Layout of Motor Driver Capacitors

The component layout guidelines for motor driver ICs are similar to other types of power ICs. The bypass capacitor should be placed as close as possible to the device power pin, while the large capacity capacitor should be placed next to it. Many motor driver ICs use guide and/or charge pump capacitors, which should also be placed near the IC.

Most signals are routed directly at the top level. The power supply is routed from the large capacity capacitor to the bypass and charge pump capacitor at the bottom layer, while multiple through holes are used at the transition points of each layer.

The bottom layer of TSSOP and QFN packaged devices has a large exposed IC board. The IC board is connected to the back of the chip to remove heat from the device. The IC board must be fully soldered onto the PCB to consume power.

The mold opening used for depositing the solder paste on the IC board may not necessarily be detailed in the IC data sheet. Usually, SMT process engineers have their own rules for how much solder should be deposited on the mold and what patterns should be used on the mold.

If a single opening similar to the size of an IC board is used, a large amount of solder paste will deposit. This may cause the device to be lifted due to the surface tension during the melting of the solder. Another issue is solder voids (cavities or gaps in the solder area). In the reflow soldering process, when the volatile components of the flux evaporate or boil, solder voids will appear. This may cause the solder to be pushed out of the welding point.

To solve these problems, for IC boards with an area greater than about 2 square millimetre, solder paste is usually deposited in several small square or circular areas. Dividing the solder paste into smaller areas can make it easier for the volatile components of the solder to escape without causing the solder to shift.

The solder mold packaged by QFN has four small openings for depositing solder paste on the central IC board.

Standard lead packaging (such as SOIC and SOT-23 packaging) is typically used in low-power motor drivers.

 In order to fully improve the power consumption of lead packaging, a "flip chip lead frame" structure is adopted. Without the use of bonding wires, copper bumps and solder are used to bond the chip to metal leads, allowing heat to be transferred from the chip to the PCB through the leads.

The flip chip lead frame structure helps to fully improve the power consumption capability of lead packaging.

By connecting larger copper areas to leads carrying larger currents, thermal performance can be optimized. On the motor driver IC, the power, ground, and output pins are usually connected to the copper area.

Please note that there are no hot air solder pads on the SMT board; They are firmly connected to the copper area. This is crucial for achieving good thermal performance.

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