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Apr 9 2019

What Is A Chip Fixed Resistor?

Warm hints: This article contains about 4000 words and reading time is about 12 mins.

Introduction

The electronic component body of the non-patch component can carry more production information, such as specifications, manufacturers, product serial numbers, and the like. The volume or size of the patch component is in millimeters. The component body is not allowed to label too much information. The marking method usually has: 1) simplified marking method. Simplify the conventional identification model, such as the 74LS14 (six-inverter digital IC) as LS14; 2) the code labeling method, which further simplifies the identification, called code labeling. Such as the chip transistor -24, 1L, etc., more like a password, you need to use the data "deciphered" to know the meaning of the component specification model behind the logo; 3) no logo. Low-power (such as 16/1W) chip resistors, and (PF-level) small-capacity capacitors, because the component body is too small to print the mark, it simply becomes a non-marking component.

The chip fixed resistor is one of the most widely used components on the circuit board. The shape is rectangular, black, and the resistor is generally marked with white numbers (small resistors without marking, no printed chip resistors). The inverter manufacturer is on the circuit board. The serial number of the component marked above is R (such as R1, R147, etc.).

Article Core

Chip  Fixed Resistor

Purpose

Introduce something about chip fixed resistor.

Application

Semiconductor industry.

Keywords

Chip Fixed Resistor

Catalog

Introduction


Chip Fixed Resistor Definition


Chip Fixed Resistor Characteristics


What Is the Material of the Chip Fixed Resistor?


The Chip Fixed Resistor Is Mainly Composed of Four Parts.


Working Parameters and Categories of Chip Fixed Resistors


How to Judge the Resistance and Power of the Chip Fixed Resistor?


Chip Fixed Resistance Measurement and Visual Inspection


Replacement of Chip Fixed Resistor


Chip Resistance Reading Method


Analysis of the Causes of Chip Fixed Resistor Damage

10.1 Analysis of the Causes of Chip Fixed Resistor Damage

10.2 Chip Fixed Resistor Damage Solution


ⅠChip Fixed Resistor Definition

The chip fixed resistor is one of the metallic glass uranium resistors. It is a resistor made of a high-power chip resistor printed on a substrate by mixing metal powder and glass uranium powder. Resistant to humidity, high temperature and low temperature coefficient. The application of surface mount technology (SMT) is very common, and the proportion of electronic products assembled by SMT has exceeded 90%. China has been involved in SMT technology since the 1980s. With the development of small SMT production equipment, the application scope of SMT is further expanded. In the fields of aviation, aerospace, instrumentation, machine tools, etc., SMT is also used to produce various electronic products or components with small quantities.

chip resistor

Resistors are commonly referred to as resistors in everyday life. It is a current-limiting component. After the resistor is connected to the circuit, the resistance of the resistor is fixed. Generally, it is two pins, which can limit the current through the branch connected to it. A resistor cannot be changed and is called a fixed resistor. A variable resistance is called a potentiometer or a variable resistor. The ideal resistor is linear, ie the instantaneous current through the resistor is proportional to the applied instantaneous voltage. Variable resistor for voltage division. On the exposed resistor body, one or two movable metal contacts are pressed. The contact position determines the resistance between either end of the resistor body and the contact.


Ⅱ Chip Fixed Resistor Characteristics

Small size and light weight;

Adapt to reflow and wave soldering;

Stable electrical performance and high reliability;

Low assembly cost and matching with automatic mounting equipment;

High mechanical strength and superior high frequency characteristics.


Ⅲ What Is the Material of the Chip Fixed Resistor?

SMD resistors are typically fabricated from the following materials:

The substrate is alumina and the resistive material is yttrium oxide.

(1) Substrate (ceramic substrate)

(2) resistance paste (R paste)

(3) backing material

(4) Positive guiding material and side guiding material (Ag slurry)

(5) Primary protective glass G16. Secondary protective glass G27. Mark marking material.

chip resistor


Ⅳ The Chip Fixed Resistor Is Mainly Composed of Four Parts.

(1) Substrate:

The substrate material is generally 96% alumina ceramic. In addition to good electrical insulation, the substrate should have excellent thermal conductivity at high temperatures. Characteristics such as electrical properties and mechanical strength. In addition, the substrate is required to be flat and the scribing is accurate. Standard to fully guarantee the resistance. The electrode paste is printed in place.

(2) Resistive film:

It is printed on a ceramic substrate with a resistive paste having a certain resistivity and then sintered. The resistive paste is generally made of cerium oxide.

