cancel
Showing results for 
Search instead for 
Did you mean: 

PSoC 4 MCU

LiFi_1601451
New Contributor

My project is a single waterproof cap touch button on a car body. The button sensor is a FPC 10mm diameter pad. Th FPC is 0.25 mm thickness. On the top layer, the button is surrounded by shield electrode and guard ring. The question is that the bottom of the FPC should be a Ground hatch or shield hatch. What is the weakness or strength if we place a shield hatch at the bottom of the FPC

Besides, the button is surrounded by metal car body. What is the minimum distance between the shield electrode and metal car body

0 Likes
Reply
1 Solution
BragadeeshV
Moderator
Moderator

Hello Lin,

1. Connect the bottom layer hatch to the shield.

"When there is a grounded hatch fill or a trace then, when a liquid droplet falls on the touch surface, it may cause sensor false triggers. Even if there is a shield electrode in between the sensor and ground, the effect of the shield electrode will be totally masked out and sensors may false trigger.

Follow these guidelines to implement the shield electrode in two-layer and four-layer PCBs:

Two-Layer PCB:

 Top layer: Hatch fill with 7-mil trace and 45-mil grid (25 percent fill). Hatch fill should be connected to the driven-shield signal.

 Bottom layer: Hatch fill with 7-mil trace and 70-mil grid (17 percent fill). Hatch fill should be connected to the driven-shield signal. "

You can find this information in the section Layout Guidelines for Liquid Tolerance (Pg no 110) of PSoC 4 Capsense design guide.

http://www.cypress.com/file/46081/download

2. We recommend a minimum air gap of 1.6 mm.

Regards,

Bragadeesh

Regards,
Bragadeesh

View solution in original post

0 Likes
Reply
1 Reply
BragadeeshV
Moderator
Moderator

Hello Lin,

1. Connect the bottom layer hatch to the shield.

"When there is a grounded hatch fill or a trace then, when a liquid droplet falls on the touch surface, it may cause sensor false triggers. Even if there is a shield electrode in between the sensor and ground, the effect of the shield electrode will be totally masked out and sensors may false trigger.

Follow these guidelines to implement the shield electrode in two-layer and four-layer PCBs:

Two-Layer PCB:

 Top layer: Hatch fill with 7-mil trace and 45-mil grid (25 percent fill). Hatch fill should be connected to the driven-shield signal.

 Bottom layer: Hatch fill with 7-mil trace and 70-mil grid (17 percent fill). Hatch fill should be connected to the driven-shield signal. "

You can find this information in the section Layout Guidelines for Liquid Tolerance (Pg no 110) of PSoC 4 Capsense design guide.

http://www.cypress.com/file/46081/download

2. We recommend a minimum air gap of 1.6 mm.

Regards,

Bragadeesh

Regards,
Bragadeesh

View solution in original post

0 Likes
Reply