AN1850 Freescale Semiconductor / Motorola, AN1850 Datasheet - Page 7

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

Board-Level Reliability
1.4 Board-Level Reliability
The two package types behave quite differently with regard to the solder jointÕs ability to withstand repeated
board-mounted thermal cycles. The CBGA substrate, with a coefÞcient of thermal expansion (CTE) of
6.7 ppm/¡C, is mismatched to most epoxy/glass motherboards which have a CTE of around 16 to 22
ppm/¡C. This package to motherboard expansion difference causes the solder balls at the CBGA corners
followed by the edge to fail Þrst in repeated board-level thermal cycling.
The silicon die itself has a CTE of 2.6 ppm/¡C that results in a mismatch with respect to the ceramic
substrate. However, because the ceramic is relatively stiff, the die has minimal inßuence on the CBGA
solder joints. The reliability of the interconnection between the die and ceramic substrate (in effect, the
bumps) is excellent due to the presence of an underÞll.
Figure 7 shows two-parameter Weibull plot of the board-level reliability of the Motorola XPC107 503-pin
CBGA with a 32.5 mm body size cycled from 0 to 100¡C while mounted to a 1.57 mm thick, four-layer test
board. Data is supplied using both the CBGA and PBGA-sized pads. Both cases used a solder-paste volume
3
of 0.079 mm
.
Figure 7. Two Parameter Weibull Plot of the Board-Level Reliability
of the Motorola XPC107 503-pin CBGA
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Flip-Chip PBGA Package ConstructionÑ Assembly and Board-Level Reliability