A reflow profile is not “copying a set of temperatures” onto the oven. First take the window from the solder paste maker’s data sheet (ramp rate, soak, time above liquidus TAL, peak and cooling), then measure the temperatures the board actually reaches with thermocouples on a real board, adjust zone by zone until every thermocouple falls within the window, and finally freeze the conveyor speed and zone settings and re-measure regularly. This article breaks setting up the first profile for a new product into six steps.
For how to read a profile once you have it, see How to read a reflow profile: check these 5 numbers first; for PWI, TAL and the two profile shapes RSS and RTS, see How to read the process window index (PWI). This article covers only how to set it, adjust it and control it. Figures in it come from actual production documents (with company, customer and part numbers removed) and are single-case values, not general specifications; for your conditions, follow the paste maker’s data sheet and component specifications.
1. Take the window first: five numbers from the paste data sheet
Q: What is the first step in setting a profile? A: Copy down the window from the paste maker’s data sheet — ramp rate, soak time, time above liquidus (TAL), peak and cooling rate — then compare it with the temperature limit of the most heat-sensitive component on the board. The window comes from the paste maker, not the oven; change the paste and you need to look again.
One lead-free no-clean paste data sheet we read (an older edition) gives: ramp rate 0.5–2.5 °C/s (0.5–1 preferred), TAL 30–100 s (45–60 s preferred), peak 12–50 °C above the melting point, cooling rate 0.5–6 °C/s. A production profile report sets a different window: ramp rate up to 3 °C/s (target 1.5), soak at 155–185 °C for 25–55 s, above 220 °C for 30–60 s, peak 240–255 °C. The two sets of numbers differ, which shows that the window must follow your paste and product.
On the component side: check the upper peak limit against the temperature rating in the component data sheet (for moisture-sensitive parts, the peak temperature on the classification label), and take the stricter of the two.
2. Choose measurement points: the hottest and coolest places on the board
Q: Where should the thermocouples go? A: At least three kinds of location: the component with the largest heat capacity (the center of a large BGA, near large copper areas), the component with the smallest heat capacity (small passives, board edges), and the body of the most heat-sensitive component. The profile must make “even the coolest point melt fully and even the hottest point not overshoot”, so you measure the two ends of the temperature spread, not an average.
For how to make a profiling board, whether a bare board can be used and how to embed points in BGA balls, see How to make a reflow profiling board; attaching thermocouples with tape, high-temperature solder or adhesive can make a difference of up to 9 °C — see How to attach thermocouples for oven profiling. For equipment, use a reflow profiler with thermocouple wires; the profiler goes through the oven in a thermal barrier, and how long the barrier lasts is shown in the thermal barrier temperature table.
3. Starting settings: calculate from time, don’t guess
Q: With no previous profile to copy, how do you fill in the first set of zone temperatures? A: First decide the conveyor speed (which sets how long the board stays in each zone), then set the zones front to back against the window: preheat zones bring the board up to soak temperature at the target ramp rate, soak zones hold it in the middle of the window, reflow zones put the peak in the middle to lower part of the window, and cooling zones follow the paste maker’s recommendation.
Preheat time can be calculated first: (soak start temperature − room temperature) ÷ ramp rate. One production summary we read gives the example: from 25 °C to 150 °C takes about 42 s at 3 °C/s and about 85 s at 1.5 °C/s; preheat takes about a quarter to a third of the oven length; peak is usually about 25–30 °C above the paste melting point. These are starting points, not answers — after the first measurement you almost always need to adjust again.
For very dense or thick boards or boards with large copper areas, lean the starting settings toward “slow ramp, long soak” to narrow the temperature difference between large and small components first, then deal with the peak.
4. Measure and adjust: change one variable at a time
Q: If the measurement isn’t in the window, what do you adjust first? A: First see which item and which thermocouple is out, then change one variable at a time (one zone’s temperature or the conveyor speed), measure once and record once. Change several zones at once, and whether the result improves or worsens you can’t say why.
