Designing Additive and Semi-Additive PCBs


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With components getting smaller and electronic devices becoming more compact, we are reaching the physical limits of the typical etched fabrication processes. To address these limits, new additive and semi-additive processes are being developed to fit into the current fabricators’ production lines without too much disruption or extra cost.

That leaves the design engineer with a few questions: Will additive and semi-additive processes really reduce layer count and sizes? Are there signal integrity and impedance advantages and disadvantages? When does it makes sense to switch to additive or semi-additive? Are my DFMs going to be any different?

Answers to these questions and many more are still being developed. However, I’ve found a few answers that I’m happy to share with you. 

First, let’s look at liquid metal ink. LMI is ultra-thin and ultra-dense, conforms to any 3D surface, works with different pure metals and their alloys (copper, gold, silver, palladium, platinum, etc.), and is non-aqueous, which enables low-cost manufacturing.

Here are some fundamentals for these very small features. Figure 1 depicts some examples of the additive processes used to create fine copper traces on a printed circuit board. One of the first things you’ll notice are the shapes of the traces: They are not trapezoidal. 

Litson_fig1_0422.jpg

To read this entire article, which appeared in the April 2022 issue of Design007 Magazine, click here.

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