Higher Reliability 'Oriented' Plastic Packages

摘要

Plastic IC Packages are generally considered to be not as reliable as their ceramic counterparts. One of the major reasons is the question of hermeticity. Plastic materials generally allow moisture/ humidity to penetrate through the body of the package. When moisture reaches the chip, the chip gets damaged and fails. With ceramic packages, moisture is kept out and the chips last much longer. However, if we analyze the problem more closely, we would find that the penetration of the moisture into the package is accelerated by "Micro-Cracks" that occur at the interface between the metal leads and the plastic encapsulation, where the plastic material hugs and wraps around the leads. The tiny cracks, in essence, separate the plastic material from the lead metal. The cracks start at the edge of the plastic body and then propagate gradually inwards. Moisture gets into the cracks and follows them until it reaches the chip and damages it. Moisture penetration via the cracks is much faster than through the solid plastic body. So, if we reduce or eliminate the chance of the occurrence of these micro cracks, then we would prolong the life of the plastic packages. The author believes that the present design of plastic packages contributes largely to the creation of the micro-cracks, especially in the presence of thermal cycling and similar environmental conditions. The author has arrived at a solution that would reduce the occurrence of such cracks, thus improving the reliability of plastic packages. This paper will describe the proposed solution.