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Loads in the TCT testUsually the mechanical reliability of electronic The temperature during TCT testing is given in Figure packages is qualified by temperature cycle tests (TCT). 2, which is applied isothermally to the module. The However this is a more or less isothermal test, while in temperature is varied between -40 'C and 125 'C with a operating condition temperatures can have a non-unifo*r cycle time of 1 hour. Heating and cooling is slow enough distribution, because thermal transient effects are present to exclude transient effects. Before starting a TCT cycle This effect can play an important role in packages that the product is cooled down from 150 .C to room generate heat, like the module with power amplifier, that temperature. This in fact simulates the soldering process we studied in this work. The transient theal l g in .used to produce the module. Soldering is done at 200°C we sudid iths wrk.Thetranien thrma lodin in and the solder material stiffens; i.e. starts carrying load; the active areas in the flip chip power amplifier causes .. . . ' i thermo-mechanical stresses that may cause fatigue upon cooling. Fixation is assumed at 150 'C. This stress free start at 150°C was also used for the transient fractures in the solder bumps and eventually failure of the si at wth wer c lng module.~~~~~~~~~~~simulations with power cycling module.In this paper we simulate the operating conditions and a TCT. For this purpose a FEA model was created with a new way of working to handle major challenges regarding the large differences in length and time scale. The required element size in the bumps was approximately a factor 200 smaller than that required in the PCB. Furthermore the combination of the heat penetration depth of the short (milliseconds) power pulses together with the heating time of approximately half an hour for the complete module makes conventional simulation methods very time consuming.The new method showed to be accurate and efficient.The simulation results show that in TCT the loading is very different than in power cycling. The critical bump -was in power cycling in the middle of the heating area, while in TCT is located at the corner. We have also calculated an acceleration factor for the TCT test. IntroductionThe flip chip power amplifier is used in mobile phones for receiving and sending RF signals. Figure 1 shows the module. The left (large) flip chip is the (top picte) te a e d evaluated power amplifier. In this amplifier either the left .)() 0 ( 0 or the right side is active depending on the sending w er standard used in different countries. The effect of the 0 C)000 0 a G0 0. 0 other two flip chip dies is not taken into account. o O o o o o o o o o The heat in the flip chip is generated at the bottom 00 1a surface of the power amplifier near the solder bumps. The oo o0 0 0a a 0 0 bottom picture of Figure 1 shows these active areas and 0 000 U Q 000 )U 0 QQQC 0 the bump pattern. The active areas are located between Figure 1.-The module (top picture), the active die with the bumps. bumps...

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