Peak Package Reflow Temperatures - Peak Package Reflow Temperatures - AM013

For sophisticated boards with a substantial mix of large and small components, it is critical to minimize the ΔT across the board (<10°C) to minimize board warpage and thus, attain higher assembly yields. Minimizing the ΔT is accomplished by using a slower rate in the warm-up and preheating stages.

It is also important to minimize the temperature gradient on the component, between top surface and bottom side, especially during the cooling down phase. The key is to optimize cooling while maintaining a minimal temperature differential between the top surface of the package and the solder joint area. The temperature differential between the top surface of the component and the solder balls must be maintained at less than 7°C during the critical region of the cooling phase of the reflow process. This critical region is in the part of the cooling phase where the balls are not completely solidified to the board yet, usually between the 200°C–217°C range. To efficiently cool the parts, divide the cooling section into multiple zones, with each zone operating at different temperatures.

Consider these factors when determining optimal profile: solder paste/flux type, board size, component density, and component mix. Establish profiles for all new board designs using thermocouples at multiple locations on the component. If the board has a mixture of devices, check the profile at various board locations, as shown in the thermocouple pictures. Make sure the minimum reflow temperature reaches the larger components without exceeding the threshold temperature that damages the smaller, heat sensitive components.