Solder Paste to ground driver to pill?

Jfowler

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My first mod was updating the driver and LED/MCPCB in an old Streamlight ProTac HL. It was a success! Old components came out pretty easily, and my guesses were right for the 22mm driver and 16mm MCPCB and LED. I had to file the driver a tiny bit to fit snug in the aluminum pill, and I just crimped the sides down onto the driver to secure and ground the board- it worked perfectly.

So now that I am overconfident, I have a handful of parts en route to build some new light engines for my fancy lights. I am going to be filing down 15mm drivers to fit snugly into 14mm pills. Old threads from the designer of these drivers tell me that plan should work fine. It is the grounding part that concerns me. It seems I may have gotten lucky with the crimp trick first time around, as everything I read/watch suggests soldering the outer edge of the driver board to the pill to establish a ground.

I am cool with that as a best practice, but I would really like a cleaner look to the finished light engine. I do have flux and solder paste. I am wondering if there are people who clean the board and pill, apply some flux, then some solder paste, and heat the outer edge of the pill with a flame or soldering iron to hit that magic temperature and create the joint. Alternatively, am I overthinking it? If the fit is so tight between the driver and the pill that it is virtually a press fit, would the ground already be established?

Id really appreciate some thoughts before I begin experimenting on my own. Thanks!
 

marcdilnutt

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I have tried soldering back in the distant past when modding Arc AAs to Luxeon ) showing my age here!) and found it a right pain to solder to aluminium. I ended up crimping it every time.

Sent from my [null] using Tapatalk
 

Jfowler

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Appreciate the vote to leave the soldering iron in the drawer. I’ll sleep better knowing that a press fit will work fine.
 

Buck91

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Nothing beats a good soldered connection. I haven’t used paste but if you can work with a hot iron it’s possible to almost run a solder bead like you do when welding. At least that’s how I think about it and I can sometimes get a good yet smooth finished joint.
 

DIWdiver

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I wasn't aware that there was a way to solder to aluminum at soldering iron temperatures. AFAIK it requires at least propane torch temps. That might actually be brazing. I've done that, but not with a circuit board, which would have been ruined at that temperature.

A press fit is good if you are sure you have metal-to-metal contact. But once you've filed the edge of the board, how can you be sure of that?

My preferred methods are:
1. Brass pin driven into a hole in the aluminum - solder to the pin
2. Screw clamp (as in a tailcap to body connection)
3. Spring force.
 

Jfowler

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I think that if I am careful and remove material slowly from 15mm down to 14mm, there should be a point where the fit is essentially perfect metal on metal contact. But I am interested in the comment about spring force. The drivers I ordered come with a bypassed spring soldered in place - so the force from the spring + a snug fit + a bit of crimping (if possible) and I’m good to go? That would have been the exact recipe for my first successful mod. Sometimes it is good to be lucky.

Thoughts on glue? Is that an option to keep things snug and in place?
 

DrafterDan

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I've done press-fit and/ or crimp, it works well. Should be noted that soldering aluminum to a point where it might actually work, would unflow (I totally just made that word up) the LED from the mpcb.

Must admit, I like DIW's idea of a press fit brass/ copper/ anything but aluminum pin into the alu board, then work with that. Simple is often the best.
 

Jfowler

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I appreciate the replies.

The fancy pills I am working with arrived, and they are not aluminum. I think plated brass - Aleph cans if anyone cares. There is a really old post from Dons site that shows how he grounded the driver with a soldered wire attached to the old style 2 piece pill. I think I’ll go that route.

I’ve got a couple other old stream lights that will serve as entertaining mod fodder. They use aluminum pills, and will get some sort of crimp/glue/press treatment.
 
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