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Aerospace and Military
Aerospace and Military designs have one primary requirement that may be summed up in two words – high reliability. Designs must also be amenable to fast implementation and testing within the imposed severe environmental conditions. In other words, the time from design concept to production must be as short as reasonably possible. Obviously, vendors with a good track record in this area are normally desired by the customer. A vendor with an excellent Quality Management System is looked upon favorably by these high technology customers.
Established in 1986, Aptek Laboratories, Inc., Valencia, California provides custom formulated adhesives, coatings, encapsulants, and specialty fabricated films/substrates to highly sophisticated end users such as Boeing Satellite Systems, Raytheon Company, Northrop Grumman/Litton, Lockheed Martin, Delco, TRW, and many others. To support the requirements and technical demands of these customers, Aptek devotes a major portion of its resources for research and development, technical service, quality assurance, and state-of-the-art production equipment. Although Aptek has targeted high-tech applications as a major market thrust, this same philosophy and expertise is applied to the high-end commercial markets as well.
Atomic Oxygen Resistant
Single oxygen atoms are monatomic as compared to regular oxygen molecules (two oxygen atoms) found in air. Monatomic oxygen is found in the upper atmosphere where it has been created by solar radiation. It is extremely reactive and corrodes most materials rapidly. There are many fine articles on Atomic Oxygen. The reader is directed to the site of the Infrared Multilayer Laboratory for more information. Aptek has developed several space grade adhesives and coatings which through field-evaluations are verified to be resistant to monatomic oxygen. APTEK 2719 A/B, a thermal radiative coating, is an example of this technology.
The registered trademark of Aptek Laboratories, Inc. for their unique family of adhesives designed to bond dissimilar, thermally-mismatched components and substrates. B/C/B are low modulus, flexible, void-free and electrically insulating hybrid urethane films. DAT-A-THERM 1303 B/C/B describes one of these film adhesives in detail while a more in-depth discussion of B/C/B may be found in the Tutorial section.
Ball Grid Array (BGA)
A ball grid array is a type of surface-mount packaging used for integrated circuits. See the Tutorial section for further information.
The intermediate stage during the curing process of a thermosetting resin when the material has gelled but is only partially cured is defined as B-Stage.
Coefficient of Thermal Expansion (CTE)
The symbol for Coefficient of Thermal Expansion is alpha, a. During heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. When the stored energy increases, so does the length of the molecular bond. As a result, solids typically* expand in response to heating and contract on cooling; this response to temperature change is expressed as its coefficient of thermal expansion:
The coefficient of thermal expansion is used:
- in linear thermal expansion
- in area thermal expansion
- in volumetric thermal expansion
These characteristics are closely related. The volumetric thermal expansion coefficient can be measured for all substances of condensed matter (liquids and solid state). The linear thermal expansion can only be measured in the solid state and is common in engineering applications.
*Some substances have a negative expansion coefficient, and will expand when cooled (e.g. freezing water).
The above, from Wikipedia, is further explained here.
A material applied to electronic circuitry to act as protection against moisture, dust, chemicals, and temperature extremes that if left uncoated could result in a failure of the electronics system. The primary specification for military conformal coatings is MIL-I-48056C. Aptek Labs has several coatings based on epoxy and urethane technologies, as well as UV cured coatings, that meet this specification. Aptek has the only known urethane conformal coating (APTEK 2512-A/B) that is military approved and also resistant to JP 10 fuel.
A thermosetting polymer that is essentially fully cross-linked and cured is defined as C-Stage
A custom formulator will manufacture a material exclusively for you to your exact specifications. These custom formulations could range in complexity from a single ingredient to many different components and as such might involve the development of a new formulation to that of modifying an existing material. Aptek Labs has an extensive reputation and expertise in custom formulating and has found that many times that they already have an existing custom formulation that meets the customer's needs. Actually, the trademarked motto of Aptek Laboratories, Inc. is "Formulations Are Your Solutions"
A trademark of Aptek Laboratories, Inc. for a flexible, void-free, thermoset urethane polymer that is designed to fill air gaps and dissipate heat between devices and substrates. This material has excellent hydrolytic stability as well as being low outgassing.
The relative dielectric constant of a material under given conditions is a measure of the extent to which it concentrates electrostatic lines of flux. It is the ratio of the amount of stored electrical energy when a potential is applied, relative to the permittivity of a vacuum. The relative dielectric constant is also called relative static permittivity. This complex subject is covered in more detail by Wikipedia in an article here.
