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Reflow Oven Calibration



Reflow Oven Calibration | 5 March, 2002

I have recently been handed all responsibility of our Reflow Ovens. Upon my inspection, I discovered that any possible device on the ovens that you would think would require calibration, has a sticker indicating no calibration required. The practice at all of my previous employers was for the ovens (and all of its accessories) to be calibrated at a determined interval. My question is 2-part really. One, has anyone else ever experienced and dealt with a company debate regarding whether or not your reflow ovens should or should not be calibrated? And two, does anyone have an opinion on the need for oven calibration if you are using profiling equipment that is calibrated by an outside source?

I'd be happy to hear any stories or recommendations related to reflow ovens and the need for calibration.



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Reflow Oven Calibration | 6 March, 2002

Oven heating zone temps, rate-of-change and conveyor speed can be measured with a device offered by ECD called the OvenRider. KIC and Datapaq also offer some thing similar(just to mention the top 3). This is a function of maintenance to ensure the oven is to spec.

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Reflow Oven Calibration | 6 March, 2002

I worked for a medical instrument manufacturer a few years ago and we had to calibrate all measurement devices. That included everything from our vapor phase oven's thermocouples to 6 inch steel rulers.

I don't see any logical justification if you're regularly profiling with calibrated instruments, though, unless your company is particularly sensitive to agency regulations, i.e. medical, mil, aviation, etc. It's probably more a matter of redundancy for auditor types than anything else.

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Reflow Oven Calibration | 6 March, 2002

First, congratulations on becoming [more] involved in this fascinating area.

>One, has anyone else ever experienced and dealt with a company debate regarding whether or not your reflow ovens should or should not be calibrated?

Sure, it�s an excellent debating topic. We argue about stuff like this all the time. See, somebody�ll be stewin� about something and they�ll go out and root-out some meaningless piece of trivia, and then table it in a meeting with a agenda that has about as much pertinence to the new topic as dirt. [Although, we have argued about dirt, also.]

So, everyone rolls their eyes toward the heavens and prays that the meeting chair ignores the stewer and moves on to close the meeting, giving us the slimmest of chances that we can get some �work� done today, but that rarely happens. So, then we get assigned to another task team, which seals our fate that we never get anything done in the shop during normal working hours.

>And two, does anyone have an opinion on the need for oven calibration if you are using profiling equipment that is calibrated by an outside source?

Where�s the deal � * ISO9000, 4.11.1 has words like you must "...establish and maintain documented procedures to control, calibrate, and maintain inspection, measuring and test equipment demonstrate the conformance of product to specified requirements." This indicates that you only need to calibrate equipment that you use for inspection and test. * Then 4.11.2 b that tells us we must "identify all inspection, measuring, and test equipment that can affect product quality, and calibrate and adjust them..." So, this brings process control equipment into the scope, in addition to inspection and test.

Here's the difference. There is a distinction made between Inspection, Measuring, and Test Equipment [IM&TE] that is specifically used for demonstrating conformance (including conformance to internal requirements, such as process variables), and IM&TE used when demonstration of conformance is not required.

In the first case, documented procedures are required. In the second case, it's not so clear.

For instruments that are not used to demonstrate conformance, many companies label them 'for reference only' when conformance is demonstrated later in the process. Whether this is permissible, and whether it is a good idea, is situation-dependent and I can't generalize. Often, all that is called for is an 'operational check' rather than a full, traceable calibration.

Philip Stein�s [ ] rule of thumb is pretty simple [he says] and he has restated it many times. He says: * If trust in the value that results from a measurement is important, calibrate it whether you think calibration is required or not. * If you don't need to trust the value, why are you making the measurement at all? (This is not a rhetorical question, sometimes you do need some sort of reference number but the actual value isn't all that important, but you should always ask the questions.)

We record a profile as an oven first piece on each lot that is included in the work package. So, we calibrate. But, I could see checking a recipe [maybe on a flow line], recording the data on a chart, and living happily ever after. For us, it came down to �How often are you changing the recipe?�

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Dason C


Reflow Oven Calibration | 7 March, 2002

Ron, you need to check all the thermal couples are in good shape and clean before ask the outside service to do the calibration.

After the machine calibrated and I suggest that you run 2 profiles and all the heating zone set at the same temperture, one at lower ie 120C and the other set at higher, ie 250C on the bare FAB material, ie FR4 or the wave pallet materials, secure your thermal couple on the same horizontal line by epoxy or the escaplated material. Now you can compare the profile to define any machine issue.


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Reflow Oven Calibration | 20 March, 2002


Some places want/need oven calibration and some don't, just need a profile. I've worked for both. If you need oven calibration, an easy, inexpensive way is to parallel thermalcouple wire to your existing thermalcouples. Terminate the ends of the paralleled wires to a female thermalcouple connenctor. Mount all of these to a panel somewhere on the oven. Now you can take a CALIBRATED hand-held thermocouple and "plug into" your oven thermocouples. Check your hand-held reading to your oven reading. Usually they are pretty close. The next thing is conveyor speed. A lot of people forget this one. Get a calibrated digital stop watch and ruler. Measure one foot on your conveyor and time your conveyor. If it's running at 5.5 feet per minute, then divide 1 minunte by 5.5 feet and this will equal 0.182 minutes per foot.

Next, you need to know your profile. Set-up a profile board that you can use over and over. Using a profile that best fits your standard profile, run you profiler and board through the oven. This profile will be you bench mark to compare to. Generally peak temps and range of temps from part to part are the major things to look at.

Now each month or what ever your interval is, you can check the calibration of your oven and your profile. I guess you could go anal and verify your conveyor width, flux contamination in the oven etc. But these things have no direct affect to the quality of the product.

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