Author - Brian Steeves Component Engineering Systems, LLC

Size: px

Start display at page:

Download "Author - Brian Steeves Component Engineering Systems, LLC"

Harriet Rice
5 years ago
Views:

1 PASSIVE COMPONENTS Author - Brian Steeves Component Engineering Systems, LLC DEFINITION: A resistor is a device used to restrict the flow of electrons (current). Fixed resistors have two connections per resistive element (axial or radial), separated by some type of resistive element (such as a carbon composition, carbon composition film or nichrome film). Variable resistors have three contacts - 2 fixed and 1 moveable and are usually used as voltage dividers. Another type of resistor () has a nichrome wire wrapped around a ceramic core. The current flow follows Ohm's Law (V = I x R) and the current flow generates heat according to P = I 2 x R. Various forms of resistors are shown in Fig. 1. Standard resistance values are shown in Table 1. Thermistors are temperature sensitive resistors which change resistance (either positively or negatively) with change of temperature. KEY SPECIFICATIONS (SEE RESISTOR GLOSSARY) TYPE/MATERIAL: Carbon composition rod, carbon film, nichrome film or nichrome wire VALUE: Micro ohms (µ?), Milliohms (m?), Ohms (?), Kilohms (k?) or Megohms (M?) VOLTAGE: The voltage values are specified as VDC or VAC TEMPERATURE COEFFICIENT (TC): The TC is specified as parts per million per o F or o C (ppm/ o For ppm/ o C) VOLTAGE COEFFIICIENT (VC): The change of resistance with change of voltage (ppm/ o For ppm/ o C) NOISE: In an RF circuit, spurious noise is induced in a resistor due to charge carriers. It may be significant a high frequencies FREQUENCY RESPONSE: The change in resistance with change of frequency in an RF circuit. PACKAGE STYLE: Axial or radial leaded, surface mount (SMT or SMD) or array. PACKAGE SIZE: Chips: 0203 to 2512, where the first 2 digits are the length and the last 2 digits are the width in mm. Fixed carbon composition, fixed film and power resistors are defined in inches. RELIABILITY: The mean time between failures (MTBF) of a part. The determination of which type of resistor is to be used, is primarily determined by the circuit board, if any, on which the resistor will be mounted, the voltage applied to it, and the anticipated power which the resistor will have to dissipate. If the resistor will be mounted as a through-hole element, then an axial leaded (with bent leads, or radial leaded resistor would be used. the size of either of these would be determined bythe anticipated power the resistor would have to dissipate. If the resistor is going to be mounted on a printed circuit board, then a chip resistor would be used, and, once again, the size of the chip would be determined by the power to be dissipated. NOTE: If you purchase a 10% tolerance part, the actual value of the part may be anywhere from 90 ohms to 110 ohms for a part specified as 100 ohms and still comply with the part designated value. Failure Modes: Most resistor failures occur when either there is too much voltage applied, or current flowing through it, which causes heating which vaporizes the resistive material. TYPICAL RESISTOR DESCRIPTION: Arrays consist of multiple resistive elements on a single substrate. They are either chip type or IC-type packages Carbon Composition resistors are, generally, not used very much now, so they are not discussed above. Carbon film and nichrome film resistors have a film of material deposited on an inert material (usually ceramic) then a laser cut is made into the film to arrive at the desired resistance value. Wire wound resistors are usually wound with nichrome resistance wire, in the lower resistance value ranges. resistors are, generally, made from thicker nichrome wire wound on a ceramic core Surface mount resistors are ceramic chips onto which restive material has been deposited and are relatively low power. The resistance value is laser trimmed to the specific value desired Style Array Carbon or Nichrome Film Axial or Radial Leaded Carbon Film Axial Leaded Metal Film Resistors Surface Mount Chip Carbon Composition Metal Film Wire Wound (Chassis Mount) Resistance Resistance Range Tolerance TCR 10 ohm to 0.1% to 1 % (/element) ±0.2 %/oc to 25 mw to 2.5W ±500 %/oc 0 ohm to 0.1, 1, 2, 5, 0.25W, 0.5W 10Mohm & 10 % & 1W 4.9 ohms to 1, 2, & 5 % 100 or 200 ppm/oc W to ±0.2 ppm/oc to ±1 % to ±30 % 100 Gohm 10 W ±1300 ppm/oc 1 ohm to 0.22 ohms to 5 Mohms 0.1 ohms to 1 Gohm ±2% and ±5% 0.125W to 0.5W 0.1% to 1% 0.125W to 1W ±300ppm/oC 25 ppm/oc to 200 ppm/oc ±0.1 & to ±5% 0.125W to 50W ±10ppm/oC to ±650ppm/oC 0.1 % to 5% 5W to 2500W ±15ppm/?C to ±500 ppm/?

