Optimization of the gull wing lead

Summary form only given. The long-term reliability of fine-pitch gull wing leads was investigated in a temperature cycling environment of -40 degrees C to 125 degrees C. The test vehicle was a 208-lead fine pitch quad flat pack (FQFP) plastic package, with lead pitch of 0.5 mm. The leads were specially prepared in the following configuration: two different foot lengths, 0.5 mm and 0.8 mm; two different foot angles, 2 degrees and 14 degrees ; two different lower bend radii, 14 mils and 21 mils; two different solder compositions, 63/37 Sn/Pb and 62/36/2 Sn/Pb/Ag; coplanarity for all leads of 1.4 mils or less; coplanarity of all eight corner leads deformed in the range of 1.5 to 2.9 mils; and coplanarity of all eight corner leads deformed in the range of 3.0 to 4.4 mils. A Taguchi experiment design with an L8 orthogonal array was employed in this investigation.<
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