SMD resistors

NTCs are available as SMD resistors (surface mounted divices), as well as in special packages like glass-coated or fitted to lead frames. The size of the NTC can be as small as 1 mm x 0.5 mm x 0.6 mm (and smaller) or there are discs of 25 mm diameter [1],... 

A large and increasing part of the fixed resistor market is taken by surface mounted device (SMD) resistors. These resistors are mounted dhectly on the printed circuit board. Electrical contacts are provided at the sides of the resistor. 

For most SMD resistors the substrate is a rectangular piece of ceramic, usually alumina. At the upper side conductors are deposited along two edges. The resistive film is deposited between and partly over these electrodes. The resistance value is adjusted by laser trimming. A protective coating is appHed over the resistive film. Contacts are made over the edges these usually extend over the sides of the ceramic and even some distance over the lower side to improve the soldering quality. 

For the resistive layer in general purpose resistors thick film technology is normally used. In most cases the contacts are made by dipping a conductive paste. Sometimes evaporated or sputtered contacts are used. To ensure good soldering the contacts are covered with a solder or tin layer. Standard SMD resistors have a tolerance of 5% and a TCR of 200 ppm/°C. With special thick-fihn techniques and appropriate contacts, tolerances of 1% and a TCR of 50 ppm/°C can be made. 

For precision SMD resistors metal films are used. These films are made of the same alloys as used for cylindrical metal hhn resistors. Tolerances down to 0.1% and a TCR of 25 ppm/°C are available. 

FIGURE 2.23 Maximum permissible peak pulse power (Pmax) for a 1206 SMD resistor as a function of pulse duration for single pulses and for repetitive pulses with a pulse frequency that is 1000 times the pulse duration. 

Both the capacitance and the inductance tend to increase with larger dimensions of resistors. The series inductance is high for resistors with a resistive element such as a cod. This is found in most cylindrical film resistors and especially in wire wound resistors. Special types are available with two coils wound in opposite direction to minimize the inductance. Very low inductances and capacitances are found for small rectangular SMD resistors. One should remember that here interactions with the rest of the circuit may be much more important than the impedance of the resistor itself. 

The new user of surface mount designs (SMDs) must rapidly learn the packaging sizes and types for SMDs. Resistors, capacitors, and most other passive devices come in two-terminal packages, as shown in Fig. 11.17, which have end-terminations designed to rest on substrate pads/lands. 

The parasitics are also responsible for the limited bandwidth of printed resistors. Their influence is, however, smaller compared to equivalent sur-face-moxmted device (SMD) resistors. 

Ru02 resistors are commercial small-power (volume of few mm3) electronic components. They belong to the group of smd (surface mount device) thick-film resistors and are... 

Note that the electronic industry produces smd components called thin-film resistors of the same shape and size of Ru02 thermistors. They are usually made of a thin layer of Ni-Cr. Their resistance is extremely stable with temperature and hence they find application as inexpensive (punctual) heaters (see e.g. Chapter 11). 

Rd - dynamic resistance of the PIN photodiode 1 k 2 L - inductance generated by the photodiode SMD carrier Rn - thin film resistor for reverse bias voltage 2 kQ Ra - input impedance 50 Q of the ideal amplifier... 

Metal electrode facebonding (MELF) resistors are special type of SMD device. Their resistive elements are identical to those of cylindrical film resistors. Instead of wires, they have solderable caps, which are soldered directly on the printed circuitboard. Different kinds of resistive films are used, and their properties are comparable to those of similar conventional film resistors. 

Mounting of resistors is often more expensive than the components themselves. The use of the smallest SMD components is often limited by the difficulty of handling them. The amount of handling and mounting can be reduced by combining a number of resistors with their interconnections to a network on one substrate. This also makes it easier to use smaller resistors. 

There is a growing demand for SMD types of nonlinear resistors. 

CMCs Chip resistors SMD transistors SO package types QFP package tjqjes Electroplated pure tin... 

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