IPC pass/fail

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Hi all. A recent board has shown some issues with graping an... - Nov 30, 2020 by kyleh04

Did you try a ramp to spike profile? My thought is that you ... - Nov 30, 2020 by Evtimov

Hi Kyle, As per IPC 610, for class 3, this is not acceptabl... - Dec 02, 2020 by Tommy Magyar

> Hi Kyle, As per IPC 610, for class 3, this is <... - Dec 02, 2020 by kyleh04

kyleh04

#85942

IPC pass/fail | 30 November, 2020

Hi all. A recent board has shown some issues with graping and non-wetting on some 0402 capacitors. I believe we have the issue sorted. A combination of a 4 mil stencil with 2 mil reduction not giving us enough paste, and too long of a soak profile.

I am curious if you think these pass IPC class 2. Since IPC-610 requires "Wetting is evident on the vertical surface(s)of the component termination." I don't know exactly how much wetting they are referring to. I would guess that it probably does not pass, but is close.

We did a test heating the wetted terminal with an iron and trying to move the component. It did not move, so both terminals are fully soldered, but not fully wetting on the one side.

Thoughts?

Attachments:

20201127_112159.jpg [1.9M]

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Evtimov

#85946

IPC pass/fail | 30 November, 2020

Did you try a ramp to spike profile? My thought is that you burn all your flux in your long soak and when the actual reflow happens, you have no flux activators working. Also will be interesting to see your profile and know more about the defects. Is it same package, locations, side of the part? What kind of oven you use, chemistry and board finish.... Regards,

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Tommy Magyar

#85960

IPC pass/fail | 2 December, 2020

Hi Kyle,

As per IPC 610, for class 3, this is not acceptable, as your minimum fillet height has to be either one of these two, whichever is less: - solder thickness + 25% of the termination height - solder thickness + 0.5 mm (0.02 in) For IPC Class 1 and 2, you only need evident fillet height on face of component.

In the pictures you uploaded, it is not evident that there is a fillet, therefore I would say that the assembly is non-conform (the brown capacitor is good according to IPC Class 2, as there is evidence of fillet, but the grey capacitor has no fillet at all -> fail)

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kyleh04

#85961

IPC pass/fail | 2 December, 2020

> Hi Kyle,

As per IPC 610, for class 3, this is
> not acceptable, as your minimum fillet height has
> to be either one of these two, whichever is
> less: - solder thickness + 25% of the termination
> height - solder thickness + 0.5 mm (0.02 in) For
> IPC Class 1 and 2, you only need evident fillet
> height on face of component.

In the pictures you
> uploaded, it is not evident that there is a
> fillet, therefore I would say that the assembly
> is non-conform (the brown capacitor is good
> according to IPC Class 2, as there is evidence of
> fillet, but the grey capacitor has no fillet at
> all -> fail)

Great! Thanks for that detailed answer. That's exactly the conclusion we came to as well. Just wanted some other eyes to confirm.

As for the cause, we narrowed it down to three things, when we changed, the issue went completely away.

1) We switched to a new water wash RMA paste, which has a really narrow working window. We used a soak profile, which seemed to burn off a lot of the flux. We since switched to a short RTS profile, like would be suggested for a true water Soluble flux.

2) Our 0402 apertures were much too small, so there was less paste than should have been. We increased the size to 5 mil stencil with 2mill reduction.

3) The paste only was allowed to sit at room temperature for around an hour. This seemed to be a key for us. The viscosity of this improperly warmed paste, vs one warmed overnight was pretty drastic. It seems that moisture condensed on the paste, ruining the flux.

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