# Reflow Oven Belt Speed and Ramp Rate Calculator

> Source: https://netray.co/tools/reflow-oven-belt-speed-ramp-rate-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Relate conveyor belt speed to dwell time per zone, total oven time and average preheat ramp rate, then back-solve belt speed for a target ramp.

## Category

electronics

## Industry

Electronics Manufacturing

## Audience

- SMT process engineer
- Reflow oven technician
- PCBA quality engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Belt speed

**Key:** belt

**Type:** slider

**Default:** 80

**Min:** 30

**Max:** 160

**Step:** 1

**Unit:** cm/min

#### Length of each zone

**Key:** zone_len

**Type:** number

**Default:** 30

**Min:** 5

**Step:** 1

**Unit:** cm

#### Preheat and soak zones

**Key:** pre_zones

**Type:** number

**Default:** 5

**Min:** 1

**Step:** 1

**Unit:** zones

#### Reflow (peak) zones

**Key:** peak_zones

**Type:** number

**Default:** 2

**Min:** 1

**Step:** 1

**Unit:** zones

#### Cooling zones

**Key:** cool_zones

**Type:** number

**Default:** 2

**Min:** 0

**Step:** 1

**Unit:** zones

#### Board start temperature

**Key:** t_start

**Type:** number

**Default:** 25

**Min:** 0

**Step:** 1

**Unit:** C

#### Temperature at end of preheat

**Key:** t_soak

**Type:** number

**Default:** 150

**Min:** 50

**Step:** 5

**Unit:** C

#### Target average ramp rate

**Key:** ramp_max

**Type:** number

**Default:** 1.5

**Min:** 0.1

**Step:** 0.1

**Unit:** C/s

**Help:** Take the limit from the solder paste datasheet.

**Outputs:**

#### Dwell time per zone

**Key:** per_zone

**Expr:** zone_len / belt * 60

**Format:** decimal

**Description:** Seconds per zone.

#### Preheat time

**Key:** pre_time

**Expr:** pre_zones * per_zone

**Format:** decimal

**Description:** Seconds.

#### Average preheat ramp rate

**Key:** ramp

**Expr:** (t_soak - t_start) / pre_time

**Format:** decimal

**Primary:** true

**Description:** C per second.

#### Time in reflow zones

**Key:** peak_time

**Expr:** peak_zones * per_zone

**Format:** decimal

**Description:** Upper bound on time above liquidus.

#### Total oven time

**Key:** total

**Expr:** (pre_zones + peak_zones + cool_zones) * per_zone

**Format:** decimal

**Description:** Seconds.

#### Belt speed for target ramp

**Key:** belt_needed

**Expr:** ramp_max * pre_zones * zone_len * 60 / (t_soak - t_start)

**Format:** decimal

**Primary:** true

**Description:** cm per minute that gives the target average ramp. Slower belt gives a lower ramp.

**Chart:**

#### Average preheat ramp rate vs belt speed

**Type:** line

**X:** belt

**From:** 30

**To:** 160

**Steps:** 30

**Series:**

- ramp

**Disclaimer:** This is an average from zone timing. The actual board temperature depends on thermal mass, zone setpoints, airflow and component density, so confirm with a thermocouple profile.

## Content

**Intro:** Belt speed is the first knob a process engineer turns when a profile misses. This calculator links belt speed, zone length and zone count to dwell time and the average ramp rate, and it back-solves the speed for a paste's maximum ramp.

**Sections:**

#### How to use it

**Body:** Enter the belt speed and the length and count of preheat, reflow and cooling zones from your oven manual. Enter the start temperature and the temperature at the end of preheat, then your target ramp from the paste datasheet. The tool shows the time per zone, average ramp rate and the belt speed that would hit the target.

#### The math

**Body:** Dwell time per zone in seconds equals zone length divided by belt speed times 60. Preheat time is that value times the number of preheat zones. Average ramp rate equals the temperature rise divided by preheat time. The belt speed for a target ramp is found by solving that equation for belt speed.

**Bullets:**

- Doubling belt speed halves every dwell time
- Ramp rate scales directly with belt speed
- Time in the reflow zones bounds time above liquidus

#### Reading the result

**Body:** At 80 cm/min with 30 cm zones, each zone takes 22.5 seconds, so five preheat zones take about 112 seconds, and a 125 C rise averages about 1.1 C/s. If the paste calls for no more than 3 C/s and a long soak, you have room to speed up the belt, and the back-solved speed shows the limit.

#### Common mistakes

**Body:** Treating oven zone setpoints as board temperatures is the classic error. The board lags the air and heavy parts lag the board. Another is changing belt speed without revisiting setpoints, which shifts the whole profile. Always measure with a profiler on the board that has the most thermal mass.

**Cta:** Netray can store approved reflow profiles against item and routing records in your ERP so every job runs the released recipe.

**Faq:**

#### What ramp rate is typical?

**Answer:** Many lead-free paste datasheets recommend an average ramp below about 2 to 3 C/s to limit slumping and thermal shock. Always use the number from your paste and component datasheets.

#### Why is time in reflow zones only an upper bound for TAL?

**Answer:** Time above liquidus begins after the board crosses its liquidus temperature inside the reflow zones, and ends in cooling. So it is shorter than the zone dwell time.

#### Does belt speed affect cooling rate?

**Answer:** Yes. A faster belt shortens time in the cooling section, which raises the average cooling slope. Check the paste and component limits for cooling rate as well.

#### Can I enter zones of different lengths?

**Answer:** This model assumes equal zone lengths. For mixed lengths, use total preheat length divided by belt speed to get preheat time and enter it as one zone of that length.

## Search terms

reflow belt speed calculator, reflow oven ramp rate, reflow time in oven, conveyor speed reflow profile, preheat ramp rate calculator, reflow zone dwell time, smt reflow profile belt speed, reflow oven zone length

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