Abstract Thermal conductivity and normalized thermal resistance measurements on eight bulk solders and three tri-layer samples were performed using the laser flash technique. In this study, the laser flash technique is demonstrated to be capable of measuring thermal conductivity of 0.7-mm-thick solders ranged from 20 to 90 W/mK with an average uncertainty of 11%. Laser flash was then used to measure the intrinsic thermal resistance of Cu/Solder/Cu, tri-layer sandwich structures. Analysis shows that the total intrinsic thermal resistance measurement is confounded by sample voiding. C-SAM scanning ultrasonic microscope metrology was shown to be useful in providing information regarding solder voiding and the quality of the solder/copper interfaces. The laser flash method also proved to be useful in assessing voiding effects resulting from different assembly processes and different contacting surfaces on package thermal performance.
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