FEATURE SWITCHES & RELAYS
NEW APPROACHES TO CONNECTION SYSTEMS
Rob Dixon, Senior Product Manager – Relays & Connectors at Panasonic Electric Worksinvestigates the latest switch technology
process are no longer relevant. Important considerations for a good press-fit
component are correct material choice, shape and tolerance concerns. The pre-centreing of the component is important in order that a reproducible, high-quality process can be guaranteed. The joining forces when analysed macroscopically highlight that only a microscopically small contact area actually occurs, this in essence becomes a cold-formed and cold-welded contact junction. A further advantage of the press-fit terminal is that the joint effectively becomes one with a lower possibility of pockets that could ultimately lead to corrosion “hot spots”. The press-fit connection effectively could be considered as a non gas permeable connection. Even with all these positive features the
T
he right connection interface is what matters. When the limits of what is technically possible are exhausted, the urge is for developers to constantly push for newer solutions. Components such as micro switches are continuously being introduced with new constructions or adapted product revisions to current conditions. Parameters such as miniaturisation, cost reduction and production process optimisation are key points in industrial production and contribute significantly to the creation of production net value. The ASQM switch developed by Panasonic has been a prime example on implementation of these topics. The sub miniature ASQM is the newest
member in the Family of sliding contact switches from the company. As a further development to the proven ASQ Switch, the potential is there to reduce the part volume by 45% by limiting switching function to either SPST-NC or SPST-NO contact configuration. The ASQM therefore follows the requirements of the automotive industry who are constantly looking for weight loss and optimising the building space.
MINIATURISATION It can be expected that an IEC529 (IP67) compliant switch fulfilled all the features of this construction resulting in both a silent and virtually bounce-free operation. A long over travel distance (at least 2.2mm) and lateral actuation to 45 degrees allow great compliance in the tolerance chain and the
10 MAY 2016 | ELECTRONICS
interplay between other components in the application installation. This helps prevent accumulating tolerances becoming an issue during assembly of the unit. Despite the small size, the ASQM switch can be fitted with a variety of lever choices if required without the need for additional plastic components, keeping both cost and size at a minimum. In addition to the SPST function (NO or NC) of the ASQM and its associated componentry seal integrity is maintained by joining the base plate to the case by use of an adhesive free process. Instead a laser welding process was introduced, thereby the process times are reduced and this maximises the use of materials efficiently. The wiper system was designed so that in conjunction with the Cup Grease used (silicone-free ) the self-cleaning features are efficient enough that an expensive gold plating process for the contacts could be dispensed with. These Further developments lead to significant cost advantages.
PROCESS OPTIMISATION PRESS-FIT TECHNOLOGY The micro switch has always been a classic link between mechanics and electronics in the automotive sector, a departure from the solder joints to press-fit connection technology was the logical next step. There are good reasons that with this technique process costs can be optimised without a fear of quality loss when connections have to be made. Mechanical changes to the component due to thermal influences, for example during the soldering
Figure 1:
ASQM switches from Panasonic
frictional connection still needs to meet all requirements for shock and vibration resistance, temperature range and permanently low contact resistance. Low terminal resistance is ensured by the specific shape of the terminal pin, the connections legs are shaped as a fork contact effectively acting as a bifurcated connection. For ease on insertion the component can be pre centred by locating it on the switch retaining bolt, after this is pressed into position by potting the Contact points, deterioration is excluded due to the prevention of environmental influencing factors. Comprehensive Evaluation test must be conducted to the aging and reliability of such compounds. These include Shock and vibration tests, different Temperature and humidity cycles, Influence of harmful gases, measurement of pulling forces, creation of cross sections, etc.
DESIGNING THE WAY FORWARD The press-fit connections are a useful complement to the well-known and established soldering and cable connections for the micro switch. However, close cooperation between switch manufacturers and OEM users is needed to ensure that the suitable material combinations and connection technology are defined for the ideal application method to suit the application. When using the press-fit connection system a real synergy in terms of reliability and costs of installation during production is realised.
Panasonic Electric Works
www.panasonic-electric-works.co.uk E:
Info.pewuk@
eu.panasonic.com
/ ELECTRONICS
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