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Home > Basis of terminals and pins > About press-fit terminals and pins

About press-fit terminals and pins

index

Press-Fit terminals

Press-Fit Connectors

Recent years have seen an increased use of solderless press-fit connectors in the assembly processes of devices with circuit boards. In contrast to conventional connectors that are soldered when they are attached to the board, press-fit connectors can be attached by simply press-fitting them, simplifying the production process. More specifically, it is possible to eliminate the solder application and reflow processes. The simplified solderless mounting process leads to the reduction of energy consumption, establishment of an eco-friendly production process, and significant reduction of production costs.

In addition, with the increasing social call to reduce harmful substances and environmentally damaging substances, all manufacturers, regardless of their specialties, are required to produce products that do not contain such substances.

Press-fit connectors provide solutions for production processes that meet the needs of the times.

The terminals (press-fit parts) of a press-fit connector are inserted into through-holes in the printed circuit board, where pressure is applied due to the deformation of the press-fit sections, causing contact between the holes and the terminals to pass electric current. In other words, the press-fit section of each terminal forms a tight fit with a through-hole in the printed circuit board due to the restoring force generated as a result of the elastic deformation at the time of press-fitting. This tight-fit state maintains the contact to allow electricity to pass through.

In order to achieve this state, the press-fitting machine is required to have enough power to insert the terminals. In most cases, when mounting a press-fit connector on a circuit board, the connector is lightly fitted into the board by hand before it is fully inserted and mounted using a connector press-fitting machine. A special press-fitting jig is also required to mount a press-fit connector onto a printed circuit board.

press-fit terminals

Solderless Connection with the Press- Fitting Technology

The solderless connection is a method of mounting a connector onto a circuit board. This mounting method involves press-fitting an elastic contact (which deforms when force is applied, and becomes restored when the force is released) called the compliant section or press-fit section into a through-hole in the printed circuit board to create an airtight (gastight) contact with the inside surface of the through-hole utilizing the deformation of the elastic section of the contact.

This technology, developed in the US, is not a novel one but a mature technology, which has been mainly used for the mounting of multipolar connectors on motherboards. Individual connector manufacturers created their own specific shapes for the compliant section to give elasticity to terminals and obtained patents. The terminals were provided with cut sections at which they would elastically deform.

Their advantage is that terminal pins, or the entire connector, can be replaced in the event of a problem such as the bending of a terminal after mounting (it is possible to insert a new terminal into the same through-hole up to three times or so under normal conditions).

It is essential to appropriately control the press-fitting force and to dimensionally control the drilled inside diameters and the plating thicknesses for the through-holes.

Example: A pin with an S-shaped press-fit section Square-type press-fit terminal (S-shaped cross section) with a crushed portion in the middle

Square-type press-fit terminal (S-shaped cross section) with a crushed portion in the middle

 

 

 

Insertion Force and Retention Force

The following shows an example of insertion force and retention force with a printed circuit board for evaluation.

・Printed circuit board specifications

Board material: FR-4

Board thickness: 1.6 mm

Hole diameter: ø1.02 ± 0.05

Surface treatment: Gold flash plating on copper undercoat

・Terminal specifications

Material: Phosphor bronze square pin (square of side 0.64 mm)

Surface treatment: Tin reflow plating on nickel undercoat

Insertion Force and Retention Force (press-fit terminal)

Application of Press-Fitting Technology

Environmentally damaging substances or the use of lead-free solder can lead to non-negligible deterioration in solder reliability. In addition, there have emerged various issues, such as the necessity to avoid thermal shock to the chip components due to soldering heat and the need for automatic mounting. Reflecting these circumstances, press-fitting technology is applied, for example, to connections between automotive control system circuit boards such as those for onboard equipment, antilock braking systems, vehicle stability control, navigation systems, hybrid drive systems, and tire pressure monitoring systems.

