LiP DFN unstuffedIn the land of protorypes, sometimes "close enough" is good enough. That can save money on PC boards and assembly when a particular package version of your part is out of stock. But, it's not universal. Sometimes you can't go that way.

I've got an MCP78338 Li Poly charger chip. It comes in 10-DFN and 10-MSOP packages. I originally used the MSOP version on my first PCB pass. Everthing worked just fine, so I re-layed out the board to be about half the area. That meant that wherever possible, passives went from 0603 to 0402 and chips went from whatever to QFN/DFN pacakges.

LiP MSOP on DFN padUnfortunately, the DFN package Li Poly charger seems to be out of stock with long lead times. That got me looking at my options. Option 1, would of course be to just wait. Option 2 would be to re-lay out the board for the MSOP part in that space. Option three is to use the "we'll make it fit" mantra. There are no gurantees at this point, but sometimes it's worth a try.

But... Twas not to be. If you look at the second image, you can see that the footprint of the MSOP part leads is wider than the land pads for the DFN. I suppose there are still a few really messy and potentially expensive options You could solder a small wire on to the pads, sticking out from the pads, effectively making them big enough to accomodate the chip. Very ugly, but might work. Probably too spendy though.

Duane Benson
Carpe DFN


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J-leads will work. Been there, made that mistake. What matters is the lead-to-lead spacing.
The other one I've been bit by is the standard-vs-wide package. Atmel in particular seem to love to put the same device in both a 0.208 and 0.150 wide package. And for some reason they call the 0.150 "wide"
Love your blog, as digital designer, I've learned a lot about layout "best practices."

I learned a lot in your blog thanks for informing us in such details.

I agree, the Bending the legs into a J lead may be the best solution

Bending the legs into J leads might just work. That does sometimes put undo strain on the chip package though.

Bend the legs under the chip and treat it like a PLCC chip perhaps? What are they called, J-leads?

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