A press-fit pin is a solderless PCB termination: a contact with a springy “compliant” zone that is pressed into a plated-through hole, where it deforms and cold-welds against the barrel copper to form a gas-tight joint. No heat, no flux, no reflow. This guide explains how compliant pins work, the pin styles and hole requirements, the two governing standards (IEC 60352-5 and IPC-9797), and when press-fit beats soldering.
Key takeaways
- A press-fit pin and its plated-through hole are one system; the compliant zone springs against the barrel to make a gas-tight, cold-welded contact without solder.
- Compliant pins (C-section, action pin, eye-of-the-needle) replaced solid pins because they need less insertion force and damage the board less.
- IEC 60352-5 requires ≥25 µm copper in the plated-through hole; IPC-9797 is the automotive / high-reliability acceptance standard and targets 1.6–3.2 mm boards.
- Typical per-pin numbers: 1–3 N contact normal force, <2.5 mΩ contact resistance, and 3–5 A current for automotive-grade pins.
- Compliant pins tolerate roughly three insertion / extraction cycles; each cycle wears the hole plating, so production repairs use new connectors.
- Press-fit is standard in telecom backplanes, automotive ECUs, and EV power electronics because it survives vibration and −40 to +125 °C cycling without solder-joint fatigue.
What is a press-fit pin?
A press-fit pin is a stamped metal contact designed to be pushed into a plated-through hole (PTH) rather than soldered to it. The pin carries a compliant section: a deformable zone that acts like a spring, sized slightly larger than the hole. As the pin enters, that zone compresses and presses outward against the copper barrel. The high local pressure creates a cold weld that is both the electrical and the mechanical joint (TE/Tyco).
[IMAGE 1: cross-section of a compliant press-fit pin seated in a plated-through hole, compliant arms pressed against the copper barrel | alt: “Cross-section of a compliant press-fit pin cold-welded against a plated-through-hole barrel”]
Because the pin and the hole work only as a pair, connector makers specify the compliant pin together with a finished hole-diameter range; the two together are the press-fit system (TE Connectivity). The result is gas-tight: contact pressure keeps oxygen, moisture, and sulfur out of the interface, so contact resistance stays stable for the life of the board. The idea descends from wire-wrap, where a round wire wound onto a square post bit into the corners to make a gas-tight joint (TE/Tyco). Press-fit keeps that reliability but industrializes it for automatic insertion.
Solid vs. compliant press-fit pins
Two families exist. A solid press-fit pin has a rigid press-in zone; it does not deform, so the hole must absorb all of the interference. That demands very tight hole tolerance (historically about ±0.002 in) and risks barrel and pad damage that is invisible after insertion (US patent literature). A compliant press-fit pin instead deforms its own compliant section, absorbing hole-diameter variation and cutting insertion force.
TE Connectivity states plainly that solid press-fit pins no longer exist in automotive applications; compliant designs took over because they make fewer demands on the PCB and cause less damage (TE Connectivity; Positronic). Solid pins survive only in niches. Nearly every modern connector uses a compliant pin, which is why the terms “press-fit pin” and “compliant pin” are now used interchangeably.
Compliant pin styles
Compliant zones come in a few recognizable shapes, and the geometry sets the insertion force, the retention, and how much hole tolerance the pin can swallow.
[IMAGE 2: three compliant press-fit pin styles side by side — C-section, split-beam action pin, and eye of the needle | alt: “Three compliant press-fit pin styles: C-section, split-beam action pin, and eye of the needle”]
| Style | How it works | Where it fits |
| C-section | A curved, slit cross-section that flexes as one springy wall | General-purpose signal and power pins |
| Action pin (split-beam) | A slot splits the pin into two beams that flex inward | Long-serving backplane and telecom design (AMP/TE ACTION PIN) |
| Eye of the needle (EON) | A central opening leaves two arms that squeeze together | The dominant modern style; scales to small vias and pitches |
The eye of the needle is now the default. It is stamped and coined from copper strip, and its central opening lets the two arms comply over a defined hole-diameter range (IPC APEX). The industry trend is toward smaller EON pins and vias to improve signal integrity at the launch (IPC APEX). TE’s NanoMultispring EON, for example, targets a 0.6 mm finished hole per IEC 60352-5, and Autosplice’s 0.4 mm EON zone is designed for a 0.60 ±0.05 mm hole.
