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fillets on fine pitch parts/poor wetting

bpan

#22297

fillets on fine pitch parts/poor wetting | 6 November, 2002

Hello All, Having a problem during reflow and would like your opinions. We are using Kester r562 water soluble paste and I am using a Kic 2000 profiler in a 4 zone oven (top only). We are seeing poor wetting or fillets that are not "passable" per IPC specs. The profile when run with the Kic, shows that the soak time and reflow time are very acceptable (but the results are not). The Kic has always worked to perfection for us so I am not sure what has happened. The problem occurs on different fine pitch parts (at least they are more noticable). To get better results, I have had to turn up the temp in the 3rd and 4th zone 10 and 20 deg. C. The problem with doing this is that it's still not perfect and if I look at the Kic profiler it shows that the components and/or board is heating to 230 deg. C which is not acceptable. Can anyone help....Think I am loosing my hair over this one.....

Oh....speed and zones are as follows 14 in/min 175-180-200-275 board size 6x4

Any input would be great.

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#22299

fillets on fine pitch parts/poor wetting | 6 November, 2002

I would also consider paste control (don't take it personally...I always have to get after people about this one), time on the stencil, time between print and reflow, solderability of the component leads, paste volume (that one really got us once....it doesn't take much volume loss on a 10mil wide pad to get insufficient wetting).

You might need to have your KIC calibrated, but that isn't where I'd normally look first.

By the way, when you see "poor wetting or fillets that are not "passable" per IPC specs", what do you mean? Not enough solder on the pads, leads, no toe/heel fillet, dewetting....? Some of that will help solve the puzzle.

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SIGEP man

#22302

fillets on fine pitch parts/poor wetting | 6 November, 2002

If you are certain that reflow process is good, I would suggest starting checking the following:

1. Check to see if leads / pads are contaminated or oxidized. However, this usually results poor solder quality throughout the board. 2. Check the amount of solder for those devices. Maybe there aren't enough solder to form an acceptable solder joint.

Hope these work...

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bpan

#22316

fillets on fine pitch parts/poor wetting | 7 November, 2002

Thanks for the ideas guys. My QC inspector can take a pick and move the back part of the lead....even though the front of the lead is soldered enough to hold. There is SOME NOT ALL areas where there is no solder on the curved portion of the lead.The paste was the first place I went and it didnt make a difference on the paste thickness (although we are using 6 mil). Just ran some other boards with the same paste/printer and have had no problems.

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#22320

fillets on fine pitch parts/poor wetting | 7 November, 2002

Sounds like you're talking about the "heel" of the lead not being soldered, in other words, no heel fillet, which IS necessary.

That problem, for us, was attributed primarily to poor layout (insufficient length of pad extension to provide room for heel fillet), but also compounded by insufficient solder due to poor registration, poor release, bad stencil design, etc., etc.,....

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