A guide to PCB standoffs

What is a standoff?

A PCB standoff separates a circuit board from other components. It’s used in electronic applications to create spacing between PCBs or an individual PCB and the chassis. Its other purpose is to prevent components from touching each other and the conductive surface to avoid electrical shorts, making the device safe to use. Raising the PCB with standoffs also creates airflow underneath to help dissipate heat.

Ideal when mechanical strength is needed, a standoff is also known as a PCB standoff screw, as it’s a type of fastener. It secures the board to the device to prevent movement when the device is being used. The job it does is similar to that of a PCB spacer, but they’re not the same. Circuit-board standoffs are threaded, while spacers are not. Standoffs are also available in female-female, male-male or male-female configurations. You’ll use a nut for male ends to secure the standoff.

As well as understanding what a PCB standoff does, we'll also cover:

• How do electrical standoffs work?
• Types of PCB mounting standoffs
• What are motherboard standoffs made of?
• PCB standoff sizes

>How do electrical standoffs work?

Installation is straightforward: they’re inserted in pre-drilled holes on the PCB. A screw is then fastened over the standoff’s thread to secure it in place. If using a female standoff, it can be screwed into a male standoff with the same-size thread. Standoffs can be unscrewed if needed, but you can also use adhesive circuit board standoffs for quick installation. These, too, can be released by pinching the standoff.

Types of PCB mounting standoffs

Standoffs are available in round or hexagonal shapes. Choose hexagonal if you want more torque when affixing the standoff, but otherwise, round will serve you well. Hexagonal can also be slightly easier to screw down than round. Styles vary, but the most common printed circuit board standoffs include the following:

What are motherboard standoffs made of?

First, you’ll need to think about the materials that make your PCB, which contain the transmission lines and components that enable radio frequency/microwave circuits.

As to your computer standoffs, it really comes down to metal standoffs vs. plastic standoffs, which in turn should be determined by what you’re trying to achieve.

Use a metal standoff spacer if your goal is to maintain electrical conductivity in order to preserve a circuit. An example is if you want to maintain electrical contact between the PCB and the chassis, or the PCB’s enclosure. In this instance, aluminum is a good choice, as long as it’s not unfinished or anodized. This would cause the formation of layers of oxide, which in turn would disrupt the connection.

Brass PCB standoffs can do the job quite well. Brass is non-magnetic, conductive and resists corrosion. It can also be soldered for grounding. Zinc-plated stainless steel gives optimum corrosion resistance and strength, and while it’s conductive, it’s not the most conductive of metals.

Metal PCB standoffs are also good if you want to add some weight to your application. The drawback with metal is cost – aluminum is the least expensive metal, however – so it’s smart to make sure plastics can’t do the same job you’re after.

Plastic PCB standoffs

If you want electrical insulation, then nylon PCB standoffs are your best option for avoiding electrical shorts. Nylon – like all plastics – is non-conductive. It’s also chemical resistant but it’s not suitable for applications that be used in damp or humid environments. Over time, nylon tends to absorb moisture.

If you need a lightweight material, then nylon motherboard standoffs are your best bet. Nylon is also strong, but care will need to be taken when torquing so that it doesn’t shear. You can also get standoffs in glass-filled nylon, which is excellent for heavy-duty applications when extra strength is needed. Peek® is an excellent material that can withstand heat of up to 365˚F. It provides outstanding mechanical strength and stiffness, while resisting tensile and bending loads.

At a glance: nylon vs brass standoffs

These are the two most popular materials for standoffs. Here’s a look at how they compare. Note, while nylon is strong, brass is stronger, so we’re only acknowledging brass for that characteristic.

Nylon and brass circuit board standoffs

You can also get the best of both worlds in nylon standoffs with brass inserts. The brass gives you the conductivity you’re after, but the nylon reduces the chance of electrical shorts.

PCB standoff sizes

Computer standoff thread sizes are the same as common screw sizes. To measure a standoff, you measure the body’s outside diameter, the length of the body and the thread size. Standoffs are often listed by their screw-number sizes, but not always.

Examples: U.S. Screw Diameters

The height you choose is based on the amount of space you want to create between individual PCBs or the PCB and its chassis.

Metric standoffs

It’s now easy to find an M3 PCB standoff in the U.S., along with other metric sizes. Here’s how metric and standard compare:

Metric or standard?

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Questions?

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