How to solder pinpoint leads to pinpoint traces?

[solderjs]

I’m trying to replace some broken ZIF sockets on my Nintendo New 3DS XL. They’re pinpoint leads with pinpoint traces (see pics).

Pics:









I’m a bit of a newbie, but I’ve been able to SMD solder training kits without a hitch thanks to various tips and tricks I’ve learned here and there (including EEVBlog on YouTube).

I’ve used a 13.5x head mount magnifier.

I’ve tried 0.4mm 63/37 solder.
I’ve tried 0.8mm 60/40 solder.
I’ve tried a paste flux.
I’ve tried pure colophony flux.
I’ve tried running the leads first (epic fail on the back leads with 0 spacing).
I’ve tried alcohol + glycerin + colophony dust.
I’ve tried a solder paste with a heat gun (plastic melted before the paste would flow).
I’ve been to scared to try my toaster oven reflow box (still working the kinks out on practice boards).
I’ve tried putting too much solder on and wicking it off (epic fail on the back).
I’ve tried a 0.4mm conical tip.
I’ve tried my screw driver tip.
I think I even tried with my bevel tip.

I’m willing to bet it’s just my technique that’s the problem, I just don’t know what to do.

I’m thinking maybe to heat the board up to 150 C in the toaster oven (with foil to protect from direct heat from the elements) and then blasting it with the heat gun right at 250 so the traces cant wick the heat away from the solder paste and cause the plastic to melt (i.e. if the heat gun is set above 275 C).

Does anyone have a suggestion or a link to something I might watch or read?

[sleemanj]

I would

  clean the pads
  flux the pads
  tin the pads with soldering iron sufficiently that there is enough solder on them as will be required total, that is, a small hill of solder on each pad
  flux it again
  flux the connector
  use hot air to heat the solder until it's molten
  with your other hand use tweezers to drop the connector onto the molten solder and push it gently to help it snap into place with surface tension

 

[dgtl]

The ground traces are the most difficult to heat up, as the ground plane is wicking the heat away.
When soldering with a soldering iron, use a powerful enugh soldering iron, any random iron won't do it. It also helps to pre-heat the board on hot-plate or with hot air.
Alternatively, as the component seems to be hot-air reflow capable, you can just reflow it in place using hot air (and a pre-heating the whole board would help there as well).
Using plenty of flux helps.

[KL27x]

Might want to buy some bismuth alloy solder. I can't remember the brand name, but I think it's ChipQuick. Or QuikChip. Or something like that. Apply it to the pins, liberally. If you can blob them all together, so much the better. Then put a big old tip on there that will touch all the pads at once.

If the plastic melts... who cares? You're replacing it. Pull the thing off and take the pins out one at a time, if you have to. Clearing the ground plane pins might be tricky, though.

[kony]

Bring it to closest mobile phone repair shop. Should be under 3 minutes job with preheat and hotair rework station. Soldering iron is wrong tool here.

[Doctorandus_P]

I'm with Kony.

With the right tools and experience this is a job done in 5 minutes, and those phone shops have the tools & experience and can do it therefore in 5 minutes and it probably won't cost you much.

Without the right tools and experience it easily becomes a nightmare and your're likely to damage the PCB, which can make repair very difficult.

[solderjs]

Wow! I didn't know I had replies waiting (apparently my email-on-replies settings aren't turned on).

Ruling Things Out...

My goal isn't to fix this as much as it is to learn how to fix it, so although I appreciate the advice on visiting a phone repair shop, that would side-step my real purpose.

I've used Quick Chip / Chip Quick (or rather a knock-off from ebay) and it was AMAZING. However, I think that's a bit too much cheating - and it would quite possibly melt during normal use (58˚C!!).

I could get and use a micro soldering iron perhaps, but I'd only get the front four pins and the back side (which is underneath of the component).

This is so small... I don't think dropping it onto the solder will "do the business". It's pinpoint. Though might work for the backside which is a little larger. Maybe I should consider it further... but with how fast the heat dissipates from these tiny parts, I don't think it's going to work.

Possible Path Forward

I've got a toaster oven and I've pre-baked stuff in there, but I haven't tried a true reflow... well, not on anything that I intended to use again anyway.

I created a mounting bracket with standoffs and shielded it from the direct heat of the element (melted a test board that was otherwise within temp that way), but I'm a little concerned since it's double sided that parts might fall off.

What should I worry about and what shouldn't I worry about?

[AndyC_772]

The problem here isn't that the pads are tiny, it's that some of them blend straight into a solid plane without any thermal relief. The heat you apply flows straight into the plane, and it's virtually impossible to get the pads hot enough for solder to melt.

A tip small enough for those pins just isn't physically capable of conducting enough heat through that tiny contact area to raise the temperature of the pad high enough to melt the solder.

For the manufacturer, that's not a problem, because the reflow oven heats the entire board - parts, plane and all.

If you asked me to solder one of those connectors using the equipment I have in my lab, I'd:

- pre-heat the board from below using a hot plate until the whole PCB is at 150C. An IR thermometer or thermal camera is a good way to see what temperature the board has reached.
- select a reasonably large chisel tip
- apply flux to the board and tin the pads
- place the component
- reflow the component using hot air
- allow the board to cool gently
- clean with an anti-static brush and IPA

I'd direct the flow of hot air near to (but not directly at) the component, so as not to melt it. The heat is conducted through the plane into each joint, which helps ensure the component doesn't melt. The idea is to ensure that the whole area gets to - but not too far above - the melting point of solder.

The whole board will have been assembled using lead free solder, so even if the use of lead is still permitted where you are, contaminating the joints with lead may affect long-term reliability. It's always best to rework a board using a similar type of solder to what was originally used.

[amyk]

Get a hot air station... SMD work becomes much easier (and sometimes even possible) when you have one.