Information Technology

Contact Geometry And It’s Bearing On Reliability For Electrical Connections

<p style="text-align: justify;">The innocuous and sometimes commoditized and casually perceived connector systems play a critical role in performance and reliability in any system-be it a pervasive cellular phone, laptops/desktops, HD LED TVs, POTS, Cellular Network Equipements, long-distance telecom/Data Networks Equipment, industrial electronics products, transportation electronics and very critical military electronics, naval electronics, avionics or space electronics. The application of electronics is most pervasive today in all fields of life, and a critical but often neglected or taken casually are Signal Transmission Systems. &nbsp;</p><p style="text-align: justify;">Connector and cabling systems form the most fundamental signal transmission system, and even with the proliferation of wireless RF technologies over the past 20 years, it remains overbearing for signal transmission wirelessly. &nbsp;</p><p style="text-align: justify;">Please recall your own experience of a simple kitchen gadget as a mixer cum grinder not working or stopping suddenly, and you had to push the plug harder onto your wall mount electrical socket to get it working again-this happens all the time, and I am sure sometime or the other you would have experienced it. Likewise, for a TV appliance, a desktop computer at your office/home, or a cell phone not charging, etc. The cause is a loose connection. &nbsp;</p><p style="text-align: justify;">The choice and role of materials on connectivity performance and reliability is another diverse area, and volumes can be written on the same. However, I am restricting this brief article to the scope of contact geometry on connectivity solutions and its bearing on performance and reliability. &nbsp;</p><p style="text-align: justify;">Very broadly, contacts can be single beam/dual beam or line contacts where a continuous set of asperities (high spots or irregularities) make an almost continuous line contact offering maximum redundancy. The representative picture below depicts a typical dual beam early entry contact. &nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;"><img style="display: block; margin-left: auto; margin-right: auto;" src="" width="268" height="247" /></p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">You can see that when the male pin connects with the female pin, it establishes a contact between these two insulated connectors at two or more points which is where the dual beam design comes in. The more contacts are made, the more redundancy contributes to reliability/lesser failure and improved integrity of the solution. Do note that the contact is an early entry contact- an early engagement action the moment the male and female connectors are joined. &nbsp;</p><p style="text-align: justify;">This early entry ensures a good wiping action on the male pin resulting in oxide film breakage and an 'intimate gas-tight connection,' which results in quantum improvement of connection integrity besides removal of oxides-a much desirable action and an impediment to reliable connections. &nbsp;</p><p style="text-align: justify;">Now, visualize a single beam connecting with the male pin after traversing some distance as per the picture below. Such a design is a Single Beam Late Entry Contact where contact is only made at one or marginally more points, providing lesser redundancy, and obviously, the wipe action and oxide film breakage for the reliable gas-tight connection needs to be included.&nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;"><img style="display: block; margin-left: auto; margin-right: auto;" src="" width="339" height="226" /></p><p style="text-align: justify;"><img style="display: block; margin-left: auto; margin-right: auto;" src="" width="216" height="23" /></p><p style="text-align: justify;">Since the metal-to-metal connection is made only after the male pin traverses a certain distance(mm) and not immediately when the male and female connectors are joined, such a design is called a late entry contact. &nbsp;</p><p style="text-align: justify;">Besides, even in connector designs when dual beam early entry contacts are incorporated, normal forces acting perpendicularly down on the contact area can be a major factor in contributing to the life of the connector and rapid deterioration in materials characteristics or increased wear and tear with repeated usage particularly when 'High Pin Counts' or larger number of contact pins are involved in the Late Entry Single Beam Contact connector design. Illustrated below is an excellent CTW(Crimp to Wire) contact that has proven most successful for decades at a premium price. &nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;"><img style="display: block; margin-left: auto; margin-right: auto;" src="" width="309" height="210" /></p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">It's possible that except for very discerning engineering eyes, a key contact geometry attribute like Hertzian Stress (two curved surfaces come in contact and generate stress) generated by Hertzian Dots acting in the upper direction opposing the downwards normal force would have been overlooked by many people and users.&nbsp;</p><p style="text-align: justify;">Economics and pricing also play a significant role in business and products, and more so with a shorter shelf life of products in increasingly changing dynamic markets, as surely perfect contact geometries for higher connections reliability also come with an added price. &nbsp;</p><p style="text-align: justify;">India, with a renewed focus on leapfrogging towards a global manufacturing centre, and the world becoming more of a globally networked marketplace but often the costs of failures/replacement or troubleshooting causative agents for failure far outweigh the incremental price increases. Similar concepts apply to the highest technology space products, and emerging new standards, and I cannot imagine Space/Satellite/Rocket Engineers and designers ignoring similar attributes where failure is not an option and there are indeterminate costs for the same and more relevant for example in space where India wants the Global launching center for foreign satellites at the optimum time and costs.</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;"><span style="font-size: 10pt;"><em>This article was contributed by our expert <a href="" target="_blank" rel="noopener">Subho Bhattacharya</a>&nbsp;</em></span></p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">&nbsp;</p><p style="text-align: justify;">&nbsp;</p>
KR Expert - Subho Bhattacharya

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