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A proposal suggests reducing the thermal mismatch between ceramic modules surface mounted on a printed circuit board (PCB) by using multiple PCBs containing differing percentages of metal.
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Sandwich Composite PCBS for Minimizing Solder Interconnection/Strain
A proposal suggests reducing the thermal mismatch between ceramic
modules surface mounted on a printed circuit board (PCB) by using multiple
PCBs containing differing percentages of metal.
In packaging devices, the different thermal coefficient of expansion between
the ceramic module and the metallic PCB can result in thermal strains affecting
the solder posts and lead to failures. The proposed solution to this condition is to
construct a sandwich of multiple PCBs each made up of a core metal (e.g.
INVAR) clad with copper. The copper-core metal ratio will be different in each
PCB so as to minimize the thermal mismatch between elements in the structure.
The number of PCBs required in the structure and the ratio of the copper/core
metal making up the individual PCB will vary according to the design of the
An example of a structure using multiple PCBs, three in this instance, is given
in Fig. 1. The ceramic chip carrier (CCC) 1 is connected by solder posts 2 to the
first PCB 3. It, in turn, is connected to the second PCB 4 which is connected to
the third, and final, PCB 5. The ratio of Cu to INVAR is 55:45 in PCB 1, 72:28 in
PCB 2, while PCB 3 is 100% Cu. There is no drastic differences in TCEs
between the CCC and its adjacent PCB nor between the PCBs. This minimizes
solder strain thereby increasing reliability of the device.