Package structure comprising buffer layer for reducing thermal stress and method of forming the same

A method of forming a package structure, comprising:

• mounting a first die and a second die on a carrier;
• forming a buffer material to conformally cover the first die and the second die;
• performing an exposure process on the buffer material by using a mask with an opening corresponding to the second die, wherein the opening comprises a frame shape surrounding a perimeter of the second die;
• performing a developing process to remove a portion of the buffer material to form a buffer layer that extends continuously from a sidewall of the second die to cover a sidewall of the first die adjacent to the second die;
• and
• forming a first encapsulant encapsulating the first die and the second die, wherein the second die has a second encapsulant encapsulating a die stack, the buffer layer is formed between the first encapsulant and the second encapsulant, and the buffer layer has a Young's modulus less than a Young's modulus of the first encapsulant and a Young's modulus of the second encapsulant.

A method of forming a package structure, comprising:

• mounting a first die and a second die on a carrier;
• forming a buffer material to conformally cover the first die and the second die;
• forming an encapsulant material layer on the buffer material;
• and
• performing a first planarization process to remove the encapsulant material layer and the buffer material over the first die and the second die, so as to form a first encapsulant and a buffer layer in a single process,
• wherein the buffer layer extends continuously from a sidewall of the second die to cover a sidewall of the first die adjacent to the second die and further covers a corner of the second die, a top surface of a passivation layer of the second die, and a sidewall of a connector of the second die.