INVESTIGATION OF THE INFLUENCE OF THE SHAPE FACTOR OF INTERLAYER TRANSITIONS ON THE PROCESS OF CRACKING OF METAL-CERAMIC BOARDS AND CHIP HOUSINGS

PACQMI

Abstract

The article considers the process of formation of cracks in ceramic-metal boards in the zone of localization of interlayer vias formed on the basis of tungsten two-fraction metallization pastes with an average particle size of 0.9 and 2.0 μm, which provide electrical connection between the switching layers of microcircuit packages. A study was made of the influence of the "form factor" of interlayer vias, their structure and placement density on the process of cracking of ceramic-metal boards. The size effect of the direct proportional dependence of the temperature shrinkage of interlayer vias on the diameter and density of their placement on the board is revealed, which has a significant effect on the cracking of boards in the zone of interlayer vias. It has been established that the fineness of the powder filler of the paste intended for the formation of interlayer vias has a significant effect on the degree of consistency between the temperature shrinkage of ceramics and the interlayer via, and hence on the magnitude of stresses at the boundary of the system of elements under consideration, which contribute to the formation of microcracks. It was revealed that the toroidal shape of the interlayer via, characterized by the presence of a cylindrical cavity, which in turn is the initiator of tangential stresses in the volume of the transition, leads to the formation of microcracks. At the same time, continuous interlayer vias have an increased resistance to temperature effects, but do not exclude the possibility of microcracks formation at the “ceramics - interlayer via” boundary. The conditions for the formation of interlayer vias of a toroidal shape with a diameter of 0.1 to 0.5 mm are considered. The dominating effect of the viscosity of metallizing tungsten pastes in the range from 1000 to 70000 Poise on the possibility of the formation of a cylindrical cavity in the volume of the interlayer via has been established. Practical methods for preventing their occurrence are proposed. An estimate of tangential stresses in the volume of toroidal interlayer transitions is given. It has been proven that the formation of an internal cavity in the center of the interlayer via, during its formation, leads to a decrease in temperature shrinkage by 4% relative to the values of thermal shrinkage of a continuous interlayer via. Comparative analysis of temperature shrinkage was carried out for cermet boards containing interlayer vias from 0.3 to 0.5 mm in their volume.