hand-build LFCSP?

[awallin]

Hi all,
we've prototyped a design using ready made evaluation-boards where the main chip is in a 64-lead LFCSP package with an exposed pad in the middle.

If we make our own PCB for this, how hard/easy will it be to solder the LFCSP chip using e.g. solderpaste, laser-cut metal stencil, and a reflow oven? Any particular gotcha's or things to watch out for?

thanks!
AW

[Precipice]

That should be tricky but OK if you're careful.
Definitely extend the pads outwards, so you can see the solder flow and rework with an iron if you need.
Don't paste much on the belly pad. 50% coverage works OK for prototypes, where I need to encourage the package to sit low, to make it easiest for the pins to solder. 70% for production, for a tuned process, leaves less void space, but I really doubt you care about sucking the heat out of that package!

Be brutal when checking your solderpaste before assembly - wipe it off, clean, and do again, if you're at all concerned. It's generally a lot quicker to do this a couple of times than chase bugs and rework.

In production, these things are bread and butter. In prototyping, they just need you to pay full attention. Dodgy placement and dodgy solderpaste don't help, these things don't have the self centering of an 0603 or SO-8. They're less annoying than MSOP-10, though, which appears to be my nemesis at the moment.