(3) Protective film:

The protective film is covered on the resistive film mainly for protecting the resistor body. On the one hand, it acts as a mechanical protection, on the other hand, it makes the surface of the resistor body insulative, and prevents the resistor from coming into contact with the adjacent conductor to cause a malfunction. In the process of electrically crossing the intermediate electrode, it is also possible to prevent the erosion of the resistive film by the electric fluid, resulting in a decrease in electrical resistance performance. The protective film is generally a low-melting glass paste which is formed by printing and sintering.

chip resistor

(4) Electrode:

In order to ensure good solderability and reliability of the resistor, a three-layer electrode structure is generally used: internal. in. Outer electrode. The inner layer electrode is an internal electrode connected to the resistor body, and the electrode material should have a small contact resistance with the resistive film, strong bonding force with the ceramic substrate, and good chemical resistance, and is easy to perform plating work. It is usually printed and sintered with silver-palladium alloy. The middle layer electrode is a nickel plated layer, also known as a barrier layer. Its function is to improve the heat resistance of the resistor during soldering and to buffer the thermal shock during soldering. It also prevents the migration of silver ions to the resistive layer and avoids the internal electrode being etched (the internal electrode is etched by the solder). The outer electrode is a tin-lead layer, also known as a solderable layer. Its function is to make the electrode have good solderability and prolong the storage period of the electrode. It is usually plated with tin-lead alloy.

The rectangular chip resistor is divided into a film type resistor and a thick film resistor by a resistance material. Among them, the film type resistor has high precision and low temperature coefficient of resistance. Good stability, but a narrow range of resistance, suitable for precision and high frequency applications. Thick film resistors are widely used in circuits.

chip resistor


Ⅴ Working Parameters and Categories of Chip Fixed Resistors

The basic parameters of the chip resistor are nominal resistance, rated power, error level, and the highest use voltage, temperature coefficient, etc., we only need to pay attention to the nominal resistance value and rated power value.

(1) Rated resistance. 

The most common is the digital identification method.

a. Use a 3-digit digital resistor value. The first two digits are ten digits, the ones digit value, which is a valid value, and the third digit is the number of zeros or the X power of ten. If it is labeled 152, it is 1500Ω; 101 is 100Ω; 103 is 10000Ω (10 kΩ).

A value of 1 Ω or less plus R indicates, for example, 1R5, that is, 1.5 Ω; and R10, that is, 0.01 Ω.

b. The resistance value is represented by 4 digits. The first 3 digits are valid values, that is, thousands, hundreds, and one-bit values, and the fourth digit is the number of zeros. If it is labeled 1501, it is 1500Ω; if it is marked as 1000, it is 100Ω; if it is marked as 681, it is 680 Ω; if it is marked as 1003, it is 100kΩ. The value below 1 Ω plus R is the same as above.

3 color ring and 4 color ring resistance value labeling method, not common, the labeling rules are the same as ordinary resistors, not to be repeated; precision chip resistors, code notation, consisting of two digits plus one code, the first two digits For a valid value, the third letter is a multiplier value. Such as 01A - 100Ω, 02 C - 100kΩ, not common, but be careful!

(2) Rated power. 

The chip resistors with digital identification are mostly black, and their power levels are divided into 1/20W, 1/16W, 1/8W, 1/10W, 1/4W, 1/2W, 1W, etc., to 1/16W, 1/ 8W, 1/10W, 1/4W are the most widely used. Generally, the larger the power, the larger the resistance volume, and the power level is gradually increased with the size. In addition, the same shape, the darker the color, the greater the power value. Resistors with a power dissipation of 1W or more must not be in direct contact with the printed circuit board in consideration of heat dissipation requirements. Therefore, the chip resistors used on all circuit boards are generally less than 1W. The power value of the chip resistor is limited. Therefore, where a large power resistor is required in the circuit, multiple chip resistors are often used in parallel (plus series) to increase the power value. The power value of the chip resistor is not directly marked on the resistor body, and the magnitude of the resistor power value can be judged according to the "head" of the resistor.

When switching to a resistive component, look at the resistance value of the digital label, and look at the volume of the resistor. If the two conditions are met, it can be replaced.

(3) Chip fuse resistor. 

This is a special type of chip resistor. For circuit safety reasons, it is not advisable to replace it with a common chip resistor, or it is easy to short the wire.

The chip fuse resistor is a special chip resistor that acts as a fuse protection in the circuit. It is generally connected in series to the power supply branch of a unit circuit. When the current flowing through the resistor exceeds a certain value, its resistance The layer is quickly blown, and the power supply of the unit circuit is cut off to avoid the expansion of the fault. The figure of the resistor body is labeled as 000 or 0, which is characteristic of the chip fuse resistor, and its normal resistance value is measured as 0 Ω.

