Original article by Mr. Gaosu | Huang Gang
Do you want green oil? Don’t want green oil? Do you want green oil? Don’t want green oil? Have you ever thought about this question when you are running the surface line? If not, then I can only say…
Then I can only say, congratulations, you don’t have to be as entangled as Mr. Gaosu, hahahaha. Speaking of the difference between inner layer routing and outer layer routing, everyone will involuntarily think of green oil. Friends who have read our Mr. Gaosu’s articles before will know that we once had an article about the electrical performance of green oil, which is quite amazing.
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The DK/DF of a typical green oil is shown below. What! The DF reaches 0.029! ! The loss is definitely worse than that of ordinary FR4.
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So some colleagues with SI knowledge will put forward such a point of view: If the surface traces are covered with green oil, won’t the loss be very large? Especially when the DF of the board we use is very small, such as M6 level or above, the impact of green oil on loss is even greater. Therefore, it is better to remove the green oil on the surface during processing and directly expose the copper, which will greatly reduce the loss.
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According to their simulation results, it is indeed much better without green oil.
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Yes! It seems that this theory really makes sense. There is a theoretical basis and so-called simulation results. But this is obviously not enough for us, Mr. Gaosuo. Sometimes, Mr. Gaosuo does much more than a simulation to prove a theory. For example, we will make a test board to verify it. We do it as soon as we say it, and then it is done. A comparison of a line with green oil and a line without green oil is made.
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Then we tested them immediately, and the result was like this...
Wait, let's review the previous theoretical statements and "simulation" results. Do you remember? It seems that the loss without green oil will be much better than that with green oil, right?
Well, let's see what the actual processing will be like according to this idea! The loss comparison is still the same, the label is still the same, the color is still the same, but the content is not the same as before.
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What! The test result is that the loss of the routing without green oil is greater than that with green oil! The previous theoretical guidance was flawless, and even a preliminary simulation was done, but the test results showed the opposite.
Could it be that the label was written in reverse? Let's verify from another aspect whether it is reversed. It's very simple. There is a conclusion that must be correct, that is, the routing without green oil will definitely transmit faster than the one with green oil in the time domain. There will be no doubt about this. Because when there is no green oil, there is air above the routing, and the theoretical DK=1, then it will definitely be faster.
Well, now I can confirm that I did not get it wrong. From the test results in the time domain, the routing without green oil is indeed faster than the one with green oil.
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Okay, after confirming that the test results are like this, I will definitely think about the reason. In theory, the DF of green oil is very large, so why does the loss increase instead of decrease after the green oil is removed? This is the question of this issue.
This content is originally created by yvonneGan , a netizen of the EEWORLD forum. If you need to reprint or use it for commercial purposes, you must obtain the author's consent and indicate the source
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