Electrical properties of fine pitch lead frames for glass sealed ceramic QFP

The electrical properties of ceramic-quad flat packages (C-QFPs) have been considered not good enough in the case of fine lead pitch, because lead resistance, lead inductance, and capacitance between leads should increase as lead pitch decreases. The authors studied these electrical parameters and found that the resistance and the inductance can be decreased by an easy method of coating the entire surface of the leads inside the package with aluminum thin film, and that changes in the capacitance can be calculated from the thickness and space leads. On the basis of these findings, the design of very small C-QFPs becomes possible with little cost increase. As an example, an attempt was made to produce an evaluate a very compact 208-lead C-QFP with an outer size of 23 mm square.<>