CHAPTER 5 SOLDER JOINT RELIABILITY

The reliability results of mounting the same package on printed wiring boards of various thicknesses and then performing temperature cycle testing are shown below.
In the condition range used this time, the temperature cycle life was longer for thinner printed wiring boards. This is thought to be due to the fact that, in the case of a thick printed wiring board, it is more difficult for the board to keep up with the package's thermal expansion and contraction, which results in greater thermal stress on the solder joints.

♦ Temperature cycling test condition     • -40 to 125°C/10 minutes ♦ Package     • 16 x 16mm, 224 pin FPBGA,        0.8mm pitch, Daisy chain     • Ball composition: Sn-3Ag-0.5Cu ♦ Printed wiring board     • Size:       124 x 130 x t1.2mm/t1.6mm     • Material: FR-4, 4 layers     • Pad size: Cu 0.4, SR 0.55mm     • Pad surface treatment: Pre-flux ♦ Stencil     • Thickness: 150µm     • Aperture: 0.4mm ♦ Solder paste     • Sn-3Ag-0.5Cu ♦ Soldering temperature    (package surface)     • Sn-3Ag-0.5Cu ball: Max. 260°C ♦ Failure definition     • 20% nominal resistance increase