Is Mixing and Matching Connectors Ever a Good Idea?

The events of the last few years have taught us that supply chain security is something that we should all consider. The electronics industry has experienced other periods of shortages or extended lead times. Sometimes caused by increased demand from a growth industry or a shortage of raw materials, these events cause component manufacturers to extend their lead times.

Empty warehouses force us to make rash decisions.

Large customers often respond by placing multiple orders to try and secure what stock is available, making the problem worse. In the past, the connector market has usually been immune from this problem, but the supply chain issues of recent years have been felt across all industries. Under these circumstances, many customers have asked themselves whether they could find an alternative source for their components. However, in the case of the connector industry, this question is complicated by a feature of connectors that is at once simple and obvious but is worth stating clearly.

Connectors come in pairs.

There are a few exceptions, with card edge connectors presenting themselves as one of the most popular examples. Despite this, the vast majority are two-part systems - pin and socket, male and female, plug and receptacle.

It is interesting to note that the two halves of a connector pair are often purchased separately. This should be easier to understand when we look at how the electronics industry works. Only the largest companies have the luxury of in-house production lines, and most companies will depend on the services of contract manufacturers to build their products. However, assembling printed circuit boards is a very different task to the creation of cables and harnesses, and contract manufacturers tend to specialise in one or the other.

As a result, we frequently see that the cable-mounted half of a connector pair will be purchased by a cable assembly company in one country, while the board-mounting mating halves could be sourced halfway around the world in another. With uncertainty in the global supply chain, it is entirely possible that one of these items could be hard to locate. Under these circumstances, purchasers will be under pressure to locate an alternative.

For some components, this presents little challenge. For example, a capacitor is a discreet component. If a customer can locate an alternative in the same package size as the original, it should be a simple task to change production to accept the new article. The same is not true of connectors, because one half of the connector pair needs to be entirely compatible with the other. Mixing and matching connectors from two different manufacturers is called cross-mating.

Looking for an alternative? Take your pick...

Trying to find an alternative mating half for a connector is not an easy task, and involves diving into a sea of data sheets, catalogues and technical drawings. Manufacturers use lots of phrases to describe their connectors – compatible, conforms, equivalent. However, the engineer must be very careful when making such a selection. The physical dimensions of a connector – especially the geometry of the mating face that plugs into its opposite half – represent only part of the equation. Engineers also need to consider the electrical and environmental performance of the whole system.

There are some connectors that are intended to be cross-mated. I have written previously about military specifications. The goal of publishing a military standard is to create a connector that can be cross-mated with confidence. It does not matter which manufacturer made the connector – the user mates a plug to an equivalent socket with absolute confidence. The standards dictate every aspect of the connector design, from dimensions to materials, therefore ensuring that both halves will deliver the same performance. The same is not necessarily true for other similar connector types. The D-Subminiature connector – known to many as the simple D-sub – gives us the clearest example.

The D-sub has been on the market for well over 60 years and has provided reliable service across almost every sector of the electronics industry. The familiar trapezoidal shape makes it easy to assume that every D-sub is compatible with every other. However, this is where we need to dive deeper into the word “compatible”.

It is true that the physical dimensions of the D-sub should mean that they can be cross-mated, but physical compatibility is only part of the picture. Let us use two examples from the RS catalogue, a commercial D-Sub from RS Pro (544-3806) and an industrial-grade example from Molex FCT (213-4917) . They are physically equivalent – they are both fixed, solder bucket-type connectors with 25 contacts. However, the RS Pro part has a current rating of 5 Amps per pin and a maximum operating temperature of 105°C, whereas the Molex item delivers 7.5 Amps at a maximum temperature of 125°C.

Does that make the RS Pro version bad? Of course not – there are plenty of applications for which the performance of a commercial connector is more than enough. It is crazy to pay for connector performance if it is not needed. However, if your design calls for high currents at high ambient temperatures then the Molex option would be the right solution. In this circumstance, these two connectors are not compatible. This is not even the most extreme comparison. There are D-subs out there that cost cents and there are others, designed for aviation or spaceflight, that might cost hundreds of dollars. The key to choosing alternatives is to know when each is required.

Finally, we must look at those connectors that are not governed by an international standard. There is a huge selection of relatively cheap wire-to-wire or wire-to-board connectors from dozens of manufacturers. Many of these plastic-shelled connectors look very similar and are available in a range of common pitch sizes (pitch is the distance between the centres of adjacent contacts). They may appear to be compatible, but insulator materials and their accompanying operating temperature ratings, contact materials and plating, locking systems and even wire housings are all potential “hidden” differences that are ready to catch the unwary designer.

You might even be lucky and get away with it, but the minute that something goes wrong the question becomes one of liability. If you are using two connectors from competing manufacturers and the connection fails, to whom should you turn for a fix? Although you may have assembled both connectors perfectly in accordance with the published instructions, the manufacturers may be less than supportive if they realise that you are cross-mating with another manufacturer’s product.

Mixing and matching may seem like a solution to your supply problems, but it might just create more problems than it solves.