What’s UCSP Package?
Micro (μ) or Ultra Chip Scale Package (UCSP) is a packaging technology that eliminates the traditional plastic package used to encapsulate integrated circuits (ICs). Soldering the silicon directly to a PCB saves board space, but at the sacrifice of some of the advantages of a traditional package, especially heat dissipation.
Ultra Chip Scale Package (UCSP)
Most packages used for audio amplifiers have some type of exposed pad that allows the substrate of the IC to be connected directly to either a heat sink or the PCB’s ground plane. This design provides a low-thermal impedance path for the heat transferred from the IC to its surroundings, and thus keeps the device from overheating.
With a UCSP package, however, the IC is directly soldered to the PCB using bumps on the bottom surface of the device. While there are direct paths from the substrate to the PCB through the ground bumps and these bumps have a low thermal impedance, their area is much less than a typical exposed pad. Consequently, thermal dissipation is reduced. Nonground bumps also help dissipate heat, but at a reduced capacity compared to ground bumps. Top-side thermal dissipation through a heat sink is impractical due to the space constants of most systems using UCSP devices. The UCSP package is, moreover, not as mechanically robust as other packages typically used with heatsinks. A UCSP can actually become damaged while in contact with the heat sink. The thermal capabilities of a UCSP device are therefore determined by combining the heat dissipated by the grounded bumps with the rest of the bumps on the device.
Audio amplifiers are generally offered in multiple packages and characterized using the package option with the most power dissipation. In most cases these packages prevent the power dissipated by the package itself from limiting the possible output power.
Clearly one must consider the power dissipation of the various package options when choosing an audio amplifier. In many cases only some, not all, package choices can achieve the same continuous output power. In fact, the UCSP often sustains less continuous power than packages with an exposed pad. One can overcome this power dissipation problem not by abandoning the benefits of UCSP, but by using more efficient Class D amplifiers instead of Class AB. That design modification will allow the UCSP package to be used in many more applications.