Divyanshu67/squad_v2 huggingface dataset:
Bacteria

Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids. In contrast, gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. Lipopolysaccharides, also called endotoxins, are composed of polysaccharides and lipid A that is responsible for much of the toxicity of gram-negative bacteria. Most bacteria have the gram-negative cell wall, and only the Firmicutes and Actinobacteria have the alternative gram-positive arrangement. These two groups were previously known as the low G+C and high G+C Gram-positive bacteria, respectively. These differences in structure can produce differences in antibiotic susceptibility; for instance, vancomycin can kill only gram-positive bacteria and is ineffective against gram-negative pathogens, such as Haemophilus influenzae or Pseudomonas aeruginosa. If the bacterial cell wall is entirely removed, it is called a protoplast, whereas if it is partially removed, it is called a spheroplast. β-Lactam antibiotics, such as penicillin, inhibit the formation of peptidoglycan cross-links in the bacterial cell wall. The enzyme lysozyme, found in human tears, also digests the cell wall of bacteria and is the body's main defense against eye infections.

Question: What does gram-positive bacteria have?
Answer: thick cell wall containing many layers of peptidoglycan and teichoic acids

Question: What can be endotoxins called?
Answer: Lipopolysaccharides

Question: Why gram-negative cell bacteria is more toxic than gram-positive bacteria?
Answer: polysaccharides and lipid A

Question: What can different structure of the cell walls of bacteria effect?
Answer: differences in antibiotic susceptibility

Question: What is the main defense of human body against eye infections?
Answer: enzyme lysozyme, found in human tears
Bacteria

Acid-fast bacteria, such as Mycobacteria, are resistant to decolorization by acids during staining procedures. The high mycolic acid content of Mycobacteria, is responsible for the staining pattern of poor absorption followed by high retention. The most common staining technique used to identify acid-fast bacteria is the Ziehl-Neelsen stain or acid-fast stain, in which the acid-fast bacilli are stained bright-red and stand out clearly against a blue background. L-form bacteria are strains of bacteria that lack cell walls. The main pathogenic bacteria in this class is Mycoplasma (not to be confused with Mycobacteria).

Question: What helps Mycobacteria be resistant to decolorization?
Answer: high mycolic acid content

Question: What is mycolic acid is responsible for in Mycobacteria?
Answer: staining pattern of poor absorption followed by high retention.

Question: What is the most typical staining technique used to identify acid-fast bacteria?
Answer: Ziehl-Neelsen stain

Question: What is the main pathogenic bacteria in L-form class ?
Answer: Mycoplasma
Bacteria

Fimbriae (sometimes called "attachment pili") are fine filaments of protein, usually 2–10 nanometres in diameter and up to several micrometers in length. They are distributed over the surface of the cell, and resemble fine hairs when seen under the electron microscope. Fimbriae are believed to be involved in attachment to solid surfaces or to other cells, and are essential for the virulence of some bacterial pathogens. Pili (sing. pilus) are cellular appendages, slightly larger than fimbriae, that can transfer genetic material between bacterial cells in a process called conjugation where they are called conjugation pili or "sex pili" (see bacterial genetics, below). They can also generate movement where they are called type IV pili (see movement, below).

Question: What are fimbriae?
Answer: fine filaments of protein

Question: What is the diameter of fimbriae?
Answer: 2–10 nanometres

Question: What are fimbriae liable for?
Answer: involved in attachment to solid surfaces or to other cells

Question: What are pili?
Answer: cellular appendages
Bacteria

Bacteria exhibit an extremely wide variety of metabolic types. The distribution of metabolic traits within a group of bacteria has traditionally been used to define their taxonomy, but these traits often do not correspond with modern genetic classifications. Bacterial metabolism is classified into nutritional groups on the basis of three major criteria: the kind of energy used for growth, the source of carbon, and the electron donors used for growth. An additional criterion of respiratory microorganisms are the electron acceptors used for aerobic or anaerobic respiration.

Question: What is commonly used to determine taxonomy of bacteria?
Answer: The distribution of metabolic traits

Question: How is bacterial metabolism determined?
Answer: nutritional groups

Question: What are three main criterias of bacterial metabolism?
Answer: the kind of energy used for growth, the source of carbon, and the electron donors

Question: What are electron acceptors accountable for?
Answer: aerobic or anaerobic respiration
Bacteria

Bacteria are further divided into lithotrophs that use inorganic electron donors and organotrophs that use organic compounds as electron donors. Chemotrophic organisms use the respective electron donors for energy conservation (by aerobic/anaerobic respiration or fermentation) and biosynthetic reactions (e.g., carbon dioxide fixation), whereas phototrophic organisms use them only for biosynthetic purposes. Respiratory organisms use chemical compounds as a source of energy by taking electrons from the reduced substrate and transferring them to a terminal electron acceptor in a redox reaction. This reaction releases energy that can be used to synthesise ATP and drive metabolism. In aerobic organisms, oxygen is used as the electron acceptor. In anaerobic organisms other inorganic compounds, such as nitrate, sulfate or carbon dioxide are used as electron acceptors. This leads to the ecologically important processes of denitrification, sulfate reduction, and acetogenesis, respectively.

