Content area
Full text
An evaluation of this packaging option's assembly and reliability.
The need for smaller, lighter, faster and cheaper products drives new and innovative packaging and interconnect schemes to meet cost requirements without compromising product performance. Ball-grid array (BGA) packages have become a preferred option for applications requiring more than 300 interconnects.1BGAs provide higher interconnect density while mitigating assembly problems associated with QFPs (quad flat packs). Today, PCB assemblies with multiple BGA devices of greater than 600 I/Os are mass-produced, with less than 15 defects/ppm (parts per million) assembly defects.2 Beyond BGAs, chip-scale packages (CSPs) and direct chip attach (DCA) interconnects, are probably the next steps in the technology roadmap of electronics packaging. Despite the density and performance benefits they provide, CSP and DCA technologies need to be cost effective with matured support infrastructure before they will become common interconnect options.
Double-sided mirror-imaged (DSMI) BGA assembly is a packaging option that provides increased interconnect density and performance without a significant increase in cost. It is a board-level packaging technique in which BGAs or QFPs can be mounted on a double-sided PCB assembly that is mirror imaged, as illustrated in Figure 1. Obviously, with increased device I/O counts, the circuitry escape routing becomes a critical limitation. However, the increased capabilities of substrate manufacturing in microvia and reduced trace size fabrication mitigate the need for increased board layers typically associated with increased I/O counts. Hence, DSMI BGA assembly can be utilized without a significant increase in the cost of a bare PCB.
Another critical consideration in high-density interconnect is the device-to-board level attachment reliability. Increased I/O count, which typically results in increased device size, directly affects the reliability of solder joints. Possible reduction in solder joint volume due to diminished ball size, combined with increased device size, has significant effects on attachment reliability. These effects are due to the increase in the thermal expansion mismatch strain with increased device dimension. The results of the experimental study that investigated assembly and solder joint reliability effects of DSS BGA assembly on high I/O count (> 400 I/O) devices are presented.
Experimental Procedures
The objective of the experiment was to evaluate the effect of DSMI BGA assembly on solder joint reliability. The evaluation was focused on high UO count (>...