A registered trademark of Aptek Laboratories, Inc. for their family of thermally conductive adhesives.
A trademark of Aptek Laboratories, Inc. for tiles that are fully-crosslinked, low density, composite foam substrates which exhibit a low dielectric constant and low loss tangent characteristics in the microwave frequency range. Aptek Labs specializes in customizing these substrates to meet clients' exact needs. A representative selection guide of several custom tuned dielectric substrates developed by Aptek Labs for patch radiator applications may be found on the Aptek website under Products/Microwave/RF substrates.
Materials that are friendly to the environment including coatings with low or no Volatile Organic Materials (VOC), or can cure at room or low temperature, or have the capability to cure fast (snap cure) to minimize heating times. Also included are UV-cured materials, lead-free adhesives that substitute for solder and advanced thermal coatings that improve solar panel efficiencies. Eco-Friendly materials are discussed further in the Tutorials section.
Electrically Conductive Adhesive
An adhesive that exhibits electrical conductivity and allows the passage of current. With rare exception, adhesives obtain their conductivity characteristics through the incorporation of conductive fillers. One must be careful in selection of electrically conductive adhesives since their initial properties may deteriorate over time in specific environments. For detailed information, contact a well-experienced formulator such as Aptek Laboratories, Inc. who has extensive expertise with electrically conductive adhesives.
Electro Static Discharge (ESD)
Electrostatic discharge (ESD) is the sudden and momentary electric current that flows between two objects at different electrical potentials. The term is usually used in the electronics and other industries to describe momentary unwanted currents that may cause damage to electronic equipment. Further information on ESD may be found in the Tutorials section.
Fiberoptics is the technology of the transmission of light signals via glass fibers. An excellent Tutorial on the Basics of Fiber Optic Cable may be found here.
Normally defined as 20 mils thickness or less, may be conductive or non-conductive. Aptek Labs produces various films such as DAT-A-THERM 1000, THERMPAD™, and B/C/B films for a variety of applications
Glass Transition Temperature, Tg
The glass transition temperature , Tg, is really a range of temperature. Upon cooling, a resin passing through it will have its mechanical properties change from those of a rubber (elastic) to those of a glass (brittle). Similarly, vice versa, in which heating a resin thought Tg, will change properties from brittle to elastic. This is a critical material's property and is discussed in detail in the Tutorial section.
High Performance Polymer
Polymers that are designed with the ability to perform reliably for a given application. Typically in the aerospace and high technology industries, a high performance polymer may require high and low temperature characteristics, excellent hydrolytic stability and low outgassing among its requirements.
High Temperature Materials
High temperature is a relative term depending upon application. For thermosetting polymers, silicones and poyimides with capabilities over 250 degrees F are common.
Under various conditions of temperature and humidity, many polymers will weaken and possibly revert back to its liquid state under extreme conditions. There are numerous accelerated tests to determine the potential ability of a polymer's hydrolytic stability. Aptek Labs has extensive experience and expertise in this area and has incorporated excellent hydrolytic stability into all of its products.
Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of microwaves. Infrared radiation has wavelengths in the range of 750 nm to 1 mm.
Infrared light emitting diodes are basically a display technology that uses a semiconductor diode that emits visible light or invisible infrared radiation when charged. IR LED lamps, provide illumination for infrared-sensitive equipment for capturing images in total darkness or in low-light conditions.
Iridium is one of the transition elements and is a member of the platinum family of metals. It has a symbol "Ir" and an Atomic Number of 77. The registered trademark Iridium is that of Iridium LLC, a world-wide satellite telephone system that uses low-orbit satellites to provide universal global communications coverage. Aptek Labs developed the patch radiator tiles for the Iridium program. This was a most demanding task in that the foam tiles had critical low dielectric constant. low loss factor, low density, low outgassing and high strength requirements. Aptek Labs is a world-leader in custom formulating microwave/RF dielectric substates as well as producing a family of DI-STRATE dielectric substrate materials.
