Main » 2012 » June » 30 » Printed Circuit Passive Components
11:48 AM Printed Circuit Passive Components |
| Resistors are ubiquitous. Because of this their efficiency is taken for granted, provided they're operated within their energy, voltage and environmental ratings this really is reasonable, since after millions of accumulated resistor-years encounter there is certainly little left for their manufacturers to uncover. But there are nevertheless applications exactly where specifying and applying resistors demands to be handled with some care. Resistor types - Surface mount chip The most typical common goal resistor is the thick film surface mount chip sort. Accessible in substantial quantities and incredibly low costs, it's the workhorse in the resistor planet. The construction is quite easy and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations includes a resistive ink film printed or otherwise deposited on its top surface. The terminations are coated using a solder dip to make sure ease of wetting when the portion is soldered into spot, as well as the leading in the part is IBM Certified Sales Specialist coated with an epoxy or glass layer to safeguard the resistive element. Distinctive manufacturers make numerous claims for the ruggedness and efficiency of their parts however the standard features are related. Energy dissipation is largely controlled by the thermal properties with the PCB pads to which the chip is soldered, and should you be operating close to the rated energy in the component it's going to be necessary to confirm that your pad style agrees using the manufacturer's suggestions. You may also get metal film chip resistors for higher efficiency applications, but these are much more highly-priced than the typical thick film. The resistive ink technique utilized for chips can also make standard axial-lead resistors (metal glaze) of modest size, and may be made use of directly onto a substrate to generate printed resistors. This strategy is often used in hybrid circuits and is pretty cost-effective in particular when significant numbers of similar values are required. It is actually probable to print resistors straight onto fibreglass printed circuit board, though the outcome is of very poor top quality and can not be utilised where a stable, predictable worth (compared with conventional kinds) is required. Metal film The next most typical type could be the metal film, in its many guises. This is the common part for industrial and military purposes. Probably the most common varieties of leaded metal film are hardly any a lot more high priced than carbon film and, given their superior characteristics, particularly temperature coefficient, noise and power handling capability, lots of gear manufacturers do not locate it worthwhile to bother with carbon film. Variants in the common metal film cater for high or low resistance desires. The "metal" within a metal film can be a nickel-chromium alloy of varying composition for various resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the end caps and leads are force-fitted towards the tubular assembly and the resistance element IBM Certified Integration Developer is trimmed to worth by cutting a helical groove of controlled dimensions in it, which permits the identical film composition to become applied over fairly a wide range of nominal values. The whole component is then coated in epoxy and marked. The disadvantage on the helical trimming method is that it inherently increases the resistor's stray inductance, as well as limits its pulse handling capability. Carbon The most common leaded resistor for commercial applications could be the carbon film. It is definitely cheap - much less than a penny in quantity. It also has the least impressive efficiency with regards to tolerance and temperature coefficient, however it is normally sufficient for general objective use. The other sort which uses pure carbon because the resistive element is carbon composition, which was the earliest type of resistor but these days finds a use in particular applications which involve an assured pulse withstand capability. Wirewound For medium and high power (higher than 2W) applications the wirewound resistor is almost universally applied. It really is pretty low-priced and readily readily available. Its disadvantages are its bulk, though this permits a lower surface temperature for any given energy dissipation; and that as a result of its construction it really is noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound forms are offered either using a vitreous enamel or cement coating, or in an aluminium housing which might be mounted to a heatsink. Aluminium housings can provide energy dissipations exceeding 100W per unit. Precision resistors Once circuit requirements start out to call for accuracy and drift specifications exceeding the usual metal film skills, the expense increases substantially. It can be nevertheless possible to have metal film resistors of "precision" performance as much as an order of magnitude greater than the common, though at prices an order of magnitude or extra higher. Drift needs of much less than ten parts-per-million per °C introduce lots of a lot more important factors into the overall performance equation, for instance thermal emf, mechanical and thermal anxiety, and terminating resistance. These can be dealt with, and the resistive and substrate supplies might be optimised, but the unit fees are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form quite a few resistors at the moment, which is then encapsulated to form a multi-resistor single package. The resulting resistors have exactly the same performance as a single thick film chip, though