The invention relates to microelectronic circuit chip packaging and more particularly to a thermally balanced leadless chip package.
A continuing problem in the manufacture of electronic equipment employing microcircuit chips has been the requirement of mounting or packaging the chip in such a way as to provide adequate heat sinking of the chip while permitting ease of mechanical and electrical connection and detachment between the package and its receiving surface, which is usually a printed circuit board.
Underlying the problem is the thermal incompatibility of the chip carrier material, ceramic, and the typical printed circuit board materials, such as triazine, polyimide and epoxy glass. A direct mounting of the chip carrier to a PC board would result in intolerable differential expansion causing fracture of the chip carrier and/or the stressing and eventual breakage of solder joints leads connected between the chip carrier and board, under all but benign temperature conditions.
Numerous prior art approaches have sought to solve this problem. In one arrangement, ceramic chip carriers are mounted to a ceramic mother board which in turn is connected to the PC board by stress relief leads. In another arrangement, the chip carrier is directly mounted to the PC board using stress relief leads. In some configurations, heat sinks have been brazed to the outside of the chip carrier.
In some prior art packages little or no attempt is made to heat sink the chip and in others, particularly in leadless chip carriers soldered to boards, the differential expansion problem is not treated. Thus, their applications are limited.
In memory applications, chip packages have generally been attached to boards by means of sockets to permit quick replacement of failed chips. Non-memory applications typically have the packages soldered to the board.
Heretofore, chip packages have not provided heat sinking in a leadless chip carrier that can be directly mounted to a board with non-soldered or soldered electrical connections.
A survery of various prior art approaches is set forth in an article "Packaging Technology Responds to the Demand for Higher Densities," by Jerry Lyman, Electronics, Sept. 28, 1978, Vol. 51, No. 20.