Reflow Oven Burning Part

[JohnSL]

I have a T962A reflow oven that I've been using for a while to make PCBs, using lead-free solder. Yesterday I made a circuit board where one of the connectors got burned, as you can see in the enclosed photo. I've not had other parts burned before, so I'm wondering if anyone has any advice. Here is the part that was burned: https://www.sparkfun.com/products/8612.

The profile I'm using on this oven is Wave 3.

Any ideas?

[wreeve]

cover with a little tin-foil to reflect the heat.

[mazurov]

Why do you need 250C peak? Mine (crude homemade toaster-oven based) reflows fine at 230C peak using SAC305.

[rx8pilot]

Do you have a thermocouple to verify the temp? I would definitely question the data on the display.

Also, that oven is direct IR right? That can create a challenge from heating up the surfaces too fast. The aluminum foil idea or Kapton  tape to provide a little insulation.

Are there any solder balls after reflow that may indicate high temp? Do you have access to temp indicating crayons? I used those to get a sense of how heat was distributed in my oven. That was a helpful experiment.


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[fivefish]

Try wrapping the part with kapton tape.

[Psi]

My toaster oven reflows perfectly with the temp around 205-210degC for 4min. (temp from fluke thermoprobe poked into oven)

Also, check the heating elements in your oven. If they are glowing red then they are emitting lots of IR which will scorch things. You want them to be just under glowing. If you can't get the temp you need without red elements then you need more elements.
Usually a toaster oven with elements top and bottom are fine for getting to 210C without any element glow.
Single sided ovens maybe different.

You don't want to use the ovens built in thermostat. Its too slow, it will get red hot for a while, then switch off for a while.
You want a solid state control system or a variac

[miguelvp]

It doesn't help that the datasheet in https://www.sparkfun.com/products/8612 doesn't have reflow characteristics.

Maybe it's not intended to be used in a reflow oven to begin with.

[wraper]

It doesn't help that the datasheet in https://www.sparkfun.com/products/8612 doesn't have reflow characteristics.

Maybe it's not intended to be used in a reflow oven to begin with.

Then for what it is intended? If you look at the part, it just cannot be soldered in other way. This is not datasheet BTW, just drawing.

[rx8pilot]

I don't think the problem is with the part. It is with the limitations of an entry level oven. You can work around those limitations though as the others have pointed out. Shield the part, reduce the temp, orient the PCB in a 'cold spot' of the oven, etc.

[amyk]

I think you're going far higher than 250C. Either the temperature sensor is inaccurate or there are hot spots in the oven. The linked datasheet (rev.A) says material is Nylon 46 which melts at ~300C, but if you go to the actual manufacturer, 4UCON, their datasheet (rev.B1) they changed to PA6T but that also melts around the same temperature. The recommended profile for PA6T has a 260C peak so 250 should be no problem.

Since you're actually burning the material and not just melting it, the temperature must be far higher than that...

[rx8pilot]

I think you're going far higher than 250C. Either the temperature sensor is inaccurate or there are hot spots in the oven. The linked datasheet (rev.A) says material is Nylon 46 which melts at ~300C, but if you go to the actual manufacturer, 4UCON, their datasheet (rev.B1) they changed to PA6T but that also melts around the same temperature. The recommended profile for PA6T has a 260C peak so 250 should be no problem.

Since you're actually burning the material and not just melting it, the temperature must be far higher than that...

Agreed. Nice backup links.

As a reference, I use a profile that peaks close to 290C for some lead free. Nylon parts have had no problem with it at all. Most of the time I use a slightly lower peak, but that is to ensure bigger inductors re-flow.

[JohnSL]

Thanks everyone for the replies. I sent my question just before moving houses, which of course sucked up far more time than I expected (I guess I'm optimistic).

Any, I forgot to mention that I'm using lead-free solder, and the recommended profile has a peak of 249C, which is why I chose the profile I did. Here is the PDF that contains the recommended profile: http://www.chipquik.com/datasheets/SMD291SNL10.pdf

One thing I can see looking at the profile is that the peak should be at 4 minutes, whereas the profile I chose on my reflow oven peaks at 5 minutes. I've read that this oven doesn't do a good job of keeping track of time, so it actually runs slow. But I also like the idea of measuring the temperature in the oven before I use it again. I don't have a thermocouple, but a quick search turned up this very inexpensive one:

http://www.amazon.com/Signstek-6802-Channel-Thermometer-Thermocouple/dp/B00FFYEPVQ/ref=lp_8992804011_1_5?srs=8992804011&ie=UTF8&qid=1440385515&sr=8-5

Does that looks like a reasonable instrument for checking my reflow oven?

[fivefish]

I use a similar one bought from eBay