A die inside a 23 x 23 mm Plastic Ball Grid Array, CABGA, package with 233 I/O's controls the I/O and read/ write function of the HDD. The goal is to combine functions and increase HDD data transfer rate with minimal System On Chip, SOC, package modification and total cost. As the data transfer rate increases the power, die junction temperature [Tj] and voltage increase in the same manner. The Tj must be maintained below the specified temperature of 115 °C for reliability.

To maintaining Tj below 115 °C as the data rate is increased, cost competitive thermal solutions are engineered. The existing design has a stainless steel [SS] PCBA protection cover with a foam insert for acoustic noise reduction. In one of the thermal solutions, the SS cover is utilized as a heat spreader. Thermally conductive interface material is placed in the gap between the CABGA and the heat spreader.

Three distinct interface configurations were considered for the design. The first uses a thermal conductive tape, 1.8mm [70.9 mils] thick, as an interface to conduct heat from the CABGA to the SS heat spreader. The second uses a laminate: an aluminum plate sandwiched between two thermally conductive tapes of different thickness. This laminate is placed between CABGA and HDD base. The third utilizes a thermal tape to fix an aluminum plate to the top of the CABGA in the absence of the SS cover.

Tests are conducted in an environment with 60 °C ambient temperature. The CABGA, without any thermal enhancement, generated 1.64-1.78 watts at Tj of 115 °C. With 1.8mm thick, thermal conductive tape between the chip and the SS heat spreader, the wattage increased to about 2.0 watts, while maintaining Tj of 115 °C. In the second and third design, with laminate consisting of thermal tapes and aluminum, wattage increased to 2.22-2.30 at Tj of 115 °C. This translates to an improvement of 15.9% and 26.5%, respectively. Data transfer rate could perform from below 400 Mbits per second to, and over, 800 Mbits per second, respectively. Cost of implementing thermal solutions ranged from US$0.11-0.27 per drive. The CABGA has 233 I/Os, which allow all self-testing functions. It would be advantageous to use the same package for high data transfer rate. To achieve beyond 1400 Mbits per second, thermally enhanced QFP [Quad Flat Pack] would be an attractive option. Commercially available 176 and 208 e-PAD QFP's under consideration and some of the testing functions would need to be eliminated. The cost advantage of 176 I/O thermal QFP is the absence of external thermal solution and price benefit of about US$0.70 compared to the 233 I/O CABGA.

For the case study, analytical and experimental thermal data are utilized to design a package that would allow higher data transfer rate with existing components and ease of assembly. The total component and assembly cost was considered in the design to meet the target cost.

Key words: CABGA, packaging, thermal management.