fiXtress Rapid-based Stress Derating for Electronic Design
The practice known as “derating”, which can be performed manually, and summarized in a spreadsheet format, is often a time consuming and laborious task for PCB designers, and eventually causes errors in calculations. Derating, the technique which either reduces stresses on a part, or increases the strength of that part by replacing a component, is best done using CARE’s stress derating module.
This module uses the stresses that have been inserted by the user, in order to check if the components’ ‘rating’ values meet the derating criteria. These derating criteria can be defined in different tables for every type of component as a function of temperature, and they include Standard, Military, Industrial and customized derating curves.
The component stress should be in the green area, rather than in the yellow or red area.
The stress parameters used include Power, Voltage, Current and temperature. Over-stressed and over-designed components are reported and a recommendation is made for the optimal rating. In other words, the applied value (power, voltage, current) of a particular component is multiplied by its derated factor value which also depends on temperature, and only if after derating, the ‘applied value’ exceeds the maximum rating assigned to it, then the stress derating analysis will offer a recommendation of what needs to be done in order to have less stress on the component. This can include replacing the component with a better one (increasing the rating value), relocating the component on the PCB to a cooler area, or adding a fan or heat-sink in order to reduce the temperature.
As an example, below is the stress parameters of a resistor. The maximum power as defined by the component datasheet is 5W, and although the applied value is 4W, the derating curve states that it needs to be 51.7% of the maximum rating. This will allow dissipating only 2.5862W. If we divide 4W with 2.5862W, the result will be that the component is overstressed by 154.7%. Since this is 80% of the rating, the software will place one asterisk in that row, stating that this is a critical item that needs to be corrected. If the power dissipation surpasses 100% of the rating, two asterisks will appear.