A flexible semiconductor package is formed by interposing a flexible substrate between a tungsten stiffener and a die. A tungsten stiffener is bonded to a first surface of the flexible substrate prior to flip chip bonding or die attach of a die to a second surface of the flexible substrate. The tungsten stiffener is dimensioned so as to substantially overlap the die and provide a rigid and flat surface on which the die/flexible substrate bonding occurs. The flat and rigid characteristic of a tungsten stiffener optimizes the electrical and mechanical bond between the die and the flexible substrate as well as minimizing CTE mismatch.