Xilinx Kria K26 SOM - Page 48

Proles should be established for all new board designs using thermocouples placed at mulple
locaons on the component. In addion, if there is a mixture of devices on the board, then the
prole should be checked at various board locaons to ensure that the minimum reow
temperature is reached on the larger components, and at the same me the temperature does
not exceed the threshold that might damage the smaller, heat sensive components.
The following tables and gures provide the recommended guidelines for Pb-free solder PCB
assembly reow. In general, a gradual-linear ramp into a spike is proven, by various sources, to be
the opmal reow prole for Pb-free solder. This prole results in a beer weng yield and less
thermal shock than the convenonal ramp-soak-spike prole. It is a known fact that SnAgCu
(SAC) alloy reaches its full liquidus at a temperature of 235°C. In the reow proling, the coldest
solder joints need to be idened and to ensure that they reach a minimum peak temperature of
235°C for at least 10 seconds. Reowing at high-peak temperatures of 260°C or above can
damage the heat sensive components and cause board warpage. Refer to the latest IPC/JEDEC
J-STD-020 standard for allowable peak temperature on the components. The allowable
component peak temperature is determined by the component size. The following table lists the
reow soldering temperature prole informaon. In any case, use as low of a peak temperature
reow prole as possible. The following image shows an example of the reow temperature
prole.
Table 16: Recommended Reflow Soldering Temperature Profile
Profile Feature Convection, IR/Convection
Preheat ramp-up rate 30°–150°C 3°C/s maximum
Preheat temperature soak time 150°–200°C 60–120 seconds
Temperature maintained above 217°C 60–120 seconds (60–90 seconds typical)
Time within 5°C of actual peak temperature 30 seconds maximum
Peak temperature (lead/ball) 235°C–245°C typical (depends on solder paste, board size,
component mixture)
Ramp-down rate 4°C/s maximum
Figure 10: Recommended Reflow Soldering Temperature Profile
Chapter 3: Mechanical Design Considerations
UG1091 (v1.0) April 20, 2021 www.xilinx.com
Carrier Card Design for Kria SOM 48
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