(4) Chip exclusion. This is another type of chip resistor, most commonly 4-pin 2-element chip exclusion, 8-pin 4-element chip resistor and 10-pin 8-element chip exclusion, 8-pin 4-element patch It has four independent resistor elements with the same resistance value inside, and the chip exclusion is marked as 472. It means that there are 4 resistance elements with resistance value of 4.7k inside, which are used to concentrate the circuit with the same resistance resistance element. For example, the upper resistor of the MCU pin is used more in the interface circuit of the MCU.

Figure 2 Chip Exclusion and Internal Equivalent Circuit

Figure 2 Chip Exclusion and Internal Equivalent Circuit


Ⅵ How to Judge the Resistance and Power of the Chip Fixed Resistor?

If the digital identification on the chip resistor is clearly visible, there is of course no problem in judging the resistance value and the power value. If the damage resistance itself is not marked, or has been burned out beyond recognition, and the label is not clear, then the resistance value before the replacement will be a little bit difficult, and it must be done in order to make the next repair. What methods are available to make more accurate judgments?

(1) Refer to the resistance value of the corresponding component in the same circuit of this model. There are many identical circuits in the inverter circuit, such as 6 IGBT drive pulse transmission channels, 6 of which are exactly the same, from the MCU pulse signal output pin, to the buffer circuit, to the drive IC, to the IGBT grid, shot Polar circuit. Any resistor or other component in one or several of the branches may be damaged. Reference may be made to the parameter value of the patch component in the undamaged branch. If there is no marking, the component may be measured on the board or the component soldered off the board. Determination. The transmission channel of the 3-phase output current (analog signal), the three signal detection circuits are also generally the same. When there is damage in one way, the component parameters in the two paths may not be damaged, and the parameter values of the damaged components may be determined.

As shown in Figure 2, the component parameters of the peripheral circuits of the PC5 and PC6 two-way driver ICs are exactly the same; the peripheral component parameters of the PC3 and PC8 two-way driver ICs are identical, R17=R51, R23=R48, R22=R49......, When the components on the periphery of the PC3 are damaged, it can be "removed" to repair the parameter values of the PC5 corresponding peripheral components.

Similarly, for damage to other components such as transistors, diodes, IC chips, etc., when it is not possible to determine the parameters of the damaged components, the parameter values of the same type of circuit components can be referred to for repair.

(2) Determine the component parameters according to the circuit type. If the pull-up and pull-down resistors connected to the MCU (microcontroller) pins are damaged, the MCU needs to externally pull-up and pull-down resistors. The internal port is generally open-drain, and the pull-up or pull-down resistors can be used to avoid I/O. The port has a level drift state that maintains a static stable level. The value of the resistor is generally 10kΩ, 6.8kΩ, 5.1kΩ, 4.7kΩ, 3.3kΩ, etc. The value is too small to increase the power consumption. If the value is too large, the level drift or the interference is easily introduced. As long as it is determined that the damaged chip resistor is the upper and lower resistors of the MCU pin, it can be directly determined that the resistance of the damaged component is also within the range of 3.3 to 10 kΩ. Of course, you can also refer to the resistance values of other upper and pull-down resistors.

Figure 3 Refers to the component parameters in the same circuit

Figure 3 Refers to the component parameters in the same circuit

Figure 4 Circuit diagram of the pull-up resistor of the MCU pin

Figure 4 Circuit diagram of the pull-up resistor of the MCU pin

As shown in Figure 4, the pull-up resistor of the U2 pulse pin is 5.1k, which is in the range of 3.3~10kΩ.

(3) Determine component parameter values with reference to similar models. There is no reference to the same circuit, nor can it approximate the parameters of the component like the pull-up and pull-down resistors. Find similar models for comparison and determine the parameter values of the damaged components.

(4) Adjust the test to obtain the parameter values of the components. If there is no similar model for reference, it takes a little effort to map out the part of the circuit, understand the position and specific function of the damaged resistor in the circuit, and the connection method with other components, "estimate" the approximate resistance value, if still Grasp, damage the resistor, temporarily plug in the potentiometer, power on the inverter, adjust the potentiometer to test, match the artificial signal given, the response of the subsequent circuit to the signal, the panel display, etc., measure the resistance value of the potentiometer, and then Determine the parameters of the damaged resistor.


Ⅶ Chip Fixed Resistance Measurement and Visual Inspection

(1) On-line measurement with a multimeter, when the resistance value is greater than the nominal value, it indicates that the component has a circuit breaker fault or the resistance value becomes large and has been damaged; when the measured resistance value is smaller than the nominal value, it should be considered that the peripheral parallel component is The effect should be measured by disconnecting one or both ends of the component from the circuit to obtain an accurate measurement.

