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Profiling - suspect flux burn out before reflow trouble shooting

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#55373

Profiling - suspect flux burn out before reflow trouble shooting | 3 July, 2008

5 Zone HVA70 Oven Board 6 layer, 10" x 13" lots of space, most critical is 100 pin QFP AIM Water Soluble 487 Tin Lead paste on SN100C HASL boards

This board is giving me disproportionate grief! I am running 23 in / min which gives me about 3.1 minutes in the oven. AIM recommended this. The only way I can get acceptable results is to add flux with a spray bottle. I have tried lowering my activation zones, more heat from the bottom etc. My peak temp is 220 using IR probe looking in from the end, and I am getting approximately 1 min above liquidous. Tomorrow I will use the MOLE more, but we had started with a profile based on the mole which looked like it would be suitable. With this post I am mainly looking for suggestions on differentiating between the flux being burned out by the time it gets to reflow, and or inadequate peak temp or duration in liquidous. In the past I have seen flux burn out on boards where small parts alone on the board did not solder, but busier areas of the board did. This is generally not the case with what I am seeing here. Reply with suggested profiles and I will compare them to what I have been testing so far. Thanks Pete

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#55374

Profiling - suspect flux burn out before reflow trouble shooting | 4 July, 2008

Try a linear, very flat ramp rate on the order of 0.5 degrees celcius per second. I know this is hard to accomplish with a five zone, but try to lower the first couple of zones (the preheat zone), and then spike to reflow aggressively during your last 2 zones, while keeping the ramp rate less than 3 degrees celcius per second when you go from preheat to spike.

A very low initial ramp should be enough to activate the flux, but at the same time preserve the activators in your flux prior to entering reflow.

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#55377

Profiling - suspect flux burn out before reflow trouble shooting | 4 July, 2008

Thanks, I'll give this a try. Peter

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#55422

Profiling - suspect flux burn out before reflow trouble shooting | 8 July, 2008

I made progress and almost acceptable results by adding heat to the bottom of zone 4 HOWEVER, the core problem I uncovered last night/this morning was that the #4 top side blower had failed. I think this is the key why I was having so much trouble. Tomorrow AM I will be verifying/refining my profile and I expect to be able to nail it down very quickly and get back to running normally - hope! Pete

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#55447

Profiling - suspect flux burn out before reflow trouble shooting | 10 July, 2008

I guess the paste is Leaded hence the 220 Peak temp and the Sn100c is Eutectic at 227C so you need to be hotter to melt the HASL finish or you are relying on it alloying together with the paste which takes much longer. suggest running peak temp of 235C it should fix it OK By adding more flux it maybe be giving better heat transfer to the little heat you have Hope it helps Cheers Greg York

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reflow oven profiler

Reflow Oven