Press-fitting technology, which enables easy removal of connectors and other such components, is also advantageous when it comes to compliance with the Waste Electrical and Electronic Equipment Directive (WEEE Directive) in Europe. Accordingly, the application of this technology has also been expanded to conventional consumer products, including personal computers, servers, and multifunction printers.

Forms of Press-Fit Terminals

1)Press-fit terminal which is processed from a wire.

  • Press-fit terminal/Separate terminal (pin)
    1. Separate terminal (pin)
  • Press-fit terminal/End-to-end terminals (pins)
    2. End-to-end terminals (pins)
  • Press-fit terminal/Bandolier terminals (pins)
    3. Bandolier terminals (pins)

2)Press-fit terminal which is processed from metal strips.

  • Press-fit terminal/Center Carrier type press-fit terminal
    1.Center Carrier type
  • Press-fit terminal/One –side Carrier type press-fit terminal
    2. One –side Carrier type

 

 

Materials of Press-Fit Terminals

1) Applicable Printed Circuit Board Materials(designations and corresponding JIS standards)

Recommendations:

FR-4.0 and FR-4.1: JIS C 6484:2005 (Base materials for printed circuits — Epoxide woven E-glass laminated sheet of defined flammability (vertical burning test))

<Explanation as to Printed Circuit Boards>

flame retardant grade

flame retardant grade

The FR (flame retardant) grade is an indicator of incombustibility of a copper-clad laminate, a structural component of a printed wiring board.

It is represented as “FR-X,” where X is a numeral between 1 and 6, and the most nonflammable grade is FR-6.

The printed wiring boards that are familiar to electronic equipment designers are FR-4 boards. This means that they are printed wiring boards that include copper-clad laminates graded as FR-4. FR-4 boards are copper-clad laminates with an ordinary level of heat resistance made using flame-retardant glass-cloth epoxy resin.

Copper-clad laminates graded as FR-5 may be used for printed wiring boards that require a higher level of heat resistance, such as those for automotive applications. Incidentally, new designations have been adopted in the revised UL standard, as follows:

- FR-4 products (Brominated flame-retardant products) changed to FR-4.0

- FR-4 products (Non-halogen flame-retardant products) changed to FR-4.1

2) Materials for Press-Fit Terminals (designations and corresponding JIS standards)

Recommendations:

・Phosphor bronze

C5191W: JIS H 3270:2012 (Copper beryllium alloy, phosphor bronze and nickel silver rods, bars and wires)

C5212W: JIS H 3270:2012 (Copper beryllium alloy, phosphor bronze and nickel silver rods, bars and wires)

・ Copper-beryllium alloy

C1720W: JIS H 3270:2012 (Copper beryllium alloy, phosphor bronze and nickel silver rods, bars and wires)

・Corson copper alloy ; Cu-Ni-Si based (Corson alloy)

<Explanation as to Materials>

The material used needs to be elastic inside the through-hole in a printed circuit board. In other words, material with a high level of spring-like property is to be used. Material prices should also be considered.

When using beryllium alloy, it is necessary to consider the precipitation hardening treatment.

FINECS processes both metal strips and wire.
Please feel free to contact us.

Surface Treatment of Press-Fit Terminals

1) Tin reflow plating on nickel undercoat on wire

Ni: 1–1.5 µm + Sn: 1.5–2.5 µm (reflow plating)

2) Bandolier pins: It is also possible to apply gold plating to only the end portions of terminals.

Arrangement pitch: 2.0 mm, 2.54 mm (0.1"), 3.0 mm, etc.

<Recommended Through-Hole Specifications>

In addition to hot air leveling (HAL), the specifications listed below have become increasingly important. Based on different characteristics, such as mechanical strength and the coefficient of friction, we recommend the following through-hole specifications.