Question: What do lithotrophs use ?
Answer: inorganic electron donors

Question: What type of electron donors organotrophs use?
Answer: organic compounds

Question: What do respiratory organisms use as electron donors?
Answer: chemical compounds

Question: In what organisms is oxygen used as eelectron acceptor?
Answer: anaerobic organisms
Bacteria

Regardless of the type of metabolic process they employ, the majority of bacteria are able to take in raw materials only in the form of relatively small molecules, which enter the cell by diffusion or through molecular channels in cell membranes. The Planctomycetes are the exception (as they are in possessing membranes around their nuclear material). It has recently been shown that Gemmata obscuriglobus is able to take in large molecules via a process that in some ways resembles endocytosis, the process used by eukaryotic cells to engulf external items.

Question: How can bacteria obtain raw materials from the environment?
Answer: in the form of relatively small molecules

Question: What chemical process  helps bacteria to absorb raw materials?
Answer: diffusion

Question: What process is used by eukaryotic cells to absorb external items?
Answer: endocytosis

Question: What part of bacteria cell is used during diffusion?
Answer: molecular channels in cell membranes
Bacteria

In the laboratory, bacteria are usually grown using solid or liquid media. Solid growth media, such as agar plates, are used to isolate pure cultures of a bacterial strain. However, liquid growth media are used when measurement of growth or large volumes of cells are required. Growth in stirred liquid media occurs as an even cell suspension, making the cultures easy to divide and transfer, although isolating single bacteria from liquid media is difficult. The use of selective media (media with specific nutrients added or deficient, or with antibiotics added) can help identify specific organisms.

Question: In what environment are bacteria being cultivated in labs?
Answer: solid or liquid media

Question: What is typical solid setting?
Answer: agar plates

Question: Which media is preffered to grow larger volumes of bacteria?
Answer: liquid growth media

Question: Which environment is better to isolate a single example of bacteria strain?
Answer: agar plates

Question: What can help to indentify specific bacteria?
Answer: The use of selective media
Bacteria

Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment. The first phase of growth is the lag phase, a period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth. The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The second phase of growth is the log phase, also known as the logarithmic or exponential phase. The log phase is marked by rapid exponential growth. The rate at which cells grow during this phase is known as the growth rate (k), and the time it takes the cells to double is known as the generation time (g). During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth is the stationary phase and is caused by depleted nutrients. The cells reduce their metabolic activity and consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repair, antioxidant metabolism and nutrient transport. The final phase is the death phase where the bacteria run out of nutrients and die.

Question: How many phase are in the growth of bacteria?
Answer: four phases

Question: What is the first stage of bacteria adaptation?
Answer: lag phase

Question: What is the second phase of bacteria growth known for?
Answer: rapid exponential growth

Question: What is called the third statge of growth of bacteria?
Answer: stationary phase

Question: The absence of what causes the last stage of bacteria growth?
Answer: nutrients
Bacteria

Bacterial species differ in the number and arrangement of flagella on their surface; some have a single flagellum (monotrichous), a flagellum at each end (amphitrichous), clusters of flagella at the poles of the cell (lophotrichous), while others have flagella distributed over the entire surface of the cell (peritrichous). The bacterial flagella is the best-understood motility structure in any organism and is made of about 20 proteins, with approximately another 30 proteins required for its regulation and assembly. The flagellum is a rotating structure driven by a reversible motor at the base that uses the electrochemical gradient across the membrane for power. This motor drives the motion of the filament, which acts as a propeller.

Question: What is monotrichous?
Answer: single flagellum

Question: If bacteria has flagellum at each end what is the name of the species?
Answer: amphitrichous

Question: When flagellum is distributed throughout the surface of the cell?
Answer: peritrichous

Question: How many proteins is typical flagellum consist os?
Answer: 20 proteins

Question: How does flagellum function within the cell?
Answer: uses the electrochemical gradient across the membrane
Bacteria

If bacteria form a parasitic association with other organisms, they are classed as pathogens. Pathogenic bacteria are a major cause of human death and disease and cause infections such as tetanus, typhoid fever, diphtheria, syphilis, cholera, foodborne illness, leprosy and tuberculosis. A pathogenic cause for a known medical disease may only be discovered many years after, as was the case with Helicobacter pylori and peptic ulcer disease. Bacterial diseases are also important in agriculture, with bacteria causing leaf spot, fire blight and wilts in plants, as well as Johne's disease, mastitis, salmonella and anthrax in farm animals.

