Little Things That Matter In The World Of Designing Tiny Connectors

By Vinay Prabhakar Minj

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There are several important aspects concerning connectors: their physical design, communication protocols and standards, and their connectivity concerning PCB versus the external world, both from the consumer and non-consumer perspectives. Wireless connectivity is also an emerging trend that is gradually revolutionising the way we communicate. Here is a discussion between some experts on the subject.

Connectors have come a long way since they were conceptualised and invented. With changing times, they have undergone many different modifications. And with the ongoing technological developments, they will certainly go through more.

Compared to several years ago, connectors nowadays have become high-end and miniaturised. Also, earlier we used to rely on European connector manufacturers for our needs, but with the entry of many Chinese and Indian connector manufacturers, the same quality of products is now available at a much lower cost.

Due to globalisation and increasing awareness concerning certification, certain standards have been now introduced for India (as compared to European ones like CE mark, UL certification, etc, which we used to follow earlier). The flame-retardability characteristics of the connectors are also improving.

“Connectors are the heart of everything. Even if you design electronics with the best microcontroller, best semiconductor chips and best software/firmware, the failure of the connector means the failure of the product. If a connector fails, then the design fails.

Therefore, connector selection is very vital,” says Mahendra Karandikar, GM-Developments & Projects, JISL.

Adding to that, Abhinav Behl, R&D engineer at Logic Fruit Technologies says, “Connectors help establish contact with an electronic device. While choosing a connector type, the first thing to consider should be its durability. Any misalignment should not cause failure in the connector or the PCB.”

Considerations for selecting a connector

First go through the datasheet and specification of a particular connector to have clarity regarding details such as its current carrying capacity, voltage rating, and type of insulation material used. Then check the other aspects. For instance, if it is a pluggable connector, check how hard it is to plug it in and plug it out, whether the locking arrangement is proper or not, and whether the polarisation is clearly mentioned or not.

When pulling out the connector, especially a PCB-to-wire connector, the physical design should also be taken into consideration. If there are any sharp edges in the connector, it can hurt fingers while pulling-out or pushing-in.

Before finalising a connector, Mahendra Karandikar prefers to get some samples and cut them open to see their internal design. Most connectors are made of brass, generally, with tinplating, chrome-plating, or zinc-plating. The other factors he checks for include surface area for contact, design of the spring action inside a connector (Is it robust enough to last long after repeated connections?), and current capacity ratings.

Consumer-domain perspective

Initially, there used to be many different types of USBs such as micro-USB Type-B-port, and Type-C port. There were separate connectors for USB 3.0 and USB 2.0. The socket for Type-A was different. It was a complicated scenario.

But now, all of that has collapsed into Type-C, which is ‘idiot-proof.’ It has a simple interface, which can be plugged in any direction. It is also compatible with USB 2.0 and USB 3.0, while supporting both power delivery and data connectivity.

“Type-C has completely revolutionised the way we connect. You do not need a separate power port and data port. You can have a single port connected with both of those. Soon HDMI and Ethernet cable will go away and will be replaced with Type-C,” says Rajanikant Mohan, director-product management, business development and marketing, Mindtree.
Will Type-C replace HDMI and Ethernet cables?

“Absolutely,” agrees Abhishek Satish, co-founder and CTO, Vicara. Many smartphones earlier came with micro-USB that made these cables popular among consumers. But what if today your microcontroller did not support micro-USB? Then you will need to manage your firmware updates and wired-in applications in a completely different way, making things really complicated.

However, Type-C has changed everything. “Nowadays, everything is supported by Type-C. This was difficult to achieve back then when all electronic devices such as laptops used to come with their own separate adaptors. Now it is a lot easier for the consumer to have a single device charger/cable that connects with all. So, I definitely see Type-C being the future, especially since it supports tremendous amounts of bandwidths,” he says.

Stating his experience as a MacBook user that has a Type-C port, he finds it extremely convenient to charge his laptop with a power bank (which also has a Type-C port) while on the go. Consumers find it much easier to have a single Type-C cable that connects with everything.

This is an interesting point, given that the traditional USB 3.0 port or USB 2.0 port earlier provided 4.5W of power (9mA of current at 5V), which was not enough. With Type-C, one can go up to 5A over 20V, which allows you to charge your laptop, run a monitor, and do much more – using just a single port.

Designing a PCB that can support power coming in from Type-C is not a trivial task. A controller tells the power circuitry about the power rating of the device that the cable is connected to regarding how much current is going to get driven out of the power lines (connected to the USB port). From that perspective, several reference designs are being created by semicon companies, which need to be studied if you are trying to get your device charged and powered from a USB Type-C port.

Non-consumer domain

In the consumer domain, the way power is distributed is getting standardised to USB Type-C. However, the same is not happening from an industrial point of view as there is no specific standard for connectivity. “In the case of consumer electronics, you have to collect power and data together through USB connection; the same cable is used for charging a phone and data extraction. As far as industrial communication is concerned, there are a variety of communication standards,” says Mahendra Karandikar.

