as possible there is the mechanical issue of securing the large heat sink to the much smaller die in a robust fashion particularly in portable applications where significant stresses may be encountered an insufficient mechanical connection may result in displacement of the heat sink 27 while a rigid connection may result in stress or even irreparable damage to the die itself in applications where thermal grease or phase change material is used as the heat transfer material at interface 29 it is conventionally necessary to provide a physical attachment between the heat sink 27 and the printed circuit board to provide a secure mechanical connection such a connection is not shown in fig4 but may take various conventional forms such as for example pins or screws extending from the heat sink 27 to the printed circuit board regardless of the attachment mechanism conventional approaches typically require that the heat sink 27 be installed on the flip chip assembly at the time of system assembly as opposed to flip chip package assembly thus adding additional steps and possibilities for error at the system assembly level the common errors are package socket misalignment and thick interface material a thick interface material will degrade thermal performance for example in a high power cpu package even a 0 01.