Question: What are the pathogenes?
Answer: bacteria form a parasitic association with other organisms

Question: What can pathogenes cause?
Answer: human death and disease

Question: Can cause for most pathogenic diseases be found soon?
Answer: may only be discovered many years after
Bacteria

Bacterial infections may be treated with antibiotics, which are classified as bacteriocidal if they kill bacteria, or bacteriostatic if they just prevent bacterial growth. There are many types of antibiotics and each class inhibits a process that is different in the pathogen from that found in the host. An example of how antibiotics produce selective toxicity are chloramphenicol and puromycin, which inhibit the bacterial ribosome, but not the structurally different eukaryotic ribosome. Antibiotics are used both in treating human disease and in intensive farming to promote animal growth, where they may be contributing to the rapid development of antibiotic resistance in bacterial populations. Infections can be prevented by antiseptic measures such as sterilizing the skin prior to piercing it with the needle of a syringe, and by proper care of indwelling catheters. Surgical and dental instruments are also sterilized to prevent contamination by bacteria. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection.

Question: What type of antibiotics called bacterocidal?
Answer: if they kill bacteria

Question: What kind of antibiotics are used for prevention of bacterial growth
Answer: bacteriostatic

Question: Besides in treating human disease where else are antibiotics used?
Answer: in intensive farming to promote animal growth

Question: What is the drawback of using antibiotics if agriculture?
Answer: rapid development of antibiotic resistance in bacterial populations

Question: What is common prevention method of infections in medicine?
Answer: sterilizing
Bacteria

Though it was known in the nineteenth century that bacteria are the cause of many diseases, no effective antibacterial treatments were available. In 1910, Paul Ehrlich developed the first antibiotic, by changing dyes that selectively stained Treponema pallidum — the spirochaete that causes syphilis — into compounds that selectively killed the pathogen. Ehrlich had been awarded a 1908 Nobel Prize for his work on immunology, and pioneered the use of stains to detect and identify bacteria, with his work being the basis of the Gram stain and the Ziehl–Neelsen stain.

Question: When was the first antibiotic discovered?
Answer: In 1910

Question: Who was the creator of antibiotic?
Answer: Paul Ehrlich

Question: What bacteria did he treat first?
Answer: Treponema pallidum

Question: How was his discovery aknowledged?
Answer: had been awarded a 1908 Nobel Prize

Question: Who based their research on Enrlich's stains works?
Answer: Gram stain and the Ziehl–Neelsen
Printed_circuit_board

When the board has no embedded components it is more correctly called a printed wiring board (PWB) or etched wiring board. However, the term printed wiring board has fallen into disuse. A PCB populated with electronic components is called a printed circuit assembly (PCA), printed circuit board assembly or PCB assembly (PCBA). The IPC preferred term for assembled boards is circuit card assembly (CCA), and for assembled backplanes it is backplane assemblies. The term PCB is used informally both for bare and assembled boards.

Question: What's the more appropriate, but mostly unused, name for a printed circuit board when it doesn't have embedded components?
Answer: printed wiring board

Question: What's the abbreviation for a printed wiring board?
Answer: PWB

Question: What would we call a printed circuit board with embedded electronics, abbreviated PCA?
Answer: printed circuit assembly

Question: What organization likes the term "circuit card assembly" for boards that have already been assembled?
Answer: IPC

Question: What abbreviation would the IPC use for an assembled circuit board?
Answer: CCA

Question: When the board has embedded components it is called what?

Question: A painted wiring board can also be called what?

Question: The term painted wiring board has fallen into what?

Question: The IPC preferred term for assembled bags is what?

Question: The IPC preferred term for assembled backplates is what?
Printed_circuit_board

Initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads. Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. To fabricate the board, the finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards.

Question: What did PCB designers used to employ on a mylar sheet?
Answer: photomask

Question: In the old PCB design method, what was used to connect component pin pads?
Answer: traces

Question: What were traces originally made out of?
Answer: self-adhesive tape

Question: Designers would rub on a dry transfer of what to make the process of laying out components simpler?
Answer: common component footprints

Question: What kind of metal coated the blank boards used to make PCBs?
Answer: copper

Question: Initially PCBs were designed mechanically how?

Question: Pin pads were laid out on the nylon and then what?

Question: Self-adhesive mylar was used to make what?

Question: Pre-printed reproducing grids on the mylar assisted in what?

