SNAS674B September 2015 – February 2017 LMK61E2
Ensured Thermal Reliability, Best Practices for Signal Integrity and Recommended Solder Reflow Profile provide recommendations for board layout, solder reflow profile and power supply bypassing when using LMK61E2 to ensure good thermal / electrical performance and overall signal integrity of entire system.
The LMK61E2 is a high performance device. Therefore careful attention must be paid to device configuration and printed circuit board (PCB) layout with respect to power consumption. The ground pin needs to be connected to the ground plane of the PCB through three vias or more, as shown in Figure 34, to maximize thermal dissipation out of the package.
Equation 3 describes the relationship between the PCB temperature around the LMK61E2 and its junction temperature.
In order to ensure that the maximum junction temperature of LMK61E2 is below 125°C, it can be calculated that the maximum PCB temperature without airflow should be at 100°C or below when the device is optimized for best performance resulting in maximum on-chip power dissipation of 0.68 W.
For best electrical performance and signal integrity of entire system with LMK61E2, it is recommended to route vias into decoupling capacitors and then into the LMK61E2. It is also recommended to increase the via count and width of the traces wherever possible. These steps ensure lowest impedance and shortest path for high frequency current flow. Figure 34 shows the layout recommendation for LMK61E2.
It is recommended to follow the solder paste supplier's recommendations to optimize flux activity and to achieve proper melting temperatures of the alloy within the guidelines of J-STD-20. It is preferable for the LMK61E2 to be processed with the lowest peak temperature possible while also remaining below the components peak temperature rating as listed on the MSL label. The exact temperature profile would depend on several factors including maximum peak temperature for the component as rated on the MSL label, Board thickness, PCB material type, PCB geometries, component locations, sizes, densities within PCB, as well solder manufactures recommended profile, and capability of the reflow equipment to as confirmed by the SMT assembly operation.