Moisture Sensitivity Level (MSL) Capability of Plastic-Encapsulated Packages

Abstract

While it is fairly common to achieve MSL 1 (85°C/85% RH, 168 h) compliance with a standard eutectic lead/tin solder reflow range of 220–235°C, the ability to extrapolate to 260°C is proving very difficult. The usual failure mode in moisture sensitivity testing is delamination at the various interfaces of the package followed most of the time by fracture of the mold compound material, the well-known popcorn-cracking phenomena. The primary objective of this chapter is to correlate adhesion and subsequent delamination with various mold compound properties in an attempt to determine which properties from a user standpoint are important in the selection of a proper mold compound to withstand the stresses induced by MSL 1 moisture loading and subsequent reflow at 260°C. Moisture diffusion and adhesion characteristics of various mold compound chemistries are investigated to determine whether these properties can be correlated with MSL 260°C performance. The ultimate goal is to determine whether it is possible to predict compound properties that can be used as a screening method to compare and choose the best candidate compounds. Adhesion performance to bare copper is investigated as a function of moisture loading and reflow. The ability of a dry package to meet MSL performance is established through adhesion testing and actual package performance. Moisture absorption characteristics are then studied. Lastly MSL performance data on actual product at both MSL 1 and 3 conditions are presented. A correlation analysis is performed between moisture absorption data, adhesion, and MSL performance which establishes several conclusions which are discussed. Of primary importance is data analysis which shows the combination of room temperature, adhesion strength, and low moisture absorption to be a good predictor variable for performance of a mold compound when exposed to MSL testing.