In this series, we are looking at connector design. We will investigate how the design of the contacts within a connector affects not only its electrical performance but also its physical practicality. As we saw in the previous article, many connectors use a conventional pin-and-socket arrangement, but there are alternatives.
Last time we looked at power contacts, and how blade contacts offer advantages over conventional designs when power needs to be transmitted but space is tight. In this article, we will look at the other end of the spectrum. Electronic components are getting smaller every year, and while power connectors depend on size to do their job, they are too large for the latest handheld or wearable devices.
Figure: Modern miniaturised electronics require miniature connectors
There are two key features of any connector when the time comes to miniaturise any design. The first is the shape and size of the contact itself, and the other is the pitch. Pitch is defined as the distance between the centreline of one contact to the centreline of its nearest neighbour. When creating smaller connectors for microelectronics, pitch is critical.
When printed circuit boards (PCB) first became common in the 1970s, the pitch of connectors was a generous 2.54mm (or one-tenth of an inch). The majority of the components on the PCBs of the time used the same pitch, and so the connector was not especially troublesome for designers.
As we know, however, designs have become smaller. Microprocessors are far more capable whilst still becoming far smaller, and the same trend can be found in many other components. Assisted by the development of surface mount technology and automated assembly, smaller components are now both practical and desirable.
The result is that the connector is now one of the largest components on any PCB. Partially this is due to practicality – connectors are designed to be connected, and this is often a manual process during final assembly. Connectors therefore still need to be both large enough for workers to handle, and robust enough to withstand everyday use.
This is where another alternative to the pin-and-socket connector becomes important. The beam contact offers a far slimmer alternative to conventional designs. To illustrate the differences, here are two videos from connector manufacturer Samtec. Both are standard designs fitted to different connectors within the Samtec product range. These animations show very clearly how different contacts work.
The first video shows a conventional machined contact pair, very similar to those found in countless connector types across the industry. These are highly reliable and capable of impressive current ratings. However, please note the overall size of the socket part (the lower half) compared to the diameter of the pin. You will see that the overall connector is quite bulky.
Now, if we contrast the machined contact above with the beam contact shown in the video below, it should be clear that these offer a far slimmer design.
This is a result of the manufacturing process. These beam contacts are stamped from a flat sheet of metal and lack the 3-dimensional shape of a more conventional design. This stamping process is far cheaper than the machining process of the contact in the first video. It is also simpler than the stamping and forming process that is required by other contact types.
Essentially a 2-dimensional design, the beam contact is ideal for connectors that require a smaller pitch. The slim, flat format allows far more contacts to be packed into a given space within the connector housing, with a reduced distance between them.
It is contacts like these that enable the ultra-fine pitch connectors that we are seeing today. The Samtec Razor Beam™ (507-7263) is a 0.635mm pitch, 2-row connector that can deliver data speeds of up to 25 Gbps (Gigibits per second). Here is a closeup of how these connectors use the Razor Beam contact.
Samtec Razor Beam™
The Razor Beam is a great example of another potential advantage of beam contacts. This is a self-mating or hermaphroditic connector. The two halves of the mating pair are identical and interchangeable - there is no "plug and socket". Not only does this simplify the supply chain, but it also provides a huge amount of flexibility for any modular design. For any equipment where different PCBs need to be connected in different arrangements, a single interchangeable connector such as the Razor Beam makes this far easier. It is a feature that is simply not possible with conventional contact designs.
For even finer pitch - the kind of connector that the latest smart watches require - we can look at the Quad-Row connector from Molex. The Quad-Row is a 4-row connector in which the alternating rows are staggered. The effective pitch of this connector is a staggering 0.175mm, equivalent to the thickness of just a few sheets of paper. This miniaturised design is only possible with beam contacts.
The Rare and Unusual
Contact design therefore has an enormous role to play in creating the connectors that modern electronic systems need. Join us again next time for the final instalment of this series, in which we will look at unusual connector designs, including one that boasts no conventional contacts at all...
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