I’m trying to solder on the flex cable for a PicoFly. I’ve added some solder to the bottom two points that are touching the metal surrounding the CPU. However, I seem to only be making a bigger and bigger ball of solder when trying to melt it. I’ve upped the temperature on my iron but that doesn’t seem to be doing anything. What am I doing wrong?
So to solder properly, the important part to heat up is the metal you are attaching to, such as the copper pad. Hot solder on cold metal doesn’t really work. That is the most advice I can give. Try searching for some videos on EEVblog. That is how I learned to solder, even if I am not super good.
are you using any flux? didn’t see it mentioned, but if you’re not, you’ll need some.
Absolutely, I just forgot to mention it. I’m using Chipquik flux. Last attempt I made before having to wrap things up for the time being, I believe I had my iron set to 400° Celsius.
Flux is important. If you aren’t using flux core solder, that could be part of the problem. Flux cleans the surface and it’s easier for the solder to stick. (Flux also comes separately and it a wide variety of formulations.)
If flux isn’t the issue, then it absolutely is heat. I tried to Google for a picture of the “metal surrounding the CPU”, but I couldn’t find one. From your description, it sounds like that metal is still sinking too much heat away which also wouldn’t allow solder to flow.
Soldering to larger metal pieces is always a challenge. You likely need a lot more heat applied for the shortest time possible. Another option is to heat up the entire board with a hot air gun first, but I suspect that is not an option for you.
Big soldering tips can be used to flow as much heat into the part as fast as possible before the heat gets a chance to spread out.
(A picture of your problem would be a nice-to-have. I am not familiar with your exact components, but I solder things quite a bit.)
The metal shield maybe? There’s probably a word for it but I mean the bit the white arrow is pointing. The board in this picture isn’t the same board, but I’m not able to grab a picture of the board in question at the moment. I can reply with a picture of the board & solder once I’m able to grab one. I am using flux, I just hadn’t mentioned it. I did try heating it up with a hot air gun since I have a two in one rework station but that didn’t seem to do the trick. I’m guessing I wasn’t applying sufficient heat for long enough.
Thanks for the pic! That helps visualize the situation for me. Unfortunately, I can’t be much more of a help.
Getting a sense of how hot to get everything with air is a dark art. I can only say that it’s needs to be below the solder melting point and too hot to touch any part of the component.
On top of the shield sinking heat, the board is likely using silver-based solder, which also requires high heat. (Flux would have a dual role in cleaning the area and also flowing some heat around the solder joint a hair more efficiently.)
If it were my equipment, I would YOLO the iron temps and experiment with contact timing to get the factory solder melted enough to flow in some lead/tin solder. My tolerance for damaging my own stuff is super high though. (Brute-forcing as much heat on a small area before it gets the chance to dissipate is the logic here.)
Practice makes perfect. If you have an old wifi/Bluetooth device you can risk destroying, it might have shields you can practice removing or soldering around. (Noise sensitive audio components are something else that might use shields as well.)
I would be reallllly careful using a heat gun - that can very easily destroy the big BGA chip on that board.
If I had to guess, the pads aren’t properly cleaned and also your iron’s tip may not be cleaned and tinned properly. Ribbon cable pads aren’t very small, so solder should melt onto them and stick quite quickly - you don’t have to heat a board long for that to happen.
Also, the metal shield you’re referring to is exactly that - an EMI shield, usually. A big piece of metal that is grounded and meant to help prevent interference. They’re typically made of steel, so solder usually does not stick directly to them! You’d have trouble soldering wires right onto an EMI shield unless it happened to be copper, which again, it likely is not.
I just brought the shield up as a point of reference to describe what I’m referring to. However, in the videos and posts I’ve seen for the chip I have, they all seem to have some portion of solder touching the shield.
