UW Electrical & Computer Engineering

Electronic Components


Components of WEEE (e-waste)

Below, we chronicle the life-cycle of common electronic components found in major everyday products, including:


Transistors    |    Resistors    |    Capacitors    |    Diodes    |    Integrated Circuits    |    Printed Circuit Boards


Transistors-whiteWhat does a transistor do?


A transistor is an electronic device that is used in almost all integrated circuit “chips”, but it can also be sold in a “discrete” (single device) package.  When sold as a discrete device, the transistor often plays a key role in power electronics.  It is a major part of what it takes to control, convert, and condition currents and voltages associated with providing accurate and consistent power to many, many modern devices ranging from battery operated portable products to hybrid and electric vehicles to smart electric grid circuits.   When we think of transistors, we often think of microprocessors and memory, but the truth is, the market for discrete transistors is much, much larger than the market for integrated digital devices!


How many are there?


The worldwide market for transistors has slumped in the past few years to a mere $9 billion or so dollars, but has recovered and is expected to surpass $14 billion dollars in the coming years.  With an average selling price of less than a dollar, this can mean hundreds of billions of transistors purchased and used every year.  Imagine the waste stream for those that are no longer useful!


What are transistors made of?


Power transistors are most often made of silicon, the second most abundant element in the earth’s crust, after oxygen.   However, as applications for these transistors get demanding, Gallium Nitride (GaN) and Silicon Carbide (SiC) are getting  increasingly popular for the power electronics market.


Are transistors dangerous?


Left to themselves, discrete transistors are typically not toxic.  Silicon, Carbide, and Gallium are not toxic, nor are the plastic case or wires making up the package of the transistor.   Solder used to connect the transistors to the rest of the product may contain lead (Pb) which can cause nerve damage, reproductive problems, damage to the fetus in pregnant women, and poor muscle coordination.  Lead is an even more serious problem in children as it can delay neurological development and decrease IQ.   Fortunately lead-free (ROHS compliant) solders are available.   Some ceramic fillers used in discrete transistors and other discrete electronic components may contain alumina whose dust may cause lung disorders.  Plastic packages can also cause harm when burned.


What parts of a transistor can be recycled?1st-Transistor


The metal legs or leads can be separated from discrete transistors and recycled as scrap metal.   Unfortunately, the remainder of a transistor is typically not recycled and discarded as waste (although this waste is usually non-toxic).


What’s interesting about transistors?


The original transistor, built by Bell Labs in 1947, was large enough that it could be pieced together (assembled) by hand. By contrast, more than 100 million modern day transistors could fit onto the head of a pin.   The discrete power transistor lies somewhere in between these two extremes of size!





What does a resistor do?


Resistors are used in a wide variety of electronic circuits to limit current, reduce voltage, or control other key characteristics of circuit performance.   For example, a resistor can be used to limit the current travelling through an LED so that the LED is not damaged during operation.  Resistors can also be used to control the amount of amplification a circuit provides, the frequency at which filters begin to eliminate signals, the frequency at which antennas communicate, and so on.


How many are there?


Annual resistor sales are about $600 million.  At pennies per resistor, that’s BILLIONS AND BILLIONS of resistors sold EVERY year.


What is the resistor made of?


One of the most common (and most inexpensive) forms of resistor is the metal film resistor which contains (a) a metal (like nickel alloy) or metal oxide (like tin oxide) that is wound around (b) a ceramic filler and (c) connecting wires which are often soldered onto the body of the resistor.  The thicker the metal coating on the ceramic filler, the smaller the resistance.


Are resistors dangerous?


Lead (Pb) may be present in the solder (between connecting wires and the body of the resistor) which can cause neurological damage and cancer if ingested or inhaled. These risks can be avoided by staying away from eating resistors or shredding them, or by buying only ROHS compliant resistors (which do not contain Lead).


Some ceramic fillers may contain alumina whose dust may cause lung disorders.  This risk can be avoided by staying away from shredding resistors.


What parts of a resistor can be recycled?


The connecting wires (made of tinned copper plated steel) can be recycled at scrap metal recycling facilities.  The body of the resistor is typically relegated to a landfill.  However, resistors rarely fail and can be re-used over and over again if disassembled from printed circuit boards and other electronic assemblies.


What’s interesting about the resistor?


The value of the resistor is rarely printed on the resistor itself.  Instead, the first three colors indicate the value of the resistor (see color band calculator for how this works).   The last band of color indicates how accurate the resistor is.  For example, if the last band is gold, the actual value of the resistor will be within 5% of the value advertised by the other three color bands on the resistor.



What does a capacitor do?


Capacitors are energy-storing devices. A capacitor hinders the flow of electricity betweencapacitors two ends so that it can store that energy. This saved energy can be used later as needed. For example, once a capacitor gets charged, it can replace a battery in a circuit for a short period of time. Therefore, we can say that a capacitor acts like a battery. Most capacitors quickly run out of stored energy but unlike batteries, they be charged again very quickly and reused.


