QFN and TSSOP Packaging for Motor Drivers

The TSSOP package is rectangular and uses two rows of pins. The TSSOP packaging of motor driver ICs usually has a large exposed board at the bottom of the packaging to remove heat from the device.

TSSOP packaging typically has a large exposed plate at the bottom to remove heat.

The QFN package is a lead-free package with a board around the outer edge of the device and a larger board at the bottom center of the device. This larger board is used to absorb heat from the chip.

To eliminate the heat in these packages, the exposed boards must be well welded. Exposed boards are usually at ground potential, so they can be connected to the PCB ground plane.

In an ideal situation, the hot through-hole is directly located in the plate area. In the example of TSSOP packaging, an 18 through hole array with a drilling diameter of 0.38 mm was used. The calculated thermal resistance of this through-hole array is approximately 7.7 ° C/W.

Usually, these hot through-holes use drilling diameters of 0.4 mm or smaller to prevent tin penetration. If the SMT process requires the use of smaller pore sizes, the number of pores should be increased to maintain the overall thermal resistance as low as possible.

In addition to the through holes located in the board area, there are also hot through holes in the external area of the IC body. In TSSOP packaging, the copper area can extend beyond the end of the package, providing another way for the heat in the device to pass through the top copper layer.

Avoid using copper layers at the top to absorb heat on the boards around the edges of QFN device packaging. Hot through-holes must be used to dissipate heat to the inner layer or bottom layer of the PCB.

If the PCB layout is a small QFN (4 × 4 mm) device. In the exposed panel area, only nine hot through-holes are accommodated. Therefore, the thermal performance of this PCB is not as good as that of TSSOP packaging.

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