Resistors are ubiquitous. Because of this their performance is taken for granted, supplied they are operated within their energy, voltage, and environmental rankings this is reasonable since right after millions of accumulated resistor-years encounter there is little left for or manufacturers to discover. But you may still find applications were specifying as well as applying resistors needs to be dealt with some care. Look into the Best info about rigid flex pcb.
Resistor varieties – Surface mount food
The most common general-purpose resistor is the thick film exterior mount chip type. Found in huge quantities and at very rates, it is the workhorse of the resistor world. The construction is very simple along with hardly varies from company to manufacturer. An alumina (aluminum oxide ceramic) espèce with nickel-plated terminations has a resistive ink video printed or otherwise deposited about its top surface.
Typically the terminations are coated which has a solder dip to ensure simple wetting when the part is usually soldered into place, plus the top of the part is sprayed with an epoxy or wine glass layer to protect the resistive element.
Different manufacturers help make various claims for the ruggedness and performance of their parts though the basic features are similar. Electrical power dissipation is largely controlled by the arctic properties of the PCB shields to which the chip is usually soldered, and if you are working close to the rated power of the business it will be necessary to confirm that your pad design agrees with the actual manufacturer’s recommendations.
You can also obtain metal film chip resistors for higher performance programs, but these are more expensive than the typical thick film. The resistive ink technique used for potato chips can also produce standard axial-lead resistors (metal glaze) associated with small sizes and can be utilized directly onto a base to generate printed resistors.
This method is frequently used in hybrid brake lines and is very cost-effective particularly when large numbers of similar values are needed. It is possible to print resistors straight onto fiberglass printed signal board, though the result is actually of very poor quality as well as cannot be used where a steady, predictable value (compared with conventional types) is required.
Metallic film
The next most common kind is a metal film, in various guises. This is the regular part for industrial as well as military purposes. The most popular types of leaded metal film tend to be hardly any more expensive than co2 film and, given their superior characteristics, particularly temperature coefficient, noise, and energy handling ability, many gear manufacturers do not find it advantageous to bother with carbon film.
Variations of the standard metal video cater to high or very low-resistance needs. The “metal” in a metal film can be a nickel-chromium alloy of numerous compositions for different resistance varieties. A film of this alloy is usually plated onto an alumina substrate.
For leaded areas, the end caps and potential buyers are force-fitted to the tubular assembly and the resistance factor is trimmed to price by cutting a helical groove of controlled proportions in it, which allows the same video composition to be used over an amazingly wide range of nominal values.
The full part is then coated with epoxy and marked. The drawback of the helical trimming course of action is that it inherently increases the resistor’s stray inductance, and also boundaries its pulse handling functionality.
Carbon
The most common leaded resistor for commercial applications could be carbon film. It is certainly affordable – less than a penny throughout quantity. It also has the very least impressive performance in terms of building up a tolerance and temperature coefficient, but it is normally adequate for standard purpose use.
The other variety which uses pure and also carbon as the resistive element is usually carbon composition, which was the primary type of resistor but currently finds use in particular applications which involve a great assured pulse withstand ability.
Wirewound
For medium and also high power (greater as compared to 2W) applications the wire-wound resistor is almost universally applied. It is fairly cheap and also readily available. Its disadvantages are usually its bulk, though this permits a lower surface temperature to get a given power dissipation; and this is because of its construction it is substantially inductive, which limits it is use in high frequency or heartbeat applications.
Wirewound types can be obtained either with a vitreous enameled surface or cement coating or perhaps in an aluminum housing which is often mounted to a heatsink. Lightweight alloy housings can offer power débauche exceeding 100W per product.
Precision resistors
Once routine requirements start to call for reliability and drift specifications far above the usual metal film skills, the cost increases substantially. It truly is still possible to get metal motion picture resistors of “precision” efficiency up to order regarding magnitude better than the standard, even though at prices a buy of magnitude or bigger.
Drift requirements of a lot less than 10 parts per million per °C introduce many more significant components into the performance equation, including thermal emf, mechanical in addition to thermal stress, and terminating resistance. These can be treated, and the resistive and Principe materials can be optimized, even so, the unit costs are now tested in pounds, and supply times stretch to several months.
Resistor networks
Thick picture resistor networks are manufactured including chips. A resistive printer is a screen printed onto a new ceramic substrate to form quite a few resistors at once, which is in that case encapsulated to form a multi-resistor single package. The resulting resistors have the same performance as a sole thick film chip, nevertheless with reduced breakdown discord and power handling power.
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