1. 1970-1980: The “hard” years
- 1970 – Siemens & ITT introduce the first rigid press-fit pin: a solid brass nail that relied on oversize hole interference. High insertion force (300 N), cracked PTHs, limited to telecom back-planes .
- 1974 – Eye-of-the-Needle flexible zone patented by Siemens (DE 24 27 526): a stamped diamond slot that buckled elastically → insertion force ↓ 40 %, reliability ↑ 10×.
- 1977 – Amphenol files US 4 159 157 on the C-Press split-barrel, giving a continuous circumferential contact.
Key insight: replace brute interference with elastic compliance.
2. 1980-1990: Telecom boom & the birth of “compliant” families
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Year Brand Name Patent / trademark Innovation 1983 Siemens TCom pin EP 0 100 678 Rectangular wire formed into twin-beam spring, 0.8 mm pitch capability. 1985 Amp Compliant Pin US 4 533 305 First stamped S-shape; 25 µm Sn plating spec’d. 1988 Berg Action Pin US 4 533 305 (assigned) Multi-lance cuts → lower peak force, self-centring. By 1989 press-fit outsold solder headers in European central-office frames.
3. 1990-2000: Automotive & the rise of TE Connectivity
TE’s dual-platform strategy (still dominant today)
a) ACTION PIN
- 1990 – Tyco acquires AMP; brands the multi-lance pin “ACTION PIN”.
- 1996 – US 5 700 167 adds lead-in bullet for blind insertion on robotic lines.
- Feature: four longitudinal lances create radial beams; insertion 70-120 N, retention ≥ 60 N in 1.0 mm PTH.
b) MULTISPRING (MS)
- 1992 – Internal R&D; 1997 commercial release.
- Patent family: US 6 132 372; EP 1 037 303.
- Concept: two symmetrical spring windows stamped from strip; wall thickness 0.6 mm (standard), 0.4 mm (Nano MS), 0.8 mm (Power MS).
- Benefit: 30 % lower insertion than ACTION PIN, same retention; ideal for 0.8 mm pitch ECUs.
TE data sheet: “MS is 10× more reliable than IDC or solder under IEC 60352-5”
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4. European answers: Elo Pin, C-Press, H-Pin
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Pin type Origin Shape Force profile Patent expiry Elo Pin Bosch / Kostal / FCI Hour-glass double S-bend Very low peak, smooth plateau EP 0 605 847 (exp. 2004) C-Press Amphenol Open C cross-section Continuous, no stress concentration US 4 533 305 (exp. 2002) H-Pin FCI / Delphi H beam, two parallel slots High retention, small holes US 5 897 401 (exp. 2017) Elo Pin became the default for sealed automotive bulk-head connectors because its smooth force curve keeps the PTH deformation below 50 µm.
5. 2000-today: Miniaturisation & open patents
- 2005 – JST files US 7 377 823 on wire-based press-fit (cost ↓ 20 %, patent expired 2025) .
- 2013 – TE launches Nano MULTISPRING 0.4 mm wall, 0.3 mm pitch, 30 N insertion – target 112 G PAM4 back-plane .
- 2020 – EP 3 694 055 (TE) adds anti-rotation rib for 0.8 mm pitch three-phase power modules .
Most fundamental patents (Siemens diamond, AMP S-shape, TE multi-lance) expired ≥ 2010, opening the door for Asian stampers to ship “generic compliant pins” at USD 0.002 each.
6. Material & plating evolution
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Era Alloy Conductivity Stress-relaxation Plating 1980 CuSn4 20 % IACS 100 °C/500 h 2 µm SnPb 1995 CuNiSi (C7025) 40 % IACS 150 °C/1000 h 3 µm Sn 2010 CuCrZr (C18150) 80 % IACS 175 °C/1000 h 1 µm Ni + 1 µm SnAg Today’s automotive 150 °C zones use CrZr; below 125 °C NiSi wins on cost.
7. Key learning for designers
- Patent walls are down—feel free to copy the 1980 shapes, but watch brand trademarks (MULTISPRING®, ACTION PIN®).
- Choose Elo/H for lowest peak force, MULTISPRING for highest density, ACTION PIN for brute-current.
- Specify hole quality first: 25 µm Cu, ±50 µm dia., no burr—pin is only half the story.
From a 1970 “nail” to a 0.3 mm micro-spring, the press-fit pin has soldered nothing—and yet connected everything.
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