Fabrication of Die Embedded Substrate and Mechanical Stress Evaluation at Active Area of the Embedded Die

Measurement and modeling for the stress on the active area of the die embedded in an organic resin system has been studied. Embedded structure was successfully realized by doing a sequential lamination process using no other materials but conventional build-up materials, used in printed circuit board, in the organic substrate except die. Embedding process consists of lamination process, laser drilling at the electrode Cu pads of the die, electroless Cu plating, and circuit formation process, i.e. photolithography, electrolytic Cu plating, and etching. The piezoresistive gauges located at the active area of the embedded die were used to measure a stress induced by embedding process. Finite element modeling reveals that the experimental results are well explained. The stress level on the active area is greatly affected by the thickness of the embedded die and by the lamination material species. The die size and the test position in a die, however, have small effects on the stress level change. On the die active surface, highest stress concentrates at the die edge. The stress going exponentially higher only near the 30% point to the diagonal edge from the chip center and the other whole area shows near constant stress level. Due to the CTE and other mechanical properties' difference, stress on the die in prepreg is about 32% higher than filler containing resin system after fabrication. Furthermore, when thickness of die decreases thinner as 140 um (normal case _~ 280 um), the lowered strength of die might lead about 1.57 times higher stress.