Suddenly 0.5mm QFN becomes a piece of cake..

[nctnico]

The past few days I've been putting together various prototypes. This one is interesting. It has a 0.4mm QFN on it. It makes a 0.5mm QFN look like a walk in the park. On the right is the tip I used to solder both chips. The extended pads make it easy to solder these chips by hand. I just add some flux, put solder on the tip and gently swipe the soldering iron along the pads after fixating the chip by soldering a few pads.

[Dave]

Looks great.
How did you solder the large center pad?

[mikeselectricstuff]

Looks great.
How did you solder the large center pad?

Unless it's needed for thermal  or decoupling reasons, you can often just leave it unsoldered.
An option is to either put a big-ish hole underneath to manually solder, or some thermal vias and leave a hole in the underside resist, so you can paste it using heat applied from below.
 

[nctnico]

Looks great.
How did you solder the large center pad?

Thermal via's like this (if imageshack is working):

I use the same tip to let solder flow in 2 or 3 vias and then wait until the solder gets sucked up into the other vias.

[NiHaoMike]

QFNs are easy if you have a small heat gun, try doing a BGA if you really want something difficult...

[westfw]

Will a special QFN package created with "extra long" pads for hand soldering end up interfering with automated assembly?

[Smokey]

Will a special QFN package created with "extra long" pads for hand soldering end up interfering with automated assembly?

They already make these.....  they call them QFP   the pads even stick out the sides like legs
(Ill be here all week)

[poorchava]

Will a special QFN package created with "extra long" pads for hand soldering end up interfering with automated assembly?

Yes they may. It generally depends on multiple factors like paste screen thickness, paste particle size, paste bonding agent density, reflow profile and type of metallization on pcb and components.

In general the failure mode is excess solder on pads which forms a droplet and makes QFN float. Sometimes the chip will yank to the side and some pads will remain unconnected. It's all about process parameters.

[nctnico]

Will a special QFN package created with "extra long" pads for hand soldering end up interfering with automated assembly?

As far as my experience goes it doesn't interfere. I'm using these footprints on boards which get manufactured by the hundreds.

[poorchava]

It will function most of the time, yes. But in some industries the customer will come to you with a 50k units claim about "wrong shape of solder meniscus, according to this and this and that standard". No experience with avionics or military, but that approach is typical in automotive and medical industry. "100% like in the book or else we don't buy it"