CapSense Liquid Tolerance Layout

[taas_3144281]

Hi.

My customer use CapSense.

My customer wants a liquid tolerance layout in one layer.

So I thought about the layout as shown below.

The guard sensor will be cut off in order to realize it with one layer.

Is the function of the guard sensor maintained even in this case?

I would appreciate any other advice on layout.

Best Regards.

[AikoO_51]

It should be normally followed 7.4.12.2 Layout guidelines for Guard Sensor in PSoC® 4 and PSoC 6 MCU CapSense® Design Guide.

Also the guard sensor should be in the shape of a rectangle with curved edges and should surround all the sensors.

But we could provide some suggestions in accordance with your request.

Could you tell me more details below?

• what is the application?
• what material will be used? PCB, FPC, ITO, or etc?
• is this just for evaluation or production?
• What is the structure of layer? thickness and material of overlay.

[taas_3144281]

Dear AikoO_51-san

Thank you for your answer.

>what is the application?

It can be a washing machine, a bathroom remote controller, etc.

>what material will be used? PCB, FPC, ITO, or etc?

FPC

>is this just for evaluation or production?

The current stage is evaluation.

Production is expected in the future.

>What is the structure of layer? thickness and material of overlay.

My customer wants a one-layer structure.

This is because the cost can be reduced compared to creating with two layers.

I understand that two or more layers are recommended.

The overlay is an acrylic plate with a thickness of 2 mm.

However, this is still in the evaluation stage, so I would appreciate it if you could let me know if you have a good idea.

Best Regards,

Asanuma

[AikoO_51]

• In this current design, there would be some noise on all sensor traces.

          > Manual tuning is needed very carefully, but it would be quite hard to tune properly.

• If customer touches sensor traces, instead of sensor pad, it would detects “touch” wrongly.
• If the application is Washing Machine, we can imagen the shield area is too large to infect noise.
• If the application is Bath room Remote controller, it could be temperature/humidity are very high. In this situation, it is necessary to tune/estimate feasibility for long time.

          > Note that this is CapSense general concern not only for design layers.

Based on these consideration, we still recommend multiple layer for this.

[taas_3144281]

Dear AikoO_51-san

Thank you for your answer.

I understand that waterproof design with one layer is difficult.

Have you ever realized a water resistant design with one layer?

I would appreciate it if you could let me know.

Best Regards,

Asanuma

[taas_3144281]

I have an additional question.

The guard sensor must surround the button sensor.

If the guard sensor is interrupted a little in the middle, will it not be able to function as a function?

Best Regards,

Asanuma

[AikoO_51]

> Have you ever realized a water resistant design with one layer?

Just for water proof design, it is YES.

However, for production, we need more consideration, e.g. EMC/ESD…, in addition to Post #3.

> If the guard sensor is interrupted a little in the middle, will it not be able to function as a function?

We are sorry… we don’t really understand this question.

Could you please elaborate this question?

[taas_3144281]

Dear AikoO_51-san

Thank you for your answer.

I'm sorry it's hard to understand.

As shown in the figure below, the guard sensor is designed to be interrupted a little in the middle.

I understand that this layout itself is not good.

Will this layout play a role as a guard sensor?

Best Regards,

Asanuma

[AikoO_51 · Accepted solution]

This is comments for liquid proof of 1 layer CapSense sensor design.

Liquid Proof:

• On mechanism, a guide sensor is just a special button sensor. Its function is(implement in firmware by users): when it is triggered, other sensors won’t report touch.
• With fine tuning(and users firmware code):  when the liquid dropped on guide sensor (like circle A B C), the guard sensor will be triggered. In this situation, this will stop touch report even finger touch on those 3 buttons. This is good.
• If liquid dropped on the sensor traces or sensors(like D E F):  due to Shield hatch layer existed, there is no couple between the liquid and GND. In this case, it won’t generate extra capacitance between the liquid drop and GND, so there won’t false touch caused by the that liquid drop. This is good.

Other consideration for 1-layer CapSense sensor pattern design:

  If finger touch on Sensor traces (like circle G H), it has risk to cause false touch report. This will increase the difficult of tuning.

[taas_3144281]

Dear AikoO_51-san

Thank you for your answer.

I got a better understanding of liquid tolerance layout.

Best Regards,

Asanuma