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Reflow Specs.



Reflow Specs. | 13 August, 2001

Normally the specs I monitored in our temperature profiles are Slope 1-2 Deg C/sec, preheat 60 - 120 Sec at 120 Deg C - 150 Deg C, peak 215+/- 10 Deg C, above 183 Deg C is 45 - 75 Sec, total reflow is 3 - 5 minutes.

Why is it that we don't monitor the spec on the time between 150 deg C to 183 deg C ? What actually happen at this stage ?

Pls help me to understand. Thx.

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Reflow Specs. | 13 August, 2001

What??? You don�t have enough things to monitor?

The origin of some profiles is mysterious. It�s probably good to try to understand such mysteries. Certainly, the important determinants in the design of your reflow profile are: * Paste you�ve selected. * Assembly you want to solder. * Features and capabilities of your oven.

The principal types of profiles are: TRADITIONAL: four distinct temperature ramp rates in ovens that are primarily convection. TENT: two distinct temperature ramp rates in ovens that are primarily convection.

You appear to be using a traditional profile. Typical temperature control times of a reflow profile are: PREHEAT TIME: Time from when the profile starts and the beginning of the ramp to peak temperature. SOAK TIME: Portion of Preheat Time prior to the beginning of the ramp to peak temperature when the temperature change is small. LIQUIDOUS TIME: Time when the solder is liquid. COOLING TIME: The time after the assembly cools below liquid temperatures.

But these things are not controllable on a reflow oven. So a typical profile control points are: PREHEAT RAMP: 2-3�C/sec ramp to 100-125�C DWELL: Very low ramp to approximately 183�C over a 90-150 sec period REFLOW ZONE: Peak temperature 30-90 sec over 183�C and a max temperature of 230�C COOLING ZONE: 10�C/sec.

Before moving on, let�s be basic. Your solder is not liquid at 183�C. That temperature is the school boy answer to �What is the temperature when eutectic solder transitions directly between solid and liquid states?�. The liquidous temperature of your solder is at least 20�C higher than the school boy�s, because your solder is NOT eutectic, your are NOT measuring the solder temperature, nothing ever works like you think it should, etc.

REASONS FOR NOT MONITORING WHATEVER ... REASON #1: Your profile starts the ramp to peak temperature at 150�C. You selected 150�C to give the oven time for a running start in overcoming the thermal inertia of sitting below 150�C for a couple minutes and still get a running shot at hitting the peak. REASON #2: Who cares? As long as your flux has activated during soak, you have activated the flux too fast, you get above the minimum peak temperature, stay below the maximum peak temperature, and have a steep cool-down ramp; you should get good connections. So, how ARE your connections, anywho?

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Reflow Specs. | 14 August, 2001


Just to clarify the terms,

traditional : aka : Ramp-Soak-Spike (RSS) profiling method tent : aka : Ramp-To-Spike (RTS) profiling method

By search engines (eg. Yahoo), you can find more example profiles for your ref.

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Reflow Specs. | 13 June, 2002

I am attach to Quality Dept. I want to know what are the important parameters to check before buying-off the reflow for production use.

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Reflow Specs. | 13 June, 2002

Sorry to hear about the Quality Department thing, but we all have our cross to bear, eh?

Through an extended period, say 8 hours, understand change of critical controls in the following: * Conveyor speed. * Side to side temperature differences. * Time above liquidous.

If you want to the 'Bayanbaru, the nutty QA guy' thing, in measuring these temperatures, run a 1/4� thick piece of aluminum the size of your test board through the oven just before you run the test board. Actually, we like doing this to compare the reponsiveness of two different ovens. It's unclear that this would tell you anything about a single oven.

As an administrative aside: If you restart an old thread, try to stay on topic. If you�re not on topic or starting a new idea, start new thread. On the other side of things, thanks for searching the SMTnet Archives.

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