e. noise on ground is coming from elsewhere in the factory

Power Line EMI FiltersThese filters suppress noise on power lines and provide load (in our case – soldering iron) with relatively clean power. Some EMI filters also suppress

noise in ground line.

Figure 7 shows recommended application of power line EMI filter with the soldering iron. It is important to connect ground of your workbench or tool to the ground terminal of the filter, not to the facility ground – the filter creates quiet “EMI ecosystem” at its output. Figure 8 shows the current from the tip of the iron used with OnFILTER’ APN515LG filter optimized for soldering process under the same noise on power lines as in Figure 4. As seen, the current from the tip becomes negligibly low.

This requires specially-designed filter optimized for soldering process properties – please refer to [9] for details.

Ground Line FiltersIf there is no appreciable noise on power lines, but ground has noise which is propagated from somewhere else, then a ground line filter may be a good alternative to a power line filter – it will be less expensive than a more complex power line filter. Connect ground line filter between your facility ground and your workbench/tool. Ground line filter needs to be selected properly in order to provide safe and noise-free environment.

ConclusionHigh-frequency signals on power lines and ground can cause high currents into sensitive devices during soldering resulting in electrical overstress and device damage. Proper analysis of the soldering environment, as well as any environment where conductive objects come

Figure 8: Soldering Tip Current After Power Line EMI Filter (OnFILTER Model APN515LG)

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in contact with the sensitive devices and implementation of preventive and corrective measures improves yield and reduces EOS-caused failures.

References1. Electrical Overstress (EOS) and Its Effects on Today’s Manufacturing, V. Kraz, Pulse Magazine, April 17, 2012 http://www.onfilter.com/library/eeweb-pulse-2012-42-OnFILTER, Inc.pdf

2. ESDA STM13.1-2000 http://www.esda.org

3. MIL-STD-2000 Military Standard: Standard Requirements for Soldered Electrical and Electronic Assemblies

4. IPC-A-610-E-2010, Acceptability of Electronic Assemblies, IPC https://portal.ipc.org/Association/Index.htm

5. IPC-7711B Rework, Modification and Repair of Electronic Assemblies, IPC https://portal.ipc.org/Association/Index.htm

6. AC Current Probes, Tektronix http://www.tek.com/sites/

tek.com/files/media/media/resources/60W_12572_2.pdf

7. EOS from Soldering Irons Connected to Faulty 120VAC Receptacles, Raytheon, W. Farrel et.al. ESD Symposium Proceeds, 2005

8. How Good is Your Ground? V. Kraz and P. Gagnon, Evaluation Engineering, 2001 http://www.onfilter.com/library/How Good Is Your Ground_.pdf

9. EOS Damage by Electrical Fast Transients on AC Power, A. Wallash, V. Kraz, Proceeds of ESD Symposium, 2010 http://www.onfilter.com/library/1B.2.pdf

About the AuthorVladimir Kraz is a founder and a president of OnFILTER, Inc. Prior to founding OnFILTER he started and was a president of Credence Technologies, Inc., a manufacturer of ESD and EMI instrumentation, which was acquired by 3M. Mr. Kraz holds 22 U.S. Patents and is active in ESD Association’ and SEMI Standards activities. He has written a number of papers on the subject of ESD and EMI physics and management, many of which can be found at http://www.onfilter.com/library.html. ■

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