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Incomplete reflow

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#71915

Incomplete reflow | 4 April, 2014

We are in the process of launching a new product and found reflow solder issue with one of the inductors. I have set oven profile to paste specifications. I just finished profiling with thermocouple under problem component. All other components exhibit proper wetting. This is a lead free process using a AIM NC257-2 SAC305 paste. BTU Pyramax98 7 zone oven. Profile detail under component in question: max temp=237*C, TAL=56sec

Thanks in advance, GM

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#71918

Incomplete reflow | 5 April, 2014

237C max is on the low end for SAC305, especially if you have heavy leaded components. I always went with 245C and above depending on the board design. I noticed the electrolytic caps. You need to check max temp with the manufacture on those. When I left the industry 5 years ago they would not handle lead free profile temps, but the manufactures were working on new products for LF. The smaller can caps were rated at 230C max for 10 secs. Just a little advise from an old man.

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#71919

Incomplete reflow | 5 April, 2014

The middle picture shows what looks to be solder balls littered across the surface. Turn-up the heat knob!!!

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#71920

Incomplete reflow | 5 April, 2014

The 237*C is under the inductor with aTAL of 48s. I worked on the profiles this morning an got the max temp up a few degrees and the TAL to 62s. I will check the body temp of the Elec caps. The rest of the board has a max temp of 247.

Thanks Gm

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#71921

Incomplete reflow | 7 April, 2014

It's right there in front of you. Not enough overall temperature across the board. No wetting issue is evident, just looks like you need to turn up the heat, as Dave has mentioned.

SOB has mentioned the issues surrounding the Electrolytic caps, check that out too, make sure they are RoHs compatible.

If you have the wrong spec Caps, there is no amount of profiling that will save them, yet fully reflow your RoHs solder.

Good luck. 'hege

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#71922

Incomplete reflow | 7 April, 2014

Gary, We are missing something here. I see no evidence of reflow at all. If you have a thermo couple under the inductor, 237 deg with a TAL of 48 seconds should work all day long.(even though it may be on lower end of process window)

SAC melts at 217C.

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#71924

Incomplete reflow | 7 April, 2014

I drilled a small hole from the other side in order to get my thermocouple under the inductor pad. I did not have anything on hand to fill the hole, so I covered with kapton tape the best I could. I suspect that is why it looks like it should work.

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#71925

Incomplete reflow | 7 April, 2014

Found the issue. The footprint is incorrect. The inductor completely shields the paste from heat. Slid the inductor on the pad to expose the pad and paste, and perfect solder joint. This part was a last minute design change with a larger body.

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#71928

Incomplete reflow | 8 April, 2014

Ahhh...now this makes sense. Glad you found the issue.

Gary, try using aluminum tape to secure thermocouples. It works much better than kapton in my opinion. KIC sells it, but I'm sure it can be found elsewhere.

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