Press-fit vs. soldering
The whole point of press-fit is to skip the solder joint, and that trade is worth making in specific cases.
| Factor | Press-fit compliant pin | Soldered through-hole |
| Joint | Gas-tight cold weld, no filler metal | Solder fillet with intermetallic layer |
| Heat in assembly | None; no reflow or wave step | High; reflow or wave thermal exposure |
| Rework | Extract and reinsert, about 3 cycles | Desolder; risks thermal damage |
| Board cost | Higher: tight-tolerance PTH, ductile plating | Lower: standard hole tolerance |
| Tooling | Press with force monitoring required | Solder process; secondary joints often manual |
| Vibration / thermal cycling | Compliant zone flexes; no fatigue cracking | Solder-joint fatigue over cycles |
| Best for | Backplanes, automotive, high vibration, thick boards | General assembly, fine-pitch SMT, low cost |
Two caveats. First, standard press-fit alone does not match the ampacity or vibration resistance that some automotive uses need; advanced bi-spring “power” press-fit contacts add contact springs and mounting screws to close that gap (Molex; Positronic). Second, a reliability norm cited by TE (IEC 61709) rates press-fit at least ten times more reliable than soldered or IDC connections. That figure assumes a correctly designed hole and monitored insertion; it is not a free lunch.
The plated-through hole and key parameters
Half the press-fit system is the PCB. Get the hole wrong and the best pin still fails. The values below come from IEC 60352-5 and IPC-9797.
| Parameter | Requirement / typical value | Source |
| PTH copper thickness | ≥25 µm in the barrel | IEC 60352-5 |
| Finished hole tolerance | about ±0.05 mm | IPC-9797 |
| Finished hole diameter | pin max inscribed circle, +0.05 to +0.10 mm | IPC-9797 |
| Board thickness range | 1.6–3.2 mm (standard) | IPC-9797 |
| Annular ring | ≥0.25 mm on all layers | IPC-9797 guidance |
| Hole surface finish | bare copper + OSP, ENIG, or immersion tin; avoid HASL | IPC-9797 guidance |
| Contact normal force | about 1–3 N per contact point | IPC-9797 guidance |
| Contact resistance | <2.5 mΩ per pin (typ 0.5–1.0 mΩ); power pins <200 µΩ | fabricator data / PCBSync |
| Insertion force | about 2–45 lb per pin, by geometry | TE/Tyco |
| Retention (push-out) | roughly half the insertion force | TE/Tyco |
| Current per pin | 3–5 A, automotive-grade compliant pins | fabricator data |
| Reinsertion | about 3 insertion / extraction cycles | PCBSync |
HASL is the classic mistake: it deposits tin unevenly and moves the finished hole size unpredictably, so insertion and retention scatter (AtlasPCB). Copper barrels must be ductile enough to take the interference without cracking, which is why press-fit boards effectively run at IPC-6012 Class 3 plating quality. The 2012 edition of IEC 60352-5 even deleted its old hole-dimension tables, because those numbers had been inherited from obsolete wire-wrap post sizes (IEC).
The two standards: IEC 60352-5 and IPC-9797
Two documents govern press-fit. IEC 60352-5, “Solderless connections – Press-in connections,” sets general requirements, test methods, and materials; it fixes the ≥25 µm copper minimum and names typical pin alloys such as copper-tin bronze and beryllium copper. Its 2020 fifth edition broadened the scope from telecom to all electrical and electronic equipment, added definitions for metal boards, dropped the old bending test, and added press-in and push-out force graphs (IEC).
IPC-9797, “Press-Fit Standard for Automotive Requirements and Other High-Reliability Applications,” is the industry-consensus acceptance standard. It defines characterization, qualification, and acceptance criteria for compliant press-fit in harsh environments and is backed by the IPC-HDBK-9798 handbook (IPC). For vehicles, press-fit designs also meet AEC-Q200 and OEM specs such as VW 80808, BMW GS 95024, and Daimler DBL 9741 (AtlasPCB). In production, both standards lean on 100% insertion-force monitoring: each pin’s force-distance curve becomes a built-in quality record (TE Connectivity).
Where press-fit pins are used
Press-fit earns its keep wherever heat, vibration, or scale rule out soldering.
