How Current Density In PCB Trace Can Affect Functionality

July 10, 2019 Cadence PCB Solutions

Data in binary pouring out from the head of a bottle’s neck

 

I plead guilty for being a workaholic. During the early years of starting up my PCB design firm, I was personally involved in four different designs while overseeing firmware development and post-production issues. Needless to say, I suffered a massive burnout after 6 months, and it took a while to recover from that.

As humans, there is only a limit to what we can take on, hence the need to delegate and leverage. That experience made me pay more attention to PCB design, particularly on the current density in PCB traces. Like us, there’s a limit to the amount of current that flows through a single trace before it starts breaking apart.

What Is PCB Trace Current Density 

Amidst the excitement of PCB design, PCB trace current density is an often overlooked factor that may lead to disastrous results. PCB trace current density is defined by the amount of current flowing through a unit area of the conductive material.

In typical PCBs, the traces are made of copper. While copper is highly conductive, it is not a perfect conductor as such material doesn’t exist. It does have a certain amount of resistance, and this can limit the amount of current going through before the copper trace heats up substantially.

The formula of calculating the rise in temperature in relative to current and copper trace width is given in the IPC-2221 Generic Standard on Printed Board Design. If you’re not keen on manual calculations, there are various PCB trace current calculators available. 

Effects Of High PCB Trace Current Density On Product Functionality 

If you’re lucky, overlooking PCB trace current density will let you off scot-free. But it’s only a matter of time before you start getting complaints of overheating circuit boards or in some extreme cases, smoke billowing from broken traces.

A healthy blood vessel is meant to withstand a certain degree of blood pressure. Anything higher will give your doctor a cause for concern. The same applies to PCB traces. If they are not designed to handle the amount of current that passes through, excessive heat will be dissipated, and the copper may deteriorate.

The problem with overlooking PCB trace current density is that the effect may not be visible right away. In one of my designs, the issue was not detected during the prototype phase, and it was only the frequent complaints of an overheated PCB by unhappy technicians that revealed the mistakes in the PCB. 

 

Green circuit board with a burn mark in an enclosure

Be prepared for smokes and fire when overlooking PCB trace current density.

 

Also, there were cases where PCB traces on the prototype are blown away the moment it was powered on. It is a blatant case of not having ample width on the PCB trace to handle the current passing through. 

Even if you escaped from such dramatic consequences, current density issues could affect power delivery. You may find the voltage drops along the trace before it reaches the components placed towards the end of the delivery network.

Either way, overlooking PCB trace current density is costly, and yet, they can be resolved easily during the design phase. 

How To Ensure PCB Trace Current Density Stays Below Allowable Limit

The next time you take on a new PCB design, you’ll need to ensure that the PCB traces are adequate to handle the amount of current passing through. This is especially true when you’re designing products involving high-current parts, such as power transistors, or super-bright LEDs. 

Use PCB trace current density calculators to ensure that the traces carrying high current are routed with the minimum required width. Bear in mind that not only the width of copper traces are crucial but the interconnecting vias as well. It will be pointless to have wide traces but only a small via connecting both layers. 

 

Drawing of a schematic on a chalkboard

Ensure thicker trace for high current with calculated width.

 

Having wider traces to mitigate current density issues mean you’re having lesser spaces on the PCB. In today’s trend of smaller electronics, you may want to opt for thicker copper from the PCB manufacturer. It allows you to decrease the width of the trace while maintaining an adequate conductive area. 

It also helps to design your product on a top-notch PCB design software like Cadence. Using OrCAD PCB Designer, your design and layout issues will be resolved by top-notch design software capable of making tricky issues seamless. Furthermore, if the design rules and editors aren’t enough, you can always get a better picture of the current density along with any signal or power demands with the SI/PI Analysis Integrated Solution.

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

 

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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