Question: Printed copper-clad boards were used to make what?
Printed_circuit_board

Panelization is a procedure whereby a number of PCBs are grouped for manufacturing onto a larger board - the panel. Usually a panel consists of a single design but sometimes multiple designs are mixed on a single panel. There are two types of panels: assembly panels - often called arrays - and bare board manufacturing panels. The assemblers often mount components on panels rather than single PCBs because this is efficient. The bare board manufactures always uses panels, not only for efficiency, but because of the requirements the plating process. Thus a manufacturing panel can consist of a grouping of individual PCBs or of arrays, depending on what must be delivered.

Question: What process groups PCBs before transfer to a panel?
Answer: Panelization

Question: Is it more common for panels to have a single design or many designs?
Answer: a single design

Question: What type of panels can also be referred to as an "array?'
Answer: assembly panels

Question: Besides assembly panels, what's the other type of panel?
Answer: bare board manufacturing panels

Question: What step of the bare board manufacture would be impossible if panels weren't always used?
Answer: the plating process

Question: Usually a panel consists of multiple designs, but sometimes what?

Question: The two types of portals are what?

Question: Depending on what must be discussed, a manufacturing panel can consist of what?

Question: Assemblers often mount components on portals rather than single PCBs why?
Printed_circuit_board

The panel is eventually broken apart into individual PCBs; this is called depaneling. Separating the individual PCBs is frequently aided by drilling or routing perforations along the boundaries of the individual circuits, much like a sheet of postage stamps. Another method, which takes less space, is to cut V-shaped grooves across the full dimension of the panel. The individual PCBs can then be broken apart along this line of weakness. Today depaneling is often done by lasers which cut the board with no contact. Laser panelization reduces stress on the fragile circuits.

Question: What is the process called whereby the individual PCBs are separated?
Answer: depaneling

Question: What boundaries would you follow to separate PCBs on a panel?
Answer: individual circuits

Question: What technology has made depaneling possible without needing to physically interact with the board?
Answer: lasers

Question: What does the V-shaped groove method save?
Answer: space

Question: What delicate component is less likely to be damaged if laser depanelization is used?
Answer: circuits

Question: The panel is eventually merged into what?

Question: The process of deadpanning is what?

Question: Individual PCBs can be merged along what line?

Question: In the old days, depaneling was often done how?
Printed_circuit_board

Subtractive methods remove copper from an entirely copper-coated board to leave only the desired copper pattern. In additive methods the pattern is electroplated onto a bare substrate using a complex process. The advantage of the additive method is that less material is needed and less waste is produced. In the full additive process the bare laminate is covered with a photosensitive film which is imaged (exposed to light through a mask and then developed which removes the unexposed film). The exposed areas are sensitized in a chemical bath, usually containing palladium and similar to that used for through hole plating which makes the exposed area capable of bonding metal ions. The laminate is then plated with copper in the sensitized areas. When the mask is stripped, the PCB is finished.

Question: Do additive or subtractive methods use less raw materials?
Answer: additive

Question: What chemical element is often present in the bath used to sensitive exposed film after it's been imaged?
Answer: palladium

Question: What object is used to expose selected parts of the photosensitive film to light?
Answer: mask

Question: In subtractive methods, what metal covers the board and is then partially removed?
Answer: copper

Question: In the additive method, which parts of the laminate are plated with copper?
Answer: sensitized areas

Question: The advantage of the subtractive method is that less what?

Question: Bare laminate is placed on top of photosensitive film in what process?

Question: The exposed areas are sensitized using plutonium in what process?

Question: The laminate is plated with silver during what process?

Question: When the PCB is stripped, what is finished?
Printed_circuit_board

Semi-additive is the most common process: The unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed bare original copper laminate from the board, isolating the individual traces. Some single-sided boards which have plated-through holes are made in this way. General Electric made consumer radio sets in the late 1960s using additive boards.

Question: In the semi-additive process, what do the areas exposed by the mask become at the end?
Answer: traces

Question: What metal is used to plate the unmasked parts of the board in the semi-additive method?
Answer: copper

Question: After the mask comes off of the board, what step takes off the original plating?
Answer: etching

Question: What company used to make radios with additive boards in the mid-20th century?
Answer: General Electric

Question: What weight of plating is possible with copper?
Answer: any

Question: Fully additive is the most common what?

Question: Additional silver is plated onto what?

Question: Who made consumer radio sets in the late 1940s using additive boards?

Question: The patterned board has a thin layer of what already on it?
Printed_circuit_board

The simplest method, used for small-scale production and often by hobbyists, is immersion etching, in which the board is submerged in etching solution such as ferric chloride. Compared with methods used for mass production, the etching time is long. Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching. Splash etching uses a motor-driven paddle to splash boards with etchant; the process has become commercially obsolete since it is not as fast as spray etching. In spray etching, the etchant solution is distributed over the boards by nozzles, and recirculated by pumps. Adjustment of the nozzle pattern, flow rate, temperature, and etchant composition gives predictable control of etching rates and high production rates.

