CHAPTER 5 SOLDER JOINT RELIABILITY

The results of mounting the same package on printed wiring boards with an NSMD and SMD land structure and then performing temperature cycle testing are shown below.

For the following conditions range, the NSMD structure has a longer temperature cycle life than the SMD structure.
This is believed to be due to the fact that, when the NSMD structure is used, the solder connection strength is greater because the pad sides are also soldered.
On the other hand, use of the NSMD structure has the demerit that the neck part of the pad lead-out wiring can easily break due to mechanical stress. Therefore, the land structure must be selected according to the intended application.

♦ Temperature cycling test conditions     • -40 to 125°C/10 minutes ♦ Package     • 13 x 13mm, 225 pin FPBGA,        0.65mm pitch, Daisy chain     • Ball composition: Sn-37Pb ♦ Printed wiring board     • Size:       124 x 130 x t0.8mm     • Material: FR-4, 4 layers     • Pad size       NSMD: Cu 0.35, SR 0.45mm       SMD: Cu 0.45, SR 0.35mm     • Pad surface treatment: Pre-flux ♦ Stencil     • Thickness: 150µm     • Aperture: 0.35mm ♦ Solder paste     • Sn-37Pb ♦ Soldering temperature    (package surface)     • Max. 235°C ♦ Failure definition     • 20% nominal resistance increase