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I need to replace a broken planar circut (a Hall effect sensor) that was attached to a plastic hull of another unit (a rotor wheel assembly). And, most probably, will need to move the entire connector to a replacement assembly eventually.

The (remains of) the old circuit and its resting place look like this. The pads are thin copper. The whole depression was filled with some amber-like mass, remnants of which can be seen in the photo to the right (bonus points for any ideas what it might be).

enter image description here

Can someone explain how this connector was made, and how it's supposed to be worked on? For example:

  • If I try to just solder the new circuit in, I'm probably going to melt the underlying plastic in the process
  • It's unclear how whoever made this was able to place the pads by hand with such precision (the IC's size is 2x5 mm). This is clearly not any kind of printed design.

Looking around the Net found plenty of guides on soldering surface mount components, but nothing on non-PCB placement or dealing with a melty surface.


Photo from the side with all the amber-like mass removed:

enter image description here

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    \$\begingroup\$ Unfortunately, I can't tell what it is from the photo. Try to take a better one if you can, it might help to cover the brigth shiny metal ring. Could it be a small piece of flex PCB? The pads look like they are more than 1mm long and more than 0.5mm wide, if I have understood you correctly. In which case hand soldering them would not be at all difficult for an experienced assembly technician. \$\endgroup\$
    – Jack B
    May 17, 2020 at 9:52
  • \$\begingroup\$ @JackB the component whose remnants are in the center is SS511AT. The entire depression was originally filled with some amber-like mass (bonus points if you have any ideas what it might be), so I can't see if there's anything else below the pads, either. I'll now scrub it off completely and see if there's anything. \$\endgroup\$ May 17, 2020 at 12:16
  • \$\begingroup\$ @JackB You were right! The pads do rest on a transparent plate about half a mm thick. It's round and fllls the entire depression so its edges couldn't be seen from above. It has tiny grooves on the other side like a PCB does. Will it give enough heat insulation to avoid melting the plastic beneath? \$\endgroup\$ May 17, 2020 at 12:32
  • \$\begingroup\$ Added a photo from the side with the amber-like mass removed. \$\endgroup\$ May 17, 2020 at 16:38
  • \$\begingroup\$ I'd put it on small piece of PCB, maybe a standard breakout one. Or else carefully point to point wire it. And in either case then consider some sort of potting solution to mount the result, assuming it's an application where something like VHB tape and hoping for the best is not sufficiently reliable. \$\endgroup\$ May 17, 2020 at 19:31

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As @JackB correctly guessed, the pads actually sat on a thin round PCB. It has the same color as the amber-like filling mass (which I guess is epoxy) so it was indistinguishable from it until I scrubbed it all off and found out that indeed, the thing that is beneath is actually something different.

It was glued to the plastic, so all soldering had been done away from it, making the melting problem irrelevant.

Here it is, with the new component soldered in:

enter image description here

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