LED footprint

[Alex Eisenhut]

I've been tasked with improving a layout that uses these LEDs

http://www.digikey.ca/product-detail/en/kingbright/APHB1608ZGSURKC/754-1650-2-ND/2683994

My boss told me to use a much bigger pad for each pin for manual rework. OK.

I want to use a larger copper pad, but with a solder paste blob the same size as before, and with a soldermask dam to keep the solder in place, yet provide thermal contact for the soldering iron.

How about the attached footprint? It's not to scale, just something I threw together.

The yellow is the LED, the large gray rectangles are the copper, the green is the dam, and the blue is roughly where the solderpaste will be.

I worry that the LED won't solder properly if I use 1:1 solder paste, that the LED will float away to one side or the other?

[T3sl4co1l]

Why make the pads so oversized, but choke the soldermask down on them?  It's not really pad then, because it's not solderable...

I've seen very little reason to customize solder paste; I don't bother doing anything with very large pads either (which are usually drawn in chunks to get better uniformity).  The assemblers customize the mask, and they know their process better than I do.. 

To facilitate hand soldering on a part like this, I extend the pads (on at least one outer side) about 0.5mm beyond the package side (MMC).

It won't float away, as long as the pairs of pads have made contact, which the paste should do.  Once all four pads are touching with a solder fillet, no reasonable amount of solder will cause a problem; it will just float up higher.

It could slide to one side and end up entirely on one pair of pads, if the heating is uneven or something.  Making the pads narrow (so they are only extended in the lengthwise direction, say) prevents one dimension of it, at least.

You can also refuse and make your boss purchase a hot air machine instead.

Tim