PCB Minimum Etch Technique Explained

February 17, 2021 Cadence PCB Solutions

Key Takeaways

  • Understand minimum etch technique with regard to PCB fabrication.

  • Find out why minimum etch technique is important in the PCB design stage.

  • Learn how to optimize a design using PCB minimum etch technique.

Is it just me or have all of us had at least one terrible haircut in our lives? People comfort us by saying that it will grow back, but the time it takes to do so can feel like an eternity. So, what do those bad haircuts typically all have in common? Well, I think most bad haircuts involve removing more hair than we would have liked. 

In the PCB realm, removing too much copper in the etching process can be a bit like a bad haircut, potentially causing a multitude of problems. And since copper can’t grow back like hair can, let’s take a look at why PCB minimum etch technique can be helpful and how we can implement it in our future designs. 

What Is PCB Minimum Etch Technique?

Even if you’ve never fabricated a PCB, you might be familiar with the process. PCB etching involves the application of UV-resistant laminate to a pre-sensitized photoresist copper layer, which is then exposed to UV rays. Areas that are not covered will be etched off in a special etching solution.

The PCB minimum etch technique has more to do with what happens at the design stage than the process of PCB etching itself. It refers to the idea of keeping as much copper area on the PCB as possible. Effectively, what minimum etch does is impose a tradeoff - it improves heat dissipation, while making parasitic capacitance more prominent. 

When you’re working on a double-sided PCB, you often have ground planes on the top and bottom surfaces. However, it’s unlikely that ground copper exists on each part of the layer. Sections of copper that are not connected to the ground are removed during etching.

A PCB with removed copper from minimum etch technique

PCB minimum etch technique ensures a uniform ground plane.

You can see in the image how small areas between the traces on the PCB are not covered by ground-connected copper. 

If the PCB minimum etch technique is employed, there wouldn’t be pockets of copperless areas on the PCB. The surface of the PCB would be uniformly covered by copper pour, which is connected to the ground. 

What’s the Purpose of PCB Minimum Etch Technique?

PCB minimum etching acts as a shield for sensitive traces.

If you are not sure of the answer to this question, just know that PCB minimum etch technique is an unfamiliar term even to some experienced designers. However, there’s a legitimate reason to employ PCB minimum etch technique in certain scenarios. The grounded copper plane is known for its shielding effect and that’s what makes it a useful strategy in mitigating on-board interference.

If you’re designing a mixed-signal PCB, the rule of thumb is to keep analog and digital signals apart. Failure to do so will risk digital noise coupling into adjacent traces. Yet, you don’t always have the luxury of more space on a PCB. In such circumstances, PCB minimum etching is a handy design consideration.

By having more copper on the surface of the PCB, you won’t be leaving sensitive traces unguarded. The copper acts like a shield that protects analog signals from being compromised by digital noise. It also ensures that you have a better-filled ground plane that acts as the return path to adjacent signals. 

How to Optimize for PCB Minimum Etch Technique

A PCB that used minimum etch technique

Ensure that empty surfaces are poured with ground copper.

There are bound to be uncovered areas on a PCB if you’re not taking proactive steps to optimize it with PCB minimum etch technique. Thankfully, it’s quite easy to ensure that you’re leaving as much copper area on the finished PCB as possible. 

First, you’ll need to create a copper pour for the ground plane. Then, look for areas that are left out in the copper pour. Usually, these areas are not connected to the ground net. You’ll need to manually create a ground net in the area by using vias or by adjusting nearby traces to make space for a ground connection. Once that’s done, repour the ground plane. 

By now, you ought to have a copper plane that’s covering most of the surfaces. There shouldn’t be any odd areas that are left uncovered. Finally, run a DRC check to ensure that all the segments of ground planes are connected.

If you’re using the right PCB design and analysis software, the PCB minimum etch technique will be an easy consideration to incorporate. Check out the OrCAD software from Cadence if PCB minimum etch technique is a difficult task with your current software tool.

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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