SMTA International Conference Proceedings


Author: Carlos Fiol
Company: Delphi Corporation
Date Published: 9/22/2002   Conference: SMTA International

Abstract: Many TQFP packages are now offered with exposed metal pads at the part center. This central plane is soldered to the circuit board in order to enhance thermal and electrical performance. These packages raise questions in the areas of circuit board design, solder paste print, standoff height, and second level reliability.

The effect of thermal via size and quantity must be understood in relation to heat transfer and assembly yield. Optimal solder paste patterns and print variables must be found to insure high first time quality. Assembly yield must also be understood with variations in standoff height between the exposed pad and perimeter leads.

A Six Sigma Black Belt approach was used to design and analyze two experiments in order to define circuit board design guidelines, assembly process variables, and thermal cycle reliability for various sized exposed pad thin quad flat packs (ETQFP).

The sensitivity of assembly yield to varying thermal via patterns, paste print variables, and component standoff heights are discussed. Reliability results at thermal cycle regimens required for automotive electronics is presented. Fatigue life data is presented for both -40 to +125°C and -40 to +150°C cycling.

Key words: epad, exposed pad, ETQFP, automotive.

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