Finite element analysis of the open window plastic package for optical sensors

Abstract

Sensor packaging has become a critical element of a competitive sensor industry, being a determinant of sensor performance and cost. In the recent past, we worked on a new packaging concept that enabled the development of a low-cost open window plastic package. A first product was developed for an optical sensor. This new development behaved very well on almost all reliability tests performed, i.e., temperature storage, resistance to solvents, gross leak test, Thermal Cycling Test (TCT), pressure pot test, thermal shock, functional/visual test. However, the product failed the solder dip test. The glass lid mounted on top of the package was popping out or was cracked during the test. The package failed because of the stress induced inside the package by the high temperature and air pressure built inside the package cavity. This paper presents a new solution that solves the failure problem arisen in the first development of the Open Quad Flat Pack (OQFP). In order to get to the appropriate solution, we had to analyze the stress levels in critical points within the package. The finite element analysis was applied on the initial version of the OQFP, as well as on new possible solutions. It enabled us to compare the results for each new possible development with those for the first OQFP. From stress analysis results we were able to choose the optimal solution for a reliable, low-cost product. This new solution was manufactured and is being tested.