Question: What non-professionals might use immersion etching, since it's the easiest way to make a PCB?
Answer: hobbyists

Question: Is the immersion etching process long or short compared to other production methods?
Answer: long

Question: If you wanted to speed up the etching process, you could agitate the bath up or add what to it?
Answer: Heat

Question: What funny name is used for the etching process where air is blown through the etching solution to get it moving around?
Answer: bubble etching

Question: What's the fastest and most easily controlled process for etching?
Answer: spray etching

Question: Immaculate etching is the process where what?

Question: Etching time is short compared to what?

Question: What gives unpredictable control of etching rates and high production rates?

Question: Air is passed through the etchant bath to slow the etching in what process?
Printed_circuit_board

Multi-layer printed circuit boards have trace layers inside the board. This is achieved by laminating a stack of materials in a press by applying pressure and heat for a period of time. This results in an inseparable one piece product. For example, a four-layer PCB can be fabricated by starting from a two-sided copper-clad laminate, etch the circuitry on both sides, then laminate to the top and bottom pre-preg and copper foil. It is then drilled, plated, and etched again to get traces on top and bottom layers.

Question: If you started with a two-sided laminate etched on either side, laminated to the top and bottom, and processed it again to get traces on the outside layers, how many layers would your final PCB have?
Answer: four

Question: What makes up the inside of a multi-layer PCB?
Answer: trace layers

Question: Pressure is one thing you need to apply to make a multi-layer PCB; what's the other thing?
Answer: heat

Question: What tool is used to push the trace layers in a multi-layer PCB together?
Answer: press

Question: Single-layer printed circuit boards have trace layers where?

Question: A five-layer PCB can be fabricated how?

Question: What kind of circuit boards result from applying pressure and cold air for a period of time?

Question: A silver-clad laminate can be found in what kind of circuit board?

Question: A five-layer PCB uses what kind of foil?
Printed_circuit_board

Holes through a PCB are typically drilled with small-diameter drill bits made of solid coated tungsten carbide. Coated tungsten carbide is recommended since many board materials are very abrasive and drilling must be high RPM and high feed to be cost effective. Drill bits must also remain sharp so as not to mar or tear the traces. Drilling with high-speed-steel is simply not feasible since the drill bits will dull quickly and thus tear the copper and ruin the boards. The drilling is performed by automated drilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole.

Question: What kind of drill bit do you need to drill holes in a PCB?
Answer: coated tungsten carbide

Question: What kind of material sometimes used for drilling will lose sharpness quickly if used for PCBs?
Answer: high-speed-steel

Question: What property do PCBs have that makes them tough to drill through?
Answer: abrasive

Question: What does the "NCD" in "NCD files" mean?
Answer: numerically controlled drill

Question: What's another name for NCD files that has an "x" in it?
Answer: Excellon files

Question: Holes through a PBC are drilled how?

Question: Drill bits must remain dull why?

Question: Drilling with high-speed-steel is feasible why?

Question: The dull file describes what?

Question: Drilling must be low RPM and high feed to be what?
Printed_circuit_board

The hole walls for boards with two or more layers can be made conductive and then electroplated with copper to form plated-through holes.  These holes electrically connect the conducting layers of the PCB. For multi-layer boards, those with three layers or more, drilling typically produces a smear of the high temperature decomposition products of bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch. The de-smear process ensures that a good connection is made to the copper layers when the hole is plated through. On high reliability boards a process called etch-back is performed chemically with a potassium permanganate based etchant or plasma. The etch-back removes resin and the glass fibers so that the copper layers extend into the hole and as the hole is plated become integral with the deposited copper.

Question: What do the hole walls in two-layer PCBs have to be before they can be electroplated?
Answer: conductive

Question: What's the minimum number of layers a PCB can have to be considered "multi-layer"?
Answer: three

Question: What process does a multi-layer PCB usually undergo before plating to make sure the layers have good connectivity with each other?
Answer: de-smear

Question: What type of boards undergo the etch-back process?
Answer: high reliability

Question: Etch-back removes glass fibers and what other material?
Answer: resin

Question: What connects the conducting layers of the PAB?

Question: Smears are removed with a chemical smear what?

Question: The process used on low-reliability boards is called what?

Question: The back-etch removes what?

