AN1850 Freescale Semiconductor / Motorola, AN1850 Datasheet - Page 8

• Manufacturer Part Number: AN1850
• Description: Flip-Chip PBGA Package Construction Assembly and Board-Level Reliability
• Manufacturer: Freescale Semiconductor / Motorola

Board-Level Reliability
Motorola has extensive board-level reliability data on every CBGA body size used for products. Figure 7
contains solder-joint reliability data for the 503-pin, 32.5 mm body Motorola XPC107 mounted to a 1.57-
mm thick, four-copper-layer FR-402 epoxy/glass test board that is thermally cycled from 0 to 100¡C with
Þve-minute ramps and ten-minute dwells. This is currently the largest CBGA body size offered by
Motorola; see package drawing in Figure 8. This package contains seven perimeter rows of solder balls with
an 11x11 array depopulated in the center. The board-level failure data in Figure 7 is plotted on two
parameter Weibull axes, and data is presented for both the CBGA and PBGA preferred motherboard pad
sizes of 0.72 and 0.58 mm, respectively. Each point on the lines represents a package failure which is
deÞned as the series resistance through all the joints going over 300 Ohms during continuous in-situ
monitoring. The PBGA recommended pad actually has a higher Eta or cycles to 63.2% failure, but due to
the lower slope of the line (Beta) for the PBGA-sized pad, the cycles to failure for lower failure rates such
as 0.1% and 0.01% are somewhat worse for this optional pad.
Conversely to the CBGA, the FC PBGAÕs epoxy/glass substrate is well matched in terms of expansion to
most motherboards. The FC PBGA substrate has a CTE of approximately 12 to 14 ppm/¡C. It also relies
on underÞll to provide adequate die-to-package interconnect reliability, but since the FC PBGA substrate is
not as stiff as the CBGAÕs, the die can have some inßuence on the reliability of solder joints proximate to
the die edge. The dieÕs inßuence is mitigated by the use of 1.0-mm thick substrate on all Motorola FC
PBGAs and by depopulating the solder balls under the die edge on some designs such as the 503-pin
package.
The Motorola XPC107 in a 503-pin FC PBGA (see Figure 9) has passed 6,000 0¡C to 100¡C thermal cycles
with no fails. This equates to an expected 6x increase in board-level reliability relative to the same size
CBGA for which data was presented in Figure 7. Because the 503-pin is a perimeter package with no solder
balls under the die edge, the board-level reliability for full-array FC PBGAs such as the 255- and 360-pin
packages may not exhibit the same increase, but they will still provide a signiÞcant board-level reliability
improvement over CBGA. Board-level cycling on the 360-pin, 25 mm FC PBGA is currently underway
with no fails out to 3,000 cycles, which represents an approximate 3x increase in life relative to the
equivalent CBGA. Cycling on this 360-pin FC PBGA is being carried out using both the FC PBGA and the
CBGA-sized motherboard pads with no fails on either pad size.
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Flip-Chip PBGA Package ConstructionÑ Assembly and Board-Level Reliability