ISO 9001-2000:AS9100B Revision B Certified
Aptek Laboratories, Inc. has been awarded certification to SAE International Standard AS9100 Revision B. This is a Quality Management System for aerospace requirements. This standard is being increasingly used by aerospace companies because it meets the compliance and registration requirements of ISO 9000 while providing increased assurance of meeting the stringent and complex aerospace requirements for reliability, maintainability and safety. AS9100B places emphasis on the design and development process, risk identification, main characteristics and supply chain quality. The Certificate of Registration to Aptek Laboratories, Inc. was issued by ISA International Standards Authority, Inc., Chino, CA. (www.isaregistrar.com)
Jet Fuel Resistant Conformal Coating
A key missile manufacturer has an additional requirement beyond MIL-I-46058C for resistance to JP 10 aviation fuel. Aptek Labs has developed a JP 10 fuel resistant coating that meets this MIL specification and has excellent resistance to JP 10 aviation fuel. This coating is identified as APTEK 2512-A/B. This is the only known coating qualified to the MIL specification that is also JP 10 resistant.
In the microwave industry, K is a symbol for Dielectric Constant.
Chemically, K is the symbol for the element Potassium.
Loss Factor (Dielectric)
Loss factor, or more correctly dissipation factor (DF), is a measure of loss-rate of power of a mechanical mode, such as an oscillation in a dissipative system. This is further explained in Wikipedia as follows: Electric power is lost in all dielectric materials, usually in the form of heat. DF is expressed as the ratio of the resistive power loss to the capacitive power, and is equal to the tangent of the loss angle. For example, electric power is lost in all dielectric materials, usually in the form of heat. DF is expressed as the ratio of the resistive power loss to the capacitive power, and is equal to the tangent of the loss angle. It is also referenced as the loss tangent d, and approximate power factor. Please refer to the complete Wikipedia article here.
Low Solar Absorptance Coatings
A material's absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. An absorption spectrum is basically the opposite of an emission spectrum. Low absorptance coatings with control emittance are used in spacecraft to control temperatures within the craft. Aptek Labs has done considerable work in this area and supplies both space grade thermal control and electrostatic discharge control coatings.
Low Modulus Materials
Low modulus materials are typically soft elastomeric materials with modulus values being orders of magnitude less than hard brittle materials or metals. The modulus is an important design feature from its initial value to how it may change during temperature cycling. See Modulus (below) or Glass Transition Temperature (above).
Material Types and Characteristics
polyurethane is any polymer consisting of a chain of organic units joined by urethane links. Polyurethane polymers are formed by reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two alcohol groups in the presence of a catalyst. Polyurethane formulations cover an extremely wide range of properties with applications within the high-technology area for adhesives, coatings, encapsulants and staking compounds. Polyurethane formulations are a major factor in numerous Aptek Labs products.
An epoxy is a thermosetting epoxide polymer that cures (polymerizes and crosslinks) when mixed with a catalyzing agent or hardener. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A. Epoxies are typically strong hard materials with excellent adhesion and are capable of being modified or incorporated into hybrid resin formulations.
A silicone, more precisely called polymerized siloxanes or polysiloxanes, silicones are mixed inorganic-organic polymers with the chemical formula [R2SiO]n, where R = organic groups such as methyl, ethyl, and phenyl. These materials consist of an inorganic silicon-oxygen backbone (…-Si-O-Si-O-Si-O-…) with organic side groups attached to the silicon atoms, which are four-coordinate. In some cases organic side groups can be used to link two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a wide variety of properties and compositions. They can vary in consistency from liquid to gel to rubber to hard plastic. The most common siloxane is linear polydimethylsiloxane (PDMS), a silicone oil. The second largest group of silicone materials is based on silicone resins, which are formed by branched and cage-like oligosiloxanes. For further explanation visit Wikipedia here.
A polyimide is an aromatic polyimide made by reacting pyromellitic dianhydride with aromatic diamines. The polymer is characterized by the fact that it has rings of four carbon atoms tightly bound together which gives it improved high temperature resistance.
A polyacrylate is based on the acrylate ion (CH2=CHCOO−)which is the ion of acrylic acid. Acrylates are the salts and esters of acrylic acid. Acrylates contain vinyl groups, i.e., two carbon atoms double bonded to each other, directly attached to the carbonyl carbon. Acrylates and methacrylates (the salts and esters of methacrylic acid) are common monomers in polymer plastics, forming the acrylate polymers. Acrylates easily form polymers because the double bonds are very reactive. Many acrylate systems can be cured by ultraviolet (UV) radiation.
Specialty hybrid resins find applications where the desired features of two different resin systems are found to be attained as a mixture. Aptek Labs has considerable experience with hybrids. For example, Aptek has been certified to MIL-I-46058 for special hybrid resins that are an acrylate-urethane blend.
