Development of improved thermal performance embedded heat slug plastic ball grid array package

Abstract

Plastic Ball Grid Array (PBGA) packages with heat slugs embedded in the over-mold have been introduced to improve the thermal performance of the conventional cavity-up PBGA. By utilizing such an embedded (or dropin) heat slug with an exposed surface on the top of the package, thermal performance can be improved 10-20% (with respect to Theta JA) over a conventional PBGA with minimal cost impact. However, if more thermal performance is needed for a particular application, conversion to a cavity-down BGA solution is usually required. Due to their construction, such cavity-down packages are much more expensive than cavityup solutions. A cost effective cavity-up PBGA solution that approaches the thermal performance of a cavity-down solution is desired. Three-dimensional fmite element simulations were utilized to analyze many possible cavity-up PBGA configurations in an effort to improve the thermal performance beyond the current dropin heat slug confguration. This analysis revealed that improved performance could be realized at the lowest cost by increasing the thickness and exposed diameter of the drop-in heat slug. In order to accomplish this the over-mold of the PBGA was also widened. Based on this analysis, such a package was developed using a 680-lead cavity-up PBGA as the test vehicle. This package was tooled and the reliability proven using an existing mass production material set. Also, thermally enhanced mold and die attach materials were evaluated for reliability and effectiveness. For this purpose the same 680-lead cavity-up PBGA package was built in the following confgurations: (I) standard PBGA, (2) conventional drop-in heat slug PBGA; (3) developed wide mold body drop-in heat slug PBGA; (4) developed wide mold body drop-in heat slug PBGA with thermally enhanced mold material; and, (5) developed wide mold body drop-in heat slug PBGA with thermally enhanced mold and die attach materials. Simulations are shown to correlate quite well with tested data. Thus, the development of a cavity-up package approaching cavity-down package thermal performance is realized. Package structures, ffite element models, and test data is presented and discussed.