Page "Reflow soldering" Paragraph 4

The third section, the reflow zone, is also referred to as the “ time above reflow ” or “ time above liquidus ” ( TAL ), and is the part of the process where the maximum temperature is reached.

An important consideration is peak temperature, which is the maximum allowable temperature of the entire process.

A common peak temperature is 20 – 40 ° C above liquidus.

This limit is determined by the component on the assembly with the lowest tolerance for high temperatures ( The component most susceptible to thermal damage ).

A standard guideline is to subtract 5 ° C from the maximum temperature that the most vulnerable component can sustain to arrive at the maximum temperature for process.

It is important to monitor the process temperature to keep it from exceeding this limit.

Additionally, high temperatures ( beyond 260 ° C ) may cause damage to the internal dies of SMT components as well as foster intermetallic growth.

Conversely, a temperature that isn ’ t hot enough may prevent the paste from reflowing adequately.