Solder joint reliability of high I/O ceramic-ball-grid arrays and ceramic quad-flat-packs in computer environments: the PowerPC 603TM and PowerPC 604TM microprocessors

Recent trends in wafer fabrication techniques have produced devices with smaller feature dimensions, increasing gate count and chip inputs/outputs (I/Os). This trend has placed increased emphasis on microelectronics packaging. Surface-mountable packages such as the ceramic quad-flat-pack (CQFP) have provided solutions for many high I/O package issues. As the I/O count gets higher, the pitch has been driven smaller to the point where other solutions also become attractive. Surface-mountable ceramic-ball-grid array (CBGA) packages have proven to be good solutions in a variety of applications as designers seek to maximize electrical performance, reduce printed-circuit board real estate, and improve manufacturing process yields. In support of the PowerPC 603 and PowerPC 604 microprocessors, 21 mm CBGA (255 I/Os) and 32 mm (240 I/Os) and 40 mm (304 I/Os) CQFPs are being utilized. Both package types successfully meet computer environment applications. This paper describes test board assembly processes, accelerated thermal stress test setup, and solder joint failure criteria. Failure mechanisms for both packaging technologies will also be presented. The packages discussed in this paper were subjected to two accelerated thermal cycling conditions: 0 to 100°C and -40 to 125°C. The failure data are plotted using Weibull distributions. The accelerated failure distributions were used to predict failure distributions in application space for typical PowerPC 603 and PowerPC 604 microprocessors computer environments. To predict solder joint reliability of surface-mount technology, a key parameter is: the temperature rise above ambient at the solder joint, ΔT. In-situ field temperature measurements were taken for a range of computer platforms in an office environment, at the central-processing units. Printed-circuit boards (PCB) were not uniform, therefore only maximum temperature regions of the board were measured. These maximum temperatures revealed the mean to be less than 20°C above ambient (i.e., ΔT<20°C) regardless of the power of the device. The largest ΔT measured in any system was less than 30°C above ambient. These temperature measurements of actual computer systems are in close agreement with IPC-SM-785. By utilizing the measured PCB temperature rise, solder joint fatigue life was calculated for the 21 mm ceramic ball-aid-array (CBGA), the package for the PowerPC 603^TM and PowerPC 604^TM RISC microprocessors. The average on-off ΔT for most computer applications is approximately 20°C. For an average on-off ΔT of 30°C, the 21 mm CBGA has an estimated fatigue life of over 25 years while the 32 mm and 40 mm CQFP´s have an estimated fatigue life of over 50 years