Journal of SMT Article


Authors: Geun Sik Kim and Dong Sik Kim
Company: STATS ChipPAC Inc.
Date Published: 10/1/2007   Volume: 20-4

Abstract: As industry is moving to more integrated and miniaturized packaging for mobile applications, smaller solder ball pitch packaging is required for providing more I/Os within a given real estate without increasing package size. To meet this requirement, 0.4 mm solder ball pitch VFBGA (11mm x 11mm, 432 Leads), which is based on either 1-2-1 build up or 2L (layer) laminated substrate, has been developed. For 0.4mm solder ball pitch packaging, substrate technologies with tighter design rules such as 35µm/35µm line/space, via in pad and tailless were applied. And efforts were given for solder ball mounting technology developments to improve smaller ball diameter (0.25mm) ball pick up and placement accuracy so that assembly yield can be high enough for production.

To do solder joint evaluation, different lead-free compositions ( SAC1205Ni (Sn1.2%Ag0.5%Cu + Ni addition), SAC105 (Sn1.0%Ag0.5%Cu), SAC2505 (Sn2.5%Ag0.5%Cu) ) of solder ball on Ni/Au, OSP (Organic Solderability Preservative) and DIG (Direct Immersion Gold) finished ball pad were investigated with zone shear test and drop test with JEDEC specified condition (JESD22-B111) together with BST(Ball Shear Test) and IMC(Intermetallic Compound) cross-section analysis up to 1000hrs at 150° C. BST values of the prepared samples showed substrate surface finish dependency on its average value. Failures with OSP finish legs without pre-cleaning in the zone shear test tells that 0.4mm pitch is less favorable for removing oxide layers than larger solder ball pitch due to its small solder resist opening size. Among the combination of experimental legs, Ni/Au with SAC 105, OSP with SAC1205Ni and DIG with SAC1205Ni show similar drop performance and meet JEDEC criteria of no failure of minimum of 30 drops in the test.

Keywords: 0.4mm pitch, FBGA, Drop performance

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