Avoid taping old 35mm negatives back into strips if you can. Tape, cement, or heat splicing can damage film and spliced areas may deteriorate faster over time.

Better options mentioned were:

• scan single frames directly, if your scanner supports mounted slides or individual pieces of film
• use slide mounts to hold individual frames for scanning and easier long-term handling
• use a flatbed scanner and place single negatives on the glass, rather than rebuilding strips

If you truly need strips, use a proper film splicer with the correct archival splicing material rather than ordinary tape. But for old negatives, the safer approach is usually not to splice them at all.

So the best answer is: don’t use regular tape, and preferably don’t reassemble the negatives into strips. Scan them individually using a slide-capable film scanner, slide mounts, or a flatbed setup.