Microelectronics is a subfield of electronics and is related to the development and manufacture of electronic components. Many special materials for a variety of applications are required within the field for microelectronic equipment.
A microwave antenna operates within the range of frequencies 300 MHz to 300GHz. These include Ultra High Frequency (UHF) between 300 MHz to 3 GHz, Super High Frequency (SHF) between 3 GHz to 30 GHz and Extremely High Frequency (EHF) from 30 GHz to 300 GHz.
MIL-I-46058C Conformal Coating
The specification for conformal coatings approved for military applications. This specification covers five material types, namely, acrylic (AR), epoxy (ER), silicone (SR), polyurethane (UR) and paraxylylene (XY). A copy of the specification and the Qualified Products List (QPL) may be found here.
Aptek Labs has several conformal coatings that are qualified including Uvikote 7503 LM-A/B, Uvikote 7503 LM-PMF, Uvikote 7504 LM-A/B, Uvikote 7504 LM-PMF, APTEK 2503 A/B and APTEK 2503-A/B High Solids. If you want to know which is best for your application, contact Aptek Labs Technical Support (Phone 661/257-1677; Email: firstname.lastname@example.org.
Military Grade Polymer
Military grade polymer polymers are typically high performance polymers that usually have additional requirements. For example, for space applications a requirement for resistance against monoatomic oxygen may be imposed. Of particular concern to applications using military grade polymers is that of Life Cycle. The material must have a long life cycle without degradation (or with known minimal degradation rates) so that the equipment and system meets its mission. This is reflected in the stringent requirements of ISO 9001:2000 AS9100 Rev. B that is imposed upon suppliers to the military. To be certified to these documents (as Aptek Labs is) indicates a high level of confidence in the certified organization by the military and major suppliers.
Modulus, or more specifically, Young’s Modulus (symbolized as E), is a measure of a material’s stiffness. For small strains, modulus is defined as the ratio of stress divided by strain. Thus, in English units, stress (force/unit area divided by elongation, i.e., change in length divided by length) is shown in psi (pounds per square inch). In SI units, modulus is shown in pascals (newtons/meter squared). Modulus is discussed further in the Tutorial section. Of prime importance is the effect of temperature changes upon modulus particularly if the temperature goes into or through the glass transition zone.
Nanotechnology is a wide area of research, development and industrial activity that has been growing rapidly. It is a multidisciplinary technology wherein the defining characteristic is one of size. It involves the manufacture, processing and application of materials that are in the size range of up to 100 nanometers (nm). Nanotechnology materials also known as nanoparticles can be any shape and about any physical condition, i.e., aggregated , conglomerated, tubular, spherical, etc. Materials include carbon in many forms, nickel, silver and many others. The National Science Foundation is the US government's spearhead for nanotechnology. They have described nanotechnology as "science and technology on the scale of a nanometer--one billionth of a meter--is revolutionary. Nanotechnology refers to the ability to manipulate individual atoms and molecules, making it possible to build machines on the scale of human cells or create materials and structures from the bottom up with novel properties. Nanotechnology could change the way almost everything is designed and made, from automobile tires to vaccines to objects not yet imagined." Aptek is pursuing several nanotechnology areas to develop high thermal conductivity and also high electrical conductivity materials.
NASA Outgassing Requirements
Only materials that meet the criteria of ASTM E-595-77/84 [i.e., have a total mass loss (TML) < 1.0% and a collected volatile condensable mass (CVCM) < 0.10%] are approved for use in a space environment unless application considerations dictate otherwise. The outgassing test is conducted in a vacuum of 10-6 Torr at a temperature of 125 deg. Centigrade with a test exposure time of 24 hours. The equipment and test procedures required to conduct the outgassing test are defined by ASTM E-595-77/84. An enhanced explanation can be found on the NASA web site here.
Aptek Labs has over twenty years experience in developing materials that meet and exceed NASA outgassing requirements. If you have a design for space, contact Aptek Labs for guidance on space-approved materials.
Optoelectronics is the study and application of electronic devices that interact with light and other electromagnetic radiations. As such, many devices require materials for encapsulating wherein the encapsulants must have special properties. For example, the encapsulant may be required to be transparent to Infrared (IR) while blocking out visible light. Other examples might include encapsulants required to have a specific viscosity for blob top applications or special chemical compatibility such as not affecting polysulphone casings. Aptek Labs has extensive Optoelectronic materials experience on a global arena.
