Semiconductor device assembly with graded modulus underfill and associated methods and systems

A method, comprising:

• attaching a semiconductor die to a package substrate by bonding conductive pillars electrically coupled to bond pads of the semiconductor die to conductive pads of the package substrate such that individual conductive pillars are bonded to corresponding conductive pads by a conductive bond material;
• dispensing an underfill material between the package substrate and the semiconductor die attached thereto, the underfill material including a matrix material, first filler particles having a first size distribution, and second filler particles having a second size distribution different than the first size distribution;
• and
• forming at least first and second regions in the underfill material such that the first region has more of the first filler particles than the second filler particles and the second region has more of the second filler particles that the first filler particles.

A semiconductor assembly, comprising:

• a package substrate including conductive pads;
• a semiconductor die including integrated circuitry and bond pads electrically coupled to the integrated circuitry;
• conductive pillars, wherein individual conductive pillars are electrically coupled to a corresponding conductive pad of the package substrate and a corresponding bond pad of the semiconductor die;
• and
• an underfill material between the semiconductor die and the package substrate, wherein the underfill material includes at least a first region having a first modulus of elasticity and a second region having a second modulus of elasticity different than the first modulus.