Pushing the benefits of press-fit

ES Oct15 Pg30 PCB Toby 3Technical director of Toby Electronics, Jim Portlock, examines the often-overlooked advantages of press-fit technology.

Based on the principle of pushing contact terminals into PCB plated holes rather than soldering them, press-fit technology continues to win new converts amongst original equipment manufacturers (OEMs) and contract electronics manufacturers (CEMs). It is ideally suited to demanding connector applications such as those found in the automotive sector, but in recent years its popularity has extended in an electronics industry striving for ever-greater reliability, cost-efficiency and flexibility.

This is particularly true of the UK, where the focus is typically on high value production to exacting standards of quality and performance, often for applications characterised by tough operating conditions. But there are still many more companies that could and should consider adoption.

Eliminate rework

As the name suggests, the press-fit process is extremely straightforward. After printed circuit board (PCB) modules are assembled with surface mount components and reflow soldering is complete, the connector, pins, sockets and similar parts are pressed into plated holes. As a result, press-fit can reduce both the risk of reliability issues and the need for costly and time-consuming rework on the production line. In simple terms, this is because no thermal load is placed on the header and side-effects associated with solder vapour and welding flux residues are eliminated.

Furthermore, because the connector is fixed, both directly and mechanically, by the press-fit pins, there is no need for additional screws. Designers will also appreciate improved impedance characteristics and the potential to use long, gold-pated connector pins as a rear mating connection. As a chemical-free process, press-fit also boasts strong environmental credentials.

Simple assembly 

The assembly tooling required is relatively simple, typically comprising a manual press, with or without pneumatic assistance, and PCB support. It is therefore economic and easy to perform in-house where required. Press-fit is also readily repairable. With the potential to remove and reinsert components up to three times, it offers not just flexibility but also ease of recycling.

Inevitably however there are challenges to consider. Uppermost among these are the high insertion and extraction forces required to press the contacts into PCB holes and the need to maximise the contact area while avoiding damage to the backplane and PCB. With a press-fit connection, the cross section of the pin has a larger diameter than the plated through hole in the PCB. When the pin is pressed in, the excess material must be taken up by the deformation of the pin, or the hole.

Although press-fit is regarded as a generic term, different suppliers take different approaches to the design and manufacture of press-fit components.

For example, German-based EPT, which offers press-fit options for a range of standard and custom-design connectors, uses a bespoke, H-profile terminal pin design. This ‘press-fit zone’ is designed to facilitate consistent absorption of pin deformation, optimising the contact area while minimising the insertion force and risk of damage.

Boost reliability

In general, it is fair to say that OEMs and CEMs tend to underestimate the reliability issues and rework costs inherent in the soldering process. As a result, they also underestimate the potential value of a switch to press-fit. While there is a natural tendency to stick with the familiar when it comes to production, it is certainly worth weighing up the benefits of press-fit, which can include more robust and reliable system performance and a faster, more efficient manufacturing process.