See NASA Outgassing Requirements above.
A typical microwave microstrip patch radiator consists of a metallic half-wave length (at the operating frequency) microstrip resonator placed above a ground plane separated by a dielectric. The patch radiator can be fed directly or capacitively by a microstrip line, a coaxial probe coming up through the ground plane or a slot in the ground plane directly underneath the patch. The bandwidth of a patch radiator is narrow, typically 2%, but can be increased by increasing the ground plane spacing or adding a second resonant patch above the first patch creating a stacked patch configuration. A typical patch radiator substrate has a dielectric constant around 2.0 and a loss tangent less than 0.008. For a stacked patch, the upper substrate should have a dielectric constant around 1.2 to 1.4. Patch radiators can be fabricated using standard printed circuit board (PCB) techniques making them low cost and allowing for conformal mounting to any surface. Patch radiators are desirable since an array of them can be conformally contoured to a curved surface, such as an airplane body, as well as using them in a flat array. Typical dielectric materials for patch radiators have been limited to only a few materials with standard thicknesses and dielectric constants.
However, APTEK Laboratories, Inc. has developed light-weight syntactic foam substrate materials that have low loss, available with any specified dielectric constant, can be fabricated or machined to any thickness with good strength properties as well being suitable for space use. This is a major breakthrough in the technology. See the information on DI-STRATE materials above.
Pre-Mixed Frozen refers to how a particular polymer system is packed. Typically, the materials (resin and curing agent) are mixed in the proper ratio by the supplier, dispensed into a container (such as a syringe) and immediately frozen. This is ideal for both large scale production users as while as a low volume user. The mixing proportions are correct, the material is in an appropriate container and all the user has to do is thaw (naturally or with a little help as heat or microwave heat) and apply. Aptek Labs is one of the pioneers in Pre-Mixed Frozen technologies.
Production-Friendly Products take many forms The Pre-Mixed Frozen materials are a prime example of a Production-Friendly material for a user. In essence, many Eco-Friendly materials are Production-Friendly Products in that cure variations are available that give the user options on how best to use based on their requirements. UV-cured materials are production-friendly in that they cure quickly without the use of heat. Snap cure materials are also production-friendly being fast-production amenable. A user of materials should know his/her options with any material before committing to production.
Quality Management System
This can be defined as a set of policies, processes and procedures required for planning and execution (production/development/service) in the core business area of an organization. QMS integrates the various internal processes within the organization and intends to provide a process approach for project execution. QMS enables the organizations to identify, measure, control and improve the various core business processes that will ultimately lead to improved business performance. See Wikipedia for more details if needed. Aptek Labs is proud to be certified to the Quality Management System defined as ISO 9001:2000/AS 9100 Revision B.
Radio/Frequencies (RF) frequencies range from about 3Hz to 300GHz, while microwave frequencies range from about 300Mhz to 300Ghz. See Microwave Antenna above.
RF/Microwave Substrates, Custom Tuned
See DI-STRATE and also patch radiator.
Most acrylate coatings that cure by exposure to UV light do not cure when they are under a component and shielded from the UV source. To effect a cure, i.e., curing of an acrylate that is shielded, a shadow cure acrylate is needed. This material will normally cure at room temperature over several weeks period or faster with some added heat. Aptek Labs has developed UVIKOTE 7503-PMF which is a shadow curing acrylate.
SMT - Surface Mounted Technology / High End Electrical
is a method of fabricating electrical or electronic circuits where the components are mounted directly onto a substrate such as a printed circuit board. Wikipedia points out that SMT components are usually smaller than its leaded counterpart because it has smaller leads or no leads at all. It may contain short pins or leads of different styles, flat contacts, a mixture of balls (ball grid array), or terminations on the body of the component. Aptek Labs has developed a thermally conductive material, DIS-A-PASTE 2150-PMF, for BGA underfills. A technical article discussing this material may be found in the Aptek Labs website under Custom Formulations/BGA Underfill/Technical Article. Check out Wikipedia here for more information on Surface Mount Technology in general.
Snap-cure technology is production-oriented, for surface mount applications-allows cure during solder reflow operation. Aptek Labs has developed DIS-A-PASTE 2311-PMF thermally conductive adhesive which is high thixotropy/tack strength and holds components with minimal Z axis movement during cure. It has a stable viscosity for over 4 hours at RT- ideal for robotics. Low Tg (<50ºC) for low temperature cycling and performance with minimal stress. Excellent substrate adhesion; superior to silicones; no primer required.