How many are there?


Annual capacitor sales are about $1,200 million. That’s about $3.50 per American.



What is the capacitor made of?


Capacitor is a sandwich that consists of: two electricity- conducting plates with an insulator in between. The insulator can be anything that does not conduct electricity, but most commonly used are paper, glass, rubber, ceramic, and plastic. The conducting plates can be any metal that lets electricity flow easily — for example, aluminum, tantalum, and silver.  In general, the smaller the distance between the metal plates, better the larger the capacitor and the more energy it can store.


Are capacitors dangerous?


Capacitors themselves are not dangerous. They are mostly dangerous when charged because of the energy stored in them. During direct contact, at low energy, a capacitor can give someone a electric shock. But at high energy for larger capacitors such as those used in heavy duty appliances like furnaces or in power systems, it can make a person unconscious or be potentially fatal.

Different capacitors use different types of metals; therefore, their health effects vary. For example, in the unlikely case that these metals are ingested or inhaled, direct consumption of aluminum or tantalum dust can cause respiratory problems and coughing.


What parts of a capacitor can be recycled?


Capacitors decay by developing higher internal resistance and losing their ability to store energy over time. A useful life of a discrete capacitor is about 700 hours. After some time, the leakage current in between the metallic plates increases, which allows the current to flow through the insulator between capacitor plates and defeating the intended operation of the capacitor.  Like resistors, when disposed of, small capacitors are typically disposed of as ordinary waste although e-waste recycling centers will accept these components for recycling.  Oil filled capacitors contain PCBs (polychlorinated biphenyls) which are toxic and should be treated as hazardous waste.


What’s interesting about the capacitor?


Some super-capacitors once fully charged and can store energy for years and years. Discharging a capacitor is more dangerous than charging them. If discharging is not done safely, a charged capacitor, even one from a device as small as a camera flash, can kill a human being


What does a diode do?


A diode is often referred to as a one way valve for electricity flow. Since electricity can only flow in one direction allowing the diode to also function as an inhibitor of electrical flow in the opposite direction. A diode consists of two terminals:  the anode and the cathode, which only allow current to pass when anode is made more positive than the cathode.  A mechanical analogy to the diode is a a water valve that only allows water to flow out, thus keeping water from back flowing into the main water lines that supply a property with water.  The one way behavior of a diode is used in a wide variety of electronic circuits ranging from voltage regulators to solar cell interface circuits to digital logic.  A light emitting diode (LED) is a special kind of diode that emits light when it is conducting electricity.


How many diodes are there?


LEDs alone are responsible for over $5 billion in sales ever year with discrete diodes accounting for another $4 billion in sales.  At less than a dollar per component, this amounts to billions and billions of diodes sold around the world each year.


What are diodes made of?


Diodes usually consist of semiconductor materials such as silicon (most common), selenium and germanium. Semiconductors are ideal for diodes in that their conductivity can easily be manipulated by adding impurities in a process known as doping. Doping increases the free number of electrons available to conduct electricity and also allows the one-way current flow characteristic of a diode to work properly. The most common semiconductors used for diodes are silicon and gallium arsenide, but the underlying semiconductor material in an LED determines its color:  indium gallium nitride (InGaN) for blue, green , and UV colors, aluminum gallium indium phosphide (AlGaInP) for yellow, orange, and red colors, and aluminum gallium arsenide (AlGaAs) for red and infrared colors.


Are diodes dangerous?


Some diodes contain trace amounts of heavy metals, like arsenic which, over chronic exposures, can cause cancer and neurological problems.  Diodes often use Indium which is a rare earth material which can lead to political tension, conflict, and violence as demand continues to rise for limited supplies in certain areas of the world.  LEDs containing blue light impair circadian rhythms and sleep when used as nighttime or evening lighting. Ultraviolet LEDSs cause damage to both skin and eyes but these are mostly common in medical procedures.


What parts of a diode can be recycled?


Discrete diodes and LEDs are often disposed of in landfills, but the presence of rare earth materials in many diodes is likely to lead to new recycling practices which recover these materials for reuse.


Interesting Facts about diodes


There are many different types of diodes including LEDs, Zener diodes, power rectifiers, and photodiodes. Although all diodes operate as one way valves for current flow, differences among them lead to different functions.  Photodiodes are used a light sensors.  Zener diodes are used to regulate voltage — providing a stable voltage in battery powered devices, for example.   LEDs are used in a broad range of electronic devices and appliances, including televisions and computer monitors.

Integrated Circuits

What does an integrated circuit do?


An integrated circuit (IC) is a small chip made out of a semiconductor material that can contain hundreds to billions of transistors. Normally, ICs are sealed in a familiar black plastic package. In an IC, thousands of small electronic components are interconnected and work as one functional circuit. An IC can perform various functions. It can work as an amplifier, oscillator, timer, counter, computer memory, or microprocessor. ICs are used in almost all electronic devices including audio and video equipment, computers, televisions, smartphones, and automobiles.


