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I've arranged for a custom shaped strip of pure nickel that I intend to solder to ENIG pads on a PCB using reflow/paste.

Will we have problems getting the solder to adhere to the nickel? Is there a trick to it?

Other (potentially relevant) details:

  • The solder paste is probably lead-free, or at least it will be in production.
  • The nickel strip is 16x6x0.3 mm. This may still change but not by much.
  • The purpose of the nickel strip is to allow us to cold/spot weld LiPo cell tabs to the BMS PCB, which would otherwise be difficult if we were to attempt welding directly to the ENIG pads. The nickel strip will provide a barrier layer.
    • The cell tabs are too big for soldering.
    • One tab is nickel, and the other is nickel plated.
  • I know the ENIG surface finish already involves adding nickel to the copper foil. But then gold is added to help solder adhere. That implies that nickel is not easy to solder to, but in this case, our nickel strip is pure nickel and we've never attempted this before.
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  • \$\begingroup\$ Side note: I already found this post, but it's about using an iron, not a reflow oven. electronics.stackexchange.com/questions/607109/… \$\endgroup\$
    – Dan
    Commented Aug 25, 2022 at 3:31
  • \$\begingroup\$ We used nickel plated PCBs for one application and the nickel did not solder well with ordinary 63/37 Kester 44 solder (not a problem because the nickel was for sliding contacts). Lead free flux may be more aggressive, perhaps you should test before committing. \$\endgroup\$
    – Spehro Pefhany
    Commented Aug 25, 2022 at 3:47
  • \$\begingroup\$ This can probably solved by using a more aggressive flux on the nickel. You may have to wash with hot water after soldering to remove flux residue. A quick search found kester 742 flux and Johnson's J-35 flux. Be sure to read all the fine print. Aggressive fluxes can ruin boards over time if they are not washed off properly. \$\endgroup\$
    – user57037
    Commented Aug 25, 2022 at 4:33
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    \$\begingroup\$ Have the strip tin or gold plated at the soldering end. \$\endgroup\$
    – Tim Williams
    Commented Aug 25, 2022 at 8:43
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    \$\begingroup\$ Hi Tim, I got a response from the nickel strip manufactures and plating the strip will raise the MOQ from 10,000 to 200,000, and increase the price. I don't know how much the price is increased by because they won't quote that. I don't think this is an option. However, the manufacturer tells me that plating shouldn't be necessary. Our assembler isn't so sure, so I think I'll buy the 10,000 and just try it. \$\endgroup\$
    – Dan
    Commented Aug 29, 2022 at 4:23

1 Answer 1

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Our assembler originally recommended some special solder paste with a certain flux in it to bond the nickel strip to ENIG pads, but after a bit of trial and error, we didn't end up having to do anything different to reflowing other components. No tinning or any other special steps. It just worked reliably on every board.

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