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When to Tin and Not Tin Wires

Question: I have a connector that you insert a 7/30 wire into and hold it in place by tightening a screw. Should the wire be tinned? I have look in my IPC 620 standard and the only reference I see is Section 4.4, indicating that stranded wires should not be tinned when “wires will be used in threaded fasteners”. Not sure if this applies. Is this true?

Answer: Ok, here is the information as I found it:

IPC-J-STD-001 Rev E, page 13, section 5.1.3, “Stranded wire shall not [D1, D2, D3] be tinned when:”

  1. Wires will be used in crimp terminations
  2. Wires will be used in threaded fasteners
  3. Wires will be used in forming mesh splices

IPC-A-610 Rev E, page 4-10, Section 4.1.4.2, states under defect conditions, 6th bullet down, “Stranded wire is tinned (not shown)” this is a defective condition for any wire going under any threaded fastener.

IPC/WHMA-A-620, page 4-10, Section 4.4, same criteria as J-STD-001 as above.

Therefore to answer your question “Should the wire be tinned?” the answer is NO.

The reasoning behind not tinning the wire is, if the wire is tinned, when the screw closes down on the wire, it would break the solder joint and leave an opening within the strands, which can be susceptible to vibration, loosening and corrosion. By not tinning the wire, you can get a better gas tight joint.