Heat sink pads under components, extension

of

Good point. I usually tell them not to alter anything in the Gerbers without prior approval from me. Because once a manufacturer did that, they "improved" a design. They had to eat the whole botched run and do a rush run at no extra charge.

pin,

bottom

solder

the

The pins should help it center, but the large pad under the chip will do pretty much nothing.

Give it a little thought. The centering works by surface tension. A pin is typically not much different in size to the footprint. If movement significantly changes the shape of the solder at the edges, it will create a force from the imbalance of the two sides. But if you extend the footprint pad far beyond the pin (or in this case the large pad under the chip) the change in shape will be very small for a small movement and there will be very little force generated.

desolder

What John is saying makes sense. Use your large footprint pad, but add solder mask to define the pad area under the chip, then leave openings in the solder mask *outside* of the chip to lay your soldering irons. This will give you the proper pad area under the chip which will make the assembly house happy and give you areas to heat the thermal pad with soldering irons.

pin,

bottom

solder

the

All fine in theory, but I have seen "self centering" fail plenty of times for no reason that is obvious to me.

pin,

bottom

solder

makes the

I won't argue with that. But if you set it up to fail, it will.

I have decided to cover the excess with either solder mask or silk screen. That way, we can scrape or dremel that off in case we have to reach in with an iron. It'll only be necessary during the prototype phase (hopefully not even there).

om

ll

dd

could use peelable solder mask, but of course that's and extra step if you don't need it for anything else

-Lasse