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PSoC 4 MCU

NaMo_1534561
New Contributor II

Hi,

Regarding the GND electrode and the shield electrode, the mesh width and the distance between the meshes are described in the reference manual in a fixed manner.
What is the rationale for this value?


Also, what are the negative effects of using a solid pattern instead of a mesh for the shield electrode?

 

Regards,

Naoaki Morimoto

 

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1 Solution
Hari
Moderator
Moderator

Hello @NaMo_1534561 

 

The hatch fill percentages are chosen so that they provide the best shielding while limiting the Cp of the shield and the sensor. A dense hatch will increase the Cp of the shield (if shield is used) and increase the Cp of the sensor (if the hatch is grounded). 

 

If we use a solid pattern for shield, there are two issues. 

 

1. The Cp of the shield itself will be very high due to the larger area of the shield electrode. 

2. This will result in high emission by the shield which is not acceptable in most designs. The hatch pattern reduces the area of emission and can therefore adhere to the certification requirements. 

 

Best regards, 

Hari

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4 Replies
Hari
Moderator
Moderator

Hello @NaMo_1534561 

 

The hatch fill percentages are chosen so that they provide the best shielding while limiting the Cp of the shield and the sensor. A dense hatch will increase the Cp of the shield (if shield is used) and increase the Cp of the sensor (if the hatch is grounded). 

 

If we use a solid pattern for shield, there are two issues. 

 

1. The Cp of the shield itself will be very high due to the larger area of the shield electrode. 

2. This will result in high emission by the shield which is not acceptable in most designs. The hatch pattern reduces the area of emission and can therefore adhere to the certification requirements. 

 

Best regards, 

Hari

View solution in original post

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NaMo_1534561
New Contributor II

Hello Hari-san,

Thank you for your reply.

I understand the problems with making the shield hatch a solid pattern.

AN85951 has recommendations for hatch design.
"you should use a 25 percent hatching on the top layer (7-mil line, 45-mil spacing), and 17 percent on the bottom layer (7-mil line, 70-mil spacing)."

How do you calculate this value?
Is it possible to disclose information and optimize the percentage of hatches according to the customer's PCB conditions?

 

Best Regards,

Naoaki Morimoto

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Hari
Moderator
Moderator

Hi Naoaki-san, 

 

These are experimental data that have been our recommendation for a long time. This is the recommended pattern for all designs and is not design-specific. The spacing is given so that we have required shielding of sensors while keeping the Cp of the shield in check. 

 

Best regards, 
Hari

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NaMo_1534561
New Contributor II

Hello Hari-san,

 

Thank you for your answer. I understand it.

 

Best Regards,

Naoaki Morimoto

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