Basic knowledge of SMD resistors

 SMD resistor introduction

Chip resistors are also called chip fixed resistors. Chip fixed resistors are commonly known as SMD resistors, which are a kind of metal glass shaft resistors. It is a resistor made by mixing metal powder and glass shaft powder and printing it on the substrate by screen printing. It is resistant to humidity, high temperature, and has a small temperature coefficient.

Classification of chip resistors

SMW wire wound chip resistors

Flameproof UL94V0 molded package, resistant to heat, humidity &insulation.

SMF power metal film chip resistors

Flameproof UL94V0 molded package, resistant to heat, humidity &insulation.

MCM thick film chip resistors

Minature size can compact P.C.Board.

RMM metal film melf resistors

SMD enabled structure with excellent solder-ability.

CP Chip Resistor

High power Chip Resistors

Characteristics of chip resistors

Small size and light weight

Adapt to reflow soldering and wave soldering

Stable electrical performance and high reliability

Low assembly cost, and match with automatic placement equipment

High mechanical strength, superior high frequency characteristics

SMD resistor naming method

5% accuracy nomenclature: RS-05K102JT

1% accuracy naming: RS-05K1002FT

R- means resistance

S- means power, 0402 is 1/16W, 0603 is 1/10W, 0805 is 1/8W, 1206 is 1/4W, 1210 is 1/3W, 1812 is 1/2W, 2010 is 3/4W, 2512 is 1W .

K means the temperature coefficient is 100PPM

J- means the accuracy is 5%, F means the accuracy is 5%, F means the accuracy is 1%

T-means taping packaging

The resistance error accuracy of the chip resistor has ±1%, ±2%, ±5%, ±10% accuracy, and the most commonly used ones are ±1% and ±5%

The application of surface assembly technology SMT is very common, and the proportion of electronic products assembled by SMT has greatly increased. With the development of small SMT production equipment, the application range of SMT is further expanded. Aviation, aerospace, instrumentation, machine tools and other fields are also adopting SMT Produce all kinds of electronic products or parts in small batches.

In recent years, in addition to electronic product developers using SMD devices to develop new products, maintenance personnel have also begun to repair a large number of electronic products assembled by SMT.

At present, the models of SMD resistors are not unified. They are set by the manufacturers themselves, and the models are particularly long. If you can correctly put forward the various parameters and specifications of SMD resistors when purchasing, it will be very convenient. Order the required resistance.

Chip resistors have five parameters, size, resistance, tolerance, temperature coefficient and packaging.

1. Size series SMD resistor series generally have seven sizes, which are represented by two size codes. One size code is an EIA code represented by four digits. The first two digits and the last two digits indicate the length and width of the resistor, in inches. The other is the metric code, which is also represented by a four-digit number, and its unit is millimeters. Different sizes of resistors have different power ratings.

2. Resistance value series Nominal resistance value is determined according to the series, each series is divided by the tolerance of the resistance, the smaller the tolerance, the more the resistance is divided, the most commonly used is E-24, resistance The tolerance of resistance is ±5%.

3. Tolerance The tolerance of chip resistors has four levels, namely F level, ±1%, G level, ±2%, J level, ±5%, and K level, ±10%.

4. Temperature coefficient The temperature coefficient of chip resistors has two levels, W level, ±200ppm/℃, X level, ±100ppm/℃, only the resistance with the tolerance of F grade can use the X grade, and the resistance of other grades is general. It is W class.

5. There are mainly two types of packaging: bulk and strip-shaped rolls.

The working temperature range of the chip resistor is -55 to +125℃, and the maximum working voltage is related to the size. At present, the widely used chip resistor size codes are 0805 and 1206, and there is a tendency to develop like 0603, and the most commonly used tolerance is J level.