Reflow Thermal Profiling - How to Build a Profile Step by Step
A clean reflow profile decides joint quality, wetting and defect rates. This guide shows step by step how to capture a profile with a profiler and thermocouples per the solder paste datasheet, set the four zones and reliably hit peak, TAL and ramp rates.
View reflow accessoriesWhat is a reflow profile and why does it matter?
A reflow profile is the temperature-versus-time curve an assembly follows inside the reflow oven. It controls how the flux is activated, how the solder melts and how the intermetallic layer forms. The goal is even heating with no thermal shock and no overheating of sensitive components.
There are two profile shapes: ramp-soak-spike (RSS) with a preheat and hold zone, and ramp-to-peak (RTP) with a continuous linear rise. Which one fits is defined by the solder paste datasheet. For lead-free SAC305 paste the liquidus point is around 217 °C, and the peak is typically 235 to 249 °C.
- Preheat: gentle rise to about 150 °C, ramp rate 1 to 3 K/s.
- Soak (thermal equalization): 60 to 120 s at 150 to 200 °C, activates the flux.
- Reflow: cross the liquidus, peak per datasheet, TAL 45 to 90 s.
- Cooling: controlled at no more than 3 to 4 K/s to avoid brittle joints.
How do you attach thermocouples correctly?
The profiler measures the real temperature at the joint through type K thermocouples. Thermal coupling is critical: a poorly attached thermocouple reads air instead of the component and yields a false profile. Fix the measuring points with high-temperature solder, SMD adhesive or aluminium tape.
How do you set the profile per datasheet?
After the first run, compare the captured curve with the process window in the datasheet. Adjust the zone temperatures and belt speed iteratively until all parts stay within the limits. Delta-T control matters: the difference between the hottest and coolest measuring point should stay below 5 °C during reflow.
- Check peak: above liquidus but below the component limit per IPC J-STD-020.
- Measure Time Above Liquidus (TAL): typically 45 to 90 s for SAC305.
- Limit the reflow ramp rate: 1 to 3 K/s, avoid spikes.
- Keep the soak window so the flux fully activates.
- Control the cooling rate: below 4 K/s for a fine-grained, strong structure.
Frequently asked questions
How many thermocouples do I need?
For a reliable statement, at least three to five: on the largest and smallest component and at the board edge. That captures the full thermal spread of the assembly.
Where do peak and TAL come from?
Always from the datasheet of the solder paste in use. The maker states liquidus, recommended peak, TAL window and maximum ramp rates. These values are binding for your profile.
What does delta-T mean in profiling?
Delta-T is the temperature difference between the hottest and coolest measuring point at the same moment. A small delta-T during reflow, ideally under 5 °C, gives even joints.
Ramp-soak or ramp-to-peak?
It depends on the paste and assembly. Ramp-soak helps with high thermal mass and activates flux thoroughly, ramp-to-peak is simpler and lowers total heat load. The datasheet gives the recommendation.
Setting up a reflow profile?
We supply profilers, type K thermocouples and attachment material for reproducible profiling per solder paste datasheet.
Precise measurement
Calibrated type K thermocouples right at the joint.
Standard in view
Peak temperatures within IPC J-STD-020 limits.
Reproducible
Documented profiles for stable series production.
Expert advice
Soldering specialists support your profile setup.