New Design Formulae for Design of Electronic Components
- Paper number
IAC-07-C2.3.07
- Author
Dr. S.M. Veenaranjini, Indian Space Research Organisation (ISRO), ISAC, India
- Coauthor
Siddesh V, India
- Coauthor
Venkata Rao, Unknown
- Coauthor
Danabalan TL, Unknown
- Year
2007
- Abstract
In this paper new design formulae for computation of frequencies of QFP type of packages with and without underfills are presented. Dynamics is a very important design driver in the design of PCBs and component mounts. Compliant-leaded QFPs tend to have lower frequencies, which fall within the excitation spectrum. In such cases underfills are used to boost their local frequencies and also to reduce the responses in the global modes. Hence it is important to be able to calculate the frequencies and decide whether and what type of underfill is necessary. Flexible leadwires are necessary to reduce the thermally induced stress, which also reduce the stress response due to vibration. However, the process of making the leadwires compliant introduces additional complexity in the computation of frequencies. A typical QFP exhibits six elastic modes due to the inertia of the package and compliance of the leadwires. When an underfill is added, these modes will have contribution from the stiffness of the underfill. For the purpose of frequency estimation, components can be classified as a) components with leadwires on two sides and b) components with leadwires on all the four-sides. While the leadwires can be simplified into springs, underfills being continuum, it is necessary to solve integrals for obtaining their stiffness. This paper presents the formulae derived for calculating the modes of such packages. We can obtain the frequency of the component without underfill by making the moduli of the underfill as null. In the literature, effort has been made to predict the frequencies of components with simple mounting such as one row of leadwires etc. However no formulae are available for computation of frequencies of modern compliant-leaded-QFPs with/without underfills as yet. In this paper formulae are generated for calculation of basic modes of the components. The formulae are verified using detailed FE models and results show that errors are well within acceptable engineering limits. It is also shown that the poisons ratio of underfill plays a significant role in boosting the frequency of the component with underfill. Since the design of electronic packages, component mounts are generally driven by dynamics these formulae are very handy for design.
- Abstract document
- Manuscript document
IAC-07-C2.3.07.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.