I ordered some "AMC7135 350mA Advanced Current Regulators - SOT-89" and plan to try my hand at "stacking chips". I've read that you can avoid soldering the center pin by doing something else, I think on the backside of the chip. I just can't seem to visualize the instructions.
Can someone post some picks so I can see where and how this is accomplished?
You can solder the fat pin on the other side down to the fat pin on the chip on the board instead. If you look at the bottom of the chip you can see they are the same connection.
I recommend you solder this anyway, since it is the main heat dissipatin path for the chip.
…so basically, you’re just running solder down the backside of the two chips until it hits the bottom? In my minds eye, it just seems like kind of a shaky connection.
This is a tutorial I want to do. O-L did a great video on stacking chips,but he solders the middle pin instead of the tab. My tutorial will not be nearly as good, but I will solder the tab instead. Just another option.
The key is to make sure the solder on the bottom chip has melted so there is a good bond between the two tabs.
That would be great relic. I decided to try stacking after watching OLs video. Someone mentioned about the tab, and I want to see how it’s done.
It was me that mentioned it, I think. I’ll try to get something posted soon.
I solder both the middle pin and the back - can't hurt for thermal conduction, specially when the chip sitting on top has it's copper base directly contacting the plastic top of the chip below.
Makes sense.
When I do stacks without a board, I usually have the glue out for something else and use the excess to make 2 chip and 3 chip stacks. This makes it easier to reflow the ground tabs onto a piece of copper later. Since each tab ends up connected to a relatively large piece of copper I grind off the center pins to avoid unwanted shorts. When stacking on a board, I glue the chips down and when it sets, bend all 3 pins down and solder. Start with the solder tip on the bottom pin and draw the solder up to the upper pin. Repeat with all 3 pins plus ground tab and use flux.
What glue do you use? Wouldn’t it be easier to bend the pins down first?
Also, what’s a good tip temp when stacking?
I usually run at about 400 F with 60/40. I also bend the legs down as OL did. I usually just hold the amc7135 in place with my finger and solder one front leg. Once soldered it want move around much. Then I solder the large back ground tab. Finish the other front leg and your done. I tried the super glue method for a while and prefer just holding it with my finger and soldering one leg method. It will work either way.
What type of solder are using?
I use AS-5. You can bend them first or after the glue sets. I wait till it sets, clamp the board and the chips and bend the pins while clamped. I always worry about the integrity of the chip when bending unsupported pins(possibly needlessly, I’m a worrywart). I do this when the glue is mixed for something else and use any excess.
Great input in this thread. I’m picking up lots of valuable information. When attempting something new, I like to over prepare myself. It gives me lots of option in case one method doesn’t work for me.
My How-To on this subject is now posted, here
Rufusbduck, it certainly doesn’t hurt to solder the middle pin, and I’m sure it helps at least a little with thermal transfer. I keep the pins straight which makes that middle pin a lot harder. The solder blob required to bridge the gap will often end up bridging across pins too.
Are you sure you use 400 F? That seems way too cold to melt solder properly. I’m up around 400C which is 750 F.
I also use 60/40 rosin core solder (diameter 0.025”, 0.6mm).