with reduced breakdown voltage and power handling potential. Printed Circuit Passive Components Resistors are ubiquitous. Because of this their overall performance is taken for granted, supplied they are operated within their energy, voltage and environmental ratings this really is sensible, due to the fact following millions of accumulated resistor-years experience there's small left for their manufacturers to uncover. But you'll find nonetheless applications where specifying and applying resistors requirements to become handled with some care. Resistor forms - Surface mount chip The most prevalent general objective resistor may be the thick film surface mount chip sort. Offered in large quantities and extremely low prices, it can be the workhorse of the resistor planet. The construction is incredibly uncomplicated and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations has a resistive ink film printed or otherwise deposited on its leading surface. The terminations are coated with a solder dip to make sure ease of wetting when the component is soldered into place, plus the leading of your portion is coated with an epoxy or glass layer to protect the resistive element. Different producers make a variety of claims for the ruggedness and overall performance of their parts however the simple functions are related. Power dissipation is largely controlled by the thermal properties with the PCB pads to which the chip is soldered, and if you are running close to the rated energy in the element it is going to be essential to confirm that your pad style agrees together with the manufacturer's suggestions. You can also get metal film chip resistors for larger performance applications, but these are a lot more pricey than the popular thick film. The resistive ink method utilized for chips may also generate standard axial-lead resistors (metal glaze) of smaller size, and may be employed directly onto a substrate to generate printed resistors. This approach is often utilized in hybrid circuits and is incredibly cost-effective specially when large numbers of comparable values are necessary. It can be attainable to print resistors straight onto fibreglass printed circuit board, even though the result is of quite poor good quality and cannot be applied exactly where a stable, predictable worth (compared with conventional forms) is needed. Metal film The next most frequent sort is definitely the metal film, in its different guises. This really is the common element for industrial and military purposes. One of the most common varieties of leaded metal film are hardly any far more pricey than carbon film and, offered their superior characteristics, especially temperature coefficient, noise and energy handling ability, many equipment manufacturers do not come across it worthwhile to bother with carbon film. Variants of the normal metal film cater for high or low resistance desires. The "metal" in a metal film can be a nickel-chromium alloy of varying composition for different resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted for the tubular assembly as well as the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which will allow exactly the same film composition to be made use of over fairly a wide range of nominal values. The whole element is then coated in epoxy and marked. The disadvantage in the helical trimming method is that it inherently increases the resistor's stray inductance, and also limits its pulse IBM Certifications handling capability. Carbon The most popular leaded resistor for commercial applications is the carbon film. It is surely low-priced - much less than a penny in quantity. It also has the least impressive performance in terms of tolerance and temperature coefficient, but it is typically adequate for common purpose use. The other type which utilizes pure carbon as the resistive element is carbon composition, which was the earliest variety of resistor but these days finds a use in particular applications which involve an assured pulse withstand capability. Wirewound For medium and high power (greater than 2W) applications the wirewound resistor is pretty much universally made use of. It really is fairly low cost and readily available. Its disadvantages are its bulk, although this allows a lower surface temperature for a given power dissipation; and that as a result of its construction it can be noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound kinds are obtainable either with a vitreous enamel or cement coating, or in an aluminium housing which might be mounted to a heatsink. Aluminium housings can give energy dissipations exceeding 100W per unit. Precision resistors Once circuit specifications start out to call for accuracy and drift specifications exceeding the usual metal film abilities, the expense increases substantially. It is actually still doable to obtain metal film resistors of "precision" efficiency as much as an order of magnitude greater than the common, even though at prices an order of magnitude or far more larger. Drift needs of much less than 10 parts-per-million per °C introduce quite a few much more considerable factors into the efficiency equation, for example thermal emf, mechanical and thermal anxiety, and terminating resistance. These is often dealt with, and the resistive and substrate supplies could be optimised, but the unit expenses are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form quite a few resistors at the moment, that is then encapsulated to form a multi-resistor single package. The resulting resistors have the same overall performance as a single thick film chip, even though with decreased breakdown voltage and energy handling ability. |
|
|
| Total comments: 0 | |