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Surface Mount Components

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Chip Resistors
Source: Res-net Microwave – Res-net Microwave, Inc.

Electronic surface mount components are attached directly to the printed circuit board (PCB). They are also known as SMT components (surface mount technology) or SMD (surface mount devices). These components can be either active or passive electronic components. Some of the types of components made in these surface mount configurations include: capacitors, inductors, resistors, semiconductors, and thermistors,

The actual technology was developed in the 1960’s, but was not fully implemented or widely used until the 1980’s. This technology helped to allow for the progression of smaller and smaller electronic devices such as calculators and computers. It also helped to open the door to an entirely new industry, electronic contract manufacturing.

In this process, the components are first put on reels using a tape and reel machine. Then the boards are populated with the various SMD components usually using a pick and place machine. Next, the printed circuit boards are run through a re-flow soldering oven. This solders the components to the board itself with a minimal amount of hand labor.

Their smaller size is not without its drawbacks. Most of the surface mount components cannot carry as much power as the older thru-hole technology because of their smaller size. Sometimes the transformer or inductor must be mounted in a separate (usually by hand) process because they are too large to be tape and reeled. Hence these boards cannot be entirely populated by a pick and place machine.

All in all, however, the surface mount technology is how most components will be manufactured in the future. The call for power is decreasing, with the exception of specific applications, so the smaller size is not an issues for most computers, tablets, and cell phones. Going forward most components will be surface mount devices, if they are not already.

Disk Resistors

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Res-net Microwave Disk Resistors

A resistor is a commonly used two terminal passive electronic component. It produces a voltage across it’s terminals that is proportional to the current flowing through it. Resistors are used to limit or regulate the flow of electrical current in an electronic circuit. They are often used within a circuit for current control or to turn a current signal into a voltage signal. Resistors can be manufactured in two different ways, one by winding a resistive wire on a core (wirewound) or a second by using a film via a sputtering process or some other method (metal film).

Disk resistors, however, are not a very common component. They are a specific type of resistor that is physically small and circular. They can be either thick film or thin film and can therefore operate at higher frequencies. They can be used in lower frequency SMA terminations in lieu of a rod resistor. Since they have a symmetrical geometry there is essentially no magnetic field, which would normally create more inductance. Therefore, with the absence of this field, they are ideal for applications that require lower inductance’s. They are also often used for pulsed power systems.

A typical disk resistor, such as those produced by Res-net Microwave, are the thick film type. They have a resistance range of 5 ohms to 500 ohms. They also have a nominal power of 10 watts.

Wound Film Capacitors

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Wound Film Capacitors
Source: Arizona Capacitors, Inc.

Wound film capacitors are classified as passive electronic components that can store an electrical charge. They consist of a pair of conductors separated by a dielectric. The dielectric stores the charge when an electric static field is created between the two conductors. This capacitance that is stored is measured in a unit called farads.

Wound film capacitors are wound with a machine much like a wirewound resistor or a transformer. They can have many different types of dielectrics. These capacitors can be wound on paper, plastic, polystyrene, Teflon, polypropylene, polycarbonate, or polyester. The configurations can vary just as much as the dielectrics and they can be purchased as a standard product or custom designed to a customer’s specifications or requirements. They can be manufactured in the form of a wrap and fill, preformed case, tubular hermetic, molded, a welded case, and many more.

The capacitance can range from 50pf to 500uf and the voltages can range from 30 to 250 KVDC. So, the wound film capacitors can fill the needs of many different specific applications and for many different industries.

Some of the industries Arizona Capacitors, Inc. serves, for example, includes: railroad, audio, communications, power generation, medical equipment, aerospace, electronic controls, automotive, just to name a few. The wound film capacitor has been around for decades and will be a staple for energy storage for many decades to come.

Microwave SMA Terminations

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Res-net Microwave SMA Terminations

RF and Microwave SMA terminations are a type of high frequency passive electronic component. With most RF and microwave systems operating in 50 Ohm characteristic impedance, the need to insure maximum power transfer and minimize signal reflections is evident. This can be accomplished with an SMA termination. Just like an SMA connector, they screw into place and are thus also referred to as a connectorized or coaxial termination.

They are similar to all terminations, in that their purpose is to terminate a signal in any given circuit. In essence, they are absorbing the incident power. If unused ports, such as a test instrument, are not “terminated” they can cause interference by having the signal reflected back from the end.

The physical part consists of the connector type, SMA body, as well as a rod resistor, but disk resistors are also sometimes used as a substitute. The rod resistor is a cylindrical thin film type resistor that usually operates up to 26.5 GHz in frequency range, depending on the size of the rod.

The metal work or connector body can come in a variety of metals, but brass and copper are very popular. The SMA termination can also be plated in silver or gold and sometimes tin, depending upon the application and the customers’ preferences. Since it is a connector with threads, it is easy to install. It screws on just as a nut would on a bolt.

Air Coils

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Screen Shot 2015-10-13 at 12.42.31 PMFour Lead Air Coil

Air coils are actually inductors that do not contain a core, but instead use the surrounding air. Being classified as an air coil or an inductor means they are considered a passive electronic component.

Air coils are sometimes referred to as “self supporting” coils because there is no core to hold their shape. They are wound on a fixture or mandrel. Usually a special bondable wire must be used with either an electric current being passed through the wire to heat and cure the coating, or a solvent is used to activate it. These methods enable the wire to adhere to itself and thus hold its shape. In order for this to work, the heat or applied solvent must be applied while the winding is still on the metal mandrel. They are then removed once the wire “cures”.

Some air coils are wound by hand, but most are done on an automatic winding machine. This minimizes the about of direct labor and thus the component’s cost. This is one of the major benefits to using an air coil.

There are several other benefits to using an air coil in a design, if the electrical parameters allow for it. One of these benefits, as mentioned above, is the price. Not just because of the reduced labor, however, but a minimum amount of raw material as well helps to keep this product at a lower price than many of its counterparts.

A second advantage is that the inductance’s are unaffected by the current that is being carried. This benefit is due to the lack of an actual core.

A third benefit is the lack of iron or core losses. This, as one might imagine, is also due to the fact that there is not an actual core present to create these losses in the winding.

Finally, the fourth benefit is that they can operate at higher frequencies than those with a physical core. This ties back to the core losses, as they go higher in frequency the losses become greater. As electronics go higher and higher in the frequency spectrum, this becomes a tremendous advantage for using air coils in future circuit board designs.