How many are there?


Annual IC sales for 2014 are about $4.405 million.


What is an integrated circuit made of?


An IC is made up of thousands of tiny (nanoscale or microscale) sized resistors, diodes, capacitors, and transistors that are fabricated on and integrated into a single silicon substrate.  Trace amounts of arsenic, phosphorous, aluminum, and other materials are used to control the behavior of these semiconductors to make complex circuits.  Gold is typically used to connect an IC to other electronic components in a device, appliance, or other electronic system.


Are ICs dangerous?


ICs may contain small amounts of aluminum and arsenic.  Lead may be contained in the solder that connects ICs to other electronic components.  Inhaling or ingesting lead or arsenic can cause neurological damage, some cancers, and respiratory problems. If inhaled, aluminum dust or power also causes respiratory diseases and lung disorders.


What parts of an IC can be recycled?


ICs use different types of metal wires to make electrical connections. These wires are made of metals such as gold, aluminum, copper, and lead. Precious metals can be extracted by recycling ICs using certain chemical processes which produce toxic byproducts in their own right.  The bulk of ICs though consist of silicon and plastic and at the present time, are not considered cost-effective to recycle and are disposed of in landfills and similar waste facilities.


What’s interesting about an IC?


An IC is usually only millimeters on a side and can contain millions or even billions of microscopic (or smaller) electrical components integrated to perform complex electronic functions. A typical IC has black body with many tiny silver legs, which makes it looks like a roach.


One of most complex and advanced ICs is a microprocessor. The microprocessor controls everything from computers and cellular phones to microwave ovens to robots to clothes dryers. For this reason, microprocessors and the ICs that contain them are called the heart and brains of most circuits.



Printed Circuit Boards

What do PCBs do?


A PCB (Printed Circuit Board) is a board, typically made of non-conductive FR-4 glass epoxy and coated with copper patterns that electrically connect points on the PCB together through traces and pads.   The electrical signal passed though PCBs allows power to be directed among a wide range of electrical components according to a desired electronic circuit design. (1,2)  When used in discussions of e-waste, the PCB often refers to the board, copper pattern, and all of the components assembled onto the board.


How many PCBs are there?


PCB industries have been seeing modest growth since 2013 although some fall back has been observed in recent years. Worldwide PCB manufacturing amounts to a market worth over $60 billion, while assembly of PCBs into working electronics amounts to over $2,000 billion every year.  In recent years, PCBs containing lead (Pb) based solder have dropped to less than 25% of overall PCB production.


What are PCB’s Composed of?


A PCB is composed of many layers of different materials, which are laminated together with heat and adhesive.  The materials starting from the base of the PCB include a substrate usually made up of FR-4 or fiberglass. Next is a layer of copper which is then laminated to the substrate. These layers may repeat depending on how complex and think the PCB is.  The layer above the final layer of copper is known as solder mask which helps insulate the copper from other traces of metal, this layer also gives the PCB its green color. The upper layer of the PCB is the silkscreen which consists of letters, number and symbols  which allow for better assembly and understanding of the PCB.  Assembled onto the PCB are resistors, capacitors, transistors, integrated circuits, switches, and a variety of other electronic components that make the PCB heterogenous and complicated to recycle and dispose of in an efficient and safe way.


Are PCBs dangerous?


PCB’s can cause a variety of adverse health affects if not disposed of or recycled correctly. Ironically, the PCB becomes a more serious hazard to human health and environment when it is recycled without proper regulation and oversight as opposed to simply dumping it into a landfill.   Attempts to shred, dismantle, and burn PCBs during recycling, and to extract precious metals from these electronics during recycling often lead to releases of a variety of toxins in air, soil, and water.   Improper burning and shredding releases toxic fumes as well as dangerous particles into the air which depending on their chemistry and size can travel many miles from their point of origin.   Treating PCBs to extract precious metals and other valuable materials can release acids and toxins into surface water ways and nearby soils.   Toxins released through improper recycling of PCBs can range from heavy metals including lead, cadmium, and mercury to the most toxic substances on earth:  dioxins and furans.


What parts of  PCB can be recycled?


PCBs can be shredded, dismantled, and processed so that valuable precious metals and other materials are separated from other low-value materials.  Most urban locations in the United States have recycling facilities available for PCBs. Recycling is commonly done in both regulated and informal recycling facilities, although the former are far less dangerous to human health and ecosystem health than informal or unregulated efforts.


Interesting facts about PCBs

Most printed circuit boards are green primarily because many are made from a glass-epoxy which is naturally green.


Static electricity can damage components on PCBs and though it would be very difficult to tell, it is possible to blow copper traces right off of a PCB with enough static energy.


Printed Circuit Boards (PCBs) share an acronym with polychlorinated biphenyls (PCBs). The former are far less toxic and dangerous than the later although many PCBs contain PCBs.

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© 2015 Denise Wilson and Rachel Roberts