Project Number: C95-23

KEY ISSUES IN THE USE OF PLASTIC ENCAPSULATED MICROELECTRONICS

Point of Contact Dr. Pat McCluskey e-mail: mcclupa@calce.umd.edu Phone: (301) 405-5323 Fax: (301) 314-9269

Objectives

Background

Approach

Work Accomplished

Objectives

Define assembly techniques which will not compromise the long term reliability of PEMs. Address key issues related to the long term reliability and use of plastic encapsulated microelectronics.

Background

Improvements in materials technology have made undamaged PEMs less sensitive to temperature-humidity stress. It is important, however, to ensure that PEMs remain undamaged by assembly. The high reliability of undamaged PEMs can be compromised by delamination and cracking during infrared (IR) reflow. Moisture absorbed during storage can vaporize at soldering temperatures, causing delaminations and cracks to occur at dissimilar material interfaces in the package. This phenomenon can cause catastrophic failure by wire bond breakage or die cracking, and is believed to jeopardize the long term reliability by allowing ingress of moisture and contaminants along the cracks.

A study is needed to a) eliminate the sources of delamination and cracking and b) evaluate the effects of delamination and cracking on long term reliability.

Approach

Experiments will be conducted to develop a method for qualifying plastic packages against delamination and cracking. This will be achieved by assessing the effect of reflow ramp rate and multiple reflow cycles on delamination and cracking, as a function of IPC preconditioning level, molding compound, and die attach. A real-time X-radiography system combined with an IR heating system will be used to precisely heat the PEMs through any desired temperature profile, while simultaneously observing the X-ray image for failures. Acoustic microscopy will be used to quantify the extent of delamination and cracking.
Experiments will be designed and conducted to evaluate the effects of delamination and cracking on the rate of degradation in temperature-humidity and temperature cycling environments.

Work Accomplished

Determined the effect of IR reflow soldering ramp rate on package failure.
Determined the effect of 2nd & 3rd reflow cycles, specified in the IPC preconditioning procedure, on package failure.
Conducted preliminary experiments on the popcorning phenomenon in ball grid arrays.
Designed and conducted preliminary experiments showing the effect of different levels of delamination and cracking on the rate of degradation in temperature-humidity stress.