Space Grade Polymer
There is no standard definition for space grade polymer. Typical features normally required for a polymer in space would include high and low temperature capabilities, low outgassing, long life cycle, resistance to monatomic oxygen, and obviously nonflammable. Processing characteristics should include being manufacturing-friendly. Financial considerations for material cost is also needed.
Staking compounds provide stress relief to components on a printed wiring board or similar device. The designer should be aware that all staking compounds are not equal. Some staking materials when improperly selected or used can actually introduce problems. The NASA Workmanship Technical Committee has published excellent guidance on its website here. Aptek Labs is a leader in staking compoud materials - contact them if you need further assistance.
Stealth Technology Materials
Stealth technology covers many areas. An excellent summary on stealth technology published by the U.S. Centennial on Flight Commission may be found here. Aptek Labs has developed several coatings, sealants and adhesives that have stealth technology capabilities in that they absorb incoming electromagnetic radiation. For further details contact Aptek Labs Technical Support (Phone 661/257-1677; Email: mailto:email@example.com
Stress is induced in any design where the coefficients of thermal expansion of various components and substrates to be bonded are mismatched. The management of these stresses can only be accomplished after numerous considerations and applications. The full paper on this subject entitled "Stress Management Via Low Modulus Urethane Adhesives For Electronic Applications" written by Aptek Labs may be found on the Aptek website under Technical Articles.
See Glass Transition Temperature
Management of the effects of heat (high and/or low temperature) upon an electronics component, device or system.
Thermally Conductive Adhesive
An adhesive that exhibits thermal conductivity and allows for the passage of heat. With rare exception, adhesives obtain their conductivity characteristics through the incorporation of thermally conductive fillers. One must be careful in selection of thermally conductive adhesives since their initial properties may deteriorate over time in specific environments. For detailed information, contact a well-experienced formulator such as Aptek Laboratories, Inc. who has extensive expertise with thermally conductive adhesives.
Thermally Radiative Coatings
Coatings with a high degree of radiating incoming thermal radiation.
Aptek Labs trademark includes THERMPAD 1000 their C-stage silicone pad that is thermally conductive, very low outgassing and has a low Tg of -110° C for space applications.
A thermoplastic is a material that is plastic or deformable, melts to a liquid when heated and freezes to a brittle, glassy state when cooled sufficiently.
Capable of being changed into a substantially infusible or insoluble product when cured under application of heat or chemical means.
A registered trademark of Aptek Laboratories, Inc. for their family of ultra-violet (UV) cured adhesives.
Material systems that polymerize (cure) from exposure to ultraviolet light. Ultraviolet light has typical wave lengths of 400-200 nm. Aptek Labs has extensive expertise with UV-cured materials and further information may be found under Technical Articles in the paper entitled "Unique UV Adhesives, Coatings and Encapsulants".
A registered trademark of Aptek Laboratories, Inc. for their family of ultra-violet (UV) cured coatings.
A registered trademark of Aptek Laboratories, Inc. for their family of ultra-violet (UV) cured staking materials.
Volatile Organic Materials (VOCs) - A category of volatile organic compounds with relatively high vapor pressures, a major category of air contaminants. Most VOCs are carbon-hydrogen compounds (hydrocarbons), but they also may be aldehydes, ketones, chlorinated hydrocarbons, and others. Thousands of individual compounds exist, including the unburnt hydrocarbon compounds emitted from automobiles or industrial processes and the organic solvents lost to evaporation from household, commercial, or industrial cleaning and painting operations, and other activities. Some VOCs participate in the atmospheric reactions that lead to photochemical air pollution, and excessive exposure to certain individual compounds is associated with skin irritation, central nervous system depression, and/or an increased risk or cancer.
The process of connecting the pads on an unpackaged integrated circuit to corresponding pads on a substrate using wires that are finer than a human hair. Wire bonding may also be used to connect the pads on an unpackaged integrated circuit, hybrid, or multichip module to the leads of the component package.
Similar in principle to optical lithography, but capable of constructing much finer features due to the shorter wavelengths involved. However, X-ray lithography requires an intense source of X-rays, is more difficult to use, and is considerably more expensive than optical lithography.
The number of devices that work as planned, specified as a percentage of the total number actually fabricated.
The symbol used to represent the high-impedance state in tri-state logic.