A production profile report is a good example: four thermocouples had a ramp rate of 1.6 °C/s and 50–55 s above 220 °C, both within the window, but soak was about 80 s (window maximum 55 s) and peak about 234 °C (window minimum 240 °C) — TAL passed, yet the profile as a whole failed. The fix is to shorten soak and raise peak, not to release it because TAL looks fine. Common directions to compare:
- Ramp too fast: paste slump, solder balls; too slow: flux exhausted early, poor wetting.
- Soak too short: large temperature differences between large and small components, prone to tombstoning and voids; too long: flux exhausted, higher head-in-pillow risk.
- Peak or TAL insufficient: cold joints, dull joints, BGA balls not merging with paste; too high or too long: heat damage to components and boards, overly thick intermetallic.
- Cooling too slow: coarse joint structure; too fast: watch the cooling rate that ceramic capacitors and similar parts can tolerate.
For the full list of symptoms and how to trace causes upstream, see How to troubleshoot reflow soldering defects. In another case, poor joints were fixed by changing three things at once: the carrier was changed from “drilled holes to let heat through” to a carrier without holes for more even temperature, the profile was lengthened for more TAL, and the paste was changed to one with better tack; for carrier effects see How to choose reflow carriers, and for whether to add nitrogen see Is nitrogen in the reflow oven worth it?.
5. First article and freezing: write “this profile” down as settings that can be repeated
Q: What should be kept once the profile is tuned? A: Three things: (1) this measurement report (each thermocouple’s values), (2) the oven settings (conveyor speed, upper and lower zone temperatures, nitrogen or fan speed), and (3) the profiling board number and thermocouple locations. Then for the next changeover, shift change or customer complaint investigation, you can reproduce the same profile and compare the same points.
First article inspection (FAI) should at least confirm the peak. One production parameter control note we read doesn’t set uniform zone ranges because settings differ greatly between products; first article checks only the peak, because overheating damage is the main concern. Another controls the profile with four features: maximum ramp rate, time at 150–200 °C (target 80 ± 10 s), time above 220 °C (target 60 ± 10 s), and time to peak. Which suits you depends on which item your product is most sensitive to.
6. Control in production: daily re-measurement and live alarms
Q: Do you still need to measure the profile in production? A: Yes. A common approach has two layers: in-oven thermocouples monitor each zone against setpoint in real time, plus a measured profile with the profiling board every day (or at every product change).
One production note sets the live monitoring conditions as a warning at ±5 °C deviation from setpoint and an alarm at ±10 °C. When the daily profile check is abnormal, troubleshoot in three layers: the oven itself, the profiler and thermocouple wires, and the software connection — one weekly report we read recorded a line stop where the oven and profiler both turned out to be normal; the cause was a changed thermocouple wire and a suspected software connection problem. For new oven acceptance, one document’s approach is to measure 6 points with a profiler and require temperature accuracy within ±5 °C.
When the profile slowly drifts or the oven temperature is unstable, also think of the condenser and flux recovery: a condenser coated with flux makes oven temperature unstable and can drip flux onto products — see Reflow oven condenser cleaning.
Limitations of this article
- Figures come from the production documents we read and one paste maker’s data sheet (older edition); each is a single case. Windows differ for different pastes, components and ovens; follow the maker’s data sheet and component specifications you have.
- Internal documents have had company, customer and personal names and part numbers removed, keeping only methods and figures.
- This article does not cover thermocouple attachment, profiling board construction or PWI calculation, each of which has its own article (see links above).
FAQ
Q: Can I just use another product’s profile? A: Different board thickness, component density and largest component mean the board reaches different temperatures; you can use it as a starting setting, but always re-measure with a real board of the new product.
Q: How often should the profile be measured? A: Always when introducing a new product, changing paste, or after oven maintenance or repair; in production it is commonly measured daily or at every product change, plus live monitoring of each zone in the oven.
Q: How many measurement points? A: At least enough to cover the hottest, coolest and most heat-sensitive components; the reports we read mostly use 4 or more. If the profiler doesn’t have enough channels, keep the points at the two ends of the temperature spread first. To choose a profiler, see our comparison of reflow profilers from three makers.
To set up a profile for a new product or choose profiling equipment, contact JIAHON or email [email protected].