Press-fit connectors the alternative to solder?
Original article date: March 2000
Press fit terminations have several benefits over soldered joints, argues STEPHEN SMITH of Cambridge Connectors. And health and safety considerations are high on the list.
Soldering invariably creates fumes associated with the rosin (colophony) based fluxes used in the process. When heated to temperatures in excess of 200degC, rosin-based solder fluxes produce fumes containing a mixture of acid particulates and noxious gases – the higher the temperature, the greater the level of fumes given off. The fumes area amongst other things, believed to be a major contributor to asthma attacks.
Modern manufacturing methods, such as wave and reflow soldering, combined with safe working practices, ensure that the risk of operators being exposed to harmful fumes is minimised. However, there are occasions when heavy components such as connectors make automated soldering processes inappropriate. Manual soldering in such circumstances requires strict controls to be implemented with regard to the positioning of the work area, ventilation, exposure times and operator training.
The disciplines required to implement EN ISO 14001 have sharply focused minds on the effects of industrial processes on the environment. Each company needs to identify these effects through a review of its activities and look at how they impinge on the environment.
Many traditional heavy industrial processes have been recognised as being highly hazardous to the environment and the appropriate safeguards have been taken. It comes as a surprise to many, when developing an Environmental Policy for ISO 14001, that the soldering process can also create hazardous substances, and that the disposal of these requires very careful monitoring and control. In addition to solder and flex residues, they include solvents which are used in the preparation and cleaning of PCBs prior to and after the soldering operation.
At the present time, there is no legislation that governs leaded solder, but it is likely that within the next few years, European Directives concerning a wide range of hazardous materials will effectively prevent the use of lead in solder. The changeover from leaded to unleaded solder will involve considerable changes in production methods, with higher temperatures and narrower processing windows.
With alternative press fit techniques, no heat is required, no flux is necessary and no harsh chemical solvents are required. Joint integrity is independent of operator skills.
Improved productivity
The other major reason for adopting press fits is productivity – although individual press fit connectors can even be installed more quickly than solder versions, it is when multiple insertions are made that huge cost savings can be achieved. Typically 100 press fit BNC connectors can be installed in the same time as it takes to install just one solder type!
Until now, the main disadvantages of press fit connectors have been set-up costs and board layout changes. Also, there has been a perception that high retention forces have been difficult to achieve. But these problems can be resolved, as is illustrated by the success of a development programme that was recently undertaken by Cambridge Connectors for Pro-bel and Harting. Pro-bel makes routing, signal processing and automation equipment for the broadcasting industry. Considering the use of press fit BNC connectors on equipment rear panels (up to 128 connectors per panel) meant that the press fit BNC had to be interchangeable with solder types and have the same footprint as the equivalent solder version.
The contact shape combines traditional press fit technology (square pin in a round hole) with compliant fit theory (easily deformed, shaped contacts) to give a contact which has high retention force but with low distortion of the PCB hole. This allows the connector to be used over a range of hole sizes to suit a variety of withdrawal forces.
In the case of BNC connectors, high retention forces are required, owing to the heavy weight of the coaxial cable to which they are connected. Given the appropriate PCB hole size, retention forces of typically greater than 500N are achieved with Cambridge Connectors Press Fit BNC. The contact composition has been carefully selected to ensure that sufficient distortion takes place to give a gas-tight connection whilst maintaining lower insertion forces.
- Cambridge Connectors
March 2000