Back to results
US 4,509,096 AGranted
Chip-carrier substrates
AssigneeSmiths Industries Public Limited Company
InventorsGraham J. Baldwin, Michael O. McCann
Life of this patent
Estimating the term…
Loading patent…
Loading patent…
AssigneeSmiths Industries Public Limited Company
InventorsGraham J. Baldwin, Michael O. McCann
Estimating the term…
A substrate for a leadless chip carrier is formed on a rigid multi-layer circuit board. Layers of copper-clad invar are secured to opposite sides of the board, and on top of these are mounted respective layers of elastomeric material. An electrically-conductive layer is laid on top of the upper elastomeric layer and this is formed in a pattern of contact elements, and tracks which may be of dog-leg shape and which are interconnected to other layers of the substrate by plated holes. The chip carrier is supported on a heat transfer pad of copper which rests on the upper invar layer and is secured thereto by a layer of solder. The pad may have an integral pillar that extends through a copper-plated aperture in the substrate to a heat-dissipating pad on the surface of the lower elastomeric layer. Contact pads on the chip carrier are soldered to the contact elements, the height of the heat-transfer pad being such as to separate them and ensure a thick solder joint. The solder joints and the solder under the heat-transfer pad apply a force urging the carrier into close contact with the pad. Heat is conducted away from the underside of the carrier by the pad to the top invar layer, or, where the pad has a pillar, also to the lower invar layer and the heat-dissipating pad.
A chip-carrier substrate assembly comprising a chip-carrier substrate, a leadless chip carrier mounted on said substrate, said leadless chip carrier having a plurality of electrical contact pads spaced around its lower edge, said substrate including a substantially rigid multi-layer circuit board having electrical contact elements on its upper surface, solder joints electrically connecting said contact elements on said circuit board with respective ones of said electrical contact pads on said chip carrier, said substrate including at least one metal heat-dissipating layer, the chip-carrier substrate further including a metal pad with an upper surface and a lower surface, a layer of solder between the lower surface of said metal pad and the circuit board, said solder layer mounting said metal pad between said circuit board and the lower surface of said chip carrier, said metal pad being in thermal contact with both said heat-dissipating layer and the lower surface of the said leadless chip carrier, and the size and thickness of the said metal pad being such that the edges of said chip carrier overhang the metal pad and such that the contact pads on the chip carrier are spaced above the contact elements on the circuit board so as to increase the thickness of the said solder joint between the contact pads and the contact elements.
Dependencies are inferred from the claim text.