1.6mm以上 Thickness of the printed circuit board: 1.6 mm above

Specifications of Circuit Board Through-Holes

Specifications of Circuit Board  Through-Holes

Prepared hole diameter: 1.15 ± 0.025

Copper: 25 µm at the minimum

max.0.8µm Tin: 0.8 µm at the

Finishing diameter: 1.00–1.10 mm

Referential Standard

We have acquired reference data in connection with the standard mentioned below. For other tests, we ask that your company acquires the relevant data.

・IEC 60352-5:2012

Solderless connections

Part 5: Press-in connections –General requirement,test methods and

-Excerpt-

5.2. Mechanical tests

5.2.2.1 Bending

Bending of 15 degrees (one up-and-down movement in both directions)

【Excerpt】press-fit terminal pin1

5.2.3.4 Contact resistance

The contact resistance shall be carried out in accordance with IEC 60512,test 2a.

Excerpt】press-fit terminal pin2

Requirements after mechanical, electrical or climatic conditioning:

a) Qualification test schedule: The maximum change of contact resistance

shall be less than 0.5mΩ for each test phase.

b) Application test schedule: The maximum change of contact resistance shall be specified in the component detail standard, if any, or in the manufacturer’s specification.

 

5.2.4.4 Dry heat

The test shall be carried out in accordance with IEC 60512, test 11i.

- test temperature 105℃

- test duration 1,000 h

Appearances and Shapes of Press-Fit Terminals

We at FINECS recommend the following shapes:

 

Square-type press-fit terminal (S-shaped cross section) with a crushed portion in the middle

Square-type press-fit terminal (S-shaped cross section) with a crushed portion in the middle

 

Square-type press-fit terminal (S-shaped cross section) with a flange in the middle

Square-type press-fit terminal (S-shaped cross section) with a flange in the middle

 

Round-type press-fit terminal (S-shaped cross section) with a flange in the middle

Round-type press-fit terminal (S-shaped cross section) with a flange in the middle

 

 

Shapes other than the above are also available at the customer’s request. The pictures below show some examples of different shapes.

As specific press-fit configurations may be patented by other companies, it is necessary to check for patent infringement.

  • Boat-shaped press-fit terminal
    Boat-shaped
  • H-shaped press-fit terminal
    H-shaped
  • M-shaped press-fit terminal
    M-shaped

 

Example : Application

Stackable connection

Solid-shape Press-fit connection using the Columnar Electrode.

Press-fit portion of the terminal side, is the corner post of the rectangle. It is used in press-fitted to the inner diameter of the other party of the Columnar Electrodes. The Columnar Electrode, leave soldered to the substrate. It can be used in the ceramic substrate or other. The Columnar Electrode functions similarly to the through-hole of the printed circuit board.

 

press-fit terminal,columnar electrode

 

FINECS can form press-fit pins into custom shapes as requested.

Press-Fitting Machines and Jigs

With early press-fitting machines for press-fit connectors, the connectors, which had been lightly fitted into the board, were positioned manually one by one and then fully inserted. In general, two types of press-fitting jigs are used: the upper jig and the lower jig. Each upper jig is shaped to be suited to the shape and direction of the press-fit connector to be inserted. The lower jig is made so that the circuit board will not be deformed by the pressure to insert the press-fit connector, and that any terminals of the press-fit connector will not be damaged when the terminals penetrate the through-holes of the circuit board and stick out of the lower surface of the board.

As a matter of fact, there are various shapes of press-fit connectors, and different press-fitting methods require different jigs for which setup changes are required. Therefore, it is necessary to standardize the methods for attaching and fastening jigs to the press-fitting machine.

FINECS’ Solutions

We at FINECS have been involved over many years in the production of heading parts, such as PGA terminal pins, connector terminals, diode terminals, and rivets; the production of various kinds of heading machines and automatic precision electronic components assembly machines; and the automated assembly of precision electronic components. Based on the accumulated experience and knowhow, we provide solutions for press-fit terminals and press-fitting machines.

At FINECS, we work on producing press-fit terminal pins using both metal strips and wire.

For details, please feel free to call your nearest FINECS sales office or contact us via the form on this website.

 

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