TSSOP thermal question

That will work, as long as no later steps wash it out. Epoxy would be OK, preferably the thermally-conductive kind... but almost anything will be a hundred times better thermal conductor than air. Locktite makes a repairable, instant-bond thermally conductive glop stuff... just apply a little primer to one surface, a dab of glop to the other, and press.

Solder is of course the best; apply a bit of paste and heat the whole region.

I hope you have a lot of thermal (actually, non-"thermal"!) vias to the ground plane or a big bottomside island.

John

What, can't afford a toaster oven? ;)

For those of us without reflow ovens, has anyone come up with a way of doing this with just a soldering iron?

Unlikely to be very satisfying. The white zinc oxide filled silicone grease is nowhere near as thermally conductive as solder and will get all over the pads for the leads, making their attachment very difficult. The board is supposed to have a solder pad with lots of vias through it for the solder paste to connect the chip not only to the top layer, but to as many deeper layers as you can manage on the layout. If it is made this way, you may be able to put a small drop of solder on the chip, first, also tin the top pad of the board and then heat the back of the board while sliding the chip into place when the solder on the top of the board melts. But I would expect that it will be hard to get the position correct every time.

Yes, I've done this, make the hole big enough for a fine tipped iron, poke it through and flood the hole. Works a treat, at least with a PTH.

Paul Burke

Just going through the LT3439 data sheet. It has "a thermally enhanced 16-pin TSSOP with an exposed backside"

What gloop should I consider to thermally connect its bum to the PCB, is the normal white silicon stuff OK?

martin

Serious error. All shortcuts have disappeared. Screen. Mind. Both are blank.

Always!!! (If you want to benefit from it ;-)

/A

I'm hand soldering the prototypes, and I'm just doing the pcb patterns at the moment. I dont know how many will be made, so i was thinking of the good old fashioned Dow Corning stuff that I used to use on

martin

Serious error. All shortcuts have disappeared. Screen. Mind. Both are blank.

Maybe drill a hole in the PCB, beneath the center if yhe IC so you can solder from underneath? Just an idea

martin

Serious error. All shortcuts have disappeared. Screen. Mind. Both are blank.

They usually suggest a bunch of plated holes, eg 20 mil holes with 40 mils distance in a two dimensional array fashion. It is the copper of the PTH that conducts, less the tin filling. And yes, they are solderable from the backside. Just fill the bunch with tin after soldering the pins. Then from there, you can proceed with horizontal copper, or a heatsink.

Rene