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Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts

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#84006

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 20 December, 2019

Reflow with lead free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts While I have been an observer for years, now I am mostly new into reflow process. I tried to reflow a big 4 Layers board and without knowing much about solder pastes other than want lead free, I used the first SAC T4 type solder paste I found around that happened to be no-clean. Now I am reading no-clean is harder to deal with. I have an inexpensive radiation tube reflow oven (no zones), but I set and verify the profile as asked in the datasheet. The pin wetting looks ok and the paste appeared to flow ok. However for some reason the parts (very noticeable in resistors), come out a bit of orange/brown covering. I imagine must be burned no-clean flux? because if I clean them with a bit of IPA or flux off, this appears to go mostly away. Any suggestion if this is normal or if I am doing some wrong? Would be much better with "dirty" solder paste?

I am posting a pic in an area with some parts cleaned and other not for comparison. This is especially noticeable with the resistors that look like toasted.

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#84015

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 22 December, 2019

Did you contact your solder paste supplier? Involve them for trouble shooting.

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#84029

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 26 December, 2019

Show us your reflow profile. Most probably that will help us to troubleshoot better.

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#84031

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 26 December, 2019

Doesn't really look like no-clean to me...typically, no-clean encapsulates the solder joint after reflow, trapping any organics.

This looks like plain-old water soluble flux, that cooked a bit too much in reflow.

As you noted, it cleaned up with Flux-Off and IPA; that seems to give you your answer. Regardless of your chemistry, you're looking at post reflow flux. If you don't want that on your boards, I'd recommend a water-soluble flux in your solder paste, and a deionized water cleaning after reflow. If you need to use no-clean, I recommend accepting what the process gives you...it's designed not to be cleaned, so, don't clean it.

As mentioned above, check with your paste manufacturer for additional troubleshooting. You mentioned that you don't have zones in your reflow, but that you can profile it. Most paste manufacturers have a database of profile temps/times based on the oven, they ought to be able to provide you a baseline profile to try using.

Overall, this looks like it was too hot, or in reflow for too long. A number of pads exhibit solder pulling back from the edges, not to mention what looks like solder balls.

Cheers, ..rob

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#84049

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 27 December, 2019

Thank you for the answers. The paste is as spec No-Clean https://www.chipquik.com/datasheets/TS391SNL50.pdf

I'am writing them too. For the excessive cooking not sure, the oven sensor (that I think is about right) looks I am close to the profile, but perhaps a bit too hot and longer than needed (see attached image). The problem is that is not fast enough to reach the peak in the spec 240 sec, so I start with the interior already at 60C, and still takes 260 sec be there.

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#84056

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 30 December, 2019

Keep in mind that the oven temperature does not, necessarily, equate to the board temperature. The thermal characteristics of the parts and copper will cause the board temperature to be different, sometimes significantly, than the oven temperature.

If possible, it would be better to put a thermocouple on an actual board, and measure the temperature at that point. That way you're looking at the actual temps, rather than the chamber temps.

Cheers, ..rob

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#84057

Reflow with lead-free 96.5 /3/0.5 No-Clean T4 brown-orange burn color on parts | 30 December, 2019

We saw your profile, which in my opinion looks alright based on the guideline from the vendor. Can you tell us more about the joints that you cleaned? Are they showing nice wetting and nice and shiny finish? How about your stencil thickness? From my prespective it looks like you have could not burn all the flux, which means one of two things: 1. Flux was not activated - you need more time in preheat(150-190C) or 2. you have too much flux(paste volume)and you can't burn it all. The latter could be caused by your stencil/profile imperfection or by the paste having too much flux in it's formula. Anyway, before you blame it on the paste manufacturer, do your homework and check paste amount and a profile that is a minute or two longer in preheat, regardless that manufacturer shows different in datasheet.

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Non-heated dispensing system

Reflow Oven