- Telecom and computing backplanes. Routers, switches, and base stations use large backplanes carrying thousands of press-fit contacts. The boards are thick, high-aspect-ratio, and tightly toleranced, and connectors can even be pressed from both sides into a shared hole (connectortips).
- Automotive and EV. TE introduced press-fit to automotive in 1988, and since the mid-2000s many OEMs have migrated safety-critical and power interconnects from soldered joints to compliant press-fit (Autosplice). It survives −40 to +125 °C cycling and engine-bay vibration, and EV battery and motor-control modules use it for high-current joints (PCBSync; TE).
- Aerospace and high reliability. The gas-tight, fatigue-free joint is robust enough that press-fit connectors are being submitted for space-flight qualification (industry reports).
Design and handling mistakes that cause failures
Most press-fit problems are process, not pin.
- Wrong surface finish. Speccing HASL for press-fit holes scatters the finished diameter; call out bare copper with OSP, ENIG, or immersion tin instead (AtlasPCB).
- No hole callout. If the fabrication notes do not flag press-fit holes, the fab treats them as ordinary vias with loose tolerance. Add an explicit note, for example “Press-fit holes per IPC-9797, finished hole Ø X ±0.05 mm, 100% verification” (AtlasPCB).
- No board support. Without a backing fixture under the insertion points, the board flexes and you get barrel stress, pad lift, or cracks (AtlasPCB).
- Reinserting used connectors. Each cycle wears the plating; about three cycles is the practical ceiling, and production repairs should use new connectors, not removed ones (PCBSync).
- Ignoring board-thickness tolerance. PCBs vary about ±10% in thickness, which changes engagement length and therefore retention; pressing short pins from both sides is one way to decouple that (connectortips).
Frequently asked questions
What is the difference between a solid and a compliant press-fit pin?
A solid press-fit pin has a rigid press-in zone and forces the plated-through hole to absorb all of the interference, so it needs very tight hole tolerance and can damage the barrel. A compliant pin has a springy section that deforms instead, lowering insertion force and protecting the board. Compliant pins have largely replaced solid pins, and per TE Connectivity no longer exist in automotive use.
Can press-fit pins be removed and reused?
Compliant press-fit pins can be extracted with the right tool and reinserted, but only about three insertion / extraction cycles before hole-plating wear degrades the joint. Each cycle wears the barrel, so for production repairs you fit a new connector rather than reinsert a removed one. Solid press-fit pins are generally not suitable for multiple insertions.
What copper thickness does a press-fit hole need?
IEC 60352-5 requires at least 25 µm of copper in the plated-through-hole barrel. The copper must also be ductile enough to take the pin’s interference without cracking, which is why press-fit boards typically run at IPC-6012 Class 3 plating quality. Too little copper can delaminate during insertion; too much makes the finished hole tolerance hard to hold.
Is press-fit more reliable than soldering?
For large connectors in harsh environments, yes. A norm cited by TE (IEC 61709) rates press-fit at least ten times more reliable than soldered or IDC joints, mainly because there is no solder-joint fatigue under vibration and thermal cycling and no cold joints or bridging. That advantage assumes a correctly toleranced hole and monitored insertion; a poorly made hole erases it.
What is an eye-of-the-needle pin?
An eye-of-the-needle (EON) pin is a compliant press-fit contact with a central opening that leaves two arms. The arms squeeze together as the pin enters the hole, complying over a defined hole-diameter range. It is stamped and coined from copper strip and is the dominant modern style because it scales to small vias and fine pitches, down to a 0.6 mm hole.
The bottom line
Reach for press-fit when you have a large or high-pin-count connector, a thick board, or an environment with vibration and wide temperature swings; backplanes, automotive ECUs, and EV power modules are the textbook cases. Budget for the tighter board: ≥25 µm ductile copper, a finished hole held to about ±0.05 mm, a press-fit-friendly finish (OSP, ENIG, or immersion tin), and press tooling with force monitoring and board support. Specify the compliant pin and its hole as one system to the numbers in the connector datasheet and IPC-9797, add an explicit press-fit hole callout to your fab notes, and treat any single connection as good for about three insertions. Stay with soldering when the design is fine-pitch SMT, cost-driven, or low-vibration, where a solder joint is cheaper and the board can use standard tolerances.
