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Ms. Grace Gong

Ms. Grace Gong

Department: Marketing
Job Title: Marketing manager
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In the applications of precise resistance smaller doesn't always mean better

Equipment is now doing more and more small, the trend demands more and more small precision resistor can support more and more high power density. This usually means that as long as possible should be a table sheet resistance. Is it? SMT technology is not perfect.

Smaller sometimes means that more heat

Because of power density, table sticker sheet resistance at work when the temperature is higher than the through hole components. Table stick (SMT) devices as most by PCB heat, and the hole device as most of the heat into the surrounding air. So table paste components in the system caused by the heat accumulation will affect all the other devices on the board. Given that this excess calories, when working under high temperature resistance, long-term stability will decline.

Smaller may mean more vulnerable, more difficult to clean up

MT components can also cause structural problems. When chip aspect ratio (or aspect ratio) exceed the limits set by the reliability (usually about 2:1), circuit board bending stress may cause fracture or chip from the circuit board. Increase of chip width and make it in a 2:1 aspect ratio is not within the scope of the right solution, it is not any help for eliminating stress. Simply increase the width of the chip will be more difficult to remove after assembly legacy of solvents and rosin under the chip.

Specially designed to provide a higher value, higher power, more strict tolerance and better long term stability at the same time, use less space for circuit board and easier to clean up the solvent and the resistance of the rosin, such as configuration is moulded type rectangular box or metal seal pot precise resistance is usually the best choice, especially in high precision applications. The resistance will extend from the bottom out of the hole pin.

Figure 1: through hole components can obtain better stability, because they are not subject to thermal mechanical stress from PCB.

The circuit board needed for this method to the greatest extent reduced the space, and contains a reliable clean debris at the bottom of the support structure.

Figure 2: after thermal expansion or PCB bending with flexible terminals table precise resistance.


Little could mean too close

As we further advance device miniaturization, tightly integrated circuit board in precision applications is not always a good idea. For example, if the installation of the resistance element face is parallel with PCB, may cause microphonic noises. The parasitic effect is caused by the vibration, it will be like a diaphragm of the microphone system produce spurious signals. Horizontal arrangement of the resistance element may be because the physical vibration microphonic noise even strong acoustic effect. Microphonic noise is also avoid using SMT type feedback element of a reason. Better choice is vertically through hole components, their pin configuration can be absorbed on the surface of the PCB bending deformation.

This summary

Table sheet resistance used in modern electronic design is so popular, that they are often considered all design and assembly process of the general method. But in many applications, the hole instrumentation technology can provide better than the table to stick the chip's unique performance and reliability advantages.

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