SMTA International Conference Proceedings


Authors: Keith Kirchner and David Nelson
Company: Raytheon Company
Date Published: 9/26/2004   Conference: SMTA International

Abstract: Surface mount devices are shrinking from ball grid array (BGA) packages with ball pitches in the range of 0.80 to 1.50 millimeters to smaller chip scale package (CSP) devices with pitches to 0.50 millimeters, or smaller. Conformal coating, used as protection from the environment, is commonly required in high reliability products. However, as package sizes are reduced, there is the potential that conformal coating expansion characteristics may degrade the mechanical integrity of the solder joint.

The study investigates the impact of silicone and Parylene conformal coatings, epoxy underfill materials and a silicone sealant on a variety of area array packages while being subjected to thermal cycling. A test vehicle was created specifically for the investigation. The test vehicles were exposed to 2000 thermal cycles from -40o to 95o Centigrade with 10 minute dwell periods at each temperature extreme and a maximum temperature ramp rate of 10o Centigrade per minute.

The test vehicles were subsequently exposed to 500 additional cycles from -55o to 125o Centigrade. Continuous electrical monitoring, visual inspection and cross section techniques were used to analyze the test vehicles.

Key words: area array, solder joints, conformal coat, underfill and reliability.

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