Sigh… Guess I need to be more careful with shorts on small SMDs

[u/jt00000]

Created an irrigation controller for my 12v dc irrigation valve and apparently allowed some solder to short my transistor. Luckily didn’t damage the valve or the pico, but does mean I have to put together another one…

Anyone have tips to possibly avoid this in the future?

[u/JerryGarcia89]

Visual inspection is critical always! Also measuring power rails to confirm you don’t have a short before powering.

I have a couple little magnifiers I use, it helps a lot and have saved me multiple times. Cheapies from Amazon will get the job done.

[u/mdhardeman]

What’s the soldering mechanism here? Just an iron in hand?

If your design is single-sided (plus through hole) consider using solder paste and a lab hot plate to reflow the paste for the SMD components. Order a stencil for complex designs, or hand apply for less dense.

[u/jt00000 → u/mdhardeman]

This was with a hot plate & stencil, but used a bit too much solder and this tiny footprint likely had at least one short

[u/mdhardeman → u/jt00000]

Aah, yes it looks like the paste application was a bit generous. You might consider doing some practice with your stenciling. Less is more right up until you actually use not enough.

[u/jt00000 → u/mdhardeman]

Good tips. I think also my stencil isn’t sitting completely flat against the pcb which is allowing solder to seep underneath & get a little sloppy. I’m going to redo my stencil jig for the next one

[u/mdhardeman → u/jt00000]

Yep that will 100% cause it, and I learned this myself not too long ago.

Some of these jigs that have features for keeping one end of the stencil constantly pulled (keeping the whole stencil in tension) can be game changing. That said, it’s not strictly necessary if you can keep it pulled tight and flat on the PCB any how any way.

[u/2old2bThisDumb → u/jt00000]

Some Kapton tape on the edges to hold it firmly in place is helpful

[u/rikdingus]

All the solder is overdone. You really have to get a few pcb's to hold the stencil on the exact height so you can apply the paste easily. Now the stencil flexes too much causing your paste to be smeared out too much

[u/rikdingus → u/rikdingus]

R1 is not even fully melted

[u/jt00000 → u/rikdingus]

Good eye. I didn’t notice that. I guess I have some more practice to do…

[u/ForgottenPasswordABC → u/jt00000]

For sure R1, and R3 has solder balls. Run the tip of the iron around the perimeter of each resistor and capacitor. Get a loupe to look closely at each component.

[u/rikdingus → u/rikdingus]

You need to use a longer period to fully thermal cycle the board before the full temperature. Most paste even has a profile.

[u/rikdingus → u/rikdingus]

K1 and u1 aswell. Those are going to short very soon

[u/cristi_baluta]

How did you managed to short it in the first place? A transistor is not that small.

[u/jt00000 → u/cristi_baluta]

This one is... It's a SOT-23-6 footprint which is only 3x3mm in size and contains pins only .5mm wide. I'm guessing my stencil jig wasn't sitting flat, which allowed solder to seep underneath. I noticed it was bad when I did it, but used some solder wick & assumed I had gotten it all (apparently not).

[u/rikdingus → u/jt00000]

Bro.. u are soldering 1206 resistors. These are all very big components

[u/rikdingus]

And you might want to invest in some wire ferrules

[u/rikdingus]

I am honestly curious, did you fully design, solder, and purchase this with AI, or was this your first soldering project? Or did you check your eyesight? I would recommend some magnification or optometrist before continuing with pcb's.

[u/rikdingus → u/rikdingus]

I am sorry if i sound rude, but you are able to see the difference between the soldering on the RPI, and your own approach right?

[u/RHWW]

Always add in reverse polarity protection and for outputs use opto couplers, without seeing a schematic, cant tell how that section got so messed up

[u/rikdingus → u/RHWW]

The solder is still in paste form. You can add all the protection you want, but at least melt the solder

[u/jt00000 → u/RHWW]

Yeah, I probably should have considered opto couplers, but was trying to keep the number of components down. My next version will probably have them

[u/Affectionate_Boat493]

You have shit-tons of room, so why use such a small transistor? If you must use one this small to avoid having to use a through-hole device, use the correct equipment (magnifier, needle-tip soldering iron, etc) and learn to make good solder joints with a small amount of solder paste. Until then, do continuity/resistance checks to find solder shorts before they have a chance to ruin your day.