How-To: Add 7135 chips to a Driver Board (Stacking)

:smiley:

I find it more difficult than just using solder. The wire has to be really thin. I wonder if solder alloy is a factor… 60/40 vs 63/37. I use the former. Maybe I will pick up some of the latter and try it.

I don’t see why the wire would have to be thin. I just soldered 2 together with 20ga silicone covered wire. Like attaching a pillar in front of the legs, lol. Of course, in this application I’m leaving the wire some 3” long and using it for battery contact and emitter contact.

Hey Ouchyfoot, do you attach the top chip before soldering the legs or do you use the ground solder to hold it in place?

I don’t have anything to attach it with first, or the patience to wait for Fujik (if I had some) to dry. So I just hold it in place and solder the wide ground on the back side first then do the other 2.

I just fasten it on top of the bottom chip with a dab of super glue from the dollar store.
On my next attemp, I might pre attach small wires to the legs of the bottom chip, glue down the top chip, bend the wires up, and attach them to the top legs. I’m also finding it to be easier, and neater to link the thermal pads with a bit of narrow copper braid.

Need to get some of that. Handy for a lot of things it would appear, not the least of which is tailspring mods.

Isn’t the internal bond wire encapsulated inside the chip? I mean that inside the black part, is it just a cover, or is it like potted? If it’s potted, then it seems like that internal wire bond should be pretty secure, so I’m kind of surprised that bending the external part of the leg would break or weaken the internal bond. I haven’t worked with 7315s, but I’ve done that (bend legs/pins) many times, especially while prototyping.

I tried bending the legs down. It sounds easy, but its not, unless you are experienced, and have certain dedicated tools you use. I just ended up breaking the legs off, ruining the chip.

I am new to light modding. Added several 7135s to a few drivers. Bending the legs with needle nose pliers has worked fine for me. Def makes soldering easier.

Ouchyfoot, heat em first with your soldering iron if they’re breaking off. Once heated a bit they bend very easy. :wink:

I’m getting peaks on my solder from the iron pulling it up as I take the tip away, what am I doing wrong? Station set at around 300C (350C when soldering a copper star on a copper heat sink)

I’m always worry about heat transfering through the legs destroying the internals of the chip.
I get peaks sometimes too. I think it usually means I’ve got too much solder. When that starts happening, I keep dabbing at it with the iron to remove the excess, and wipe it off the tip. Flux could also help it to flow more evenly.

Flux and a little more heat could help with the peaks. I set mine around 375C.
The bond wire are encapsulated in the package and are bonded to the pin internally. If the act of bending the lead loosens it in the pacage even a little, it could weaken the bond. The risk is probably low. I don’t bother si ce soldering straight leads has always worked for me.

My 2 Convoy C8s and a 10-pack 7135 arrived today from FastTech and I took the plunge of trying to add 2 7135 chips to one of the C8’s drivers. :slight_smile:

I destroyed one chip (broke pin 1) but I managed to attach 2 chips to the driver (though it took very long to connect the pins since my soldering skills are very limited). The problem is that when I reassembled the flashlight, it won’t turn on.

I took the pill out again and tried connecting it to the positive (positive terminal of the 18650) and negative (body) of the flashlight and was further confused with the results. It does not turn on when I connect it normally but turns on when the positive of the driver is connected to the body and the ground of the pill to the positive of the 18650. I tried the pill of the other C8 and it functions normally. I also rechecked the wiring using the stock driver as reference and the connections seem the same.

What have I done wrong? Did the long exposure to soldering iron heat damage my driver? I’m contemplating on replacing the 2 pairs of 7135 chips I bonded to each other. I still have 7 chips left.

Help please? :bigsmile:

Here’s the picture of the Convoy C8 driver with 2 7135 chips added. I followed OL’s technique of using hemostats to hold the driver and the chips together.

Sorry for the crappy picture. I have a crappy camera. :8)

Found the problem! |(

I almost lost hope when I took a closer look at the MPCB. The black wire was connected to the ’“+” of the MPCB and the red wire was connected to the “-”.

I don’t know if Convoy made a mistake or its technicians did that on purpose. :frowning:

I connected the black wire to the positive of the driver and the red to the negative and my light now works. The light output difference of the two Convoy C8s is not evident but the 10*7135 C8 gets hot a little faster than the stock (8*7135) C8.

You make so easy Ill give a shot!:-)

I cannot stick the blob of solder on my soldering iron tip, probably my tip has been oxidized. How do you guys maintaining the soldering iron tip in healthy condition?

Sal ammoniac (ammonium chloride). Your tip will be shinny as new.

Oh really? I have browsed through few websites and couldnt find a good method, thanks for the suggestion. But I still don’t know where can I buy one.

First off, I remove the spring to get it out of the way. This makes it much easier to access the pins on the inside. I also like to bend the pins in a 90 degree angle which lets them reach down and touch the top of the legs on the chip you’re stacking on. By applying a small blob of solder paste to each leg of the existing chip first, you can set the new chip on top and have the solder already in place.

Glue the chip on top with thermal adhesive and it won’t be moving around on you. Or find a way to otherwise hold it down while soldering. (I’ve mounted my hemostats in a counter-top mini vise and angle them so they are slightly lower than the chip when the driver is held in it’s mount. Then slide the driver under the stats and that little pressure is enough to hold the chip in place while performing the delicate solder operation)

The touch and drag method easily does the larger ground pin on the neg ring side, then all it takes is a touch of the iron to the tiny legs and each leg is soldered, neatly and with little danger of overflow compromising the integrity of the board.

Then a conical spring can be inverse mounted and you’re up and running!

My Hakko 888 station came with a brass scrub pad in a hole under the iron holder. Plunging the tip into this pad keeps solder wiped off and the tip ready for the next operation. So I’d expect a similar pad found almost anywhere (most likely an electronics store but also a grocery store) would clean a hot iron of excess build-up.

I’ve learned all this in the last couple of months since acquiring the Hakko 888 and my soldering has improved tremendously!

Thanks for the tips and directions guys, playing around with it gets you in your comfort zone and makes it…well…second nature! :slight_smile:

I ran out of solder. So I squirted solder paste onto the counter-top and touched the iron to the paste to load a bit of solder. This actually worked very well, plenty of flux and a very small amount of solder allowed it to flow to the pins easily and neatly.

The ground ring is sitting on top of a 1/2” thick copper heat-sink. :slight_smile: There’s 7 chips underneath the board, and 6 on top including the 2 I added. I cored out the aluminum pill in my HD2010 and replaced that center with 2 quarter inch thick copper rounds, taper press fit one from the top and the other from the bottom and reflowed together in the middle. The XM-L2 T6 this driver is powering is de-domed and hitting over 600 yds. Very pleased with my HD2010!