Resolution of extreme warpage in ultra-thin molded array packages under High Temperature Storage Life

Abstract

The semiconductor industry is demanding miniaturization coupled with increased functionality from microelectronic packages. Ultra-thin molded array packages (TMAP) with package thickness ≤ 500 µm are desirable for applications where system integration space is limited. Such ultra-thin packages require careful selection of the epoxy molding compound (EMC) to control strip level and package level warpage. In this work, the ultra-thin MAP package (8 mm × 8 mm) has an EMC thickness of 0.250 ± 0.025 mm, substrate thickness of 0.105 ± 0.025 mm, and 0.076 mm thick die. This package was found to exhibit extreme “smiley-face” warpage (solder balls down) of 160 µm after 175°C, 504 hrs High Temperature Storage Life (HTSL) conditions, resulting in problems with automated package pick-up by the test handler arm during electrical testing. The warpage was permanent and no relaxation was observed even after one month of storage at room temperature. The primary mechanism for this warpage behavior was found to be thermal oxidation of the EMC in HTSL. High temperature causes thermo-oxidative crosslinking leading to densification and shrinkage of the EMC inducing stresses leading to package warpage. Oxidation also changes the coefficient of thermal expansion and elastic modulus of the EMC.