Question: What becomes integral with the deposited silver?
Printed_circuit_board

Matte solder is usually fused to provide a better bonding surface or stripped to bare copper. Treatments, such as benzimidazolethiol, prevent surface oxidation of bare copper. The places to which components will be mounted are typically plated, because untreated bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was coated with solder by hot air solder levelling (HASL). The HASL finish prevents oxidation from the underlying copper, thereby guaranteeing a solderable surface. This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU and US, which restricts the use of lead. One of these lead-free compounds is SN100CL, made up of 99.3% tin, 0.7% copper, 0.05% nickel, and a nominal of 60ppm germanium.

Question: What happens to untreated copper that makes it difficult to solder?
Answer: oxidizes

Question: What chemical treatment will prevent bare copper from oxidizing?
Answer: benzimidazolethiol

Question: What's the process by which bare copper gets covered in solder?
Answer: hot air solder levelling

Question: What does hot air solder leveling ensure the coated copper will have?
Answer: solderable surface

Question: What alloy can no longer be used in HASL because of restrictions on the use of one of its metal components?
Answer: tin-lead

Question: Shiny solder is usually fused to do what?

Question: What encourages surface oxidation of bare copper?

Question: Traditionally, any exposed silver was coated with what?

Question: The HASL finish encourages oxidation from what?

Question: What is now used in compliance with the RoHS directive in the EU and China?
Printed_circuit_board

Other platings used are OSP (organic surface protectant), immersion silver (IAg), immersion tin, electroless nickel with immersion gold coating (ENIG), electroless nickel electroless palladium immersion gold (ENEPIG) and direct gold plating (over nickel). Edge connectors, placed along one edge of some boards, are often nickel plated then gold plated. Another coating consideration is rapid diffusion of coating metal into Tin solder. Tin forms intermetallics such as Cu5Sn6 and Ag3Cu that dissolve into the Tin liquidus or solidus(@50C), stripping surface coating or leaving voids.

Question: What does OSP stand for?
Answer: organic surface protectant

Question: What metal is often under the gold plating on edge connectors?
Answer: nickel

Question: What's the abbreviation for immersion silver plating?
Answer: IAg

Question: Ag3Cu is one intermetallic that tin forms; what's the other one?
Answer: Cu5Sn6

Question: What might the rapid diffusion of coating metal into tin solder leave in the surface coating?
Answer: voids

Question: Main connectors, placed along one edge of some boards, are often what?

Question: The only coating consideration is what?

Question: What forms intermetallics such a Cu66n6?

Question: Electroless silver with immersion gold coating (ENIG) is an example of what?

Question: Electroless silver electroless palladium immersion gold (ENEPIG) is an example of what?
Printed_circuit_board

Electrochemical migration (ECM) is the growth of conductive metal filaments on or in a printed circuit board (PCB) under the influence of a DC voltage bias. Silver, zinc, and aluminum are known to grow whiskers under the influence of an electric field. Silver also grows conducting surface paths in the presence of halide and other ions, making it a poor choice for electronics use. Tin will grow "whiskers" due to tension in the plated surface. Tin-Lead or solder plating also grows whiskers, only reduced by the percentage Tin replaced. Reflow to melt solder or tin plate to relieve surface stress lowers whisker incidence. Another coating issue is tin pest, the transformation of tin to a powdery allotrope at low temperature.

Question: What's the process whereby metal filaments are grown on or in a PCB via DC voltage?
Answer: Electrochemical migration

Question: Along with silver and aluminum, what metal grows metal filaments when exposed to an electric field?
Answer: zinc

Question: In addition to "whiskers," what does silver sprout around ions like halide?
Answer: conducting surface paths

Question: What do scientist call the function whereby tin changes when it's very cold?
Answer: tin pest

Question: What's present in plated surfaces that causes tin to grow metal filaments?
Answer: tension

Question: What material is a good choice for electronics use?

Question: Tin plast is what type of issue?

Question: The transformation of silver to a powdery allotrope at low temperature is know as what?

Question: AC voltage bias helps promote the growth of what?
Printed_circuit_board

Areas that should not be soldered may be covered with solder resist (solder mask). One of the most common solder resists used today is called "LPI" (liquid photoimageable solder mask).  A photo-sensitive coating is applied to the surface of the PWB, then exposed to light through the solder mask image film, and finally developed where the unexposed areas are washed away. Dry film solder mask is similar to the dry film used to image the PWB for plating or etching. After being laminated to the PWB surface it is imaged and develop as LPI. Once common but no longer commonly used because of its low accuracy and resolution is to screen print epoxy ink. Solder resist also provides protection from the environment.

Question: If part of a PCB isn't solderable, what can be used instead?
Answer: solder resist

Question: What's another term used for "solder resist"?
Answer: solder mask

Question: What solder resist with a four-word name is a popular choice in the industry?
Answer: liquid photoimageable solder mask

Question: What kind of coating gets applied to the PWB before light exposure?
Answer: photo-sensitive

Question: What solder resist is so inaccurate that few choose it anymore?
Answer: screen print epoxy ink

Question: Areas that should be soldered may be covered with what?