PLC manufacturers have their own communication standards. Siemens is coming up with PROFIBUS over RS 485, PROFIBUS over Ethernet, etc. CAN bus protocol, MOD bus protocol, and RS 485 protocol are also used in industry. And every standard has its own connector design. For Ethernet, there is RJ45 while for PROFIBUS, generally, it is a 9-pin D-Sub connector. It is very rare in industry to see power and signal being delivered through the same connector cable.

“Standardisation in the consumer and IT sector is a different ball game altogether. Industrial designs are slightly flexible and there is a lot of freedom to choose the connectors. An organisation standardises as per their variety of products. If I buy a connector, then it should be able to go into ten different products. That is the standardisation done in the industry. In industry, use cases for mostly PCB-to-wire connectors can be found. Regarding other communications, especially CAN bus and RS 485, there is no specific standard for a connector. All can go in a screw terminal or 9-pin D-Sub terminal,” Mahendra Karandikar says.

From the perspective of PCB connectivity, there is no specific standardisation in the industry. BLC connectors, VGA connectors, and many others for PCB-to-wire connections are used.

The Arduino interface, which is popular for allowing modular design, can just be used for prototyping, and cannot be realistically extended to production requirements. “Arduino is kind of a processor not used in the industry. We use other versions of processors in the industry, which are embedded on the PCB. We use inter-PCB connectors for connection. We communicate using processors through SPI, UART, and I2C protocols,” says Abhinav Behl.
For high-speed data transfer at consumer end, the most popular is the USB. For industrial purposes, PCI and other high-speed protocols are used as well.

Limitations of USB

One of the limitations of USB is that it cannot be extended to longer lengths (cannot go beyond one or two metres). If an extension cable is used, then sometimes there could be a data loss. So, USB is typically fit for consumers. In industry, USB is used for short-term usage, like firmware upgrades, but certainly not for real-time data transfer.

Agreeing to this, Rajanikant Mohan says that “very often, the quality of the signal obtained through USB significantly deteriorates when the cable length increases. A lot of people don’t realise that and it could impact your design. In the PCB domain, you have the advantage of not using a cable; you can route it on the PCB. But externally, if you are using a cable, then it becomes complicated.”

Another thing noticed with Type-C is that they have become ‘smart cables.’ When you are connecting different devices, which can handle different power delivery, there is the concept of electronically marked cables which have a Type-C controller embedded inside them that helps to negotiate this power. This smart cable is popular in high-end devices.

Some design issues

“My experience with mobile charger cables is that a lot of mobile phone users put a cover on their mobile. When you use a mobile cover, it adds 1-2mm extra length for the connector. Sometimes, if you plug in the connector, the connector doesn’t get fully inserted,” says Mahendra Karandikar. “Since mobile covers have been there in the market for several years, it is still unknown why USB OTG cable manufacturers aren’t making longer versions of the connector. So, even if I have 2-3mm thick mobile cover, it should get inserted completely. Many times, we have to remove the cover of the mobile phone and plug in the charger to it to ensure that it is inserted completely.”

“We faced a lot of trouble because the connector for our miniature wearable device took up a big chunk of its area (about 5mm×4mm), due to which there was less space on the PCB for the charging circuitry, MCU, and antenna matching networks. We tried a lot of explorations by having magnetically attached cables and all sorts of paraphernalia. But we realised that there was no standard out there for any of this. In fact, to find a manufacturer who will make these miniature pluggable cables was almost impossible,” says Abhishek Satish.

He continues, “(In such a scenario) one is left with no option but to create one’s own connectors and cables. So, to reduce the total amount of space that had been taken, we opted for mid-mount USB. This was surface mount. So, it basically sat in between the PCB rather than on top or below it. That kind of saved us some space. But it came with its own set of challenges because now when you don’t have a through-hole element for a USB connector, the pad starts to fatigue (from all the constant plugging in and out). When you pull it out, it rips the USB connector from the pad, and you become stuck (as there is now no other way for charging). Probably we could have avoided it by increasing the pad thickness that the PCB connectors sat on. But because the connector standard for the USB mini cable was little, there was no scope to expand the pads.

“To resolve the issue, the connector was mechanically supported from behind the PCB, so that if it was pushed in, it didn’t get pushed back and damage the pads. In the front, the enclosure was made very tight and there was no space for the connector to get accidentally pulled out.”

According to Abhishek, the physical design of the outer packaging also has an impact. “Most people don’t realise that the manufacturers give about 1-2mm gap to account for enclosure thickness. When the consumers used to plug in the cable, the connector it used to stick out; it felt like the connector had not gone in completely. So, they pushed it further because it looked to them it hadn’t gone in completely. We (too) didn’t account for that.

And so, we had to end up increasing the enclosure thickness unnecessarily to make sure nobody forcibly pushed the connector and broke it in the process,” he says.