(2) The appearance characteristics of the chip resistor are as follows:

a, the surface of the chip resistor surface of the secondary vitreous protective film should be covered intact, appear to fall off, may have been damaged;

b, the surface of the component should be flat, if some "convex" is reproduced, it may be damaged;

c. The electrode of the component terminal should be flat, crack-free pinhole, and no discoloration. If crack occurs, it may be damaged.

d, the surface of the chip resistor body is burnt black and may be damaged;

e. The resistor body has been deformed and may be damaged.


Ⅷ Replacement of Chip Fixed Resistor

Replacement of the chip resistor, in addition to the required resistance value, also need to pay attention to the size and power value. Small signal circuits (such as MCU motherboard circuits) first require uniform dimensions for easy solder mounting. The precautions for substitution are as follows:

(1) Substituting the original parameters strictly. Analog signal processing circuits, such as proportional amplifier circuits, have strict values for input resistance and feedback resistance. The resistance value of the replacement component should be the same as the original damaged component. The difference is not allowed to be too large, otherwise the circuit operation error will be caused.

(2) Components used in digital circuits, such as the above connection, pull-up resistor, isolation resistor, etc., the selected value has a certain range, as long as the signal voltage changes significantly, in line with the requirements of high and low levels. First, the components with the same parameters should be replaced. If the same resistance component cannot be found at hand, it can be replaced by a component with a close value, which generally does not affect the circuit performance. If the 4.7kΩ resistor is damaged, it can be replaced by a 5.1kΩ or 6.8kΩ resistor.

(3) Substituting non-patch components. The damage rate of the chip resistor is extremely low, except that the drive circuit is often damaged due to possible strong electric shock (partial spare parts are available for purchase), the components of other circuits are rarely damaged, and one or two pieces may be damaged, and the types are different. Unable to purchase spare parts. In the case of such a damaged component, it is not a problem to replace it with a non-patch 1/4W or 1/8W ordinary resistor, and it is not a "crack" that causes maintenance progress without finding the original accessory. Of course, pay attention to the welding, do the lead shaping, make the lead as short as possible, if necessary after welding 704 rubber reinforcement, can also achieve high quality repair requirements.


Ⅸ Chip Fixed Resistance Reading Method

The surface of the chip resistor has a digital silk screen. As long as the meaning of the number is clear, the resistance and accuracy can be determined.

Chip resistor resistance error accuracy is ±1%, ±2%, ±5%, ±10% accuracy, the most commonly used is ±1% and ±5%, 5% accuracy is represented by three digits, The 1% accuracy is represented by four digits. Examples are as follows:

The silkscreen of the resistive surface is 103:

chip resistor

The first two digits 10 represent the significant digits, and the third digit 3 represents the magnification, ie 10^3, so the resistance of the 103 resistor is 10 & TImes; 10^3 = 10000 Ω = 10K with an accuracy of 5%.


Ⅹ Analysis of the Causes of Chip Fixed Resistor Damage

Chip resistor, one of the most common passive components, small size, light weight, suitable for reflow soldering and wave soldering; stable electrical performance, high reliability; low assembly cost, and matching with automatic mounting equipment; high mechanical strength High frequency characteristics.

When there is a problem with the chip resistor, the first reason to find the damage of the rectifier bridge caused by the thermistor is to eliminate the damage and avoid the damage caused by replacing the new rectifier bridge.


10.1 Analysis of the Causes of Chip Fixed Resistor Damage

(1) The chip resistor is too close to the power transformer, and the line impedance at both ends is very small. The inverter does not have a DC reactor and an output AC reactor, so that the rectifier bridge is under the impact mode of high-amplitude sharp pulse current of capacitor filtering. Causes premature failure of the rectifier bridge.

(2) The grid voltage becomes high instantaneously, and the lightning strike or surge voltage is too high, and the internal resistance of the grid is small. The protection of the grid resistance does not work through the breakdown and burnout, resulting in all overvoltage being applied to the rectifier bridge.

(3) The rear-stage circuit and the inverter power switching device are damaged, causing the rectifier bridge to flow through the short-circuit current and be damaged.

(4) The output current voltage is too low, so that the rectifier bridge is relieved and damaged.

(5) The purchase of the original original device, its quality is not off.

chip resistor


10.2 Chip Fixed Resistor Damage Solution

(1) Replace the new rectifier bridge and chip resistor device, ensure that the rectifier bridge is welded firmly and keep a safe distance from the surrounding devices. In addition, the application of silicone grease reduces the resistance heat too high.

(2) For the parallel rectifier bridge, the same type and the same manufacturer's products should be used to prevent the current from being uneven and damaged.

 chip resistor


You May Also Be Interested In:

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What Is the Insulation Resistance Meter and How to Test It?

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