Homebrew_PCBs

On Thu, Jul 14, 2011 at 6:55 PM, DJ Delorie <dj@...> wrote:
>
> In theory, you should be able to do 0.5mm pitch QFN with TT - 0.25mm is
> about 10 mil, which is "in range" for TT, assuming your process is
> accurate enough. You'll probably want to use 1/2 oz copper though.
>
> What I've found is that you need to extend the copper away from the qfn
> chip far enough to be able to hand solder it *also* - even with a
> hotplate, it's likely you'll need to fix the joints, and that's a lot
> easier if the pads are accessible next to the chip - lets you drag
> excess solder away from the chip, for example. To fix, use a flux pen
> along that edge, add a little solder to your iron, and TAP it along the
> edge. you don't want to drag solder along the edge, you want to drag
> extra solder away from it.
>
> If your QFN also needs a center pad, be careful to make it small enough
> to avoid solder bridges - you won't be able to see or fix those. If
> your center pad need electrical connectivity, either tie it to a pin or
> drill a big hole through the center so you can manually solder it from
> the other side.
>
>
> ------------------------------------
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
>
>
>
>

On Fri, Jul 15, 2011 at 3:23 AM, Stefan Trethan <stefan_trethan@...>wrote:

> **
>
>
> I've found QFN are easy to work with, even using TT.
>
> The fear of shorts below the part is mostly unfounded since solder is
> pushed out by surface tension (the gap is too small for beads to
> form). If it isn't soldered nicely just heat it with hot air or on a
> hotplate and tap gently on top. That will express excess solder out
> the sides where you can remove it, and also re-seat the part if it is
> not aligned right.
>
> The tip with the pads extending out is definitely a good one and very
> necessary.
>
> You can also solder QFNs without any reflow process, drag soldering
> works just fine. Small parts can even be changed with just a soldering
> iron by putting a large tip on it with a lot of solder and "contact
> heating" the top of the part. Certainly exceeds specified soldering
> conditions but I have never killed a part this way.
>
> ST
>
>
> On Thu, Jul 14, 2011 at 6:55 PM, DJ Delorie <dj@...> wrote:
> >
> > In theory, you should be able to do 0.5mm pitch QFN with TT - 0.25mm is
> > about 10 mil, which is "in range" for TT, assuming your process is
> > accurate enough. You'll probably want to use 1/2 oz copper though.
> >
> > What I've found is that you need to extend the copper away from the qfn
> > chip far enough to be able to hand solder it *also* - even with a
> > hotplate, it's likely you'll need to fix the joints, and that's a lot
> > easier if the pads are accessible next to the chip - lets you drag
> > excess solder away from the chip, for example. To fix, use a flux pen
> > along that edge, add a little solder to your iron, and TAP it along the
> > edge. you don't want to drag solder along the edge, you want to drag
> > extra solder away from it.
> >
> > If your QFN also needs a center pad, be careful to make it small enough
> > to avoid solder bridges - you won't be able to see or fix those. If
> > your center pad need electrical connectivity, either tie it to a pin or
> > drill a big hole through the center so you can manually solder it from
> > the other side.
> >
> >
> > ------------------------------------
>
> >
> > Be sure to visit the group home and check for new Links, Files, and
> Photos:
> > http://groups.yahoo.com/group/Homebrew_PCBsYahoo! Groups Links
> >
> >
> >
> >
>
>
>


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