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Step 5: Attach the New Antenna to the Chip and Test Assembly

Picture of Attach the New Antenna to the Chip and Test Assembly
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Your antenna should measure 15.0" or half of what the full antenna in your old card measured, from the first point where it makes contact with the chip, to the second point, both times as soon as it makes contact with the pads on the chip board. If these two points measure differently than 30.0" in your card, please leave a comment letting me know, but I assume these antennas are all the same size since they're all the same frequency.

For the antenna, I used: https://smile.amazon.com/gp/product/B01IJ2JJG6/ but there are probably better options out there (See discussion in the comments.)

This is one of the more annoying steps for a few reasons. In order to attach the antenna to the chip, you have to first strip the magnet wire, which is a feat in and of itself. There are many guides online, but the best way I've found is to very briefly touch a bic lighter's flame to the end of the magnet wire, and it will burn off the enamel and leave a carbon deposit all over the end of the wire. If you then take some 400 - 1000 grit sandpaper, pinch it together and use it to repeatedly sand off the carbon deposits until you see copper, it seems to work well.

Then you need to do this to both ends, and solder one end to the chip's outermost pads. Note that the pictures above are of different chips, to show different possibilities you might run into. The reason that you're soldering only one end of the new antenna to the chip is that you can pinch the other end to the opposite contact pad and then test it out on a sale to make sure that everything is still working before you start gluing things together. The easiest way that I've found to do this is to look for vending machines that accept NFC. You'll want to make a few loops of the antenna as shown in the last picture, three or four loops seem to work well, then pinch the stripped non-soldered end to the other pad while holding it up to the reader.

If it works, get yourself a drink as a reward for getting this far. If it doesn't, you may have filed too far into a trace or had something else happen. Request another card from your bank and try it again. You can also try this part before filing the chip's board down as well so that if something does happen, you can figure out where you went wrong.

As for soldering one end, solder doesn't seem terribly willing to flow onto magnet wire, so go for a liberal use of flux. In my case, I ended up just making a large blob of solder on the pad and then managing to get the magnet wire end into the middle. Less so having the solder flowing onto it, and more so just having the wire attached by the fact that it's in the middle of the blob. Less than ideal, but it worked well.