2 Style Array Carbon or Nichrome Film Axial or Radial Leaded Carbon Film Axial Leaded Metal Film Resistors Surface Mount Chip Carbon Composition Metal Film Wire Wound (Chassis Mount) Resistance Resistance Range Tolerance 10 ohm to 0.1% to 1 % (/element) 25 mw to 2.5W 0 ohm to 0.1, 1, 2, 5, 0.25W, 0.5W 10Mohm & 10 % & 1W 4.9 ohms to 1, 2, & 5 % W to ±1 % to ±30 % 100 Gohm 10 W TCR ±0.2 %/?C to ±500 %/?C 100 or 200 ppm/?c ±0.2 ppm/?c to ±1300 ppm/?c 1 ohm to ±2% and ±5% 0.125W to ±300ppm/?C 0.5W 0.22 ohms 25 ppm/?c to 0.1% to 1% 0.125W to 1W to 5 Mohms 200 ppm/?c 0.1 ohms to ±10ppm/?C to ±0.1 & to ±5% 0.125W to 50W ±650ppm/?C 1 Gohm 0.1 % to 5% 5W to 2500W ±15ppm/?C to ±500 ppm/?

3 PASSIVE DEVICES Author - Brian Steeves Component Engineering Systems, LLC Testing Environmental of resistors is divided Testsinto - These three tests basic types: may or may not be required for screening the resistor to assure that it will (A) meet Environmental the stresses - to imposed assure that upon the it device when will operated work adequately in within it's within normal the expected or abnormal environment environment. (B) (a) Physical Salt Atmosphere - to determine (Corrosion) if the device will withstand the expected (b) Humidity physical (Steady uses to State) which it will be subjected (C) (c) Electrical Immersion - to verify that the device will perform its electrical (d) function Barometric as required Pressure by (Reduced) the circuit into which it will go (e) Moisture Resistance (f) Thermal Shock (g) Seal (h) Life (at elevated ambient temperature) (a) The corrosion screen is used to simulate the effects of seacoast environments on metals with or without protective coatings, and the effectivity of these coatings to resist corrosion. (b) The humidity screen is used to evaluate the properties of the materials used in the resistor as it is influenced by the absorpton and diffusion of moisture vapor. (c) The Immersion test is performed to detect a defective terminal asembly or a partially closed seam or molded assembly. This detects such defects as faulty construction or mechanical damage. (usually used after seal testing) (d) The reduced pressure (vacuum) screen is used to simulate the low atmosphere pressure experienced by aircraft operating in high altitude flight. (e) Moisture resistance test is used to demonstrate the resistance of resistor parts and constituent materials to the deteriorative effects of high humidity and heat conditions typical of tropical environments. (f) Thermal shock is used to determine thhe resistance of the resistor to exposures at extemes of high and low temperatures and to the shock of alternate exposures of the resistor to these extremes. ( e.g. moving of the parts to and from heated enclosures in arctic areas or in aircraft going rapidly from low to high altitudes) (g) Seal testing is performed to determine the effectiveness of a resistor part which has an internal cavity (h) Life testing is conducted to determine the effects on electrical and mechanical characteristics of a resistor at elevated temperatures while the resistor is performing its operational function. Physical Characteristics Tests - These tests may or may not be required for screening the resistor to assure that it will meet the physical stresses imposed upon it when operated in it's normal and abnormal environment (a) Vibration (c) High Frequency Vibration (e) Solderability (g) Resistance to soldering heat (i) Acceleration (k) Random Vibration (m) Particle Impact Noise Detection (PIND) (b) Random Drop (d) High Impact Shock (f) Radiographic (X-ray) Inspection (h) Terminal Strength (j) Shock (Specified Pulse) (l) Resistance to Solvents (a) Vibration testing is used to determine the effect of vibration on the resistor within the p[redominant frequency rangs and magnitudesthat may be encountered during field service (b) Random drop isused to determine the effects on resistors of random repeated impact due to handling, shipping and other field service conditions. (c) High frequency vibration determines the effect on resistors of vibration in the frequency ranges of 10 to 500 Hz, 10 to 2000 Hz and/or 10 to 3000 Hz which may be encountered in heavy equipment. (d) High impact shock testing determines the ability to withstand shock of the same severity as that of collisions of vehicles and determines the resistor's ruggedness. (e) Solderability determination is made on the basis of the of the ability of terminations to be wetted by the solder and the predictability of a suitable fillet resulting from the soldering operation. (f) X-ray inspection is a non-destructive test used for detecting internal physical defects in small component parts which are otherwise visable such as improper positioning of elements, voids in encapsulation and potting compounds, foreign materials and broken elements. (g) Resistance to soldering heat determines whether wire and other component parts can stand the effects of heat to which they will be subjected during the soldering process. (h) This terminal strength test determines whether the design of the terminals and their method of attachment can withstand one or more of the applicable mechanical stresses to which they will be subjected during installation or disassembly in equipment. (i) Acceleration testing is performed to determine the effects of acceleration stress on component parts and to verify the ability of these parts to operate properly during exposure to acceleration stress.