“In connectors, we have faced issues regarding PCB-to-wire connectors with a pitch distance of 2.5mm,” says Mahendra Karandikar. “When you want to pull out the connector while testing the PCB, or for replacement during design time, there is no other option but to hold the wires connected to it and pull it out. After inserting a few times, the wires get broken internally. In such connectors, there is a plug part which is soldered onto the PCB and the receptacle part which is inside the connector. So, when we insert the receptacle into the plug, a force is required to plug-in and plug-out the connector. There are two areas where force is required: the contact itself because the receptacle will have some surface area connection which gets connected to the other part. And there is the spring action for proper electrical contact. So that offers you some kind of resistance and requires force to pull out.”

He adds, “Another thing is that the plastic part of the connector has a locking mechanism, because once you insert a connector, it shouldn’t come out accidentally or due to vibration. So, a lot of force is required on account of the locking mechanism from the plastic itself.

Electrical contacts hardly offer any resistance. So, if you are into design or testing firmware development, and need to do lot of debugging, and need to connect-disconnect a connector too often, then search for the interlocking parts on the connector, take a file and simply chop off those interlocking areas so that your connector moves in and out smoothly. That’s what you can do while designing.”

So, if the connector manufacturers (of PCB-to-wire or pluggable-to-terminals) can create a lock-release mechanism, where if you press an area then the mechanical interlocking becomes disabled or ineffective, the force required to plug out the connector will get reduced. Take for example the Ethernet cable, which has one such mechanism. Its lock pin has been built in such a way that the connector comes out smoothly, completely breaking the connection.

A few more design issues

“Another problem is that of the 9-pin D-Sub connector or the 5-pin D-Sub connector being replaced by HDMI cables,” says Mahendra Karandikar. “These cables have two screws on both sides. You put the pin and tighten the screws. What happens is that when the counter part of the screw, which is on the PCB, is unscrewed, then the counterpart also starts rotating. This leads to the counterpart, which is a nut, also coming out along with the screw. On one side the screw comes out clearly and on the other side the screw comes out with the nut. To avoid that, we apply some kind of a fastener adhesive and insert that particular nut inside the 9-pin.”

Dust problems are also a cause of concern. If a PCB is not used for a long time, then the connectors stop working properly as some connectors are sensitive to dust. “I faced an issue with the RJ 45 connector. Because it was of poor quality, due to dust accumulation it stopped responding properly and we had to change the connector/wire on the whole,” says Abhinav Behl.

An attractive option: Wireless connectivity

A lot of industrial OEMs incur huge cost in wiring. When you are setting up a factory, one of the major cost drivers is the wiring. Being able to cut that down is a huge benefit to many companies. According to Rajanikant Mohan, wireless connectivity can reduce the clutter of cables considerably.

However, it is important to also see the dangers and inconveniences that come with wireless connectivity. For instance, there can be a problem of interference, that is several wireless devices talking to each other, resulting in a clash. Also, clearing the test of RF susceptibility and immunity can cause issues.

But there is a tradeoff since your wiring is reduced with wireless connectivity. The EFTA requirements and the surge which comes through the cable is not required to be taken care of, because you do not have any cable coming in.

“If the industry goes wireless, then there are too many standards and methods of communication such as TCP-IP over Wi-Fi, Bluetooth, LoRa, Zigbee, and many more. And then there is the problem of the wireless signal passing through when direct line of sight is not available while devices are talking to one another. Then you have to install repeaters. But the moment you install repeaters, the signal is repeated and then you have the issue of bandwidth, because the amount of data transferred through wired cable is immense. If you want to take it on wireless, where there will be master-slave kind of communication or multi-node kind of communication, then it is going to be challenging,” says Mahendra Karandikar.

“What industry requires is the presence of very few kinds of communication standards and protocols. These should be laid down as per the precise requirements of the industry without any compromise. A lot of thinking needs to be done. If there are few standards, then the industry will accept it (wireless) quickly,” he says.

The good news is that some problems concerning wireless have been addressed. For instance, Bluetooth has a built-in dynamic frequency hopping as part of the protocol, although it is 2.4GHz. So, where you have Wi-Fi co-existing with Bluetooth, the in-built frequency hopping helps in improving the reliability. From an encryption point of view, the security aspect is pretty much covered. There is 128-bit AES encryption which gets built-in to the Bluetooth standard nowadays.

“Wi-Fi and Bluetooth combination is really good. You have Bluetooth for some lower speed and low-energy transmissions and Wi-Fi for higher-bandwidth stuff. I think we need to start seeing more packages with Wi-Fi and Bluetooth integrated. If we come up with an integrated solution with both Bluetooth and Wi-Fi, then that will be a flexible, all-rounded solution,” says Abhishek Satish.

Abhinav Behl concludes with the thought that, in the near future, there needs to be an improvement to the delay experienced in Bluetooth connectivity. Thanks to the powerful capabilities that the upcoming chipsets offer, a solution can surely be achieved soon.


This article is based on a panel discussion on ‘Connectors: What’s New For Design Engineers?’ during the November edition of India Technology Week.

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