Question: A photo-sensitive coating is applied beneath the surface of what?

Question: Wet film solder mask is similar to what?

Question: Screen print epoxy ink is commonly used why?

Question: What doesn't provide protection from the environment?
Printed_circuit_board

Unpopulated boards are usually bare-board tested for "shorts" and "opens". A short is a connection between two points that should not be connected. An open is a missing connection between points that should be connected. For high-volume production a fixture or a rigid needle adapter is used to make contact with copper lands on the board. Building the adapter is a significant fixed cost and is only economical for high-volume or high-value production. For small or medium volume production flying probe testers are used where test probes are moved over the board by an XY drive to make contact with the copper lands. The CAM system instructs the electrical tester to apply a voltage to each contact point as required and to check that this voltage appears on the appropriate contact points and only on these.

Question: What are bare-board tests looking for besides "opens"?
Answer: "shorts"

Question: What's an absent connection that needs to be linked up on an unpopulated board called?
Answer: An open

Question: What conductive metal are the lands on a circuit board made out of?
Answer: copper

Question: What does a flying probe tester deliver to the contact points during testing?
Answer: voltage

Question: What system tells the flying probe where to go and what to do?
Answer: CAM system

Question: Populated boards are usually what?

Question: A long is a connection between what?

Question: A closed is a missing connection between what?

Question: Building the adapter is low cost and economical for?
Printed_circuit_board

Often, through-hole and surface-mount construction must be combined in a single assembly because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress, while components that are expected to go untouched will take up less space using surface-mount techniques. For further comparison, see the SMT page.

Question: Surface-mount is one type of construction used in PCB assembly; what's the other one?
Answer: through-hole

Question: Which type of construction makes components that use more space?
Answer: through-hole

Question: Which of the two kinds of construction is weaker under strain?
Answer: surface-mount

Question: If you're building a circuit board that has a lot of components that won't be used, which construction would be better?
Answer: surface-mount

Question: What must be combined in a multiple assembly?

Question: Surface mount mounting can provide needed strength for what?

Question: Components that are expected to be touched will take up what?

Question: All required components are available only in what?
Printed_circuit_board

In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard. The JTAG test architecture provides a means to test interconnects between integrated circuits on a board without using physical test probes. JTAG tool vendors provide various types of stimulus and sophisticated algorithms, not only to detect the failing nets, but also to isolate the faults to specific nets, devices, and pins.

Question: Do test circuits create permanent or temporary connections between traces?
Answer: temporary

Question: What's the most frequently used test configuration procedure for ICs?
Answer: Joint Test Action Group

Question: What would you avoid by using the Joint Test Action Group standard?
Answer: physical test probes

Question: What component of the printed circuit board is appraised with boundary scan testing?
Answer: ICs

Question: To whom would you go to acquire the algorithms you'd use for the Joint Test Action Group procedures?
Answer: JTAG tool vendors

Question: Bouncing scan testing requires what?

Question: The least common standard test configuration procedure is what?

Question: JAG tool vendors provide various types of what?

Question: The JAG test architecture provides a means to what?
Printed_circuit_board

PCBs intended for extreme environments often have a conformal coating, which is applied by dipping or spraying after the components have been soldered. The coat prevents corrosion and leakage currents or shorting due to condensation. The earliest conformal coats were wax; modern conformal coats are usually dips of dilute solutions of silicone rubber, polyurethane, acrylic, or epoxy. Another technique for applying a conformal coating is for plastic to be sputtered onto the PCB in a vacuum chamber. The chief disadvantage of conformal coatings is that servicing of the board is rendered extremely difficult.

Question: If a PCB is intended for use in an setting with extreme conditions, what would probably be applied?
Answer: conformal coating

Question: A conformal coating can be applied by spraying the PCB or by doing what else to it?
Answer: dipping

Question: The conformal coating can prevent leaking, shorts, and what other type of moisture damage?
Answer: corrosion

Question: What material was first used for conformal coating?
Answer: wax

Question: What action is made much more difficult for boards that have a conformal coating?
Answer: servicing

Question: PABs are intended for what type of environment?

Question: What type of coat encourages corrosion?

Question: The chief advantage to conformal coatings is what?