4 (j) Shock testing (especially of a specified pulse (length and total energy)) is used to determine of the component part will withstand shock such as those which may be encountered as a rsult of rough handling, transportation and military operations. (k) Random vibration testing is used to determine the ability of resistors to withstand the stresses eperienced in various service field environments. (l) Resistance to solvents test is used to verify that part markings will remain on the parts when they are subjected to cleaning processes which involve solvents, and that protective coatings and encapsulating materials are not degraded to the point where the electrical characteristics of the parts will not be compromised. (m) PIND testing is used to detect minute particles within the internal confines of a sealed cavity device. If conductive, these particles may short out critical elements in the package. Electrical Characteristics Testing - Thhese tests ae used to verify the electrical characteristics of the resistors under test to assure that the electrical characteristics of the part are correct, adequate and sufficient for the desired application. (a) Dielectric Withstanding Voltage (c) DC Resistance (e) Current Noise Test (b) Insulation Resistance (d) Resistance - Temperature Characteristic (f) Voltage Coefficient of Resistance (a) Dielectric Withstanding testing is used to prove that the resistor can operate safely at it's rated voltage and withstand momentary overpotentials duue to switching, surges and other similar phenomena. (b) Insulation Resistance testing is used to measure he resistance offered by the insulating members of any component part to an impressed direct voltage tending to produce a leakage curret through or on the surface of these members. (c) DC Resistance testing measures the direct current (dc) resistance of resistors and conductors. (d) Resistance - Temperature Characteristic testing detects the percentage change in dc ohmic resistance from the dc ohmic resistance at the reference temperature, per unit temperature difference between the test temperature and the reference temperature. (e) The Current Noise Test is used to establishthe "noisiness" or "noise quality" of a resistor in order to determine it's suitability for use in electronic circuits having critical noise requirements. (f) The voltage coefficient of resistance measures the changes in resistance with changes in voltage which occurs in certain types of resistors. Discussion: Not everyone of these tests are performed on every resistor. Which one to be used, depends upon the anticipated os of the resistor in question. Because of the diversity of types of resistors, so there is a diversity of tests used to completely characterize each for it's paticular application. The amount of testing, frequently, is determined by the specific application of the resistive element. Thus, the testing of a resistor to be used in a home TV set is much different from the testing imposed on a part which will be used for a Mars mission, even though the end result is that we have a specific device which restricts current flow by a measureable amount.

5 Standard Resistor Values vs Tolerance Author: Brian Steeves Component Engineering Systems, LLC / / / '23.70 ' '

(RMCA, RMCB) Bulk Ceramic Composition Resistors

(RMCA, RMCB) Bulk Ceramic Composition Resistors Version: March 1, 2017 Electronics Tech. (RMC, RMCB) Bulk Ceramic Composition Resistors Web: www.direct-token.com Email: Direct Electronics Industry Co., Ltd. China: 12F, Zhong Xing Industry Bld., Chuang