A fresh look at thermal resistance in electronic packages

It has been known for a long time that existing thermal resistance theta ja component characterization techniques are inadequate. The associated error s are too great and uncertain. The emerging packages like Ball Grid Array ( BGA), Chip Scale Packaging (CSP) and Chip On Board (COB), the effect of the board cannot be ignored. System designers want and need a quick and reliab le estimating technique. Many definitions and standards on electronic packa ge thermal resistance have been expressed in different manners by leading c omponent manufacturers and standard organization i.e. JEDEC. All of these s hared the same objective to meet the practical requirement of the electroni c packages. This paper will illustrate the correlation of thermal resistanc e measurement for an electronic package determined experimentally for compa rison with computer simulated value. The computer simulation is carried out based on JEDEC standards. However, JEDEC standards provide a means for com parison of packages rather than determining the thermal resistance of a pac kage at a given environment. Thus, there is a need to convert the data obta ined by JEDEC standards to actual environmental situations. Another importa nt factor which is normally overlooked in the determination of thermal resi stance of a package is the effect of temperature (case or reference) on the thermal resistance at the operating conditions. All these factors bother t he persons evaluating the thermal resistance in the industry on a routine b asis struggling to arrive at a correct interpretation of the results obtain ed by experiment and simulation in comparison to reality. The problems in t he recent years have increased in view of the miniaturization and consequen t increase in heat flux levels. In addition to this, the package has to mee t more stringent requirements in view of harsh environment in some cases. T he present paper takes a fresh look at the determination of thermal resista nce taking into account the various factors discussed above in view of the experience accumulated in the industry over the years.