Question: Which coatings are usually dips of dilute solutions of wax rubber?
Printed_circuit_board

Many assembled PCBs are static sensitive, and therefore must be placed in antistatic bags during transport. When handling these boards, the user must be grounded (earthed). Improper handling techniques might transmit an accumulated static charge through the board, damaging or destroying components. Even bare boards are sometimes static sensitive. Traces have become so fine that it's quite possible to blow an etch off the board (or change its characteristics) with a static charge. This is especially true on non-traditional PCBs such as MCMs and microwave PCBs.

Question: What special protection are most PCBs shipped in?
Answer: antistatic bags

Question: What's another term for "grounded" in the context of PCBs?
Answer: earthed

Question: What force can easily change or even completely destroy an etch on a PCB?
Answer: static charge

Question: What class of PCBs are even more susceptible to static than standard ones?
Answer: non-traditional

Question: Non-traditional PCBs include microwave PCBs and what other type of board?
Answer: MCMs

Question: Many assembled PABs are sensitive to what?

Question: Proper handling techniques might transmit what?

Question: What must be placed in static bags during transport?

Question: An accumulated static charge though the user happens when what is done?
Printed_circuit_board

The first PCBs used through-hole technology, mounting electronic components by leads inserted through holes on one side of the board and soldered onto copper traces on the other side. Boards may be single-sided, with an unplated component side, or more compact double-sided boards, with components soldered on both sides. Horizontal installation of through-hole parts with two axial leads (such as resistors, capacitors, and diodes) is done by bending the leads 90 degrees in the same direction, inserting the part in the board (often bending leads located on the back of the board in opposite directions to improve the part's mechanical strength), soldering the leads, and trimming off the ends. Leads may be soldered either manually or by a wave soldering machine.

Question: If a lead wasn't soldered manually, what device was used?
Answer: wave soldering machine

Question: Which type of PCB construction technique was used first?
Answer: through-hole

Question: In through-hole construction, what are the leads on the front attached to on the back?
Answer: copper traces

Question: For boards with two sides, to what angle are leads bent to in order to install them horizontally?
Answer: 90 degrees

Question: What is improved by bending leads in opposite directions on the back of double-sided PCBs?
Answer: mechanical strength

Question: Vertical installation of through-hole parts with two axial leads in done how?

Question: Vertical installation is done by bending the leads what degrees?

Question: Leads have to be soldered in what way?

Question: A wave sewing machine can solder the what?
Printed_circuit_board

Through-hole manufacture adds to board cost by requiring many holes to be drilled accurately, and limits the available routing area for signal traces on layers immediately below the top layer on multi-layer boards since the holes must pass through all layers to the opposite side. Once surface-mounting came into use, small-sized SMD components were used where possible, with through-hole mounting only of components unsuitably large for surface-mounting due to power requirements or mechanical limitations, or subject to mechanical stress which might damage the PCB.

Question: Which type of construction is more expensive?
Answer: Through-hole

Question: What type of boards end up with limited routing space in through-hole manufacture?
Answer: multi-layer

Question: What force might damage a PCB if large components are surface mounted?
Answer: mechanical stress

Question: What components can be surface mounted to save space?
Answer: small-sized SMD components

Question: A component might not be able to be made any smaller because of its mechanical limitations or what other need?
Answer: power requirements

Question: What will not damage the PCB?

Question: Mechanical signs will damage the what?

Question: What increases the available routing area?

Question: Large-sized SMD components were used when?
Printed_circuit_board

Surface-mount technology emerged in the 1960s, gained momentum in the early 1980s and became widely used by the mid-1990s. Components were mechanically redesigned to have small metal tabs or end caps that could be soldered directly onto the PCB surface, instead of wire leads to pass through holes. Components became much smaller and component placement on both sides of the board became more common than with through-hole mounting, allowing much smaller PCB assemblies with much higher circuit densities. Surface mounting lends itself well to a high degree of automation, reducing labor costs and greatly increasing production rates. Components can be supplied mounted on carrier tapes. Surface mount components can be about one-quarter to one-tenth of the size and weight of through-hole components, and passive components much cheaper; prices of semiconductor surface mount devices (SMDs) are determined more by the chip itself than the package, with little price advantage over larger packages. Some wire-ended components, such as 1N4148 small-signal switch diodes, are actually significantly cheaper than SMD equivalents.

Question: When did surface-mount become a commonly used manufacturing process?
Answer: mid-1990s

Question: What did the new components with end tabs replace?
Answer: wire leads

Question: What improvement is possible with surface-mounting that enables higher production and lower labor costs?
Answer: automation

Question: What are SMDs?
Answer: surface mount devices

Question: Is it the chip or the package that influences the price of an SMD more?
Answer: chip

Question: What kind of technology emerged in the 1950s?

Question: What became widely used in the 2090s?

Question: What was redesigned to have small plastic tabs?

Question: What lends itself well to a low degree of automation?

Question: What are more expensive than SMD equivalents?