On Regret...

[tician]

...holding ~7" long strips of "tape" containing 100 pieces each of 0402-SMD resistors and capacitors, and remembering I have to place them by hand... and I still have not made/bought a solder paste stencil for the prototype boards that arrive in the next week or two.


...having two boxes of 170 pieces each of 2.4" square ~1/4W CIS solar panels sitting under my bed for >2 years, and still not having any good project ideas.


...having all the stepper motors, driver boards, extruder barrel and nozzle for a reprap for upwards of three years, and still nothing assembled and printing.


...not joining Dr. Steel's Army of Toy Soldiers before his "retirement".


...having been a member of the forums for over a year and a half, and still not yet built a bot for MechWarfare.


...opening the package for two 800+ lumen LED's (here and here) and finding that the aluminum substrate PCB's bought to mount them on do not match (PCB product page gave external dimensions of board, but not the footprint).

[sarendt]

Sounds like a bunch of goals, not regrets...

Cheers,
Scott

[tician]

Sounds like a bunch of goals, not regrets...

Glass half-full type?

I'm pretty sure I'm going to start a little design/idea contest thread soon to get some of those solar panels to better homes. I'm going to make a few RF-enabled, solar-powered soil moisture sensors to stick around the flower beds because I'm lazy and occasionally forgetful. I might also make a few small solar bots, but I can't think of much else and it seems like a waste for them to just sit there.

Another future regret? I bought a myKeepon on clearance over the weekend and I'm not sure why. I spent about a half-hour today to break out the power connector and I2C bus connector through the battery compartment (barrel connector on the back is some really small variant I couldn't match to a power supply at 12VDC). I shall call him "woobie" (destroyer of worlds?).

[Th232]

...opening the package for two 800+ lumen LED's (here and here) and finding that the aluminum substrate PCB's bought to mount them on do not match (PCB product page gave external dimensions of board, but not the footprint).

I suppose the good news is that MCPCBs are relatively cheap. Or if you're attaching them to a copper heatsink and don't have any real space/alignment concerns, you can attach it to the heatsink with a fat piece of wire running along the length of the thermal pad. May require use of both regular and low melting point solder though.

[tician]

Since I only ordered one of each of those LED's simply to see how bright they really were (and maybe stick one in a maglite), I think I'm just going to go with a small-ish FR4 board with a bunch of vias surrounding the thermal pad to connect the top and bottom thermal planes. Then bolt that to a chunk of aluminum plate with some leftover arctic silver between the plate and the bare thermal plane on the bottom of the board. Should work well enough since I don't currently have any power supplies that can hit the 3A max of the LED's.

[Th232]

Sounds possible. If you want slightly better thermal conduction (and can get vias that small), place the vias directly underneath the thermal pad then fill them with solder. If you want a stack of ideas on maglite mods and haven't already seen it, CandlePowerForums is a great place to go for that kind of stuff.

[tician]

Well, my pathetic attempt to make a cheap stencil by hand failed quite miserably, and the later attempt to add solder paste and 0402-SMD parts to the boards sitting on the stove ruined one set (too much solder paste melted off the dental picks from the heat rising off the board and it would not come off easily with solder wick). At least now I know that I can wrangle 0402 parts by hand. I am also still in a state of mild shock from the fact that I did not give myself any new scars (have burned myself with a soldering iron and grabbed hot objects on several prior occasions).

Guess I'll just bite the bullet already and buy a stencil from pololu.

Sounds possible. If you want slightly better thermal conduction (and can get vias that small), place the vias directly underneath the thermal pad then fill them with solder. If you want a stack of ideas on maglite mods and haven't already seen it, CandlePowerForums is a great place to go for that kind of stuff.

In my initial board layout I had added as many vias as I could underneath the thermal pad, but then thought about the potential for breakage and possibly too much solder wicking into the vias (lowering the part more than expected and/or balling on the opposite side). Given how much difficulty I had separating the two boards I connected with mouse bites (0.6mm drill hits spaced 1.25mm on center) and a small tab, I no longer worry about breakage. And I can always uses solder wick or some other means to remove excess solder, so I probably will follow your advice.

[jwatte]

Internet rumor has it that if you smear flux across the board, and add a thin strip of solder paste (from a syringe) across the footprints of your parts, surface tension of the solder will do the job and actually separate into the area of each pad. I have not tried it myself, though. When I finally go SMD for myself, I'll probably just laser cut my stencils at TechShop...

[tician]

Didn't even need the extra flux for the solder paste to behave like that. The problem was that a large blob of solder paste melted (liquified the binder but not the solder itself) off the pick I was using to apply the paste and spread the solder around. That blob just would not behave correctly, so after ~5 minutes of trying to get some 0402 resistors in place and remove the excess solder, I just gave up on it (also had trouble removing some stray solder from the holes for a connector). At that point, I was more than a bit frustrated as I had just ripped three pads off of another board trying to remove the excess solder with some solder wick (solder would not remelt and I tried to force it). Also there was the smell of something other than flux/solder and I didn't really want to find out what.


"Perhaps your only purpose in life is to serve as a warning to others"

[Th232]

Well, my pathetic attempt to make a cheap stencil by hand failed quite miserably, and the later attempt to add solder paste and 0402-SMD parts to the boards sitting on the stove ruined one set (too much solder paste melted off the dental picks from the heat rising off the board and it would not come off easily with solder wick).

I'm sorry if I'm reading this completely wrong, but it sounds like you were trying to put the paste on while the board was on the stove? If so, I generally apply the paste and parts before subjecting the whole thing to any heat.

In my initial board layout I had added as many vias as I could underneath the thermal pad, but then thought about the potential for breakage and possibly too much solder wicking into the vias (lowering the part more than expected and/or balling on the opposite side). Given how much difficulty I had separating the two boards I connected with mouse bites (0.6mm drill hits spaced 1.25mm on center) and a small tab, I no longer worry about breakage. And I can always uses solder wick or some other means to remove excess solder, so I probably will follow your advice.

If you do, you could put some solder in the vias first to fill them in and eliminate voids or balling, then reflow the LEDs on top of that. Just make sure that whatever the board's sitting on won't stick to the solder (don't ask...).

Internet rumor has it that if you smear flux across the board, and add a thin strip of solder paste (from a syringe) across the footprints of your parts, surface tension of the solder will do the job and actually separate into the area of each pad. I have not tried it myself, though. When I finally go SMD for myself, I'll probably just laser cut my stencils at TechShop...

This works fairly well for IC packages or other areas where you've got lots of pads sitting in a line, with a few observations:
* The thickness of the copper layer means solder can gather in the valleys between the pads. Recommend a good wash in ethanol afterward soldering to dissolve flux and remove all the excess solder balls. Running a needle or similar between each pad prior to placing the components can't hurt either.
* You need good paste. The stuff we use has a shelf life of 6 months, after around 8 months it's still useable for hand soldering, but other procedures can go funny.
* Different pastes have different ball sizes. This will limit the pad size you can successfully use this technique on.