IPC-7530A Draft Document for Industry Consensus Only August 2016
Figure 1-1 Pasty Range of SnPb Solder
1.4.3 Ramp Rate
Ramp rate is measured by dividing the net change in temperature by the total time in that zone. During the soldering operation, the ramp rate is different in different zones such as preheat zone, soak zone, reflow zone and cooling zone. Ramp rate is very high in preheat zone and very low in the soak zone.
1.4.4 Soak (Dwell)
The time/temperature an assembly is held at a very low ramp rate in the soldering process to allow all components to come to equilibrium. In a reflow operation, the soak (dwell) also ensures that the solder paste is fully dried before hitting reflow temperatures and acts as a flux activation zone for solder pastes
1.4.5 Peak
The maximum allowable temperature of the entire process. A portion of the reflow process where the temperature is raised sufficiently to cause the solder paste to reflow.
1.4.6 Melting Point
The temperature at which a solder alloy starts becoming liquid.
1.4.7 Liquidus, Solidus and Eutectic
Liquidus: The temperature at which a solder alloy is completely melted. Solidus: The temperature at which a solder alloy is completely solid. Eutectic: A temperature where solidus and liquidus temperatures are the same.
1.4.8 Time Above Melting Point (TAMP)
Time above melting point
1.4.9 Time Above Liquidus (TAL)
Time above liquidus. TAL for solder is also expressed at different liquidus temperatures. For example, for lead-free solder, TAL can be expressed at 220 or at 235 or at 245C. The higher the temperature, the shorter is TAL. When a specific temperature is not mentioned, TAL is assumed to be the time above melting point of solder 1.4.10 TAL vs
TAMP
In cases of eutectic alloys, TAL and TAMP are the same. In cases of non-eutectic alloys, TAL is less than TAMP.
1.4.11 True TAL
The solder joint on the PCB that is above melting point the shortest amount of time. In other words, the duration of time where ALL solder joints are above liquidus of solder. True TAL is less than TAL of component(s) that are smaller in thermal mass. In case of BGA, true TAL is less than TAL of BGA balls on the periphery which are in molten condition longer than BGA balls in the center of the package.
1.4.12 Delta T (profile or equipment)
The largest temperature difference between two or more measurement points at a given point in time.
1.4.13 Phase Diagram
A graphic representation that shows limits of stability of various phases in a metallurgical alloy system at equilibrium with respect to variables such as composition and temperature.
1.4.14 Superheat
The temperature between the peak reflow temperature and the liquidus of the alloy. Superheat is generally around 25C in SAC lead free and 30 to 40 C in tin-lead or low-temperature lead-free alloys.
1.4.15 Cooldown
The time for the assembly to return to ambient temperature after a soldering operation.
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